KINKEN
Research Highlights
2019

Institute for Materials Research, Tohoku University

KINKEN Research Highlights 2019
Contents
Preface���������������������������������������������������������������������������������������������������������������������������������������������������������� 4

Research Highlights

1. Infrastructural Materials
Microstructure Design of Structural Metallic Materials Research Laboratory���������������������������������������������� 8
Environmentally Robust Materials Research Laboratory������������������������������������������������������������������������������ 9
Advanced Crystal Engineering Laboratory������������������������������������������������������������������������������������������������ 10
Deformation Processing Research Laboratory�������������������������������������������������������������������������������������������11
Analytical Science Research Laboratory��������������������������������������������������������������������������������������������������� 12
Creation of Life Innovation Materials for Interdisciplinary and International Researcher Development������ 13
Professional development Consortium for Computational Materials Scientists (PCoMS)�������������������������� 14

2. Energy-Related Materials
Crystal Physics Research Laboratory�������������������������������������������������������������������������������������������������������� 16
Materials Design by Computer Simulation Research Laboratory��������������������������������������������������������������� 17
Nuclear Materials Engineering Research Laboratory�������������������������������������������������������������������������������� 18
Chemical Physics of Non-Crystalline Materials Research Laboratory������������������������������������������������������� 19
Structure-Controlled Functional Materials Research Laboratory��������������������������������������������������������������� 20
Non-Equilibrium Materials Research Laboratory���������������������������������������������������������������������������������������� 21
Magnetic Materials Research Laboratory�������������������������������������������������������������������������������������������������� 22
Hydrogen Functional Materials Research Laboratory�������������������������������������������������������������������������������� 23

3. Electronic Materials
Theory of Solid State Physics Research Laboratory���������������������������������������������������������������������������������� 26
Magnetism Research Laboratory��������������������������������������������������������������������������������������������������������������� 27
Surface and Interface Research Laboratory���������������������������������������������������������������������������������������������� 28
Low Temperature Physics Research Laboratory���������������������������������������������������������������������������������������� 29
Low Temperature Condensed State Physics Research Laboratory����������������������������������������������������������� 30
Quantum Beam Materials Physics Research Laboratory��������������������������������������������������������������������������� 31
Quantum Functional Materials Physics Research Laboratory�������������������������������������������������������������������� 32
Irradiation Effects in Nuclear and Their Related Materials Research Laboratory��������������������������������������� 33
Physics of Electronic Materials Research Laboratory�������������������������������������������������������������������������������� 34
Solid-State Metal-Complex Chemistry Research Laboratory��������������������������������������������������������������������� 35
Crystal Chemistry Research Laboratory���������������������������������������������������������������������������������������������������� 36
Actinide Materials Science Research Laboratory�������������������������������������������������������������������������������������� 37
Materials Science of Non-Stoichiometric Compounds Research Laboratory�������������������������������������������� 38

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

Author Index����������������������������������������������������������������������������������������������������������������������������������������������� 52

Keyword Index������������������������������������������������������������������������������������������������������������������������������������������� 53

Preface

Dear Colleagues,

We are pleased to present KINKEN Research Highlights 2019, which is the annual report that
includes a collection of research outputs of the past year from the Institute for Materials Research (IMR),
Tohoku University. KINKEN is the abbreviation for “Kinzoku Zairyo Kenkyujo,” the Japanese name for
IMR, which is well known in the materials science community.

IMR celebrated its centenary in 2016. Professor Kotaro Honda established the IMR at the Tohoku
Imperial University in 1916 as the 2nd Division of the Provisional Institute of Physical and Chemical
Research. At that time the primary research focus was steel. Thereafter, the research domains graduallybroadened to include various types of alloys and metals. The name was changed into the ResearchInstitute for Iron, Steel and Other Metals (RIISOM) in 1922. Subsequently, the institute developed into a
global center for fundamental and applied research covering all types of materials, including nonmetals.
In 1987 the institute was reorganized into a national collaborative research institute affiliated with Tohoku
University, and consequently renamed to the present Institute for Materials Research (IMR).

IMR has greatly contributed to the advancement of materials science and engineering. The inventionof KS steel in 1916, the strongest permanent magnet at that time, was the first great achievement. In
subsequent years, many different types of practically useable materials have successfully beendeveloped, including new KS steel, Sendust alloy, SiC fibers, various intermetallic compounds, andmore recently, amorphous alloys. In addition, considerable effort was dedicated to basic research formaterials development, which paved the way for pioneering research in magnetism, superconductivity,

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IMR KINKEN Research Highlights 2019

Director Prof. Koki Takanashi

optical properties, and microstructure analyses of materials. Recently, IMR has created a wide array of
new materials, including high-performance, high-quality, and multifunctional materials such as bulk
metallic glasses, nanostructured materials, nanocomposites, ceramics, crystals, oxides, nitrides,
hydrides, complexes, organic materials, etc., which are useful for electronic, optical, magnetic, spintronic,
biological, energetic, and infrastructural applications.

In the 21st Century, we face worldwide environmental problems such as global warming and thedepletion of resources and energy. There is an increasing need to preserve the environment and work
towards achieving sustainable societies. IMR upholds these themes with the objective of “contributing
to the well being of the human race and the development of civilization through the creation of newmaterials that are truly useful to society”.

We hope that the KINKEN Research Highlights will enable you to better understand our recent
research activities and will aid the promotion of worldwide collaboration with IMR. We ask for yourcontinued support and welcome any suggestions.

IMR KINKEN Research Highlights 20195

Infrastructural Materials

IMR KINKEN Research Highlights 2019

Research

Infrastructural Materials

Microstructure of Reverted Austenite in Fe-0.3N MartensiteThe reverse transformation behavior during inter-critical annealing was studied in Fe-0.3mass%N binary alloy.
Two morphologies of acicular and globular austenite are formed during the reversion process. The globular
austenite has almost the same orientation as one of adjacent prior austenite grains and grows into the martensite
with a larger deviation angle from the Kurdjumov–Sachs orientation relationship (K-S OR). In contrast, the acicularaustenite holds a near K-S OR with its surrounding martensite matrix. A large amount of retained austenite wasobtained through simple inter-critical annealing owing to an enrichment of nitrogen in the reverted austenite.
Nitrogen, an interstitial element frequently usedin steel other than carbon, thermodynamicallystabilizes austenite (γ) and shows a similar tendency
to that of carbon in terms of the change in Ms
temperature or lattice parameter change [1, 2]. In
contrast, nitrogen has larger solubility limits in ferrite(α) or γ phases with respect to ferrous nitride than in
the case of carbon with respect to cementite,leading to a higher eutectoid composition and alower eutectoid temperature. It is therefore possible
to decrease the annealing temperature in α + γ twophase region, and to enrich more nitrogen into γ,
thereby implying that more retained austenite canbe obtained.
In this study, Fe-0.3mass%N martensite wasprepared using the nitriding and quenching (N-Q)
process [3]. A sample was then heated to650–750 °C within the α+γ two-phase region andinter-critically annealed for 3–3,600 s. The
microstructures of the heat-treated samples wereobserved using FE-SEM, and the volume fractionsof the constituent phases were determined throughpoint counting and XRD.
Figure 1 shows the microstructure evolution
during inter-critical annealing at 650 °C and 750 °C.
Two types of reverted γ were observed, namely,
globular austenite (γG) nucleated at the prior γ grainboundary, and acicular austenite (γA) nucleated atboth the lath and block boundaries of martensite.
This reverse transformation behavior is extremely
similar to that of carbon-containing alloys [4].
Figure 2 shows the reverse transformation kinetics
curves at 650 and 750 °C. At each temperature, thevolume fraction of the reverted γ increased with anincrease in the holding time and eventually reachedequilibrium. The γ retained was obtained at eachtemperature, the maximum value of which wasapproximately 6% at 750 °C, and approximately 10%
at 650 °C. It was confirmed that simple inter-criticalannealing can achieve a large amount of retained
austenite in nitrogen-contained steel.

Fig. 1 SEM images of Fe-0.3N alloy annealed at (a) 650°C for 3 s, (b) 650 °C for 3,600 s, (c) 750 °C for 3 s, and(d) 750 °C for 3,600 s.

Fig. 2 Reverse transformation kinetics curves of Fe-0.3N
alloy annealed at (a) 650 °C and (b) 750 °C.

References[1] L. Chen and E. J. Mittemeijer, Scripta Metall. Mater. 24, 509(1990).
[2] T. Bell and J. Iron Steel Inst. 206, 1017 (1968).
[3] J. Takeuchi, T. Iguchi, and T. Ishihara, J. Jpn. Soc. Heat
Treatment 21, 26 (1981).
[4] X.-G. Zhang, G. Miyamoto, Y. Toji, S. Nambu, T. Koseki, and T.
Furuhara, Acta Mater. 144, 601 (2018).

Keywords: steel, phase transformation, microstructure
Mitsutaka Sato (Microstructure Design of Structural Metallic Materials Research Laboratory)
E-mail: m-sato@imr.tohoku.ac.jp
URL: http://www.st-mat.imr.tohoku.ac.jp

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IMR KINKEN Research Highlights 2019

IMR KINKEN Research Highlights 2019

Hydrogen Embrittlement Property of a High Strength TRIPAided Bainitic Ferrite SteelO

ur investigation based on a tensile test of hydrogen-charged Transformation induced plasticity (TRIP) aided
bainite ferrite steel showed a tensile strength of 1.2 GPa at various strain rates, and microscopic observations
indicated that hydrogen-induced crack initiation from the martensitic transformation of the retained austenite,and subsequent crack propagation under the existence of hydrogen, are key factors.
Transformation induced plasticity (TRIP) aided
bainite ferrite (TBF) steel with a bainitic ferrite matrix
exhibits excellent formability and impact and fatigue
properties, and thus the use of such steel is
expected for automotive frame parts. However,owing to a high strength, hydrogen embrittlement(HE) is an unavoidable subject, as is the use oftwining induced plasticity (TWIP) steel [1]. Although
it has been reported that the HE resistance of TRIP
steel evaluated through a tensile test is affected by
the strain rate, the effect of the strain rate on the HE
of TBF steel has yet to be clarified. Our present
study aims at clarifying the role of the strain rate on
the HE behavior and an understanding of themechanism of the HE of TBF steel [2].
Figure 1 shows the change in total elongation(TEl) and the time to fracture of hydrogen-charged
TBF steel with a tensile strength of 1.2 GPa as afunction of the strain rate. Clearly, TEl decreases as
the strain rate decreases; i.e., the susceptibility ofsteel to HE was enhanced. Because the time tofracture monotonically increases with a decrease in
the strain rate, the apparent susceptibility to HE ispresumably influenced by hydrogen diffusion.
Observations of the fracture surface and crosssection revealed that facets (Fig. 2) were formed inhydrogen-charged steel owing to the martensitic
transformation of the retained austenite and to thesupersaturation of hydrogen in the newly formed
martensite caused by a significant loss of thehydrogen solubility.
The facet formation marks the beginning of afracture, and an accumulation of diffusible hydrogenfrom the matrix and the martensite transformed fromthe retained austenite within the vicinity of the tips ofthe initiated facets is likely necessary for crack
propagation, and is thus considered to be thereason for the strain rate dependence of the total
elongation.

Fig. 1 Effects of strain rate on the total elongation and time
to fracture of a TBF steel.

Fig. 2 (a) Transmission electron micrograph and (b) inverse
pole figure map around a facet formed in hydrogenprecharged TBF steel tested at 5.56 × 10 –6 s-1.

References[1] I. B. Tuǧluca, M. Koyama, B. Balb, D. Canadinc, E. Akiyama,
and K. Tsuzaki: Mater. Sci. Eng. A 717, 78 (2018).
[2] T. Hojo, R. Kikuchi, H. Waki, F. Nishimura, Y. Ukai, and E.
Akiyama: ISIJ Int. 58, 751 (2018).

Keywords: high strength steel, fracture, phase transformation
Tomohiko Hojo (Environmentally Robust Materials Research Laboratory)
E-mail: hojo@imr.tohoku.ac.jp
URL: https://akiyamaimr-e.amebaownd.com

IMR KINKEN Research Highlights 20199

Infrastructural Materials

Growth and Scintillation Properties of Two-Inch-Diameter
Eu:SrI2 Single Crystals

Eu-doped SrI (Eu:SrI ) has been recognized as a high-performance scintillator with a high light yield and22high energy resolution. In this study, we successfully grew Eu:SrI2 single crystals 2-inch in diameter and 4-inch
in length. The light output of the 2-inch diameter Eu:SrI2 was estimated to be 70,000 photons/MeV, and thecalculated energy resolution was 3.4% (662 keV, FWHM) at room temperature.

Eu-doped SrI2 (Eu:SrI2) single crystals have beenstudied intensively owing to their possible applications inradiation detectors. A growth system simply representing aseeded Bridgman technique was recently developed, andthe growth of Eu-doped SrI2 crystals of 1 inch in diameter
was established [1]. However, the crystals reported in Ref.
[1] are not crack-free, and their dimensions are insufficientfor many practical applications. Therefore, the purpose of
the current study was to develop a crystal growth process
suitable for the fabrication of relatively large (more than 2
inches in diameter) and macro-defect-free crystals [2, 3].
The Eu:SrI2 single crystals were grown from the meltof a (Sr0.98Eu0.02)I2 composition using carbon crucibles.
The 2-inch diameter macro-defect-free Eu:SrI2 crystals
were grown using a vertical Bridgman method with acrystal growth apparatus that was originally designed forthe micro-pulling-down crystal growth process.
The number of bubbles captured by the crystals wasconsiderably reduced after preliminary vacuum degassing.
The decrease in the temperature of the melt during theinitial stage of growth with the corresponding elimination of
the seed over-melting resulted in the formation of macrodefect-free Eu:SrI2 crystals. An additional treatment of theinterior of the crucible results in reduced wetting between
the SrI2 melt and the crucible approaching the Liquinert
process (Fig. 1). A cut and packaged Eu:SrI2 specimen (2inches in diameter and length) demonstrated a light output
exceeding 70,000 photons/MeV and an energy resolutionof 3.4% (662 keV, FWHM).
After an evaluation of single crystals, we developed
Eu:SrI2 array detectors. The photographs of the developed
Eu:SrI2 arrays are shown in Fig. 2. Fig. 2(a) shows a 4 x 4matrix and a 3 x 3 x 3 mm3 pixel array, and the right side ofFig. 2(b) shows a 9 x 9 matrix and a 1 x 1 x 1 mm3 pixel
array. We obtained the best energy resolution of 4.1%
(FWHM) at a gamma-ray of 662 keV.

θ= 70.67 (deg.)

θ= 79.68 (deg.)

Θ = 69.32 (deg.)

1 mm

1 mm

SiC polymer coating

Graphite

1 mm

High density carbon

Fig. 1 Top, SrI2 crystals produced from different crucibles;
middle, their corresponding wetting angles; andbottom, the pulse height spectra of Eu:SrI2. Specimen
and Tl doped NaI.
(a)

(b)

Fig. 2 Photographs of developed Eu:SrI2 arrays. (a), 3 x 3 x 3mm3 and 4 x 4 matrix; (b), 1 x 1 x 1 mm3 and 9 x 9 matrix.

References[1] Y. Yokota, K. Nishimoto, K. Kurosawa, D. Totsuka, and A. Yoshikawa,
J. Cryst. Growth 375, 49 (2013).
[2] A. Yoshikawa, Y. Shoji, Y. Yokota, S. Kurosawa, S. Hayasaka, V. I.
Chani, T. Ito, K. Kamada, Y. Ohashi, V. Kochurikhin, and A. Yoshikawa,

Keywords: scintillator, crystal growth
Akira Yoshikawa (Advanced Crystal Engineering Laboratory)
E-mail: yoshikawa@imr.tohoku.ac.jp
URL: http://yoshikawa-lab.imr.tohoku.ac.jp/index.html

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IMR KINKEN Research Highlights 2019

J. Cryst. Growth 452, 73 (2016).
[3] Y. Shoji, S. Kurosawa, Y. Yokota, S. Hayasaka, K. Kamada, M. Yoshino,
A. Yamaji, V. Chani, Y. Ohashi, S. Sakuragi, and A. Yoshikawa, Cryst.
Growth Des. 18, 3747 (2018).

IMR KINKEN Research Highlights 2019

Electron Beam Melting of Boron-Modified Ti-6Al-2Sn-4Zr-2Mo-0.1Si
Alloy with Superior Tensile Strength and Oxidation Resistancew

e succeeded in fabricating Ti–6Al–2Sn–4Zr–2Mo–0.1Si–1B alloy with superior tensile strength and oxidation
resistance by applying an electron beam melting (EBM) additive manufacturing process. Owing to the rapid
solidification process during EBM, much finer TiB precipitates with a nanometer width are obtained in an EBM
built alloy as compared with a wrought alloy. These refined TiB precipitates contribute to an enhanced strengthand greater oxidation resistance.
Electron beam melting (EBM) is an innovative
additive manufacturing process whereby various
parts are created layer by layer directly from acomputer-aided design file. This has promisingadvantages such as a design freedom and highefficiency, and can easily be used to fabricate defectfree components with complex shapes and a low
residual stress. Titanium and its alloys are ofsignificant interest regarding EBM because Ti alloys
combine broad industry applications with highmachining costs and long lead times in conventional
processing.
In the aerospace industry, lightweight engines
are a key to improving the fuel efficiency. Lighter
heat-resistant Ti-based alloys are expected to be
developed to replace heavy Ni-based alloys used forhigh-pressure compressor blades where both a highstrength and significant oxidation resistance at hightemperatures are required.
Ti–6Al–2Sn–4Zr–2Mo–0.1Si alloy, often referred
to as Ti–6242S, has been chosen as a heat-resistant
Ti alloy. It was reported that TiB precipitates canimprove the strength of Ti-based alloys owing to their
good mechanical properties, high thermal stability,
and a similar thermal expansion as that of a Ti matrix[1]. However, coarse-sized TiB precipitates formed
through conventional casting or forging have a limited
contribution to strength.
Much finer and more uniformly dispersed TiB
precipitates are obtained in EBM built alloy ascompared with conventional wrought alloy, as shownin Fig. 1. This is mainly ascribed to the rapid
solidification process during EBM. These refined TiB
precipitates can act more effectively as obstacles of
dislocation motion. Consequently, the tensile strengthof EBM specimens is higher than that of the wrought
specimens at elevated temperatures of up to 873 K.
The tensile strength of an EBM specimen at 873 K
was approximately 1.4-times that of a wrought
specimen, as shown in Fig. 2.
In addition, the oxidation resistance was also

Fig. 1 SEM-BSE images and EPMA elemental mappingsof B and Ti of (a) wrought and (b) EBM specimens [2].

Fig. 2 Temperature dependence of ultimate tensile stressin wrought and EBM specimens [2].

significantly improved in EBM built alloy as comparedwith a conventional wrought alloy.
This improvement is mainly ascribed to theformation of dense oxidation layers caused by thehomogenous dispersion of fine TiB precipitates,
which prevents further oxidation in EBM built alloy.
References[1] X. Guo, L. Wang, M. Wang, J. Qin, D. Zhang, and W. Lu, Acta
Mater. 60, 2656 (2012).
[2] T. Fujieda, Y. Cui, K. Aoyagi, Y. Koizumi, and A. Chiba, Materialia.
4, 367 (2018).

