KINKEN
Research Highlights
2023

Institute for Materials Research, Tohoku University

KINKEN Research Highlights 2023
Contents
Preface���������������������������������������������������������������������������������������������������������������������������������������������������������� 4
Research Highlights
1. Infrastructural Materials
Microstructure Design of Structural Metallic Materials Research Laboratory���������������������������������������������� 8
Materials Design by Computer Simulation Research Laboratory����������������������������������������������������������������� 9
Irradiation Effects in Nuclear and Their Related Materials Research Laboratory��������������������������������������� 10
Environmentally Robust Materials Research Laboratory�����������������������������������������������������������������������������11
Deformation Processing Research Laboratory������������������������������������������������������������������������������������������ 12
Design & Engineering by Joint Inverse Innovation for Materials Architecture�������������������������������������������� 13
Professional development Consortium for Computational Materials Scientists (PCoMS)�������������������������� 14

2. Energy-Related Materials
Crystal Physics Research Laboratory�������������������������������������������������������������������������������������������������������� 16
Nuclear Materials Engineering Research Laboratory�������������������������������������������������������������������������������� 17
Chemical Physics of Non-Crystalline Materials Research Laboratory������������������������������������������������������� 18
Non-Equilibrium Materials Research Laboratory���������������������������������������������������������������������������������������� 19
Crystal Chemistry Research Laboratory���������������������������������������������������������������������������������������������������� 20
Hydrogen Functional Materials Research Laboratory�������������������������������������������������������������������������������� 21
Multi-Functional Materials Science Research Laboratory�������������������������������������������������������������������������� 22
Analytical Science Research Laboratory��������������������������������������������������������������������������������������������������� 23
Exploratory Research Laboratory�������������������������������������������������������������������������������������������������������������� 24

3. Electronic Materials
Magnetism Research Laboratory��������������������������������������������������������������������������������������������������������������� 26
Low Temperature Physics Research Laboratory���������������������������������������������������������������������������������������� 27
Low Temperature Condensed State Physics Research Laboratory����������������������������������������������������������� 28
Quantum Beam Materials Physics Research Laboratory��������������������������������������������������������������������������� 29
Quantum Functional Materials Physics Research Laboratory�������������������������������������������������������������������� 30
Advanced Crystal Engineering Research Laboratory�������������������������������������������������������������������������������� 31
Structure-Controlled Functional Materials Research Laboratory��������������������������������������������������������������� 32

Solid-State Metal-Complex Chemistry Research Laboratory��������������������������������������������������������������������� 33
Magnetic Materials Research Laboratory�������������������������������������������������������������������������������������������������� 34
Actinide Materials Science Research Laboratory�������������������������������������������������������������������������������������� 35
Tokyo Electron Additive Manufacturing for Multimaterials Research Laboratory��������������������������������������� 36

Research Centers
International Research Center for Nuclear Materials Science�������������������������������������������������������������������� 38
Cooperative Research and Development Center for Advanced Materials������������������������������������������������ 39
High Field Laboratory for Superconducting Materials�������������������������������������������������������������������������������� 40
Trans-Regional Corporation Center for Industrial Materials Research������������������������������������������������������� 41
Collaborative Research Center on Energy Materials���������������������������������������������������������������������������������� 42
Center for Computational Materials Science���������������������������������������������������������������������������������������������� 43
Center of Neutron Science for Advanced Materials����������������������������������������������������������������������������������� 44
International Collaboration Center (ICC-IMR)��������������������������������������������������������������������������������������������� 45
Center for Advanced Light Source and Materials Science������������������������������������������������������������������������ 46
Laboratory of Low Temperature Materials Science������������������������������������������������������������������������������������ 47
Laboratory of Alpha-Ray Emitters�������������������������������������������������������������������������������������������������������������� 48
Analytical Research Core for Advanced Materials������������������������������������������������������������������������������������� 49

International Collaborative Research
Magnetism Research Laboratory��������������������������������������������������������������������������������������������������������������� 52
Non-Equilibrium Materials Research Laboratory���������������������������������������������������������������������������������������� 53
Deformation Processing Research Laboratory������������������������������������������������������������������������������������������ 54
Actinide Materials Science Research Laboratory�������������������������������������������������������������������������������������� 55
International Research Center for Nuclear Materials Science�������������������������������������������������������������������� 56
Cooperative Research and Development Center for Advanced Materials������������������������������������������������ 57
High Field Laboratory for Superconducting Materials�������������������������������������������������������������������������������� 58
Center for Computational Materials Science���������������������������������������������������������������������������������������������� 59
Center of Neutron Science for Advanced Materials����������������������������������������������������������������������������������� 60
Analytical Research Core for Advanced Materials������������������������������������������������������������������������������������� 61

Preface

Dear Colleagues,

We are delighted to present “KINKEN Research Highlights 2023,” our annual report that showcases
research findings from the Institute for Materials Research (IMR) at Tohoku University for the past year.
KINKEN is the abbreviation for “Kinzoku Zairyo Kenkyusho,” the Japanese name for IMR, and is wellknown in the materials science community.

IMR has a rich history spanning over one hundred years since its establishment in 1916. Initially, thefocus was on iron and steel materials, but as times changed and research progressed, its scope
expanded to include the fundamentals and applications of various materials, including non-metals suchas semiconductors and ceramics. With these changes, the institute changed its name from the ResearchInstitute for Iron, Steel and Other Metals (RIISOM) to the current one in 1987. Ever since Dr. Honda, its
first director, invented the world’s first artificial permanent magnet called KS magnet steel, the institutehas developed many new materials for practical use, including Sendust alloy, SiC fibers, and soft
magnetic amorphous alloys, and has also conducted not only fundamental research, but also pioneeringresearch in the search for new materials and the elucidation of physical properties such as magnetismand superconductivity. It has become a global center in materials science.

A key feature of IMR is its fusion of fundamental and applied research, as well as science andengineering fields. Additionally, the institute stands out for its joint research with both domestic andinternational researchers, utilizing world-class facilities for experiments (high-energy irradiation testing,high magnetic fields, supercomputers, etc.) and for the creation and evaluation of new materials. In

4

IMR KINKEN Research Highlights 2023

Director Prof. Takahiko Sasaki

2018, IMR was certified as the International Joint Usage/Research Center for Materials Science, known
as “Global Institute for Materials Research Tohoku” (GIMRT). IMR is committed to further promoting
research and fostering the next generation of researchers, and putting into practice Dr. Honda’s words,“Industry is the training ground of academics,” it also focuses on the likes of industry-academia
collaboration and engineer training.

IMR is committed to creating a sustainable society, a goal shared by the global community. Its
materials science research has the power not only to solve issues but also to positively transform society.
The institute is dedicated to supporting the international competitiveness of Japan’s materials
manufacturing and engaging in global endeavors to create academic intellectual property shared byhumankind. IMR will continue to work on innovative materials science research that will bring about aparadigm shift with a long-term vision and contribute to developing human resources who will lead thefuture.

We hope KINKEN Research Highlights will provide insights into our recent research activities andhelp encourage worldwide collaboration with IMR. We value your continued support and welcome anysuggestions.

IMR KINKEN Research Highlights 2023

5

Infrastructural Materials

IMR KINKEN Research Highlights 2023

Research

Infrastructural Materials

Strengthening of Low-Carbon Steel using Nano-Sized
Vanadium Carbide in Ferrite and Tempered Martensite

Precipitation behaviors and strengthening mechanisms of a vanadium-microalloyed low-carbon steel,produced by either tempering of martensite or ferrite transformation with interphase precipitation, werecomparatively studied. The yield strength of the steel can be satisfactorily explained by cumulatively consideringvarious strengthening factors, whereas the higher yield strength of tempered martensite can be attributed to its
finer grain size and higher dislocation density, although its dispersion of precipitates is relatively coarser.
The precipitation of nano-sized alloy carbides,
which induces a large strengthening effect incommercial ferritic steels microalloyed with strong
carbide-forming elements can be generally obtainedusing two different methods. One is precipitation by
aging in the conventional quenching and tempering
process, which corresponds to the secondary
hardening of martensitic structures [1]. The othermethod is the newly developed interphase precipitation
technique, which occurs as a result of nucleation at the
migrating interphase boundary during ferrite
transformation [2]. In this study, the microstructuralfeatures in a vanadium-microalloyed low-carbon steel
produced by these two treatments were systematicallyinvestigated via various characterization techniques,to directly compare their effects on the precipitation
behaviors and strengthening mechanisms under thesame conditions.
An Fe-0.1C-0.4V-1.5Mn (mass%) alloy was used.
After austenitization at 1473 K for 0.6 ks, the alloy waseither quenched and tempered, or isothermallytransformed at 923 K multiple times for up to 172.8
ks. Subsequently, electron backscattering diffraction,
X-ray diffraction, and a three-dimensional atom probe
were used to quantify the grain size, dislocation
density, and dispersion of VC, respectively, whereas
tensile tests were performed to analyze themechanical properties of the specimens.
Figure 1 shows the dispersion of VC formed inferrite and tempered martensite [3]. The number
density of VC gradually increases initially and later
decreases because of the coarsening of tempered
martensite, whereas the size of VC simply becomeslarger with holding time. The dispersion of VC isalways relatively coarser in tempered martensite
than in ferrite. Conversely, the grain size of tempered
martensite was confirmed to be relatively finer intempered martensite than in ferrite, with a higher
dislocation density.
Figure 2 shows the strength contributions ofvarious microstructural features in ferrite andtempered martensite, which were calculated using

Fig. 1 Variation in (a) number density and (b) average radiusof VC in steel with isothermal holding time at 923 K [3].

Fig. 2 Contributions of various factors to yield strength of steel
that is (a) isothermally transformed and (b) tempered at 923
K [3]. σ0: friction stress; σss: solid solution strengthening;
σgb: grain boundary strengthening; σppt: precipitation
strengthening; σdis: dislocation strengthening.

the proposed models [3]. The experimentallymeasured yield strength shows good agreementwith the summation of various factors. When
compared to ferrite, tempered martensite ischaracterized by its higher yield strength, which canbe attributed to its finer grain size and higher
dislocation density, regardless of its coarser
dispersion of VC precipitates.
References[1] Y.-J. Zhang, C. Zhao, M. Sato, G. Miyamoto, and T. Furuhara,
ISIJ Int. 61, 1641 (2021).
[2] Y.-J. Zhang, E. Chandiran, H.-K. Dong, N. Kamikawa, G.
Miyamoto, and T. Furuhara, JOM 73, 3214 (2021).
[3] Y.-J. Zhang, M. Sato, G. Miyamoto, and T. Furuhara, ISIJ Int.
62, 2016 (2022).

Yongjie Zhang (Microstructure Design of Structural Metallic Materials Research Laboratory)
E-mail: yongjie.zhang.a5@tohoku.ac.jp
URL: http://www.st-mat.imr.tohoku.ac.jp/en/index.html

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IMR KINKEN Research Highlights 2023

IMR KINKEN Research Highlights 2023

Computational Design of High-Functional and Durable
Materials Based on Molecular Dynamics SimulationT

he computational design of high-functional and durable materials requires a deep understanding of multiphysics phenomena including chemical reactions, friction, stress, and fluid dynamics. We applied ourdeveloped molecular-dynamics-based multi-physics simulator to revealing the multi-physics phenomena,
contributing materials design in fields related to mechanical engineering, such as automobile engineering,aerospace instrumentation, and tribology.
High-functional and highly durable materials are
required in a wide variety of research fields such as
power plants, electronics, and tribology for achievinga safe and secure society. Recently, researchers haverecognized that a deep understanding of multi-physics
phenomena including chemical reactions, friction,
stress, and fluid dynamics is required for thecomputational design of materials. However, thetraditional simulation methods such as first-principles
calculation and fluid mechanics cannot simulate theabove multi-physics phenomena. Thus, we applied
our developed multi-physics simulator based on
methods such as coarse-grained molecular dynamics(CGMD) and reactive molecular dynamics method. forpioneering next-generation material design [1-3].
Slide-ring (SR) gels with slidable cross-linked
cyclic molecules exhibit considerably higher fracture
toughness than conventional fixed cross-link (FC)gels. To elucidate the reason for the higher fracture
toughness of SR gels, we conducted tensile strain
simulations of FC and SR gels using the CGMD
method (Fig. 1) [1]. In FC gels, the axis chains breakunder a low strain because the FCs constrain thepolymer chain, resulting in stress concentration at
the axis chains (Fig. 1c). Conversely, in SR gels, theaxis chains did not break until a high strain, and thecross-linked cyclic molecules can slide without
stress concentration (Fig. 1d). This is because thecross-linked and un-cross-linked cyclic moleculesslide on the axis chains and are stacked around thechain-ends, resulting in stress concentration aroundthe chain-ends without breaking of the axis chain.
We conducted a reactive molecular dynamics
sliding simulation of an amorphous SiC (a-SiC)/water
system to elucidate the formation mechanism of aself-forming tribolayer, which contributes to the low
friction of the SiC/water interface [2]. We determinedthat the selective oxidation of the a-SiC substrate bywater generates colloidal silica, which forms a layer ofsilica hydrate on the a-SiC substrate (Fig. 2). Moreover,carbon atoms remained at the a-SiC surface andformed a C-rich layer. Then, further friction caused the

(a)

(b)

(c) FC gel(d) SR gel

Fig. 1 (a) Schematic of fixed cross-link (FC) and slide-ring(SR) gels. (b) Initial structure of tensile strain simulation ofSlide
Fixed cross‐link
FC gels. Local mechanical stress distributionof (c)(FC)
FCgel
End of chainand (d) SR gels at strain of 5.76.
Crosslinking bycovalent bondAxis chain
Crosslinks
Cyclic moleculeadhesion of silica

Fig. 2 Time variation of the interface structure between a-SiC/
water system during sliding simulation.

C-rich layer to change to an amorphous carbon layerthat exhibits low friction. We propose that colloidal
silica, silica hydrate, and amorphous carbon can act
as tribolayers to reduce friction.
References[1] S. Uehara, Y. Wang, Y. Ootani, N. Ozawa, and M. Kubo,
Macromolecules 55, 1946 (2022).
[2] Y. Ootani, J. Xu, F. Nakamura, M. Kawaura, S. Uehara, K.
Kanda, Y. Wang, N. Ozawa, K. Adachi, and M. Kubo, J. Phys.
Chem. C 126, 2728 (2022).
[3] Q. Chen, J. Xu, Y. Su, S. Uehara, S. Bai, Y. Wang, Y. Ootani, N.
Ozawa, and M. Kubo, Comput. Mater. Sci. 208, 111354 (2022).

Momoji Kubo (Materials Design by Computer Simulation Research Laboratory)
E-mail: momoji@tohoku.ac.jp
URL: https://www.simulation.imr.tohoku.ac.jp/eng/index.html

IMR KINKEN Research Highlights 2023

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Infrastructural Materials

Irradiation-Induced Growth and Precipitation of Metallic
Materials Elucidated via In Situ Electron Microscopy

Atomic-scale thermal structural changes strongly influence the mechanical properties in metallic alloys. We visualized

two atomic-scale behaviors in metals based on in situ heating transmission electron microscopy: a hardening
mechanism by asymmetric growth of Frank loops in Al–Cu alloy and precipitation behavior with vacancy diffusion in
Fe–Si ordered alloy.

The in situ heating transmission electron
microscopy (TEM) is a promising method for elucidating
atomic-scale behaviors, which combines the effects ofelectron irradiation-induced displacement and heatinginduced diffusion enhancement. Here, we show theadvanced dynamical observation results of a solidsolution alloy, Al–Cu [1], and an ordered alloy, Fe–Si [2],as fundamental metallic materials.
Figures 1(a), (b) show high-resolution TEM images
that were captured at room temperature at 540 and 640
s after starting electron irradiation. Before observation,
the initial defects that generated during sample
preparation were removed by annealing in vacuum. The
electron-beam-irradiation-induced vacancies wereclustered on the {111} plane and formed flank-type
dislocation loops. The flank loops expanded by climbing
the edge dislocations (red) to <112> with increasing
irradiation duration, while the edge dislocations (blue)
were stabilized. These stable dislocations are connected
to a strain contrast area, which would be a cluster of Cu
atoms (Guinier–Preston (G.P.) zone), as shown in Fig. 1(c). The molecular dynamics simulation suggests that
this behavior is caused by the repulsive interactions
between G.P. zones and edge dislocations.
Figures 2(a), (b) show the TEM images of Fe–15 at%
Si D03-ordered alloy at 650 °C captured from a movie fileat 0 and 670 s. The nano-sized α-Fe particles, which isunpredictable on the phase diagram, were precipitatedand grew in the ordered matrix phase, as shown by theenergy dispersive X-ray spectroscopy results (Figs. 2(c)-(e)). This phenomenon occurs because of theselective formation of irradiation vacancies at Si sites
and the difference in diffusion rates of Fe and Si atoms in
the D03 structure. Conversely, an Fe-depleted layer wasformed around α-Fe particles of approximately 20 nm
diameter, suggesting that the diffusion of Fe atoms andfurther coarsening of the particles were suppressed.
Our results indicate that in situ TEM enables the
dynamic visualization of microstructural changes, aswell as the elucidation of mechanisms related to theappearance of functions and microstructural formationin practical materials by using TEM environments suchas high vacuum and electron irradiation, and using

Fig. 1 In situ high-resolution transmission electron microscopy(TEM) images of the Al–1.7Cu captured at 540 s (a), 640 s(b); the arrow shows the strain contrast. (c) Schematic
diagram showing coherent Cu precipitate sandwiched
between two Frank loops.

Fig. 2 TEM images for 0 s (a) and 670 s (b) after reaching atemperature of 650 °C. (c) shows magnified high-angle
annular dark field –scanning TEM image of the α-Fe
nanoparticles, and elemental maps of Fe (d), Si (e), and O (f).

thin samples.
References[1] J. Chen, K. Yoshida, T. Suzudo, Y. Shimada, K. Inoue, T. J. Konno,
and Y. Nagai, Mater. Trans. 63, 468 (2022).
[2] Y. Shimada, Y. Ikeda, K. Yoshida, M. Sato, J. Chen, Y. Du, K. Inoue,
R. Maaß, Y. Nagai, and T. J. Konno, J Appl. Phys. 131, 16902(2022).

Yusuke Shimada (Irradiation Effects in Nuclear and Their Related Materials Research Laboratory)
E-mail: yusuke.shimada.e1@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/11.html

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IMR KINKEN Research Highlights 2023

IMR KINKEN Research Highlights 2023

Real-Time 2D Imaging of Atomic-State Hydrogen in Metals
Using an Ultrasensitive Hydrogenochromic Sensor

Hydrogen atoms cause the embrittlement of metals. Observing the behavior of hydrogen in metals is crucial
for elucidating the embrittlement mechanisms; however, hydrogen imaging remains challenging. In this study,
we succeeded in real-time hydrogen visualization using a polymeric sensor. The sensor paves the way for
analyzing hydrogen behaviors in metals owing to its high sensitivity and high spatial resolution.
A small amount of hydrogen in metallic materials
causes plasticity-induced cracking, which is calledhydrogen embrittlement. Observing the hydrogen
behaviors in metals is essential for elucidating themechanism of hydrogen embrittlement. However,real-time visualization of the large area of thehydrogen distribution in metals remains a challenge.
Thus, we developed a hydrogenochromic
sensor consisting of Ni interfacial layer andpolyaniline (PANI) layers and successfully visualized
the atomic-state hydrogen in a metal with highsensitivity. Figure 1 shows the hydrogen visualization
mechanism using a hydrogenochromic sensor [1].
Hydrogen atoms are introduced from an aqueous
solution and diffuse to the other side of the specimen
where PANI is polymerized on the Ni interfacial
layer. As the color of PANI changes because of thehydrogenation reaction, the hydrogen distribution
can be visualized based on the color distribution of
PANI. Figure 2 shows the optical images of thehydrogenochromic sensor before and afterhydrogen charging. The green area inside theO-ring is PANI. The left and right halves of thepolyaniline layer correspond to the hydrogenuncharged
andhydrogen-charged
areas,
respectively. Figure 2(b) shows that only thehydrogen-charged area was brightened, indicatingthat PANI changed its color owing to the reaction
with the atomic-state hydrogen that permeatedthrough the metal. The hydrogenochromic reactionof PANI was observed to be catalyzed by the Ni
interfacial layer, achieving a high sensitivity of 2
mol･m-2 and high spatial resolution of hundreds ofmicrometers [1].
Inanactualenvironment,
hydrogenembrittlement is often caused by a significantly
small amount of hydrogen introduced by corrosion.
Therefore, the mechanism of hydrogen entry undercorrosion conditions is of significant interest. The
hydrogenochromic sensor was then applied tovisualize the hydrogen distribution in an Fe sheet
under corrosion conditions. Owing to its highsensitivity to hydrogen, the sensor visualized theSoln. Metal+

H

Ni
Polyaniline (in air)

H

0

H

0

H

N

0

+ 2H

0

H

0

N
H

H+
H+

N

N
H

Hydrogenation

Fig. 1 Mechanism of visualizing hydrogen in a metal using
the hydrogenochromic sensor [1].

H-uncharged area
H-charged area(a)(b)
H charging

1 cm

Fig. 2 Optical images of the hydrogenochromic sensor (a)before and after (b) 1 h of hydrogen charging [1].

corrosion-induced hydrogen entry and elucidated
the correlation between the hydrogen entry andcorrosion reactions [2,3]. This hydrogenochromic
sensor paves the way for analyzing hydrogen
behaviors in metals, leading to the development of
next-generation materials for the hydrogen energy
society.
References[1] H. Kakinuma, S. Ajito, T. Hojo, M. Koyama, and E. Akiyama,Adv. Mater. Interfaces 9, 2101984 (2022).
[2] H. Kakinuma, S. Ajito, T. Hojo, M. Koyama, S. Hiromoto, and E.
Akiyama, Corros. Sci. 206, 110534 (2022).
[3] H. Kakinuma, S. Ajito, T. Hojo, M. Koyama, S. Hiromoto, and E.
Akiyama, Int. J. Hydrog. Energy 47, 38468 (2022).

Hiroshi Kakinuma (Environmentally Robust Materials Research Laboratory)
E-mail: hiroshi.kakinuma.a1@tohoku.ac.jp
URL: http://akiyamaimr-e.amebaownd.com/

IMR KINKEN Research Highlights 2023

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Infrastructural Materials

Ball-Milling Treatment of Gas-Atomized Ti–48Al–2Cr–2Nb Powder and its Effecton Preventing Smoking in Powder Bed Fusion Electron Beam Melting Process

Smoking, which is an unexpected and explosive splashing of powder caused by electrostatic force, is one of the main obstacles

hindering the stability and applicability of the powder bed fusion electron beam technology. In this study, the effectiveness of
mechanical ball milling to suppress powder bed smoke in the powder bed fusion electron beam melting process was investigatedusing gas-atomized Ti–48Al–2Cr–2Nb powder.

