KINKEN
Research Highlights
2024

Institute for Materials Research, Tohoku University

KINKEN Research Highlights 2024
Contents
Preface���������������������������������������������������������������������������������������������������������������������������������������������������������� 4
Research Highlights
1. Infrastructural Materials
Quantum Beam Materials Physics Research Laboratory����������������������������������������������������������������������������� 8
Microstructure Design of Structural Metallic Materials Research Laboratory G ���������������������������������������� 9
Materials Design by Computer Simulation Research Laboratory��������������������������������������������������������������� 10
Environmentally Robust Materials Research Laboratory�����������������������������������������������������������������������������11
Deformation Processing Research Laboratory������������������������������������������������������������������������������������������ 12
Analytical Science Research Laboratory I ��������������������������������������������������������������������������������������������� 13
Design & Engineering by Joint Inverse Innovation for Materials Architecture�������������������������������������������� 14

2. Energy-Related Materials
Crystal Physics Research Laboratory G I ��������������������������������������������������������������������������������������������� 16
Irradiation Effects in Nuclear and Their Related Materials Research Laboratory G ��������������������������������� 17
Nuclear Materials Engineering Research Laboratory�������������������������������������������������������������������������������� 18
Advanced Crystal Engineering Research Laboratory�������������������������������������������������������������������������������� 19
Structure-Controlled Functional Materials Research Laboratory��������������������������������������������������������������� 20
Non-Equilibrium Materials Research Laboratory I ��������������������������������������������������������������������������������� 21
Crystal Chemistry Research Laboratory���������������������������������������������������������������������������������������������������� 22
Hydrogen Functional Materials Research Laboratory I �������������������������������������������������������������������������� 23
Multi-Functional Materials Science Research Laboratory I �������������������������������������������������������������������� 24
Exploratory Research Laboratory�������������������������������������������������������������������������������������������������������������� 25

3. Electronic Materials
Magnetism Research Laboratory G ��������������������������������������������������������������������������������������������������������� 28
Low Temperature Physics Research Laboratory���������������������������������������������������������������������������������������� 29
Low Temperature Condensed State Physics Research Laboratory����������������������������������������������������������� 30
Quantum Functional Materials Physics Research Laboratory�������������������������������������������������������������������� 31
Chemical Physics of Non-Crystalline Materials Research Laboratory������������������������������������������������������� 32
Solid-State Metal-Complex Chemistry Research Laboratory G I ��������������������������������������������������������� 33
Magnetic Materials Research Laboratory�������������������������������������������������������������������������������������������������� 34
Actinide Materials Science Research Laboratory I �������������������������������������������������������������������������������� 35

Research Centers
International Research Center for Nuclear Materials Science G I �������������������������������������������������������� 38
International Research Center for Nuclear Materials Science G I �������������������������������������������������������� 39
Cooperative Research and Development Center for Advanced Materials������������������������������������������������ 40
High Field Laboratory for Superconducting Materials I ������������������������������������������������������������������������� 41
High Field Laboratory for Superconducting Materials�������������������������������������������������������������������������������� 42
Trans-Regional Corporation Center for Industrial Materials Research������������������������������������������������������� 43
Collaborative Research Center on Energy Materials G I ���������������������������������������������������������������������� 44
Center for Computational Materials Science G ���������������������������������������������������������������������������������������� 45
Center of Neutron Science for Advanced Materials G I ������������������������������������������������������������������������ 46
International Collaboration Center (ICC-IMR)��������������������������������������������������������������������������������������������� 47
Center for Advanced Light Source and Materials Science������������������������������������������������������������������������ 48
Laboratory of Low Temperature Materials Science������������������������������������������������������������������������������������ 49
Laboratory of Alpha-Ray Emitters�������������������������������������������������������������������������������������������������������������� 50
Analytical Research Core for Advanced Materials������������������������������������������������������������������������������������� 51

G : GIMRT (Global Institute for Materials Research Tohoku) is a program in which researchers frominside and outside the institute conduct joint research based on a common research theme.
I : International Co-Authored Paper

Preface

Dear Colleagues,

We are delighted to present “KINKEN Research Highlights 2024,” 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. Kotaro
Honda, its first director, invented the world’s first artificial permanent magnet called KS magnet steel, theinstitute has developed many new materials for practical use, including Sendust alloy, SiC fibers, andsoft magnetic amorphous alloys, and has also conducted not only fundamental research, but also
pioneering research in the search for new materials and the elucidation of physical properties such as
magnetism and superconductivity. It has become a global center in materials science.

A key feature of IMR is its integration 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

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IMR KINKEN Research Highlights 2024

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 2024

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Infrastructural Materials

IMR KINKEN Research Highlights 2024

Research

Infrastructural Materials

Neutron Proved Time-Temperature-Dependent Structural
Transformation in a Medium-Entropy Alloy

We have succeeded in observing direct evidence of time-temperature-dependent short-/long-range structuraltransformation in a medium-entropy alloy. The results of neutron-scattering experiments show that a ternary
equiatomic alloy, Mn-Co-Ni, transforms from a face-centered cubic to a primitive tetragonal structure only in alimited time-temperature region. Our findings are possibly available to control elusive short-range ordering in
random solid solutions.

The concept of high-entropy alloys has been
received in various fields, such as structural
materials, catalysts, and the synthesis of new
superconductors. Although short-range ordering
plausibly plays a crucial role in material properties,
the clear correlation has never been demonstrated.
In particular, it is generally difficult to probe theshort-range ordering via any microscopic
experiments and thus the characterization of shortrange ordered structure is a frontier issue for thefield of high-entropy alloys. In this report, we
introduce parts of our research for a possible shortrange ordered alloy, Mn-Co-Ni [1,2].
The polycrystalline samples of Mn-Co-Ni wereprepared via the arc melting method. Parts of thesamples were annealed at several temperatures
and then examined through neutron-scattering
techniques. The neutron experiments were carriedout using a conventional triple-axis spectrometer,
TOPAN, which was installed at the 6G horizontal
beam port in JRR-3.
As shown in Fig. 1, the as-grown Mn-Co-Ni(black circles) shows a clear diffuse scattering
around the forbidden (100) reflection point,
indicating a short-range ordered structure in thisalloy. Indeed, the roughly evaluated correlation
length of the short-range superlattice structure isapproximately 1.3(1) nm, which is shorter than thatof the average structure evaluated from a width of
the fundamental (200) Bragg peak.
The effect of aging at 673 K is displayed in Fig.
1 (left). The broad peak becomes sharper withaging time and splits into two peaks, indicating thedevelopment of a long-range tetragonal phase (L10).
The evaluated correlation length is almost resolutionlimited (~40 nm) above 147.9 h. The evolution of the
diffuse scattering was only observed in a limited
temperature range of around 673 K, as shown in
Fig. 1 (right). This behavior can be explainedwith a time-temperature-transformation diagram
schematically illustrated in Fig. 2. These findings
indicate that short-/long-range ordering forms in theFig. 1 Neutron-scattering profiles of a medium-entropy
alloy, Mn-Co-Ni. The left panel shows the isothermal
evolution of the diffuse scattering profile, and the rightpanel displays the temperature variation for selected
temperatures. These figures are cited from Ref. [1].

Fig. 2 A schematic time-temperature-transformation
diagram of a medium-entropy alloy, Mn-Co-Ni.

Mn-Co-Ni alloy and is available to control withsimple heat treatment. The relationship between
such characteristic structures and material
properties, such as precipitation hardening andnovel transport properties, is of subsequent naturalinterest.
References[1] Y. Umemoto, Y. Ikeda, and M. Fujita, Mater. Trans. 64, 2018(2023).
[2] Y. Ikeda, Y. Umemoto, D. Matsumura, T. Tsuji, Y. Hashimoto, T.
Kitazawa, and M. Fujita, Mater. Trans. 64, 2254 (2023).

Yoichi IKEDA (Quantum Beam Materials Physics Research Laboratory)
E-mail: yoichi.ikeda.d2@tohoku.ac.jp
URL: http://qblab.imr.tohoku.ac.jp/index-e.html

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IMR KINKEN Research Highlights 2024

IMR KINKEN Research Highlights 2024

GIMRT

Sublattice Alloy Design of High-Strength SteelsThe sublattice alloy design in high-strength steels is proposed with emphasizing nanoscale dispersion control
of alloy carbides/nitrides in ferrite. The study uncovers interstitial–substitutional solute interactions revealinghidden nanoscale inhomogeneity via spinodal ordering. The concept of interstitial sublattice engineering is
introduced for strengthening alloyed steels in bulk and at surface.
Metallic material strengthening has been a focal
research area, addressing dislocation motion challenges
posed by microstructure obstacles. Recent studies
emphasize severe plastic deformation's role in dislocationand grain-boundary strengthening, while precipitation
strengthening remains crucial for achieving high strength.
Our research group explores nanoscale inhomogeneity inapparent solid solutions, ordering / phase separation
during thermal processes, and a novel alloy designconcept called "interstitial sublattice engineering" forstrengthening alloyed steels [1].
Carbon (C) and nitrogen (N) occupy interstitialsublattice sites in an iron (Fe) lattice, leading to various
carbides / nitrides. Most of them have the crystal structure
different from the matrix, and coherency between the αand precipitates is difficult to maintain, resulting inheterogeneous nucleation in α. On the other hand,interstitial (i)-substitutional (s) cluster develops in a bcc
α-ferrite matrix, forming coherent plate-shaped
precipitates. The solute clustering leads to a significant
surface hardening as shown in Figs. 1(a) and (b) [2].
Hardening is more significant than the precipitation of
stable B1-type MN due to finer dispersion.
Such monolayer clusters can be formed via twophase separation in the bcc lattice. Figure 1(c) shows aschematic of the free energy surface of a solid solution in
an Fe–M–X ternary system where the free energy waslargely stabilized in the high M–X concentration region
because of strong attractive X–M interaction. In such acase, there is a strong tendency toward clustering coupledwith atomic ordering. The i–s clustering in nitrided steels

can be considered similar to the "conditional ordering" or"spinodal ordering" in substitutional alloys, but in complex
substitutional and interstitial sublattices. The i–sinteractions precisely measured via solubility and internal
friction analysis are consistent with clustering behavior
observed in experiments [3]. Furthermore, theoreticalanalysis based on first principles calculation with cluster
variation method reveals a clear two-phase separation
tendency between Fe and TiN in Fe-Ti-N system. Monte
Carlo simulation confirms the planar clustering behavior of
Ti and N in the bcc matrix [1].
Strengthening of i-s clustering is also effective intempering of N martensite or even in the nitriding of fccbased systems with much larger solubility of interstitial
element than bcc lattice. It is also suggested that i-sclustering occurs at migrating interphase boundary,leading to the interphase boundary precipitation, which isused for strengthening of bulk specimen.
As described above, clearly, more attention should
be devoted to hidden nanoscale inhomogeneity in"apparent" solid solutions. Sophisticated designs for
substitutional and interstitial sublattices should be exploredfurther in the development of new engineering materials.
References[1] T. Furuhara, Y. Zhang, M. Sato, G. Miyamoto, M. Enoki, H. Ohtani, T.
Uesugi, and H. Numakura, Scripta Mater. 223, 115063 (2023).
[2] G. Miyamoto, Y. Tomio, H. Aota, K. Oh-ishi, K. Hono, and T. Furuhara,
Mater. Sci. Technol. 27, 742 (2011).
[3] G. Miyamoto, H. Numakura, M. Enoki, T. Uesugi, H. Ohtani, and T.
Furuhara, Materia Japan 59, 128 (2020).

Fig. 1 (a) Hardness profile along the depth direction from the surface of Fe-1at %M binary alloys nitrided at 823 K for 16 h. (b)High-resolution transmission electron micrographs of precipitates in the hardened layer [2], (c) Free energy surface of a solid
solution with a tendency toward coupled ordering and phase separation during separation in an Fe–M–X ternary system [1].

Goro Miyamoto (Microstructure Design of Structural Metallic Materials Research Laboratory)
E-mail: goro.miyamoto.e8@tohoku.ac.jp
URL: http://www.st-mat.imr.tohoku.ac.jp/en/index.html

IMR KINKEN Research Highlights 2024

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Infrastructural Materials

Large-Scale Molecular Dynamics Simulation for High
Functional Materials Design and Super-Precise System

To develop high functional and durable materials, an understanding of the multi-physics phenomena, including

chemical reaction, friction, stress, fluid, etc. is strongly demanded. We applied reactive molecular dynamics
simulation and ab initio calculation to reveal multi-physics phenomena toward the materials design related tomechanical engineering, catalyst, electronic device, and so on.

Development of highly functional and durable
materials is vital in many fields. Therefore, deep
understanding of multi-physics phenomena including
chemical reaction, friction, stress, and fluid etc. aredemanded. Recent advances in high-performancecomputing enable us to simulate the multi-physics
phenomena by atomic scale simulations. Therefore, weapplied reactive molecular dynamics simulation and abinitio calculation for pioneering next-generation materials
design [1-3].
High entropy alloys have showed excellent potential
in various applications. However, stress corrosion cracking
limits its practical applications. In this work, we conductedtensile simulations for FCC-type Fe40Ni40Cr20 alloy toreveal the effects of a high-temperature/pressure water
environment on the deformation mechanisms. In a vacuum,
we observed the generation of HCP phases during tensile
simulation (Fig. 1). While, in the high-temperature/pressure
water, the alloy surface was oxidized by chemical reactions
with water and this oxide surface layer suppressed the
FCC-to-HCP phase transition; instead, a BCC phase was
generated (Fig. 1), leading to a reduced ductility because
the BCC phase is typically more brittle than FCC and HCP.
Thus, the deformation mechanism of the FeNiCr alloy ischanged by high-temperature/pressure water [1].
2D transition metal di-chalcogenides have garneredattention in the nonvolatile memory field for their tunable
electrical properties. In this study, NbTe4 is identified as apromising candidate with an ultra-low melting point (Tm)and high crystallization temperature (Tc). We showed thatthe abnormally high resistance caused by the crystallization
can be attributed to the reduction of Nb 4d orbitals near
the Fermi level in collaboration with experimental groups.
The simultaneous presence of a low Tm and a high Tc canresolve important issues facing current phase-change
memory compounds like poor thermal stability of theamorphous phase [2].
To reveal Co/MFI catalyst structure with higher activity
for benzene methylation, we investigated the effects of Al
concentrations in Co/MFI on benzene methylation by DFT.
Figure 2 shows the energy profile for methane dissociation
and benzene methylation on the benzene adsorbed Co
ion in Co/MFI with the different Al concentrations. Here,Fig. 1 Tensile simulation results in vacuum (left) and hightemperature/pressure water. Green, red, blue, and grayindicate the FCC, HCP, BCC and other structure, respectively.

Fig. 2 The energy profile for methane dissociation and benzene
methylation in Co/MFI with the different Al–Al distances.

the higher the Al concentration, the closer the distance
between Al atoms. The energy profile shows that CH3 –C6H6 formation is the rate-determining step, and thecalculated apparent activation energies with 0.48 and 0.74
nm of the Al–Al distance are 196.91 kJ/mol and 75.80 kJ/
mol, respectively. The experimental apparent activationenergy (110 kJ/mol) is near the calculation value in the Co/
MFI with 0.74 nm of the Al–Al distance. Thus, Co/MFI withlower Al concentration is effective for high activity forbenzene methylation [3].
References[1] Y. Wang, H. Zhao, C. Liu, Y. Ootani, N. Ozawa, and M. Kubo, RSC Adv.
13, 6630 (2023).
[2] Y. Shuang, Q. Chen, M. Kim, Y. Wang, Y. Saito, S. Hatayama, P. Fons,
D. Ando, M. Kubo, and Y. Sutou, Adv. Mater. 35, 2303646 (2023).
[3] N. Katada, N. Ozawa, E. Tsuji, K. Kanehara, A. Otsuka, T. Sakamoto,
K. Umezawa, H. Matubara, S. Suganuma, and M. Kubo, Microporous
Mesoporous Mater. 364, 112855 (2024).

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

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IMR KINKEN Research Highlights 2024

IMR KINKEN Research Highlights 2024

Environment-Assisted Cracking of Magnesium Alloy in
Aqueous Solution Under Various Potentials

Magnesium alloys suffered from environment-assisted cracking under stress in corrosive environments. In
this study, we investigated the effect of potentials on the environment-assisted cracking behavior of a magnesium
alloy. Slow strain tensile tests in an aqueous solution under various potentials revealed that environmentassisted cracking of the magnesium alloy became more severe under relatively high potential owing to corrosion
accompanied by enhanced hydrogen absorption.

Engineering stress, σ / MPa

300

Initial strain rate: 1×10-6 s-1
Solution: 25 mM Na2B4O7•10H2O+3 g/��L NH4SCN

200

At -2.0 V
At -2.5 V

At Ecorr

In air

100

0

0

0.1

0.2
0.3
0.4
Engineering strain, ε

0.5

0.6

Fig. 1 Engineering stress-strain curves of magnesium alloy
tested in various environments with an initial strain rateof 1 x 10 -6 s-1. Ecorr represents corrosion potential [1].
Hydrogen absorption rate / wt. ppm h-1

Magnesium alloys are expected to achievepractical usages for transportation applications
because of their relatively high strength-to-weightratio. However, it is known that environment-assisted
cracking (EAC) occurs when magnesium alloys areused under stress in corrosive environments. The
main mechanism of EAC for magnesium alloys is
considered to be hydrogen embrittlement, which is
caused by hydrogen absorbed into the material. On
the other hand, the EAC of magnesium alloys tends
to occur at relatively noble potentials in an aqueous
solution, where hydrogen evolution reaction isrelatively slow, and the amount of hydrogen absorbed
into magnesium alloys is expected to be small. Thus,
there are many remaining unclear details of the EAC
mechanism of magnesium alloys. In this study, slow
strain rate tensile tests of a magnesium alloy (Mg3Al-1Zn by wt.%) were conducted in an aqueous
solution to clarify the effects of anodic magnesium
dissolution and hydrogen evolution reactions on the
EAC behavior of the magnesium alloy [1]. The rates
of hydrogen evolution and magnesium dissolution
reactions were varied by changing the polarization
potential of the magnesium alloy.
Figure 1 shows engineering stress-strain curvesof magnesium alloy tested in various environments.
The mechanical properties of the magnesium alloy
considerably degraded in the aqueous solution
compared to that in air. The total elongation became
smaller, and the flow stress decreased with thepositive shift in cathodic potential. From the surface
and cross-sectional observations after tensile
testing, the corrosion reaction occurred more
severely with the positive shift in cathodic potential
and many cracks were observed on the surface. The
amount of absorbed hydrogen in the magnesium
alloy was measured after the tensile testing. The
estimated hydrogen absorption rates increased withthe positive shift in cathodic potential although therate of hydrogen evolution reaction decreased (Fig.
2). This result indicates that hydrogen absorption
may be enhanced by the formation of a fresh surface

20
15
10
5
0

Ecorr

−2.0 V−2.5 V

Fig. 2 Average hydrogen absorption rates of magnesium
alloys calculated with the hydrogen content and thetime to fracture [1].

via magnesium dissolution reaction, which isenhanced by the potential shift in the positive
direction.
This study clarified that the mechanicalproperties of magnesium alloys degraded more
severely under relatively high potential owing tomagnesium dissolution accompanied by enhancedhydrogen absorption.
References[1] S. Ajito, T. Hojo, M. Koyama, S. Hiromoto, and E. Akiyama,
Corros. Sci. 218, 111195 (2023).