Keywords: alloy, microstructure, mechanical properties
Akihiko Chiba (Deformation Processing Research Laboratory)
E-mail: a.chiba@imr.tohoku.ac.jp
URL: http://www.chibalab.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201911

Infrastructural Materials

Comparison of Coherent Forward Scattering and Atomic Absorption Profilesof Ar 842.5-nm Line in Pulsed Radio Frequency Glow-Discharge PlasmaAcomparison of the coherent forward scattering (CFS) and atomic absorption (AA) of an Ar I 842.5-nm line wasconducted using pulsed radio-frequency (RF) glow discharge (GD) plasma. The locations of the highest and secondhighest number densities of the excited argon atoms in the lower state of an Ar I 842.5-nm transition could be determined.
The coherent forward scattering (CFS) technique
is based on two crossed polarizers, a polarizer and ananalyzer, which block the probe light when no atomic
interactions occur. Because of the anisotropy ofresonant analyte atoms, which is induced by theexternal magnetic field applied, the state of lightpolarization is changed when passing through theatomic vapor between the polarizer and analyzer, andlight is transmitted. Without a light interaction withresonant atoms, the transmitted intensity is zero. The
transmitted CFS intensity is approximately proportional
to the square of the number density of the atoms.
The CFS and AA spectra of an Ar I 842.5-nm line
in pulsed RF GD plasma were recorded using a CFS
spectrometer in a Faraday configuration with permanent
double-ring magnets and a diode laser source.
Zeeman splitting of the conventional AA spectrum andthe self-absorption profile of CFS radiation could beobserved for different magnetic fields of above ~50
and ~10 mT, respectively. This might be explained byassuming that the CFS radiation consists of left- andright-handed circularly polarized radiation for higher
and lower off-resonance frequencies, respectively.
Based on the simulated absorption profiles, Zeeman
splitting can be observed at above ~50 mT for aconventional AA signal and below ~10 mT for the selfabsorption of CFS radiation [1].
Because the presence of a magnetic field does
not require observation of an AA signal, the measured
profile provides information regarding the location of
the highest number density of the excited argon atoms
in the lower state of the Ar I 842.5-nm transition. In
contrast, the self-absorption profile of the CFS radiation
provides information regarding the location of thesecond-highest number density. This is because CFS
radiation is generated when a magnetic field and thehighest number density of the measured atoms both
occur. This CFS radiation operates as a light source forthe subsequent AA at the location of the secondhighest number density.
The magnetic field determined by the measured
Zeeman splitting (Fig. 1) and a calculation of the axial
variation of the magnetic field of the GD tube (Fig. 2)

Fig. 1 Conventional AA spectrum and the self-absorption
profile of CFS radiation at an RF power of 5 W

Fig. 2 Axial variation of the magnetic field and the position of
the magnetic field determined from the AA and CFS profiles

allowed us to determine the locations of the highest
and second-highest relative maximum number densityof the excited argon atoms in the lower state of the Ar I
842.5-nm transition.
References[1] H. Matsuta, Spectrochim. Acta Part B 149, 150 (2018).

Keywords: spectroscopy, glow discharge plasma, magnetic properties
Hideyuki Matsuta (Analytical Science Research Laboratory)
E-mail: matsuta@imr.tohoku.ac.jp
URL: http://wagatsuma.imr.tohoku.ac.jp/

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IMR KINKEN Research Highlights 2019

IMR KINKEN Research Highlights 2019

Fatigue Improvement of Biomedical Co-Cr-Mo Alloy Fabricatedby Using Electron Beam MeltingB

iomedical Co-Cr-Mo alloys fabricated using additive manufacturing techniques generally exhibit relatively
non-uniform microstructures and poor mechanical properties. Herein, we modified the microstructures andenhanced the fatigue properties of Co-Cr-Mo alloy fabricated through electron beam melting by utilizing anaccessible post production heat treatment regime, which provides an avenue for improving the serviceabilityof the additive manufactured metallic components.
Biomedical Co-Cr-Mo alloys are widely used inorthopedic implants such as artificial knee and hip
joints. In contrast, electron beam melting (EBM), a
layer-by-layer additive manufacturing technique, hasbeen utilized for fabricating near-net-shaped metallic
components with complex shapes and geometries.
However, the non-uniform microstructures andmechanical properties are the main drawbacks
constraining the serviceability of as-EBM built
components.
We recently demonstrated the microstructuralcharacteristics of as-built biomedical Co-Cr-Mo
alloys [1], and subsequently improved the fatigue
properties based on manipulating the microstructure
through an accessible post-production heat
treatment regime [2]. The as-built γ/ε dual phasestructures were selectively transformed into apredominant ε phase by ageing at 800 °C for 12 h,
and then reverse transformed into a predominant γphase by further ageing at 1000 °C for 10 min. As aresult, both stress- and strain-controlled fatigue
properties were improved, as illustrated in Fig. 1.
Figure. 2 shows STEM images demonstrating
the microstructures of the as-built (Fig. 2a), HT (Fig.
2b), and RT (Fig. 2c) specimens after applying
stress-controlled fatigue until failure. Bands or lathsof the ε-phase were formed in the γ matrix of the asbuilt and reverse-transformed samples by means ofa γ→ε strain-induced martensite transformation
while under fatigue. This transformation is attributed
to the motion of the partial Shockley dislocations on
the alternative {111} panes of the γ phase. However,a single ε-phase without a band structure wasobserved in the heat-treated sample, wherein the
ε-matrix contained a high density of dislocations.
This indicates that the fatigue proceeded mainly
through plastic deformation of the ε-matrix. In thepresent study, the fatigue properties of as-EBMbuilt biomedical Co-Cr-Mo alloy were significantly

Fig. 1 (a) Number of cycles until failure under stresscontrolled fatigue and (b) maximum tensile stress ofstrain-controlled fatigue of the as-EBM built, heat treated(HT), and reverse-transformed (RT) Co-Cr-Mo alloys.

Fig. 2 STEM images showing microstructures of (a) asEBM built, (b) heat-treated, and (c) reverse-transformed
biomedical Co-Cr-Mo alloys after stress-controlled
fatigue was applied until failure. The incident beam isparallel to {111}γ //(0001)ε.

improved by manipulating the fatigue deformation
behaviors.
References[1] D. Wei, Y. Koizumi, A. Chiba, K. Ueki, K. Ueda, T. Narushima,
Y. Tsutsumi, and T. Hanawa, Additive Manuf. 24, 103 (2018).
[2] D. Wei, Y. Koizumi, T. Takashima, M. Nagasako, and A. Chiba,
Mater. Res. Lett. 6 (1), 93 (2018).

Keywords: microstructure, mechanical properties, fatigue
Daixiu Wei (Creation of Life Innovation Materials for Interdisciplinary and International Researcher Development)
E-mail: wei1987xiu@imr.tohoku.ac.jp
Hidemi Kato (Leader of Creation of Life Innovation Materials for Interdisciplinary and International Researcher Development)
E-mail: hikato@imr.tohoku.ac.jp
URL: http://life-pro.imr.tohoku.ac.jp/index.html

IMR KINKEN Research Highlights 201913

Infrastructural Materials

Development of Integrated Education Program for Young
Researchers in Computational Materials ScienceP

0.1

number of new doctors

More than 50 years have passed since researchusing supercomputers started in the field of materials
science (MS). Progress in computational materials science(CMS) has recently accelerated the discovery of advanced
and novel materials. However, there have been few
quantitative analyses regarding the trend in the number ofdoctors in CMS in Japan. In addition, doctors in Japan
have recently been expected to work not only in academia,
but also in industry. However, doctors in non-academia are
still limited. They are demanded to have not only highexpertise, but also wide knowledge of MS and humanskills as advanced industry experts. There are somemismatches between the required knowledge and skills of
doctors in industry and the contents of education in CMS.
We estimated the change in the number of doctors in
CMS in Japan during the last 50 years by analyzing the
subjects of doctoral dissertations found in a Japanese
doctoral dissertation database [1]. Figure 1 shows thechanges in the new doctors of science and engineering(SE) at sixteen domestic research universities and the new
doctors of CMS at the same universities during the last 50
years. The number of doctors in SE, which rapidly
increased during the 1990s owing to a reconstruction of
the graduate school, peaked at approximately 2000, andhas since rapidly decreased owing to the recent birthrate
decline in Japan. In contrast, the number of doctors in
CMS continued to increase until 2010, and the rate ofdecrease thereafter has been small. Consequently, theratio of doctors in CMS to those in SE has continued toincrease, exceeding 0.07 in 2015. This indicates that theimportance of researchers in CMS is increasing.
In general, CMS lectures and human skills trainings
are given by experts independently. There are few students
and young researchers actively participating in humanskills trainings. Therefore, we developed and assessed an
integrated education program of CMS and the training of
human skills in supporting young researchers to overcome
the gaps among fundamental research, applied research,and practical applications [2]. One of our unique elective
courses is PCoMS three-day seminar. The main contents

3000

fraction of new doctors
in computational & theoreticalmaterials sciencerofessional development Consortium for Computational Materials Scientists (PCoMS) supports young researchers in thearea of computational materials science (CMS) to develop their broader view and extensive knowledge in interdisciplinary
areas including materials science (MS), condensed matter physics, molecular science, and material design. A recent
activity by key members of PCoMS is introduced. Professors Terada and Mohri are developing and assessing the integrated
education program of “specialized CMS” and “training of human skills.”

0.08
0.06

2000

0.04
1000
0

0.02
1970 1980 1990 2000 2010

year

0

total number of
new doctors in SE
number of
new doctors
in computational& theoretical MS
fraction of
new doctors
in computational& theoretical MS

Fig. 1 Number of new doctors of 16 domestic research
universities in Japan in last fifty years.

of this seminar are (1) lectures and practical computational
training given by experts in both academia and industry,and (2) group discussions regarding research proposals
related to both seminar topics and group member research
topics. After seminars were conducted in 2016, 2017, and2018, all 32 participants were emailed a link to a web
survey. Among them, 24 of the participants answered thequestionnaires. Based on the analysis of the questionnaire
survey, we found that the satisfaction of the participants ishigh, although they think that a group discussion is adifficult task. Students and researchers typically do nothave a sufficient chance to communicate with others in
different research fields. After the discussion, they
improved their human skills for communication with otherstudents and researchers in different research fields, andcame to understand the need for wide MS knowledge andhuman skills for scientific communication for interdisciplinary
studies and innovation.
References[1] Y. Terada and T. Mohri, A study on trend of doctors in JapaneseComputational Materials Science in last fifty years, JIM Annual Spring
Meeting 2019, Mar. 20, 2019.
[2] Y. Terada and T. Mohri, Integration of “specialized educational sciencelectures” and “training of human skills” and transferable skills” incomputational materials science, SMS2018, P64, Abstracts of
SMS2018, Oct. 30, 2018.

Keywords: computational materials science, higher education
Yayoi Terada (Professional development Consortium for Computational Materials Scientists)
E-mail: terada@imr.tohoku.ac.jp
Tetsuo Mohri (Project Leader of Professional development Consortium for Computational Materials Scientists)
URL: http://pcoms.imr.tohoku.ac.jp/

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IMR KINKEN Research Highlights 2019

Energy-Related Materials

IMR KINKEN Research Highlights 2019

Research

Energy-Related Materials

Self-Arrangement of Dislocations at Crystal/melt Interface
During Directional Solidification of SiliconT

he formation of small-angle grain boundaries (SAGBs) at a silicon crystal/melt interface during directional
solidification was directly observed. Dislocations were demonstrated to self-arrange through polygonization
into an energetically favorable SAGB configuration at the crystal/melt interface. The present results suggestthat there is considerable dislocation motion at the solid/melt interface and that polygonization can occur
during solidification.
The efficiency of solar cells manufactured using
multicrystalline silicon (mc-Si) substrates is limited
because of the various defects that exist in suchmaterial. Among the different types of GBs, smallangle GBs (SAGBs), which have a lower
misorientation, have been confirmed to possess ahigh capability for impurity gettering. Studies on therelationship between the SAGB structure and thesolar cell performance have found that a certain
type of structural dislocation in SAGBs is responsible
for an absolute performance loss of up to
approximately 5%. Understanding the evolution of
SAGBs during directional solidification would help
in improving the quality of mc-Si substrates. In thisstudy, we attempted to reveal the mechanisms
behind the emergence and extension of SAGBs in
mc-Si.
Figure 1 shows photographs taken during an insitu observation of the solidification of silicon [1].
The solidification rate ranges from 40 to 70 μm s-1,
which is moderately faster than the growth rate ofindustrial mc-Si (33.3 μm s-1) while providing
comparable conditions for observing the behaviorof crystal growth. It is clearly shown that SAGBs,
which appear as white lines almost perpendicular tothe solid/melt interface, are propagating along the
growth direction. The emergence of new SAGBs
was observed at the moving crystal/milt interface.
Figure 2 shows photographs of areas taken
through an in situ observation of the directional
solidification and using an SEM after crystallization[1]. The places of origin of the SAGBs, as observed
through an SEM after Sopori etching, are shown.
The dislocations aggregate and exhibit a linear
arrangement during solidification.
Polygonization of the dislocations in various
materials has been extensively investigated;
however, little attention has been paid to a crystal/melt interface. In this study, we directly observed
the formation of SAGBs at a crystal/melt interface.
The results indicate that the dislocation motion at
Keywords: crystal growth, defects, solar cells
Kozo Fujiwara (Crystal Physics Research Laboratory)
E-mail: kozo@imr.tohoku.ac.jp
URL: http://www.xtalphys.imr.tohoku.ac.jp/

16

IMR KINKEN Research Highlights 2019

Fig. 1 Emergence of SAGBs at a moving crystal/meltinterface.

Fig. 2 Etch pit distributions before and after SAGB
formation.

the crystal/melt interface is extremely active. The
present results clearly show that the formation of
SAGBs occurs at a crystal/melt interface during
directional solidification, not only during the coolingprocess after solidification.
References[1] L.-C. Chuang, K. Maeda, H. Morito, K. Shiga, and K. Fujiwara,
Materialia 3, 347 (2018).

IMR KINKEN Research Highlights 2019

Materials Design for Super-Precise System Based on
Molecular Dynamics Simulation

Recent materials design for super-precise systems strongly requires a deep understanding of multi-physics

phenomena, including the chemical reactions, friction, impact, fluid, and heat. We applied our multi-physics
computational simulator based on a molecular dynamics method and revealed the multi-physics phenomena that
contribute to the materials design in the mechanical engineering field such as solar cells, electronics, tribology etc.

High-functional and high-performance materials
are necessary in a wide variety of research fields, suchas solar cells, electronics, tribology etc., to develop
super-precision systems. For the materials design, we
need a deep understanding of the multi-physics
phenomena, including the chemical reactions, friction,
fluid, and heat. However, traditional simulation methods
such as fluid mechanics and first-principle calculations
cannot simulate the multi-physics phenomena. Thus,
we applied our multi-physics simulators based onclassical molecular dynamics (MD), tight-binding
quantum chemical MD, first-principles MD, etc., forpioneering next-generation materials design [1-3].
An ionic liquid (IL)-assisted vacuum deposition
method has recently been introduced for the fabricationof single-crystal pentacene for organic solar cells andorganic electronic devices. This experimental study
suggested that a higher diffusion of IL tends to provide
a higher quality of the pentacene crystal. We thus
investigated the diffusion coefficient of ions in a thinfilm ionic liquid (TF-IL)-on α-Al2O3(0001) through MD
simulations (Fig. 1a) [1]. The simulation results showthat the diffusion coefficient in a 2 nm thin-film issignificantly lower than that at other thicknesses (Fig.
1b) because the layered structure of ILs is formed on
the substrate. We suggest that the TF-IL thickness
should be above the layered structure to avoid a low
diffusion coefficient and low quality of pentacene
crystal in IL-assisted vacuum deposition.
Diamond-like carbon (DLC) is a promising solid
lubricant used to reduce the friction against α-Al2O3.
The friction of DLC/α-Al2O3 strongly depends on
temperature. To reveal the friction mechanism, weinvestigate the friction behaviors of DLC/α-Al2O3 atvarious temperatures using our developed tightbinding quantum chemical MD simulator [2].
Interestingly,
thevolcano-typetemperaturedependence of the friction coefficients is observed(Fig. 2a). At 300–600 K, DLC/α-Al2O3 shows smoothsliding. However, at 600–800 K, interfacial C–O and
C–Al bonds are generated, and the friction coefficients
increase. Over 800 K, the number of interfacial bonds

Fig. 1 (a) Schematic of a thin-film ionic liquid (TF-IL) on
α-Al2O3(0001) substrate. (b) Self-diffusion coefficient in
the out-of-plane direction.

Fig. 2 (a) Friction coefficients of DLC/α-Al2O3 at eachtemperature. DLC film structures (b) before and (c) after
friction at 800 K.

and friction coefficients decease. It is interesting to notethat chemically stable graphite is formed on the DLC
surface during the friction at 800 K (Fig. 2b, c), andinhibits the interfacial bond generation. We revealed
the unique friction mechanism of DLC/α-Al2O3 owing to
the structural changes in the friction interface throughthe multi-physics phenomena of the chemical reaction,
friction, and heat.
References[1] S. Maruyama, I.B.H. Prastiawan, K. Toyabe, Y. Higuchi, T.
Koganezawa, M. Kubo, and Y. Matsumoto, ACS Nano 12, 10509(2018).
[2] Y. Wang, J. Xu, J. Zhang, Q. Chen, Y. Ootani, Y. Higuchi, N. Ozawa,J. M. Martin, K. Adachi, and M. Kubo, Carbon 133, 350 (2018).
[3] Y. Ootani, J. Xu, T. Hatano, and M. Kubo, J. Phys. Chem. C 122,
10459 (2018).

Keywords: simulation, molecular dynamics, interface
Momoji Kubo (Materials Design by Computer Simulation Research Laboratory)
E-mail: momoji@imr.tohoku.ac.jp
URL: http://www.simulation.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201917

Energy-Related Materials

Chemical State Mapping of Be12Ti and Be12V Beryllides bySoft X-Ray Emission Spectrometry

Be-rich intermetallics (beryllides) have been expected to be adopted for high-temperature environments,
such as fusion reactors and gas turbines. Here, the chemical state micromapping of Be12M (M = Ti,V) is shown
based on the valence electron structure revealed using an electron probe microanalyzer with a novel soft X-ray
emission spectroscope.

Beryllides have a great potential to be used inindustrial
applicationsforhigh-temperatureenvironments, including structural materials foraerospace systems and refractory materials,
because of their high strength and light weight.
Recently, Be-rich intermetallics, such as Be12M (M =Ti,V), have been expected to be neutron multipliers
for fusion reactors as a substitute for pure metallic
Be because of their significant advantage inoxidation resistance at elevated temperatures.
Elemental microanalysis by measuring acharacteristic X-ray with electron microscopy is an
essential approach in the development of oxidationresistant beryllides. However, low-Z (Z: atomic
number) elements such as Be (Z = 4) are difficult to
detect by the conventional approaches using
energy- and wavelength- dispersive spectrometers(EDS and WDS) for electron microscopy. Thus, anovel soft X-ray emission spectrometer (SXES)
attached to an electron probe microanalyzer wasused, which covers a low energy range (50-210 eV)with ultrahigh-energy resolutions of 0.22 eV for
obtaining the chemical state map of the low-Z

elements such as boron [1] and beryllium.
The Be–K spectra from the Be12M phases show
significantly lower densities of the occupied statesnear the Be–K edge than those of metallic pureberyllium. Density functional theory calculations
indicate that changes in the valence electron
structure are derived from the large downward shiftof the Fermi level in Be12M, by at least 0.8 eV. Basedon the knowledge of the valence electron structures
and the chemical shift, chemical-state mappings of
BeO and Be12V in the oxidized beryllide specimen
were successfully obtained, as shown in Fig. 1 [2].
The present approach is applicable forvisualization and identification of metallic/oxidized
phase in light-element compounds by an electron
microscope.
References[1] R. Kasada, Y. Ha, T. Higuchi, and K. Sakamoto, Sci. Rep. 6,
25700 (2016).
[2] K. Mukai, R. Kasada, K. Yabuuchi, S. Konishi, J.-H. Kim, and
M. Nakamichi, ACS Applied Energy Mater. 2, 2889 (2019).