Powder bed fusion electron beam (PBF-EB), an additive
manufacturing technique, has attracted considerable attention
in the fabrication of non-weldable or brittle materials because of
its high preheating temperature. However, unexpected powder
scattering (also known as “smoking”) during the preheatingprocess degrades the stability of the manufacturing process
and applicability of the PBF-EB technique. The aim of this study
was to investigate the effectiveness of mechanical stimulation
using ball milling on smoke suppression in the PBF-EB process.
The gas-atomized Ti–48Al–2Cr–2Nb powder wasmechanically ball-milled under rotating speeds ofapproximately 200–400 rpm for 30 min in an air atmosphere.
The electrical resistance of the powders was characterizedusing a tailored impedance spectroscopy system.
Figure 1 shows the schematic of the PBF-EB processwith the corresponding equivalent electrical circuit (EEC). In
the EEC model for the PBF-EB process, IEB is the amount of
irradiated electron beam current, RPB and CPB are parallel
resistors and capacitors of the powder bed, respectively, RBP
is the resistor of the base plate, and IG is the discharged
current through the ground wire. Thus, the electrical charging
of the powder bed is predominantly affected by the resistor–
capacitor circuit in the PBF-EB process (Fig. 1c). In the
impedance test using the powder, the EEC of the powder bed
was predominantly affected by their oxide film states (Fig. 1d).
Figure 2 shows the Nyquist plots of the virgin and ballmilled powders. A semi-circular arc shape indicating
capacitive response was observed for BM200, BM250, andBM300 powders. The diameter of the semicircle (Roxide)
decreased with the increasing milling velocities up to 300 rpm(Fig. 2a). Conversely, the imaginary component of the
impedance in the BM350 and BM400 powders changed to a
positive value associated with the inductive response (Fig.
2b). This result indicates that the capacitive oxide film of raw
powder was transitioned to a conductive oxide film via
mechanical stimulation using the ball-milling process with avelocity above 350 rpm [1,2].

Fig. 1 Schematics of the (a) powder bed fusion electron beam (PBFEB) process, (b) impedance spectroscopy, (c) equivalent electricalcircuit (EEC) in the PBF-EB process, and (d) Nyquist plot with thecorresponding EEC.

References[1] S. Yim, K. Aoyagi, K. Yamanaka, and A. Chiba, Addit. Manuf. 51, 102634(2022).
[2] S. Yim, K. Aoyagi, and A. Chiba, J. Mater. Sci. Technol. 137, 36 (2023).

Kenta Aoyagi (Deformation Processing Research Laboratory)
E-mail: kenta.aoyagi.e7@tohoku.ac.jp
URL: http://www.chibalab.imr.tohoku.ac.jp/english/index.html

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IMR KINKEN Research Highlights 2023

Fig. 2 Nyquist plots of Ti–48Al–2Cr–2Nb powders; (a) gas-atomized,
BM200, BM250, BM300, (b) BM350, BM400. (Number indicatesball-milling velocity)

IMR KINKEN Research Highlights 2023

Functionality in N-Doped Ti Under Visible-Light IrradiationTi and its alloys are frequently used as biomaterials because of their good biocompatibility and high corrosion
resistance. In this study, N-doped TiO2 was formed on a Ti substrate, and the antibacterial activity and reactive
oxygen species resulting from the visible-light-induced photocatalytic activity of the N-doped TiO2 were investigated.
TiO2 is often formed on Ti surfaces, which is
responsible for the biocompatibility of Ti. Numerous
studies have reported that anatase-type TiO2
exhibits high photocatalytic activity; when it isirradiated with ultraviolet light, it reacts with thesurrounding water or O2 and generates reactive
oxygen species (ROS). Moreover, hydrogen
peroxide and OH radicals are known to be generated
as ROS on TiO2 photocatalysts. N-doped TiO2 also
exhibits visible-light-induced photocatalytic activity.
When N-doped TiO2 is subjected to NaOH and hot
water and heated in an atmosphere of gaseous
NH3, visible-light-induced antimicrobial activity andbiocalcification ability were exhibited [1, 2].
Conversely, as a related study, we also conducted astudy on TiNbSn alloys using sodium tartrateelectrolyte [3].
The objective of this study was to investigate
the antibacterial activity and the OH radicals
generated via visible-light-induced photocatalytic
activity on N-doped TiO2.
To prepare the N-doped TiO2, we polishedcommercial-grade pure Ti (cp Ti) plates and soaked
them in NaOH solution and hot water. These plates
were subsequently heated at 500 °C for 3 h underan NH3 gas atmosphere in a tubular electric furnace.
Measurements confirmed the formation of OH
radicals. Electron-spin resonance spectroscopy
was performed to quantify the OH radicals.
Figure 1 shows the measurement results of OH
radicals generated by the visible-light photocatalysis
of cp Ti or N-doped TiO2 (500 °C, 3 h). The results
show that more OH radicals were generated with an
N-doped TiO2 plate than with a cp Ti plate.
Figure 2 shows the antibacterial effect of thesamples of cp Ti and N-doped TiO2 plates (500°C,3 h) on Escherichia coli (E. coli) and Staphylococcus
aureus (S. aureus) when subjected to visible-lightirradiation. The count of viable E. coli and S. aureus
were lower after the treatment in the N-doped TiO2
plate than in the cp Ti plate.
The N-doped TiO2 prepared in this study
exhibited photocatalytic activity under visible-lightirradiation, and OH radicals were generated. The

Fig. 1 Electron-spin resonance spectra under visible-lightirradiation of (a) a pure Ti plate (cp Ti) and (b) an
N-doped Ti plate (500 °C, 3 h).

Fig. 2 Viable count of (a) Escherichia coli and (b)Staphylococcus aureus on cp Ti and N-doped TiO2
plates (500 °C, 3 h) under visible-light irradiation (mean± standard deviation; n = 3).

results suggested that ROS generated by thephotocatalytic reaction contributed to theantibacterial effects.
References[1] M. Kawashita, N. Endo, T. Watanabe, T. Miyazaki, M. Furuya,
K. Yokota, Y. Abiko, H. Kanetaka, and N. Takahashi, Colloids
and Surf. B 145, 285 (2016).
[2] M. Iwatsu, H. Kanetaka, T. Mokudai, T. Ogawa, M. Kawashita,
and K. Sasaki, J. Biomed. Mater. Res Part B Appl. Biomater.
108(2), 451 (2020).
[3] H. Kurishima, Y. Mori, K. Ishii, H. Inoue, T. Mokudai, S. Fujimori,
E. Itoi, S. Hanada, N. Masahashi, and T. Aizawa, Front Bioeng.
Biotechnol. 10, 883335 (2022).

Takayuki Mokudai (Design & Engineering by Joint Inverse Innovation for Materials Architecture)E-mail: tmokudai@tohoku.ac.jp
Hidemi Kato (Project Leader of Design & Engineering by Joint Inverse Innovation for Materials Architecture)E-mail: hidemi.kato.b7@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/29.html

IMR KINKEN Research Highlights 2023

13

Infrastructural Materials

Recent Trend of Fostering PhD Candidates and Doctoral Degree
Holders in Computational Materials Science: Wave of Integrationof Data Science and Materials Science

Professional development Consortium for Computational Materials Scientists (PCoMS) supports young researchers incomputational materials science (CMS) to develop a broader view and extensive knowledge of interdisciplinary areasin the fields of materials science (MS), condensed matter physics, molecular science, and materials design. This article
introduces a recent activity carried out by a key member of PCoMS, Prof. Terada, who analyzed the trend of humanresource development in PhD candidates and doctoral degree holders in CMS in Japan.
In recent years, the demand for researchers who
are knowledgeable in computational materials science(CMS), materials informatics, and materials integration,connecting CMS and experimental materials science
with data science, has increased. As proposed by the
Cross-ministerial Strategic Innovation Promotion
Program (SIP), materials integration is a comprehensive
materials technology tool that aims to support materials
research and development by utilizing the results ofmaterials science (MS) and integrating all the scientifictechnologies, including theory, experiment, analysis,
simulation, and databases.
We have analyzed the titles of approximately
150,000 doctoral dissertations in engineering andscience (ES) from domestic universities over the past 50
years and approximately 10,000 doctoral dissertationsof several research-oriented universities in the USA andEurope over the past 20–50 years as references. Using
text data mining techniques with keywords in the field of
CMS, we estimated the number of doctoral degree
holders in the CMS and related fields, including materials
informatics and materials integration.
Our recent research revealed how materials
informatics and materials integration in Japan has
encouraged doctoral degree holders in ES.
In the 1990s, many doctoral dissertations in
fundamental fields such as statistical physics had titles
that included the keywords of the basic researchmethods of data science, such as "neural network" and"inverse problem". Subsequently, after the 2000s,
although the variety of keywords from other data sciencefields in the title increased, the number of dissertations
including basic concepts such as “neural network” and“inverse problem” decreased, and the number ofdissertations related to data science did not increase in
the MS field. In the 2010s, the number of doctoral
degrees related to data science in MS increased, andthe variety of keywords in dissertation titles diversified
further.

Our previous analysis about CMS has shown thatwhen a new research method is proposed, new material
is produced, or major research breakthrough is made,the number of doctoral dissertations containing therelated new keywords increases rapidly for some time
immediately after the breakthrough. However, as the
new concepts related to the keywords become moregeneralized, they tended to disappear from the doctoral
dissertation titles.
In this case, after the basic research methods andconcepts such as “neural network” and “inverse
problems" were actively studied, they became extremelycommon, and frequency of these terms in doctoral
dissertation topics had increased for a period of time,then decreased; subsequently, various related keywords
appeared. Our analysis suggested the spread ofmaterials informatics in MS from the 1990s to 2010s;
however, the ratio of the number of doctoral degree
holders in materials informatics and materials integration
to the total number of doctoral degree holders in ES was
still small until 2020.
Our updated analysis results also suggest that theratio of the number of doctoral degree holders in CMS tothat in “science and engineering” in Japan had been
continuously increasing until 2020, up to nearly 10%.
However, it is still lesser than that of research-oriented
universities in the USA and Europe. Moreover, theproportion of the doctoral degree holders in CMS whooriented toward fundamental research in Japan is also
lesser than that in the USA and Europe.
These results suggest that the number of thedoctoral degree holders in CMS, materials informatics,
and materials integration in Japan needs to increase [1].
References[1] Y. Terada, “Recent change of number of doctors in computational
materials science: Widespread of integration of data science,experimentation, and computation”, JIM Annual Fall Meeting 2022,
Sep 22, 2022.

Yayoi Terada (Professional development Consortium for Computational Materials Scientists)
E-mail: yayoi.terada.b8@tohoku.ac.jp
Momoji Kubo (Project Leader of Professional development Consortium for Computational Materials Scientists)
URL: http://pcoms.imr.tohoku.ac.jp/index_e.html

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IMR KINKEN Research Highlights 2023

Energy-Related Materials

IMR KINKEN Research Highlights 2023

Research

Energy-Related Materials

In Situ Observation of Solidification and Subsequent Evolutionof Ni–Si Eutectic Alloys

Eutectic growth in Ni–Si alloy with a composition of Ni Si was observed in situ during directional solidification. Two
44

56

intermetallic phases, NiSi and NiSi2, were formed behind the solidifying interface, generating a lamellar, regular eutectic.
Continuous migration of the phase boundaries occurred during the cooling stage, resulting in a myriad patterns.
Eutectic
solidification
createsvariousmorphologies with multiple phases. A regular eutectic
system exhibits the simultaneous, side-by-side
solidification of two non-faceted solid phases from a
melt, resulting in a lamellar microstructure of two
participating phases. Eutectic growth can produce insitu composite materials, and a better knowledge of its
growth kinetics allows scientists and engineers to
explain the myriad patterns in the as-grown materials.
In this study, we performed in situ observations of theformation and subsequent evolution of eutectic alloys
solidified from a binary melt of Ni and Si.
Experiments were performed using an in situ
observation system that consisted of an optical
microscope and a crystal growth furnace. Two graphite
heaters were installed in the furnace for controlling thetemperature gradient during solidification. High-purity
Si (Czochralski-grown wafer) and Ni (6N) raw materials
were melted in a quartz crucible under an argon
atmosphere and the temperature gradient was tuned
to achieve directional solidification. The composition of
Ni and Si in this study was 44:56 at%, which is thelowest eutectic point in the Ni–Si binary system.
Without seeds, the solidification started from the innerwall of the crucible. The crystal growth process wasrecorded using an optical microscope. After
solidification, the as-grown samples were analyzed via
scanning electron microscopy and energy-dispersive
X-ray spectroscopy (EDS) to determine themicrostructure and elemental composition.
Figure 1 shows a series of snapshots recorded

during directional solidification of the Ni–Si eutectic ata cooling rate of −2 °C min−1. The temperature gradientacross the crucible was approximately 3.66 °C mm−1.
Lamellae were formed at the solid/melt interface, as
shown in the snapshot captured at 1 s. The averagephase widths of the primary (bright) and secondary(dark) phases measured from the snapshot were 5.75
and 4.36 μm, respectively. After solidification forseveral seconds, the lamellar spacing widened
marginally (refer the snapshot at 10 s), and the averagephase widths of primary and secondary phases grew
to 6.73 and 5.30 μm, respectively. During thesubsequent cooling process, the lamellae developed
into a rough pattern (refer the snapshot at 180 s) andaverage phase widths enlarged to 23.62 and 16.52 μm
for primary and secondary phases, respectively.
According to the EDS results, the primary phase was
NiSi2 and the secondary phase was NiSi, and bothphases were intermetallic. The results indicate that thetwo intermetallic phases are non-faceted duringsolidification, and the phase boundaries of the eutectic
alloy continuously migrated even in the solid state at atemperature near melting point. This study revealed avaluable point that the actual lamellae spacing can bemeasured in situ despite subsequent microstructural
evolution during the cooling process.
References[1] L.-C. Chuang, K. Maeda, H. Morito, and K. Fujiwara, Scr. Mater.
211, 114513 (2022).

Fig. 1 Snapshots of solid/melt interface during directional solidification of Ni44Si56 alloy and the subsequent microstructure evolution
at a cooling rate of 2 °C min−1, recorded using an optical microscope at different times. The growth direction is toward the right [1].

Lu-Chung Chuang (Crystal Physics Research Laboratory)
E-mail: chuang.lu.chung.e8@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/02.html

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IMR KINKEN Research Highlights 2023

IMR KINKEN Research Highlights 2023

New-Grade Oxide dispersion strengthened Cu Alloy and UltraSmall Testing Technologies

Oxide dispersion strengthened (ODS) alloys and high-temperature ceramics are used in advanced nuclear fission
and fusion reactor systems because of their superior irradiation tolerance and high-temperature strength. We
developed a new-grade ODS Cu alloy with superior strength and thermal diffusivity through nano-dispersion of Y–Zr
complex oxide particles. Furthermore, we developed and applied ultra-small testing technologies for evaluating themechanical strength of nuclear materials.
Materials resistant to extreme environments such asoxide dispersion strengthened (ODS) alloys [1,2] andceramics [3] are crucial for achieving advanced nuclear
systems.
Cu alloys with their superior thermal conductivity
and strength are essential materials in high-efficiency
energy transportation and conversion equipment, andeven in a fusion reactor divertor heat sink. However, touse Cu alloys at high temperatures, the precipitates ordispersoids that strengthen the material must be stable
at high temperatures. We developed a new-grade ODS
Cu alloy with Zr addition that is strengthened by nanosized dispersion particles of Y–Zr complex oxides
obtained by mechanical alloying [1]. This new alloy was
1.5 times stronger than the conventional ODS Cu alloy
with yttrium oxide dispersion particles (Fig.1). Moreover,guidelines were obtained regarding the conditions foralloy fabrication and heat treatment to suppress thedecrease in thermal conductivity properties, which istradeoff with the increase in strength.
SiC and its composites exhibit several advantageous
properties as a future nuclear material, such as superior
high-temperature properties, high corrosion resistance,and low radioactivation. Oxidation of SiC fibers is apotential factor limiting the service temperature of SiCf/
SiC composites. Ultra-small testing technologies, suchas nanoindentation and micro-pillar compression tests,
are crucial for estimating the mechanical properties ofnuclear materials after high-energy particle irradiation
under harsh environments. Micro-pillar compression
tests of pillars with a diameter of 1 μm fabricated at thecenter of the SiC fiber cross section revealed that thefiber strength may have been reduced by the internaloxidation reaction between residual C and O (Fig. 2).
Moreover, we suggest a simple and powerful
method to measure the indentation hardness of materials
with less uncertainty at the zero-point of indentation
depth on the surface [4,5].

Fig.1 (a) Vickers hardness in oxide dispersion strengthened(ODS) Cu and Zr-added ODS Cu. (b) Temperaturedependence of thermal diffusivity of ODS Cu alloys.

Fig.2 (a) Schematic view of micro-pillar compression test, (b) amicro-pillar fabricated in SiC fiber, and (c) load-displacement
curve obtained by the micro-pillar compression tests.
[2] H. Wang, H. Yu, J. Liu, S. Kondo, N. Okubo, and R. Kasada, Corros.
Sci. 209, 110818 (2022).
[3] X. Yuan, S. Kondo, K. Shimoda, H. Yu, Y. Okuno, and R. Kasada, J.
Eur. Ceram. Soc. 42, 5334 (2022).
[4] D. Geng, H. Yu, Y. Okuno, S. Kondo, and R. Kasada, Sci. Rep. 12,

References[1] Z. Gao, H. Yu, D. Geng, Y. Liu, S. Kondo, Y. Okuno, and R. Kasada,J. Alloys & Comp. 899, 163328 (2022).

6391 (2022).
[5] D. Geng, H. Yu, S. Kondo, and R. Kasada, J. Mater. Sci. 57, 13736(2022).

Ryuta Kasada, Sosuke Kondo, Hao Yu, and Yasuyuki Ogino (Nuclear Materials Engineering Research Laboratory)
E-mail: ryuta.kasada.e7@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/13.html

IMR KINKEN Research Highlights 2023

17

Energy-Related Materials

Orientational Ordering of Hydroxy Groups in Kulanite

Single-crystal X-ray diffraction experiments on kulanite [Ba(Fe , Mn, Mg) (Al, Fe ) (PO ) (OH) ] were
2+

2

3+ 2

4 3

3

performed to investigate the orientational ordering of its hydroxyl groups. Structural refinements did not show aphase transition between 120 and 353 K. The orientation of the hydroxyl groups was uniquely determinedalong the c-axis in this temperature range [1].

Kulanite is a barium iron aluminum phosphate
belonging to the Bjarebyite group characterized by
the co-existence of heavy elements (i.e., Ba, Sr, Pb,
and transition metals). This mineral also contains
oxygen atoms in the form of hydroxyl groups; theirorientational disorder is one of the structuralcharacteristics of kulanite. Single-crystal X-ray
diffraction of kulanite at low temperatures was
performed to investigate the orientational orderingof the OH groups in kulanite.
A kulanite sample was extracted from Rapid
Creek (Yukon Territory, Canada). A single crystal
specimen of size 0.05×0.07×0.08 mm was attached
to a glass fiber, and its diffraction intensities were
measured using a Rigaku XtaLAB Synergy–S
system. The temperature was controlled using aliquid nitrogen cryo-stream. The cell volumes andcorresponding unit cell parameters monotonicallydecreased at lower temperatures, and no phasetransition was detected. The results of the structuralrefinement were similar to those of kulanite refined atroom temperature [2], except for the spatial
distribution of the free OH group (O8-H1). Figure 1
shows the structure of kulanite and the difference
Fourier maps obtained from structural refinement,
indicating the hydrogen atom distribution. Contrarily
to previous reports, our results showed that the freeOH group lies on the mirror plane and does notpresent a disordered orientation. This spatial
distribution did not change within the measured
temperature range (120–353 K).
Previous Raman and infrared spectra
measurements of kulanite focused on the 2600–
4000 cm-1 region, highlighting a sharp peak at 3530
cm-1 and a broad peak at 3200 cm-1 [3]. Theirshapes resembled those of solvents with free andhydrogen-bonded OH groups. Additionally, free OH
stretching vibrations appear at a higher frequency
than that of hydrogen-bonded OH, suggesting
weakening of the covalent bond with hydrogenbond formation. Thus, kulanite contained both freeand hydrogen-bonded OH groups. The differencein the bond strengths of O8-H1 and O9-H2 wasreflected in the magnitude of the decrease in theFig. 1 (A) Difference Fourier maps in the mirror plane andthe plane through the free OH group (O8-H1), at RT. (B)Difference Fourier maps in the plane through the freeOH group at 120, RT, and 353 K.

O8-O6 and O9-O3 distances with thermal
expansion: from 2.668(2) Å and 3.367(2), at 120 K,
to 2.680(2) Å and 3.377(2) Å, at 353 K, respectively.
References[1] R. Yamane, M. Tokuda, and K. Sugiyama, J. Min. Petrol. Sci.
118, 220701 (2023).
[2] M. Cooper and F. C. Hawthorne, Can. Mineral. 32, 15 (1994).
[3] R. L. Frost, S. J. Palmer, Y. Xi, J. Čejka, J. Sejkora, and J.
Plášil, Spectrochim. Acta A Mol. Biomol. Spectrosc. 103, 431(2013).

Ryo Yamane (Chemical Physics of Non-Crystalline Materials Research Laboratory)
E-mail: ryo.yamane.c2@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/15.html

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IMR KINKEN Research Highlights 2023

Fabrication of Ultrafine Nanoporous Intermetallic Catalysts via High-Temperature
Liquid Metal Dealloying for Electrochemical Hydrogen Production

I

ntermetallic compounds formed from nonprecious transition metals are promising cost-effective and robust catalysts
for electrochemical hydrogen production. Herein, we report the fabrication of nanoporous Co7Mo6 intermetallic
compounds via liquid metal dealloying. The fabricated nanoporous Co7Mo6 exhibited high catalytic activity anddurability in electrochemical hydrogen evolution reactions, demonstrating its potential as an advanced electrocatalyst.
Electrochemical hydrogen production through water
splitting has emerged as a promising strategy for theeffective utilization and storage of intermittent renewableenergy. Crucial to this technology is the development ofhigh-efficiency electrocatalytic hydrogen evolution
reactions (HERs), particularly in alkaline media [1]. When
compared to solid-solution alloys, intermetallic
compounds with ordered atomic structures havehomogeneous and intensified active sites, as well as thecapability to form unique crystal structures to enhancegeometric and electronic effects [2]. Accordingly, nonnoble nanoporous intermetallics with sufficiently high HER
activity and robustness have not yet been developed.
We report a liquid metal dealloying (LMD) strategy
conducted at elevated temperatures to fabricate 3D
nanoporous Mo-based intermetallic compounds aselectrocatalysts to promote HERs [3]. Coupled with thesimultaneous evolution of the 3D bicontinuous open
porosity during the dealloying of single-phase precursors,
the high-temperature LMD process overcomes the energy
barrier, driving the direct formation of chemically orderedintermetallic phases. Combined experimental analyses
and molecular dynamics simulations uncovered anintermetallic effect; consequently, high-temperaturechemical ordering during nanopore formation suppressed
dealloyed nanostructure coarsening (Fig. 1).
The ultrafine 3D nanoporous μ-Co7Mo6, with a large
accessible surface area and abundant active sites,
exhibits catalytic activity that is close to yet inferior to thatdrop-casted electrodes of Pt/C; however, the catalytic
activity is improved in nanoporous μ-Co7Mo6 sheet
electrodes (Figs. 2a-b). Along with superior electrocatalytic
activity, the nanoporous μ-Co7Mo6 electrodes exhibitedsuperior durability after 5000 cycles of accelerated
degradation testing, showing a negligible shift in the HER
polarization curves and negligible change in its porous
structure (Fig. 2c), and delivered a high current density of~170 mA cm-2 at an overpotential of 150 mV, without
significant current decay over a long-term
chronoamperometry test for 48 h (Fig. 2d). This study
sheds light on the development of advanced nanoporous
intermetallic electrocatalysts.

Fig. 1 Schematic illustrations of the fabrication of ultrafine
nanoporous μ-Co7Mo6 intermetallic compound via liquid
metal dealloying.

Fig. 2 iR-corrected hydrogen evolution reaction polarization
curves of nanoporous μ-Co7Mo6 (a) compared with thereference materials on a disk electrode, (b) compared to ahigh-load Pt/C catalyst, and (c) collected before and after theaccelerated degradation test for 5000 cycles. Inset: Scanningelectron microscopy image of the np-Co7Mo6 sheet after thestability measurement. (d) Long-term stability measurements
for 48 h at 150 mV overpotential.