Saya Ajito (Environmentally Robust Materials Research Laboratory)
E-mail: saya.ajito.d1@tohoku.ac.jp
URL: http://akiyamaimr-e.amebaownd.com/

IMR KINKEN Research Highlights 2024

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Infrastructural Materials

Suzuki Segregation in High-Entropy AlloysD

etermining elemental segregation at stacking faults (SFs), i.e., Suzuki segregation, has been a longstanding
issue in concentrated solid-solution alloys, drawing attention from both the scientific and industrial communities.
With the aid of scanning transmission electron microscopy (STEM) techniques, we successfully captured a
trace of Suzuki segregation in a solid solution of high-entropy alloys (HEAs)
The segregation of alloying elements into latticedefects plays a crucial role in determining themechanical properties of structural alloys. Suzuki
segregation, involving chemical interactions
between alloying elements and SFs, serves as avital strengthening mechanism, especially forconcentrated face-centered cubic solid-solution
alloys with low stacking fault energy (SFE).
Traditionally, Suzuki segregation and the resulting
hardening have been employed in commercialized
Co−Ni−Cr−Mo alloys, developed through an
industry-IMR collaboration [1]. These alloys are
utilized as precision springs in mechanical watches
and medical devices. Previous studies have further
highlighted its significant role in Ni-base superalloys
and Mg alloys, particularly in their high-temperature
deformation behaviors. However, unlike those in anordered structure, direct observation of Suzuki
segregation in solid solutions remains challenging
due to the relatively low segregation concentrationand the presence of severely distorted matrices.
In this study [2], we characterized Suzuki
segregation in HEAs—a new class of multiprincipal
element alloys. A Co0.95Cr0.8Fe0.25Ni1.8Mo0.475 HEA,
designed to contain a large amount of Mo (~11 at.%)[3], was processed by heavy cold-rolling (CR) andsubsequently aged at 773 K. The alloy's strength
exhibited a significant improvement after strain
aging, reaching 2.1 GPa. High-angle annular darkfield (HAADF) STEM imaging, coupled withcorresponding
energy-dispersive
X-ray
spectroscopy (EDS) elemental analysis, wasperformed on a sample carefully prepared with afocused ion beam system. Aligning the [110]crystallographic orientation of the sample withviewing direction was preferable for subsequent
STEM-EDS
analysis.
Elemental
mapping
successfully captured traces of Co enrichment at
SFs, demonstrating the pinning of Shockley partial
dislocations via segregated atoms during strain
aging. Interestingly, co-segregation of Co and Mo
atoms at SFs was otherwise observed in a strainaged specimen with a small pre-strain (Fig. 1). Thishighlights that the amount of pre-straining,

Fig. 1 (a) HAADF-STEM image, (b) STEM-EDS map, and(c) line profile of the aged specimen. (c) Calculated
local energy change profile across the SF.

dominating the density of SFs, alters the segregation
tendency in the same alloy. The local SFE with thesegregation of Co and Mo atoms was −30.6 mJ/m2
at the aging temperature, as calculated via a phasefield method. The negative SFE indicates thestabilization of SFs through segregation, leading to
the formation of wide SFs. The obtained results
enhance our fundamental understanding of Suzuki
segregation and will contribute to the design ofhigh-strength alloys.
References[1] A. Chiba and M. Kim, Mater. Trans. 42, 2112 (2001).
[2] J. Li, K. Yamanaka, Y. Hayasaka, and A. Chiba, Scr. Mater.
226, 115226 (2023).
[3] J. Li, K. Yamanaka, and A. Chiba, Mater. Sci. Eng. A 817,
141359 (2021).

Kenta Yamanaka (Deformation Processing Research Laboratory)
E-mail: kenta.yamanaka.c5@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/24.html

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IMR KINKEN Research Highlights 2024

IMR KINKEN Research Highlights 2024

International Co-Authored Paper

Enhancement of Grain-Boundary Strength by Elemental
Doping in Magnesium-Aluminate SpinelIn order to improve mechanical properties in polycrystalline magnesium-aluminate spinel material, earth-abundant
Y element was doped. Hardness and fracture toughness were slightly improved in a Y-doped specimen. Using
advanced electron microscopy and spectrometry techniques, it was confirmed that doped Y atoms were preferentiallysegregated at the grain boundary by substituting Al atoms at octahedral sites. Furthermore, those Al atoms removed
from the octahedral sites at the grain-boundary occupy the tetrahedral Mg sites in the vicinity of the grain boundary.
Magnesium aluminate spinel (MAS, MgAl2O4) is aunique ceramic material that is transparent over a wide
range from ultraviolet to mid-infrared with enhanced
toughness, which could be utilized for windows in
extreme environments, e.g. at higher temperatures.
However, fracture failures tend to occur at grainboundaries (GBs), which is one of the major limiting
factors for practical MAS applications. Mechanicalproperties at GBs can be improved by doping certain
elements through modifying atomic arrangements at
GBs in MAS. In this study, earth-abundant Y was doped
to polycrystalline MAS to improve mechanical properties
such as fracture toughness.
It was confirmed that mechanical properties withrespect to the hardness and fracture toughness in the
Y-doped MAS were slightly improved in comparison to
the pristine pure MAS. In addition, microstructure andchemistry in the vicinity of GBs of the Y-doped MAS were
examined by aberration-corrected scanning transmission
electron microscopy (STEM) with electron energy-loss
spectrometry (EELS) analysis. Figure 1 shows an atomic
resolution high-angle annular dark-field (HAADF) image
at a GB in the Y-doped MAS [1]. The brighter regions
indicate heavy atomic-number Y atoms in this imaging
mode. So that, the doped Y atoms are segregated at the
GB. And it was confirmed that Y atoms occupy octahedral
Al sites. Figure 2 shows a series of composition maps
with a HAADF-STEM image (a) at a GB in the Y-doped
MAS, quantified by EELS analysis in aberration-corrected
STEM. The Y segregations along the GB were confirmed
both through the HAADF-STEM image (Fig. 2a) and thequantified Y map (Fig. 2b). In addition to Y segregation,
Al is also segregated in the vicinity of the GB rather
broadly whereas the Mg concentration is depleted at the
GB. Based on the quantified compositional maps ofthese elements, it can be estimated that rather
complicated atomic rearrangement occurred at the GB:
doped Y atoms substitute Al atoms at the GB, then theremoved Al atoms from the GB occupied the Mg
tetrahedral sites subsequently. It was never possible tofind out such complicated segregation behaviors at the
GB without applying appropriate quantitative analysis [2].

Fig. 1 An atomic-resolution HAADF-STEM image of a GB
in Y-doped MAS.

Fig. 2 A HAADF-STEM image (a) with a series ofcomposition maps: (b) Y, (c) Mg, (d) Al, and (e) O,
quantified by EELS analysis.

References[1] A. Campos-Quiros, A. Kundu, and M. Watanabe, Microsc. Microanal.
29, Suppl. 1, 407 (2023).
[2] M. Watanabe, G. Guzzinati, P. Kükelhan, V. Gerheim, M. Linck, H.
Müller, M. Haider, T. F. Hoffman, T. Isabell, N. Shimura, and H.
Sawada, Microsc. Microanal. 29, Suppl. 1, 416 (2023).

Masashi Watanabe (Analytical Science Research Laboratory)
E-mail: masashi.watanabe.d2@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/27.html

IMR KINKEN Research Highlights 2024

13

Infrastructural Materials

Reactive Oxygen Species Generation on Nitrogen-Doped
Titanium Under Visible Light IrradiationP

ure titanium and titanium alloys such as Ti-6Al-4V are commonly used as biomaterials because of their good
biocompatibility and high corrosion resistance. In this study, Nitrogen-doped TiO2 (N-doped TiO2) was formed
on a Ti substrate, and reactive oxygen species resulting from the visible light-induced photocatalytic activity of
the N-doped TiO2 was investigated.
Titanium dioxide (TiO2) forms on surfaces oftitanium (Ti), and this titanium oxide layer is responsible
for the biocompatibility. Numerous studies have reported
that anatase-type TiO2 exhibits high photocatalytic
activity; when it is irradiated with ultraviolet light, it reacts
with water or O2 surrounding it and generates reactive
oxygen species (ROS). In addition, hydrogen peroxideand hydroxyl radicals are known to be generated as
ROS on TiO2 photocatalysts. N-doped TiO2 also exhibits
visible light-induced photocatalytic activity. N-doped
TiO2 subjected to NaOH and hot water and heated in anammonia gas atmosphere showed visible light-induced
antimicrobial activity and biocalcification ability [1,2].
On the other hand, as a related study, we also conducteda study on Ag and Cu co-doped TiO2 prepared by thechemical and thermal treatment of Ti metal [3].
The objective of this study is to investigate the ROS
generated via visible light-induced photocatalytic
activity on N-doped TiO2.
To prepare N-doped TiO2, we polished commercialgrade 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 under an ammonia gas
atmosphere in a tubular electric furnace.
Figure 1 shows the generated amount of hydroxyl
radicals for each sample, which was 0.290 μM for thecp Ti and 0.825 μM for the N-doped TiO2 plate (500-3h). The results show that more hydroxyl radicals weregenerated with a N-doped TiO2 plate than with a cp Ti
plate.
Figure 2 presents measurement results of theconcentration of hydrogen peroxide generated inpurified water, each of which carried a sample of cp Ti
or N-doped TiO2 (500-3 h), and each of which was
subjected to visible light irradiation for 15 min. The
concentration of hydrogen peroxide generated in the
purified water with cp Ti irradiated with visible light for 15
min was 0.31 μM, whereas that with N-doped TiO2 (5003 h) was 1.16 μM.
N-doped TiO2 prepared in this study exhibited
photocatalytic activity under visible light irradiation,

Fig. 1 Electron-spin resonance spectra under visible-lightirradiation of (a) cp Ti and (b) N-doped Ti plate (500-3 h).
Asterisk (*) represents a significant difference at p < 0.05

Fig. 2 Generated amount of hydrogen peroxide on cp Ti
and N-doped TiO2 (500-3 h) under visible light irradiation(all data are expressed as the average± SD; n = 3)

were generated hydroxyl radical and hydrogen peroxide.
The results suggested that ROS generated by thephotocatalytic reaction.
References[1] M. Kawashita, N. Endo, T. Watanabe, T. Miyazaki, M. Furuya, K.
Yokota, Y. Abiko, H. Kanetaka, and N. Takahashi, Colloids Surf. B:
Biointerfaces 145, 285 (2016).
[2] M. Iwatsu, H. Kanetaka, T. Mokudai, T. Ogawa, M. Kawashita, and
K. Sasaki, J. Biomed. Mater, Res. B: Applied Biomaterials 108(2),451 (2020).
[3] K. Suzuki, M. Iwatsu, T. Mokudai, H. Kanetaka, M. Shimabukuro, T.
Yokoi, and M. Kawashita, Molecules 28(2), 650 (2023).

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

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IMR KINKEN Research Highlights 2024

Energy-Related Materials

IMR KINKEN Research Highlights 2024

Research

Energy-Related Materials
GIMRTInternational Co-Authored Paper

Growth Kinetics of {100} and {110} Crystal-Melt Interfacesof SiliconDynamics of crystal-melt interface on the rough {100} and {110} planes of silicon were investigated by in situ
observation experiments. It was clearly shown that both growth velocities are similar, and the ratio of the kinetic
coefficients of both planes are comparable.
Anisotropy of the growth velocity is the mostfundamental issue in crystal growth, and the growthvelocity of silicon is well known to be anisotropic,
depending on the growth crystallographic
orientation. In general, when the driving force (Δμ)
for crystal growth is small, the growth velocity (V) is
expressed with a kinetic coefficient β as V ≈ β・(Δμ/kT), where k is the Boltzmann’s constant and T is anabsolute temperature. Since the incorporation of
atoms into the crystal surface at the crystal-melt
interface is greatly affected by the atomic smoothnessof the crystal surface, the value of β is different foreach crystallographic plane. However, the literature
contains limited reports on the anisotropy of growthvelocities of rough interfaces with different
orientations. That is, the difference in growth kinetics
between {100} and {110} interfaces, for example, is
not yet fully known. Therefore, in this study, in situ
experiments are performed in order to clarify thedifference in growth velocities (i.e., kinetic
coefficients) for the crystal-melt interfaces with
<100> and <110> rough growth directions [1].
An in situ observation system was used toobserve and record the crystal-melt interface with
<100> and <110> orientations during theunidirectional solidification process. Two siliconwafers having a crystallographic orientation of<100> and <110> in the growth direction wereplaced side by side in a silica crucible. The wafers
were carefully melted from one side and heating was
stopped to create a state in which the remaining
crystals (seed crystals) and melt are in equilibrium.
The sample was then cooled to initiate crystal growthfrom the seed crystals. Experiments were performedat three cooling rates: 3 K・min-1, 10 K・min-1 and 40
K・min-1 , and the solidification processes wererecorded using a high-speed thermal camera andthe recorded video was analyzed.
Figure 1 shows (a) the crystal-melt interface of
crystals growing in the <100> and <110> directions,and (b) the growth velocity change of both interfaces
obtained from the video analysis [1]. It can be seenthat the growth velocities of both interfaces arecomparable. Similar results were obtained for all

Fig. 1 (a) Snapshots of unidirectional solidification process
at a cooling rate of 3 K・min-1. (b) Plot of growth velocity
as function of time for {100} and {110} interfaces [1].

samples.
From the microstructural analysis of the postsolidification sample, the direction of grain boundary
movement during steady-state growth wasmeasured, and from that result and Equation (1), theratio of kinetic coefficient for growth in the <100>and <110> directions was obtained.


where φ is the grain boundary angle to the growth
direction and K(100) and K(110) are kinetic
coefficients for (100) and (110) planes, respectively.
It was found the ratio of both kinetic coefficients,
K(110)/K(100) = 1.05. In this way, it is experimentallyconfirmed that the kinetic coefficients for the {100}and {110} crystal-melt interfaces are similar, within a
5% accuracy.
References[1] S. S. Mishra, L.-C. Chang, K. Maeda, J. Nozawa, H. Morito, T.
Duffar, and K. Fujiwara, J. Crystal Growth 627, 127524 (2024).

Kozo Fujiwara (Crystal Physics Research Laboratory)
E-mail: kozo.fujiwara.c6@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/02.html

16

IMR KINKEN Research Highlights 2024

,   (1)IMR KINKEN Research Highlights 2024

GIMRT

Direct Observation of Voids Decorated with Transmuted
Rhenium Atoms in Neutron-irradiated Tungsten by Transmission
Electron Microscopy and Atom Probe Tomography

Radiation damage in tungsten which is a candidate material for the plasma-facing components of fusion reactors

was investigated by both transmission electron microscopy and atom probe tomography. Voids decorated withtransmuted rhenium atoms in (initially pure) tungsten neutron-irradiated in the fast-neutron experimental reactor Joyo
were clearly observed, which contribute to understanding the formation mechanism of the irradiation-induced defects.
Tungsten (W) is a candidate material for the plasmafacing components of fusion reactors. Plasma-facing
materials are exposed to an intense neutron-irradiation
field during fusion reactor operation. Neutron-irradiationof W causes degradation of its mechanical and thermal
properties, which is due to the formation of irradiationinduced defect clusters (e.g., voids and dislocation loops)
by displacement damage, such as vacancies and selfinterstitial atoms, and the formation of irradiation-induced
clusters or precipitates by solid transmutation elements
such as rhenium (Re) and osmium (Os) in W. Therefore, it
is important to understand microstructural changes in W
caused by the irradiation [1].
Transmission electron microscopy (TEM) can reveal
the structure of defects formed by neutron-irradiation, but
it is difficult to observe compositional changes due tonuclear transmutation. On the other hand, atom probe
tomography (APT) cannot obtain information about thedefect structure, but can detect the compositionalchanges. In the present study, we applied correlative
microscopy using TEM and APT to (initially pure) W
neutron-irradiated up to 1.54 dpa at 750 ˚C in the fastneutron experimental reactor Joyo where the thermal
neutron ratio is low, and investigated the structure andchemistry of the defects formed by neutron- irradiation [2].
Figure 1 shows a TEM image and an APT map for Re
obtained from the same area of the needle specimen.
Voids with a high number density were clearly observedin the TEM image, which was taken in an under-focusedcondition to emphasize the voids. Re-enriched clusters
were observed in the APT map. It should be noted that
APT cannot obtain an elemental map of the whole needle
specimen, but only the central part. By comparing the
TEM image and the APT map, a one-to-one
correspondence was clearly obtained between the voidsin the TEM image and the Re-enriched clusters in the APTmap. It was found that the voids and the Re-enrichedclusters do not exist independently but are present at thesame position. The size distribution for the Re-enrichedclusters is almost the same as that for the voids. The
above results show that all voids are decorated with

Fig. 1 TEM image and APT map for Re obtained from the sameneedle specimen of (initially pure) W neutron-irradiated in the
fast-neutron experimental reactor Joyo. A one-to-one
correspondence was clearly obtained between the voids in
the TEM image and the Re-enriched clusters in the APT map.

transmuted Re atoms in the (initially pure) W neutronirradiated in Joyo where the thermal neutron ratio is low,
and that no Re-enriched clusters or Re-precipitates areunrelated to voids.
References[1] Y. Hatano, J. Wang, T. Toyama, T. Hinoki, K. Yabuuchi, Y. Zhang, B.
Ma, A. V. Spitsyn, N. P. Bobyr, K. Inoue, and Y. Nagai, Materials &Design 229, 111899 (2023).
[2] K. Inoue, T. Yamashita, S. Nogami, A. Hasegawa, T. Toyama, and Y.
Nagai, Materialia 32, 101963 (2023).