PA

X-ray intensity (a.u.)

1
2
3
4
5
6
7
8
9

96

98

High

PC

PB

Scale/matrix interface

BeO scale

BeO

MatrixLow

100 102 104 106 108 110 112

X-ray energy (eV)

PB/PA

5 µm

PC/PA

5 µm

Fig. 1 Be–K spectra (left) by the SXES from nine measuring areas of the steamed Be12V specimen: reconstructed images by
calculating the peak area ratio of PB/PA and Pc/PA, showing chemical-state mappings of BeO (center) and Be12V (right) [2]

Keywords: nuclear materials, electronic structure, electron microscopy
Ryuta Kasada (Nuclear Materials Engineering Research Laboratory)
E-mail: r-kasada@imr.tohoku.ac.jp
URL: http://web.tohoku.ac.jp/imr-numat/

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IMR KINKEN Research Highlights 2019

IMR KINKEN Research Highlights 2019

Locations of Mn and Fe in Andalusite from Västanåberget, Sweden

Local structural features around Mn and Fe in Mn-bearing andalusite from Västanåberget, Sweden, were investigatedby anomalous X-ray scattering (AXS) and X-ray absorption fine structure (XAFS) spectroscopy. The elemental
distribution map of Mn obtained by AXS and the extended X-ray absorption fine structure (EXAFS) spectra indicatethat Mn atoms exclusively occupy the Al1 sites. EXAFS analyses reveal that Fe occupies both Al1 and Al2 sites.
Utilizing the local structural information around Mn and Fe, a conventional single-crystal structural refinement
converges at R = 2.34%, with a structural formula of (Al0.82Mn0.16Fe0.02)[6](Al0.99Fe0.01)[5]SiO5.

Mn-bearing andalusite has a structural formulaof (Al2-x-y Mnx Fey) SiO5. The stability and opticalproperties of andalusite strongly depend on thesubstitution of transition metals and their coordination
environments, as shown in Fig. 1. In general,presence of even a small amount of Mn and thecoexisting Fe lead to uncertainties in the modelingof the site preferences for two distinct Al sites, when
only conventional single-crystal X-ray diffraction(XRD) data are considered. Herein, we report direct
evidence for the site preferences of Mn and Fe in
andalusite using anomalous X-ray scattering (AXS)and X-ray absorption fine structure (XAFS)
spectroscopy.
To revise the structural model, results of the
AXS analysis were used. Figure 2 shows the
distribution maps of Mn at z = 0 and 0.25 obtainedby a difference Fourier synthesis of the Mn AXS
data. The distribution of Mn is observed exclusively
at the Al1 site. This result suggests a strong
preference of Mn for the Al1 site. Similarly, thedistribution map for Fe indicates that Fe occupies
both Al1 and Al2 sites. Based on these results, wewere able to improve the structural model.
During the XANES analysis of the local structureof Mn and Fe, we employed a multiple-scattering
simulation method using the structural parameters
obtained by single-crystal XRD. These data support
the observation that Mn exclusively occupies theAl1 site. Furthermore, a distorted octahedron is
deduced from the bond distances obtained at 1.87–
2.26 Å, and the average value of <Mn–O> = 2.03 Åsuggests the Jahn–Teller distortion of the Mn3+O6
octahedra. Notably, the <Mn–O> distance iscomparable to the distance between the Al1 site
and O atom in kanonaite, which is fully occupied by
Mn and Fe atoms. This result indicates that the local
Mn–O bond distances in andalusite are comparable
to those of kanonaite regardless of the Mn content.
This phenomenon is known as complete structural
relaxation, where Mn retains its atomic size. These
local structures around Mn suggest strong

Fig. 1 Crystal structure of the Mn-bearing andalusite from
Västanåberget, Sweden, and coordination environmentsof the Al1 and Al2 sites.

Fig. 2 Mn distribution maps at (a) z = 0 and (b) z = 0.25 obtainedby AXS measurement at the Mn K-absorption edge.

correlation to the Mn-site preference and maximum
possible Mn content in the andalusite structure. The
recent first-principles study by Wang et al. (2017)shows that a large number of Mn atoms can occupy
Al1 sites due to the large Jahn–Teller distortion of
Mn3+O6 octahedra and low bulk modulus of theandalusite phase, which further suggests the
structural relaxation phenomenon discussed
previously. However, the EXAFS spectrum of Fe is
not reproduced by the simulated models derived bysubstituting the atoms in Al1 or Al2 sites with an Fe
atom.
References[1] H. Arima, Y. Tani, K. Sugiyama, and A. Yoshiasa, J. Min. Pet.
Sci. 113, 273 (2018).

Keywords: XAFS, XRD, synchrotron
Hiroshi Arima (Chemical Physics of Non-Crystalline Materials Research Laboratory)
E-mail: h_arima@cross.or.jp
URL:http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/15.html

IMR KINKEN Research Highlights 201919

Energy-Related Materials

Fast Diffusion of Multivalent Ions in Cathode Materials Facilitated byConcerted Interaction with Monovalent Ions ― A Perspective on Constructing
Novel Rechargeable Batteries with Safety & High-Energy Density

We are currently constructing a new type of rechargeable battery using divalent Mg cations. We determinedthrough electrochemical experiments combined with first-principles calculations that the diffusion of divalent
Mg ions, whose diffusion in cathode materials is usually sluggish, is dramatically facilitated by the concerted
interaction between Mg and monovalent Li ions.

In terms of energy and environmental concerns,
modern industrial society strongly demands highenergy-density rechargeable storage batteries. Lithium
ion batteries (LIBs) are being widely used for a numberof practical applications, although their performance isgradually approaching the theoretical limit. If lithium
metal itself could be used as an anode material insteadof the currently used carbonaceous materials, LIBs
would have demonstrated significantly high energy
densities; however, this is difficult owing to the notorious
problem of “dendritic growth” of Li metal during acharge, which leads to a dangerous short circuit.
As an alternative to a Li metal-anode battery,
multivalent-ion (Mg2+, Zn2+, Al3+, etc.) batteries haveattracted attention because a safe and high-capacity
metal can be employed as an anode material; forexample, in the case of Mg, its capacity (~2,200mAhg−1) largely exceeds that of current carbonaceous
anode materials (~370 mAhg−1). However, the diffusionof multivalent ions in cathode materials is known to be
typically sluggish, which causes an increase in the
overpotential.
Because these problems are difficult to be solvedin a single-carrier ion battery system, we designed a
new battery technology utilizing both Li and Mg ions,which we refer to as a Li-Mg dual-cation battery [1]. We
experimentally confirmed that the co-electrodepositionof Li-Mg dual cations can significantly suppress Li
dendritic growth, and that the concomitant intercalationof both ions into a Mo6S8 Chevrel or MgCo2O4 spinelcathode occurs in Li-Mg dual-cation batteries with amuch lower overpotential than that in a Mg singlecarrier ion battery [1]. This indicates that divalent Mg
ion diffusion is promoted by the presence of monovalent
Li ions in a cathode.
We elucidated through first-principles calculations
that the activation energy of Mg diffusion in Mo6S8 isreduced remarkably in a Li-Mg dual-cation system by
the “concerted” motion of the following Mg and leading
Li ions with the Li-Mg distance remaining nearly
constant, as shown in Fig. 1 [2]. This proves that dualion systems are a promising way to construct novel
high-performance rechargeable batteries employing
multivalent ions with an enhanced diffusion rate.
References[1] H. Li, T. Ichitsubo, S. Yagi, and E. Matsubara, J. Mater. Chem. A 5,3534 (2017).
[2] H. Li, N. L. Okamoto, T. Hatakayama, Y. Kumagai, F. Oba, and T.
Ichitsubo, Adv. Energy Mater. 8, 1801475 (2018).

Fig. 1 (a) Activation energies computed using the nudged elastic band method for the diffusion processes. (b) Schematic
figure illustrating the minimum energy diffusion path of Mg ions in a LiMo6S8 host.

Keywords: energy storage, crystal structure, diffusion
Tetsu Ichitsubo, Norihiko L. Okamoto, Hiroshi Tanimura, and Tomoya Kawaguchi (Structure-Controlled Functional
Materials Research Laboratory)
E-mail: tichi@imr.tohoku.ac.jp
URL: http://ilab.imr.tohoku.ac.jp/index.html

20

IMR KINKEN Research Highlights 2019

IMR KINKEN Research Highlights 2019

Investigation of Structure and Properties of Nano andSubmicrometer Porous Metals Formed by Liquid Metal DealloyingT

he liquid metal dealloying (LMD) technique facilitates preparation of fine porous materials with base metalelements, which is difficult to achieve by means of the conventional chemical dealloying techniques. In thisstudy, the mechanism of morphology formation during LMD was studied by scanning electron microscopy,
X-ray diffraction, electron backscatter diffraction, and X-ray and electron tomography.
Nano and submicrometer porous metals haveattracted considerable attention for their excellent
functional properties. The most promising techniqueused to prepare such porous metals is dealloying inaqueous solution. Nanoporous noble metals
including Au have been prepared from binary alloy
precursors. The less noble metals, unstable inaqueous solution, are oxidized immediately when
they contact water at a given potential, so thisprocess is only possible for noble metals. Porous
structures with less noble metals, such as Ti or Fe,
are highly desired for various applications, including
energy-harvesting devices. To overcome thislimitation, a liquid metal dealloying (LMD) was
developed at the Kato Lab. LMD is a selective
dissolution phenomenon of a mono-phase alloy
solid precursor: one component (referred to as a“soluble component”) is soluble in the metallic melt,
while the other (referred to as the “targetedcomponent”) is not. When the solid precursor
contacts the metallic melt, only atoms of the solublecomponent dissolve into the melt, inducing a
spontaneously organized bicontinuous structure ata microstructure level. The LMD has enabled the
preparation of nano and submicrometer porous
structures in less noble metals, such as Ti, Ni, Si, Fe,
Nb, Co, and Cr. In this study, the mechanism ofmorphology formation during the LMD process wasthree dimensionally analyzed in situ and ex situ
using X-ray tomography [1].
Figure 1(a) shows a scanning electron
microscopy (SEM) image and reconstructed 3D
structure (inset) of porous Fe-Cr alloy prepared froma Fe40Cr10Ni50 (at.%) precursor. Two phases (metal
and air) can be clearly distinguished in thereconstructed 3D image. This 3D morphologicalanalysis made it possible to evaluate quantitatively
the volume fraction of phases, surface area,connectivity, and tortuosity more precisely than withthe 2D analyses done previously. Figure 1(b) showsthe experimental setup for 3D observation of thedealloying process in situ. The LMD cell was put

Figure 1 (a) SEM image and reconstructed 3D structure(inset) of porous Fe–Cr alloy prepared from Fe40Cr10Ni50
precursor, (b) experimental setup for 3D in situ
observation of dealloying in the ESRF beam line and (c)evolution of porous metal layer by LMD in the Fe40Cr10Ni50
needle precursor in the longitudinal cross section at
different reaction times of 45, 90, and 165 s — thetransverse cross section image at 165 s is also shown

into the intense X-ray beam line at the European
Synchrotron Radiation Facility (ESRF). The cell washeated by the laser, and a tomogram image was
acquired. The bottom of Fig 1(c), shows the evolutionof the porous metal layer in Fe40Cr10Ni50 needle
precursor at 45, 90, and 165 s. The dark area andbright area in the needle sample correspond todealloyed porous metal and an undealloyed layer,
respectively. The thickness of the porous metal layer
linearly increases with time, indicating that thedealloying reaction kinetic was controlled by theinterfacial reaction in this cell.
References[1] M. Mokhtari, C. L. Bourlot, J. Adrien, A. Bonnin, T. Wada J.
Duchet-Rumeauc, H. Kato, and E. Maire, Mater. Charact. 144,
166 (2018).

Keywords: foam, porosity, 3D structure
Hidemi Kato (Non-Equilibrium Materials Research Laboratory)
E-mail: hikato@imr.tohoku.ac.jp
URL: http://www.nem2.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201921

Energy-Related Materials

Visualization of Anomalous Ettingshausen Effect in an FePt
Ferromagnetic Thin FilmThe anomalous Ettingshausen effect (AEE) is one of the well-known thermoelectric effects in ferromagnets, although
only a few studies on AEE have been reported for bulk materials. Here, we show a visualization of the temperature
modulation owing to the AEE in an FePt ferromagnetic thin film by utilizing a lock-in thermography technique.
Interconversion between an electric charge
current (Jc) and a heat current (Jq) mediated by aspin current (Js), which has frequently been called“spin-caloritronics” [1], has fascinated researchers
ever since the progress made in energy harvesting
has necessitated a new route toward a highly
efficient thermoelectric conversion. The anomalous
Nernst effect (ANE) and anomalous Ettingshausen
effect (AEE) are well-known thermoelectric
phenomena, in which the coexistence ofmagnetization (M) and the temperature gradient(∇T) produces an anomalous Nernst voltage,
whereas that of Jc and M leads to ∇T owing to theAEE. The ANE has been widely studied for various
types of ferromagnetic bulks and thin films. In
contrast to the ANE, there have been no reports on
the AEE in a ferromagnetic thin film, although a few
studies on the AEE in ferromagnetic bulks havebeen reported. When a heating/cooling device
based on the spin-caloritronic phenomena isdesigned, the detailed spatial distribution of thetemperature modulation in a reduced dimension
needs to be known.
Herein, we report the observation of the AEE ina ferromagnetic thin film [2, 3]. We chose FePt alloy
as a material for visualizing the AEE. A 10-nm thick
FePt (100) film was epitaxially grown on a SrTiO3(100) substrate at 350 °C using an ultrahigh vacuum
magnetron sputtering system. For thermal imagingof the AEE, the lock-in thermography (LIT) technique
was used. The infrared radiation thermally emitted
from the sample surface was detected while
applying rectangular-wave modulated Jc to a
U-shaped FePt (Fig. 1(a)). Only the first harmonic
response was fed to separate the AEE from theJoule heating.
Figure 1(b) shows the amplitude (A) and phase(φ) images of the temperature modulation for the inplane magnetized FePt. An increase in A appears in
the y-directional wires with the opposite φ in the rightand left wires. This means that the sign of thetemperature modulation is reversed when reversing
the vector product of M and Jc. The spatial
Keywords: magnetic properties, thermo-electricity, thin films
Koki Takanashi (Magnetic Materials Research Laboratory)
E-mail: koki@imr.tohoku.ac.jp
URL: http://magmatelab.imr.tohoku.ac.jp/

22

IMR KINKEN Research Highlights 2019aInfrared
camera

Jc

M

b H
∇T

SrTiO3 Subs.

c

Jc

H

FePt
Jc

-

y
x

+

Jc
0.5 mmA (mK)0

1

0

φ (deg.)360

Fig. 1 (a) Schematic illustration of U-shaped FePt alongwith the lock-in thermography setup. The relationshipbetween charge current (Jc) and temperature gradient(∇T) for the perpendicular magnetization (M) is also
shown. (b) Amplitude (A) and phase (φ) images oftemperature modulation for the in-plane and (c)perpendicularly magnetized FePt.

distribution of the temperature modulation iscompletely changed by changing the FePt
magnetization from in-plane to out-of-plane. Figure1(c) shows the thermal image of the perpendicularly
magnetized FePt. Clear A signals appear aroundthe edges of the U-shaped wire, and the φ difference
between the inside and outside edges is ~180°.
These temperature modulations are wellunderstood by considering the symmetry of theAEE. In addition, our numerical calculation suggeststhat the different distribution of the heat sources forthe in-plane and perpendicularly magnetized FePt
lead to different temperature profiles of the AEE fora thin-film structure, which is an important finding in
the design of spin-caloritronic devices.
References[1] S. R. Boona, R. C. Myers, and J. P. Heremans, Energy Environ.
Sci. 7, 885 (2014).
[2] T. Seki, R. Iguchi, K. Takanashi, and K. Uchida, Appl. Phys.
Lett. 112, 152403 (2018).
[3] T. Seki, R. Iguchi, K. Takanashi, and K. Uchida, J. Phys. D:
Appl. Phys. 51, 254001 (2018).

IMR KINKEN Research Highlights 2019

Intermediate Hydrogen Sates in the Formation Process of aComplex Transition Metal HydrideT

he hydrogen states during the formation process of a complex transition metal hydride LaMg2NiH7 composedof La3+, Mg2+, [NiH4]4–, and H – was investigated, which is indispensable to obtain guideline for designing highhydrogen density storage materials. The results indicate the presence of intermediate hydrogen states prior to
the formation of [NiH4]4– and H –.
Complex transition metal hydrides composedof metal cations (e.g. Mg2+) and complex anions(e.g., [NiH4]4– with covalent hydrogen (Hcov.)) are
attractive for use in energy-related materials such ashydrogen storage materials. The formation processof hydrogen states in compounds is therefore
important because hydrogen exhibits various states,
which are interstitial hydrogen (H0), proton (H+),
hydride ion (H –), and Hcov., and related withdesigning high hydrogen density storage materials.
Focusing on a complex transition metal hydride,
LaMg2NiH7 composed of La3+, Mg2+, [NiH4]4–, andH –, we clarified the formation process of LaMg2NiH7
studied using powder neutron diffraction (PND) andinelastic neutron scattering (INS).
Using PND, LaMg2NiH7 was revealed to form
through an interstitial hydride LaMg2NiH0.05 with H0and an intermediate hydride LaMg2NiH4.6 withmaintaining of local atomic arrangements (Fig. 1) [1,2]. In LaMg2NiH4.6, hydrogen atoms were locatedaround Ni with the formation of NiH2 and NiH3 units
and in tetrahedral sites (T–site).
To identify the hydrogen states in NiH2 andNiH3 units and H in T–sites in LaMg2NiH4.6, hydrogenvibrations in LaMg2NiH4.6 (Fig. 2) and LaMg2NiH7
were studied using the INS [3]. The results indicatethat hydrogen atoms in NiH2 and NiH3 units in
LaMg2NiH4.6 are covalently bound with Ni due to theobservation of a H–Ni–H deformation and Ni–H
stretching modes. However, the NiH2 and NiH3 units
are not complex anions as [NiH4]4– due to the lackof NiH2 and NiH3 libration modes. Furthermore, awavenumber range of hydrogen vibrations in the T–sites in LaMg2NiH4.6 is between H0 and H –. The INS
results suggest the presence of intermediatehydrogen states in LaMg2NiH4.6 prior to the formationof [NiH4]4– and H –. Thus, NiH2 and NiH3 units andhydrogen atoms in the T–sites have been suggested
as precursors for [NiH4]4– and H – in LaMg2NiH7.

Fig. 1 Local atomic arrangements of (a) LaMg2Ni, (b)LaMg2NiH 0.05, (c) LaMg2NiH4.6, and (d) LaMg2NiH7.
Grey, orange, green, and blue circles indicate La, Mg,
Ni, and H, respectively.