References[1] J. Kibsgaard and I. Chorkendorff, Nat. Energy 4, 430 (2019).
[2] Y. Yan, J. S. Du, K. D. Gilroy, D. Yang, Y. Xia, and H. Zhang, Adv.
Mater. 29, 1605997 (2017).
[3] R. Song, J. Han, M. Okugawa, R. Belosludov, T. Wada, J. Jiang, D. Wei,
A. Kudo, Y. Tian, M. Chen, and H. Kato, Nat. Commun. 13, 5157 (2022).

Hidemi Kato (Non-Equilibrium Materials Research Laboratory)
E-mail: hidemi.kato.b7@tohoku.ac.jp
URL: http://www.nem2.imr.tohoku.ac.jp/index-e.html

IMR KINKEN Research Highlights 2023

19

Energy-Related Materials

Heteroepitaxial Fabrication of Binary Colloidal Crystals by
Balancing Interparticle Interaction and Lattice SpacingT

he colloidal epitaxy utilizing a patterned substrate is used to fabricate colloidal crystals with the samestructure and lattice spacing with the substrate. However, this technique has been primarily limited to a singlecomponent system. We show that the heteroepitaxial growth technique enables the fabrication of complex
multicomponent colloidal crystals that significantly facilitate versatile applications of the colloidal crystals.
When compared to single-component colloidal
crystals, binary colloidal crystals (b-CCs) havegained considerable attention owing to their various
structures, which are critical for versatile applications
such as biosensors [1] and photonic crystals [2].
However, controlling the growth and structures of theb-CCs is still challenging because of their complex
structures. Recently, we reported that onedimensional (1D) heteroepitaxy occurs when growingb-CCs [3]. The b-CCs grow epitaxially at the edge ofpreviously formed single-component colloidal
crystals. In this study, based on the availability of 1D
heteroepitaxy, we demonstrated two-dimensional(2D) heteroepitaxial growth of b-CCs [4].
The heteroepitaxial growth for the binary systemis achieved by the following procedure. A convective
assembly technique utilizes solution evaporation togather and arrange particles into thin colloidal
crystal layers. Colloidal suspensions that are
dropped on cover glass gradually evaporate to forma thin colloidal crystal as the substrate. Epitaxiallygrown colloidal crystals that were observed from thebottom using inverted optical microscopy andstacking structures were identified using a confocal
laser scanning microscope. Various types of b-CCs
were created by adjusting the particle size ratio andpolymer concentration, as shown in Fig. 1. This is
the first time that various types of b-CCS are createdby heteroepitaxial growth. Our heteroepitaxial
growth technique can be used in a new approachfor structure-controlled colloidal self-assembly inmulticomponent systems such as fabricating
photonic bandgap materials.
References[1] G. Singh, H.J. Griesser, K. Bremmell, and P. Kingshott, Adv.
Funct. Mater. 21, 540 (2011).
[2] A.P. Hynninen, J.H. Thijssen, E.C. Vermolen, M. Dijkstra, andA. van Blaaderen, Nat. Mater. 6, 202 (2007).
[3] J. Nozawa, S. Uda, A. Toyotama, J. Yamanaka, H. Niinomi,
and J. Okada, Cryst. Growth Des. 20, 3247 (2020).
[4] J. Nozawa, S. Uda, A. Toyotama, J. Yamanaka, H. Niinomi,
and J. Okada, J. Colloid Interface Sci. 608, 873 (2022).

Junpei Okada (Crystal Chemistry Research Laboratory)
E-mail: jun.nozawa.e3@tohoku.ac.jp
URL: http://www.imr.uda-lab.imr.tohoku.ac.jp/index-e.html

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IMR KINKEN Research Highlights 2023

Fig. 1 Various binary colloidal crystals formed via
heteroepitaxial growth are plotted with respect to theparticle size ratio of R1 (dB/dA) and R2 (dA/dsub),where dA, dB, and dsub are the particle sizes of large,
small, and substrate particles, respectively. Epitaxiallygrown unary colloidal crystals (Epi), a-AB2-phase (aAB2), b-AB2-phase (b-AB2), dodecagonal structure(Dodeca),AB6-structure(AB6),
AB-structure(triangular) (AB), rhombic structure (Rhomb.), domain
structure (Domain.), pentagon structure (pentagon),random structure (Random), AB3-structure (AB3),
honeycomb structure (hc), triangular structure (tri), andkagome lattice structure (Kagome) are plotted.

IMR KINKEN Research Highlights 2023

Pseudorotating Hydride Complexes with Ninefold Hydrogen
Coordination at Temperatures Far Below Room Temperature

Solid-state materials containing rotatable polyanions constitute a peculiar class of ionic conductors because of

their unique transport mechanism, where the reorientational motions induce phase transitions with several ordersof magnitude enhancement in counterion conductivities. A major drawback is the high temperature required toactivate rotation; consequently, low conductivities are observed at room temperature. In this regard, we havetheoretically demonstrated a novel strategy of drastically reducing the temperature by utilizing “pseudorotation”
of hydride complexes with high hydrogen coordination as a new class of rotatable polyanions. Here, we provide
experimental evidence of the low-temperature activation of the rotational motion of hydride complexes with
ninefold hydrogen coordination.

1
S(Q,E) [a.u]Currently, there is a strong demand to replaceorganic liquid electrolytes used in conventional
batteries with solid-state electrolytes owing to theirmultiple advantages, such as better safety and higher
energy density. Considerable effort has been devoted
to identifying materials with superior transport
properties.
Among the diverse solid-state electrolytes, thosecontaining rotatable polyanions constitute a peculiar
class of materials owing to their unique transport
behavior, i.e., polyanions rotate at an elevatedtemperature, thereby promoting phase transitions withseveral orders of magnitude enhancement incounterion conductivities. However, a major drawback
is the high temperature required to activate rotation,
resulting in low conductivities at room temperature(RT). Thus, we recently proposed a novel approach tosignificantly reduce the temperature based on the useof hydride complexes with high hydrogen coordination,
wherein hydrogen is the sole ligand species that canbe covalently bound to single transition metals. The
essence of the approach is that, unlike other polyanions,the rotation only requires small displacements of highly
mobile hydrogen and therefore occurs with low
activation energy. We applied this approach to an
existing hydride Li5MoH11 containing a ninefold
hydrogen coordination hydride complex MoH93− [1],and theoretically demonstrated the use of this material
as a novel RT lithium superionic conductor [2].
In this study, we conducted quasielastic neutron
scattering (QENS) measurements of Li5MoH11 toexperimentally demonstrate the low-temperature
activation of pseudorotation.
Figure 1 shows the dynamic structure factor
S(Q,E) of Li5MoH11 measured in a temperature rangeof 10–300 K. We observed that a QENS signal
appeared at a temperature >150 K because of therelaxation of hydrogen atoms. The intermediate
scattering functions derived from the QENS spectra

Q = 1.2 Å−1
300 K
270 K
240 K
210 K
180 K
150 K

0.1
0.01

10 K

0.001
0.0001

-400

0

400
ΔE [µeV]

800

Fig. 1 Quasielastic neutron scattering spectra of Li5MoH11
measured at various temperatures at Q = 1.2 Å−1.

were satisfactorily fitted using a stretched exponentialfunction called the Kohlrausch–Williams–Watts
function with an anomalously small stretching exponent
β ≈ 0.3–0.4, suggesting a wide relaxation time
distribution. The Q dependence of the elastic
incoherent structure factor was reproduced by therotational diffusion of MoH93−. The results weresatisfactorily supported by a van Hove analysis of the
motion of hydrogen atoms obtained using firstprinciples molecular dynamics calculations. We
conclude that the wide relaxation time distribution of
the MoH93− rotation is due to the positional disorder ofthe surrounding Li ions that arise because of thesignificant Li+ diffusion and deformation of MoH9 unit
by pseudorotation [3].
References[1] S. Takagi, Y. Iijima, T. Sato, H. Saitoh, K. Ikeda, T. Otomo, K. Miwa,
T. Ikeshoji, and S. Orimo, Sci. Rep. 7, 44253 (2017).
[2] S. Takagi, T. Ikeshoji, T. Sato, and S. Orimo, Appl. Phys. Lett. 116,173901 (2020).
[3] Y. Ohmasa, S. Takagi, K. Toshima, K. Yokoyama, W. Endo, S.
Orimo, H. Saitoh, T. Yamada, Y. Kawakita, K. Ikeda, T. Otomo, H.
Akiba, and O. Yamamuro, Phys. Rev. Res. 4, 033215 (2022).

Shigeyuki Takagi and Shin-ichi Orimo (Hydrogen Functional Materials Research Laboratory)
E-mail: shigeyuki.takagi.c5@tohoku.ac.jp
URL: http://www.hydrogen.imr.tohoku.ac.jp/en/index.html

IMR KINKEN Research Highlights 2023

21

Energy-Related Materials

Hole Doping in Cu-Based Semiconductors with an Isovalent
CationP-type doping in Cu(I)-based semiconductors is pivotal for various applications as semiconductors. Impurity
doping is a fundamental technology to overcome the intrinsic limits of hole concentration controlled by native
defects. Recently, we reported that alkali metal impurities are prominent p-type dopants for the Cu(I)-based
cation-deficient hole conductors. When the size mismatch with Cu+ in the host lattice is increased, theseisovalent impurities are preferentially located at interstitial positions to form stable impurity–defect complexes.
We demonstrate that the Cs impurity in γ-CuI semiconductors enhances hole concentration controllability forboth single crystals and thin films. Our first-principles calculations indicate that the Cs impurity forms impurity–
defect complexes that act as shallow acceptors. This isovalent doping provides an approach for controlled
doping into cation-deficient semiconductors through an interaction of impurities with native defects.
(a)

4

2

i

0

IMR KINKEN Research Highlights 2023

Cu

2-/3-

VCu

O
Na

0/VCu

Cu

0

0.25 0.5 0.75 1.0 1.25 1.5 1.75
Fermi level (eV)Fig. 1 (a) Theoretical point defect energetics of native
point defects, isovalent Na dopants, and their defectcomplexes in Cu2O as a function of the Fermi level. (b)Atomic structure of the Na-related complex defect.

(a)

(b)
+

−

−

+

+

−

−

+

+

A

acceptor type

+

−

+

−

+

−

+

−

+

−

−

+

−

+

Anion Cation:Cu

−

VCu

−
+

Ai

+

−

−

+
−

−

VCu

−
+

+

Fig. 2 Schematic defect formation models for isovalentcation dopants. If the ionic radius of the impurity is
sufficiently large against the interstitial vacant space topush away the nearest neighboring Cu cations, multiple
Cu vacancies are generated.

References[1] T. Matsuzaki, N. Tsunoda, Y. Kumagai, Y. Tang, K. Nomura, F.
Oba, and H. Hosono, J. Am. Chem. Soc. 144, 16572 (2022).

Yu Kumagai (Multi-Functional Materials Science Research Laboratory)
E-mail: yukumagai@tohoku.ac.jp
URL: https://kumagailab.imr.tohoku.ac.jp/en/

22

-/2-

NaCu

0
-1

Nai

VCu(split)

1 Na −2V(b)+

Nai−4VCu
3 Nai−3VCu

Formation energy (eV)

Adding impurities with acceptor or donor
properties, known as impurity doping, is thebenchmark method for bolstering the transport
properties of semiconductors and device
performance. Conventionally, ions with lower
valency than the constituent atoms have been usedas such impurities. However, in Cu(I)-based
semiconductors, which have multiple applications,e.g., hole transport layer in perovskite solar cells,
ions with a valence lower than that of monovalent Cu
ions do not exist, and thus the p-type doping has
not been established so far [1].
To propose a new carrier doping design for thep-type doping, we focused on the alkali impurity
effect, which has been empirically used for hole
doping in Cu monovalent semiconductors, Cu2O
and Cu(In,Ga)Se2. First, we experimentallydemonstrated that p-type doping with alkali-ion
impurities, which has the same valence as Cu but alarger size, can improve conductivity in Cu(I)-based
semiconductors. Our theoretical analyses show thatthe complex defects composed of alkali-ion impurity
and vacancies of Cu ions, are an origin of the p-typeconductivity (Fig. 1).
Based on the p-type doping mechanism toform acceptor-type Cu vacancy defect complex, weinvestigated larger alkaline ions, such as Na, Rb,
and Cs, as acceptor impurities in γ-CuI. Amongthem, the Cs ions could bind more Cu vacancies,
leading to a greater concentration of stable charge
carriers (1013 – 1019 cm-3) both in single crystals andthin films prepared from the solution. This suggeststhat the method can be used to fine-tune carrier
concentrations under low-temperature processing
for specific applications and devices. This would
allow a whole new range of applications for thesep-type materials.

IMR KINKEN Research Highlights 2023

Laser-Induced Breakdown Spectroscopy for Quantitative
Three-Dimensional Hydrogen Mapping

For the development and maintenance of materials and infrastructures that enable the achievement of “hydrogensociety,” an analytical technique capable of determining hydrogen distribution is highly desirable. We present a
method for obtaining a three-dimensional quantitative hydrogen distribution in an Ni–metal hydride (MH) battery
cathode using laser-induced breakdown spectroscopy (LIBS) and demonstrate that the reaction distribution in
the cathode can be interpreted based on a state-of-charge distribution converted from the hydrogen distribution.
In this method, we measured the hydrogen emission-line intensities at 656.28 nm for a commercial Ni–MH
battery cathode cycled 1000 times at 1 C under a 3000 Pa helium atmosphere. The proposed LIBS method
allows us to understand the deterioration mechanism of an Ni–MH battery and improve its cycle life and capacity.

“Hydrogen society,” which refers to the use ofhydrogen in daily life and industrial activities, hasrecently attracted attention owing to a worldwide
effort to achieve net-zero emissions of greenhousegases [1]. For achieving a hydrogen society, thedevelopment of materials related to hydrogenproduction,hydrogenstorage,hydrogentransportation, and electric power generation usinghydrogen is crucial. Accordingly, efficient analyticaltechniques for mapping hydrogen with a spatial
resolution in tens of micrometers along the planarand depth directions are essential for the fabricationand maintenance of such materials. To satisfy thisrequirement, we focused on laser-induced breakdown
spectroscopy (LIBS) and developed a LIBS-based
method to quantitatively acquire the threedimensional hydrogen distribution using an Ni–metal
hydride (MH) battery cathode as an analyte.
Quantitative hydrogen and state-of-charge(SOC) distributions for a commercial Ni–MH battery
cathode cycled 1000 times at 1 C were acquired bymeasuring the hydrogen emission intensity at 656.28
nm under a 3000 Pa helium atmosphere. Thismeasurement condition was established in ourprevious study [2, 3].
For determining the hydrogen and SOC
distributions, Ni–MH battery cathodes weredischarged or charged once at a C-rate of 0.1 C,
which was considered as reference samples. The
SOC distributions were obtained based on theassumption that the SOCs of the discharged andcharged Ni–MH battery cathodes were 0 and 100%,
respectively, and the SOC decreased linearly with anincrease in hydrogen emission intensity at 656.28
nm. SOC maps of the commercial Ni–MH battery
cathode after the 1000th charging at 1 C exhibitedan inhomogeneous distribution (Fig. 1), demonstratingthat the degradation of the commercial Ni–MH
battery occurred uniformly in the planar and depth

Fig. 1 Three-dimensional state-of-charge maps of thecommercial Ni–metal hydride battery cathode after the
1000th charging at 1 C [4].

directions of the cathode. This SOC distribution canbe explained on the basis of proton transfer in thecathode. The average SOC of the layer that was 75
μm deep from the surface is 21%, as shown in Fig. 1,
which is nearly consistent with the SOC evaluatedfrom the charge–discharge curves (37%). These
results indicate that the present LIBS measurement
system can provide three-dimensional quantitative
SOC maps of Ni–MH battery cathodes.
References[1] I. Staffell, D. Scamman, A. Velazquez Abad, P. Balcombe, P. E.
Dodds, P. Ekins, N. Shah, and K. R. Ward, Energy Environ. Sci.
12, 463 (2019).
[2] S. Imashuku, T. Kamimura, S. Kashiwakura, and K. Wagatsuma,
Anal. Chem. 92, 11171 (2020).
[3] S. Imashuku, T. Kamimura, T. Kawaguchi, and T. Ichitsubo, e-J.
Surf. Sci. Nanotechnol. 20, 7 (2022).
[4] S. Imashuku, T. Kamimura, T. Ichitsubo, and K. Wagatsuma,
Analyst 147, 5161 (2022).

Susumu Imashuku (Analytical Science Research Laboratory)
E-mail: susumu.imashuku.e8@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/27.html

IMR KINKEN Research Highlights 2023

23

Energy-Related Materials

Structural Quantum Criticality—Broken Translational
Symmetry by Controlling the Chemical CompositionQuantum criticality, where symmetry breaking is suppressed to absolute zero, induces exotic phenomena. By
combining x-ray, neutron, calorimetry measurements, and first-principle calculation, we show complete
suppression of the structural transition by controlling the chemical composition. Near the structural quantum
critical point, crystalline and amorphous characteristics with partially broken translation symmetry are realised.
Symmetry breaking is a fundamental concept incondensed matter physics. In solids, exotic quantum
phases with broken spatial- or time-reversal
symmetries have been extensively studied over the
past decades. These broken symmetries always
accompany phase transitions. A typical phasetransition involves a change in the crystal structure.
Such structural phase transitions usually occur at
finite temperatures. However, certain perturbations
can lower the transition temperature to absolute
zero. The transition point at absolute zero is called
the structural quantum critical point.
We aimed to demonstrate that chemicalcomposition can lead to structural quantum criticality,
where a translation symmetry, an essential
component of crystal symmetry, is partially broken
by complete suppression of a structural phasetransition [1].
BaAl2O4 is a dielectric compound, showing a
structural phase transition at TC = 450 K from thespace group P6322 to P63 on cooling (Fig.1(a)). This
structural phase transition is driven by the acoustic
soft phonon mode owing to the tilting of AlO4
tetrahedra, whose vibration is similar to that of soundwaves. The soft mode is tunable by chemicalcomposition as Ba1-x Srx Al2O4. Figure 1(a) shows that
TC is rapidly suppressed by substituting Sr for Ba
atoms and disappears near x = 0.1. For thecomposition regime of 0.1 ≤ x ≤ 0.5, diffuse scattering
can be observed in electron diffraction, whichindicates that the soft mode exists at significantly low
or nearly zero frequencies. A further increase in x
induces another structural phase transition to thespace group P21 at x > 0.55.
To investigate phonons from microscopic views,
an inelastic neutron scattering experiment was
performed on powder samples. Figure 1(b) shows
the intensities observed for different values of x. The
sample with x = 0 shows crystalline characteristics,
i.e., peak formations. A shoulder (filled triangle) near
the peak at approximately 5 meV originates from theacoustic phonons. The experimental findings arewell accounted for by our first-principle calculation.
Yusuke Nambu (Exploratory Research Laboratory)
E-mail: nambu@tohoku.ac.jp
URL: http://nambu.imr.tohoku.ac.jp/en/

24

IMR KINKEN Research Highlights 2023

Fig. 1 (a) Phase diagram of Ba1-x Srx Al2O4 and inset shows
the crystal structure of BaAl2O4 (P63). (b) Inelastic
neutron scattering spectra integrated over |Q| = 2–4
Å−1, with Ei = 17.255 meV. Profiles are shifted verticallyfor clarity.

With increasing x, the peaks started broadening,
and they entirely disappeared at x ≥ 0.07 and formeda broad peak, reflecting amorphous characteristics.
We also determined that when x was greaterthan the structural quantum critical point, Ba1x Srx Al2O4 exhibited the thermal characteristic ofamorphous materials, i.e., low thermal conductivity
comparable to that of glassy materials. This indicatesthat a part of the crystal structure loses periodicity
because of the incoherently stopped acoustic soft
phonon mode. When combined with the pair
distribution function analysis, a combination of a
glassy AlO4 network and a periodic Ba/Srarrangement is realised.
Thus, we succeeded in creating hybrid materials
thatcombinecrystalline
andamorphouscharacteristics, and elucidated the physics related
to structural quantum criticality [1]. This research canlead to further development of high-heat-resistancematerials, that can be utilised for insulation materials
in harsh environments such as outer space.
References[1] Y. Ishii, A. Yamamoto, N. Sato, Y. Nambu, S. Ohira-Kawamura,
N. Murai, K. Ohara, S. Kawaguchi, T. Mori, and S. Mori, Phys.
Rev. B 106, 134111 (2022).

Electronic Materials

IMR KINKEN Research Highlights 2023

ResearchElectronic Materials

Determination of Exchange Coupling in Heterometal Ring Cluster
using High-Frequency Electron Paramagnetic ResonanceW

e investigated a series of heterometallic ring clusters {ScnGdn} (n=4, 6, and 8) with the aim of controllingspin-wave excitations. While Gd3+ has S=7/2 spin, an Sc3+ ion has no magnetic moment and works as amagnetic linker between the Gd3+ ions. High-frequency electron paramagnetic resonance measurements
revealed a nontrivial resonance peak with a shift via antiferromagnetic exchange coupling caused by themixing between the f-state of Gd and the d-states of Sc.
Recently, the possibility of controlling spin waves
for future device applications and information sciencehas been intensively studied. Various ferromagnetic
and antiferromagnetic compounds have been used
as target systems for engineering spin-wave
excitations. Bulk magnetic materials or thin films arecomposed of boundaries or interfaces, and theformation of these broken symmetries causes
difficulties in the handling of spin waves. Moreover,the size of the system cannot be scaled down to thenanometer scale.
A ring cluster complex is a new breakthrough inthe field of “spintronics” because of its inherent
advantages. First, a spin wave can be excited withina nanoscale cluster in a ring shape with a perfectcyclic boundary condition. The coupling between
clusters is negligibly small. Owing to the ring shape,a series of spin waves can be excited as higher-order
excitations. However, to utilize these advantages, wemust overcome two challenges: 1) synthesis of ideal
ring compounds and 2) control of spin waves.
Using amino-polyalcohol ligands with both N
and O donors, we obtained a series of Sc–Gd
heterometallic rings with ring topologies. As a basic
unit, we used cyclic compounds and regulated thereaction conditions for a self-assembling clustersynthesis [1]. When n=8, Sc8Gd8 exhibits a saddleshaped cluster and the crystal packing is tetragonalwith S4 symmetry. The average Sc–Gd distance is
3.51 Å and the small distribution results in a magnetic
ring with a single exchange coupling parameter.
When n=6, Sc6Gd6 exhibits a wheel-like cluster with
C3 symmetry, and the crystal packing is trigonal. The
average Sc–Gd distance is 3.52 Å. When n=4,Sc4Gd4 also exhibits a wheel-like cluster with amonoclinic crystal. The average Sc–Gd distance is
3.71 Å.
The spin-wave excitations are dominated by themagnetic interactions between the Gd spins. There
are two types of interactions: exchange and dipole–
dipole interactions. The latter type of interaction isusually significantly weak, but is important for
Hiroyuki Nojiri (Magnetism Research Laboratory)
E-mail: hiroyuki.nojiri.e8@tohoku.ac.jp
URL: http://www.hfpm.imr.tohoku.ac.jp

26

IMR KINKEN Research Highlights 2023

Fig. 1 High-frequency electron spin resonance shows the
spectra of different shifts for three compounds. The
exchange coupling parameter can be determined by
the high resolution of TESRA-IMR [3].

magnetic anisotropy.
The key experiment involved determining the
Gd–Sc exchange coupling via high-frequency
electron paramagnetic resonance (EPR). We
observed the systematic frequency dependence of
the EPR spectra at frequencies between 190 and
360 GHz using a terahertz electron spin resonance(ESR) system called Terahertz ESR ApparatusInstitute of Materials Research (IMR) developed by
the magnetism division of IMR [2]. The spectra show
the linear frequency-field relations with small zerofield gaps. The gaps are attributed to the exchange
constants of −0.01, −0.01, and −0.03 cm –1 for n=8,
6, and 4 compounds, respectively. These values are
consistent with the variations in Sc–Gd distances.
References[1] H. L Zhang, Y. Q. Zhai, H. Nojiri, C. Schröder, H. K. Hsu, Y. T.
Chan, Z. Fu, and Y. Z. Zheng, J. Am. Chem. Soc. 144,15193(2022).
[2] H. Nojiri, Y. Ajiro, T. Asano, and J.-P. Boucher, New J. Phys. 8,
218 (2006).
[3] Reprinted with permission from {/doi.org/10.1021/jacs.2c05421}.
Copyright 2022 American Chemical Society.