Yasuyoshi Nagai and Koji Inoue (Irradiation Effects in Nuclear and Their Related Materials Research Laboratory)
E-mail: koji.inoue.e2@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/11.html

IMR KINKEN Research Highlights 2024

17

Energy-Related Materials

Volumetric Change of SiC Under Irradiation

Silicon carbide (SiC) fiber-reinforced matrix composite (SiCf/SiC) is a candidate material for advanced fusion
reactor blankets. We clarified the volumetric change of SiC due to irradiation and its effect to the mechanicalproperties using ultra-small testing technologies (USTT). Furthermore, we utilized the USTTs for evaluating theinterfacial mechanical strength of tungsten-coated ferritic steel for fusion reactors.

Materials resistant to extreme environments such asoxide dispersion strengthened (ODS) alloys [1], ceramics[2-4] and heavy alloys [5] are crucial for realizing
advanced nuclear systems, such as Gen IV fission
reactors and fusion reactors.
Silicon carbide (SiC) fiber-reinforced matrix
composite (SiCf/SiC) is a candidate ceramic material for
fusion reactor blankets because of its high-temperatureenvironmental resistance, low activation properties, andirradiation resistance. This study investigated the effectof annealing temperature on the proportion of shrinkage
and swelling of SiC fiber in SiCf/SiC irradiated at 30 °C to
100 dpa by Si-ion beam [2]. After the irradiation, thecompressive displacement of > 60% of the fibers before
failure increased to more than 1.5 times that of the asreceived specimen. Significant swelling indicates thatthe proportion of swelling was higher than that ofshrinkage after irradiation. This can be attributed to theamorphization of SiC, and its amorphization thresholddose increased with decreasing grain boundary volume
fraction. These findings provide insights into themechanism of irradiation-induced fiber amorphization of
SiC. In order to obtain high-strength TiB-TiB2 ceramics
by low-temperature sintering, a new mechanically milled
sintering aids was also developed [3].
In fusion reactors, plasma facing components needhigh-temperature stability, resistance to surface
sputtering, low-retention of tritium and irradiation
resistance. Vacuum plasma spray (VPS) coating is a
prospective technology for the fabrication of tungstencoated reduced activation ferritic steel (W-RAF steel).
However, detailed evaluation on the mechanicalproperties of W-RAF steel joints has been limited
because of the thin coating layer. In this study [5], themechanical properties of the W coating and W–RAF
steel interface were evaluated using double-notchedmicropillar compression tests. The ultimate shear
strength of the interface area exhibited a similar to that of
the W layer and higher than that of the RAF steel (F82H)
substrate, as shown in Fig. 2. The fracture microstructure
elucidated the importance of improving the massdensities of W coatings to improve the mechanicalperformance of vacuum-plasma-sprayed W–steel joints.
Effective bonding of a W/F82H interface and the adjacent
RAF steel substrate via VPS results in high strength andFig. 1 Load–displacement curves of the two types of fibers [2].

Fig. 2 Ultimate nominal shear stress versus shear sectional
area of the tested DNS samples [5].

ductility of the interface area, and hence the W-RAF
steel joint, against shearing and bending loads.
References[1] H. Yu, S. Kondo, R. Kasada, and S. Ukai, Corr. Sci. 212, 110933(2023).
[2] X. Yuan, S. Kondo, K. Yabuuchi, H. Yu, Y. Ogino, and R. Kasada, J.
Eur. Ceram. Soc. 43, 5125 (2023).
[3] Y. Jimba, Y. Okuno, S. Kondo, H. Yu, Y. Ogino, S. Nogami, and R.
Kasada, Ceram. Int. 49, 34863 (2023).
[4] S. Iwamoto, S. Kondo, H. Katsui, K. Shimoda, H. Yu, Y. Ogino, and
R. Kasada, Int. J. Appl. Ceram. Technol., 1-9 (2023) in press.
[5] X. Wu, S. Kondo, H. Yu, T. Nagasaka, and R. Kasada, Surf. Coat.
Technol. 462, 129468 (2023).

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

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IMR KINKEN Research Highlights 2024

Beyond Tantalum and Tungsten: The Rise of Single-Crystal
Alloys in Resistance Heating

We have developed single-crystal alloy wires using the crystal growth method, which has resulted in a
breakthrough in resistance heating wires. The new alloy wires offer improved workability, high-temperature
durability, and lower power consumption, overcoming the limitations of traditional Ta and W wires. This innovation
opens up previously unattainable alloy systems, promising new industrial applications.

Around 20 years after Edison's invention ofusing bamboo as a filament for incandescent lamps
in 1883, it was discovered that tantalum (Ta) could
also be used as a metal filament. However, despite
its excellent ductility, Ta wire was soon replaced bytungsten (W) filaments due to the disadvantage ofdeterioration caused by grain growth. Althoughincandescent lamps have been replaced by newer
technologies such as fluorescent lamps, LEDs, andorganic ELs, refractory metals such as W, Mo, andTa have been used as high-temperature metal
resistance heating elements for over 100 years.
An important application of resistance heating
wire is in vacuum deposition cells, which are also
used for organic EL deposition. The Ta wirecommonly used in these cells gradually forms a
nodular structure and deteriorates with use, requiring
replacement approximately every 1,000 hrs.
Therefore, due to the increasing use of organic EL in
recent years, there is a demand for a new resistanceheating wire that is more durable, consumes lesspower, and is easy to process at room temperature.
We addressed this problem by considering thepossibility of expanding the range of material
selection by single-crystallizing the wire to essentiallyeliminate intergranular cracking and provide
workability. The micro-pulling-down method (μ-PD
method) is a fast and effective way to fabricate
single crystals several centimeters in size. However,it was originally designed only for screening
purposes. To replace the current plastic forming
method with the μ-PD method, certain challenges
had to be overcome: the method had to be capableof producing tens of meters or more of wire per daywith an accuracy of φ0.8 mm ±12 μm or less, and it
had to have no casting defects inside or on thesurface of the wire.
Through the analysis of the μ-PD method, we
found that excellent shape controllability can beachieved under certain wetting conditions, and we
also found conditions that allow crystal growth atseveral hundred mm/min, which is several tens oftimes faster than conventional methods [1,2].

Fig. 1(a) shows the grown wire of Ruscaloy and (b) shows theimage of deposition cell.

Additionally, we developed Ruscaloy, a novel alloy
suitable for this method, and successfully fabricateda deposition cell to perform organic EL film
deposition [3]. This alloy exhibited excellent
properties such as flexibility and strength(εrp=~80%, σTS=~550MPa) that can be easily
processed at room temperature, and exhibits morethan 3 times higher temperature durability(>3000h@1600°C), 10% lower power consumption,and 2 times faster return to deposition rate compared
to conventional Ta wire.
Our results shed new light on alloys that werepreviously unusable due to workability issues withthe crystal growth method. We also demonstrated
new possibilities for traditional materials like
resistance heating wire. There is still much to be
explored, not only in terms of alloy properties, butalso in terms of the physics of crystal growth, which
is of inexhaustible interest.
References[1] R. Murakami, K. Oikawa, K. Kamada, and A. Yoshikawa, ACS
Omega 6, 8131 (2021).
[2] R. Murakami, K. Oikawa, K. Kamada, S. Itoi, and A. Yoshikawa,
J. Cryst. Growth 629, 127565 (2023).
[3] R. Murakami, K. Kamada, K. Umetsu, T. Yoshioka, K. Oikawa,
J. Kido, and A. Yoshikawa, Int. J. Refract. Met. Hard Mater. 114,
106235 (2023).

Rikito Murakami (Advanced Crystal Engineering Research Laboratory)
E-mail: rikito.murakami.d4@tohoku.ac.jp
URL: http://yoshikawa-lab.imr.tohoku.ac.jp/index-e.html

IMR KINKEN Research Highlights 2024

19

Energy-Related Materials

Larger Amounts of Water Intercalation into Heat-Storage
Layered MnO2 Induced by Interlayer-Cation Disorder

Layered manganese dioxide containing K cations and water molecules in between the MnO layers exhibits
2

reversible heat storage properties via a water-intercalation mechanism with a certain amount of an irreversible
capacity of water intercalation after the initial thermal cycle. We have elucidated that the irreversibility originatesin the occupation behavior of the interlayer K cations that compete for the most stable sites with excess watermolecules existing in the as-synthesized state.
(a) Pristine(b) Heat-treated
Mn

K

K at 2c
MnO2

H 2O[0001]

1 nm

K[1120]

RT(c)[1100]

Competition

250℃

H 2O

2c

2c

Fig. 1 STEM images of (a) pristine and (b) heat-treated
K-containing MnO2 taken along the a-axis direction. (c)Schematic illustrations of potential energy surfaces forthe interlayer K cations and water molecules during thefirst release/absorption of water molecules from/to
K0.33MnO2.

interlayer cations that change the interaction
between the interlayer cations and water molecules
will be effective.
References[1] T. Hatakeyama, N. L. Okamoto, S. Otake, H. Sato, H. Li, and T.
Ichitsubo, Nat. Commun. 13, 1452 (2022).
[2] N. L. Okamoto, H. Yoshisako, and T. Ichitsubo, Energy Stor.
Mater. 61, 102912 (2023).
[3] N. L. Okamoto, H. Yoshisako, and T. Ichitsubo, J. Phys. Chem.
C 127, 20956 (2023).

Norihiko L. Okamoto and Tetsu Ichitsubo (Structure-Controlled Functional Materials Research Laboratory)
E-mail: nlokamoto@tohoku.ac.jp, tichi@tohoku.ac.jp
URL: http://ilab.imr.tohoku.ac.jp/

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IMR KINKEN Research Highlights 2024

O

RT

Heat storage materials can store waste heatand release the thermal energy on demands.
Among those materials, a K-containing layered
manganese dioxide (K0.33MnO2⋅0.83H2O) has beenfound to exhibit excellent heat-storage properties,
including high environmental integrity, high thermalenergy density, fast charge/discharge rates, andgood cyclability, owing to a water-intercalation
mechanism [1]. The K-containing MnO2 canreversibly absorb and release 0.50 mol molecules
per MnO2 resulting in a reversible thermal energy
density exceeding 1,000 MJ/m3. However, it exhibits
irreversible capacity of water intercalation (0.33 mol
per MnO2) in the initial heating/cooling cycle, which
limits the reversibly available energy density of thematerial for the subsequent cycles.
To elucidate the origin of the initial irreversible
capacity, we investigated the crystal structure of thelayered manganese dioxide in the as-synthesize
and heat-treated states by atomic-resolution
scanning transmission electron microscopy (STEM)[2,3]. The interlayer K cations in the as-synthesizedstate are randomly arranged in some of theinterlayers (open yellow arrows in Fig. 1(a)) because
excess water molecules prevent the K cations fromoccupying the most stable interlayer site (Wyckoff
2c site in space group P63/mmc). After heat
treatment at 250°C, on the other hand, the interlayer
K cations occupy every third 2c site in all theinterlayers, showing a tripled periodicity along thea-axis direction (solid yellow arrows in Fig. 1(b)).
This infers that simultaneous occupancy at the 2csite of the K cation and the water molecules cannot
be realized, and the heat treatment allows the K
cation to move from its metastable position to themost stable position (2c site) in the absence of watermolecules at high temperatures. This competitive
occupancy is schematically illustrated in Fig. 1(c).
To minimize the irreversible capacity of waterintercalation, and hence, to increase the thermalenergy density, replacing interlayer K cations withother species and/or optimizing the content of

IMR KINKEN Research Highlights 2024

International Co-Authored Paper

Partial Liquid Metal Dealloying to Synthesize Nickel-Containing
Porous Ferrous and High-Entropy Alloys

Liquid metal dealloying is a promising technique to produce bicontinuous porous metals with high specificsurface areas. However, it has not been applied to produce nickel-containing porous metals because of thelack of a suitable metallic bath. Here we show that nickel-containing porous and composite metals can beproduced by partial liquid metal dealloying.
Nanoporous
metalswithbicontinuous
microstructures are attracting increasing attention
owing to their outstanding performance. Suchnanoporous materials are prepared by the selective
removal of a component from a solid alloy, also known
as dealloying. Dealloying was initially introduced as
an electrochemical process whereby the less-noble
component of the precursor selectively dissolves into
an aqueous solution, whereas the remaining noble
component self-organizes into a three-dimensional
nanoporous structure. However, this electrochemical
technique is only applicable to elaborate nanoporous
structures comprising noble metals.
Liquid metal dealloying (LMD) has emerged as aversatile method that can be used to produce porousand composite metals with various elements [1]. In
LMD, the selective dissolution is driven by the mixing
enthalpy between species. Let us consider a genericA-B precursor alloy immersed in a liquid metal C.
Selective dissolution of B and formation of nanoporous
A, as shown in Fig.1(a), occurs if A is immiscible in C(∆Hmix A-C large) and B is miscible in C (∆HmixB-C≲0).
Using LMD, porous and composite materials
comprising less-noble metals and alloys have beensuccessfully fabricated. These materials present
advantageous functional properties for battery
electrodes, electrolytic capacitors, and catalytic
materials. In the previous LMD studies, Mg, Cu, andBi are commonly used in the metallic baths, however,
the high miscibility of Ni in these liquids precludes theapplication of LMD to the production of Ni-containing
porous alloys, although Ni alloys exhibit excellent
functional properties such as shape-memory effectand catalytic properties.
In this work, we developed new LMD technologythat adding an amount of B(Ni) to the liquid bath suchthat only a fraction of B(Ni) dissolves from the A-B
precursor (Fig.1(b)). The dealloying naturally stops
when an equilibrium is reached between solid
ligament and liquid phases. In such a system, byimmersing a precursor of A1-x’Bx’ (x’>x) in a ByC1-ybath, the content of B in the precursor decreases until
the composition of the solid ligaments reaches A1-xBx

Fig. 1 Schematic illustration showing porous metalformation by (a) LMD and (b) PLMD. SEM image and
EDX maps for the Ni-containing nanoporous (c) stainlesssteel and (d) high-entropy alloy synthesized by PLMD

to achieve thermodynamic equilibrium. This is referred
to as partial liquid metal dealloying (PLMD) [2].
Using the concept of PLMD, we demonstrated tofabricate austenitic stainless steel (equivalent to
SUS316L) and high-entropy alloys. Figure 1(c) shows
cross-sections of the microstructures obtained after
immersinga(Fe0.657Cr0.194Ni0.134Mo0.015)30Ni70
precursor in (Mg0.75Bi0.25)92Ni7Cr1 bath at 1023 K for
10 min, followed by etching in nitric acid The EDX
maps indicate the uniform distribution of Fe, Cr, Ni,
and Mo in the ligaments. The average composition of
the porous metal was Fe64.9Cr20.1Ni13.6Mo1.4(at.%),showing excellent agreement with the composition
range of SUS316L. Figure 1(d) shows (V0.15Cr0.15Fe0.20
Co0.25Ni0.25)50Ni50
precursor
immersedin(Mg0.5Bi0.5)98.2Ni1.5Cr0.3 bath at 1023 K for 30 min.
The EDX composition maps acquired from the crosssection of ligaments reveal uniform distribution of thedesired elements. Average composition was
V14.9Cr11.9Fe18.8Co21.3Ni33.2, falling into the definitionof high entropy alloy. These ligaments had a facecentered cubic structure in the both porous metals
confirmed by the X-ray diffraction spectrum.
References[1] T. Wada, K. Yubuta, A. Inoue, and H. Kato, Mater. Lett. 65, 1076
(2011).
[2] T. Wada, P.-A. Geslin, D. Wei, and H. Kato, Commun. Mater. 4,
43 (2023).

Takeshi Wada and Hidemi Kato (Non-Equilibrium Materials Research Laboratory)
E-mail: takeshi.wada.d7@tohoku.ac.jp, hidemi.kato.b7@tohoku.ac.jp
URL: http://www.nem2.imr.tohoku.ac.jp/index-e.html

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Energy-Related Materials

Atomic and Electronic Structure in MgO-SiO2

Understanding disordered structure is difficult due to insufficient information in experimental data. To

investigate oxygen packing and network topology in glassy (g-) and liquid (l-) MgO-SiO2 based on a comparison
with the crystalline topology, we used a combination of diffraction and simulation. We find that the glassforming ability (GFA) of MgO-SiO2 binary is dominated by the atomic structure in terms of network topology.

The MgO–SiO2 system is very important in bothglass science and geoscience [1] since g-MgO–
SiO2 is a typical binary silicate glass system andcrystalline (c)-MgSiO3 (enstatite) and c-Mg2SiO4(forsterite) are Mg-end members of main
components of the Earth’s mantle. Liquid Mg2SiO4
can be classified as a fragile liquid, while l-MgSiO3
is a stronger liquid according to Angell [2].
Particularly, viscosity under high pressure and hightemperature is an important thermophysicalproperty to understand magma ocean solidification[3].
In this study, we performed high-energy X-ray
diffraction and neutron diffraction measurements on
l-MgSiO3 and l-Mg2SiO4 to obtain detailed structural
information about the liquids. To investigate atomic
configurations with detailed electronic structures ofg- and l-MgO–SiO2, we conducted advanced
density functional – molecular dynamics simulations
for g- and l-MgO–SiO2 using the measured densityof l-Mg2SiO4 by an electrostatic levitation furnace
under microgravity at the International Space
Station. Moreover, we performed several topologicalanalyses (ring, polyhedral connection analysis, andpersistent homology) on c-, g-, and l-MgO–SiO2 toextract topological similarity among the crystal,glass, and liquid to understand the relationshipbetween the topology and GFA.