Fig. 2 (a) Experimentally observed and calculated INS
spectra of LaMg2NiH4.6, and calculated contributions of H
atoms in (b) NiH2 and NiH3 and (c) T-sites. Insets areschematic figures of H vibrations in NiH2, NiH3, and T-sites.
B. Hauback, G. Li, S. Takagi, and S. Orimo, J. Phys. Chem. C
120, 5926 (2016).
[2] T. Sato, K. Ikeda, M. Matsuo, K. Miwa, T. Otomo, S. Deledda,
B. Hauback, G. Li, S. Takagi, and S. Orimo, Int. J. Hydrogen
Energy 42, 22449 (2017).

References[1] K. Miwa, T. Sato, M. Matsuo, K. Ikeda, T. Otomo, S. Deledda,[3] T. Sato. A. J. Ramirez–Cuesta, L. L. Daemen, Y. –Q. Cheng,
and S. Orimo, Inorg. Chem. 57, 867 (2018).

Keywords: hydride, crystal structure, neutron scattering
Toyoto Sato and Shin-ichi Orimo (Hydrogen Functional Materials Research Laboratory)
E-mail: toyoto@imr.tohoku.ac.jp
URL: http://www.hydrogen.imr.tohoku.ac.jp/index.html

IMR KINKEN Research Highlights 201923

Electronic Materials

IMR KINKEN Research Highlights 2019

ResearchElectronic Materials

Theory of Topologically Nontrivial Spin-Wave SolitonsThe formation of spin-wave solitons in static and dynamic (Floquet) analogs of the Haldane model is considered.
The nonlinearity arising from the crystalline anisotropy and magnon–magnon interactions is essential for theformation of solitons. We can observe different phases of solitons due to the interplay with the topologically
nontrivial band structure.
(a)1
1

E/JS 1
3.5

K

2

Pi /Pmax
1

2
3.0

0.25
-0.25

-1 1
11
(b)

2
14.4

P0
1

0
C = ±1
±1

18.2

22

2.5
2
0
C = ±10

Fig. 1 (a) Soliton phase diagram in the parameter space ofanisotropy constant K and power P0, In the dark-blue area,
solitons do not form. The other colors indicate the calculated
soliton energies E. ① and ② denote the distinct regions of
the phase diagram. The right panels display the
representative soliton density distributions found in ① (thetop one) and ②. Green- and red-dashed lines mark thethresholds Pc1 and Pc2, respectively. The right panels plot
the soliton wave function intensity at each site Pi, normalized
by the maximum in that panel Pmax with the indicated color
code. (b) The topology of solitons on the Haldane lattice
below and above the threshold Pc2. The blue region is thesoliton core that, at high intensities, has a different Chern
number C from the rest of the lattice (embedded in a
medium with C = 0).

Our findings provide interesting but challenging
experimental results for magnetic 2D van der Waals
materials, such as CrBr3, and magneto-dipolar
magnonic lattices. Solitons found in our study andthe corresponding topological classifications canserve as an information resource or as anexperimental technique to reveal these novel
magnonic edge modes.
References[1] M. Elyasi, K. Sato, and G. E. W. Bauer, Phys. Rev. B 99, 134402(2019).

Keywords: spin wave, spintronics
Mehrdad Elyasi, Koji Sato, and Gerrit Ernst-Wilhelm Bauer (Theory of Solid State Physics Research Laboratory)
E-mail: melyasi@imr.tohoku.ac.jp
URL: http://www.bauer-lab.imr.tohoku.ac.jp/?page=&lang=en

26

IMR KINKEN Research Highlights 2019

0.5
0

K

There has been a surge in the classification of
topological phases of matter for electronic systems,
which pertain to band structures with a global
nontrivial quantized phase quantified by a Chern
number.
Topologically
nontrivial
spin-wave(magnons) phases can also be realized inperiodically modulated magnetic systems, called
magnonic crystals. Solitons are self-localized wave
packets that exist by compensating the frequency
dispersion with nonlinearity. We combine the idea ofsolitons and the nontrivial band structure inmagnonic crystals to open new avenues for
spintronic applications [1]. For instance, the spinwave solitons presented here can serve as memory
bits with two topologically distinct phases cantransfer information locally to a proximity magnetic
system.
We consider a honeycomb spin lattice,analogous to the Haldane model, which includes
the nearest neighbor exchange interaction and a
Dzyaloshinskii–Moriya
spin-orbit
interaction
generated in a static or dynamic (induced byexcitation) manner. The magneto-crystalline
anisotropy and non-local magnon–magnon
interactions contribute to the nonlinearities. We
developed a self-consistent mean-field method todetermine the soliton modes in the spin-wave bandgap.
We identified several soliton phases dependingon the crystalline anisotropy coefficient (K) and the
input power (P0), as illustrated in Fig. 1(a). For agiven K, the system supports solitons above a
critical power Pc1 (green-dashed line). We also
observe a second threshold, Pc2 (red-dashed line),
which we identified to be a topological phasechange, viz. the inside and outside of the soliton
have different topologies. It is well-established thatthe boundary between regions with different
topological phases hosts robust edge modes.
Indeed, the solitons above Pc2 have a finite densityof states of edge modes at this dynamic boundary.
Figure 1(b) shows the topologies of the distinct
classes of solitons that have been identified.

IMR KINKEN Research Highlights 2019

Quantum Critical Point of Charge Density Wave Ground State Is Foundby Very High Magnetic Field X-ray Scattering with a 33-T Minicoil

The quantum critical point (QCP) hidden in the superconducting dome of underdoped hole-doped YBa Cu O was
23x

examined by x-ray scattering experiment by combining a free electron laser with a unique high-field pulsed minicoil
developed at the Institute for Materials Research. The charge density wave state, which has been found in very highmagnetic fields, terminates at a doping concentration of 0.08. The breakdown of the translational symmetry was
associated with the QCP.

In strongly correlated electron systems, such as
high-Tc superconductors, a competition between
localized and itinerant states is the source of their richand complex phase diagrams. In underdoped doped
YBa2Cu3Oax, in addition to the superconductivity atzero field, different phases, such as a spin density
wave, an antiferromagnetic, pseudo gap, and low-fieldcharge density wave (CDW) phases, have been foundby tuning the system by chemical doping, temperature,pressure, and a high magnetic field. Because of those,
the nature of the CDW phases is under intensive
investigation.
Until the striking discovery that there appear two
types of CDW state in low- and high-magnetic-fieldareas, the role of a high magnetic field is consideredsimply to suppress the superconductivity in acontinuous manner. In contrast to this expectation, thethree-dimensional (3D) CDW phase appears only inthe high-magnetic-field regime, and it is different fromthe short-ranged two-dimensional CDW that appears
in the pseud gap regime [1].
The next question is whether there is a terminating
point of the 3D CDW phase along with the holeconcentration. To clarify this point, a systematic study
was conducted on x-ray scattering in very highmagnetic fields of as much as 33 T in the holeconcentration between 0.07 and 0.12. There are two
experimental key points: one is the use of a highintensely pulsed x-ray source from the x-ray-freeelectron laser at the Linac Coherent Light Source at
the Stanford National Accelerator Laboratory, and theother is the use of a compact minicoil developed at theInstitute for Materials Research (IMR) that can generate
35-40-T-class pulsed magnetic fields.
Figure 1 shows a picture of a minicoil with anouter diameter of 30 mm. By using a compact pulsed
power generator developed at the magnetism division
at IMR, 40 and 50 T were available with a split-pair coiland a solenoid coil, respectively, as of 2018.
The determined hole concentration dependenceof the 3D CDW signal is depicted in Fig. 1. The

Fig. 1 IMR’s mini-split-pair coil for x-ray scatteringexperiments and the hole concentration dependence of
Bragg peak integrated intensity of 3D CDW signal (thecolored area is eye guides)

integrated intensity decreases with decreasing holeconcentration from 0.12 to 0.07. In the concentration of
0.07, it was not possible to find a CDW peak, even if
the superconductivity was completely suppressed. Ata slightly increased hole concentration of 0.08, a tiny
peak shows up above 15 T, and a sizable intensity isfound. These results indicate clearly that the 3D CDW
phase terminates at approximately a hole concentrationof 0.08 [2].
The present result shows the existence of aquantum critical point (QCP) at approximately 0.08.
The end point of the spin density wave phase and thetermination point of the field-induced phase transition
found in the ultrasound experiment were also
approximately 0.08. These evidences establish theexistence of a QCP of high-field phase in YBa2Cu3Oax.
Because this QCP is hidden in zero or lower magnetic
fields, the high-field ability provides a unique route toaccess there.
References[1] S. Gerber et al., Science 357, 71 (2017).
[2] H. Jang et al., Phys. Rev. B 97, 224513 (2018).

Keywords: high magnetic field, superconducting, X-ray scattering
Hiroyuki Nojiri (Magnetism Research Laboratory)
E-mail: nojiri@imr.tohoku.ac.jp
URL: http://www.hfpm.imr.tohoku.ac.jp

IMR KINKEN Research Highlights 201927

Electronic Materials

Demonstration of Spin Current SwitchingS

pin current switching was discovered in Cr2O3, which allows information processing using fully spin-based
devices. Our demonstration fills in a missing piece in spintronic devices and is the equivalent of using atransistor to control the flow of electricity.
Spintronics is an emerging field of nanoscale
electronics that utilizes not only the charge of theelectrons but also the degree of freedom of their spin.
In this field, a spin current, a flow of spin-angularmomentum, plays an essential role. Owing to thedevelopment of spintronics, the detection andgeneration technologies for the spin current havebeen well established. However, there is a missing
fundamental component in spintronics, namely, a
spin-current switch. Here, we demonstrate that atrilayer-film structure consisting of yttrium-iron-garnet
YIG (Y3Fe5O12)/Cr2O3/Pt operates as a spin-current
switch in which the spin-current transmission from
YIG to Pt through Cr2O3 can be modulated by up to500% at the antiferromagnetic transition temperatureof approximately TN = 296 K for Cr2O3 [1].
We fabricated a trilayer film where an
antiferromagnetic insulator Cr2O3 is sandwiched
between a magnetic insulator YIG and a heavy metal
Pt film (Fig. 1a). Here, the YIG serves as a spincurrent source. By applying a temperature gradient,∇T, perpendicular to the film planes, the spin Seebeck
effect (SSE) [2] generates a spin accumulation at theinterface of YIG/Cr2O3, which drives a spin current(Jsin) into the Cr2O3 layer (Fig. 1b). The spin currents
transmitted through the Cr2O3 layer to the Pt interface(Jsout) are converted into an electric voltage throughthe inverse spin Hall effect (ISHE).
Figure 2 shows the temperature dependence of
the SSE voltage VSSE at H = 0.1 T for the YIG/Cr2O3/
Pt trilayer device. Surprisingly, the voltage exhibits anabrupt change of more than 100 times around the
Néel temperature of TN = 296 K. The results indicatethat the spin-current transmissivity Ts = Jsout/Jsin of
Cr2O3 changes by more than 100 times atapproximately TN. We also found that the spin-current
transmissivity Ts of Cr2O3 has an anisotropic responseto the applied magnetic field H and exhibits a nearly
500% increase under the application of a magnetic
field slightly below TN (see the inset in Fig. 2). These
results indicate that the device operates as a spincurrent switch when crossing the TN of Cr2O3 orapplying a magnetic field. These results are explained
through a combination of the anisotropic spin-current
transmission of the antiferromagnet and the device

Fig. 1 (a) A cross-sectional TEM image of the YIG/Cr2O3/
Pt trilayer device used in this study. (b) A schematic
illustration of the spin-current transmission in YIG/
Cr2O3/Pt induced by the SSE in YIG.

Fig. 2 The temperature dependence of the SSE voltage
VSSE at H = 0.1 T for the YIG/Cr2O3/Pt trilayer device
with a Cr2O3 thickness of 12 nm. The inset shows thetemperature dependence of the Ts change ratio,
Ratio(Ts)@H, at several H values when the magnetic field
H having an out-of-plane component is applied.

geometry, which is correlated with the Néel vector
and the anisotropy of Cr2O3 [1].
References[1] Z. Qiu, D. Hou, J. Barker, K. Yamamoto, O. Gomonay, and E.
Saitoh, Nat. Mater. 17, 577 (2018).
[2] K. Uchida, H. Adachi, T. Kikkawa, A. Kirihara, M. Ishida, S.
Yorozu, S. Maekawa, and E. Saitoh, Proc. IEEE 104, 1946(2016).

Keywords: spintronics, spin current, antiferromagnets
Takashi Kikkawa and Eiji Saitoh (Surface and Interface Research Laboratory)
E-mail: t.kikkawa@imr.tohoku.ac.jp, eizi@imr.tohoku.ac.jp
URL: http://saitoh.imr.tohoku.ac.jp/

28

IMR KINKEN Research Highlights 2019

IMR KINKEN Research Highlights 2019

Taking Aim at the Surface State in Topological Insulator Films

A

thin-film fabrication and Fermi-level tuning of a three-dimensional topological insulator (3D-TI) are essential
for observing the exotic physical properties originating from Dirac electronic states. In this study, we succeededin the thin-film growth of a representative 3D-TI Bi2Se3 and control of its Fermi level through chemical doping
and an electrostatic gating technique. Our achievements will pave the way for an exploration of novel quantum
phenomena based on the surface states of 3D-TI.
(a)

(b)

EF

(c) 2015
Rxx (kΩ)A three-dimensional topological insulator (3DTI) (known as a newly discovered class of materials)
consists of an insulator in its interior but contains a
metallic state at its surfaces (Fig. 1(a)) [1,2]. The
metallic surface state hosts a linearly dispersive
electronic band, called a Dirac band (green area in
Fig. 1(b)). The emergence of exotic physicalproperties is anticipated in a Dirac-like surface bandof 3D-TIs.
To observe the Dirac features from an electricaltransport, a tuning of the Fermi-level (EF) into thebulk band gap is required. However, Bi2Se3, atypical 3D-TI, tends to be an n-type degenerate
semiconductor, leaving EF in the bulk conduction
band (gray in Fig. 1(b)). To tackle this issue, we
attempted to control EF in thin films andheterostructures.
A molecular-beam epitaxy (MBE) has beenutilized to grow Bi2Se3 -based alloy thin films. The(Bi1-x Sbx)2Se3 layers were epitaxially grown on asemi-insulating InP(111) substrate with an
isostructural Bi2Se3 buffer layer [3]. We observed aclear conversion of the carrier type from an n-type
to a p-type by increasing the Sb composition while
maintaining the topological nature, which
demonstrates the successful tuning of EF into thesurface state.
Aiming at further precise control of EF, wefabricated a field-effect transistor based on achannel consisting of a (Bi0.26Sb0.74)2Se3/Bi2Se2
bilayer, as schematically shown in the inset of Fig.
1(c) [4]. The gate-voltage (VG) dependence of thechannel resistance (Rxx) exhibits a clear peak (redline), which is absent in a non-doped Bi2Se3 layer(black line). Such a marked VG dependence of Rxx isa characteristic of a Dirac electron system, with EF
scanned by VG across the charge-neutral point.
The developed EF tuning techniques provide a
new arena of Bi2Se3 heterostructures for the
exploration of exotic phenomena in a Dirac surface
state.

10
5
0
-80

VG
Au/Ti
In Parylene In(Bi,Sb)2Se3
17 nm
Bi2Se3 3 nm
Sub.

EF
EF

B=0T
T = 1.5 K

Bi2Se3-400
VG (V)

40

80

Fig. 1 (a) Schematics of helical surface state of a 3D
topological insulator and (b) energy dispersion of the
Dirac (green) and bulk (gray) bands. (c) Gate-voltage(VG) dependence of the sheet resistance (Rxx) in fieldeffect transistors based on non-doped Bi2Se3 (black)and (Bi0.26Sb0.74)2Se3 films (red).

References[1] X. L. Qi and S. C. Zhang, Rev. Mod. Phys. 83, 1057 (2011).
[2] Y. Tokura, K. Yasuda, and A. Tsukazaki, Nature Rev. Phys. 1,
126 (2019).
[3] Y. Satake, J. Shiogai, D. Takane, K. Yamada, K. Fujiwara, S.
Souma, T. Sato, T. Takahashi, and A. Tsukazaki, J. Phys.
Condens. Matter 30, 085501 (2018).
[4] Y. Satake, J. Shiogai, K. Fujiwara, and, A. Tsukazaki, Phys.
Rev. B 98, 125415 (2018).

Keywords: topological insulator, molecular-beam epitaxy (MBE), thin films
Junichi Shiogai (Low Temperature Physics Research Laboratory)
E-mail: junichi.shiogai@imr.tohoku.ac.jp
URL: http://mu.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201929

Electronic Materials

Self-Assembled Structure and Related Mesoscopic TwoDimensional Charge Transport in Conductive Polymer Films

T

he self-assembled structure and related charge-transport properties in a conductive polymer PEDOT:PSS
were revealed by using high-resolution wide-angle X-ray scattering with synchrotron radiation andmagnetotransport studies. The results indicate that a mesoscopic two-dimensional coherent transport can berealized owing to the self-assembled laminated structure in a polymer film.
Poly (3,4-ethylenedioxythiophene):poly(styrene
sulfonate), abbreviated as PEDOT:PSS, is one of themost commonly utilized conducting polymers inorganic electronics. Its electrical conductivity
exceeding 1,000 S/cm has been achieved throughan improvement of the film fabrication process.
Despite such progress, the charge-transportmechanism is still under debate and remains
unresolved. The electrical properties of PEDOT:PSS
films are strongly related to their complicatedmacromolecular structures [1], and hence
clarification of the correlations between theirelectrical and structural properties is an active
research area in polymer science. We haveattempted to reveal this issue through simultaneous
structural and transport experiments [2].
The inset in Fig. 1 shows a schematic illustrationof a PEDOT:PSS film structure based on grazingincidence wide-angle X-ray scattering (GIWAXS)
experiments conducted using synchrotron radiation
light (SPring-8, BL40B2). We investigated that highly
conductive PEDOT:PSS films with nearly 1,000 S/cm
at room temperature have a nanometer-scale selfassembled laminated structure, which is composedof PEDOT nanocrystals wrapped by insulating
sheets consisting of amorphous PSSs. Thislaminated structure has a characteristic period of~3.0 nm along the vertical direction.
To elucidate the charge-transport mechanism
within such a self-assembled structure in detail, we
conducted
high-fieldmagnetoconductancemeasurements at up to 15 T [2]. Interestingly, weobservedaremarkable
positivemagnetoconductance at low temperatures, whichindicates the existence of the weak localization
effects,
as
shown
in
Fig.
1.
These
magnetoconductance curves are quite anisotropic
and show good agreement with the theoreticalmodel of a two-dimensional weak localization. The
inelastic scattering length obtained, i.e., the average
distance a charge travels between inelastic
collisions, is approximately 3.5 nm at 100 K and

Fig. 1 Magnetconductance curves at various temperatures.
The inset shows a schematic of the film structure basedon X-ray scattering experiments conducted at SPring-8.

increases with a decrease in temperature.
Importantly, if a charge is confined within a layer
thinner than the inelastic scattering length, thecharge transport is regarded as a two-dimensional
system from the viewpoint of not only the absolute
conductivity but also the electronic coherence. Thiscondition can be satisfied at below 100 K; that is,
the results strongly suggest that the motion ofelectrons is confined within the laminated structure
at low temperatures. The results indicate that a twodimensional coherent transport can be realizedeven in polymer films fabricated using a simple
drop-casting method for commonly used materials.
References[1] T. Takano, H. Masunaga, A. Fujiwara, H. Okuzaki, and T.
Sasaki, Macromolecules 45, 3859 (2012).
[2] Y. Honma, K. Itoh, H. Masunaga, A. Fujiwara, T. Nishizaki, S.
Iguchi, and T. Sasaki, Adv. Electron. Mater. 4, 1700490 (2018).