IMR KINKEN Research Highlights 2023

Electronic Functionality Sensitive to Crystalline Ordering in
Ferromagnetic Alloy Thin Films

We fabricated ferromagnetic thin films of a full-Heusler alloy Co2FeSn, which is theoretically proposed to havea topological band structure in the L21-type ordered phase. By establishing an annealing method to promote
the L21-type crystalline ordering, we examined the changes in the electrical and thermoelectric transport
properties. Our results highlight the critical importance of controlling the crystalline ordering when exploring the
topological electronic states and exotic functionality in full-Heusler alloy thin films.
Ordered alloys have been investigatedintensively in the field of spintronics because there
are several useful ferromagnetic materials with highCurie temperatures and spin polarization. Of
particular interest is a ternary system called the L21type full-Heusler alloy, which is an intermetallic
compound with the stoichiometric composition of
X2YZ (in general, X and Y are transition elements,
and Z is a typical element). In the past decade, theresearch on full-Heusler alloys has been expanded
to topological physics focusing on the investigations
on nontrivial electronic states emerging in solids.
Specific crystal lattices, symmetries, and spin-orbit
coupling play a role in yielding topological features.
The feasibility of incorporating various elements andcontrolling the degree of the crystalline ordering(and consequently, the lattice symmetry) in X2YZ
alloys makes this system particularly appealing tostudy the structure-topological property relationship.
Motivated by this point, we attempted tofabricate thin films of a nodal line semimetal
candidate, Co2FeSn [1]. The nodal line semimetal isa class of topological materials in which finite
contributions of Berry curvature arise near theenergy of the nodal lines produced by bandcrossing, resulting in giant anomalous Hall andNernst effects. Despite the possible superiortransport properties, methods to promote thecrystalline ordering of the Co–Fe–Sn ternary alloy ina thin-film form have not yet been established. By
combining the co-sputtering deposition at a lowtemperature (150 °C) and annealing at a hightemperature (600–700 °C), we successfully
promoted the crystalline ordering from the lessordered B2-type (Fig. 1(a)) to the L21-type (Fig. 1(b))
in Co2FeSn thin films on MgO(001) [2]. Moreover, bylaunching a measurement system capable ofevaluating electrical and thermoelectric transport
properties in thin films, we revealed the strong andqualitatively different influences of the crystalline
ordering on the anomalous Hall effect. As shown in
Fig. 1(c), the Hall conductivity becomes almost

Fig. 1 Crystal structures of (a) B2-type and (b) L21-type
Co2YZ. (c) Annealing temperature dependence of
anomalous Hall conductivity. For comparison, thetheoretical value [1] is included.

equal to the theoretical value by performing thehigh-temperature annealing that induces the L21type ordering. This result provides a platform for
exploring giant magnetic responses in Co2FeSn by
Fermi-energy tuning. Boosted by these newly added
aspects of topological physics, the interest in
metallic alloys will continue to be inexhaustible.
References[1] J. Noky, J. Gooth, C. Felser, and Y. Sun, Phys. Rev. B 98,
241106(R) (2018).
[2] K. Fujiwara, K. Shibata, S. Nishimura, J. Shiogai, and A.
Tsukazaki, AIP Adv. 12, 065030 (2022).

Kohei Fujiwara (Low Temperature Physics Research Laboratory)
E-mail: kohei.fujiwara@tohoku.ac.jp
URL: http://mu.imr.tohoku.ac.jp/index_en.html

IMR KINKEN Research Highlights 2023

27

Electronic Materials

Understanding the Mechanism of Quantum Spin-LiquidState in Organic Materials

Inelastic neutron scattering measurements have revealed an abrupt change in the phonon damping at the 6 K
anomaly in the quantum spin-liquid candidate κ-(BEDT-TTF)2Cu2(CN)3. This is interpreted as a phase transition
to the valence-bond solid state on the basis of an effective model describing the spin-charge coupling in the
dimer-Mott system.
Experimental observation of lattice vibrations byinelastic neutron scattering experiments has been
limited to a few exceptional materials because large
single crystals are required for these experiments. Aninternational collaborative research group has recently
succeeded in observing lattice vibrations coupled withelectronic dielectricity and antiferromagnetic ordering in
the molecular organic Mott insulator κ-(BEDTTTF)2Cu[N(CN)2]Cl, where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene [1]. Such couplings andthe inter-correlated degrees of freedom among charge,
spin, and lattice states in a strongly correlated electron
system are important for the possible quantum liquidstate.
We succeeded in obtaining a clear lattice vibration
signal from the quantum spin-liquid candidate κ-(BEDTTTF)2Cu2(CN)3 via inelastic neutron scatteringexperiments [2]. This experiment was conducted as aninternational remote experiment through online remote
operation and online meetings between Japan andEurope because overseas travel was not possible owing
to the global spread of the coronavirus infection at thetime of the experiments.
In the inelastic neutron experiment, we observedthat the optical mode at E = 4.7 meV, which is considered
to be the breathing mode of the BEDT-TTF moleculardimer, is strongly over-damped above 6 K. Below 6 K,
the line width rapidly narrows to the instrumental
resolution and changes to a normally decaying state.
The breathing mode of the BEDT-TTF molecular dimer iscommon to both κ-(BEDT-TTF)2Cu[N(CN)2]Cl andκ-(BEDT-TTF)2Cu2(CN)3 and is closely related to thechange in the π-electron state. The coupling between
the π-electron and the breathing mode is a common
property of the dimer-Mott-type molecular organic
conductors. Comparison of this temperature change inthe breathing mode with a theoretical model thatconsiders the π-electron charge disproportionation
within the BEDT-TTF dimer suggests that a spin singlet
state, in which BEDT-TTF molecules form a tetramer, i.e.,a valence-bond-solid (VBS) state, is expected below 6
K, rather than the quantum spin-liquid state in which thegeometrical frustration in the triangular lattice has beenFig. 1 International remote inelastic neutron scatteringexperiment conducted between France, Germany, andJapan.

Fig. 2 Conceptual diagram of electronic state of κ-(BEDTTTF)2Cu2(CN)3. Transition from molecular dimer state(paramagnetic state) to molecular tetramer state (spinsinglet state) with the development of antiferromagnetic
correlations

discussed as the origin so far (Fig. 2).
References[1] M. Matsuura, T. Sasaki, S. Iguchi, E. Gati, J. Mueller, O. Stockert, A.
Piovano, M. Bohm, J. T. Park, S. Biswas, S. M. Winter, R. Valenti, A.
Nakao, and M. Lang, Phys. Rev. Lett. 123, 027601 (2019).
[2] M. Matsuura, T. Sasaki, M. Naka, J. Mueller, O. Stockert, A. Piovano,N. Yoneyama, and M. Lang, Phys. Rev. Research 4, L042047 (2022).

Takahiko Sasaki (Low Temperature Condensed State Physics Research Laboratory)
E-mail: takahiko.sasaki.d3@tohoku.ac.jp
URL: http://cond-phys.imr.tohoku.ac.jp/index_e.html

28

IMR KINKEN Research Highlights 2023

IMR KINKEN Research Highlights 2023

Low-Energy Spin Dynamics Coupled with Hole Mobility inT*-Type La0.86Eu0.86Sr0.28CuO4

T

he interplay between low-energy spin dynamics and the mobility of doped holes in a T*-type La0.86Eu0.86Sr0.28CuO4(LESCO) was investigated via 139La-nuclear magnetic resonance and electrical resistivity measurements. We
clarified the reduction in the spin fluctuations due to the localization of the holes with decreasing temperature. The
result suggests a coupling between the spin and charge degrees of freedom in LESCO.
The magnetic properties of CuO2 layers in hightemperature superconducting (SC) materials are
significantly dependent on the charge mobility.
Therefore, the evolution of spin correlation withdoping has been extensively studied. It is wellknown that a small amount of hole doping into
La2CuO4 having distorted K2NiF4-type crystal
structure containing CuO6 octahedral tilts destroys
the antiferromagnetic order. Sufficient number ofhole carriers induces incommensurate spin
structure, which is concomitant with the emergenceof the SC phase. However, such doping-dependent
evolution of magnetism is recently thought to be
influenced by the local structure around the CuO2
plane and Cu coordination through the modificationof the electronic state.
Our study on T*-type La1-x/2Eu1-x/2Srx CuO4
(LESCO) having CuO5 coordination with one site ofapical oxygen revealed the appearance of an SC
phase with marginal hole doping with x ≤ 0.20. The
phase diagram of LESCO shows a possibility for the
emergence of superconductivity in an Sr-freecompound, similar to the SC phase for T’-type La2x (Sr,Ca)x CuO4 with planer coordination. Therefore,
we investigated the low-energy spin dynamics via
139 La-nuclear magnetic resonance measurementsof LESCO.
In Fig. 1, the spin-lattice relaxation rate (1/T1)
and the electrical resistivity (ρ) are plotted for theas-sintered compound as a function of inverse
temperature [1]. The compound was a nonsuperconductor and exhibited spin-glass behavioratlowtemperatures.
Similartemperaturedependence can be observed for two parameters.
Considering the relations of ρ ∝ exp(Eg/kBT) and 1/T1
∝ exp(2J/kBT), we evaluated that 2J/kBT = 7.8 ± 0.7
and Eg/kBT = 6.0 ± 0.1. The comparable values of 2J
and Eg suggest that the energy of the transport gap(Eg) and the characteristic energy of the spin
dynamics (2J) in the as-sintered compound isnearly the same. Therefore, the charge and spin
dynamics could be coupled with each other.
A comparable energy scale of Eg and 2J are

Fig. 1 1/T dependence of 1/T1 (red circles: spin-lattice
relaxation rate) and ρ (blue line: electrical resistivity) in
as-sintered La0.86Eu0.86Sr0.28CuO4 (LESCO). Inset
represents 2J/kB and Eg/kB for LESCO andLa2-x Srx CuO4.

reported for the lightly doped La2-xSrxCuO4 (LSCO).
The low-energy spin dynamics is governed by holemobility; that is, the spin fluctuations slow down
owing to the localization of mobile carriers when thetemperature is lowered. The inset in Fig. 1 shows
two values for the LESCO located nearly the
extrapolated positions for LSCO, suggesting asimilar mechanism in suppressing low-energy spin
dynamics. This spin fluctuations disappear whensuperconductivity emerges owing to oxidation
annealing, indicating a drastic variation in spincorrelations
associatedwithmetal-insulatortransition.
References[1] T. Taniguchi, S. Kitagawa, K. Ishida, S. Asano, K. Kudo, M.
Takahama, P. Xie, T. Noji, and M. Fujita, J. Phys. Soc. Jpn. 91,
074710 (2022).

Masaki Fujita (Quantum Beam Materials Physics Research Laboratory)
E-mail: fujita@tohoku.ac.jp
URL: http://qblab.imr.tohoku.ac.jp/index-e.html

IMR KINKEN Research Highlights 2023

29

Electronic Materials

Electric Quadrupolar Correlation in the Frustrated Quantum
Magnet Tb2Ti2O7

G

eometrically frustrated systems have been serving as a fertile ground for studying nontrivial magnetic
phenomena. The pyrochlore lattice is a prototypical structure having geometrical frustration. Among the various
pyrochlore materials, Tb2Ti2O7 shows unique magnetic properties because Tb3+ ions have an electric
quadrupole. Here, we investigated the quadrupole correlation in Tb-rich Tb2Ti2O7 by measuring the elastic
constant and magnetostriction.

In Tb2Ti2O7, Tb3+ ions have a total angularmomentum J = 6. The trigonal crystalline electricfield partially lifts the degeneracy and produces a
low-energy level scheme, that consists of groundstate and first-excited doublets separated by anenergy gap of only ≈ 18 K. In addition to a magnetic
dipole moment, these doublets carry a large electric
quadrupolar moment, which couples to the local
strain. Recently, the quadrupole order wasdetermined to be approximately 0.5 K for Tb-rich
Tb2Ti2O7 crystals. These findings imply that thequadrupolar moment plays an important role in thissystem. Thus, this system can be viewed as afrustrating system with electric quadrupole degreeof freedom. To probe the correlation of the electric
quadrupole, we measured the elastic constant andmagnetostriction and compared the experimental
results with the calculation based on a single-ion
model [1].
Figure 1 shows the experimentally observedand calculated magnetostriction based on a singleion model at various temperatures. Although thecalculation reproduced experimental data above 10
K, a discrepancy was observed between thecalculated and experimental data in the lower
temperature region. This observation implies theevolution of electric quadrupole correlation below
10 K. A similar conclusion was obtained for theelastic constant experiment.
Figure 2 shows the magnetic phase diagram in
Tb-rich Tb2Ti2O7. While the orbital ordering isobserved at the low-temperature (T<0.4 K) and lowmagnetic-field region, a strong quadrupole
correlation exists in the higher temperature andhigher magnetic-field region (the cyan-colored
region in Fig. 2). The evolution of correlation seems
to be induced by the geometrical frustration in thissystem.

Fig. 1 Magnetostriction at various temperatures [1]. The
calculations based on a single-ion model are alsoplotted for comparison.

Fig. 2 Magnetic phase diagram in Tb-rich Tb2Ti2O7 [1].

Tomioka, T. Nojima, and Y. Onose, Phys. Rev. B 105, 094414

References(2022).

[1] Y. Nii, Y. Hirokane, S. Nakamura, N. Kabeya, S. Kimura, Y.

Yoshinori Onose (Quantum Functional Materials Physics Research Laboratory)
E-mail: yoshinori.onose.b4@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/08.html

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IMR KINKEN Research Highlights 2023

IMR KINKEN Research Highlights 2023

Development of Optical-Guiding Crystal Scintillators forHigh-Resolution Radiation Imaging

Anovel optical-guiding crystal scintillator and its fabrication method were developed. The scintillator consistsof a halide single-crystal scintillator core and glass clad. The scintillation light generated in the core with anangle greater than the critical angle is completely reflected at the interface with the glass, thereby functioning
as an optical waveguide such as an optical fiber. Owing to the light guiding system, the optical-guiding crystal
scintillator shows high sensitivity and high spatial resolution for radioactive particles.
Scintillators coupled with photodetectors are widelyused in radiation imaging applications such medical
imaging, security, high-energy physics, astrophysics,
and oil-well logging. In X-ray imaging applications,radiation imaging sensors are composed ofphotodetector arrays coupled with a scintillator plate.
Here, we propose a novel optical-guiding crystal
scintillator (OCS). It consists of a halide single-crystal
scintillator core such as Tl-activated CsI (Tl:CsI), Eudoped SrI2 (Eu:SrI2) scintillators with a borosilicate glass
clad. The scintillation light that is generated with anangle greater than the critical angle is completelyreflected at the interface with the glass, functioning as
an optical waveguide such as optical and scintillatingfibers (Fig.1-left). Here, the critical angles of Tl:CsI(nD=1.78) and Eu:SrI2 (nD=2.05) with borosilicate glasstype (nD=1.47) OCSs were calculated to be as small as
55.7° and 45.8°, respectively. Figure 1-right shows thephotograph of OCS fiber scintillators under ultraviolet(UV) irradiation at an edge that was cut from the side ofa fabricated fiber with a total length of approximately
200–300 m. The light generated after UV irradiation islight guided to the other side of the fibers. Figure 2
shows micrographs of an OCS fiber. The central
scintillator crystal fiber was covered by glass. An OCS
fiber with a minimum core diameter of 15.4 μm with 5.1
μm thick clad was obtained. Figure 3 shows thephotographs and backscattered electron image (BEI) of
a 1 mm thick bundled OCS plate. The image from the
top shows several fiber scintillators of 30 μm diameterbundled together. Figure 4 shows a BEI of the bundled
OCS plate and corresponding electron backscattereddiffraction images. The scintillator cores were single
grains. Position resolution was evaluated using the plateand α-ray. The full width at half maximum (spatial
resolution) was 37.2 μm. The obtained spatial resolution
was equivalent to that of the core diameter. Owing to thelight guiding system, the bundled OCS plate exhibitedhigh spatial resolution for radioactive particles.
References[1] R. Yajima et al., Ceramic International (2023) in press.

Fig. 1 Schematic of optical-guiding crystal scintillator(OCS) (left) and the photograph of OCS fibers underultraviolet excitation (right).

Fig. 2 Micrographs of OCS fibers

Fig. 3 Photograph of bundled OCS (left), 1 mm thickbundled OCS plate (right)

Fig. 4 Backscattered electron mage of the bundled OCS
plate and corresponding electron backscatter diffraction.

Akira Yoshikawa (Advanced Crystal Engineering Research Laboratory)
E-mail: akira.yoshikawa.d8@tohoku.ac.jp
URL: http://yoshikawa-lab.imr.tohoku.ac.jp/index-e.html

IMR KINKEN Research Highlights 2023

31

Electronic Materials

Nonthermal Melting of Charge Density Wave Order in VTe2

U

ltrafast phase control of materials by femtosecond laser pulses is expected to be a significantly crucial techniquefor future photonic devices such as phase change materials. In this work, the ultrafast optical response of VTe2, atypical transition-metal dichalcogenide showing the charge density wave (CDW), was investigated. We clarified themechanism and timescale of photoinduced phase transition in VTe2 originating from the melting of the CDW order.
Photoexcitation of semiconductor materials using
femtosecond lasers can induce a nonthermal ultrafast
phase transition, which is primarily dominated byelectron excitations [1]. This process is called as
photoinduced phase transition (PIPT). In the research
field of PIPT, transition-metal dichalcogenides (TMDCs)
are fascinating targets owing to their distorted crystal
structure originating from a charge density wave
(CDW). The PIPT from a CDW to non-CDW phase iscalled “CDW melting,” and researchers have reported
CDW melting in several TMDCs so far [2,3].
In this work, we investigated the mechanism of
CDW melting in VTe2, a typical TMDC, which exhibits a
CDW phase below 480 K, using ultrafast optical
spectroscopy (UOS) [5]. UOS generally enables us toinvestigate the ultrafast optical response of materials bymeasuring a transient reflectivity change as a functionof elapsed time. A unique feature of our measurement
system is the use of white light as the probe light, using
which we can simultaneously observe the reflectivity
changes over a wide range of wavelengths. The
wavelength of pump light used here was 800 nm. A
single-crystal sample was grown using the Bridgman
method. A clean (110) surface was prepared using the
Scotch-tape method, and it was mounted on a thermo/
cryostat. UOS was performed at a sample temperatureof 78 K.
Figure 1 shows the UOS responses after pumping
different excitation fluences (F), which was monitored
using a 500 nm probe. At each fluence, the reflectivity
decreased just after photoexcitation, and the degree of
decrease was greater at a higher F. The oscillation
during reflectivity change is called “coherent opticalphonon” (COP), originating from nonthermal atomic
oscillations induced by electron excitation. As thefrequencies of COP coincide with those of the allsymmetric Raman active modes of substances, theoscillation analysis enables us to identify the (CDW or
non-CDW) phases of VTe2. The inset of Figure 1 shows
the fast Fourier transforms of the time derivative ofreflectivity changes. At the lower F range (F < 1.21 mJcm-2), two modes are observed at around 1.6 and 2.5
THz; these are attributed to the CDW phase, indicatingthat the CDW phase of VTe2 remained even after the
lower fluence excitation. At a higher F range (F ≧1.21

Fig. 1 Transient reflectivity changes after photoexcitation
as functions of elapsed time monitored by 500 nm
probe. The inset indicates fast Fourier transform (FFT)
results of time derivative of reflectivity change. The FFTtime range is from 0 to 3 ps.

mJ cm-2), a new mode can be observed at approximately
4.4 THz. This mode can be attributed to the A1g modeof the non-CDW phase. A simple evaluation of thesample temperature after excitation on the adiabatic
condition indicated that the temperature did not exceed
the transition temperature in the F range used in thisstudy. Thus, we clearly observed that the CDW meltingof VTe2 proceeds in a nonthermal manner within an
ultrashort time duration (picosecond order). In addition
to the previous literature employing ultrafast electron
diffraction method for VTe2 [4], our recent UOS study[5] has accumulated more detailed information on thetransformation mode and time scale of PIPT in VTe2.
References[1] S. K. Sundaram and E. Mazur, Nat. Mater. 1, 217 (2002).
[2] E. Möhr-Vorobeva, S. L. Johnson, P. Beaud, U. Staub, R. De
Souza, C. Milne, G. Ingold, J. Demsar, H. Schaefer, and A. Titov,Phys. Rev. Lett. 107, 036403 (2011).
[3] J. Lee, J. Bang, and J. Kang, J. Phys. Chem. Lett. 13, 5711 (2022).
[4] A. Nakamura, T. Shimojima, Y. Chiashi, M. Kamitani, H. Sakai, S.
Iwashita, H. Li, and K. Ishizaka, Nano Lett. 20, 4932 (2020).
[5] H. Tanimura, N. L. Okamoto, T. Homma, Y. Sato, A. Ishii, H.
Takamura, and T. Ichitsubo, Phys. Rev. B 105, 245402 (2022).

Hiroshi Tanimura (Structure-Controlled Functional Materials Research Laboratory)
E-mail: hiroshi.tanimura.b7@tohoku.ac.jp
URL: http://ilab.imr.tohoku.ac.jp/

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IMR KINKEN Research Highlights 2023

Host–Guest Electron Transfer Mechanism for Magnetism ManipulationIn porous materials, the host–guest electron transfer (HGET) mechanism, which affects both the electronic
structure and spin states of the host framework, is an effective tool for manipulating physical properties. We
successfully demonstrated a reversible magnetic phase change between an antiferromagnet and a paramagnet
by exposing or evacuating I2 as a guest molecule, which is based on the HGET mechanism in a chargevariable layered porous magnet.
Host–guest electron transfer (HGET) in
molecular framework systems, such as metal–organic frameworks (MOFs), is a critical trigger for
implementing drastic changes in both the hostframework and the guest, and can enable thepossible modulation of the electronic and magnetic
properties
offrameworks.
Post-synthetic
incorporation of redox-active guests into redoxactive MOFs is a fascinating strategy for achieving
guest-driven
reversible
HGET.
However,demonstrating a reversible phase change related tomagnetic and electronic long-range ordering is asignificant challenge [1].
In this study, a porous magnetic MOF, [{Ru2(2,6F2PhCO2)4}2(BTDA-TCNQ)] (1), where 2,6-F2PhCO2−
and BTDA-TCNQ represent 2,6-difluorobenzoate
and bis[1,2,5]dithiazolotetracyanoquinodimethane,respectively, was synthesized, which showed a
HGET-induced magnetic phase change using I2 asa redox-active guest [2]. Pristine porous compound
1 was post-synthetically transformed into [{Ru2(2,6F2PhCO2)4}2(BTDA-TCNQ)]I3 (1-I3) via I2 vapor
treatment. Notably, compound 1 was recovered
reversibly via a crystal-to-crystal transformation
upon evacuation of the I2-adsorbed solid sample
1-I3 at 100 °C (Fig. 1). The pristine guest-freecompound 1 was an antiferromagnet with a Néel
temperature of 90 K (= TN) (Fig. 2) due to thepresence of interlayer antiferromagnetic interactions
between ferrimagnetically ordered layers with a[{Ru2II,III}+–(BTDA-TCNQ)•− –{Ru2II,II}0] ∞ composition(Fig. 1), in which [Ru2II,III]+, [Ru2II,II], and BTDATCNQ•− possess spin states of S = 3/2, 1, and 1/2,
respectively, whereas the I2-exposed 1-I3 compoundtransformed into a paramagnet with the formula of[{Ru2II,III}+–(BTDA-TCNQ)0 –{Ru2II,II}](I3−) (Fig. 1),
demonstrating the occurrence of HGET expressedas BTDA-TCNQ•− + 3/2(I2) → BTDA-TCNQ0 + I3−.
This HGET in the MOF pores resulted in theparamagnetic behavior of 1-I3 (Fig. 2) with isolated
spin sets of S = 3/2 and 1 for [RuII,III2]+ and [RuII,II2],
respectively.
Notably, the 1-I3 paramagnet, despite
containing a neutral BTDA-TCNQ moiety, exhibited

Fig. 1 Formula units schematics for the guest-freecompound 1 and I2-adsorbed compound 1-I3.