Diffraction
measurements
anddensityfunctional – molecular
dynamics
simulations
demonstrated that the packing of oxygen atoms is
an important structural descriptor to understand thedifference between MgSiO3 and Mg2SiO4 andbetween glass and liquid [4]. The analysis ofelectronic and topological structures suggests that
an electronic state does not change quite a lot
between MgSiO3 and Mg2SiO4, and the topologicalsimilarity between c- and g- (l-) Mg2SiO4 is thesignature of low GFA. On the other hand, high GFA
g- (l-) MgSiO3 shows a unique glass topology, which
is different from c-MgSiO3. These results show thatthe atomic structure in terms of network topology is
an important factor to understand GFA. Systematiccomparison among crystal, glass, and liquid is
important to understand the nature of glass andliquid.
References[1] B. Mysen and P. Richet, Silicate Glasses and Melts, Second
Edition (Elsevier, 2019).
[2] C. A. Angell, Science 267, 1924 (1995).
[3] L. Xie, A. Yoneda, D. Yamazaki, G. Manthilake, Y. Higo, Y.
Tange, N. Guignot, A. King, M. Scheel, and D. Andrault, Nat.
Commun. 11, 548 (2020).
[4] Y. Shuseki et al., J. Phys. Chem. A 128, 716 (2024).

Fig. 1 Isosurface plots of the partial charge density around the HOMO and the LUMO levels for g-MgSiO3.

Junpei Okada (Crystal Chemistry Research Laboratory)
E-mail: junpei.okada.b6@tohoku.ac.jp
URL: http://www.imr.uda-lab.imr.tohoku.ac.jp/index-e.html

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IMR KINKEN Research Highlights 2024

International Co-Authored Paper

Calcium Metal Batteries with Long Cycle Life with aHydride-Based Electrolyte and Copper Sulfide ElectrodeA

long-cycle-life calcium metal battery is developed using a copper sulfide/carbon (CuS/C) composite and a
tailored monocarborane electrolyte of Ca(CB11H12)2 in DME/THF, which enables reversible calcium plating/
stripping at room temperature. The combination affords a calcium metal battery with a long cycle life of over
500 cycles and capacity retention of 90% based on the capacity of the 10th cycle.
Batteries with Ca metal anodes appear
competitive in terms of realizing high energy
densities, given the high volumetric/gravimetriccapacities (2072 mAh cm−3/1337 mAh g−1) and low
reduction potential (−2.87 V vs. the standardhydrogen electrode) of the Ca metal. Additionally, as
the charge density of Ca2+ (0.49 e Å−3) is lower thanthat of other divalent ions such as Mg2+ and Zn2+
(1.28 and 1.18 e Å−3, respectively), the softness of
Ca2+ ions induces a tendency to form more covalentbonds with host anions, which may accelerate iontransport and diffusion in electrolytes and cathodematerials. These advantageous characteristics of
Ca—in addition to its abundance in the crust andenvironmental
compatibility—highlightthesignificance of Ca metal batteries as a promising
post-Li ion battery (LiB) candidate. However, theresearch and development of Ca metal batteries
involve various challenges, including the lack of an
efficient electrolyte and a practical cathode that
promotes the reversible Ca2+ storage reaction [1].
To overcome these limitations, the applicabilityof a CuS cathode in Ca metal batteries and its
electrochemical properties are verified herein. Exsitu spectroscopy and electron microscopy results
show that a CuS cathode comprising nanoparticles
that are well dispersed in a high-surface-areacarbon matrix can serve as an effective cathode forCa2+ storage via the conversion reaction. This
optimally functioning cathode is coupled with atailored, weakly coordinating monocarborane-anion
electrolyte,viz.
Ca(CB11H12)2in
1,2-dimethoxyethane(DME) /tetrahydrofuran(THF),
which enables reversible Ca plating/stripping atroom temperature [2]. The combination affords a Ca
metal battery with a long cycle life of over 500 cycles
and capacity retention of 92% based on the capacityof the 10th cycle. Furthermore, the battery candeliver a reasonable energy density of 144 Wh kg−1
at a high power density of 4000 W kg−1, which iscomparable to that of previously reported dualcation-system Ca metal batteries.
The prototype CuS/Ca batteries with theFig. 1 (a) Schematic of a prototype Ca metal battery. The
battery comprises a Ca2+ storing positive electrodecontaining the CuS cathode and Ca metal anode with ahydrogen cluster electrolyte. (b) Cycling performanceof the Ca–CuS battery.

Ca(CB11H12)2 in DME/THF electrolyte exhibited
higher performance than state-of-the-art Ca andcycle life. This study highlights the potential metal
batteries in terms of both the rate capability ofdeveloping practical batteries using Ca metal [3].
The use of cathodes at voltages >3 V could enableimprovements in the energy density of Ca metal
batteries and facilitate the use of Ca-ion batteries aspractical alternatives to existing LIBs.
References[1] M. E. Arroyo-de Dompablo, A. Ponrouch, P. Johansson, and
M. R. Palacin, Chem. Rev. 120, 6331 (2020).
[2] K. Kisu, S. Kim, T. Shinohara, K. Zhao, A. Zuttel, and S. Orimo,
Sci. Rep. 11, 7563 (2021).
[3] K. Kisu, R. Mohtadi, and S. Orimo, Adv. Sci. 10, e2301178(2023).

Kazuaki Kisu and Shin-ichi Orimo (Hydrogen Functional Materials Research Laboratory)
E-mail: kazuaki.kisu.b2@tohoku.ac.jp
URL: http://www.hydrogen.imr.tohoku.ac.jp/en/index.html

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Energy-Related Materials
International Co-Authored Paper

Alkali Mono-Pnictides: A New Class of Photovoltaic Materials
by Element Mutation

S

elenium-based solar cells, with a maximum efficiency of 6.5%, can be improved using element mutation withGroup 15 elements (P, As, Sb) and alkali metals (Li, Na, K, Rb, Cs). NaP shows promise due to its abundantelements, suitable band gap, high absorption, and effective charge carrier properties, though P vacancies may
limit its performance. Solutions for reducing these vacancies and preliminary NaP sample results with a 1.66
eV band gap indicate potential in photovoltaic technology.
In 1873, Willoughby Smith reported thatselenium (Se) exhibits photoconductivity and three
years later, Adams and Day demonstrated the firstsolid-state solar cell using Se. However, the best
power conversion efficiency reaches only 6.5% [1].
One contributing factor is the larger band gap of 1.8
eV compared to the optimal value around 1.3–1.5
eV. Substituting elements while maintaining charge
neutrality, often referred to as element mutation is acommon practice in the search for new materials.
Instead of simply substituting one element with two,
while keeping the average oxidation state, we
introduce ions into the vacant sites within the
structure, and mutate the elements while preserving
overall neutral charge.
Because Se is a Group 16 element in a neutral
charge state, we replace Se with -1 anions andintercalate +1 cations, namely alkali metals (M),between the chains to maintain a charge balance(see Fig. 1). To retain the chain-like structures in
t-Se, we consider Group 15 pnictogens as anions(Pn).
One advantage of the MPn composition is thatthe physical properties can be optimized bychanging the cation-anion combinations. Indeed,
the band gap is controllable within a range of optimalband gaps for solar cells as shown later. Anotheradvantage is the cations should attract the anion
chains more strongly, which results in greater
stability.
In this study, we performed first principles
calculations on the phase stability and optoelectronic
properties of MPn compounds to investigate thepotential as photovoltaic materials [2]. It is foundthat a series of MPn cover the appropriate band gap
range for solar cells and exhibit relatively strong
optical absorption onsets and low electron and holeeffective masses. We also calculated the point
defects in NaP, a representative of MPn composedof non-toxic and earth abundant elements. Our
calculations reveal that P vacancies (VP) haverelatively low formation energies and show deep

Fig. 1 Crystal structures of (left) trigonal Se and (right)
orthorhombic NaP. The blue and red circled arrows
depict the helical chain rotation directions from theback of the paper to the front.

levels, which should be detrimental to photovoltaic
efficiency based on the Shockley-Read-Hall (SRH)
theory for non-radiative recombination. Indeed,
calculations of non-radiative carrier capture rates
reveal the carrier recombination by VP is likely to besignificant. To reduce VP concentrations, we propose
to control the Fermi level by adjusting growth
conditions and/or introducing dopants. To verify our
calculations, we synthesized NaP and measured its
direct band gap using a diffuse reflection
measurement. Our experiment shows that theobserved direct band gap is 1.66 eV, which closely
matched the calculated direct band gap of 1.62 eV.
References[1] T. K. Todorov, S. Singh, D. M. Bishop, O. Gunawan, Y.-S. Lee,T. S. Gershon, K. W. Brew, P. D. Antunez, and R. Haight, Nat.
Commun. 8, 682 (2017).
[2] Y. Kumagai, S. R. Kavanagh, I. Suzuki, T. Omata, A. Walsh, D.
O. Scanlon, and H. Morito, PRX Energy 2, 043002 (2023).

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

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IMR KINKEN Research Highlights 2024

Stabilizing LiMn2O4-Based Spinel Cathode Materials for
Advanced Photo-Rechargeable Batteries

Photo-rechargeable batteries (PRBs), which integrate solar-energy harvesting and storage, are promising forsustainable energy use. However, limited cathode materials have hindered their development. Here we provide
a fundamental understanding of the structure design of LiMn2O4-based spinel cathode materials and showthat LiMn1.5Fe0.5O4 exhibits a remarkably high stability during photocharging.
Utilizing solar energy is key to establishing asustainable society. Although solar cells can convert
solar energy to electricity, they must be connected
to rechargeable batteries for storing the energy. To
minimize the size and cost, an integrated systemcalled photo-rechargeable batteries (PRBs) has
been proposed. Figure 1(a) shows a schematic
illustration of a kind of PRB, where electrons are
excited under illumination by a photoactive material
located with a cathode material [1]. If the energy
levels of holes and excited electrons are adequate
compared with those of the cathode and anodematerials, the battery can be photocharged without
external electric charging, which is necessary for
usual batteries.
One of the serious problems is the lack of
cathode materials suitable for PRBs due to thestability under illumination. In our previous study [1],we demonstrated the photocharging of a 4-V class
LiMn2O4 cathode for the first time by using TiO2
nanoparticles and K2S2O8 as an electron acceptor.
Li extraction from LiMn2O4 proceeds under theillumination of UV-visible light (300–600 nm);however, an obvious irreversible capacity wasobserved for long-term illumination. Further analyses
suggested that it was probably because of thedisproportionation of Mn3+ on the surface of theparticle, resulting in the dissolution of Mn2+ into theelectrolyte.
Partial replacement of Mn with other elements
is an effective way to prevent degradation due to thedisproportionation. To investigate it, here wecompared the photocharging performance of
LiMn1.5M 0.5O4 (M = Fe, Co, Ni, Zn) [2], in addition to
LiMn2O4. While divalent Ni2+ and Zn2+ highly
stabilized the structure, the capacity from Mn3+
decreased because of the charge compensation. In
the case of Co, its high catalytic activity underillumination would lead to side reactions. On thecontrary, trivalent Fe3+ was appropriate both interms of stability and capacity, as shown in Fig. 1(b)and 1(c). Specifically, the reversible charging rate
was kept at approximately 23 mA/g even for the 2-hFig. 1(a) Charging mechanism of PRBs [1]. (b) Potentialchange of LiMn1.5Fe0.5O4 during the photocharging
process. (c) Discharge capacity of LiMn1.5M 0.5O4 (M =Fe, Co) and LiMn2O4 after the photocharging process [2].

photocharging process.
Towards the development of practical PRBs,
there are remaining issues such as the structure
design of anode and electrolyte. Although thecurrent system is a half-cell only focusing on thecathode performance, we believe that this work
provides fundamental design guidelines for theelectrode materials of PRBs. In addition, spineloxide is highly designable, and therefore further
improvements in the photocharging performance
would be achieved in the future.
References[1] K. Shimokawa, S. Matsubara, A. Okamoto, and T. Ichitsubo,Chem. Commun. 58, 9634 (2022).
[2] K. Shimokawa, S. Matsubara, T. Kawaguchi, A. Okamoto, andT. Ichitsubo, Chem. Commun. 59, 7947 (2023).

Kohei Shimokawa (Exploratory Research Laboratory)
E-mail: kohei.shimokawa.b7@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/33.html

IMR KINKEN Research Highlights 202425

Electronic Materials

IMR KINKEN Research Highlights 2024

ResearchElectronic Materials
GIMRT

Automated Pulsed Magnet System for Neutron Diffraction
Experiments

An automatic operational pulsed magnet system has been developed for high magnetic field neutron

diffraction at the Materials and Life Science Experimental Facility in Japan Proton Accelerator ResearchComplex(J-PARC) by the collaboration research between IMR and J-PARC. The combinations of 4 K and 35 T
is available with a wide scattering angle of 42 degrees.

Neutron diffraction is a unique method todetermine the magnetic structure in magnetic
ordered state. When strong magnetic fields areapplied to magnetic materials, varieties of magnetic
field induced phase transitions such as metamagnetictransition, spin reorientation, spin density wave etc.
are observed. To determine the change of magnetic
structure in such phase transitions, it is necessary to
conduct a neutron diffraction in high magnetic fields.
Application of pulsed magnetic field enables
the high magnetic field neutron diffraction in themagnetic field beyond 30 T. Pulsed magnetic field
experiments has been conducted in JRR3, J-PARC,
SNS, ILL and ISIS with the leading contribution of themagnetism division of IMR. In J-PARC, combinationsof white neutron and a pulsed magnetic field enables
us to access a wide range of reciprocal space, yetaccumulation of a few hundred shots is required toobtain a practical statistic. One of the most important
points is how to implement a pulsed magnet system
into the user operation spectrometer. The key issue
is the long-time automatic operation capability withthe less contribution of a specialist.
We have developed an automatic operational
pulsed magnetic system up to 35 T to achieve thisimportant objective. We have installed a GMrefrigerator for sample cooling. It has two merits.
One is the easy operation for low temperature asuser do not need experience of handling liquid He.
The other is the simpler vacuum chamber setup witha wide scattering angle. The scattering angle isincreased from 28 degree to 42 degree. In the wider
angle, most of magnetic scattering in low-q region
can be covered easily.
Another key improvement is the increase of themagnetic field from 30 T to 35 T by using a newcompact and reinforced coil. The coil is cooled downby the liquid nitrogen and thus the cooling efficiency
is high compared with the solid contact cooling. The
liquid nitrogen is automatically filled during theexperiment and the long-term automatic running ispossible without the access to the cryostat. It is also
important from the viewpoint of safety, because user
Hiroyuki Nojiri (Magnetism Research Laboratory)
E-mail: hiroyuki.nojiri.e8@tohoku.ac.jp
URL: http://www.hfpm.imr.tohoku.ac.jp

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IMR KINKEN Research Highlights 2024

Fig. 1(a) Schematic view of the automatic 35 T pulsed
magnet system for neutron diffraction [1].

is not required to access the pulsed coil duringexperiments.
For the automatic operation, the sensing of thesystem anomaly such as a irregular discharge or coilbreak down is important. The present system has acontroller to examine the output waveform of apulsed magnetic system during the operation. If adeviation from the standard magnetic field curve isobserved, the system dumps into the locked modeand the pulsed field generation is halted automatically.
In summary, our new automatic pulsed magnet
system for neutron diffraction provides user theaccess for the extreme environment combining 35 T
and 4 K at J-PARC.
References[1] M. Watanabe, T. Kihara, and H. Nojiri, Quantum Beam Science7(1), 1 (2023).

IMR KINKEN Research Highlights 2024

Topochemical Reduction Leads to Superconducting
Infinite-Layer Nickelate Thin Films

T

he recent discovery of superconductivity in infinite-layer nickelates has garnered significant interest due totheir potential analogy to high Curie temperature Tc cuprates. Through topochemical reduction, the infinite-layer
structure has been synthesized from the perovskite structure. By tuning the reduction temperature precisely, weachieved highly crystalline films exhibiting a higher Tc. Our results emphasize the critical role of the topochemical
reduction process for stabilization of high-Tc phase of the superconducting infinite-layer nickelate thin films.
The discovery of nickelate superconductors
creates exciting opportunities for exploring
unconventional superconductivity, due to theirpotential analogy to high Curie temperature Tc
cuprates, where both cases derive from doping atransition
metal
3d9
configuration[1].
Superconductivity has been observed in nanoscalethin films, which are epitaxially stabilized through a
topochemical reduction from the perovskite
precursor phase. This reduction process selectively
removes apical oxygen atoms from Ni-O octahedra,
resulting in low-valence layered nickelates where theoxidation state of Ni ions changes from Ni3+ (3d7) toNi+ (3d9) (Fig. 1a). Although some notable
distinctions, such as the multi-band nature of theelectronic structure associated with the rare-earth
5d orbitals and the absence of magnetic long-rangeorder in nickelates, have been discussed,
experimental efforts have been limited due to thechallenges of material synthesis. In this context,
understanding and achieving significant advancesin the synthesis process are crucial.
With this notion, we address this critical issue bysystematically tuning the reduction temperature [2].
The precursor phase of La1-x Srx NiO3 was grown bypulsed laser deposition, and the infinite-layer phase
was achieved by ex-situ low-temperature annealing
within sealed glass tubes containing CaH2 powder.
Gradual tuning of the topochemical reduction
temperature from 280 to 410oC leads to thetransformation of nickelate films from an insulatingstate into a superconducting state (Fig. 1b). Notably,
the superconducting transition temperature Tc
reaches ~14 K for Sr content x = 0.20, which is higher
than that reported in previous studies with same
composition
films.
Furthermore,
systematic
optimization results in an expansion of thesuperconducting dome in the temperature versus Srcontent x phase space, with a higher Tc and a wider
Sr content x regime.
Our findings provide insight into the
topochemical reduction process and its role in theFig. 1(a) Simplified picture of topochemical transformationof perovskite LaNiO3 films into infinite-layer LaNiO2
films. (b) Temperature dependent resistivity ρxx /ρ20K-T
curves for La0.8Sr0.2NiO2 films upon topochemical
reduction. Resistivity is normalized at 20 K.

electronic transport properties, with significant
implications for the synthesis of nickelate
superconductors. The optimized process willcontribute to the stabilization of highly crystalline
infinite-layer nickelate films, which leads to the further
studies for revealing similarities and differences insuperconductivity in nickelates and cuprates.
References[1] D. Li, K. Lee, B. Y. Wang, M. Osada, S. Crossley, H. R. Lee, Y.
Cui, Y. Hikita, and H. Y. Hwang, Nature 572, 624 (2019).
[2] M. Osada, K. Fujiwara, T. Nojima, and A. Tsukazaki, Phys. Rev.
Mater. 7, L051801 (2023).