Keywords: polymer, GIWAXS, magnetoconductance
Takahiko Sasaki (Low Temperature Condensed State Physics Research Laboratory)
E-mail: takahiko@imr.tohoku.ac.jp
URL: http://cond-phys.imr.tohoku.ac.jp/30

IMR KINKEN Research Highlights 2019

IMR KINKEN Research Highlights 2019

Reduction Annealing Effects on Electronic States in T’-Structured
Cuprates Studied by X-Ray Absorption SpectroscopyBoth cation-site substitution and post annealing in a reducing atmosphere are key treatments for the
emergence of superconductivity in T’-structured cuprates. To reveal the effects of reduction annealing on theelectronic states, we conducted a Cu K-edge X-ray absorption spectroscopy study on superconducting andnon-superconducting T’-structured Pr2-x Cex CuO4+α- δ (PCCO) samples. An X-ray absorption near-edge structure(XANES) shows a clear increase in the number of electron carriers in the annealed samples. Based on thisresult, we suggest that the annealing effect on PCCO is qualitatively equivalent to that of the cation, e.g., Ce,substitution. Furthermore, an analysis of the XANES spectra indicates that, in addition to electrons, hole carriers
possibly exist in heavily doped Pr2-x Cex CuO4+α- δ samples.
as-sintered Pr2-xCexCuO4+α-δAbsorption coefficient (a.u.)

1.4

x=0
x = 0.04
x = 0.08
x = 0.12
x = 0.16
x = 0.18
x = 0.20
Cu2O Cu+ 1s-4pπ

1.2
1.0
0.8
0.6

0.4

C

D 1s-4pσ

0.3
0.2

0.4

0.1

A

0.2
0
8970

8980

1s-4pπ

B 0.0

8975

8980

8990
Energy (eV)

8985

9000

9010

Fig. 1 Cu K-edge absorption near-edge spectra for the assintered Pr2-x Cex CuO4+α-δ. The spectrum of Cu2O is shown asa reference.

annealed Pr2-xCexCuO4+α-δ
0.10

0.10

x=0

x = 0.08

0.08

IAN (a.u.)

0.08
x = 0.12

0.06

x = 0.16

0.04

0.04

x = 0.08
x = 0.12

0.02
0

0.06

x=0

annealed 900 °C
annealed 940 °C
0

0.01

0.02
0.03
Oxygen Loss δ

0.04

nAN (per Cu)

RE2-xCexCuO4 (RE = Pr, Nd, Sm, Eu) with a T'type structure is a family of high-temperature
superconductors. In this system, both Ce substitution
and reduction annealing are needed for an
emergence of the bulk superconductivity. Angleresolved photoemission spectroscopy studies haverecently revealed that the number of electrons per
Cu ion increases through an appropriate heat
treatment in a reducing atmosphere [1]. This result
suggests that the carrier concentration is strongly
affected by the non-stoichiometry of oxygen.
However, the relationship between the concentrationof oxygen vacancies, δ, and the carrier number has
yet to be clarified. Therefore, clarifying the effects ofannealing in a reducing atmosphere is an important
issue. In this study, we succeeded in estimating thecarrier concentration in PCCO through Cu K-edge
XANES measurements [2].
Figure 1 shows Cu K-edge XANES spectra for
as-sintered PCCO with x = 0 - 0.2. The XANES
spectra vary with the Ce substitution. A peak at
8980 eV corresponds to the 1s-4pπ dipole transitionsof Cu+ ions. The peak intensity gradually increases
with an increase in x, indicating an increase in thenumber of Cu+ ions. Because the number of Cu+
ions is proportional to the number of electron
carriers, we can evaluate the effective variation of
the carrier concentration by analyzing the change in
intensity at 8980 eV. In the as-sintered PCCO
system, we found that the number of electrons
evaluated, nCe, is proportional to x. In contrast, the
XANES intensity at 8980 eV shows a strange
variation as a function of oxygen loss δ, as displayedin Fig. 2. This means that the number of doped
electrons, nAN, in the annealed PCCO system is notequal to 2δ. Considering the charge neutrality, adeviation of nAN from 2δ suggests that two types ofcarriers are doped in the system.

0.02

0
0.05

Fig. 2 Variation of intensity of the Cu+ 1s-4pπ dipole transition as
a function of δ. The right axis shows the evaluated number ofelectrons per Cu ion. The solid line represents a relation of nAN= 2δ, which is expected from the charge naturality.

References[1] D. Song et al., Phys. Rev. Lett. 118, 137001 (2017).
[2] S. Asano et al., J. Phys. Soc. Jpn. 87, 094710 (2018).

Keywords: electronic structure, superconducting, XAFS
Masaki Fujita (Quantum Beam Materials Physics Research Laboratory)
E-mail: fujita@imr.tohoku.ac.jp
URL: http://qblab.imr.tohoku.ac.jp/ index.html

IMR KINKEN Research Highlights 201931

Electronic Materials

Surface Acoustic Wave on Multiferroics

M

ultiferroics are functional materials having both ferroelectricity and magnetism. The interplay between themgives rise to unique material functionalities such as a magneto-electric effect. Herein, we demonstrated themagnetic field dependent surface acoustic wave (SAW) propagation on the multiferroics BiFeO3 and CuB2O4.
This phenomenon is induced through an interplay between magnetism and piezoelectricity.
(a)[1-10]IMR KINKEN Research Highlights 20197T

[11-2]

H
θ

0.1

6T

k

0.5 mm

-40

(b)

First

5T

∆R/R

-35

Third

-45

4T

-50
-55

3T

-60

1T

-65
-70
0

50 100 150 200
Frequency (MHz)250

θ (deg.)Fig.1 (a) Optical microscope image of BiFeO3 device. The
two IDT electrodes are deposited on a BiFeO3 single
crystal. (b) Transmission spectrum between two IDTs.
The sharp peak at approximately 50 MHz is induced
through SAW propagation. (c) The relative change of
the SAW propagation amplitude as a function of theangle of the magnetic field at various magnitudes.

antiferromagnetic
magnons.
Magnetic
field
modulation through coupling is also observed.
References[1] Y. Ishii, R. Sasaki, Y. Nii, T. Ito, and Y. Onose, Phys. Rev.
Applied 9, 034034 (2018).
[2] R. Sasaki, Y. Nii, and Y. Onose, Phys. Rev. B 99, 014418(2019).

Keywords: multi-ferroics, piezoelectric, devices
Yoshinori Onose (Quantum Functional Materials Physics Research Laboratory)
E-mail: onose@imr.tohoku.ac.jp
URL: http://onoselab.imr.tohoku.ac.jp/index.html

32

(c)

BiFeO3Al[111]

S12 (dB)

A surface acoustic wave (SAW) is an elastic
wave propagating on the surface of a material. The
excitation and detection of a SAW can be achieved
using an interdigital transducer (IDT) on a
piezoelectric material. As shown in Fig. 1(a), the IDT
is composed of a pair of comb-like electrodes. Only
when the SAW wavelength coincides with twice thesum of the finger width and space, the IDT can
operate as a SAW electromagnetic wave transducer,
and the electromagnetic signal can transmit fromone IDT to another through SAW propagation. In thisway, a device composed of two IDTs on a
piezoelectric substrate operates as a band passfilter. A SAW filter can be considerably miniaturized,
and thus such band-pass filters are widely appliedin electronics used in small spaces. If the substrateof a SAW band-pass filter device is replaced with amultiferroic material, the transmission strength andfrequency can be controlled using an external
magnetic field. The novel functionality of a field
tunable band-pass filter seems to be useful for
future high-frequency electronics.
We observed SAW propagation on a multiferroic
BiFeO3. Figure 1(b) shows the transmittance
between the IDTs for the BiFeO3 SAW device. A
sharp peak is discerned at approximately 50 MHz.
This peak is induced by SAW propagation between
the IDTs. The broad peak at approximately 150 MHz
is the remnant of the third harmonics. To study theeffects of multiferroicity on the SAW propagation, weinvestigated the magnetic field variation of SAW
propagation. Figure 1(c) shows the transmission
change as a function of the magnitude and angle ofthe magnetic field for the BiFeO3 SAW device. The
SAW transmission becomes dependent on theangle of the magnetic field in a high field region. The
magnetic field dependence can be explained
based on the magnetoelastic coupling in ahelimagnetic state, as detailed in [1]. We also
observed SAW propagation in other multiferroic
CuB2O4 [2]. We fabricated the IDTs using a finger
period of 800 nm. As a result, SAW excitation
reaches as high as 3 GHz and is coupled to theIMR KINKEN Research Highlights 2019

Hydrogen Behavior in Al2O3/HfxSi1-xO2/SiO2 Gate Dielectric
Stacks in Memory Device Structures Analyzed by Atom
Probe Tomography

Hydrogen (H) plays an important role in determining the reliability and performance of high-k dielectric

electronic memory devices. To understand the H behavior, deuterium (D), an isotope of H, was introduced intoa poly-Si cap of Al2O3/HfxSi1-xO2/SiO2 high-k stacks. Our results obtained through atom probe tomographydemonstrated that Al2O3 blocks the H atoms at the surface, preventing them from diffusing into the high-k
dielectrics during the H2 annealing process.
Hf Si OAl2O3 x 1-x 2 SiO2

(a)Native oxide

Poly-Si

Si(100)substrate

D implantation

Analysis region:
φ20 x 50 nm cylinder

8
6
4
2
0

0

50

(b) Si Al Hf O p2

100
Depth (nm)D-implanted

150

200

(c)

600 K 10 min

900 K 10 min

0.8
Concentration of p2 (ionic %)Expected D
concentration( x1021 cm-3)

Aluminum oxide (Al2O3) can be used in
combination with high-permittivity (high-k) materials
based on hafnium oxide (HfO2) as gate dielectrics in
non-volatile memory devices. In general, hydrogen(H2) sintering, i.e., annealing in H2 ambient in the
back-end-of-line (BEOL) process, is required toacquire a high-quality interface. However, excess
H2 diffusion into the substrate or dielectric region
can affect the device performance. The exact
mechanism or trapping capability in metal oxides
has yet to be properly investigated. It has beensuggested that control of the H species diffusion
should be taken into consideration during theprocess optimization from the viewpoint of reliability.
Laser-assisted atom probe tomography (APT)
has been proven useful to obtain three-dimensional
atom maps of semiconductor materials [1, 2]. Aswith other conventional techniques, observation
and a quantitative analysis of H remain difficult in
APT owing to the absorption of H atoms fromresidual gas in the analysis chamber as an artifact
during the measurement. Therefore, we implanted
deuterium (D), an isotope of H, into the samples at ahigh dose to distinguish it from H in the residual gas.
Here, we report an APT study of ion-implanted D
behavior in Al2O3/HfxSi1-xO2/SiO2 (AHO) high-k
stacks with poly-Si cap, as shown in Fig. 1(a), under
different annealing temperatures [3].
Figure 1(b) shows atom maps of elements
containing the AHO as-implanted regions, annealed
at 600 or 900 K for 10 min. Peak 2 (p2) of the massto-charge state ratio obtained from the APT mass
spectrum is defined as D. In the sample annealed at
900 K for 10 min, a clear segregation of p2 wasobserved (Fig. 1(c)), meaning that the D atoms
diffused toward the AHO region and becametrapped at the poly-Si/Al2O3 interface. This indicatesthat the use of Al2O3 can effectively prevent H
diffusion at the interface during the BEOL process.

D-implanted
600 K 10 min
900 K 10 min

0.6

0.4

0.2

0
10 nm

0

10 20 30 40
Distance (nm)50

Fig.1 (a) Schematic illustration of the sample structure andthe expected D concentration on the basis of simulation.
(b) Atom maps and (c) concentration profiles of peak 2
in a φ20x50 nm cylinder containing the AHO regions
processed under different conditions.

The current study provides an example of the H
behavior in semiconductors using APT.
References[1] A. D. Giddings, S. Koelling, Y. Shimizu, R. Estivill, K. Inoue, W.
Vandervorst, and W. K. Yeoh, Scripta Mater. 148, 82 (2018).
[2] Y. Tu, Y. Shimizu, Y. Kunimune, Y. Shimada, T. Katayama, T.
Ide, M. Inoue, F. Yano, K. Inoue, and Y. Nagai, J. Appl. Phys.
124, 155702 (2018).
[3] Y. Tu, B. Han, Y. Shimizu, Y. Kunimune, Y. Shimada, T.
Katayama, T. Ide, M. Inoue, F. Yano, K. Inoue, and Y. Nagai,
Appl. Phys. Lett. 112, 032902 (2018).

Keywords: atom probe tomography, hydrogen implantation, electronic material
Yasuo Shimizu, Koji Inoue, Kazuaki Nagumo, and Yasuyoshi Nagai (Irradiation Effects in Nuclear and Their RelatedMaterials Research Laboratory)
E-mail: yshimizu@imr.tohoku.ac.jp
URL: http://wani.imr.tohoku.ac.jp/index.html

IMR KINKEN Research Highlights 201933

Electronic Materials

History of Research on Nitride Semiconductors and Recent Results

Since the proposal of the material InGaAlN for blue-emitting diodes in 1986 and the success in the epitaxial growthof single-crystalline InGaN as a blue-light emitting material in 1989 by Nippon Telegraph & Telephone, research has
continued on the new field of nitride semiconductors as materials and their device applications to realize a sustainable
society, in the Department of Electronic Materials of the Institute for Materials Research for more than 14 years till theretirement at the end of March 2019. The main themes and the recent results are shown below.

2. High-quality InN epitaxial growth
InN is the last immerging material among nitride
semiconductor InGaAlN. For a long time, a single
crystalline InN has not been obtained, because of theextremely high equilibrium vapor pressure of nitrogen.
Single-crystalline InN was obtained by using theN-polar growth and the pressurized-reactor MOVPE
system developed in-house. This result can extend theemitting wavelength region of InGaAlN to the infrared.

electrons
as carriers

Sapphire Substrate

Fig. 1 Structure of N-polar HEMT

500
400
ID (mA/mm)

Historical Research
1. 
Crystalline polarity originated from wurtzite
N-Polarity GaN on Sapphire Substrate Grown by
MOVPE
Ga-polar GaN used in blue LEDs was used on(0001) sapphire by metalorganic vapor-phase
epitaxy (MOVPE). N-polar GaN with the samecharacteristics as G-polar one was successfullygrown. This result gives the flexibility for device
design, because the direction of the spontaneouspolarization depends on the polarity.

300
200
100
0

3. Measurement of internal electric fields
A nitride semiconductor has a strong polarizationinduced internal electric field, which affects thedevice performance. The direct measurement of theinternal electric field was done successfully.
4. Observation of dislocation in GaN
A three-dimensional imaging of threading
dislocations in GaN was demonstrated by using
multiphoton-excitation photoluminescence [1]. Thismethod can be considered a novel method forcharacterizing defects in GaN films without any
destructive preparations.
Recent Result
An N-polar high-electron-mobility transistor(HEMT) consists of a structure advantageous tohigh-performance device characteristics for a shortlength of a gate, because the channel at the top
surface makes the carrier confinement high.
Because the N-polar growth is said to be difficult

IMR KINKEN Research Highlights 20192

4

6
VDS (V)

8

10

Fig. 2 Source–drain voltage vs. drain current

from compared with the Ga-polar one, there are notso many reports on these devices. By optimizing the
growth conditions, including the off-cut angle of asapphire substrate, it was possible to obtain the
HEMT structure without hillocks and step-bunching.
A HEMT was also fabricated, and the operation offield-effect transistors was confirmed. Suppressing
the step-bunching by using a small off-cut angle
made it possible to obtain the device characteristics
with less anisotropy, compared with the previously
reported N-polar HEMT [2]. This result is very
important for the device design.
References[1] T. Tanikawa, K. Ohnishi, M. Kanoh, T. Mukai, and T. Matsuoka,
Appl. Phys. Express 11, 031004 (2018).
[2] K. Prasertsuk, T. Tanikawa, T. Kimura, S. Kuboya, T. Suemitsu,
and T. Matsuoka, Appl. Phys. Express 11, 015503 (2018).

Keywords: nitride semiconductors, GaN, epitaxial growth
Takashi Matsuoka (Physics of Electronic Materials Research Laboratory)
E-mail: matsuoka@imr.tohoku.ac.jp
URL: http://www.matsuoka-lab.imr.tohoku.ac.jp

340IMR KINKEN Research Highlights 2019

Gas-Responsive Porous Magnet Distinguishes the Electron
Spin of Molecular Oxygen

Gas-sensing materials are of increasing societal importance, although differentiating between similarly sizedgases such as N2 and O2 remains a significant challenge. Herein, we report a porous ferrimagnet that
distinguishes diamagnetic N2 and CO2 gases from paramagnetic O2 gas.

Studies on molecular porous materials, socalled metal-organic frameworks (MOFs), haveattracted significant attention, in which the design ofgas-responsive magnetic materials is a critical issue.
We reported a compound responsive to an organicsolvent vapor showing a drastic change in themagnetic ordering temperature (TC) [1]. Nevertheless,a lack of candidates in magnetic materials responsive
to common gases such as N2, CO2, and O2 is rather
curious. Herein, we report the first porous magnetic
material whose magnetic phases are switchable
through gas adsorption/desorption, i.e., a gasresponsive porous magnet [2].
A porous ferrimagnet with TC = 76 K, which iscomposed of a 2:1 assembly of a paddlewheel-type
diruthenium(II,II) complex and a derivative of
7,7,8,8-tetracyano-p-quinodimethane(TCNQ),
exhibits reversible gas sorption properties for N2,
CO2, and O2, accompanying a structural modulation.
Whereas the uptake of N2 and CO2, despite their
diamagnetic characteristics, leads to an increase of
TC to 88 K and 92 K, respectively, the uptake of O2
reveals a continuous phase change from aferrimagnet involving the increase of TC at low gaspressures to an antiferromagnet at high gaspressures (Fig. 1a). The observed increase of TC
through a gas insertion is explained by a gasinduced structural modification, i.e., the modificationof magnetic pathways, whereas the insertion ofparamagnetic O2 induces a magnetic phase switch
between a ferrimagnet and an antiferromagnet
based on the formation of new magnetic pathways
which O2 itself mediates (Fig. 1b). The magnetic
switching between a ferrimagnet and an
antiferromagnet is quite fast and reversible (Fig. 1c).
This chameleonic material, the first with switchable
magnetism that can discriminate between similarly
sized N2 and O2 gases, provides a wide scope of
new gas-responsive porous magnets.
References[1] J. Zhang, W. Kosaka, K. Sugimoto, and H. Miyasaka, J. Am.

Fig. 1 (a) Temperature dependence of magnetization
under O2. (b) Crystal structure of O2-adsorbed phasefocused on adsorbed O2 and scheme of the magnetic
moment alignment. (c) ON/OFF switching ofmagnetization through O2 desorption/adsorption at 85
K and Hdc = 100 Oe.

[2] W. Kosaka, Z. Liu, J. Zhang, Y. Sato, A. Hori, R. Matsuda, S.
Kitagawa, and H. Miyasaka, Nat. Commun. 9, 5420 (2018).

Chem. Soc. 140, 5644 (2018).