Fig. 2 Temperature dependence of field-cooledmagnetization curves measured at 100 Oe for 1 (gray)and 1-I3 (purple).

a hundred-fold increase in electrical conductivity
when compared to that of compound 1 after I2
adsorption. This could be due to the hopping
electronic transfer between partially chargedelocalized [Ru2] units ([Ru(1)2](1–δ)+ and [Ru(2)2]δ+units (δ ≈ 0.2)) via the neutral BTDA-TCNQ moiety,as confirmed by theoretical calculations. This work
demonstrates the first investigation of magnetic
phase switching and electronic modulation via
HGET in a porous magnetic MOF. The proposed
HGET strategy will not only pave a new path toward
the development of chemo-responsive magnets,
but will also facilitate extensive applications as a
new class of memories, sensors, and switches.
References[1] H. Miyasaka, Bull. Chem. Soc. Jpn. 94, 2929 (2021).
[2] J. Zhang, W. Kosaka, Y. Kitagawa, and H. Miyasaka, Angew.
Chem. Int. Ed. 61, e202115976 (2022).

Jun Zhang and Hitoshi Miyasaka (Solid-State Metal-Complex Chemistry Research Laboratory)
E-mail: zhangjun@imr.tohoku.ac.jp, hitoshi.miyasaka.e7@tohoku.ac.jp
URL: http://www.miyasaka-lab.imr.tohoku.ac.jp/cn5/HOME-Eng.html

IMR KINKEN Research Highlights 2023

33

Electronic Materials

Observation of Large Antisymmetric Interlayer Exchange Couplingin Synthetic Antiferromagnet with Wedge-Shaped Layers

Antisymmetric interlayer exchange coupling (AIEC) plays pivotal roles in the magnetization switching of asynthetic antiferromagnet by inducing magnetization canting. We observed a large AIEC for perpendicularly
magnetized Pt/Co/Ir/Co/Pt with wedge-shaped layers. The effective field of the AIEC is related to the symmetricinterlayer exchange coupling, providing guides to enhance the AIEC. We also demonstrated that perpendicularmagnetization can be switched solely by applying an in-plane magnetic field owing to a large AIEC.

Interlayer exchange coupling (IEC) has been
widely studied since the 1980s in various metallic
superlattices. The symmetric IEC energy isexpressed as JAF(m1·m2), where JAF denotes theantiferromagnetic coupling strength, and m1 and m2
represent the magnetization vectors of two
ferromagnets separated by a nonmagnet. The
symmetric IEC aligning m1 and m2 in antiparallel
provides a synthetic antiferromagnet.
Recently, antisymmetric IEC (AIEC) was
reported in metallic superlattices when the in-planespatial inversion symmetry was broken [1,2]. The
AIEC energy is expressed as DAIEC·(m1 × m2), where
DAIEC is the AIEC vector determined by the systemsymmetry. Thus, the AIEC cants the magnetizationsin the two ferromagnetic layers, which leads to chiralmagnetic configurations. However, the controllability
and applicability of AIEC have not yet been
examined, and the systematic experiments
exploiting well-controlled in-plane structural
asymmetry are indispensable.
We exploited the wedge-shaped layers tointentionally break the in-plane spatial inversion
symmetry, and investigated the AIEC for theperpendicularly magnetized Pt/Co/Ir/Co/Pt withwedge-shaped layers to clarify the nature of AIEC
[3]. A double-wedged sample (DWS) of Ta (1)/Pt (2)/Co (tCo)/Ir (tIr)/Co (0.5)/Pt (2)/Ta (1) (thickness innanometers) was deposited on a SiOx substrate.
The values of tCo and tIr were continuously varied
from 0.6 to 1.6 nm and from 0 to 1.5 nm, respectively.
The wedge direction of the Ir layer was orthogonal
to that of the wedged Co layer at the bottom, as
illustrated in Fig. 1a. DWS was patterned into Hallbar-shaped devices, and the magnetic properties
were investigated by exploiting the anomalous Hall
effect (AHE). The AHE curves exhibited the periodic
variation in the saturation field (µ0Hs) against tIr,
indicating a symmetric IEC between two Co layers.
The AHE curves were significantly shifted byapplying an additional in-plane magnetic field(µ0Hip) of 50 mT (Fig. 1b), indicating the existence ofTakeshi Seki (Magnetic Materials Research Laboratory)
E-mail: takeshi.seki@tohoku.ac.jp
URL: http://magmatelab.imr.tohoku.ac.jp/

34

IMR KINKEN Research Highlights 2023

(a )

9 mm

m

9m

Pt (2)(b)

Ta (1)Co (0.5)
Ir (tIr)
Co (tCo)Pt (2)z

Ta (1)
SiOx sub.

yxFig. 1 (a) Illustration of double-wedged sample (DWS). (b)Anomalous Hall effect curves without µ0Hip (blue) andwith µ0Hip (red and black) for DWS at tCo ~ 0.80 nm andtIr ~ 0.27 nm.

AIEC. The largest switching field shift (µ0∆Hsw) was
14.8 mT at tCo = 0.80 nm and tIr = 0.27 nm, which
was an order of magnitude larger than the values
reported previously (0.7–1.7 mT [1,2]). Similar to thetIr dependence of μ0Hs, µ0∆Hsw showed theoscillatory change against tIr, suggesting that theeffective field of AIEC is related to the symmetric
IEC. Moreover, we experimentally demonstrated theperpendicular magnetization switching solely
induced by µ0Hip via the AIEC. This study provides
crucial information to manipulate three-dimensional
chiral magnetic structures utilizing the AIEC.
References[1] D.-S. Han, K. Lee, J.-P. Hanke, Y. Mokrousov, K.-W. Kim, W.
Yoo, Y. L. W. van Hees, T.-W. Kim, R. Lavrijsen, C.-Y. You, H. J.
M. Swagten, M.-H. Jung, and M. Kläui, Nat. Mater. 18, 703(2019).
[2] A. Fernández-Pacheco, E. Vedmedenko, D. Petit, and R. P.
Cowburn, Nat. Mater. 18, 679 (2019).
[3] H. Masuda, T. Seki, Y. Yamane, R. Modak, K. Uchida, J. Ieda,
Y. C. Lau, S. Fukami, and K. Takanashi, Phys. Rev. Appl. 17,054036 (2022).

IMR KINKEN Research Highlights 2023

Fermi Surfaces of Spin-Triplet Superconductor UTe2 Unveiledby Quantum Oscillations

Quantum oscillations (de Haas–van Aphen oscillations) were successfully observed for the first time in the spin-

triplet superconductor UTe2 using ultra-clean single crystals grown by the flux method. Two types of cylindrical
Fermi surfaces with strong corrugations were detected. The experimental results were in good agreement withthose of band calculations considering the onsite Coulomb repulsion U. The detected cyclotron effective masses
were significantly large, ranging from 32 to 57 m 0, revealing the heavy electronic states that play a dominant rolein unusual superconducting properties.
UTe2 is one of the hottest materials in condensed
matter physics [1]. Superconductivity was observed at
1.6-2 K without magnetic ordering at very low
temperatures. The most remarkable feature is the fieldrobust superconductivity, revealing field-reentrant
superconductivity up to 35 T, when the field is appliedalong the hard-magnetization b-axis in an orthorhombic
structure. Another spectacular event is the multiple
superconducting phases that can be observed underpressure and a magnetic field, indicating the different
superconducting order parameters [2]. These
properties are consistent with a scenario for spin-triplet
superconductivity, which is also an informative field of
research for studying topological superconductivity.
To understand this fascinating superconducting
mechanism, the electronic states must be
experimentally clarified. We succeeded in growing
ultra-clean single crystals of UTe2 using the NaCl/KClflux method, and clearly detected the quantum
oscillations, that is, the de Haas–van Alphen (dHvA)
oscillations for the first time [3]. Figure 1(a) shows thedHvA oscillations when the field is tilted from the c- to
a-axis. Clear dHvA oscillations appeared above thesuperconducting upper critical field, Hc2, which aredenoted by the arrows pointing upward. The angulardependence of the dHvA frequencies are shown in
Fig. 1(b). The frequencies increase with field angle,
indicating two types of corrugated cylindrical Fermi
surfaces, as shown in the inset of Fig.1(b). The
experimental results are in good agreement with theresults of band calculations with the Coulomb repulsion
U (U=2eV). The detected cyclotron effective masses
were significantly large, ranging from 32 to 57 m 0,
where m 0 is the rest mass of electron, which is inagreement with the heavy electronic states as well as
the mixed valence states of UTe2.

Fig.1 (a) de Haas–van Alphen (dHvA) oscillations at
different field angles tilted from H || c to a-axes in UTe2.
(b) Angular dependence of dHvA frequencies and thecalculated Fermi surfaces in UTe2.
[2] H. Fujibayashi, G. Nakamine, K. Kinjo, S. Kitagawa, K. Ishida, Y.
Tokunaga, H. Sakai, S. Kambe, A. Nakamura, Y. Shimizu, Y.
Homma, D. Li, F. Honda, and D. Aoki, J. Phys. Soc. Jpn. 91,

References

043705 (2022).

[1] D. Aoki, J. P. Brison, J. Flouquet, K. Ishida, G. Knebel, Y.

[3] D. Aoki, H. Sakai, P. Opletal, Y. Tokiwa, J. Ishizuka, Y. Yanase, H.

Tokunaga, and Y. Yanase, J. Phys. Condens. Matter 34, 243002

Harima, A. Nakamura, D. Li, Y. Homma, Y. Shimizu, G. Knebel, J.

(2022).

Flouquet, and Y. Haga, J. Phys. Soc. Jpn. 91, 083704 (2022).

Dai Aoki (Actinide Materials Science Research Laboratory)
E-mail: dai.aoki.c2@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/25.html

IMR KINKEN Research Highlights 2023

35

Electronic Materials

Building of Si and Si/SiC Composite Materials by Electron
Beam Additive Manufacturing

We successfully fabricated Si and Si/SiC composite materials for the first time using electron beam additive

manufacturing (EBM). As Si and Si/SiC are non-metals and have high electrical resistance, manufacturing
these materials has been challenging. This successful case is a result that expands the possibilities of EBM.

Si and Si/SiC composite materials are primarily
used in the field of semiconductor production
equipment, the use of additive manufacturing isdesired for the development of these materials.
Electron beam additive manufacturing (EBM) isa high-temperature vacuum process that enables
manufacturing with less defect formation andoxidation contamination, and is suitable for
manufacturing Si-based materials, which are brittle
and require high purity. However, the biggest
problem is the phenomenon called "smoking," inwhich the powder bed can scatter and disappear
similar to smoke owing to the charge-up of electrons.
The smoking phenomenon is related to the bulk
properties of the powder, dielectric properties of thesurface oxide film [1], and number of contact points
between the powders (coordination number [2]). As
Si-based materials are semi-metallic materials andhave high electrical resistance, manufacturing themusing EBM is considered to be difficult.
Our research team measured the electricalresistance of the powder and confirmed that theelectrical properties of the Si powder are at a levelthat can be built. Moreover, by adding Si to the SiC
powder to create a Si/SiC composite material
powder, the electrical properties of the Si/SiC
composite material were confirmed to be at thesame level as that of Si (Fig. 1).
We built the above material and succeeded in
producing a cylindrical sample of 10 mm φ×10 mm.
These samples exhibited significantly few internal
defects and were composed of high-density objects
with a relative density (which is the ratio of themeasured density to the theoretical density) close to100%. In the Si/SiC composite material, SiC particles
were uniformly dispersed in the Si matrix, which isconsidered to be a structure obtained by the rapid
solidification characteristic of the EBM (Fig. 2).
This result is a breakthrough that modifies theconventional wisdom that the EBM method can only
be used for metal powders, and is considered to bea successful case that is expected to significantly
contribute to technological progress.

Fig. 1 Plot of electrical resistivity of powder for electron
beam additive manufacturing versus time.

Fig. 2 Scanning electron microscopy-backscatteredelectron image of Si/SiC composite material.

References[1] A. Chiba, Y. Daino, K. Aoyagi, and K. Yamanaka, Materials 14,4662 (2021).
[2] S. Yim, H. Bian, K. Aoyagi, K. Yamanaka, and A. Chiba, Addit.
Manuf. 51, 102634 (2022).

Takayuki Ishii and Akihiko Chiba (Tokyo Electron Additive Manufacturing for Multimaterials Research Laboratory)
E-mail: takayuki.ishii.q4@dc.tohoku.ac.jp, akihiko.chiba.d3@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/31.html

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IMR KINKEN Research Highlights 2023

Research Centers

IMR KINKEN Research Highlights 2023

ResearchResearch Centers

High Thermal Conductivity in Wafer-Scale Cubic Silicon
Carbide Crystals
International Research Center for Nuclear Materials Science

An isotropic high thermal conductivity exceeding 500 W/m·K at room temperature in high-quality wafer-scale
cubic SiC (3C-SiC) crystals was reported, which is the second highest among large crystals (only surpassedby diamond). Furthermore, the thermal conductivity of 3C-SiC films was even higher than that of diamond thinfilms of equivalent thickness.

SiC plays a fundamental role in power electronics,
optoelectronics, and quantum computing. In the field of
power electronics, SiC-based power devices
demonstrate significant potential for replacing Si-based
technology owing to its fast-switching speeds, lowlosses, and high breakdown voltage. SiC can be in theform of multiple types of crystals with different atomic
arrangements, such as hexagonal (4H, 6H, etc.) andcubic (3C) structures. The hexagonal 4H-SiC and6H-SiC have been widely developed andcommercialized. Cubic-structured 3C-SiC has arelatively simple crystal structure; therefore, it isexpected to exhibit high thermal conductivity. However,
the reported thermal conductivity (90 W/m·K) of 3C-SiC
is lower than that of the structurally more complex 6H
and 4H phases (320 W/m·K) and the theoretically
predicted intrinsic thermal conductivity of 3C-SiC.
Here, we report a high isotropic thermal
conductivity exceeding 500 W/m·K at room temperature
in a high-purity wafer-scale free-standing 3C-SiC bulk
crystal grown via low-temperature chemical vapor
deposition [1]. The measured thermal conductivity
agrees well with the intrinsic thermal conductivity of aperfect single-crystal 3C-SiC that was predicted using
first-principles calculations. The in- and cross-plane
thermal conductivities of the corresponding 3C-SiC
thin films are measured using a beam-offset method
based on time-domain thermoreflectance. The crystal
structure analysis was performed via transmission
electron microscopy (TEM) and X-ray diffraction.
Figures 1(a) and (b) show a high-resolution TEM
image and the selected-area electron diffraction patternof 3C-SiC, respectively. The fast Fourier Transform of
the TEM image is shown in the inset of Fig. 1(a). These
results confirmed the cubic phase of the 3C-SiC crystal.
Figure 1(c) shows a comparison of the measured
thermal conductivity of 3C-SiC at room temperature
with that of other high-thermal-conductivity crystals as
a function of wafer size. The recently reported boronbased crystals exhibit high thermal conductivity;

Fig. 1 (a) High-resolution transmission electron microscopy
image and (b) selected-area electron diffraction patternof cubic SiC (3C-SiC), and (c) measured thermal
conductivity of 3C-SiC at room temperature is comparedwith those of other high-thermal-conductivity crystals
as a function of wafer size.

however, only millimeter-scale or smaller crystal sizes
are achievable.
The 3C-SiC wafer reported in this work can reachup to 6 inch in size with a high isotropic thermal
conductivity exceeding 500 W/m·K. The measured
thermal conductivity of 3C-SiC was higher than that of
all other metals and the second highest among all large
crystals (only surpassed by that of single-crystal
diamond). The thermal conductivity of 3C-SiC at room
temperature was 50% higher than that of the 6H-SiC
and AlN, and 40% higher than that of the 4H-SiC.
References[1] Z. Cheng, J. Liang, K. Kawamura, H. Zhou, H. Asamura, H.
Uratani, J. Tiwari, S. Graham, Y. Ohno, Y. Nagai, T. Feng, N.
Shigekawa, and D. Cahill, Nat. Comm. 13, 7201 (2022).

Jianbo Liang (Corresponding Author, Graduate School of Engineering, Osaka Metropolitan University)
E-mail: liang@omu.ac.jp
Yasuyoshi Nagai (Head of International Research Center for Nuclear Materials Science)
E-mail: yasuyoshi.nagai.e2@tohoku.ac.jp
URL: http://www.imr-oarai.jp/en/38

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IMR KINKEN Research Highlights 2023

Fabrication and Properties of Functional Spherical Powders
Cooperative Research and Development Center for Advanced Materials

Researchers at the Cooperative Research and Development Center for Advanced Materials have studied

various fabrication processes for advanced materials and explored the possibility of the application of thesematerials as multifunctional materials for future technologies in collaboration with global universities andresearch institutes. Here, the recent research and development status of the creation of spherical metallic
powders and related technologies for industrial applications are highlighted.

Gas atomization involves spraying a high-pressure
cooling medium, such as inert gas or water, on amolten-metal stream that is pulverized into small
droplets. This technique allows the preparation of
powders with spherical particles and high flowability.
Gas atomization using an inert gas facilitates thesynthesis of high-quality powders with superior
flowability because of their clean surface [1]. However,gas atomized powders contain internal pores, and thevolume of the pores is higher than that in powders
formed via other techniques such as the plasma
rotating electrode process, which may degrade various
properties of the final product.
The Cooperative Research and Development
Center introduced a new gas atomization apparatus in
FY2022, as shown in Fig. 1, which is capable of higher
output in the high-frequency melting section thanconventional systems, enabling powder preparation of
metals with high melting points of up to approximately
1600 °C.
Figures 2(a) and (b) show 3D images of particles
and changes in the volume ratio of internal pores in Febased powders prepared via gas atomization using Ar
and Ar+H2 gas, respectively; these results were
captured using synchrotron X-ray computed
tomography method. The obtained particles exhibitedan average diameter of 50 μm and a sphericalmorphology (Fig. 2(a)); moreover, we identified thatmixing a small amount of hydrogen gas in an inert gas
reduces the internal pores in the powder by inhibiting
the formation of an oxide layer (Fig. 2 (b)) [2]. This result
indicates that the possibility of using the powder as araw material for additive manufacturing was obtainedby controlling the composition of the mixed gas.
Moreover, as an example for the evaluation ofsupersaturated solid solution powders obtained via gas
atomization, observation of nanoscale structuralchanges due to in situ heat treatment using transmission
electron microscopy for the investigation of the aging
behavior of atomized powder [3] is also in progress.

Fig. 1 Gas atomization apparatus (RQP1, MAKABE R&D
Co., Ltd.)(a) 200 µm(b)Fig. 2 (a) Three-dimensional image of atomized powder
and (b) porosity volume ratio in the powders as captured
using synchrotron X-ray computed tomography.

By combining these methods, the research anddevelopment of Cu-, Fe- and Ti-based functional metal
powders will continue advancing.
References[1] N. Ciftci, N. Ellendt, E. S. Barreto, L. Madler, and V. Uhlenwinkel,
Adv. Powder Technol. 29, 380 (2018).
[2] N. Yodoshi, T. Endo, and N. Masahashi, Mater. Trans. 62, 1549
(2021).
[3] Y. Shimada, Y. Ikeda, K. Yoshida, M. Sato, J. Chen, Y. Du, K. Inoue,
R. Maaβ, Y. Nagai, and T. J. Konno, J. Appl. Phys. 131, 164902(2022).

Mitsutaka Sato (Corresponding Author, Cooperative Research and Development Center for Advanced Materials)
E-mail: mitsutaka.sato.a3@tohoku.ac.jp
Naoya Masahashi (Head of Cooperative Research and Development Center for Advanced Materials)
E-mail: naoya.masahashi.e6@tohoku.ac.jp
URL: http://www.crdam.imr.tohoku.ac.jp/en/index-en.html

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Research Centers

Enhancement of the Magnetoelectric Effect Using the Dynamic
Jahn-Teller Effect in a Transition-Metal Complex
High Field Laboratory for Superconducting Materials

We developed a new mechanism to enhance the magnetoelectric coupling between magnetism and electric

polarization, using the dynamic Jahn-Teller (JT) effect. The electric dipole, generated by the JT distortion, canbe aligned by magnetic fields because of the coupling between the JT distortion and spin via the spin-orbit
interaction, inducing a large electric polarization. We observed an electric polarization higher than 100 µC/m2
owing to the second-order magnetoelectric effect in the transition metal complex, [MnIII(taa)].

The magnetoelectric (ME) effect has attracted
significant interest because of its potential device
applications,
includingvoltage-controllable
magnetic memories [1]. The practical application of
the ME effect requires improved coupling between
electric polarization and magnetism. The electric
dipole generated by atomic displacement can beused to improve ME coupling. We propose a new
method to achieve a strong ME effect using the
dynamic Jahn-Teller (JT) effect, which efficiently
couples an electric dipole and spin. The atomic
displacements caused by the Jahn-Teller distortion,
which generates an electric dipole by lowering thesymmetry of the coordination complex, can couple
with spin via spin-orbit interactions. Therefore, thespin polarization generated by applying an external
magnetic field causes JT distortion to align, leading
to field-induced macroscopic electric polarization.
The transition metal complex [MnIII(taa)], wheretaa is the deprotonated form of tris[1-(2-azolyl)-2azabuten-4-yl]amine, crystallizes in the Td point
group. The C3 symmetry of the MnIII ion does not
eliminate the degeneracy of the d ϒ orbitals in thehigh-spin state and leads to JT distortion of themolecule. This JT distortion is dynamicallydisordered and generates a large fluctuating electric
dipole (1.25 D) that reorients one direction to otherson [MnIII(taa)]. Its piezoelectric Td point group allows
macroscopic electric polarization (P) with external
magnetic fields because of the second-order ME
effect. Pz along the [001] axis, induced by amagnetic field applied in the (001) plane, can be
expressed as Pz = β・H2・sin(2θ), where β is thesecond order ME susceptibility, H the magnetic fieldand θ the angle between the [100] axis and magnetic
field. Figure 1 shows the temperature evolution of Pz
in a rotating magnetic field [2]. Pz varied with sin2θ.
The temperature dependence of Pz at θ = 45°, where

Fig. 1 Temperature evolution of the electric polarization(Pz) along the [001] axis with 15.7 T magnetic fields
rotating in the (001) plane. The inset shows thetemperature dependence of Pz at θ = 45°.