Motoki Osada (Low Temperature Physics Research Laboratory)
E-mail: mosada@tohoku.ac.jp
URL: http://mu.imr.tohoku.ac.jp/?page_id=1128&lang=en

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Electronic Materials

Preformed Cooper Pair Near Mott Transition Probed by NMR

A

peculiar electronic state, referred to as the pseudogap-like state, emerges near the correlation-driven Mott
transition. In this study, we demonstrate that unconventional preformation of Cooper pairs is the origin of thepseudogap-like behavior near the Mott transition in layered organic superconductors. Our findings clarify that
Cooper pair preformation is significantly enhanced on the verge of the Mott transition.
A layered organic material, κ-(ET)2X, where ET
representsbis(ethylenedithio)-tetrathiafulvalene,
with a half-ﬁlled band exhibits unconventional
superconductivity (d-wave) emerged from Mott
insulators without doping but by varying the
bandwidth, which controls the relative strength of
the interactions to the kinetic energy. It is wellrecognized that the application of physical pressure
and/or chemical pressure by anion X substitution
ﬁnely tunes the interaction strength. In particular,
κ-(ET)2Cu[N(CN)2]Br with all protons in ET
substituted by deuterons (abbreviated to κ-dBr) ison the verge of the correlation-driven Mott
transition(Fig. 1(a)). In ordinary metals, nuclear spinlattice relaxation rate divided by temperature,(T1T)−1, is independent of temperature and magnetic
ﬁeld because the dynamic spin susceptibility of
conduction electrons does not sensitively vary withthose parameters. However, the metallic phase of
κ-dBr shows an anomalous decrease in (T1T)−1 oncooling from above Tc, which is compared to thepseudogap in the high-Tc cuprates.
The present work [1] explores the anomalous
suppression of spin excitations in κ-dBr through 13C
NMR under tuning interaction strength by He-gas
pressureandsystematicallysuppressing
superconductivity by magnetic ﬁelds over a 20-foldrange (0.9 to 18 T). We found that the anomalous
decrease in spin excitations on cooling occurs
mainly in the channel of antiferromagnetic
ﬂuctuations very probably with Q = (π, π), which isenhanced near the Mott transition(Fig. 1(b)), and theanomaly fades out along with superconductivity
under increasing magnetic ﬁeld(Fig. 1(c)). Our
further investigation of different materials, which arelocated in different “distances” from the Mott
transition by chemical pressure, suggests that thephenomena cannot be explained by conventional
superconducting amplitude ﬂuctuations but is anindication of unconventional superconducting
phase ﬂuctuations due to preformation of Cooper
pairs.
We note that this observation is free from theintricate issue of competing or coexisting orders as

Fig. 1(a) Crystal structure of κ-dBr. (b,c) pressure (b) andmagnetic field (c) dependence of anomalous behavior
of (T1T)−1.

observed in high-Tc cuprates, because in themeasured temperatures, pressures, and magnetic
ﬁelds, the NMR spectra do not show any splitting,broadening or complicated structures indicative of
symmetry breaking such as charge order in a
metallic phase.
References[1] T. Furukawa, K. Miyagawa, M. Matsumoto, T. Sasaki, and K.
Kanoda, Phys. Rev. Research 5, 023165 (2023).

Tetsuya Furukawa (Low Temperature Condensed State Physics Research Laboratory)
E-mail: tetsuya.furukawa.c1@tohoku.ac.jp
URL: http://cond-phys.imr.tohoku.ac.jp/index_e.html

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IMR KINKEN Research Highlights 2024

Topological Surface Acoustic Wave

W

hile the topological aspect of the electronic state has been attracting much attention recently, the concept
of topology can be applied also to the phononic state. Here we demonstrate the formation of a topologicalphononic edge state between two mutually inverted topological phononic crystals fabricated on a surface
acoustic wave device.
To realize the topological edge state of acoustic
waves, we fabricate periodically arranged nanopillars
forming honeycomb lattices on a surface acoustic
device [1]. Their unit cell consists of two different Au
cylinder-like pillars. They are expected to work as
phononic crystals that show the acoustic version of
the quantum valley Hall effect. To realize a topologicalwaveguide, we fabricate two honeycomb lattices next
to each other, which have valley Chern numbers of
opposite signs. They are denoted as A and B lattices
as shown in Fig. 1. The upper panel of Figure 2 shows
the atomic force microscopy AFM image of thefabricated A and B lattices.
Then, we observe the image of topological edge
state, utilizing the technique of pulse-type microwave
impedance microscopy MIM, which can visualize thesurface acoustic wave on the phononic crystal. For
this purpose, we develop a pulse-type MIM imaging
system based on a commercial AFM system. The
unique feature that differentiates this from conventional
MIM systems is the use of pulse-modulated
microwaves with a pulse duration of 150 ns. In thissystem, one can separate SAW and electromagnetic
crosstalk in the time domain. The lower panel of
Figure 2 shows the MIM image of a surface acoustic
wave with a frequency of 2.35GHz propagating on
the A and B lattices. At this frequency, the bulk surface
acoustic state is gapped but the edge state should
emerge according to a band calculation. This is inagreement with the experimental observation; theSAW intensity is discernible only around the interface.
Thus, we have succeeded in demonstrating
topological SAW mode around 2.4 GHz in ahoneycomb lattice made of metallic pillars on a
LiNbO3 piezoelectric substrate. While a similar
topological edge state was previously realized in apurely two-dimensional system, the present resultshows that the topological edge mode traveling along
the surface is robust against hybridization with theinterior Bulk modes of the substrate. The method of
topological patterning on a substrate seems quite
useful for implementing topological waveguides andother functionalities into practical acoustic devices
working at gigahertz frequencies. The achievements
may contribute to the further development of SAW

Fig. 1 Scanning electron microscopy SEM images of two
topological phononic crystals.

Fig. 2 Upper panel: AFM image of A-B domain boundary.
Lower panel: MIM image of A-B domain boundary at
2.38 GHz. Scale bars are 2 μm.

devices for various purposes.
References[1] Y. Nii and Y. Onose, Phys. Rev. Appl. 19, 014001 (2023).

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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Electronic Materials

New Hexagonal Approximant ζ´-AlMnCo

The structure of ζ´-Al Mn Co was analyzed using single-crystal X-ray diffraction. The diffraction pattern
80

16

4

indicated that the ζ´-AlMnCo phase has a hexagonal unit cell with a space group P63/m, a = 30.5173(5) Å, c =12.4742(2) Å, and the a-axis is √3-times as large as that of the ζ-phases in the Al-Cr-Cu and Al-Cr-Ni systems.
Mn atoms prefer icosahedral coordination similar to that of Cr in the ζ-phase, and the Co atoms are located in
the interstitial area formed by the connection of the icosahedra [1].

ζ´-Al80Mn16Co4 sample was prepared from an
ingot of Al80Mn17Co3. The solidified ingot was
crushed into grains several millimeters in size,
heated in an evacuated furnace at 1000 °C for 24 h,and subsequently cooled to 750 °C. A single-crystal
sample with dimensions of 0.079 × 0.071 × 0.054(mm) was cut from the prepared sample. Intensity
measurements were performed on the sample usinga Rigaku XtaLAB Synergy-S diffractometerequipped with a HyPix–6000HE hybrid photon
counting (HPC) detector and a Mo microfocussealed X-ray source. Least-squares refinement was
performed using the SHELXL software program.
Figures 1(a) and (b) indicate that the structureof ζ´-Al80Mn16Co4 is composed of rod structures:hR, hR´, and tR. The overall geometrical features ofhR and hR´ appear to be similar but differ based on
the presence or absence of Co at the center. Atomic
arrangements in the central area and harmonic
displacements of the Al sites in the rod structure
also indicate the contrast of the Co distributions.
These structural features suggest that the distributionof Co and the corresponding structural realization is
an important factor in the development ofsuperstructures.
The structures of decagonal and icosahedral
quasicrystals in Al–Mn-based systems arecomposed of pentagonal columnar clusters in
Al3Mn, an icosahedral Mackay cluster in α-AlMnSi,
and a Bergman cluster. Similar atomic arrangements
can be found in ζ´-AlMnCo structure and Figure 2
shows some selected examples. The I3 cluster has
three local five-fold rotational axes along thedirections of the vertex-shared icosahedral pair andthe pentagonal columnar cluster of an icosahedronaround Mn (Mn–Al10Mn2), a bicapped pentagonal
prism around Al (Al–Mn2 Al10), and an icosahedronaround Mn (Mn–Al10Mn2) as shown in Fig. 2(a). This
columnar cluster could be further extended by
I-type connections along the a-axis. Figure 2(b)shows an icosahedral cluster around Mn13. The firstneighbor shell around the Mn13 site is an icosahedral
12 Al, and the second shell shows an icosahedral

Fig. 1 The c-axis projection of ζ´-AlMnCo and ζ-AlCrNi
structures. (a) heavy metal sites, (b) Al sites of ζ´AlMnCo.

Fig. 2 The pentagonal columnar and icosahedral clustersin ζ´-AlMnCo.

symmetry with a harmony of icosidodecahedronand truncated icosahedron. Interestingly, anotherpartial Bergman cluster is observed around theicosahedrally coordinated Al. Figure 2(c) shows apartial Bergman cluster around Al21. The Al21 site
is surrounded by seven Al and five Mn atoms; thesecond shell is a dodecahedron, and the sevenpentagons are capped by Al, Co, or Mn in the
Bergman fashion.
References[1] Y. Makino, T. Kawamata, and K. Sugiyama, J. Phys.: Conf. Ser.
2461, 012010 (2023).

Kazumasa Sugiyama (Chemical Physics of Non-Crystalline Materials Research Laboratory)
E-mail: kazumasa.sugiyama.e6@tohoku.ac.jp
URL: https://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/15.html

32

IMR KINKEN Research Highlights 2024

IMR KINKEN Research Highlights 2024

GIMRTInternational Co-Authored Paper

CO2-Switched Porous Magnet with Long-Range Order

This study presents the first CO -responsive magnet creation by modifying a paramagnetic compound with2

CO2, leading to an antiferromagnetic state. This transformation, driven by electron transfer during CO2
adsorption/desorption, also alters electrical conductivity, offering potential for multifunctional molecular devices.

In the era of the Internet of Things (IoT), there isa growing need for smart sensors that drive thedevelopment of multifunctional materials. Amongthem, magnetic porous coordination polymers(PCPs) and metal-organic frameworks (MOFs) canchange their physical properties in response toenvironmental stimuli, such as electric and magnetic
fields, light, temperature, or gaseous adsorbates.
Such gas-responsive materials are particularly
promising because of their rapid and reversible
nature. However, the investigation of gas-responsive
porous magnets applicable to ubiquitous gases
such as O2, N2, CO2, and so on (hereafter referred
to as common gases) is still in its infancy.
Some reasons likely arise from: i) the conflict
between the magnetic ordering and porosity in asingle material because shorter organic linkers are
generally associated with stronger magnetic
coupling but consequently produce smaller pores;ii) the necessity of thorny intrinsic spin modifications
from structural malformations induced by gas
adsorbates; and iii) the difficulty in changing thecoordination environment considerably via gas
adsorption, as observed in magnetic sponges. Thisis probably due to the relatively weak interactions
between the common gases and porous magnet
frameworks. Due to these challenges, there havebeen few relevant reports on gas-responsive
magnets. Recently, studies have progressed inlayered electronic–state–flexible magnets, for which
only three examples have been reported: (i) aparamagnetic O2-sensitive magnet, in which themagnetic interaction between ferrimagneticallyordered layers was changed from ferromagnetic to
antiferromagnetic coupling via magnetic exchange
coupling with introduced paramagnetic O2; (ii) a
CO2-responsive magnetic phase change, where theinterlayer-accommodated CO2 molecules induced
an increment of interlayer distance directly
associated with the sign of interlayer magnetic
interaction; and (iii) a CO2-responsive magnetic
erasure, where a ferrimagnet was converted into aparamagnet by CO2 adsorption via electronic state
modulation. However, in contrast to the magnetic
phase transition that involves magnet erasure,Fig. 1 Field-cooling magnetization curves at H = 100 Oe
between 1 (black) and 1⊃CO2 (orange) upon dosing of
CO2 and evacuation. Inset shows the crystal structureof 1⊃CO2 .

magnet creation, that is, the formation of spontaneous
magnetization through gas adsorption, has not yet
been reported.
We report a CO2-induced antiferromagnet witha Neel temperature of 62 K modified from aparamagnetic charge-flexible layered compound,[{Ru2(2,4-F2 ArCO2)4}2TCNQ(OEt)2] (1; 2,4-F2 ArCO2−= 2,4-difluorobenzoate; TCNQ(OEt)2 = 2,5-diethoxy7,7,8,8-tetracyanoquinodimethane), in which threemolar equivalents of CO2 were accommodated at a
CO2 pressure of 100 kPa (Fig. 1) [1]. The magnetic
change originates from charge fluctuation due tothe transfer of electrons moving from the electron
donor to the electron acceptor unit or vice versa,
resulting in a change in the electron distribution
induced by CO2 adsorption/desorption in the donoracceptor-type charge transfer framework. Owing to
the reversible electronic state change upon CO2
adsorption/desorption, these magnetic phases are
switched, accompanied by modification of theelectrical conductivity, which is boosted by CO2
accommodation. This is the first example of thecreation of a CO2-responsive magnet that ispromising for novel molecular multifunctional
devices.
References[1] J. Zhang, W. Kosaka, Q. Liu, N. Amamizu, Y. Kitagawa, and H.
Miyasaka, J. Am. Chem. Soc. 145, 26179 (2023).

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

IMR KINKEN Research Highlights 2024

33

Electronic Materials

Impact of Epitaxial Growth on Spin Current Transmission in
Antiferromagnetic Insulator NiO

We investigated the spin current transmission in epitaxial and polycrystalline NiO antiferromagnetic insulators.

Exploiting the thermo-spin effect measurement technique, we found that the epitaxial NiO exhibits nonmonotonic spin current transmission with respect to NiO layer thickness, while this behavior becomes smearedout in the polycrystalline NiO. This difference is partly attributed to the difference in the NiO layer thickness
dependence of antiferromagnetic order between epitaxial and polycrystalline NiO, suggesting that the
improvement of antiferromagnetic order is pronounced with epitaxial growth.

Antiferromagnets possess great potential in thefield of spintronics as an alternative to ferromagnets
owing to their unique characteristics: robustness toexternal magnetic field, low magnetic stray field, andterahertz resonance. Since antiferromagnets canachieve effective spin injection, propagation, andconversion, their spin transport properties have been
intensively studied. NiO is one of the representative
antiferromagnetic insulators, and its spin current
transmission has been investigated. While the majorityof spin and/or magnon transport studies have focusedon polycrystalline NiO, the exploration of epitaxial NiO
remains limited. Furthermore, reported values for the
spin transmission length in epitaxial NiO films vary
widely: ranging from ~2 nm [1] to well over 100 nm [2].
Thus, more systematic investigation is indispensable
to unravel the physics behind.
This study focuses on the effect of epitaxial
growth on spin current transmission in NiO films. As
illustrated in Fig. 1(a), the thermo-spin effects that
output a heat current in Pt/NiO/Co20Fe60B20 (CoFeB)
trilayer are used as a probe of the spin current
transmission in NiO. The Pt(10 nm)/NiO(tNiO)/
CoFeB(20 nm) films were deposited on MgO(111)substrates using magnetron sputtering. By controllingthe sputtering condition, epitaxial and polycrystalline
NiO films were grown. To evaluate the spin current
transmission in NiO, we investigated tNiO dependenceof the normalized temperature amplitude induced bythermo-spin effects Aodd/E, which was detected
through the use of lock-in thermoreflectance method[3]. We found that the tNiO dependence of Aodd/E for
epitaxial NiO exhibits nonmonotonic behavior, whichbecomes less remarkable in polycrystalline NiO [Fig.
1(b)]. This is clearly different from the previous studies
reporting that the dependence of spin current
transmission on tNiO exhibited a simple exponential
decay [1]. The inset of Figure 1(b) shows the coercivity
Hc of CoFeB layer in Pt(10 nm)/NiO(tNiO)/CoFeB(3 nm)
stacks as a function of tNiO. Hc drastically increases
with increasing tNiO from 5 to 10 nm for epitaxial NiO,(a)Magnetization

IMR KINKEN Research Highlights 2024

Temperature
gradient

NiO
Pt

Spin current
Charge current(b)
Epitaxial

Poly.

Epitaxial

Poly.