Keywords: ferromagnetic, antiferromagnetic, porosity
Wataru Kosaka and Hitoshi Miyasaka (Solid-State Metal-Complex Chemistry Research Laboratory)
E-mail: w-kosaka@imr.tohoku.ac.jp (W. K.); miyasaka@imr.tohoku.ac.jp (H. M.)
URL: http://www.miyasaka-lab.imr.tohoku.ac.jp/cn5/HOME-Eng.html

IMR KINKEN Research Highlights 201935

Electronic Materials

Crystallization “Manipulated” by Plasmonic Optical Tweezers

Control of the crystallization by an external field impacts the creation of functional crystalline materials. Herein,

we show that plasmonic optical tweezers, the trapping force of which relies on an electrical field gradient
generated by the plasmonic near-field within the proximity of a metal nanostructure, can reversibly “manipulate”
the crystallization/dissolution of a dielectric material in a solution.

Completespatiotemporalcontrolofcrystallization through an external field impacts not
only the technology used to create functional
crystalline materials but also the exploration during
the early stage of dynamics of crystallization hiddenin the stochastic nature of nucleation. Tremendous
efforts have been recently devoted to the control ofcrystallization by trapping dielectric molecularclusters in a solution using optical tweezers, thetrapping force of which relies on the gradient of theelectrical field generated by focusing a laser with an
optical lens [1]. This strategy has induced a forced
crystallization even from an unsaturated solution.
However, light focusing applied to enhance thetrapping force is intrinsically limited by the diffraction
limit of the optical lens, hindering an increase in thecontrollability. To overcome this limitation, in thepresent study, we applied a near-field confinedbeyond the diffraction limit generated by the surface
plasmon resonance (SPR) on a metal nanostructure.
A Au gammadion nanolattice was fabricated ona cover glass using electron beam lithography (Fig.
1a). An aqueous solution of acetaminophen
saturated at room temperature (24 °C) was dropped
on the nanolattice, and a thin layer solution was thenformed by the capillarity. Continuous-wave circularly
polarized laser (λ = 1,064 nm, 6.4×109 W/m2) was
focused on the nanolattice to excite the SPR throughan objective lens on an optical microscope while
conducting in-situ observations.
The plasmon excitation allowed molecules tocrystallize in an annular distribution with a size of
1,000 nm for each crystal (Fig. 1b). A numericalanalysis of the electromagnetic field and temperature
distribution measurement indicate that the annularpattern is probably a consequence of the balance
between the electrical field gradient force toward
the focal spot and the opposite thermophoretic
force from plasmonic heating [2, 3]. The position of
the pattern was found to be manipulatable througha coupled dissolution/precipitation process bymoving the position of the focal spot. The stoppingof the plasmon excitation resulted in a disappearanceof the crystals through an unprecedented two-step
Keywords: nucleation & growth, metal, nanostructure
Hiromasa Niinomi (Crystal Chemistry Research Laboratory)
E-mail: h.niinomi@imr.tohoku.ac.jp
URL: http://www.uda-lab.imr.tohoku.ac.jp

36

IMR KINKEN Research Highlights 2019

Fig. 1 (a) Experimental setup and electrical field
distribution analyzed using FDTD method. (b) In-situ
observation of crystallization dynamics.

dissolution process, and the transformation into
liquid droplets followed through relaxation bydiffusion. Our results indicate that plasmonic opticaltweezers can “manipulate” the crystallization
precisely, and lead to unprecedented phenomena.
References[1] K. Yuyama, M. J. Islam, K. Takahashi, T. Nakamura, and V.
Biju, Angew. Chem. Int. Ed. 130, 13612 (2018).
[2] H. Niinomi, T. Sugiyama, S. Uda, M. Tagawa, T. Ujihara, K.
Miyamoto, and T. Omatsu, Cryst. Growth Des. 19, 529 (2019).
[3] T. Shoji and Y. Tsuboi, J. Phys. Chem. Lett. 17, 2957 (2014).

IMR KINKEN Research Highlights 2019

Splitting Fermi Surfaces in Non-Centrosymmetric Heavy
Fermion Compound U3Ni3Sn4

We investigated the Fermi surface properties on non-centrosymmetric heavy fermion compounds U Ni Sn
33

4

based on de Haas-van Alphen experiments using a high-quality single crystal. Many closed Fermi surfaces
with heavy effective masses of up to 35 m0 were clearly detected. Compared to the LDA band structure
calculations, it was determined that they originate from the splitting band owing to an antisymmetric spin-orbit
coupling. To the best of our knowledge, the splitting Fermi surface from the non-centrosymmetric nature of
5f-electron systems was detected experimentally for the first time.

Non-centrosymmetriccompounds
have
attracted significant attention owing to theiranomalous behaviors such as unconventional
parity-mixing superconductivity, magnetic skyrmion,
multipole orders, and chiral fermiology. Spin-orbit
coupling plays an important role in thesecompounds. Actinide compounds are particularly
important targets in this context, because 5f
electrons of actinide elements have a large spinorbit coupling and the electron correlations arestrong.
We grew single crystals of a noncentrosymmetric compound, U3Ni3Sn4, using theBridgeman method and measured the them throughde Haas-van Alphen (dHvA) experiments [1]. The
residual resistivity ratio (RRR) is 300, indicating avery high quality of the obtained single crystals.
U3Ni3Sn4 is a paramagnet with a cubic structure(space group: #220, I43d). A large Sommerfeld
coefficient shows a heavy electronic state, and it istherefore believed that U3Ni3Sn4 is located at theverge of the antiferromagnetic quantum criticalpoint.
Figure 1 shows typical dHvA oscillations andthe corresponding FFT spectrum. Many fundamental
FFT peaks were detected, indicating many Fermi
surfaces. The angular dependence of the dHvA
frequencies is in good agreement with the results of
the LDA band structure calculations. It was foundthat most of the Fermi surfaces are spherical inshape, derived from 12 bands crossing the Fermi
energy. In Fig. 1, the calculated Fermi surfaces forbranches β and β’ are also shown. The bands are
split owing to the antisymmetric spin-orbit coupling,
and the splitting energy is estimated to be 20–100
K. The relatively small splitting energy is most likely
due to the large effective mass.
This work was conducted in collaboration with
A. Maurya, H. Harima, A. Nakamura, Y. Shimizu, Y.
Homma, D.X. Li, F. Honda, and Y. J. Sato.

Fig. 1 Typical dHvA oscillations and the corresponding
FFT spectrum in a non-centrosymmetric heavy fermion
compound, U3Ni3Sn4. The calculated splitting Fermi
surfaces (branches β and β’) due to the antisymmetricspin-orbit coupling are shown on the left-hand side.

References[1] A. Maurya, H. Harima, A. Nakamura, Y. Shimizu, Y. Homma, D.
X. Li, F. Honda, Y. J. Sato and D. Aoki: J. Phys. Soc. Jpn. 87,
044703 (2018).

Keywords: superconducting, heavy fermion, fermi surface
Dai Aoki (Actinide Materials Science Research Laboratory)
E-mail: aoki@imr.tohoku.ac.jp

IMR KINKEN Research Highlights 201937

Electronic Materials

Formation of ZrO2-Based Ferroelectric Thin Films

F

erroelectricity in epitaxially grown Fe-doped ZrO2 thin films has been demonstrated. The structures of the
30-nm-thick xFe2O3 -(1−x)ZrO2 thin films (x = 0, 0.03, 0.05, and 0.07, nominal composition) have been examinedby X-ray diffraction and scanning transmission electron microscopy, revealing that the monoclinic phase (spacegroup: P21/c) dominates for x = 0, while the films containing Fe exhibit multidomain structures consisting of themonoclinic and orthorhombic phases.
Ferroelectric thin oxide films have been
extensively studied as a key material in electronic
applications, including nonvolatile memories andlow-power transistors. Among them, hafnia (HfO2)and zirconia (ZrO2)-based thin films, which areenvironmentally friendly and thermodynamicallycompatible with Si substrates, have recently attracted
much attention since the discovery of ferroelectricity
in a Si-doped HfO2 thin film. The dielectric propertiesof these oxide films are directly related to their crystal
structures, and the basic phase transition schemefrom high to low temperatures is cubic (c), tetragonal(t), and monoclinic (m). The m-phase (a = 0.515, b =0.520, and c = 0.532 nm, β = 99.25o)is nonpolar andexhibits a simple dielectric behavior, while theemergence of ferroelectricity is ascribed to the polar
orthorhombic phase (o, space group: Pbc21,a =0.507, b = 0.526, and c = 0.508 nm), and much effort
has been devoted to the stabilization of the polarphase.
In this study, epitaxial ZrO2 thin films have been
formed on(100)YSZ and (100)ITO//(100)YSZ
substrates (YSZ: yttria stabilized zirconia, ITO:
indium tin oxide) by sputtering and postannealing.
[1, 2] The sputtering targets were prepared bypressing the mixture of Fe2O3 and ZrO2 powders.
The crystal structure was investigated by using and
X-ray diffractometer. The microstructure wasobserved by high-angle annular dark-field scanningtransmission electron microscopy (HAADF-STEM)
operating at 200 kV, with the convergent semiangle(α) and acceptance semiangle of the HAADF
detector (β in-β out) set to 20 and 90-175 mrad,respectively.
Figure 1(a) shows cross-sectional HAADFSTEM images of 0.03Fe2O3 -0.97ZrO2 thin films,
deposited on the (100) YSZ substrates. Bright spots
indicate heavy atoms, i.e., cations. As seen, thefilms are composed with the regions having different
crystallographic orientation, or domains. As seen,
no misfit dislocation has been observed at theinterface. That is, the interface is coherent. Yet, thedark contrast suggests the presence of coherent

Fig. 1 (a) Cross-sectional HAADF-STEM images of the
0.03Fe2O3 -0.97ZrO2 thin films on YSZ substrates
viewed along the 100 axis of the substrate, and (b), (c),and (d) simulated HAADF-STEM images of the o-phase(Pbc21) for O1, O2, and O3 domains, respectively

strain within the film — especially, near the substrate.
A comparison of the observed images with simulatedones, as in Figs. 1(b)-(d), reveals that, inside thefilm, m- and o-phases coexist, as indicated by M3,
O1, and O2, thereby forming a multidomain structure.
The contrasts in the vicinities of boundaries of these
domains are generally dark, indicating the presenceof strain fields.
References[1] S. Choi, T. Shiraishi, T. Kiguchi, T. Shimizu, H. Funakubo, andT. J. Konno, Appl. Phys. Lett. 113, 262903 (2018).
[2] T. Shiraishi,S. Choi, T. Kiguchi, T. Shimizu, H. Funakubo, andT. J. Konno, Jpn. J. Appl. Phys. 57, 11UF02 (2018).

Keywords: dielectric, oxide, thin films
Toyohiko J. Konno (Materials Science of Non-Stoichiometric Compounds Research Laboratory)
E-mail: tjkonno@imr.tohoku.ac.jp
URL: http://konno-lab.imr.tohoku.ac.jp/

38

IMR KINKEN Research Highlights 2019

Research Centers

IMR KINKEN Research Highlights 2019

ResearchResearch Centers

Actinide Oxide Ion Formation in Collision/Reaction Cell of
ICP-MS/MS
International Research Center for Nuclear Materials Science

A

+

1000
0
1000

500

0
3000

Np
+
Np
+
Np

+

Np
+
NpO
+
NpO2

2000

+

+

Pu
+
PuO
+
PuO2

+

1000

0
40000

+

+

20000

600
+

Am

Am

AmO

Am

AmO2

+
+

0

400

+

Am

+

200

+

0
+

Cm
+
Cm

1000

+

IMR KINKEN Research Highlights 2019

U
+
UO
+
UO2

Pu
+
Pu
+
Pu

+

Cm
+
CmO

500
0
0

50
O2 gas ﬂow rate / %100

Fig. 1 Oxygen gas flow rate effect on intensities of detected
ion species. 100% of flow rate is defined as 1.5 mL/minin nitrogen gas flow.

related to the 5f-electron orbital. From the results
obtained, we found the feasibility of an isobaric
discrimination through a comparison of the yieldusing different oxygen gas flow rates.
References[1] T. Suzuki, T. Yamamura, C. Abe, K. Konashi, and Y. Shikamori,J. Radioanal. Nucl. Chem. 318, 221 (2018).

Keywords: actinide, mass spectrometry
Tatsuya Suzuki (Corresponding Author, Nagaoka University of Technology)
E-mail: tasuzuki@vos.nagaokaut.ac.jp
Nagai Yasuyoshi (Head of International Research Center for Nuclear Materials Science)
E-mail: nagai@imr.tohoku.ac.jp
URL: http://www.imr-oarai.jp/

40

+

U
+
U
+
U

2000

AmO2 intensity /cps

The importance of a quantitative actinide andisotope ratio analyses has increased in the nuclear
and radioanalytical fields, namely, radio waste
management, nuclear forensics, and safeguards.
For actinide analyses, α-spectrometry and thermal
ionization mass spectrometry (TIMS) have beenused. Although these methods have high accuracy
and high precision, the measurement time is quite
long, and pretreatments are time-consuming. An
inductively-coupled plasma mass spectrometer(ICP-MS) has recently come to be used in actinide
analyses owing to a short measurement time. Fromthe viewpoint of an accurate and precise actinide
analysis, isobaric interferences are a critical issue
because actinides have many isotopes, such as
241Pu and 241Am. The mass shift when using
molecular ion formations in a collision/reaction cellof ICP-MS is one method with the potential of an
isobaric discrimination. Thus, we studied the oxide
molecular ion formations of actinides using oxygengas [1]. A quadrupole type ICP-MS/MS (Agilent
8900), which has two MSs and one collision/reaction
cell between them, was used in the present study.
The ions with a mass equivalent to each objective
actinide nuclide (M) were allowed through the firstMS, and the detected ions through the second mass
after the reaction with oxygen gas were M+, M16O+,
and M16O2+. The effect of the oxygen flow rate on
the oxide ion formation is shown in Fig. 1. The mass
shift of M+ → MO+ → MO2+ with an increase in theoxygen flow rate was confirmed for all actinides,
and this shift in actinides with a lower atomic number
occurs at a lower oxygen flow rate. It was also
confirmed that the oxide ion formation behaviors of
the lighter and heavier actinides on the oxygen flowrate are also substantially different. The difference inmolecular ion formations among the actinides canbe explained based on the electron configuration

Am , AmO intensity /cps
Signal intensity /cps
Signal intensity /cps
Signal intensity /cps
Signal intensity /cps

ctinide oxide ion formations in collision/reaction cells of ICP-MS/MS were investigated to explore thepossibility of an isobaric discrimination for actinide analyses. We found that the dominant ions are oxide ions,and the ratio of monoxide ion/dioxide ions increases with the atomic number under the same oxygen gas flow
rate. The percentages of actinide ions and oxide ions depend on the oxygen gas flow rate, and the number ofoxygen ions attached to actinides increases with the oxygen gas flow rate.

IMR KINKEN Research Highlights 2019

Contribution of Irradiation-Induced Small Dislocation Loops toHardening Mechanism of Nuclear Reactor Pressure Vessel
Steels Identified by Electron Microscopy
International Research Center for Nuclear Materials ScienceT

he number density and size distribution of dislocation loops in surveillance test specimens of a European pressurizedwater reactor were systematically evaluated using weak-beam scanning transmission electron microscopy, and theircontributions to hardening were more accurately calculated. The hardening caused by the dislocation loops was
revealed to be comparable with that by solute clusters, which provides important insight into understanding theembrittlement mechanism in RPV steels.
The International Research Center for Nuclear
Materials Science (IRCNMS) is the leading and globally
opened center in Japan for research of nuclear materials
and actinides. A collaboration between IRCNMS and theBelgian Nuclear Research Center as a new breakthroughon the life prediction of light-water reactor materials.
The irradiation embrittlement of reactor pressure
vessel (RPV) steels is a vital issue for ensuring the safe
operation of plants. Numerous studies have revealed thatthe origins of embrittlement are dislocation loops andsolute clusters. Both are induced by long-term neutron
irradiation. Contributions of solute clusters have been
identified as a main cause of the hardening using atom
probe tomography in the 2010's. However, the irradiationInduced small dislocation Loops does not show any
sufficient determination for their roles in the embrittlement.
Recently, IRCNMS developed the weak-beamscanning transmission electron microscopy (WB-STEM)[1], which makes it possible to quantify such dislocation
loops with higher resolution and without interference
artifacts in a large field of view. It provides considerable
accuracy about the number density measurement of
dislocation loops. We firstly applied the WB-STEM tovarious RPV surveillance test specimens to quantify the
number densities of irradiation-induced dislocation loops,
together with atom probe tomography and positronannihilation spectroscopy [2].
Low-Cu surveillance test specimens of a European
pressurized water reactor were irradiated to the fluencesof 1.3×1023, 3.4×1023, 8.2×1023, and 1.2×1024 n m-2,
called T1–T4, respectively. Solute clusters were densely
formed in the high fluences (T3 and T4) at a number
density of ~3×1023 m-3. The estimated hardening causedby solute clusters was more than half of the actual
hardening, indicating that solute clusters should be amain source of hardening in the high fluences. However,dislocation loops also formed in the high fluences (T3and T4), as shown in Fig. 1. The average size was ~4 nm

Fig. 1(a)–(d) Color intensity maps of WB-STEM images forsurveillance test specimens — (a) unirradiated, and (b)–(d) irradiated to the fluences of 3.4×1023 n m-2 (T2),
8.2×1023 n m-2 (T3), and 1.2×1024 n m-2 (T4)in diameter both for T3 and T4, and the number densities
were 1.3×1022 m-3 in T3 and 3.4×1022 m-3 in T4. These
number densities are approximately three times higher
than those in previous reports, implying the advantage of
WB-STEM. The hardening resulting from the dislocation
loops was also estimated, and it was revealed that thecontribution of the dislocation loops is comparable to thatcaused by solute clusters. This is an important insight fora more-precise understanding of the embrittlement
mechanism in RPV steels, especially in high fluences.
References[1] K. Yoshida, M. Shimodaira, T. Toyama, Y. Shimizu, K. Inoue, T.
Yoshiie, K. J. Milan, R. Gerard, and Y. Nagai, Microsc. 66, 120 (2017).
[2] M. Shimodaira, T. Toyama, K. Yoshida, K. Inoue, N. Ebisawa, K.
Tomura, T. Yoshiie, M. J. Konstantinovic, R. Gerard, and Y. Nagai,
Acta Mater. 155, 402 (2018).