Pz is maximum, is plotted in the inset in Fig. 1. Pz
increases at lower temperatures, reaching morethan 100 µC/m2. However, it drastically decreases
below 43 K as the dynamic JT distortion disappears
with the spin-state transition to the low-spin state.
This provides unequivocal proof that the ME effectis enhanced by the dynamic JT effect. Our
procedure for enhancing the ME effect can facilitate
the development of new methods for the practicaluse of the ME effect.
References[1] Y. Tokura, S. Seki, and N. Nagaosa, Rep. Prog. Phys. 77,
076501 (2014).
[2] Y. Otsuki, S. Kimura, S. Awaji, and M. Nakano, Phys. Rev. Lett.
128, 117601 (2022).

Shojiro Kimura (Corresponding Author, High Field Laboratory for Superconducting Materials)
E-mail: shojiro.kimura.b5@tohoku.ac.jp
Satoshi Awaji (Head of High Field Laboratory for Superconducting Materials)
E-mail: satoshi.awaji.e8@tohoku.ac.jp
URL: http://www.hflsm.imr.tohoku.ac.jp/cgi-bin/index-e.cgi

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IMR KINKEN Research Highlights 2023

Scientific Breakthrough Toward the Creation of New Industrial Materials
Trans-Regional Corporation Center for Industrial Materials ResearchThe Institute for Materials Research (IMR) launched the Trans-Regional Corporation Center, a comprehensive IMR-wide effort thatpairs the research groups associated with IMR across the innovation spectrum to solve the current industrial challenges and transformthe future global energy problems. The center was established in 2016 based on an agreement between the IMR, the Osaka Prefecture
Government, and enterprises sponsored by the government, and took control of the Osaka and Kansai center projects.
The Trans-Reginal Corporation Center was establishedin Osaka as a special unit by the Institute for Materials
Rsesearch (IMR), Tohoku University in April 2016 based on
an agreement with the Osaka Prefecture Government. The
Center is sponsored by the government (Ministry of Education,
Culture, Sports, Science and Technology) and took chargeover the Kansai Center, which was operational from 2012 to2016. The Center has three missions. First, the Center aims tosolve technical problems that industries have struggled toresolve. Second, the Center introduces academic output toindustries, with the aim of applying such output to society.
Third, the Center helps in the education of next-generation
scientists and researchers in the field of material science. We
organized a bimonthly forum named “Monodukuri Kisokoza,”
which focuses on special topics regarding materials andmaterial processing. Projects are conducted through wide
collaborations between the government, universities,
research institutions, and other organizations. The Center has
four venues to cover the Kansai and Tohoku area: the Osaka
office at Osaka Prefecture University, Hyogo office at the
University of Hyogo, Sendai office in IMR, and Monozukuri
Business Information Center Osaka in the Creation Core
Higashi-Osaka.
The Center has developed various materials undercollaboration with industries and universities. One of them
was the development of a novel bioactive TiNbSn alloy [1].
Figure 1 shows the scanning electron microscopy images of
the anodized TiNbSn alloy, showing porous microstructuresirrespective of the electrolyte compositions for anodization.
The amounts of •OH measured via electron spin resonanceanalysis increased with ultraviolet (UV) light illumination time.
Figure 2 shows the results of an antibacterial test using
methicillin-resistant Staphylococcus aureus, meticillinsensitive Staphylococcus aureus, and Escherichia coli,
revealing that the antibacterial activity values increased with
UV illumination. The values increased with UV illumination
time for the anodized alloy in comparison to that of thereference (glass). The values of the anodized TiNbSn weremore than 2.0 and higher than those of the glass. A clear
effect of the H2O2 addition in the electrolyte on the anodizationof the values was not found.
This study revealed that the anodized TiNbSn with aporous microstructure exhibits superior antibacterial

Fig. 1 Scanning electron microscopy images of the anodic oxides
prepared in a sodium tartrate electrolyte with H2O2 (a,b) andwithout H2O2 (c,d).

Fig. 2 Plots of logarithmic reduction values in the antibacterial tests
conducted using methicillin-resistant Staphylococcus aureus,
meticillin-sensitive Staphylococcus aureus, and Escherichia colion the anodized TiNbSn and glass (n = 5).

activities, and the results correlated well with the number ofhydroxyl radicals generated upon UV light illumination.
Similar collaborative studies have been in progress. The
Center will attempt to innovate the metallic material industry
through its alliance with the partners, and promote scientificresearch in materials science.
References[1] H. Kurishima, Y. Mori, K. Ishii, H. Inoue, T. Mokudai, S. Fujimori, E. Itoi, S.
Hanada, N. Masahashi, and T. Aizawa, Front. Bioeng. Biotechnol. 10,883335 (2022).

Naoya Masahashi (Head of Trans-Regional Corporation Center for Industrial Materials Research)
E-mail: naoya.masahashi.e6@ tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/facilities/04.html

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Research Centers

Gated CO2 Adsorption Behavior in One-Dimensional Porous
Coordination Polymers Based on Paddlewheel-Type Dimetal
Complexes: What Determines Gate-Opening Temperatures?
Collaborative Research Center on Energy Materials

G

ated CO2 adsorption behavior was investigated in a series of one-dimensional chains based on paddlewheel
diruthenium(II, II) complexes. A newly synthesized compound demonstrated gated behavior at a significantly
higher temperature of 385 K under 100 kPa of CO2 than that reported in previous research for this type of chain
compounds, which usually occurred at a temperature range of 200−270 K. This specificity is ascribed to thehigher topological dimensionality of pores for CO2 accommodation that was observed in this chain.
Low-dimensional coordination polymers suchas one-dimensional chains often exhibit gated guest
sorption accompanying structural transition at atemperature (TG) [1], which is associated with an
external pressure induced by the guest (PG), which
is characteristic to the material and guest used. Thisphenomenon can be evaluated in the Clausius–Clapeyron (CC) relationship with the equation ofd(lnPG)/d(1/TG) = ∆HG/R, where ∆HG and R are thetransition enthalpy and gas constant, respectively.
In this study, the gated CO2 adsorption behavior
was investigated in a one-dimensional chain basedonabenzoate-bridged
paddlewheel
diruthenium(II,II) complex with a phenazine (phz)linker, [Ru2(p-MeOPhCO2)4(phz)] (1), where
p-MeOPhCO2– represents p-anisate [2].
The gas-adsorption isotherm and isobar of 1 for
CO2 were measured using an automatic volumetricadsorption apparatus connected to a cryostat
system (Fig. 1a). Surprisingly, compound 1
underwent gate-opening/closing at a significantly
higher TGC of 385 K under PCO2 = 100 kPa thanthose previously reported for such chain compounds,
which usually appeared in the temperature range of
200–270 K [3]. CC analysis resulted in a similar ∆HGvalue for these compounds (inset of Fig. 1a),indicating that the transition entropy ∆SG in eachsystem plays a key role in shifting TG; compound 1
results in a much smaller |∆SG| in the series. In situ
powder/single-crystal x-ray diffraction measurement
under CO2 revealed the crystal structure of the CO2accommodated phase (1⊃CO2, Fig. 1b). Only
compound 1 produced a CO2-accessible twodimensional topological pore in its CO2-adsorbed
phase of 1⊃CO2 (Fig. 1c). In contrast, the others
reported previously produced one-dimensional or
discrete topological pores for CO2 accommodation.

Fig. 1(a) CO2 adsorption isobars for 1 at several CO2
pressures measured upon cooling. (inset) Log-scaleplots of CO2 pressure versus the inverse of the gateopening temperature (Clausius–Clapeyron analyses). (b)Views of the crystal structure of 1⊃CO2 along a-axis. (c)Connolly surface representation of micropores (probe
radius: 1.4 Å) with CO2 adsorption sites for 1⊃CO2.

These findings strongly reflect the degree of freedomof CO2 molecules in pores, which is related to ∆SG.
References[1] J. Zhang, W. Kosaka, and H. Miyasaka, Chem. Lett. 48, 1308
(2019).
[2] W. Kosaka, J. Zhang, Y. Watanabe, and H. Miyasaka, Inorg.
Chem. 61, 12698 (2022).
[3] W. Kosaka, K. Yamagishi, J. Zhang, and H. Miyasaka, J. Am.
Chem. Soc. 136, 12304 (2014).

Wataru Kosaka and Hitoshi Miyasaka (Corresponding Authors, Solid-State Metal-Complex Research Laboratory)
E-mail: wataru.kosaka.c1@tohoku.ac.jp, hitoshi.miyasaka.e7@tohoku.ac.jp
Tetsu Ichitsubo (Head of Collaborative Research Center on Energy Materials)
E-mail: tichi@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/facilities/05.html

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IMR KINKEN Research Highlights 2023

Thermodynamic Stabilities and Electronic Structures of Nanoalloys
Center for Computational Materials Science

Nanoalloys are attracting considerable attention as an emerging field. Their thermodynamic stabilities andelectronic structures are different from those of the bulk phase. Thermodynamic stabilities and electronic
structures of nanoalloys have been clarified on the basis of first-principles calculations. The development of acomputational scheme is anticipated for rapidly discovering novel nanoalloys with unique properties.

The central focus of alloy studies has been bulk
systems. Recently, nanoalloys have been emerging,
especially, in the field of catalysis. The thermodynamic
stability of nanoalloys is known to differ from that of thebulk alloys [1]. A large degree of freedom exists in theelemental configuration within a nanoparticle (NP), andthe stability of the configuration depends on the
combination and composition of the constituent elements[2]. Figure 1 shows an example of predicting the stability
and elemental configuration of ternary alloy under finite
temperatures based on first-principles calculations
combined with statistical science and machine learning.
The electronic structure of constituent elements is also
known to be strongly dependent on the local configuration[3]. A first-principles calculation of the model configurationof an octonary high-entropy alloy (HEA), as shown in Fig.
2(a), results in local d-band centers, as shown in Fig.
2(b). The d-band centers of surface Pt atoms (Fig. 2(c))
are drastically different from those in monometallic Pt NP(Fig. 2(d)). This indicates the emergence of uniqueproperties in the nanoalloy that are significantly different
from those of the bulk structures.
There are about 60 stable metal elements.
Approximately 2,000 combinations of elements exist forbinary systems, which increases up to several millions
for quinary systems. When we also consider the freedomof composition, synthetic conditions, etc., theexperimental exploration of such a vast material space isa daunting challenge. Therefore, the effective use ofcomputational technologies is inevitable. Consequently,
the development of a computational scheme byintegrating the first-principles method, machine learning,and statistical science for the rapid screening of thethermodynamic stability and material properties isimportant.
References[1] T. Ishimoto and M. Koyama, J. Phys. Chem. Lett. 7, 736 (2016).

Fig. 1 Thermodynamic stability at (a) 300 and (b) 1000 K, and(c) stable PdRuIr nanoparticle (NP) configurations. Adaptedwith permission from [2]. Copyright 2021 The Chemical
Society of Japan.

Fig. 2 (a) Density functional theory model of high-entropy
alloy (HEA) NP. (b) d-band center map of surface atoms in
HEA NP. (c) d-band center of the surface Pt atoms in the
HEA NP. The other atoms are shown in white for visualization.
(d) d-band center value in Pt NP. Adapted with permission
from [3]. Copyright 2022 American Chemical Society.

[2] Y. Nanba and M. Koyama, Bull. Chem. Soc. Jpn. 94, 2484 (2021).
[3] D. Wu, K. Kusada, Y. Nanba, M. Koyama, T. Yamamoto, T. Toriyama,
S. Matsumura, O. Seo, I. Gueye, J. Kim, L. S. R. Kumara, O. Sakata,

S. Kawaguchi, Y. Kubota, and H. Kitagawa, J. Am. Chem. Soc., 144,
3365 (2022).

Michihisa Koyama (Corresponding Author, Shinshu University)
E-mail: koyama_michihisa@shinshu-u.ac.jp
Momoji Kubo (Head of Center for Computational Materials Science)
E-mail: momoji@tohoku.ac.jp
URL: http://www.sc.imr.tohoku.ac.jp/eng/

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Research Centers

Current Status of Collaborative Research Programs of CNSAM
Center of Neutron Science for Advanced Materials

T

he Center of Neutron Science for Advanced Materials is a neutron facility that focuses on research in the fieldof novel materials science under the Institute for Materials Research. This center manages four neutron
instruments at the research reactor facility, Japanese Research Reactor (JRR)-3 and the spallation neutron
source at the Japan Proton Accelerator Research Complex at the Materials and Life Science Experimental
Facility. Here, we report the current status of the research program and the outcome obtained from JRR-3,
where reoperations were started in 2021.
The Center of Neutron Science for Advanced
Materials (CNSAM) was established in 2010 topromote novel materials science research using
neutrons. CNSAM operates one diffractometer(HERMES) and two neutron spectrometers (Tohoku
University
Polarization
Analysis
NeutronSpectrometer (TOPAN) and AKANE) at the Japanese
Research Reactor (JRR)-3 of the Japan Atomic
Energy Agency. HERMES can determine thearrangement of atoms and spins, while their motions
are examined by AKANE and TOPAN. POLANO,
located at the Materials and Life Science
Experimental Facility (MLF) at the Japan Proton
Accelerator Research Complex, is a spectrometer
designed to perform polarization analysis in higher
energy regions beyond those measured using
conventional triple-axis spectrometers. POLANO
and TOPAN are equipped with polarized options
and can disentangle nuclear and magnetic
contributions. We aim to contribute to condensed
matter physics and materials science using themultipurpose neutron instruments of PATH, which isa collective term for neutron instruments managed
by the CNSAM.
To achieve this purpose, we established aninternational collaborative research program underthe Institute for Materials Research from FY 2019.
We provide opportunities not only for experimentswith neutron beams but also for the development of
neutron devices and analysis methods, and even for
theoretical work using our neutron data. Proposals
can be submitted under several categories, such as“Neutron experiment at MLF/JRR-3,” “Instrumental
development,” “Development in analysis method,”“Structural analysis and data handling,” and “Others.”
Under the category “Others,” proposals on thecomplementary use of neutrons and other quantum
beams, such as X-ray and muon beams, areaccepted. In FY 2022, we received 28 and 3
proposals from domestic and overseas researchers,
respectively. Furthermore, reoperations were started

Fig. 1 Acoustic phonon branches in La1.925Sr0.075CuO4.

at the research reactor JRR-3 in February 2021, andwe received 38 proposals for the use of our neutron
instrument at JRR-3 through the user program
managed by the Institute for Solid State Physics, theUniversity of Tokyo. The number of proposals isincreasing annually. Moreover, the scientific results
obtained using our instrument at JRR-3 are steadily
being published [1-3].
After resuming operations of JRR-3, we havemade efforts to improve the instrument and sample
environment. Consequently, we succeeded inproviding opportunities for structural analysis andinvestigation of spin/lattice dynamics. Figure 1
shows the inelastic neutron scattering profiles ofsuperconducting
La1.925Sr0.075CuO4.
Acoustic
phonon branches around (200) Bragg position are
clearly seen. Such measurements are vigorously
performed by users.
References[1] T. Taniguchi, S. Kitagawa, K. Ishida, S. Asano, K. Kudo, M.
Takahama, P. Xie, T. Noji, and M. Fujita, J. Phys. Soc. Jpn, 91,
074710 (2022).
[2] Y. Mizuguchi, Md. Riad Kasem, and Y. Ikeda, J. Phys. Soc.
Jpn. 91, 103601 (2022).
[3] Md Riad Kasem, H. Arima, Y. Ikeda, A. Yamashita, and Y.
Mizuguchi, J. Phys. Mater. 5, 045001 (2022).

Masaki Fujita (Head of Center of Neutron Science for Advanced Materials)
E-mail: fujita@tohoku.ac.jp
URL: http://nc-imr.imr.tohoku.ac.jp/index-e.html, http://qblab.imr.tohoku.ac.jp

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IMR KINKEN Research Highlights 2023

Role of Pre-straining on Local Hydrogen Diffusivity and HydrogenAssisted Cracking Site in a Nitrogen-Doped Duplex SteelInternational Collaboration CenterT

he hydrogen embrittlement behavior of nitrogen-doped ferrite/austenite duplex stainless steel was investigatedin this study. Significant hydrogen embrittlement occurred, and the cracking behavior consisted of deformation
twins and ferrite/austenite interfaces. Interestingly, pre-straining altered the preferential hydrogen localizationand cracking sites to the ferrite grain interior. These results demonstrate the potential for the development ofhydrogen-resistant high-strength steels.
The prevention of hydrogen embrittlement is anurgent issue for increasing the durability of highstrength steels for automobiles and hydrogenenergy-related infrastructures. An effective method
to suppress hydrogen embrittlement is thedevelopment of new high-strength hydrogenresistant steels. In this context, microstructure andalloy design strategies for hydrogen-resistant steels
have been proposed. In particular, the introductionof austenite and addition of solute nitrogen are key
to achieving high strength and superior hydrogen
resistance. In this study, we characterized thehydrogen-related cracking behavior of nitrogendoped ferrite/austenite duplex stainless steels andinvestigated the role of pre-straining on cracking
behavior using tensile testing in conjunction withmicrostructural observations and a hydrogenvisualization technique (Ag decoration technique).
Hydrogen charging of a nitrogen-doped duplex
steel(Fe-3Mn-24Cr-1.6Mo-3.6Ni-0.4Cu-0.02C0.27N) in an aqueous solution of 3% NaCl+3 g/L
NH4SCN at 10 A/m2 for seven days decreased thetotal tensile elongation. The preferential crack
initiation sites were deformation twins at the austenite
and ferrite/austenite interfaces [1]. The hydrogeninduced cracking behavior was unconventional
when compared to that of other ferrite/austenite
duplex stainless steels without solute nitrogen.
Interestingly, 22% pre-straining of the steel
achieved tensile strength of 1 GPa even withhydrogen, although the ductility decreased and thepre-strain changed the preferential crack initiationsite to the ferrite interior.
Silver decoration revealed that diffusiblehydrogen was preferentially located in the ferrite or
grain boundaries of the undeformed steel, whereas
the 22% pre-strained steel contained diffusible

Fig. 1 Phase map and secondary electron image (inset)
showing deposition of Ag particles, which corresponds
to high hydrogen flux, in the hydrogen-charged duplex
steel with 22% pre-strain. The location of the image
shown as the inset corresponds to the area highlighted
by the black square.

hydrogen in austenite. However, pre-straining
suppressed the macroscopic hydrogen diffusion
and local diffusion in ferrite and austenite byincreasing the dislocation density. The degree ofsuppression of the local diffusion was moresignificant in ferrite than in austenite. The pre-strain
effects on the cracking behavior and hydrogen
diffusivity may play an important role in improving
the resistance of nitrogen-doped duplex steel tohydrogen embrittlement [2].
References[1] M. Y. Maeda, M. Koyama, H. Nishimura, O. M. Cintho, and E.
Akiyama, Int. J. Hydrog. Energy 46, 2716 (2021).
[2] M. Y. Maeda, M. Koyama, H. Nishimura, O. M. Cintho, and E.
Akiyama, Scr. Mater. 207, 114272 (2022).

Milene Yumi Maeda (Corresponding Author, State University of Ponta Grossa)
E-mail: milenemaeda@gmail.com
Eiji Akiyama (Corresponding Author, Environmentally Robust Materials Research Laboratory)
E-mail: eiji.akiyama.d1@tohoku.ac.jp
Hiroyuki Nojiri (Head of International Collaboration Center)
E-mail: icc-imr@grp.tohoku.ac.jp
URL: http://www.icc-imr.imr.tohoku.ac.jp/

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Research Centers

Structure of the Al3Mn Amorphous Alloy Prepared via Magnetron
Sputtering
Center for Advanced Light Source and Materials ScienceThe structure of an Al3Mn amorphous alloy synthesized via magnetron sputtering was investigated usingsynchrotron anomalous X-ray scattering. The structural features around Mn were significantly different from thoseinferred by the dense random packing hard-sphere model, suggesting that the environmental structure around thismetal is influenced by chemical interactions, similar to those of crystalline Al3Mn. Our analysis also showed thatthe medium-range ordering structure, corresponding to a pre-peak signal, was associated with Al-Mn and Mn-Mn
correlations accompanied by number density modulation and the non-Bernal-type coordination geometry [1].
A 25 µm Al3Mn amorphous-alloy thin film was
prepared on a single-crystal Si wafer via multi-target
magnetron sputtering. Ordinary and anomalous X-ray
scattering (AXS) measurements at the Mn K absorption
edge were performed at the beamline station BL-7C,
Institute of Materials Structure Science, High Energy
Accelerator Research Organization, Tsukuba, Japan. An
initial model of 25,000 atoms (Al: 18,750 and Mn: 6,250)
with a dense random packing (DRP) structure, in a cubic
hypercell with a unit size (L) of 7.546 nm, was used for thereverse Monte Carlo (RMC) simulation. Figure 1 showsthe experimental and calculated (using the DRP and
RMC structural models) interference functions. A prepeak signal around Q = 16 nm-1, showing the uniquemedium-range ordering, is well reproduced by the RMC
model. This result clearly shows the advantage of AXSRMC analysis for a detailed discussion of fine structures.
The partial pair distribution functions calculated from the
RMC model indicate that the pre-peak signal(approximately 0.45 nm) is associated with Mn-Mn and
Mn-Al correlations.
The combination of common neighbor analysis(CNA) and Bernal polyhedral analysis (BPA) is useful for
discussing atomic arrangements in the middle rangeordering (MRO) region. CNA analysis clearly showed theextensive development of [333]CN root pairs for Mn-Mn
and Al-Mn; however, a strong elemental selectivity was
not identified in the common neighbors of [333]CN,suggesting that the tetrahedral linkage structure of MnAl3 -Mn, a unique fragment of the Mackay-type icosahedralcluster, is not the predominant short range ordering(SRO) structure in amorphous Al3Mn. The features of the
non-Bernal polyhedra associated with the [211]CN of MnMn and Mn-Al root pairs indicated the preference of nonBernal polyhedra, leading to a significant fluctuation in
number density. Considering that there was no significant
chemical concentration among the common neighborsfor [211]CN, the number density fluctuations realized inFig. 1 Ordinary and environmental Q(i)Qs obtained bysynchrotron AXS analysis and theoretical calculations(DRP and RMC).

the Al3Mn amorphous alloys are unique geometricalshort range ordering (GSROs) with no strong chemicalcorrelations.
These structural features can be compared to thoseobtained for a Zr80Pt20 amorphous alloy, where an
icosahedral quasicrystal was formed by low-temperature
heat treatment [2]. In this alloy, the density fluctuations
were accompanied by fluctuations in elemental
concentrations; that is, both the Pt-Zr3 -Pt tetrahedral
linkage units, reminiscent of the Mackay cluster, and nonBernal polyhedral regions were enriched in Pt.
References[1] T. Kawamata and K. Sugiyama, J. Phys. Conf. Ser. 2461, 012017(2023).
[2] T. Kawamata, T. Muto, and K. Sugiyama, Mater. Trans. 62, 20 (2021).