Fig. 1(a) Schematic of spin current transmission measurement
through the thermo-spin effects. (b) tNiO dependence of
Aodd/E. Inset shows Hc as a function of tNiO.

suggesting that the antiferromagnetic order isstrengthened and the drastic change of Aodd/E at tNiO
= 10 nm for epitaxial NiO is attributed to the improved
antiferromagnetic order. These results suggest thatthe spin current transmission in epitaxial NiO cannot
be explained solely within the framework of simple
magnon diffusion. Although further investigation isrequired to understand the tNiO dependence behavior
fully, this study has provided essential insights into thespin current transmission in the epitaxial NiO film.
References[1] L. Baldrati, C. Schneider, T. Niizeki, R. Ramos, J. Cramer, A.
Ross, E. Saitoh, and M. Kläui, Phys. Rev. B 98, 014409 (2018).
[2] T. Ikebuchi, Y. Kobayashi, I. Sugiura, Y. Shiota, T. Ono, and T.
Moriyama, Appl. Phys. Express 14, 123001 (2021).
[3] T. Yamazaki, T. Seki, T. Kubota, and K. Takanashi, Appl. Phys.
Express 16, 083003 (2023).

Takumi Yamazaki and Takeshi Seki (Magnetic Materials Research Laboratory)
E-mail: takumi.yamazaki.d5@tohoku.ac.jp
URL: http://magmatelab.imr.tohoku.ac.jp/

34

CoFeB

IMR KINKEN Research Highlights 2024

International Co-Authored Paper

Quasi-Two-Dimensional Fermi Surfaces Detected by
Quantum Oscillations in Spin-Triplet Superconductor UTe2

U

(a)

(b)
FFT amplitude (arb.unit)

UTe2
H || c-axis~ 80 mK

15

20

25

30

2

1

2 2
0

H (T)

5
dHvA Frequency (kT)10

Fig. 1 dHvA oscillations and the corresponding FFT
spectrum for the field along c-axis in UTe2.
(a) Experiment
10

dHvA Frequency (kT)UTe2 is one of the hottest materials in thecondensed matter physics [1]. It is a heavy fermion
paramagnet and gets superconducting below Tc=1.52.1K. The huge superconducting upper critical field,
Hc2, with the field-reentrant behavior resembles thoseobserved in ferromagnetic superconductors, such as
URhGe and UCoGe. In ferromagnetic superconductors,
strong ferromagnetic fluctuations are developed when
the field is applied along the hard-magnetization axis
associated with the collapse of the Curie temperature ata high field. On the other hand, UTe2 has no magnetic
order, but the characteristic crossover temperature islinked to the first-order metamagnetic transition at
Hm=35T, where the field-reentrant superconductivity is
abruptly
suppressed.
Furthermore,
multiplesuperconducting phases under pressure and at highfields are detected in UTe2. These unusual
superconducting properties are consistent with thespin-triplet state of superconductivity.
In order to clarify the superconducting mechanism,
it is important to elucidate the electronic states from a
microscopic point of view. Thus, we performed thequantum oscillation measurements, namely the deHaas-van Alphen (dHvA) experiments at high fields up
to 30T and at low temperatures down to 30 mK both at
Oarai and at Nijmegen, using our ultra-clean samples
grown by the liquid-transport molten salt flux method[2,3].
Figure 1 shows the dHvA oscillations and the FFTspectrum. Three fundamental dHvA frequencies,
named α1, α2, and β are detected. These dHvA
frequencies correspond to two kinds of quasi-twodimensional Fermi surfaces.
Figure 2(a) shows the angular dependence of thedHvA frequencies when the field is tilted from c to
a-axis. The experimental results are in good agreementwith the theoretical prediction based on the bandcalculation for 5f-itinerant model of 5f3 configuration.
The on-site Coulomb repulsion U must be taken into
account in the calculation. This may suggest a mixed
valence states of U3+ and U4+ in UTe2, which is also
implied by the field and pressure response of UTe2.
From the temperature dependence of the dHvA
amplitude, we detected the large cyclotron effective

dHvA signal (arb.unit)

sing our ultra-clean single crystal of UTe2, we successfully observed the quantum oscillations ofmagnetization, that is de Haas-van Alphen effect, and clarified two quasi-two-dimensional Fermi surfaces. The
large cyclotron effective masses are detected up to 43 m0 for the field along c-axis.

(b) Calculation

UTe2

U = 2 eVholeelectron
2

5

, '
1'

hole

this work
previous work
0
0
c

30

c

electron

1

60

a
90 0
a c

Field Angle (deg)

30

60

90
a

Field Angle (deg)Fig. 2 Angular dependence of the dHvA frequencies from(a) experiments and (b) band calculations in UTe2. The
inset of panel (b) shows the calculated Fermi surfaces.

masses, which are 43m0, 39m0 and 33m0 for branches
α2, β and α1, respectively. These large masses indicate
the strong correlations of the electronic states, which
are responsible for field-robust superconductivity.
References[1] D. Aoki, J. P. Brison, J. Flouquet, K. Ishida, G. Knebel, Y. Tokunaga,
and Y. Yanase, J. Phys. Condens. Matter 34, 243002 (2022).
[2] D. Aoki, H. Sakai, P. Opletal, Y. Tokiwa, J. Ishizuka, Y. Yanase, H.
Harima, A. Nakamura, D. Li, Y. Homma, Y. Shimizu, G. Knebel, J.
Flouquet, and Y. Haga, J. Phys. Soc. Jpn. 91, 083704 (2022).
[3] D. Aoki, I. Sheikin, A. McCollam, J. Ishizuka, Y. Yanase, G.
Lapertot, J. Flouquet, and G. Knebel, J. Phys. Soc. Jpn. 92, 065002(2023).

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 2024

35

Research Centers

IMR KINKEN Research Highlights 2024

ResearchResearch Centers
GIMRTInternational Co-Authored Paper

Quasi-One-Dimensional Ferromagnetism with Ising Anisotropyin Single Crystal UNi4P2
International Research Center for Nuclear Materials Science

We have successfully grown for the first time single crystals of a ferromagnet UNi P using the self-flux technique and performed the
4 2

magnetization, resistivity, and specific heat measurements. The uniaxial magnetic anisotropy was found not only between a and c-axes,
but also in the tetragonal basal plane due to the quasi-one-dimensional crystal structure, revealing the anisotropic electronic correlations.

Uranium compounds attract much attention because of
the unusual properties. One of the highlights is coexistence offerromagnetism and superconductivity discovered in the weakferromagnets, such as URhGe and UCoGe [1]. The huge andre-entrant upper critical fields, Hc2, are detected when the field
is applied along the hard-magnetization axis within the Isingferromagnetic state. This is due to the strong enhancement offerromagnetic fluctuations under magnetic fields, which play a
crucial role for the spin-triplet states of superconductivity.
Recently a heavy fermion paramagnet, UTe2 was found to be a
new candidate for the spin-triplet superconductor [2]. UTe2 was
believed to be an end member of ferromagnetic superconductors
associated with strong ferromagnetic fluctuations. However, themechanism for superconductivity is more complicated thanthose for ferromagnetic superconductors. In any case, the fieldreentrant superconductivity and the multiple superconducting
phases give a strong support for spin-triplet superconductivity,
which also provides a good playground for studying topologicalsuperconductivity.
To search for a new system, we focus on the dimensionality,
crystal structure, and Ising ferromagnetism, and choose UNi4P2[3]. As shown in Fig.1(a), the crystal structure is ZrFe4Si2-type
tetragonal with the space group P42/mnm, which is categorized
as non-symmorphic space group, leading to the broken local
inversion symmetry. Single crystals were obtained by the selfflux method using a eutectic composition of Ni and P. A large
single crystal with the millimeter size was obtained, as shown in
Fig.1(b), after centrifuging the flux. Clear Laue spots with fourfold symmetry were detected by X-ray diffraction (see Fig.1(c)).
Figure 2(a) shows the resistivity curves for the different
current directions. A clear anisotropy was observed for thecurrent along c-axis and the basal planes. For J || [100] and[110], a typical heavy fermion-like behavior is observed at hightemperatures, but the resistivity rapidly drops on cooling below
the Curie temperature, 25K.
Figure 2(b) shows the magnetization curves for H || [100],[110] and [001] at low temperatures. The anisotropy between cand the basal planes are relatively large, revealing the Ising
ferromagnetic properties. From the data for easy-magnetization

(a)

Ni

UNi4P2

P

(c)

(b)
[001]

Fig. 1 (a) Tetragonal crystal structure of UNi4P2. (b) Single crystal
grown by the self-flux method. (c) Laue photograph for c-axis.
(a)Fig. 2 (a) Resistivity curves for J || [100], [110] and [001]. (b)Magnetization curves at 2K for H || [100], [110] and [001]. The inset
shows the magnetization curves at 1.4 K with pulse fields up to 55 T.

axis, the ferromagnetic ordered moment is estimated to be~0.8μB/U, which is much smaller than the expected values forfree ion of U 5f2 or 5f3. The strong anisotropy, however, persists
even at very high field up to 55 T. Interestingly, the anisotropy
between [100] and [110] also survives at high fields. These
unusually strong magnetic anisotropy even in the basal plane
may be the consequence of anisotropic electronic correlations
and the unique crystal structure.
References[1] D. Aoki, K. Ishida, and J. Flouquet, J. Phys. Soc. Jpn. 88, 022001 (2019).
[2] D. Aoki, J. P. Brison, J. Flouquet, K. Ishida, G. Knebel, Y. Tokunaga, and Y.
Yanase, J. Phys. Condens. Matter 34, 243002 (2022).
[3] A. Maurya, A. Miyake, H. Kotegawa, Y. Shimizu, Y. J. Sato, A. Nakamura, D.
Li, Y. Homma, F. Honda, M. Tokunaga, and D. Aoki, Phys. Rev. B 107, 085142(2023).

Maurya Arvind (Corresponding Author, Mizoram University)
E-mail: amaurya@mzu.edu.in
Dai Aoki (Corresponding Author, Actinide Materials Science Research Laboratory)
E-mail: dai.aoki.c2@tohoku.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

IMR KINKEN Research Highlights 2024(b)

IMR KINKEN Research Highlights 2024

International Co-Authored Paper

GIMRT

Effect of Helium/Displacement Damage Ratio on IrradiationInduced Fine Structure Formation in Steels for Fusion Reactors
International Research Center for Nuclear Materials ScienceThe effect of the ratio of Helium/Displacement per atom (dpa) on irradiation-induced cavities in martensitic
steel was investigated with TEM. It is found that a high He/dpa ratio significantly enhances the formation ofcavities, which contributes to a better understanding of irradiation-induced fine structures for fusion materials.
microscopy observations. Significant He/dpa ratio
effects on the formation of cavities have been
discovered so far [1]. The material used here is lowactivation martensitic steel F82H. To simultaneously
introduce helium and irradiation defects, helium andiron ions were co-irradiated. Figure 1a provides an
overview of TEM observations. When increasing theamount of helium (and dpa) while keeping the He/
dpa ratio constant, the size and number density ofcavities increased (see Fig. 1b and 1c). On the other
hand, even with the same dpa, a smaller He/dpa
ratio resulted in a decreased number density ofcavities (see Fig. 1c and 1d). Currently, a databaseincluding 231 alloys irradiated with simultaneous ion
beams up to 3700 appm helium and 82 dpa isavailable, aiming to provide a model estimating therelationship between He/dpa and the kinetics ofcavity formation.

Plasma facing materials in fusion reactors are
exposed to high-energy neutrons and plasma,
resulting in the accumulation of helium atoms anddisplacement damage. For first-wall materials incommercial fusion reactors, up to 2000 appm ofhelium and 200 displacements per atom (dpa) are
anticipated. This produces a high number density ofcavities (helium bubbles and voids), whichsignificantly degrades material properties. Theinteraction between helium and defects affects theformation and growth of cavities, influenced by theratio of helium content to displacement damage, He/
dpa. Particularly when simulating the neutron
irradiation environment in fusion reactors using
existing fission reactors, it is essential to consider
the impact of the He/dpa ratio on the fine structureformation of materials.
This study aims to elucidate the correlation
between the He/dpa ratio and cavity formation in
low-activation martensitic steel, which is considered
promising as a fusion reactor structural material,
through state-of-the-art transmission electron
0

References[1] T. Yamamoto, Y. Wu, K. Yabuuchi, J. Haley, K. Yoshida, A.
Kimura, and G. R. Odette, J. Nucl. Mater. 576, 154201 (2023).
1

Ion implantation

2 µm

(a)
[dpa, He(appm), He/dpa] = [25, 1200, 46](b)[45, 2100, 47]

10 nm

(c )

[45, 680, 15]

10 nm

10 nm

(d)

Fig. 1 (a) TEM observation for cavities (helium bubbles and voids) for He- and Fe-ion dual irradiated martensitic steel F82H.
(b) Cavities in the region with He/dpa=46 (25 dpa, 1200 appm He). (c) Cavities in the region with He/dpa=47 (45 dpa,
2100 appm He). (d) Cavities in the region with He/dpa=15 (45 dpa, 680 appm He).

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/

IMR KINKEN Research Highlights 2024

39

Research Centers

Development of Advanced Alloy Powders by AtmosphereControlled Gas Atomization Method
Cooperative Research and Development Center for Advanced Materials

To develop high strength, high thermal and electrical conductivity Cu alloys for fusion reactors, Y, Ti, and Fe,
which have lower solid solution limit to Cu than Al and lower oxide standard formation energy, were added to
Cu alloys, and their alloy powders were prepared by atmosphere controlled gas atomization method. The
microstructure of Cu alloy powder had a typical solidification structure regardless of the alloying elements andgas species, and Fe was in uniform solid-solution in the matrix, while Ti and Y were swept out from the matrix
to grain boundaries and particle surfaces during solidification, exhibiting different behavior depending on the
additive elements.

The gas atomization method is a process thatinvolves breaking molten metal into small dropletsby spraying high-pressure inert gas onto it as acooling medium, and a clean-surfaced sphericalpowder can be produced efficiently at a low cost,which exhibits excellent flowability. Therefore, it iscommonly used in industry as a method for
fabricating raw materials in powder metallurgy andadditive manufacturing processes. In addition, by
replacing a part of the inert gas with oxygen or
nitrogen, fine oxides or nitrides can be precipitated,enabling the development of high-strength materials
by precipitation strengthening and grain refinement
due to the pinning effect of the precipitates.
Our research group has focused on oxide
dispersion strengthened Cu (ODS-Cu) alloys, whichhave been applied as a coating material forsuperconducting coils and as a heat sink material
for divertors in fusion reactors which are expected tobe the next generation energy source, and has
being developed a new Cu alloy to replace GridcopR(Al2O3 dispersion strengthened Cu alloy) that iscurrently widely available [1]. Cu alloys for fusion
reactors are required high strength and highelectrical and thermal conductivities, however, there
is a trade-off relationship between them. Therefore,
GridcopR, which has high strength by oxide
precipitation strengthening and a composition of thebase phase close to pure copper, satisfies theserequirements. On the other hand, the solid solution
limit of Al against Cu is relatively high, and further
functional improvement is possible by selecting
appropriate elements. Therefore, we focused on Y,
Ti, and Fe, which have a lower solid solution limit
against Cu than Al and a lower oxide standard
formation energy than Cu, and prepared Cu alloy
powders in solid solution with the above elements

Ti K

Fe K

5 µm

5 µm
OK

5 µm

0
5.0

5 µm

0

OK

OK

5 µm

(wt.%)
10.0

YK

5 µm

Fig.1 Mapping of additive elements in each alloy particles
measured by FE-EPMA.

using a gas atomization method with atmosphere
control by using N2+O2 mixed gas instead of Ar gas[2].
The microstructures of the obtained alloy
powders had a typical solidification structure as
seen in cast materials, regardless of the additiveelements and gas species.
Figure 1 shows the mapping of each element in
the powder prepared using N2+O2 gas. Ti and Y
were enriched on the grain surface and grainboundaries, while Fe was locally enriched within thegrains, exhibiting different behavior depending on
the additive elements. On the other hand, O was not
only in solid solution in the matrix, but also enrichedin the same region as Y, Ti, and Fe, suggesting theformation of oxides.
References[1] B. Ma and Y. Hishinuma, Fusion Eng. Des. 161, 112045 (2020).
[2] M. Sato, Y. Shimada, Y. Hishinuma, and N. Masahashi, J. Jpn.
Soc. Powder Powder Metall., 23-00017 (2023).

Mitsutaka Sato (Corresponding Author, Cooperative Research and Development Center for Advanced Materials)
E-mail: mitsutaka.sato.a3@tohoku.ac.jp
Hidemi Kato (Head of Cooperative Research and Development Center for Advanced Materials)
E-mail: hidemi.kato.b7@tohoku.ac.jp
URL: http://www.crdam.imr.tohoku.ac.jp/english/

40

IMR KINKEN Research Highlights 2024

IMR KINKEN Research Highlights 2024

International Co-Authored Paper

Achievement of 25T with a Large-Scale 20-Stacked REBCO
Coil for 33T-Cryogen-Free Superconducting Magnet
High Field Laboratory for Superconducting Materials

Alarge-scale 20-stacked pancake coil with a robust coil structure was fabricated and achieved 24.9 T under abackground field of 14 T at 4.2 K with an operating current of 298 A. Both the screening current in REBCO tapes
and the coupling current between two-bundled REBCO tapes were observed during ramping up and down andholding the operating current. Optimization of the stress distribution in the REBCO pancake was confirmed aswell. This suggests that the robust coil structure works well in a 33-T cryogen-free superconducting magnet.
A 33T cryogen-free superconducting magnet(33T-CSM) is now being developed at HFLSM. It
consists of a 19 T REBa2Cu3Oy (REBCO, RE; Y,
rare-earth elements) insert magnet and a 14 T
Nb3Sn and NbTi Rutherford cable outsert one. The
REBCO coated conductor has a high in-field criticalcurrent density Jc and good mechanical tolerance
but has a risk of local degradation because of a
weakness for a delamination. It may give rise to aserious damage in the coil. In order to overcome
these risks, we propose the robust REBCO coilstructure with two REBCO tape co-winding, all turnseparation, and edge impregnation [1]. As one of
R&D studies, we fabricated and tested a large-scale
20-stacked REBCO pancake coil with almost thesame size of the practical REBCO pancake of the
33T-CSM. We successfully achieved 24.9 T under abackground field of 14 T at 4.2 K with an operating
current of 298 A as shown in Fig.1 (a) [2]. In addition,
two opposite contributions to the magnetic fielderrors were observed as shown in Fig. 1 (b). The
large hysteresis of magnetic field is mainly related tothe screening current induced in the REBCO tapewidth. The relaxation at the magnetic field platou is
originated to the coupling current between REBCO
tapes. It is found that the effects of the screening
current with long time constant and the couplingcurrent with short time constant are compited eachother. In addtion, we confirmed that the robust
REBCO coil structure can reduce the maximum
hoop stress by optimizing stress distribution with asimulation and a strain measurement of the coil [2,3]. The robustness of the large-scale REBCO coil
was also confirmed by the long time operation forabout one year with many thermal cycles andshutdown tests.