Keywords: nuclear materials, radiation effects, STEM
Yasuyoshi Nagai (Head of International Research Center for Nuclear Materials Science)
E-mail: nagai@imr.tohoku.ac.jp
URL: http://www.imr-oarai.jp/

IMR KINKEN Research Highlights 201941

Research Centers

Fabrication of Non-Equilibrium Mono-Dispersed Particles by
Container-Free Solidification Process and Their Applications
Cooperative Research and Development Center for Advanced Materials

T

he Cooperative Research and Development Center for Advanced Materials has contributed to the researchand development of new materials and their fabrication processes to explore the possibility of their application
as multi-functional materials for future technologies under collaboration with universities and National research
institutes. Herein, we highlight our recent research and development activities on non-equilibrium alloys forindustrial application.
We study non-equilibrium alloys such as
amorphous alloys, metallic glasses, and nanocrystal
alloys along with other institutes and privatecompanies [1-4].
A container-free solidification process enables
molten alloys to quench a non-equilibrium structure
under an environment where nucleation issuppressed. In our research, mono-dispersed
particles were fabricated using a container-freesolidification process called a pulsated orificeejection method (POEM).
Figure 1 shows the outer appearance of Febased metallic glassy mono-dispersed particles
with a 370 µm diameter. It can be confirmed that theparticles obtained have a spherical shape and are
uniform in size. We also developed a high-precision
micro-viscous flow processing technique using asingle particle, and an evaluation method for thesoft magnetic properties of nanostructured materials
by applying a single spherical particle. Figure 2(a)shows an SEM image of the micro-gear preparedthrough our micro-viscous flow process as arepresentative micro-component. It was confirmedthat the micro-component produced consists of asingle amorphous phase and shows excellent
mechanical properties. Figure 2(b) illustrates theheat treatment temperature dependency of thesaturation magnetic flux density of a single Febased particle. Using our method, the number of
inner nucleation sites is reduced in an as-quenchedstate, resulting in homogenous nanocrystalline
grains after optimum annealing.
Our process has superiority regarding the
preparation of Fe-based metallic glasses with a low
glass forming ability. We are currently attempting tofind a new application with other alloy systems using
this technology.

Fig. 1 Outer appearance of Fe-based metallic glassy
mono-dispersed particles of 370 µm in diameter
prepared using a pulsated orifice ejection method.

Fig. 2 (a) SEM image of a micro-gear prepared using our
micro-viscous flow process as a representative microcomponent, and (b) heat treatment temperaturedependency of saturation magnetic flux density ofsingle Fe-based particle.

References[1] N. Yodoshi, S. Ookawa, R. Yamada, N Nomura, K. Kikuchi,
and A. Kawasaki, Mater. Res. Lett. 6(1), 100 (2018).
[2] N. Yodoshi, S. Ookawa, R. Yamada, A. Kawasaki, and A.
Makino, J. Alloy. Comp. 679,164 (2016).
[3] J. Luan, P. Sharma, N. Yodoshi, Y. Zhang, and A. Makino, AIP
Adv. 6, 55934 (2016).
[4] N. Yodoshi, R. Yamada, A. Kawasaki, Materia 55(4), 152(2016).

Keywords: metallic glass, nanostructure, magnetic properties
Noriharu Yodoshi (Cooperative Research and Development Center for Advanced Materials)
E-mail: ynoriharu@imr.tohoku.ac.jp
Naoya Masahasi (Head of Cooperative Research and Development Center for Advanced Materials)
E-mail: crdam@imr.tohoku.ac.jp
URL: http://www.crdam.imr.tohoku.ac.jp

42

IMR KINKEN Research Highlights 2019

IMR KINKEN Research Highlights 2019

2.5-GPa 25-T High-Pressure High-Field Electron Spin Resonance
System Using a Cryogen-Free Superconducting Magnet
High Field Laboratory for Superconducting Materials

Combining multiple extreme conditions is the one of the most effective ways to investigate quantum phasetransitions of matter. Here, the development of a 2.5-GPa high-pressure electron spin resonance probe with theworld’s highest-field cryogen-free superconducting magnet, whose maximum field reaches 24.6 T, is reported.
It was used to investigate a quantum phase transition of the orthogonal dimer spin system SrCu2(BO3)2.

The orthogonal dimer spin system SrCu2(BO3)2
shows a unique dimer ground state that is given by
the product of isolated dimer wave functions despite
the strong exchange couplings acting among twodimensional arrays of S = 1/2 spins. The decouplingis caused by strong frustration between two exchange
couplings in a triangular unit composed of two dimersconnected by large intradimer interaction. The
magnitude of the frustration depends on the ratio of
two exchange interactions, and the exact dimer
singlet ground state dominates the large range of theparameter space. Theoretically, another type ofsinglet state called the “plaquette state” is expected
above the critical value between the interdimer andintradimer interactions. However, an experimental
verification has not been established yet.
To attack this long-standing problem, a few
points must be qualified experimentally. The firstone is the modulation of the exchange couplings by
the application of high pressure. This gives the mostclean and straight way to modify the ratio of
exchange parameters. According to the structuralinvestigation under high pressure, the application of
more than 2 GPa required. The second point is highmagnetic fields of 25 T. This field is needed to close
the singlet–triplet gap by the Zeeman effect. The
third point is the observation of energy levels byusing an electron spin resonance. The last point isvery important, because this phase transition is thechange between two types of singlet state. Such atransition cannot be examined by conventional
magnetic measurements, such as magnetization orsusceptibility. It should be stressed that the present
target can be achieved only by combining theseadvanced extremes and techniques.
A Kobe University group has developed
electron spin resonance under high pressure byusing pulsed magnetic fields and found the trace ofthe expected phase transition. However, the heating

Fig. 1 High-pressure cell used for the electron spinresonance experimentby an eddy current, which cannot be avoided in the
combination of a high-pressure cell and a pulsed
magnetic field, has made a clear and complete
conclusion difficult. However, a magnetic fieldprovided by superconducting magnets was notenough until the installation of a 25-T superconducting
magnet at the High Field Laboratory for
Superconducting Materials [1].
Figure 1 shows a picture of the high-pressure
electron spin resonance cell used in the experiments.
By installing the cell into a 25-T magnet, the loss ofthe pressure dependence of the singlet–triplet gap
at approximately 1.85 GPa was observed. Additional
evidence was given by the enhancement of thesinglet–triplet mixing by high-pressure application.
These two clear changes of spin excitations indicate
the existence of the expected quantum phasetransition by the high pressure. The present study
shows the power of the 25-T superconducting
magnet for studies of matter in multiple extreme
conditions.
References[1] T. Sakurai, S. Kimura, M. Kimata, H. Nojiri, S. Awaji, S. Okubo,
H. Ohta, Y. Uwatoko, K. Kudo, and Y. Koike, J Magn. Reson.
296, 1 (2018).

Keywords: high magnetic field, high pressure, quantum phase transition
Takahiro Sakurai and Hitoshi Ohta (Corresponding Authors, Kobe University)
E-mail: tsakurai@kobe-u.ac.jp
Hiroyuki Nojiri and Shojiro Kimura (High Field Laboratory for Superconducting Materials)
E-mail: nojiri@imr.tohoku.ac.jp
URL: http://www.hflsm.imr.tohoku.ac.jp/cgi-bin/index.cgi

IMR KINKEN Research Highlights 201943

Research Centers

Self-Sufficient Material Circulation System Driven by Plasma
Generated in Aqueous Phase
Trans-Regional Corporation Center for Industrial Materials ResearchW

hen applying a short-pulsed high voltage with a high repetition frequency to metal electrodes placed inwater, plasma (glow discharge) can be generated. Herein, we show the projection of a material circulation
system driven by plasma, aiming to establish a self-sufficient community.
We have been investigating applications ofdischarge plasma generated in water. We developed
a plasma system available for continuous flow water
treatment, which is difficult with a conventional
plasma generation method. [1]. Owing to the Venturi
effect, air was introduced to a water flow (at typicallyseveral liters per minute) between a couple pf ofmetal electrodes to generate stable plasma with arelatively low breakdown voltage. N2 in air was
decomposed, oxidized, and finally dissolved as
nitrate ions in the plasma-treated water. Therefore,
as shown in Fig. 1, the plasma-treated water can beutilized as a nutrient solution in a hydroponic culture.
It is important to prevent plants from up-taking
heavy metals released from electrodes or piping
materials because they cause a significant inhibitionin growth.
Plasma can be utilized for the sterilization ofwater. When Ag wires were used as electrodes forplasma generation, the treated water contained
AgNO3 with a very low concentration, which
maintained a sterilization effect against Trichophyton
and Escherichia coli for several months. Sterilization
is important in a hydroponic culture to prevent plantdisease. In addition, the restriction of an algal
exuberance is an important issue in a hydroponic
culture mainly owing to the sensuousness. Stable
plasma can be generated even in high conductive
water such as seawater using a flow plasma
generation system. Diatoms in seawater, namely,
Chaetoceros gracilis and Chaetoceros calcitrans,
were successfully deactivated [2]. The sterilization
or deactivation is considered to originate from directcontact of algae or bacteria with the plasma core,
and the contribution of in-situ formed reactive
species such as OH radicals, peroxynitrite, andAgNO3.
Using a batch plasma system, the generation ofplasma in an aqueous NH3 solution effectively(a)shoot 0.19g

root 0.09g

shoot 0.24g

root 0.12g(b)

Fig.1 Barley (Hordeum vulgare L. cv. Wasedori) cultivatedfor 8 days in (a) tap water and (b) plasma-treated water.
Approximately 30% growth promotion was observed in(b).

decomposes NH3 molecules to provide N2 and H2
gases with an almost stoichiometric molar ratio [3].
This means that plasma treatment is an effective
NH3 removal method in waste water, and an effective
H2 production method from an aqueous NH3
solution. Because the urea contained in urine isconverted into NH3 through hydrolysis or enzymatic
decomposition, the plasma treatment is expected tobe utilized in the conversion of human waste into H2.
By integrating the above processes, we cansimultaneously reduce human waste, cultivate
crops, and store H2 energy. The promotion of thismaterial circulation through plasma is expected tocontribute to maintaining the “quality of life” inenclosed environments such as disaster shelters,
space ships, and space colonies, among others.
References[1] Y. Mizukoshi, R. Katagiri, H. Horibe, S. Hatanaka, M. Asano,and Y. Nishimura, Chem. Lett. 44, 495 (2015).
[2] Y. Mizukoshi, Y. Matsuda, S. Yamanaka, T. Ikeno, K. Haraguchi,
N. Goda, Y. Nishimura, and K. Yamamoto, Chem. Lett., 47 116(2018).
[3] Y. Mizukoshi, S. Hatanaka, K. Okitsu, Y. Iseki, R. Iwasaki, T.
Sakamoto, S. Yamaguchi, H. Tanaka, and S. Tanabe, Jpn. J.
Appl. Phys. 57, 0102B7 (2018).

Keywords: glow discharge plasma, hydrogen evolution
Yoshiteru Mizukoshi (Corresponding Author, Trans-Regional Corporation Center for Industrial Materials Research)
E-mail: mizukosi@imr.tohoku.ac.jp
Naoya Masahashi (Head of Trans-Regional Corporation Center for Industrial Materials Research)
E-mail: masahasi@imr.tohoku.ac.jp
URL: http://www.trc-center.imr.tohoku.ac.jp/

44

IMR KINKEN Research Highlights 2019

IMR KINKEN Research Highlights 2019

Energy Simulation Model for Disaster Prevention System byUsing Renewable Energy and Hydrogen Energy
Collaborative Research Center on Energy MaterialsA

new energy management for disaster prevention system to use surplus energy from a solar power andbattery life extension method is being developed in Sendai City to apply to facilities such as designatedevacuation centers during a disaster. The energy simulation model for this disaster prevention program byusing hydrogen energy technology to store a large amount of electricity is also examined.
Based on the experience of the 2011 Tohoku
earthquake and tsunami, Sendai City is proceeding toestablish a “Disaster-Resilient and EnvironmentallyFriendly City” and actively create a base for disasterresistant, energy-efficient decentralized energy sources.
It is also introducing renewable energy sources. Sendai
City introduced a disaster prevention solar systemequipped with a solar power generation system and astorage battery for 194 facilities as designated evacuation
centers during a disaster. This disaster prevention solar
system does not utilize CO2-free electricity generated
from solar power at weekends and holidays, and thebattery of this system is always fully charged, whichcauses a battery life problem. A collaboration with Sendai
City is under way for developing new energy management
for next-generation disaster prevention by using surplus
energy from solar power and applying a battery life
extension method, as shown in in Fig. 1 [1]. In this project,a model will be built for deployment to a virtual power
plant. In September 2018, a joint research agreement
was reached with Sendai City and the Japan Weather
Association for enhancing this energy management
technology based on detailed weather forecast data [2].
Today's weather conditions are used for power demand
forecasting for the facility as research for environmental
improvement, and surplus power is assumed based on
tomorrow's solar radiation forecast data, and it is put incontrol. Also, in research aimed at improving disasterprevention, the solar radiation forecast data for tomorrow
will be reflected in the storage capacity of the battery, andcharging of the battery will be secured immediately inresponse to the weather warning.
A hydrogen system is one of the most effective ways
to improve a conventional battery system from theviewpoint of volumetric energy density (Wh/L). An energy
simulation model is being developed for this disasterprevention system by using a hydrogen energy system tostore a large amount of electricity, as in in Fig. 2. For
storing a large amount of hydrogen safely and easily in

lightBattery
SurplusElectricity

Battery life problem

TV
Radio

Gymnasium
Solar Panel

SchoolFig. 1 Disaster prevention solar system

BatteryPV
Hydrogenevolution

Hydrogenstorage alloy

Fuel Cell

Fig. 2 Disaster prevention solar system by adaptinghydrogen energy

this system, hydrogen storage alloy technology is the key
issue compared with a conventional high pressurehydrogen gas tank. A new hydrogen storage alloy having
a high hydrogen storage capacity is also being studied toapply to this energy system. In the future, it is planned to
improve this simulation model, establish scenarios using
real equipment, and proceed with an attempt to constructa system concept.
References[1] https://www.tohoku.ac.jp/japanese/newimg/pressimg/tohokuunivpress20180508_01_zisedaibosai.pdf (2018).
[2] https://www.tohoku.ac.jp/japanese/newimg/pressimg/tohokuunivpress20180927_01web_kishoujouhou.pdf (2018).
[3] T. Kono, J. Hydrogen Energy Syst. Soc. Jpn. 42(4), 218 (2017).

Keywords: energy storage, hydride, hydrogen evolution
Tatsuoki Kono (Collaborative Research Center on Energy Materials)
E-mail: tatsuoki@imr.tohoku.ac.jp
Shin-ichi Orimo (Head of Collaborative Research Center on Energy Materials)
E-mail: orimo@imr.tohoku.ac.jp
URL: http://www.e-imr.imr.tohoku.ac.jp/process.html

IMR KINKEN Research Highlights 201945

Research Centers

Understand Materials Properties and Find New Materials by Supercomputer
Center for Computational Materials ScienceT

he Center for Computational Materials Science supports various advanced studies on computational materials science by
providing users with an efficiently tuned high-performance computer. We introduced two major activities selected fromapproximately 150 users. Dr. Chen investigates the optical properties of dense lithium in electride phases, and Dr. Kawazoe finds
new carbon allotropes.
First-principles Study of Optical Properties of Dense
Lithium in Electride Phasesa)
Pressure alters the state of matter by squeezing electrons
into a smaller space and modifying the interactions between
particles. It is not surprising that metals are usually anticipatedto become more “metallic” at high pressure owing to expectedbroadening of the bandwidth and an overlapping of theelectronic orbitals. Lithium, as the simplest metallic element,
demonstrates how pressure turns a metal into an insulator andinduces some intricate and fascinating properties. We
calculated the dynamic dielectric response, reflectivity, andelectron energy-loss spectroscopy of high-pressure electride
phases of cI16, oC40, and oC20 of Li (Fig. 1), spanning a wide
pressure range using first-principles calculations, which
resulted in the following new findings [1]: 1) One intraband andtwo interband excitations in cI16 are induced through astructural distortion, which leads to an abnormally low
reflectivity of this weak metallic phase, 2) oC24 as a reentrant
metallic phase with a high light conductivity in the infrared andvisible light ranges point to its unique electronic structurearound a Fermi surface, and 3) an intriguing reflectivity
anisotropy in both oC40 and oC24. The origin of such diversity
and rich physics in Li electrides can be attributed to theinterplay between interstitial electron localization anddelocalization induced through compression, which leads toexotic electride phases.
How to Find New Carbon Allotropesb)
It has been a dream to find new single element carbon
system theoretically prior to experiments. We theoreticallyfound Mackay-like structures, which are extremely stable, andsome of which are topological insulators [2]. In the first case,only single element material realizes topological insulator. In
the same year, we found another material, penta-graphene(Fig. 2) [3], which is composed of pentagones with a mixtureof sp2 and sp3 bondings. This completely new structure of thinfilm carbon allotrope is stable and has many interesting
properties, the most important one is negative Poisson’s ratio

Fig. 1 High-pressure phases and calculated density of states (DOS)in lithium.

Fig. 2 Penta-graphene(penta-graphene is the first stable material having a negative
Poisson’s ratio, which can help realize new materials that do
not deform under pressure (the geometry of which is the mostimportant) and therefore applicable for macroscopic cases).
These have been continuously highly cited papers in these 3
years, and experimentally realized in some extent. We haverecently started to apply the materials informatics (MI) method
to find more interesting materials theoretically.
References[1] Z. Yu, H. Y. Geng, Y. Sun, and Y. Chen, Scientific Reports 8, 3868 (2018).
[2] H. Weng, Y. Liang, Q. Xu, R. Yu, Z. Fang, X. Dai, and Y. Kawazoe, Phys.
Rev. B 92, 45108 (2015)[3] S. H. Zhang, J. Zhou, Q. Wang, X. S. Chen, Y. Kawazoe, and P. Jena,
PNAS 112, 2372 (2015)

Keywords: optical properties, first-principles calculations, simulationa) Ying Chen (Corresponding Author, School of Engineering, Tohoku University)
E-mail: ying@rift.mech.tohoku.ac.jpb) Yoshiyuki Kawazoe (Corresponding Author, New Industry Creation Hatchery Center, Tohoku University)
E-mail: kawazoe@niche.tohoku.ac.jp
Momoji Kubo (Head of Center for Computational Materials Science)
Email: momoji@imr.tohoku.ac.jp
URL: https://www.sc.imr.tohoku.ac.jp/eng/

46

IMR KINKEN Research Highlights 2019

IMR KINKEN Research Highlights 2019

Scintillation Properties of Mg2+-Codoped (LuxGd3-x)
Al2.4Ga2.6O12:Ce Multicomponent Garnet Crystals
International Collaboration Center (ICC-IMR)

The scintillation properties of Mg -codoped (Lu Gd )Al Ga O :Ce (x = 0.2 - 0.8) crystals grown by
2+

x

3-x

2.4

2.6

12

micro-pulling down method are reported. Acceleration of scintillation decays with an expense of light yield (LY)is obtained with increasing Lu content. LGAGG:Ce,Mg (x = 0.8) exhibits high LY of 32,000 photons/MeV,
dominant decay time of 52 ns, and coincidence time resolution of 400 ps.

The positive role of Ce4+ centers stabilized by
Mg2+ - codoping has been proposed to explain the
shortening of scintillation decay time in
Gd3Al2Ga3O12:Ce [1,2] and Lu1Gd2(Ga,Al)5O12 [3]garnet crystals. In this work the Mg 500 ppm codoped (LuxGd3-x)Al2.4Ga2.6O12:Ce0.5% (x= 0.2-0.8)
crystals were grown by the micro-pulling down
method using Ir crucible under Ar + 2% O2
atmosphere at the IMR, Tohoku University, Japan.
The blue-shifted of RL band (Fig.1) was
observed with increasing Lu content in the same
trend with the 4f→5d1 absorption band (not shown).
This result can be explained by a decrease of crystal
field strength around Ce3+ at the dodecahedral siteof (LuxGd3-x)AGG:Ce crystal upon partial substitutionof Gd3+ with a smaller Lu3+ ion. Scintillation decays
and energy spectra of 137Cs ϒ rays for LGAGG:Ce,Mg
are displayed in Figs. 2 and 3, respectively. With
increasing Lu content, decay time shortening anddecrease of light yield can be attributed to a blueshifted emission spectrum (τ∼λ3) and a larger
bandgap caused by a high-energy shift of thebottom of the conduction band [4,5], respectively. It
is worthy to note that a decay time of 52 ns obtainedfor Lu0.8Gd2.2 AGG:Ce,Mg sample is faster than thatof 68 ns for Lu0.8Gd2.2 AGG:Ce one.
LGAGG:Ce,Mg (x = 0.2) crystal exhibits high LY
of 36,500 ph/MeV and dominant decay time of 62
ns whereas those values of 32,000 ph/MeV and 52
ns are obtained for the LGAGG:Ce,Mg (x = 0.8) one.
Coincidence time resolution of 400 ps was alsomeasured for the LGAGG:Ce,Mg (x = 0.8). Further
improvement of the scintillation timing characteristics
could be achieved by optimization of Ga/Al ratio
and concentration of Mg codopant.
References

Fig. 1 RL spectra of selected LGAGG:Ce,Mg crystals.