Toru Kawamata (Corresponding Author, Center for Advanced Light Source and Materials Science / Chemical Physics
of Non-Crystalline Materials Research Laboratory)
E-mail: kawamata@tohoku.ac.jp
Kazumasa Sugiyama (Head of Center for Advanced Light Source and Materials Science)
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/collaboration/08.html

46

IMR KINKEN Research Highlights 2023

IMR KINKEN Research Highlights 2023

Uncovering Fractional Quantum Hall Effect in an InAs TwoDimensional Electron Gas by Gate Tuning
Laboratory of Low Temperature Materials ScienceI

nAs is a candidate material for achieving topological states with non-Abelian quasiparticles in the form of afractional quantum Hall (FQH) insulator/superconductor hybrid. We succeeded in inducing the FQH state at
filling factors of ν = 5/3, 4/3, 2/3, and 1/3 in a two-dimensional electron gas confined to an InAs/AlGaSbquantum well by tailoring the electron wave function using a dual-gate configuration.
independently control the electron density and shape ofthe confinement potential in the QW by using the top andback gate voltages, VTG and VBG, respectively.
Magnetotransport (longitudinal and transverse resistance,
Rxx and Rxy, respectively) measurements were performedat temperatures as low as 0.48 K and magnetic fields up
to 24 T [1]. As shown in Fig. 1(b), the signatures of FQH(deep minima in Rxx and plateau in Rxy as a function of theelectron density) were observed at ν = 1/3 and 2/3 when
VTG was swept while maintaining VBG = 0 V. Moreover, as
shown in Fig. 1(c), we succeeded in inducing additional
FQH states at ν = 4/3 and 5/3 by applying VBG to alter the
distribution of the electron wave function within the QW in
combination with VFG. Our results indicate a significant
impact of the shape of the QW confinement potential on
the visibility of the FQH states and existence of asymmetric
disorder, in addition to interface roughness andbackground impurities, which affect the FQH effect.

Recently, an interface composed of a fractional
quantum Hall (FQH) insulator and an s-wave
superconductor has attracted interest as a research field
for achieving the topological states of matter with nonAbelianquasiparticles.
Among
the
varioussemiconductors, InAs is a promising candidate to achieve
such an interface, as it is known to form a transparent
contact with superconductors, such as Al. Partial
observations of the FQH effect in two-dimensional
electron gases have also been reported in high-quality
InAs/AlGaSb quantum well (QW) structures. However,
the reported FQH state was limited to the one at theLandau filling factor of ν = 4/3 (ν = nh/eB, where n theelectron density, h is the Planck’s constant, e is theelementary charge, and B is the magnetic field). This may
be caused by the asymmetric conditions of the QW, suchas the difference in roughness or charged impurities at
the top and low interfaces/barriers.
To investigate the correlation between the QW
symmetry and the visibility of the FQH state, we prepared
an InAs/AlGaSb heterostructure, as shown in Fig. 1(a), via
molecular beam epitaxy, which was designed to

GaSb (5 nm)
AlAs0.08Sb0.92(40 nm)Al0.7Ga0.3Sb (10 nm)

(b)
10

1/3

2/3

5/3

(c) 1

4/3

Rxx

6
4

100 Ω

x 10

5/3

2

1

V BG

=0V

4/3

ν

5/3

Rxy

2V

δnBG < 0

T = 0.48 K
B = 24.0 T
VBG = 0 V

40

2

6V

δnBG > 0

8V

20

sub.

Rxy (k Ω)

ν

4V

0
60

Back Gate

4/3

2

Al0.7Ga0.3Sb (10 nm)

n-GaSb (001)

Phys. Rev. B 105, 075305 (2022).

8

InAs (25 nm)

AlAs0.08Sb0.92(800 nm)ν1[1] S. Komatsu, H. Irie, T. Akiho, T. Nojima, T. Akazaki, and K. Muraki,sub.

Top Gate

Rxx (kΩ)(a)References

-0.5

0.0

0.5
1.0
V TG (V)

1.5

-0.8

-0.4

0.0
0.4
∆VTG (V)

0.8 -0.8

-0.4

0.0
0.4
∆VTG (V)0.8

Fig. 1 (a) InAs/AlGaSb heterostructure prepared in this work, where the two-dimensional electron gas located in a 25 nm wide InAs
quantum well can be controlled by both top and back gates. (b) VTG-dependence of Rxx (upper) and Rxy (lower) as measured at 0.48
K and 24 T with VBG = 0 V. (c) Rxx and Rxy traces for different VBG values at 0.48 K and 24 T. ∆VTG represents the change in VTG measured
from ν = 3/2 at each VBG [1].

Tsutomu Nojima (Corresponding Author, Laboratory of Low Temperature Materials Science)
E-mail: t.nojima@tohoku.ac.jp
Takahiko Sasaki (Head of Laboratory of Low Temperature Materials Science)
E-mail: takahiko.sasaki.d3@tohoku.ac.jp
URL: http://ltsd.imr.tohoku.ac.jp/index-e.html

IMR KINKEN Research Highlights 2023

47

Research Centers

Research Facility for Analyzing the Physical and Chemical
Properties of Radioactive and Nuclear Materials
Laboratory of Alpha-Ray Emitters

More than 170 species of radioisotopes and nuclear materials are available for study at the Laboratory ofAlpha-Ray Emitters. This laboratory is one of the most important centers worldwide for studying the physicaland chemical properties of radioactive materials such as actinide compounds. Researchers from several
leading universities and institutes all over Japan visit this facility every year to prepare a variety of materials andconduct chemical and physical experiments.

The Laboratory of Alpha-Ray Emitters provides a
research environment for the study of 170 radionuclides
and elements, especially alpha-ray emitters such as
actinides. This laboratory functions as a source for the
preparation of pure crystals of actinide compounds,
providing them to other universities and synchrotron
particle accelerators. In the past decade, actinium-225(Ac-225), an actinide, has been provided to otheruniversities and research centers for research to foster
inter-university collaboration. The radiation-controlledarea of this laboratory includes three chemical rooms,
three physical rooms, and other facilities, which areequipped with local exhaust ventilation systems,
ensuring safety while handling various types ofradioactive materials. Several spectrometers, including
those for gamma and alpha rays, are also available.
Radioisotope 90Sr (t1/2 = 28.9 y) is a major heatgenerating nuclide, similar to 137Cs, which is containedin the high-level waste (HLW) produced from nuclear
reactors. The removal of 90Sr and 137Cs from the HLW
has been studied to better manage the risks of
medium-term hazards. Dicyclohexano-18-crown-6(DCH18C6) and its derivatives are suitable for Sr (II)extraction. Thus, extensive extractions using crownethers have been developed for the treatment anddisposal of HLW. Although a system containing crownethers shows good Sr (II) extraction ability, the diluent
toxicity, low flash point, and high boiling point leaveroom for development. Further development of Sr(II)extraction relies on the availability of risk-free andeasily regenerated diluents, and the establishment ofan extraction system has drawn a significant amountof attention. Fluorinated solvents have also attracted
continuous interest in the separation and purification
technology because of their unique properties, suchas good extractability, significantly low solubility inwater (generally lower than conventional organic
solvents), and chemical and radioactive stability. The
combination of a fluorinated solvent (hydrofluorocarbon
HFC-43-based solvent) and DCH18C6 for Sr(II)solvent extraction was studied using two characteristic
Kenji Shirasaki (Head of Laboratory of Alpha-Ray Emitters)
E-mail: kenji.shirasaki.e4@tohoku.ac.jp
URL: http://alpha.imr.tohoku.ac.jp/en.html

48

IMR KINKEN Research Highlights 2023

Fig. 1 Sr(II) solvent extraction system composed of
dicyclohexano-18-crown-6 and hydrofluorocarbon
HFC-43-based solvents and its Sr(II) extractability
under different acid conditions.

acids, i.e., nitric acid, which is typically present in
HLW, and perfuruoro-3-6-9-trioxaundecane-1,11-dioic
acid with both hydrophilicity and affinity to fluorinatedsolvents [1]. The maximum distribution ratio of Sr(II)(DSr) observed for the latter acid was ~180, which wasmore than10 times larger than that of the former acid
(Fig. 1). The combination of HFC-43-based solventsand DCH18C6 exhibits significant potential for use in
extraction systems.
References[1] K. Shirasaki, M. Nagai, M. Nakase, C. Tabata, A. Sunaga, T.
Yaita, and T. Yamamura, RSC Advances 12, 26922 (2022).

IMR KINKEN Research Highlights 2023

Multiscale Characterization of Advanced Materials Using
Aberration-Corrected Analytical Transmission Electron Microscopy
Analytical Research Core for Advanced Materials

T

he Analytical Research Core for Advanced Materials serves as an infrastructure for researchers in IMR and outside theuniversity, offering various elemental analytical methods and up-to-date structural characterization techniques. These include
aberration-corrected microscopy, which allows three-dimensional and atomic resolution observations of a wide range of materials.
The Analytical Research Core for Advanced Materials(ARCAM) provides elemental composition data andsupports Transmission Electron Microscopy (TEM) analysisof metals and inorganic materials. We also develop
analytical procedures to obtain reliable analytical data. The
ARCAM assays major and trace elements in consigned
samples using the following methods: ICP-AES, ICP-MS,
flame and graphite furnace AAS, microwave induced
plasma AES, CS/ON/H analysis, XRF, ion chromatography,
and conventional chemical analyses (e.g., gravimetry,
titrimetry, and spectrophotometry). Additionally, we provide
TEM analysis services on structural and functional materials
and microdevices, enabling the evaluation of
microstructures, crystal structures, and chemicalcompositions at the nano-/meso-scale.
ARCAM is heavily involved in the user-facility networkwith government support. This includes a nanotechnology
platform (up to 2021fy) and an advanced research
infrastructure for materials and nanotechnology in Japan(ARIM, 2021fy onward), both of which are supported by the
Ministry of Education, Culture, Sports, Science andTechnology of Japan. These programs provide access toour facilities for researchers in academia and industry.
They can also request technical and scientific support for
the Center for Integrated Nanotechnology Support (CINTS)
at Tohoku University. ARCAM provides several facilities via
ARIM, including a focused-ion beam apparatus and an
aberration-corrected microscope that are extensively usedby researchers worldwide.
Multiscale characterization is fundamental tounderstanding the electric properties of iron-based
superconductors because superconducting behavior
depends on both the crystal structure and microstructure.
Here, various defects and grain boundaries play anessential role in achieving a sufficient critical current
density. Dr. Shimada and his group employed theseapparatuses to examine the real-space dispersion of
relevant phases and grain boundary structures threedimensionally, aiming to elucidate the origin of sensitive
dependence on the structure [1].

Fig.1 TEM equipped with aberration correctors both inillumination and objective lens systems. This microscopeis open to users outside the campus.

Another example employs aberration-corrected
microscopy to elucidate the crystallization behavior anddomain structure of recently developed fluorite-structuredoxides, as exemplified by Dr. Shiraishi’s group [2]. The
authors demonstrated that atomically resolved images of
CeO2-HfO2 thin films are equivalent to the direct
determination of their domain structure.
The use of ARCAM and ARIM facilities is not limited tofunctional materials and is used to study structural alloys[3] and soft matter, such as biomaterials and organic
conducting substances.
References[1] Y. Shimada, S. Tokuta, A. Yamanaka, A. Yamamoto, and T.J. Konno, J.
Alloys. Compd. 923, 166358 (2022).
[2] T. Shiraishi, S. Choi, T. Kiguchi, and T.J. Konno, Acta Mater. 235,
118091 (2022).
[3] Y. Shimada, Y. Ikeda, K. Yoshida, M. Sato, J. Chen, Y. Du, K. Inoue, R.
Maaß, Y. Nagai, and T.J. Konno, J. Appl. Phys. 131, 164902 (2022).

Toyohiko J. Konno (Corresponding Author, ARIM Project Unit, Analytical Research Core for Advanced Materials)
E-mail: tjkonno@tohoku.ac.jp
Eiji Akiyama (Head of Analytical Research Core for Advanced Materials)
E-mail: eiji.akiyama.d1@tohoku.ac.jp
URL: http://bunseki-core.imr.tohoku.ac.jp/top_eca_eng.html
http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/service-divisions/03.html

IMR KINKEN Research Highlights 2023

49

International Collaborative Research

IMR KINKEN Research Highlights 2023

Research

International Collaborative Research

Investigation of Charge Density Waves of YBa2Cu3O6.67 in
Strong Pulsed Magnetic Fields

We investigated charge density waves using pulsed magnetic fields to understand the normal states in high-Tc superconductors. Recent progress in pulsed high-magnetic-field diffraction has also been reported. The
relationship between the broken symmetry states found in optical pumping and the three-dimensional charge
density wave states reveals a new aspect of the normal state under very high magnetic fields.

Understanding high-Tc cuprates has been oneof the most important topics in strongly correlated
electron systems for several decades. The
appearance of charge density waves (CDWs) has
recently attracted considerable attention. This is asignificant challenge because of the difficulty inconducting X-ray diffraction in very high magnetic
fields and the small intensity of the superlattice
peaks caused by the CDW.
Our strategy is to combine X-rays withsignificantly high instantaneous intensity and pulsed
magnetic fields with ultra high peak intensity. For
this purpose, we used X-ray free-electron lasers(XFELs), such as the Linac Coherent Light Source(LCLS) and Spring-8 Angstrom Compact FreeElectron Laser (SACLA), as light sources.
Conversely, for the pulsed magnetic field, wedeveloped a compact pulsed magnetic field systemthat is optimal for this experiment.
Figure 1 shows an image of the backscattering
X-ray diffractometer installed at the SACLA XFEL. A
magnetic field of up to 50 T was generated using acompact conical horizontal coil. The lowest sample
temperature of 2.5 K was achieved by combining a
4He reservoir tank and 4 K Gifford–McMahon
cryocooler. It operates with a single short mode.
During the initial cooling, approximately 20 L He gas
is condensed in to the tank and then it isdepressurized using a vacuum pump thorough athin gas line. When the incoming heat is wellbalanced with the cooling power, the lowest
temperature is maintained for more than 24 h. The
combination of 50 T and 2.5 K for X-ray diffraction is
unique and is only possible with our system.
Moreover, pulsed high-field systems have been
installed in other XFEL facilities such as LCLS and
Swiss X-ray free-electron laser.
We conducted CDWs of YBa2Cu3O6.67 andidentified two types of CDWs [1]. More recently, weinvestigated the photo-pumping-induced normal
state [2]. By combing these experiments, we
obtained a comprehensive picture for the phase
diagram of YBa2Cu3O6.67
Hiroyuki Nojiri (Magnetism Research Laboratory)
E-mail: hiroyuki.nojiri.e8@imr.tohoku.ac.jp
URL: http://www.hfpm.imr.tohoku.ac.jp

52

IMR KINKEN Research Highlights 2023

Fig. 1 Experimental setup developed by the Institute forMaterials Research for high-magnetic-field X-ray
diffraction using Spring-8 Angstrom Compact FreeElectron Laser.

Fig. 2 Sample cryostat (center) and horizontal conical coil(right).

References[1] S. Gerber et al., Science 350, 949 (2015).
[2] H. Jang et al., Sci. Adv. 8, eabk0832 (2022).

IMR KINKEN Research Highlights 2023

Three-Dimensional Interconnected Nanoporous FeCo Soft Magnetic
Materials Synthesized Using Liquid Metal Dealloying

Three-dimensional interconnected nanoporous (3DNP) FeCo soft magnetic materials were produced via liquid metal dealloying(LMD). The processing temperature affected the morphology and grain boundary characteristics of 3DNP FeCo materials. The
LMD process shows its advantages for synthesizing nanostructured FeCo with high magnetization and low coercivity.
FeCo alloys are important soft magnetic materials
because of their highest saturation of magnetization, highCurie temperature, and low losses [1]. Recently,
nanostructured soft magnetic materials have been
investigated in a variety of potential applications such as
magnetic shielding, targeted drug delivery, and magnetic
resonance imaging. Consequently, nanostructured FeCo
alloys are attracting increasing attention, and several
chemical synthesis techniques have been suggested, suchas sol-gel method, hydrogen reduction, thermal
decomposition, reductive decomposition, polyol synthesis,
and liquid-phase reduction. Properties of nanostructured
FeCo materials are highly dependent on the synthesis
methodology. Moreover, typical synthesis methods exhibit
limitations such as a long processing time, use ofenvironmentally hazardous chemicals, and especially, theformation of undesirable impurities (e.g., oxide formation).
In this study, three-dimensional interconnected
nanoporous (3DNP) FeCo materials were newly synthesized
via liquid metal dealloying (LMD) [2]. Three different
precursor alloys: (FeCo)70Ni30, (FeCo)50Ni50, and(FeCo)30Ni70 (in at%) were prepared from high-purity raw
materials (over 99.9 at%) under a purified Ar atmosphere.
The LMD process was conducted for 36 min at constanttemperatures of 600, 700, and 800 °C in an Mg-10 at% Ca
metallic melt. During the LMD process, nanostructured
FeCo alloys were produced by the selective dissolution ofsolely miscible Ni atoms and self-organization of Fe and Co
atoms [3, 4].
The average porosity of the 3DNP FeCo was 32.3,
48.8, or 71.7%, depending on the concentration of Ni in the
precursor alloys. Moreover, the size of FeCo ligament varied
from 0.75 to 3.05 μm depending on the temperature andprecursor composition. Fe and Co were near equiatomic at
low temperatures; however, Co atoms became more soluble
in the melt at a high temperature of 800 °C. More importantly,
the grain boundary area was significantly reduced when theprocessing temperature increased, and the fractions of highangle grain and coincidence lattice site boundaries
decreased from 73.6 to 16.3% corresponding to a decreasein temperature from 600 to 800 ℃.
Temperature and precursor composition significantly

Fig. 1 Saturation magnetization and coercivity of nanostructured
FeCo materials.

influence the final microstructure of the 3DNP FeCo materials,
and magnetic properties are dependent on the
microstructure. The LMD process can prevent contaminationand oxidation in the Mg melt. Consequently, all samples
revealed high-saturation magnetizations of approximately
220 emu/g, which is close to that of bulk FeCo (245 emu/g).
The increase in the LMD temperature decreased thecoercivity, which is related to the reduced grain boundary
area. The LMD process exhibits advantages over othersynthesis methods in terms of high-saturation magnetizationand low coercivity (Fig. 1).
References[1] R. S. Sundar and S. C. Deevi, Int. Mater. Rev. 50(3), 157 (2005).
[2] S.-H. Joo and H. Kato, J. Alloys Compd. 908, 164688 (2022).
[3] T. Wada, K. Yubuta, A. Inoue, and H. Kato, Mater. Lett. 65(7), 1076
(2011).
[4] S.-H. Joo, T. Wada, and H. Kato, Mater. Des. 180(15), 107908 (2019).

Soo-Hyun Joo (Corresponding Author, Dankook University)
E-mail: jjsh83@dankook.ac.kr
Hidemi Kato (Non-Equilibrium Materials Research Laboratory)
E-mail: hidemi.kato.b7@tohoku.ac.jp
URL: http://www.nem2.imr.tohoku.ac.jp/index-e.html

IMR KINKEN Research Highlights 2023

53

International Collaborative Research

Alloy Design Approach for Mitigating Gas Pores in Additive
ManufacturingPorosity in additively manufactured Co−Cr−Mo alloys with varying carbon contents were characterized byquantitative X-ray computed tomography based on the collaborative work of researchers at the National Instituteof Applied Sciences of Lyon (INSA Lyon), France. Gas pores that had been entrapped in the raw powders were
eliminated during the subsequent electron beam powder bed fusion process depending on the solidification
behavior that varied with the carbon content. A novel alloy design approach for the reduction in gas pores,
which can critically influence the performance of the alloy, in the as-built materials was proposed.
Additive manufacturing (AM) is promising not
only for producing complex geometries but also
improving material properties with tailoredmicrostructures. Particularly, powder bed fusion(PBF) processes create bulk non-equilibrium
microstructures by repeating rapid cooling in aconfined melt volume. However, the mitigation ofporosity/defects is essential in metal AM for achieving
the desired properties. Generally, process-induced
defects, such as lack-of-fusion, keyhole pores, andcracking, can be reduced by optimizing the processparameters. In contrast, gas pores in the raw
powders often remain in the as-built materials, acting
as crack nucleation sites during subsequentmechanical loading [1]. Thus, efforts have been
devoted to developing high-quality powders withnegligible gas pores [2]. However, eliminating
powder-originated gas pores is still challenging.
In this study [3], we demonstrated that theamount of gas pores in electron beam PBF (EB-PBF)
materials alters depending on the solidification
behavior. A model alloy system, Co–27Cr–6Mo–(0.04–2.5)C (wt.%), which was developed forindustrial applications, e.g., cutting tools for corrosive
environments, was employed. Using X-ray computed
tomography, we successfully captured the sphericalgas pores and quantified the porosity in the raw
powders and as-built materials (Fig. 1). The results
clarified that the continuous addition of carbon
increased the porosity of the powder, suggesting a
potential effect through a significant reduction in theliquidus temperature. In contrast, the as-built alloy
specimens fabricated under an identical EB-PBF
condition showed a non-monotonous carbon
concentration dependence on porosity. When using
0.04 and 0.22 wt.% carbon, negligible pores were
captured after the EB-PBF process. The maximum
porosity in the as-built state was detected at 2.0
wt.%. Further carbon addition up to 2.5 wt.%
significantly
decreasedtheporosity.
The
microstructural characterization indicated a transition

Fig. 1 (a) Three-dimensional reconstruction images of gas
pores in the raw powders and (b) carbon concentration
dependence of porosity.

from cellular (0.04 and 0.22 wt.% carbon) to dendritic
solidification (1.5 and 2.0 wt.% carbon). A eutectic
microstructure was observed at 2.5 wt.% of carbon.
Therefore, we concluded that ensuring a smoothsolidification front during the cellular/eutectic
solidification effectively eliminates gas pores fromthe solidified portion, while the complicated solid–
liquid interfaces entrap gas bubbles in the melt pool
during dendritic solidification. The obtained findings
will aid the establishment of a novel alloy design
toward the mitigation of gas pores.
References[1] X. Shui, K. Yamanaka, M. Mori, Y. Nagata, K. Kurita, and A.
Chiba, Mater. Sci. Eng. A 680, 239 (2017).
[2] Y. Cui, Y. Zhao, H. Numata, K. Yamanaka, H. Bian, K. Aoyagi,
and A. Chiba, Powder Technol. 393, 301 (2021).
[3] S. Aota, K. Yamanaka, M. Mori, N. Sasaki, J. Adrien, E. Maire,
D. Fabrègue, and A. Chiba, Addit. Manuf. 59, 103134 (2022).

Kenta Yamanaka (Deformation Processing Research Laboratory)
E-mail: kenta.yamanaka.c5@tohoku.ac.jp
URL: http://www.chibalab.imr.tohoku.ac.jp/english/index.html

54

IMR KINKEN Research Highlights 2023

IMR KINKEN Research Highlights 2023

Anisotropic Electronic Correlations Detected via Resistivity
Measurements in the Heavy-Fermion Paramagnet UTe2

We thoroughly investigated the anisotropy of the electrical resistivity of the heavy-fermion superconductor

UTe2 under an intense magnetic field of up to 70 T for different electrical currents and magnetic field directions,and two characteristic temperatures and anisotropic resistivity coefficients were extracted. Their characteristic
behavior near the metamagnetic transition at Hm ~35 T was characterized. Anisotropic scattering processes
due to magnetic fluctuations were evidenced.
The recent discovery of unconventional
superconductivity in the heavy-fermion paramagnet
UTe2 opened a new route for investigating theinterplay between magnetism and superconductivity.
Spin-triplet superconductivity was initially proposed
for this compound as a nearly ferromagnetic system.
The spin-triplet superconductivity in UTe2 is
supported by the observation of a large upper
critical field Hc2 exceeding the Pauli limit and via
nuclearmagnetic
resonance
Knightshift
experiments. Contrary to early expectations,ferromagnetic fluctuations have never been detected
experimentally;
instead,low-dimensional
antiferromagnetic
fluctuations
withanincommensurate wave vector are detected byinelastic neutron scattering experiments. The
anisotropy of magnetic fluctuations must be
investigated up to high magnetic fields close to themetamagnetic transition field, Hm ~35 T.
In this work, we performed systematic resistivity
measurements under a high magnetic field of up to
70 T applied along the three crystallographic
directions: a, b, c-axes in the orthorhombic structure[1]. Figure 1(a) shows the temperature-field phase
diagram determined using resistivity measurements
for H || b-axis, corresponding to a hard magnetization
axis. Field-reentrant superconductivity up to Hm ~35
T, as well as two characteristic temperatures ofapproximately 15 and 35 K, were detected. The
electrical resistivity measurements were performed
using a pulse-field magnet at different temperatures.
Figure 1(b) shows the field dependence of theresistivity coefficient A, assuming Fermi liquidbehavior at low temperatures. A remarkably sharp
increase in the A coefficients up to Hm and an abrupt
drop above Hm are clearly observed, indicating thedevelopment of magnetic fluctuations. These results
are consistent with the magnetovolume effect on thefirst-order metamagnetic transition [2] and fielddependent Sommerfeld coefficients [3].