Fig. 1 (a) Magnetic field at the center of 20-stacked coil
under a background field of 14 T. (b) Field error, i.e., thedifference between the measured value and the fitted
linear line as a function of the operating current.

References[1] S. Awaji, A. Badel, T. Okada, K. Takahashi, H. Miyazaki, S.
Hanai, S. Ioka, S. Fujita, S. Muto, Y. Iijima, M. Daibo, and K.
Kajikawa, IEEE Trans. Appl. Supercond. 31, 4300105 (2021).
[2] K. Takahashi, A. Badel, A. Zampa, T. Okada, S. Awaji, G.
Nishijima, T. Uto, H. Takewa, S. Hanai, S. Ioka, and J. Inagaki,IEEE Trans. Appl. Supercond. 33, 4601405 (2023).
[3] A. Badel, K. Takahashi, A. Zampa, T. Okada, G. Nishijima, T.
Uto, H. takewa, S. Hanai, S. Ioka, J. Inagaki, and S. Awaji, IEEE
Trans. Appl. Supercond. 33, 4601505 (2023).

Kohki Takahashi (Corresponding Author, High Field Laboratory for Superconducting Materials)
E-mail: kohki.takahashi.e5@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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Surface Anisotropic Magnetoresistance in Antiferromagnetic
Semiconductor CrSb2
High Field Laboratory for Superconducting Materials

C

rSb2 is an antiferromagnetic narrow-gap semiconductor with a metallic surface state. Although the bulk
antiferromagnetic state is well understood, the magnetic properties of the surface state are elusive. Here, we
perform the low-temperature angle-dependent magnetoresistance measurements up to 24 T and reveal that
CrSb2 has an antiferromagnetic surface state with a strong spin-orbit interaction.
A narrow-gap semiconductor CrSb2 is a sistercompound of FeSb2, a topological Kondo insulator
candidate. Although the resistivity of conventional
semiconductors diverges as the temperature approaches
zero, CrSb2 and FeSb2 exhibit a resistivity plateau below~10 K, suggesting the presence of metallic surface
states. While FeSb2 and other topological materials with
topological surface states are non-magnetic, it isinteresting that CrSb2 shows a collinear antiferromagnetic
order at 273 K. This magnetic bulk state leads us to
expect that the CrSb2 surface state is also magnetic. If
so, such magnetic surface states are not expected in
topological insulators, and CrSb2 is thereby a uniquecompound in condensed matter physics and spintronics.
To unveil the physics of the CrSb2 surface state, we have
performed the angle-dependent magnetoresistance(ADMR) measurements at low temperatures and in highmagnetic fields up to 24 T with 25T-CSM at HFLSM, IMR,
Tohoku University [1].
The largest plane of the CrSb2 single crystal sample
is the ac plane [Fig. 1(a)]; on this plane, the surface state
was reported previously. ADMR was measured at low
temperatures for three rotational directions [α, β, and ϒscans in Fig. 1(b)].
Figure 1(c) shows the ADMR data of the α, β, and ϒscans measured at 24 T and 1.4 K. At this temperature,
the conductivity of the bulk state is several orders ofmagnitude smaller than that of the surface state; thus,
the observed ADMR is safely ascribed to the signals
from the surface state. As shown in Fig. 1(c), ADMR
shows clear twofold symmetry for α, β, and ϒ scans. Our
numerical calculation shows that the observed ADMR isconsistent with the anisotropic magnetoresistance (AMR)
due to the slight change in the antiparallel magnetic
structure caused by the magnetic field. The CrSb2
surface state is indeed antiferromagnetic, and surface
AMR was successfully observed.
In zero magnetic field, the collinear antiferromagnetic
moments are aligned along the easy axis and tilted by
61.5 deg. from the x-axis [Fig. 1(a)]. The exchange

Fig. 1 (a) Schematic illustration of bulk and surface states of
CrSb2.The surface state is illustrated only on the top surface
for simplicity. The relation between x, y, and z-axes andcrystallographic a, b, and c-axes are also illustrated. The
direction of electric current is represented by blue arrows
and that of antiferromagnetic moments by red arrows. The
magnetic easy axis lies in the xy plane and is tilted by 61.5
deg. from the x-axis. (b) Sketches of the definition of angles
α, β, γ and the measurement configuration of angledependent magnetoresistance (ADMR). (c) ADMR resultsof α, β and γ scans measured at 24 T and 1.4 K.

interaction and uniaxial anisotropy are so strong that theantiferromagnetic moments are only tilted slightly (~2%)
and hardly rotated even at 24 T. Nevertheless, the large
AMR is surprisingly observed. The magnitude of AMR
reaches 9.3%, comparable to that reported forferromagnetic materials.
The sizable magnitude of the surface AMR, up to
9.3%, indicates that the surface state of CrSb2 not only
has an antiferromagnetic order but also a strong spinorbit interaction. Such exotic magnetic surface states
could be useful in the emerging field of antiferromagnetic
spintronics.
References[1] K. Nakagawa, M. Kimata, T. Yokouchi, and Y. Shiomi, Phys. Rev. B
107, L180405 (2023).

Yuki Shiomi (Corresponding Author, The University of Tokyo)
E-mail: yukishiomi@g.ecc.u-tokyo.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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Scientific Breakthrough Toward Creation of New Industrial Materials
Trans-Regional Corporation Center for Industrial Materials ResearchT

he institute for Materials Research (IMR) has launched the Trans-Regional Corporation Center, a comprehensive
IMR-wide effort that pairs IMR’s research groups across the innovation spectrum to solve current industrial
challenges and transform the future global energy problems. The center was established in 2016 based on anagreement between IMR, the Osaka Prefecture Government, and enterprises sponsored by the government,
and took control of the Osaka and Kansai center projects.
The Center was established in Osaka as a
special unit in 2016 based on an agreement with the
Osaka Prefecture Government, aiming to solve
technical problems that industries have struggled toresolve, to introduce academic output to industries,
and to educate next-generation materials scientists
and researchers in industries. Projects are
conducted through collaborations between thegovernment, universities, research institutions, andother organizations. The Center has four venues: theOsaka office at Osaka Prefecture University, theHyogo office at University of Hyogo, the Sendai
office, and MOBIO in Higashi-Osaka in Osaka
Prefecture.
The Center has developed various materials
and process technology under collaboration withindustries and universities. One of them is to develop
a bioactive newly-developed TiNbSn (TNS) alloy [1].
Figure 1 shows (a, c) TEM microphotos and (b, d)
EDX line scans of the anodized (a, b) TNS and (c, d)Ti, showing that the oxide on TNS with rutile TiO2
was 1.3 μm thick and contained homogeneously
distributed pores. In contrast, the anodized Ti
exhibits anatase TiO2 with a pore-rich layer parallelto the oxide-substrate interface, and the oxide
thickness was approximately 0.3 μm. Figure 2 shows
the OCP variations during the fretting tests ofanodized (a) TNS and (b) Ti with untreated samples.
It reveals that the OCP dropped to negative directionin the untreated samples and anodized Ti, but not in
the anodized TNS. The OCP drop is attributed todepassivation. Free of negative shift in the anodized
TNS is due to a hard, adherent, and corrosionresistant TiO2. This study revealed the anodized
TiNbSn exhibits the superior tribocorrosion
properties, and the results correlated well with themicrostructure and mechanical properties of theanodic oxide. Similar collaboration researches havebeen in progress. The Center will make an effort toinnovate the metallic material industry through thealliance with the partners, and promote scientificresearch in materials science.

Fig. 1 (a, c) TEM images and (b, d) EDX scans of theanodic oxides on (a, b) TiNbSn and (c, d) Ti.

Fig. 2 OCP variations during the fretting wear tests foranodized (a) Ti and (b) TiNbSn alloy with untreatedsamples.

References[1] M. Kubota, N. Masahashi, H. Inoue, Y. Michiyama, K. Ohmura,and S. Hanada, Surf. Coat. Technol. 462, 129492 (2023).

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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GIMRTInternational Co-Authored Paper

International Joint Research on Energy Materials
Collaborative Research Center on Energy Materials

International collaborations are carried out in each unit of E-IMR, and this report introduces the international
joint research being conducted in the Solar Energy Unit.
1. Silicon crystal growth for solar cells
Silicon (Si) crystalline materials are the mostimportant material, accounting for more than 90% of theworld's practical solar cells production. To further improvethe energy conversion efficiency of solar cells, it isnecessary to improve the quality of the Si crystals, which
requires a fundamental understanding of the various
phenomena that occur during the solidification process.
The solar cell unit of E-IMR is conducting aninternational collaboration with Dr. Nathalie MangelinckNoël's group at IM2NP, Aix-Marseille University (France)
and Prof. Thierry Duffar at Grenoble Institute of Technology(France), to elucidate crystal growth mechanisms of Si. In
E-IMR, solid-liquid interface phenomena during Si crystal
growth are observed in-situ by optical methods. In IM2NP,
that is also observed in-situ by X-ray imaging method at
the European Synchrotron Radiation Facility (ESRF). Prof.
Duffar has been studying the crystal growth mechanism
theoretically and analytically. The objectives of thesegroups are in perfect agreement and a good collaboration
has been established.
To date, some experimental results by in-situ
observations obtained at E-IMR have been shared with
Prof. Duffar, and the kinetics at solid-liquid interface of Si
have been analyzed [1]. In May of this year, Prof. Fujiwara(E-IMR) participated in a 10-day Si solidification
experiments of IM2NP at ESRF. And in November of thisyear, Dr. Mangelinck-Noël visited E-IMR and introduced
their research at the E-IMR seminar (Fig. 1).
We are planning to conduct more collaborative
experiments between E-IMR and IM2NP researchers,
including students, next year.
2. Research on new thermoelectric materials
Half Heusler (HH) alloys with general formula XYZ
can be recognized as excellent thermoelectric candidates.
A collaboration was then initiated between SSN Institutions(India) and the solar energy unit of E-IMR through the
GIMRT joint research project to search for and realize newhalf-Heusler alloys with superior performance indice, ZT.
Theoretical analyses showed that ZrMnSi and
HfMnSi are half metals having band gap in spin down
channel with the band gap energy 1.268 eV and 1.311 eV,

Fig. 1 Dr. Mangelinck-Noël speaks at the E-IMR seminar.

Fig. 2 Fabrication of half-Heusler alloys at IMR.

respectively [2]. Also, it was indicated that the maximum
ZT values of ZrMnSi and HfMnSi are 0.46 and 0.31 at
1200K, respectively [2]. Therefore, these materials could
potentially be used as thermoelectric materials. Dr.
Srinivasan and a PhD student (SSN Institutions) stayed at
E-IMR and experimentally fabricated some new halfHeusler materials with Ms. Nomura (Cooperative Researchand Development Center for Advanced Materials;
CRDAM) and Prof. Okamoto (E-IMR), as in Fig. 2. Those
samples are being characterized in SSN Institutions. This
collaboration will be continued in the future.
References[1] T. S. S. Mishra, L.-C. Chang, K. Maeda, J. Nozawa, H. Morito, T.
Duffar, and K. Fujiwara, J. Crystal Growth 627, 127524 (2024).
[2] D. Shobana Priyanka, J. B. Sudharsan, M. Seinivasan, N. Elavarasan,
P. Ramasamy, and K. Fujiwara, J. Magnetism and Magnetic Materials
588, 171409 (2023).

Kozo Fujiwara (Corresponding Author, Collaborative Research Center on Energy Materials)
E-mail: kozo.fujiwara.c6@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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GIMRT

All-Electron GW Approach for Light-Element-Doped
Anatase TiO2
Center for Computational Materials ScienceAll-electron GW approach based on the many-body perturbation theory was adopted to determine the electronic

structures and understand the mechanism of band gap narrowing for anatase TiO2 doped with light elements(such as C and N) and its various defect states. It is clearly shown that the band gap could be controlled by theoxygen pressure and doping states, and C, N codoping narrowed the band gap more than monodoping.

TiO2 is known as a photocatalytic material, andits band gap corresponds to the UV region. Adding
visible-light responsive photocatalytic functionality
to TiO2 by doping of impurity elements such as C
and N could promote its technological applicability.
An example is the TiO2 coating on Ti dental implants
to achieve antibacterial properties, which are
induced by its photocatalytic reactions.
In this study, we determine the electronic
structures of C- and N-doped anatase TiO2. To dothis, we first construct various models of C and N
monodoped and codoped TiO2 considering theoxygen vacancy(ies) and estimate the stable models
through formation energy analysis as a function of
the oxygen (O2) pressure or oxygen chemical
potential. Then, for the stable models, GW
calculations using the all-electron mixed basis
approach are performed to analyze the electronic
structures and clarify the mechanism of band gap
narrowing that originates because of impurity
doping. Finally, we discuss a possible way to realize
an oxygen pressure condition under which visiblelight response TiO2 can be synthesized.
The GW method has been implemented in the
TOhoku Mixed Basis Orbitals ab initio program(TOMBO) [1]. TOMBO uses the all-electron mixedbasis approach, in which the electronic wave
function is expressed by a linear combination ofplane waves and atomic orbitals.
The stability of the C- and N-doped models
varies depending on the oxygen pressure conditions.
Furthermore, the all-electron GW calculations
indicate that the band gaps of the C- and N-doped
models are found to be narrowed primarily owing toimpurity levels introduced in the gap. Figure 1 (a)summarizes the stable models and their band gaps
as functions of the oxygen pressure at 700K or
oxygen chemical potential. It is shown that the bandgaps vary by up to 1 eV and that codoping with C
and N is more effective for narrowing the band gap

Wave Function(a)

CBM(LUMO)

HOMO

VBM

(b) Mechanism of band gap narrowing

Fig. 1 (a) Relationship between the band gap and oxygenpressure (or oxygen chemical potential) for C- andN-doped anatase TiO2, and (b) Mechanism of band’’ + C••••’’ model.
gap narrowing for the COi+ 2NO

when compared with monodoping.
Among the stably doped models identified in’’ + C••••’ model under thethis study, the COi+ 2NO
medium oxygen pressure condition exhibited thesmallest band gap (2.28 eV).
Figure 1(b) shows the mechanism of band gap’’ + C••••’ model. The band
narrowing for the COi+ 2NO
structure shows that the occupied impurity levels’’ and NO’ in the gap led to a narrowing
derived from COof the band gap. Selected wave functions of CBM(conduction band minimum), HOMO (highest
occupied molecular orbital), and VBM (valenceband maximum) are also shown.
A possible means to synthesize TiO2 could be
the thermal oxidation of Ti in the gas mixture of COCO2-N2 under intermediate oxygen pressure
conditions, which suggests that visible light
photocatalytic materials based on anatase TiO2,
could be manufactured through C and N codoping[2].
References[1] S. Ono, Y. Noguchi, R. Sahara, Y. Kawazoe, and K. Ohno,
Comput. Phys. Commun. 189, 20 (2015).
[2] T. Ishikawa, R. Sahara, K. Ohno, K. Ueda, and T. Narushima,
Comput. Mater. Sci. 220, 112059 (2023).

Ryoji Sahara (Corresponding Author, National Institute for Materials Science)
E-mail: SAHARA.Ryoji@nims.go.jp
Momoji Kubo (Head of Center for Computational Materials Science)
E-mail: momoji@tohoku.ac.jp
URL: https://www.sc.imr.tohoku.ac.jp/eng/

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GIMRTInternational Co-Authored Paper

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 which has a background of novel
materials science in IMR. This center manages four neutron instruments at the research reactor facility JRR-3
and spallation neutron sauce J-PARC MLF. Here, we report the current status of the research program and theoutcome obtained from JRR-3, which started the reoperation 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 (TOPAN
and AKANE) at the JRR-3 research reactor of theJapan Atomic Energy Agency. HERMES candetermine the arrangement of atoms and spins,
while their motions are examined by AKANE andTOPAN. POLANO, located at the Materials and Life
Science Experimental Facility (MLF) at the Japan
Proton Accelerator Research Complex (J-PARC), isa spectrometer designed to perform polarization
analysis in higher energy regions. We aim tocontribute to condensed matter physics andmaterials science with the multipurpose neutron
instruments of PATH, which is a collective term forneutron instruments managed by the CNSAM.
To achieve this purpose, we established aninternational collaborative research program in IMRfrom FY 2019. We provide opportunities not only forexperiments with neutron beams but also for thedevelopment of neutron devices and analysis
methods, and even for theoretical work with ourneutron data. Proposals can be submitted under
several categories, such as “Neutron experiment at
MLF/JRR-3,”“Instrumental
development,”“Development in analysis method,” and “Structural
analysis and data handling”. In FY 2023, we received
33 and 9 proposals from domestic and overseas
researchers, respectively. Furthermore, the research
reactor JRR-3 started the reoperation in February
2021, and we received 39 proposals for 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 year by year. The number of proposals in
FY 2023 is more than doubled of that in FY 2019,
and the ratio of accepted international proposal isover 20% of the total number. The results obtainedwith our instruments have led to publication in highimpact factor journals [1, 2]. In this way, the activities
of center are revitalizing the use of neutron beams in

Fig. 1 Neutron powder diffraction pattern of (a) as-sintered,(b) Ar-annealed, and (c) O2-annealed Pr1.6Sr0.4CuO4-δ.