Fig. 2 Scintillation decays of selected LGAGG:Ce,Mg
crystals.

Fig. 3 Pulse height spectra of 137Cs ϒ rays measured withLGAGG:Ce,Mg crystals.
[3] H. Yamaguchi et al., Opt. Mater. 61, 129 (2016).

[1] M. Nikl et al., Cryst. Growth Des. 14, 4827 (2014).

[4] L. Chen et al., Sci. Rep. 5, 11514 (2015).

[2] K. Kamada et al., Opt. Mater. 41, 63(2015).

[5] W. R. Chewpraditkul et al., Opt. Mater. 76, 162 (2018).

Keywords: (Lu,Gd)3AGG:Ce, Mg, light yield, scintillation decays
Weerapong Chewpraditkul (King Mongkut’s University of Technology Thonburi)
Email: weerapong.che@kmutt.ac.thGerrit Ernst-Wilhelm Bauer (Head of International Collaboration Center)
E-mail: icc-imr@imr.tohoku.ac.jp
URL: http://www.icc-imr.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201947

Research Centers

Starting 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 operates three neutron instruments in a research reactor facility, JRR-3,
under a general user program, and will start a new user program for a brand-new spectrometer, POLANO, at
J-PARC/MLF in April 2019. Herein, we report the current status of POLANO.
The Center of Neutron Science for Advanced
Materials (CNSAM) was established in 2010 topromote novel materials science research using
neutrons.
CNSAM
operatestwoneutronspectrometers and one diffractometer at the JRR-3
research reactor of the Japan Atomic Energy
Agency and has been constructing a polarized
neutron spectrometer, POLANO, with an intense
neutron source at the Materials and Life Science
Experimental Facility (MLF) in the Japan Proton
Accelerator Research Complex (J-PARC) [1].
POLANO is a brand-new spectrometer designed torealize a polarization analysis in higher energy
regions beyond the measurements achieved
through a conventional triple-axis spectrometer. The
construction of POLANO was initiated in 2012 undercollaboration with the High Energy Accelerator
Research Organization (KEK). After the constructionof the main part of the instruments [2], we finallysucceeded in receiving the first neutron beam at
POLANO in June 2017 and started on-beamcommissioning.
Figure 1 shows the results of the test
measurements of position-sensitive detectors. The
colors represent the neutron intensity. The scatteredneutrons from a standard sample can be
successfully detected. Using the data obtained, theefficiency of the detectors was calibrated.
Furthermore, we installed equipment including a
Fermi chopper at POLANO to carry out inelastic
scattering measurements. Figure 2 (c) shows therepresentative results of the measured magnetic
excitation spectrum from a one-dimensional spin
system, CsVCl3. As the figure indicates, a spin-wave
excitation of up to ~80 meV was clearly observed.
Thus, POLANO can provide an opportunity to study
the spin and lattice dynamics in novel materials. We
have prepared collaborative research programs of
IMR to support the experiments conducted at
POLANO, in accordance with the beginning of ageneral user program of POLANO at J-PARC MLF.

Fig. 1 Neutron intensity map measured using position
sensitive detectors of POLANO.

Fig. 2 (a) Crystal and magnetic structures of CsVCl3. (b)Scan trajectory of neutron inelastic measurements for
one-dimensional magnetic system. (c) Magnetic
excitations for CsVCl3 at POLANO.

References[1] T. Yokoo, S. Itoh, N. Kaneko, M. Fujita, T. Ino, M. Ohkawara, K.
Ohyama, and M. Sakaguchi, AIP Conf. Proc. 1969, 050001(2018).
[2] M. Ohkawara, T. Ino, Y. Ikeda, T. Yokoo, S. Itoh, K. Ohoyama,and M. Fujita, JPS Conf. Proc. 22, 011017 (2018).

Keywords: neutron scattering, instrumentation, spin excitation
Masaki Fujita (Head of Center of Neutron Science for Advanced Materials)
E-mail: nc-imr@imr.tohoku.ac.jp
URL: http://nc-imr.imr.tohoku.ac.jp/

48

IMR KINKEN Research Highlights 2019

IMR KINKEN Research Highlights 2019

Spin Trimer Formation in the Metallic Compound
Gd3Ru4Al12 with a Distorted Kagome Lattice Structure
Laboratory of Low Temperature Materials Science

We demonstrate the gradual formation of ferromagnetic trimers on a distorted (breathing) kagome lattice withdecreasing temperature in Gd3Ru4Al12 single crystals. This trimerization can induce an antiferromagnetic
intertrimer interaction and lead to an effective transformation into an antiferromagnetic triangular lattice withfrustration at low temperature.

RE3Ru4Al12 (RE = rare earth element)
compounds have been investigated intensively inrecent years because they display a variety ofphenomena at low temperatures as metallic
frustrated 4f spin systems with spin multimers.
Among them, the puzzling magnetism features of
Gd3Ru4Al12, showing a Curie-Weiss temperature of+80 K at high temperatures despite theantiferromagnetic (AFM) order at low temperatures,are an open problem [1].
We have succeeded in synthesizing single
crystals of Gd3Ru4Al12, which exhibits a distorted
kagome lattice [2]. This lattice includes small andlarge regular triangles of Gd ions, which areresponsible for the magnetic properties, as shownin Fig. 1(a). Measurements of the magnetic
susceptibility and magnetic specific heat indicatethat ferromagnetic spin trimers are gradually formedon the small triangles with a decrease in temperature
through an RKKY interaction at below 130 K. This
formation of ferromagnetic trimers induces an AFM
inter-trimer interaction between the nearest-neighbortrimers based on the oscillatory features of an RKKY
interaction. As a result, Gd3Ru4Al12 translates into an
AFM triangular lattice at low temperatures, as shownin Fig. 1(b). The magnetic entropy at the Neeltemperature of Gd3Ru4Al12 is only 40% of the fullmagnetic entropy. In this compound, the generationof ferromagnetic clusters (trimers) induces frustrationand significantly reduces the Neel temperature.

(b )

(a )

c
b

a

Sr

b
c

a

J

Fig. 1 (a) Structure of Gd3Ru4Al12 projected parallel tothe ab plane. The red, blue, and light green spheres
denote Gd, Ru, and Al ions, respectively. (b) A Gd-Al
layer projected parallel to the c-axis. The blue arrows
indicate the resultant spin, Sr (Sr = 21/2).

References[1] V. Chandragiri, K. K. Iyer, and E. V. Sampathkumaran, J. Phys.
(Cond. Mat.) 28, 286002 (2016).
[2] S. Nakamura, N. Kabeya, M. Kobayashi, K. Araki, K. Katoh,and A. Ochiai, Phys. Rev. B 98, 054410 (2018).

Keywords: magnetism, frustrated spin system
Shintaro Nakamura (Laboratory of Low Temperature Materials Science)
E-mail: nakamura@imr.tohoku.ac.jp
Takahiko Sasaki (Head of Laboratory of Low Temperature Materials Science)
E-mail: takahiko@imr.tohoku.ac.jp
URL: http://ltsd.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201949

Research Centers

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

More than 170 species of radioisotopes and nuclear materials are available for study at the Laboratory ofAlpha-Ray Emitters. This laboratory is one of the most important centers around the world for studying thephysical and chemical properties of radioactive materials, such as actinide compounds. Researchers frommany of the leading universities and institutes all over Japan visit this facility every year to prepare a variety ofmaterials and carry out chemical and physical measurements.

The Laboratory of Alpha-Ray Emitters provides
a research environment for the study of 170
radionuclides and nuclear materials, especiallyalpha-ray emitters, such as actinide. This lab
functions as a source for the preparation of purecrystals of actinide compounds, providing them toother universities and to synchrotron orbitalradiations. The radiation controlled area of thislaboratory includes three chemistry rooms, threephysical rooms, and so on, which are equipped withlocal exhaust ventilation systems making thehandling of various kinds of material possible. Many
spectrometers, including those for gamma rays andalpha rays, are available.
In the past decade, actinium-225 (Ac-225), oneof the actinide elements, has been reported becauseof its effectiveness for medical use [1, 2]. Ac-225(half-life: 10 d) decays through a chain of four alphaemissions and two beta-minus emissions to thestable isotope Bi-209. The decay process releases~28 MeV of energy to the surrounding media withchanging of the element, and the chain does not
involve noble gas, which is a chemically uncontrollable
element. All of these nuclide properties seem to besuitable for the treatment of tumors, and Ac-225 isactually used in clinical practice outside the country.
Although it is a testament to the effectiveness ofradiopharmaceuticals, very limited investigation has
been done in Japan. One of the main reasons is that
Ac-225 is subject to rigid regulation as an alpha-ray
emitter. In this study, the aim was to evaluate thedispersion of Ac-225 and its progeny nuclides. Thisevaluation is especially important for establishing a
guideline for the control standard, especially for Ac225 practical use.
For obtaining a starting material of Ac-225, a
Th-229 milking method was used. This material,
composed of 10 mL of 0.05-M HNO3 aq. containing
Ac-225, adjusted to the conditions of the dispersion

Fig. 1 Alpha-ray spectra of Ac-225 and its progeny
nuclides obtained from standard sample (a) anddispersion evaluation system (b). In the container, two
PTFE filters were placed downstream from the air inlet.
The container was set at the top of an acrylic cylinder(70-mm i.d., 80-mm o.d., and 480-mm length), andinner aspect of the acrylic cylinder was filled using a
PEN film.

experiments (liquid: acidic, neutral, and neutral
complex solutions, solid: nitric acid salt). The
dispersion experiments were carried out using a
special composition of sampling for alpha-ray
spectroscopic identification (Fig. 1). Just after theaspiration, typically 1 h, PTFE filters and some partof PEN film were ejected from the apparatus andmeasured by an alpha-ray spectrometer.
The dispersion rate of Ac-225 and its progeny
nuclides was well identified. The dispersion rate wasobtained in descending order, neutral complex >neutral > acidic, in the liquid condition. Even in thehighest, the dispersion rate was less than 10 -4/h,
which is 1/100 of the typically used value.
References[1] C. Kratochwil et al., J. Nucl. Med. 57, 1941 (2016).
[2] C. Kratochwil et al., J. Ncul. Med. 59, 795 (2018).

Keywords: actinide, alpha-ray spectroscopy, short-life alpha-ray emitter
Kenji Shirasaki (Head of Laboratory of Alpha-Ray Emitters)
E-mail: kshira@imr.tohoku.ac.jp
URL: http://alpha.imr.tohoku.ac.jp

50

IMR KINKEN Research Highlights 2019

IMR KINKEN Research Highlights 2019

Synthesis, Crystal Structure, and Luminescence Propertiesof a New Nitride Polymorph, β-Sr0.98Eu0.02AlSi4N7
Analytical Research Core for Advanced Materials

Anovel strontium aluminum silicon nitride phosphor, namely, a β-Sr0.98Eu0.02 AlSi4N7 single crystal, whichemits green light under excitation at 400 nm, was fabricated. Because identifying its crystal structure using only
XRD is quite difficult owing to the twin-defects contained in the specimen, TEM and STEM-HAADF techniques
using the latest Cs-corrected electron microscope were employed herein to characterize the detailed crystal
structure.
SrAlSiN7 doped with Eu2+ has been reported asa phosphor material for use in combination withnear ultraviolet light and a blue light LED to realize abacklight of a liquid crystal display or a white LED.
This nitride belongs to an orthorhombic structureand exhibits a red emission with a broad peak at awavelength of 635 nm under an excitation light of
450 nm [1]. In the present study, we synthesizedvermilion prismatic and yellow platelet single
crystals having similar chemical compositions froma mixture of Sr3N2, Mg3N2, EuN, AlN, and α-Si3N4
powders by heating at up to 800–2030 °C under a
N2 atmosphere. The vermillion crystals emitted red
light, whereas the yellow crystals emitted green lightunder excitation at 400 nm. A single-crystal XRD
confirmed that the vermilion crystals are
α-SrEuAlSiN7 and suggested that the yellow crystals
are new polymorph containing twin defects [2].
Therefore, analyses on the twin-boundary
structure and an identification of the unit cell of the
new polymorph have been conducted using S/TEM.
High-resolution TEM observations indicated theexistence in a single crystal specimen with twinbands at a thickness of tens of nanometers, as
shown in Fig. 1(c). The SAD pattern taken from thetwin-contained region exhibited a mirror symmetry,as shown in Fig. 1(a), which is consistent with the
XRD results; in addition, using a small selected-area
aperture, the pattern from a single crystal region
could also be obtained, as shown in Fig. 1(b).
Furthermore, direct observations of the atomarrangement using HAADF-STEM revealed that theunit cell of the new polymorph consists of thestacking of two types of layers, including and notincluding heavy Sr/Eu atoms, labeled A and B,
respectively, in Fig. 1(d). Thus, we concluded thatthenewpolymorph,
β-Sr0.98Eu0.02 AlSi4N7,

Fig. 1 SAD patterns from (a) twin and (b) single regions,and (c) HREM and (d) HAADF-STEM images takenfrom the [010] direction in β-Sr0.98Eu0.02AlSi4N7
crystal (inset (e) schematic drawing of corresponding
crystal structure)

crystalized in a monoclinic cell, as shown in Fig.
1(e).
References[1] C. Hecht, F. Stadler, P. J. Schmidt, J. Schmedt auf der Günne,V. Baumann, and W. Schnick, Chem. Mater. 21, 1595 (2009).
[2] F. Yoshimura, H. Yamane, and M. Nagasako, J. Solid State
Chem. 258, 664 (2018).

Keywords: electron microscopy, crystal structure, luminescence
Makoto Nagasako (Corresponding Author, Analytical Research Core for Advanced Materials)
E-mail: nagasako@imr.tohoku.ac.jp
Kazuaki Wagatsuma (Head of Analytical Research Core for Advanced Materials)
E-mail: wagatsuma@imr.tohoku.ac.jp
URL: http://bunseki-core.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201951

Author Index
NamepageNamepageA
Aoki, DaiArima, Hiroshi

N
Nagai, Yasuyoshi
Nagasako, Makoto
Nagumo, KazuakiNakamura, Shintaro
Niinomi, Hiromasa
Nojiri, Hiroyuki

33, 40, 41
51
33
49
36
27, 43O
Ohta, Hitoshi
Okamoto, Norihiko L.
Onose, Yoshinori
Orimo, Shin-ichi

43
20
32
23, 45

S
Saitoh, Eiji
Sakurai, Takahiro
Sasaki, TakahikoSato, Koji
Sato, Mitsutaka Sato, Toyoto
Shimizu, Yasuo
Shiogai, Junichi
Shirasaki, Kenji
Suzuki, Tatsuya

28
43
30, 49
26
8
23
33
29
50
40

T
Takanashi, Koki
Tanimura, Hiroshi
Terada, Yayoi

22
20
14

W
Wagatsuma, Kazuaki
Wei, Daixiu

51
13

Y
Yodoshi, Noriharu
Yoshikawa, Akira

42
10

B
Bauer, Gerrit E. W.

52

37
19

26, 47C
Chen, Ying
Chewpraditkul, WeerapongChiba, Akihiko

46
47
11

E
Elyasi, Mehrdad

26

F
Fujita, Masaki
Fujiwara, Kozo

31, 4816

H
Hojo, Tomohiko

9I
Ichitsubo, Tetsu
Inoue, Koji

20
33

K
Kasada, RyutaKato, HidemiKawaguchi, Tomoya
Kawazoe, Yoshiyuki
Kikkawa, Takashi
Kimura, Shojiro
Konno, Toyohiko J. 
Kono, Tatsuoki
Kosaka, WataruKubo, Momoji18
13, 21
20
46
28
43
38
45
35
17, 46M
Masahasi, Naoya
Matsuoka, TakashiMatsuta, Hideyuki
Miyasaka, Hitoshi
Mizukoshi, YoshiteruMohri, Tetsuo

42, 44
34
12
35
44
14

IMR KINKEN Research Highlights 2019

Keyword Index
Keywordpage

Keywordpage

A
actinide40, 50alloy11
alpha-ray spectroscopy
50
atom probe tomography
33
antiferromagnetic35
antiferromagnets28

high strength steel
hydridehydrogen evolutionhydrogen implantation

C
computational materials science
14
crystal growth
10, 16
crystal structure
20, 23, 51
D
3D structure
21
defects16
devices32
dielectric38
diffusion20
Eelectron microscopy
electronic material
electronic structureenergy storageepitaxial growth

18, 51
33
18, 31
20, 4534

F
fatigue13
fermi surface
37
ferromagnetic35
first principles calculations46
foam21
fracture9
frustrated spin system
49
G
GaN34
GIWAXS30
glow discharge plasma12, 44H
heavy fermion
higher education
high magnetic field
high pressure

37
14
27, 4343

923, 4544, 4533

I
instrumentation48
interface17
Llight yield
47(Lu,Gd)3AGG:Ce47
luminescence51
M
magnetic properties
12, 22, 42
magnetism49
magnetoconductance30
mass spectrometry40
mechanical properties
11, 13
metal36
metallic glass
42
Mg47
microstructure
8, 11, 13molecular beam epitaxy (MBE)
29
molecular dynamics
17
multi-ferroics32
N
nanostructure
neutron scattering
nitride semiconductors
nuclear materials
nucleation & growth

36, 4223, 4834
18, 4136

O
optical properties
46
oxide38
P
phase transformation
8, 9
piezoelectric32
polymer30
porosity
21, 35

IMR KINKEN Research Highlights 201953

Keywordpage

Keywordpage

Q
quantum phase transition

43

Rradiation effects

41

spin wave
26
spintronics
26, 28steel8superconducting27, 31, 37
synchrotron19

S
scanning transmission electron microscopy (STEM)
41
scintillation decays
47
scintillator10
short-life alpha-ray emitter
50
simulation
17, 46
solar cells
16
spectroscopy12
spin current
28
spin excitation
48

54

IMR KINKEN Research Highlights 2019T
thin films
22, 29, 38
thermo-electricity22
topological insulator
29
X
XAFS
X-ray diffraction (XRD)
X-ray scattering

19, 31
19
27

Editors
Kozo Fujiwara, Ryuta Kasada, Yoshinori Onose,
Shigeyuki Takagi, Takeshi Seki, and Norihiko L.
Okamoto

Editorial Staff
Misa Y. Tomimatsu, Aki Oikawa, and Yuko Godart

Printing
HOKUTO Corporation

Organization
Institute for Materials Research
Tohoku University
2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
Tel. +81-(0)22-215-2144 Fax. +81-(0)22-215-2482
URL: http://www.imr.tohoku.ac.jp/
E-mail: pro-adm@imr.tohoku.ac.jp© IMR July 2019