Fig.1 (a)Temperature-field phase diagram for H || b-axis in
UTe2. (b) Field dependence of the resistivity A
coefficient.

References[1] T. Thebault, M. Valiska, G. Lapertot, A. Pourret, D. Aoki, G.
Knebel, D. Braithwaite, and W. Knafo, Phys. Rev. B 106, 144406(2022).
[2] A. Miyake, M. Gen, A. Ikeda, K. Miyake, Y. Shimizu, Y. J. Sato,
D. Li, A. Nakamura, Y. Homma, F. Honda, J. Flouquet, M.
Tokunaga, and D. Aoki, J. Phys. Soc. Jpn. 91, 063703 (2022).
[3] A. Miyake, Y. Shimizu, Y. J. Sato, D. Li, A. Nakamura, Y.
Homma, F. Honda, J. Flouquet, M. Tokunaga, and D. Aoki, J.
Phys. Soc. Jpn. 90, 103702 (2021).

Dai Aoki (Actinide Materials Science Research Laboratory)
E-mail: dai.aoki.c2@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/25.html

IMR KINKEN Research Highlights 2023

55

International Collaborative ResearchElectronic States of Non-Centrosymmetric Chiral Crystal PtAl
International Research Center for Nuclear Materials Science

Symmetry-protected nontrivial states in topological compounds have attracted considerable attention. In thisstudy, we investigated the electronic states of the chiral quantum material PtAl by considering the de Haas–vanAlphen effect. The smallest Fermi pocket, α, possesses a nontrivial Berry phase in which a Weyl nodal fermion
is formed at the Γ point.

The interplay between crystalline symmetries
and band topology can lead to various exotic statesin materials, which have been intensively investigatedover the years. The chirality, degeneracy, anddimensionality of the crossing points distinguish thenumerous topological states in materials.
Nonsymmorphic symmetries can impose bandcrossings at high-symmetry points in the Brillouinzone and produce higher-fold fermions. Specifically,
cubic systems of the space group P213 (No.198),
such as Rh(Si,Ge) and (Pd,Pt)Ga, exhibit
nonsymmorphic
symmetry-protected
multifoldfermionsathigh-symmetry
pointswithunconventional low-energy excitations called thespin 3/2 Rarita–Schwinger fermion.
In this study, we investigated the topologicalquantum properties of single crystals of the chiralmaterial PtAl via magnetotransport measurements
and the de Haas–van Alphen (dHvA) oscillations [1].
High-quality single crystals were grown using the
Czochralski method in a tetra-arc furnace. The dHvA
experiments were performed using the fieldmodulation technique at high fields of up to 12 T andtemperatures as low as 1 K. Figure 1(a) shows the
crystal structure of PtAl with the space group P213,
which is classified as a nonsymmorphic chiralstructure. Figure 1(b) shows the angular dependenceof the experimental and theoretical dHvA
frequencies. Three types of Fermi surface sheets
were detected: α, γ, and δ. These sheets can split
into two owing to band splitting in the noncentrosymmetric crystal structure. The calculated
Fermi surfaces are illustrated in Fig.1(c), where theFermi surfaces α and α’ located at the Γ point
occupy significantly small volumes in the Brillouinzone. The estimated spin-split energy is 567 K,
which is reasonably high, suggesting the strong
spin-orbit strength of PtAl. From the analysis of the
Landau fan diagram, the α and α’ bands wereobserved to possess nontrivial and trivial Berryphases of 1.16π and 011π, respectively.

Fig. 1(a) Chiral crystal structure of PtAl with the spacegroup P213. (b) Angular dependence of the de Haas–
van Alphen frequencies of PtAl. The solid lines show
the results of band calculations. (c) Calculated Fermi
surfaces of PtAl.

References[1] V. Saini, S. Sasmal, R. Kulkarni, B. Singh, A. Thamizhavel, A.
Nakamura, and D. Aoki, Phys. Rev. B 106, 125126 (2022).

Arumugam Thamizhavel (Corresponding Author, Tata Institute of Fundamental Research)
E-mail: thamizh@tifr.res.in
Yasuyoshi Nagai (Head of International Research Center for Nuclear Materials Science)
E-mail: yasuyoshi.nagai.e2@tohoku.ac.jp
URL: http://www.imr-oarai.jp/en/56

IMR KINKEN Research Highlights 2023

IMR KINKEN Research Highlights 2023

Microstructure and Strength of Low-Stacking-Fault-Enegy
Cu–In Alloy Wires
Cooperative Research and Development Center for Advanced Materials

Conductive spring wires for application in electrical components require high strength, high electricalconductivity, and convenient manufacturability. We observed that Cu–In solid solution alloy wires exhibited asuperior combination of strength and conductivity, which was primarily achieved by grain refinement due totheir low stacking fault energy and high twinnability.

Innovations in electronic devices have revealed aneed for enhancing the strength and electricalconductivity of Cu-based alloy wires and sheets.
Especially, the production of solid-solutionstrengthened Cu alloys with an advantageous
combination of strength and conductivity that iscomparable to those of age-hardenable alloys for use
in electrical applications is of significant importance,
because the manufacturing process for the former
alloys is far simpler than that for the later ones. Cu–In
solid solution alloys are suitable candidates for such
wire materials [1]. Herein, we systematically investigate
the microstructure and properties of Cu–In alloy wires
fabricated via severe drawing. Then, based on the
results obtained, we discuss the strengthening
mechanism of the Cu–In alloy wires.
Figure 1 shows the inverse pole figure and grainboundary distribution maps obtained via electronbackscatter diffraction analysis of the Cu–1.0, 4.0, and
5.0 at.% In alloy rods with a diameter of 3.0 mm before
drawing and those obtained after drawing of the wires
to equivalent strains ε of 0.81 (2.0 mm) and 4.61 (0.3mm). All the Cu–In alloys show typical equiaxial Cu
solid solution grains with an average size of
approximately 10 μm. During the initial stage of drawing
to ε = 0.81, deformation twin boundaries were formed,
which increased with increasing In content (red lines inFig. 1(b)). This indicates that the In solute efficiently
reduced the stacking fault energy of the Cu matrix. The
deformation twins promote grain refinement during
subsequent drawing. The Cu–5.0 at.% In alloy wire thatwas severely drawn to ε = 4.61 possessed ultrafine
grains of approximately 100 nm in size, which wassignificantly smaller than those in the other alloys (Fig.
1(c)). Consequently, the Cu–5.0 at.% In alloy wire drawn
to ε = 4.61 exhibited superior yield and tensile strengthsof 1280 and 1340 MPa, respectively, with a conductivityof 24% of the International Annealed Copper Standard.
The performance of the solution-strengthened Cu–5.0
at.% In alloy wires that was severely drawn wasFig. 1 Inverse pole figure and grain boundary (GB) maps
obtained via electron backscatter diffraction of the crosssection of the Cu–1.0, 4.0, and 5.0 at.% In alloy rods (a) before
drawing, and after wire drawing to (b) 2.0 mm (ε = 0.81), and(c) 0.3 mm (ε = 4.61). In the GB map of (b), high-angle GBs
with a misorientation angle in excess of 15° are depictedusing solid-back lines, while twin boundaries corresponding
to an angle of 55-62.8° are indicated by red lines.

comparable to that of commercial age-hardenable Cu–
Ti and Cu–Be alloy wires. The combination of strengthand electrical conductivity of the Cu–In alloy wires will
be optimized in future studies by optimizing both thealloy compositions and the deformation mechanism.
References[1] Y. Abe, S. Semboshi, N. Masahashi, E-A. Choi, and S.Z. Han,
Metall. Mater. Trans. A, 54, 928 (2023).

Satoshi Semboshi (Corresponding Author, Cooperative Research and Development Center for Advanced Materials)
E-mail: satoshi.semboshi.c8@tohoku.ac.jp
Naoya Masahashi (Head of Cooperative Research and Development Center for Advanced Materials)
E-mail: naoya.masahashi.e6@tohoku.ac.jp
URL: http://www.crdam.imr.tohoku.ac.jp/en/index-en.html

IMR KINKEN Research Highlights 2023

57

International Collaborative Research

Improved Critical Current Density Performance in High Temperature
Superconducting Tapes using a Thermodynamic Approach
High Field Laboratory for Superconducting MaterialsT

he critical current density (Jc ∼ 130 MA/cm2) and flux pinning force density (Fp ∼ 3.17 TN/m2) for nanocomposite
rare-earth metal Ba2Cu3Oy films on metallic substrates (CCs) were successfully determined at 4.2 K using boththe thermodynamic route and size, incorporating large densities of incoherent nanoparticles. The Jc and Fp
values obtained in our CC for the over-doped REBa2Cu3Oy are the highest ever reported for superconductors.
The improvement of critical current density (Jc)
in practical high-temperature superconductors(HTSs) such as REBa2Cu3Oy (REBCO, where RE
are rare-earth metals and Y) coated conductors(CCs) has recently gained increased attention. The
nanoparticle-related
flux-pinninglandscapeimproves Jc. The higher hole-carrier density in
REBCO also improves Jc because it increases thethermodynamic departing critical current, (Jd).
However, it is difficult to optimize the carrier density
in nanoparticle-introduced REBCO films because of
the local strain induced at the interface between thenanoparticles and REBCO matrix. In this study, we
optimized carrier doping in nanoparticle-introduced
REBCO films by introducing incoherent BaHfO3
nanoparticles in REBCO films.
Figure 1 shows the critical current density in the
self-field (Jcsf) and depairing current density (Jd) ofseveral HTSs at 4.2 K. We can achieve 0.3・Jd in(Y0.77Gd0.23)Ba2Cu3Oy ((Y,Gd)123) by controllingthe carrier density; its variation leads to an intrinsic
improvement in Jc via Jd, resulting in extremely highJc values of 130 MA/cm2. These values are consistent
with a Jd enhancement by a factor of two forincoherent nanoparticle-doped (Y,Gd)123 coatedconductor (CC) films, indicating that this new
material design can achieve high critical current
densities in a wide array of superconductors. By
combining the high vortex-pinning force with thisthermodynamic and pinning optimization route,(Y,Gd)123 CCs reached ~3.17 TN/m3 at 4.2 K and
18 T (H||c) (Fig. 2), which are the highest values everreported for superconductors.
References

Fig. 1 Critical current density in self-field (Jcsf) anddepairing current density (Jd) for several HTSs at 4.2 K[1].

Fig. 2 Flux pinning force density Fp at 4.2 K for several
HTS films for B//c [1].

[1] M. Miura, G. Tsuchiya, T. Harada, K. Sakuma, H. Kurokawa,
N.Sekiya, Y. Kato, R. Yoshida, T. Kato, K. Nakaoka, T. Izumi, F.
Nabeshima, A. Maeda, T. Okada, S. Awaji, L. Civale, and B.
Maiorov, NPG Asia Materials 14, 85 (2022).

Masashi Miura (Corresponding Author, Graduate School of Science and Technology, Seikei University)
E-mail: masashi-m@st.seikei.ac.jp
Satoshi Awaji (Head of High Field Laboratory for Superconducting Materials)
E-mail: satoshi.awaji.e8@tohoku.ac.jp
URL: http://www.hflsm.imr.tohoku.ac.jp/cgi-bin/index-e.cgi

58

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IMR KINKEN Research Highlights 2023

Electronic Structures of CH3NH3PbI3/Li+@C60 and Haeckelite Compounds
Center for Computational Materials ScienceT

wo international collaborations using first-principles calculations were performed independently on the
MASAMUNE-IMR supercomputer, which was developed by the Institute for Materials Research (IMR). One wasan investigation on the effect of Li+@C60 on methyl-ammonium lead iodide perovskite solar cells, and the otherwas an investigation on the family of group III–V haeckelite compounds.
Methyl-ammonium (MA) lead iodide perovskite
solar cells have attracted attention owing to their highenergy conversion efficiency. However, these cells
exhibit a problem of low air stability. To examine therole of using Li+@C60 in a dopant material in the p-type
donor layer, Li+@C60 -adsorbed tetragonal MAPbI3(001) surfaces with MAI terminations were studied
using first-principles calculations [1]. The Li+@C60 was
adsorbed above the C position with almost 100%
ionization. In the MAPbI3/Li+@C60 system, the highest
occupied molecular orbital (HOMO) and HOMO-1
were spread out in MAPbI3, while the lowest
unoccupied molecular orbital (LUMO), LUMO+1, and
LUMO+2 were localized in Li+@C60, with an energy
gap of 0.6 eV. In the neutral MAPbI3/Li@C60 system,
the singly occupied molecular orbital (SOMO) and
LUMO were both localized in Li@C60 and their energy
gap of 0.125 eV was significantly small. The SOMO
behaves as a hole when it loses an electron to form
Li+@C60. The three almost degenerate LUMO levels
behave as good hole conductors. Thus, we concluded
that the use of Li+@C60 molecules instead of bare Li
ions as dopant materials in MAPbI3 solar cells canprevent degradation.
Eighteen III–V haeckelite compounds XY (X = B,
Al, Ga, In, Tl; Y = N, P, As, Sb) were examined using
first-principles calculations, and we determined thatInSb is a Dirac semimetal and TlN and TlP are strong
topological insulators [2]. The remaining 15 aresemiconductors. The effects of tensile andcompressive strains on the electronic structures werealso studied. These materials exhibit diverse
topological orders. Semiconducting band gaps areprimarily found between the bonding and antibonding
states of the mixed X(p)-Y(p) orbitals at the top of thevalence band and bottom of the conduction band.
The topological insulator is explained based on thedegenerate px –py orbitals and their orbital energies
relative to the pz orbitals near the Fermi energy. The
nontrivial band topologies of TlN and TlP wereconfirmed by calculating the Z2 (1;000) index, surface

HOMO

LUMO

LUMO+1

LUMO+2-6.369 eV-5.743 eV-5.722 eV-5.648 eV

Fig.1 Molecular orbitals of CH3NH3PbI3/Li+@C60.

Fig.2 Energy band of TlN at the (100) surface.

states, and Wilson loop calculations. The bands split
into two branches by including spin-orbit interactions.
The results demonstrate that haeckelite compounds
are fascinating materials with broad potential
applications in optoelectronics, and possess thepossibility of hosting emergent physical phenomena.
References[1] K.-H. Chew, R. Kuwahara, and K. Ohno, Mater. Adv. 3, 290(2022); and see the references therein.
[2] M. Khazaei, A. Ranjbar, Y.-G. Kang, Y. Liang, R. Khaledialidusti,
S. Bae, H. Raebiger, V. Wang, M. J. Han, H. Mizoguchi, M. S.
Bahramy, T. D. Kühne, R. V. Belosludov, K. Ohno, and H. Hosono,Adv. Functional Mater. 32, 2110930 (2022).

Kaoru Ohno (Corresponding Author, Yokohama National University)
E-mail: ohno@ynu.ac.jp
Momoji Kubo (Head of Center for Computational Materials Science)
E-mail: momoji@tohoku.ac.jp
URL: http://www.sc.imr.tohoku.ac.jp/eng/

IMR KINKEN Research Highlights 2023

59

International Collaborative ResearchInterplay Among Spin, Charge, and Lattice Dynamics inSuperconducting La2-x Srx CuO4
Center of Neutron Science for Advanced Materials

To clarify the origin of anomalous intensity enhancement of spin excitations in La2-x Srx CuO4 (LSCO), we
examined the spin excitations in a series of LSCO compounds with x = 0, 0.075, 0.18, and 0.30, as well as in
La5/3Sr1/3CuO4. The intensity enhancement was observed only in the superconducting samples at low
temperatures, suggesting an interplay between the spin, charge, and lattice dynamics.
In recent research on strongly correlated
electron systems, the intertwining of electron
degrees of freedom such as charge, spin, lattice,and orbital have been intensively investigated fromthe perspective of a new function. In particular,
cuprate high-temperature superconductors are
critical as model materials for doped Mott insulators,
where the intertwining of electron degrees of
freedom causes a variety of quantum phases. In atypical hole-doped superconducting (SC) system,
i.e., La2-x Srx CuO4, the shape of magnetic excitationsin the energy(ω)–momentum(Q) space changes toan hourglass-shaped one upon doping. Studies
reported that the intensity of magnetic excitations isenhanced at particular ω and Q positions, where thephonon branches intersect. However, the origin of
intensity enhancement has not been clarified.
Therefore, we performed inelastic neutron
scattering measurements on La2-x Srx CuO4 with x =0, 0.075, 0.15, and 0.30 using 4SEASONS, a timeof-flight chopper spectrometer, installed at theMaterials and Life Science Experimental Facility of
the Japan Proton Accelerator Research Complex.
As shown in Fig. 1, we observed the intensity
enhancement in the SC samples at K ~ 0 and ω ~17 meV at 5 K, while such behavior was not seen in
non-SC compounds at 200 K [1, 2]. No intensity
enhancement was confirmed for the isostructural
insulating La2-x Srx NiO4 where x = 1/3. Furthermore,
we evaluated the enhanced intensity (<M>2 (µB2)) in
the absolute unit and clarified that <M>2 as afunction of hole concentration, x, is maximized at x
~ 0.16, where the optimum superconductivity withthe highest SC transition temperature appears.
These results suggest an intertwin among spin,
charge, and lattice dynamics and a connection
betweensuchcomposite
dynamics
andsuperconductivity. We considered phonons lying
around 17-19 meV and determined that two phonons
are associated with the out-of-plane motion of Cu or
O atoms, producing a potential for trapping the

Fig. 1 Dynamical susceptibility in the ω -K plane for La2x Srx CuO4 with (a) x = 0, (b) x = 0.075, (c) x = 0.30 at T =5 K, (e) x = 0.075, (f) x = 0.30 at T = 200 K. The nuclear
Bragg points and incommensurate magnetic positionsin the H-K plane are illustrated in (d). The gray area in (d)represents the integrated area in K and range in H of thehorizontal axis for intensity maps in (a)-(c), (e), and (f).

charge stripes along the Cu–O bond direction.
Thus, these phonons could be coupled withcharges.
References[1] K. Ikeuchi, S. Wakimoto, M. Fujita, T. Fukuda, R. Kajimoto, and
M. Arai, Phys. Rev. B 105, 014508 (2022).
[2] K. Ikeuchi, S. Wakimoto, M. Fujita, T. Fukuda, R. Kajimoto, and
M. Arai, MLF Monthly Report 2, (2022).

Masaki Fujita (Head of Center of Neutron Science for Advanced Materials)
E-mail: fujita@tohoku.ac.jp
URL: http://nc-imr.imr.tohoku.ac.jp/index-e.html, http://qblab.imr.tohoku.ac.jp

60

IMR KINKEN Research Highlights 2023

IMR KINKEN Research Highlights 2023

Flexible and Tough Superelastic Co–Cr Alloys for Biomedical
Applications
Analytical Research Core for Advanced Materials

Novel body-centered cubic-type single-crystal cobalt-chromium alloys with a Young's modulus close to that ofhuman bone, large recoverable strain of up to 17.0%, superelasticity, high wear resistance, and high corrosion
resistance have been developed for potential applications in the biomedical field [1]. Scanning transmission
electron microscopy observations revealed that the unique elastic and superelastic behavior of these alloys are
related to nanoscale A2/B2 phase decomposition.
Co - Cr - Mo

1200

Gum Metal

Ti-6Al-4V
1000

Stress(MPa)β-Ti(Ti-Nb-Ta-Zr)

plastic
deformation
thermoelastic
martensitic
transformation

800

600

58Co-34Cr-3.6Al-4.4Si(<001> single Crystal )SUS316L

400

59Co-33Cr-3.4Al-4.6Si(<001> single Crystal )200

Human Bone
0

0

1

2
Strain (%)

3

4

2

3

5

Co
Co
Co

4
keV

Co

Cr
Cr
Cr
Co

1

Co

Cr

Si
Al

Cr-rich
Al 2.50
Si 6.48
Cr 42.83
Co 48.20(at.%)

Cr

Co
Al

Si

Cr
Co

Al-rich
Al 10.17
Si 5.74
Cr 28.82
Co 55.28(at.%)

Cr

0
0

Co

0

Cr

5. 0 nmCo

Cr-richAl-richCounts (a.u.)

Fig. 1 Elastic properties for Co–Cr–Al–Si alloys andconventional metallic biomaterials.

Counts (a.u.)

Metallic biomaterials are well suited as
replacements and supports for damaged hard tissues
because of their mechanical properties and high wear
resistance. However, these biomaterials must have a
low Young's modulus that is close to that of humanbone; otherwise, they inevitably cause bone atrophy.
Because materials with a low elastic modulus generally
have poor wear resistance, simultaneously achieving
both low elastic modulus and high wear resistance isdifficult. The superelastic properties of shape memory
alloys are suitable for biomedical applications, such as
vascular stents and guidewires; however, conventional
biocompatible shape memory alloys have a low
recoverable strain, and an improvement is desired.
In this study, we successfully fabricated large
single crystals of novel Co–Cr–Al–Si alloys that wereseveral centimeters in size. The key property of thesealloys is that their Young's modulus is significantly low,
ranging from 10 to 30 GPa, which is in the range of thatof human bones, as shown in Fig. 1. Furthermore, thealloy has a high wear and corrosion resistance similar
to that of conventional Co–Cr alloys. It also exhibits
superior hot workability. Moreover, the recoverable
strain is 17.0% in <001>-oriented single crystals, which
is approximately twice that of commercial Ti–Ni shapememory alloys. To clarify the factors responsible for theunique elastic and superelastic behavior of the alloy,transmission electron microscopy (TEM) and scanning
TEM (STEM) observations and in situ neutron diffraction
measurements obtained during tensile tests confirmedthat the crystal structures of the matrix and martensite
phases were B2 and L10 types, respectively. Therefore,
STEM-energy dispersive X-ray spectroscopy mapping
revealed that the matrix phase decomposed into an
Al-rich B2 phase and a Cr-rich A2 phase in the order ofa few nanometers, as shown in Fig. 2.

6

7

8

Fig. 2 Energy dispersive X-ray spectroscopy mappingand spectra extracted from the Al- and Cr-rich regions.
Narushima, M. Nagasako, S. Harjo, T. Kawasaki, L. Bodnárová, P.

References

Sedlák, H. Seiner, and R. Kainuma, Adv. Mater. 34, 2202305[1] T. Odaira, S. Xu, K. Hirata, X. Xu, T. Omori, K. Ueki, K. Ueda, T.

(2022).

Makoto Nagasako (Corresponding Author, Analytical Research Core for Advanced Materials)
E-mail: nagasako@tohoku.ac.jp
Eiji Akiyama (Head of Analytical Research Core for Advanced Materials)
E-mail: eiji.akiyama.d1@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/service-divisions/03.html

IMR KINKEN Research Highlights 2023

61

Editors
 yuta Kasada, Yoshinori Onose, Yu Kumagai, RHaruhiko Morito, Goro Miyamoto, and Yusuke Ootani

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Misa Y. Tomimatsu, Aki Oikawa, and Yuko Godart

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HOKUTO Corporation

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