Japan.
Here, we introduce an example of obtained
results from HERMES [3]. Figure 1 shows the neutron
powder diffraction pattern of as-sintered, Arannealed and O2-annealed Pr1.6Sr0.4CuO4-δ (PSCO).
By the Rietveld analysis, it was clarified that thec-axis elongates (shrinks) due to Ar-annealing (O2annealing). This trend is opposite to the annealing
effect on the c-lattice constant in other cuprateoxides. Thus, PSCO provide unique opportunity to
study the physical properties and the crystal
structure.
References[1] R. Morikawa, T. Murakami, K. Fujii, M. Avdeev, Y. Ikeda, Y.
Nambu, and M. Yashima, Commun. Mater. 4, 42 (2023).
[2] Y. Sakuda, T. Murakami, M. Avdeev, K. Fujii, Y. Yasui, J. R.
Hester, M. Hagihara, Y. Ikeda, Y. Nambu, and M. Yashima,
Chem. Mater. 35, 9774 (2023).
[3] T. Wang, P. Xie, T. Taniguchi, and M. Fujita, JPS Conf. Proc.
38, 011043 (2023).

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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Guest Induced Spin-State Switching in Hoffmann-Type
Coordination Polymers
International Collaboration CenterT

he reversible interconversion between the high-spin (HS) and low-spin (LS) states in transition metal complexes isbeing studied in the presence of different stimuli. The advantage of the porous Hoffmann-type framework is that theadsorption and desorption of gas molecules can play an important role in switching the spin state. In this project, theCO2-induced gate opening, and spin-crossover behavior were observed for the first time in the Hoffmann framework.
Traditionally, for a flexible porous crystal, the “breathing
effect” is demonstrated by a drastic expansion/contractionin the pore volume upon increasing the partial pressure.
Needless to mention that the extreme sensitivity of the spincrossover (SCO) property to minute structural changes andhost-guest interactions imposes a formidable challenge indesigning the guest responsive porous magnetic materials[1]. In that context, the Hofmann-type coordination polymers(HCPs) are of great interest, as the polymeric network
exhibits stronger cooperativity between the SCO sites linked
through covalent bonds to create a rigid lattice.
Inspired by our earlier demonstration [2] of single-tofour-step spin transition by de/re-solvation of MeOH
molecules in a 2D Hoffmann-type coordination polymer[FeIIPd(CN)4L2]・1.3MeOH (1・1.3MeOH, L = methyl
isonicotinate), we sought to rationalize the system under theeffect of a supercritical gas, like CO2, which could only
impart weak dispersive interactions in the system. Notably,
removing MeOH molecules from 1 exerts stronger
π-stacking interactions between the paneling ligands, whichleads to the intriguing gate-opening/closing mechanism.
In this collaborative project with the Miyasaka group,
we report the first case of a CO2-gated reversible spin-stateswitching in an interdigitated Hofmann-type coordination
polymer(1) showing a wide range of temperature (Teq) shift
from ~150 K at PCO2 = 0 kPa to ~250 K at PCO2 = 100 kPa.
Interestingly, the emergence of a stepped behavior below
PCO2 = 10 kPa, and overlapping magnetic susceptibility
values with no change in the transition temperature (TH)above PCO2 = 10 kPa elucidate the selective stabilization of
the LS state under the influence of the CO2 atmosphere.
Based on the magnetic response, and the phase transition
diagram obtained under the respective PCO2, a plausible
scenario of the spin-state switching can be interpreted as
1LS → (1LS + 1’LS) → (1HS + 1’LS) →1’HS → 1HS, where theCO2-free and CO2- encapsulated states are represented as
1, and 1’, respectively. The magnetic sensitivity based on
the varied external CO2 pressure corroborates a novel andintriguing case for the development of CO2- responsive
magnets henceforth.

Fig. 1 Asymmetric unit of [FeII(L)2Pd(CN)4]·1.3MeOH (L =methyl isonicotinate), and position solvent molecules in
between the layers.

Fig. 2 The CO2 pressure dependence of the magnetic
susceptibility measurements in cooling(top) and (c)heating mode(bottom).

References[1] W. Kosaka, H. Nemoto, K. Nagano, S. Kawaguchi, K. Sugimoto, and H.
Miyasaka, Chem. Sci. 14, 791 (2023).
[2] D. J. Mondal, A. Mondal, A. Paul, and S. Konar, Inorg. Chem. 61, 4572
(2022).

Sanjit Konar (Corresponding Author, International Collaborative Center)
E-mail: skonar@iiserb.ac.in
Hiroyuki Nojiri (Head of International Collaborative Center)
E-mail: icc-imr@grp.tohoku.ac.jp
URL: http://www.icc-imr.imr.tohoku.ac.jp/

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Li-Intercalation into Santabarbaraite
Center for Advanced Light Source and Materials ScienceT

his study focused on unique cation intercalation process induced by the dehydration and deprotonation of hydrous minerals.
Li-intercalation on hydrous phosphate mineral of santabarbaraite was studied, and this mineral indicates a superior capacityof Li+ compared to the partially-oxidized parent vivianite. The difference in Li+ capacity is owing to the total amount of Fe3+
derived from oxidation progress at low temperatures. The reaction rate of Li-intercalation of santabarbaraite was significantly
encouraged by the interstitial space caused by the unique dehydration process of parent vivianite [1].
Santabarbaraite is a mineral produced by thedehydration and deprotonation of vivianite. XANES
spectra of various santabarbaraite samples are shown in
Fig 1. A spectrum of 500 oC heated santabarbaraite isshown to compare the oxidation state of Fe with that of 120
oC heated one. Fe K–absorption edge of phosphophyllite
and vivianite with Fe2+ are around 7120 eV and theabsorption edge shift could be readily observed between
as synthesized vivianite and 120 oC heated santabarbaraite.
On the other hand, there was no significant sign of theoxidation progress between the 120 oC heated and 500 oC
heated santabarbaraite.
Li-intercalation performance was tested by observing
the CC-CV discharging process with vivianite- or
santabarbaraite-electrode.
The total amount of intercalated Li+ of thesantabarbaraite-electrode was about two times larger thanthat of the vivianite-electrode (156 and 70.9 mAhg-1 forsantabarbaraite and vivianite, respectively). This isbecause the total amount of Fe3+ of santabarbaraite islarger than that of vivianite.
It should be noted that the santabarbaraite-electrodes
indicate a significantly high reaction rate of Li-intercalationin comparison with that of vivianite. These features are wellattributed to the active space for Li+ diffusivity, probably
produced by the dehydration and deprotonation process
of vivianite.
Additionally, the accumulated amount of Li+ invivianite- or santabarbaraite-electrode was evaluated fromboth the electrochemical measurement and ICP-AES
analysis. Both evaluations show consistent results eachother, and santabarbaraite can accumulate Li+ about 80 %compared to the number of Fe ions. This result suggeststhat 80% of the Fe is in the trivalent Fe3+ state insantabarbaraite heated to 120 oC, and is consistent withthe results of XANES measurements, which indicate thatthe oxidation progress of santabarbaraite is almost
complete at 120 oC.
Figure 2 shows the XRD patterns of the santabarbaraite
heated to 120 oC before and after Li intercalation. A

Fig. 1 XANES spectra of as synthesized vivianite and heatedsantabarbaraite together with phosphophyllite.

Fig. 2 XRD patterns of the 120 oC heated santabarbaraite before/
after the Li-intercalation.

characteristic change was observed around the 2θ regionof 10-15°. The relative intensity profile at about 2θ = 12°
with the corresponding distance of 4.5 Å was strongly
modified by the Li intercalation. This correlation length
corresponds to the in-plane structure of the 2D Fe3(PO4)2
sheet in the parent vivianite. Since a similar change could
also be observed in the diffraction profile after the Liintercalation of the crystalline vivianite, the Li+ intercalationin santabarbaraite, as in vivianite, induces a disorder in theatomic arrangements in the 2D-Fe3(PO4)2 sheets.
References[1] R. Yamane, H. Li, T. Ichitsubo, and K. Sugiyama, Phys. Chem. Chem.
Phys. 25, 31346 (2023).

Ryo Yamane (Corresponding Author, Chemical Physics of Non-Crystalline Materials Research Laboratory)
E-mail: ryo.yamane.c2@tohoku.ac.jp
Kazumasa Sugiyama (Head of Center for Advanced Light Source and Materials Science)
E-mail: kazumasa.sugiyama.e6@tohoku.ac.jp
URL: https://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/collaboration/08.html

48

IMR KINKEN Research Highlights 2024

IMR KINKEN Research Highlights 2024

Geometrical Frustration Originated from Magnetic
Quadrupole Interactions of the RKKY Mechanism on a
Breathing Kogome Lattice
Laboratory of Low Temperature Materials ScienceWe studied frustrated spin system Gd3Ru4Al12 with a breathing Kagome lattice structure. This compound is
known as one of host materials of skyrmion [1]. We determined anisotropic magnetic phase diagrams of
Gd3Ru4Al12, and revealed that easy axis and easy plane types of magnetic anisotropies coexist in this spin
system. These anisotropies are originated from magnetic quadrupole (MQ) interactions of the RKKY mechanism.
In frustrated spin system Gd3Ru4Al12,
ferromagnetic (FM) Gd-trimers are formed below
184 K on the small triangles with decreasing
temperatures [2]. These FM trimers form an
antiferromagnetic (AFM) triangular lattice (Fig. 1).
We have determined magnetic phase diagramsof Gd3Ru- 4Al12 by specific heat and magnetic
measurements [3]. The diagrams show clear
anisotropies, which can be understood as a simple
superposition of easy axis (e. a.) and easy plane (e.
p.) types of AFM phase diagrams (Fig. 2). We
revealed that the imperfect FM trimers possess MQ
moments and that the MQ interactions of the RKKY
mechanisms lead to magnetic anisotropies. In
ordered states, two kinds of spontaneous MQ
moments appear to reduce frustration among MQ
moments, and the spin system splits into two subsystems which approximately do not interact witheach other in a quadrupole manner. This separation
results in the coexistence of the different magnetic
anisotropies depending on the sites of the trimers[3].

trimerAl

Gd

Fig. 1 The breathing kagome structure on the Gd-Al planeof Gd3Ru4Al12.

H||a

H||b*

H||c
e.p.

Gd3Ru4Al12
e.p.

e.a.

II
e.a.

Referencese.a.

[1] M. Hirschberger, T. Nakajima, S. Gao, L. Peng, A. Kikkawa, T.

III

Kurumaji, M. Kriener, Y. Yamasaki, H. Sagayama, H. Nakao, K.
Ohishi, K. Kakurai, Y. Taguchi, X. Yu, T. Arima, and Y. Tokura,Nat. Commun. 10, 5831 (2019).
[2] S. Nakamura, N. Kabeya, M. Kobayashi, K. Araki, K. Katoh,

I

I
II
e.p.

II

e.a.

I

and A. Ochiai, Phys. Rev. B 98, 054410 (2018).
[3] S. Nakamura, N. Kabeya, M. Kobayashi, K. Araki, K. Katoh,and A. Ochiai, Phys. Rev. B 107, 014422 (2023).

Fig. 2 Schematic magnetic phase diagrams of Gd3Ru4Al12.

Shintaro Nakamura (Corresponding Author, Laboratory of Low Temperature Material Science)
E-mail: shintaro.nakamura.c8@tohoku.ac.jp
Takahiko Sasaki (Head of Laboratory of Low Temperature Material Science)
E-mail: takahiko.sasaki.d3@tohoku.ac.jp
URL: http://ltsd.imr.tohoku.ac.jp

IMR KINKEN Research Highlights 2024

49

Research Centers

Research Facility for Physics and Chemistry of Radioactive
and Nuclear Materials
Laboratory of Alpha-Ray Emitters

More than 190 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 many leading
universities and institutes all over Japan visit this facility every year to prepare a variety of materials and conduct
chemical and physical experiments.

The Laboratory of Alpha-Ray Emitters provides
a research environment for the study of 190
radionuclides and elements, especially alpha-ray
emitters, such as actinide. This lab functions as asource for the preparation of pure crystals of actinide
compounds, providing them to other universities
and to synchrotron particle accelerators. In the past
decade, actinium-225 (Ac-225), one of the actinides,
has been provided as an inter-university
collaboration to other universities and research
centers. The radiation-controlled area of thislaboratory includes three chemical rooms, threephysical rooms, and other facilities that are equippedwith local exhaust ventilation systems, making thehandling of various kinds of radioactive material
possible. Many spectrometers, including those for
gamma rays and alpha rays, are available.
The past two decades have witnessed a revivalof interest in low-valent uranium chemistry such as
the unusual reactions mediated by uranium [1]. As
further development in this field relies on theavailability of U(III) starting materials such as halides
and triflate (OTf), the establishment of theirconvenient syntheses has drawn much attention.
U(III) species (e.g., UI3 and U(OTf)3) and theirsolvent adducts are typically prepared from U metal,
while other routes such as the reduction of U(IV) by
metals or other agents are less common, becauseof the difficulty of separating the spent reducing
agent from U(III) products. Recently, to shed light on
the electrochemical behavior of U(IV) triflate, weprobed the electrode reactions of U(OTf)4 in DMF
containing tetrabutylammonium triflate (TBAOTf) asa supporting electrolyte by voltammetry, using thestandard hanging mercury electrode (HME) andthat where Hg was substituted by Zn(Hg). For
comparison, we also probed the bulk electrolysis of
U(OTf)4 in the presence of Zn(II) in DMF containing
TBAOTf on both the pool Hg and the Zn(Hg)electrode. The electroseparation of Zn(II) from the
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

50

IMR KINKEN Research Highlights 2024

Fig. 1 Absorption spectra during electroseparation of zinc(II) from DMF containing 4.5 mM uranium triflate after
reduction by Zn(Hg). Inset shows changes in [Zn(II)and [U(III)]/[U]total (upper) and the electrode potential(lower).

U(III) solution prepared by the reduction of U(OTf)4
on Zn(Hg) in DMF was studied (Fig. 1) for the firsttime to evaluate the possibility of the convenientpreparation of spent reductant-free U(III) starting
materials [2]. Here, we successfully electroseparated
Zn(II) from the U(III) solution on Zn(Hg) (highest
coulombic efficiency = 0.81, final Zn(II) separation
ratio = 93.4%) after the reduction of U(OTf)4 byZn(Hg).
References[1] C. Tabata, H. Watanabe, K. Shirasaki, A. Sunaga, T. Fukuda,
D. Li, and T. Yamamura, J. Mol. Struct. 1277, 134870 (2023).
[2] K. Shirasaki, J. Appl. Electrochem. 52, 1101 (2022).

IMR KINKEN Research Highlights 2024

Microstructure and Mechanical Property of Y2O3-BasedODS-Cu Alloy Fabricated by MA-HIP with Novel Elemental
Addition Process
Analytical Research Core for Advanced Materials

T

he Analytical Research Core for Advanced Materials serves as an infrastructure for researchers not only in
IMR but also outside the university by offering various elemental analytical methods and up-to-date structuralcharacterization techniques. Here, we present recent research carried out by one of our users, where they haveelucidated the strengthening mechanism of Cu-based oxide dispersed alloys.
A combination of mechanical alloying and hot
isothermal pressing (MA-HIP) is one of the fabrication
processes of oxide dispersion strengthened (ODS)Cu alloy, which is expected to yield a high mechanicalproperty and thermal conductivity. However, theODS-Cu bulk fabricated MA-HIP process has low
ductility due to inhomogeneous oxide dispersion
and Cu grain size distribution. In this study, we
modified the MA-HIP process by changing yttrium
and oxygen addition methods to improve themicrostructure and ductility of ODS-Cu alloy. Namely,
we replaced pure Y and Cu2O powders with Cu-Y
compound and pre-heated Cu powders as thestarting materials [1].
The nanoscale structure was observed bytransmission electron microscopy (TEM) andscanning-TEM (STEM) with an acceleration voltage
of 200 keV. The electron beam convergence angle
and detection angle of a high angle annular dark
field (HAADF) STEM is 18-22 mrad and 90-370
mrad, respectively.
Figure 1 (a) shows a HAADF-STEM image of asample annealed in air. The dark, spherical particles
corresponded to Y2O3, which appear to be
distributed in the large Cu grains as indicated by thecircles in (a). As indicated by “A” in (a), coarse
precipitates larger than 500 nm are formed in thesmall Cu grain area, which was found to be coarse
Y2O3 particles by electron diffraction pattern (b) andhigh-resolution HAADF-STEM image (c). The
magnified image and elemental distribution maps
acquired from interface areas of large/small Cu grainareas show that a large amount of fine Y2O3 particles
is precipitated on grain boundaries, and some of thefine Y2O3 particles are also distributed intra-Cu grain.
The results presented here hence showed

Fig. 1 HAADF-STEM image (a) Some Y2O3 particles
precipitated, as shown by dark regions, in large Cu
grain denoted by a circle. A diffraction pattern (b), andhigh-resolution HAADF-STEM image (c).

microstructural differences: on the macroscale, theconnectivity of large/small Cu grain areas, which
was a main factor in brittle fracture, was reduced,
while on the nanoscale, yttrium precipitated andremained as yttria (Y2O3) particles within the Cu
grains. These multiscale microstructural changes
resulted on the improved mechanical property: thenewly-developed ODS-Cu bulk did not fracture atbending strains of 18% or greater, whereas it had
previously fractured at bending strains of 5% or lessin a three-point bending test. This improvement inmechanical properties through simple processcontrol suggests that ODS-Cu alloys have further
potential as structural materials.
References[1] Y. Shimada, Y. Nakajima, Y. Hishinuma, K. Ikeda, H. Noto, T.
Muroga, K. Yoshida, T. Konno, and Y. Nagai, Mater. Chem.
Phys. 307, 128223 (2023).

Yusuke Shimada (Corresponding Author, Kyushu University)
E-mail: shimada.yusuke.567@m.kyushu-u.ac.jp
Toyohiko J. Konno (Corresponding Author, ARIM Project Unit, Analytical Research Core for Advanced Materials)
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
https://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/service-divisions/03.html

IMR KINKEN Research Highlights 2024

51

Editors
 ublic Relations Editorial Committee
P
Public Relations OfficePrinting
HOKUTO Corporation

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