Details of a Researcher - Kamihara, Yoichi

Presentations -

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Magnetic Flux Density Distribution and Microstructure Analysis of H-doped SmFeAsO

Hideo Namita, Tomoki Suemura, Ryosuke Sakagami, Tsuyoshi Tamegai, Yoichi Kamihara

[International presentation] Materials Research Meeting (MRM) 2025 (横浜) ,

2025.12

Poster presentation

Superconducting Properties for a Cuprate Superconductor after Heat Treatments under Several Hydrogen Atmosphere at ~200 deg. C

Hideo Namita, Masanori Matoba, Suguru Iwasaki, Masaya Fujioka, Masashi Miura, Yoichi Kamihara

[International presentation] Materials Research Meeting (MRM) 2025 (横浜) ,

2025.12

Oral presentation (general)

Metal organic deposited partially Gd-substituted YBa2Cu3O7−delta ((Y, Gd)BCO) thin films on SrTiO3 substrate were heat-treated in hydrogen (H2) atmosphere below 300 deg. C with or without hydride (H−) bias irradiation. two kinds (Y, Gd)BCO thin films prepared as an over-doped (delta~0.05) sample and an under-doped (delta~0.35) sample were used for the heat treatments. The (Y, Gd)BCO) crystallographic phase of under-doped sample preserves during heat treatment at T = 250 deg. C, while the (Y, Gd)BCO) crystallographic phase of over-doped sample disappears. Lattice constants of the samples were compared before and after heat treatments. Each sample, which is heated at T ~200 deg. C, exhibits larger lattice volumes than that of before heat treatment. The larger lattice volumes are mainly due to possibly larger delta. The H2 atmosphere works as reductant gas for the (Y, Gd)BCO) thin films. We cannot find a crystallographic difference between samples heated “with” and “without” H− bias irradiation at T ~ 200 deg. C. Samples, which were heated at T = 210 deg. C, the value of the lattice constant c depends on “with” and “without” H− bias irradiation. The c exhibits the smaller value after the heat treatment with H− bias irradiation, although the c exhibits larger value after the heat treatment without H− bias irradiation. These results indicate that H− irradiation probably demonstrates partial H− substitution for oxygen site in (Y, Gd)BCO thin films. Theoretical lattice constants of Y0.67Gd0.33Ba2Cu3O7−xHy (x = 0, 0.16, 0.33, 0.50, 0.67, y = 0, 0.16, 0.33, 0.50, 0.67) were obtained by density functional theory (DFT) calculations. The DFT calculations were demonstrated by Vienna ab-initio Simulation Package (VASP). Indeed, the DFT results predict that a smaller c for H-substituted Y0.67Gd0.33Ba2Cu3O7−xHy appears for (x = 0.33, y = 0, 0.16, 0.33, 0.50, 0.67). In a region (x = 0.33, y = 0, 0.16, 0.33, 0.50, 0.67), the theoretical c exhibits smaller value with increasing y; i.e. amount of H− at oxygen site. The H− substitution for oxygen site in (Y, Gd)BCO thin films is supported by the DFT calculation. In MRM2025, we demonstrate transport properties and superconducting transition temperatures (Tcs) for these (Y, Gd)BCO) thin films.

Computational Chemical Analysis of Oxygen deficiency in Synthesized Samples of Mixed Anion Layered Compound Superconductor, LaNiPO1−delta

Haruyoshi Suzuki, Daiki Fujii, Aurélien Antunez, Yoichi Kamihara, Masanori Matoba

[International presentation] Materials Research Meeting (MRM) 2025 (横浜) ,

2025.12

Poster presentation

Fe-based mixed anion layered compounds (MALC), REFePnO (RE: lanthanides. Pn: P, As), exhibit a superconducting phase at low temperatures. The highest transition temperature (Tc) among Fe-based MALC is 58.1 K for SmFeAsO1-xFx. On the other hand, in nickelate superconductor, La4Ni3O1-delta has Tc of 30 K at 60 GPa. LaNiPO, Ni-based MALC, shows superconductivity at temperatures under 3 K. LaNiPO and related materials are candidates which exhibit Tc as high as those of Fe-based and metal oxide superconductors. In the synthesis of MALC superconductor, oxygen deficiency is inevitable, and it causes a decrease in superconducting performance. In Sr2VFeAsO3, oxygen deficiency (delta) and lattice volume are positively correlated. We aim to evaluate delta from analysis X-ray diffraction (XRD) of synthesized samples with lattice volume. DFT calculation is performed by Vienna ab-initio Simulation Package (VASP), a programming package for density functional theory (DFT) in projector augmented wave (PAW) method.

Introduction of slab structures and calculations of surface energy of Bi2Sr2CaCu2O8+x

Ryotaro Taniguchi, Haruyoshi Suzuki, Yoichi Kamihara, Masanori Matoba

[International presentation] Materials Research Meeting (MRM) 2025 (横浜) ,

2025.12

Poster presentation

新規n型Zintl相化合物 Rb(Cd,Zn)4As3の熱電性能

小野圭吾, 後藤陽介, 神原陽一，李哲虎

[Domestic presentation] 第22回日本熱電学会学術講演会 (「團十郎芸術劇場うらら」と「サイエンスヒルズこまつ」石川県小松市) ,

2025.09

Oral presentation (general)

143-Zintl相化合物Rb(Cd,Zn)4As3の熱電性能

小野圭吾, 後藤陽介, 村田正行, 臼井秀知, 筒井智嗣, 神原陽一, 李哲虎

[Domestic presentation] 日本物理学会第80回年次大会 (広島大学（東広島キャンパス）) ,

2025.09

Oral presentation (general)

鉄系高温超伝導体 H-doped SmFeAsO (Sm1111) の Mossbauer分光法による Debye温度の導出

何浩，松浦義実，森田勇希，神原陽一

[Domestic presentation] 第49回日本磁気学会学術講演会,

2025.09

Oral presentation (general)

Jonkerプロットを使用した複合アニオン層状化合物ワイドギャップ半導体 LaCu1-dChO (Ch = S, Se)の熱電性能評価

神原陽一

[Domestic presentation] 応用物理学会2025年応物秋季学術講演会 (名城大学天白キャンパス&オンライン) ,

2025.09

Oral presentation (general)

New Synthesis Route for Polycrystalline Samples and Chemical Calculation in Superconducting LaNiPO

Haruyoshi SUZUKI, Ryoma TAKEUCHI, Daiki FUJII, Aurelien ANTUNEZ, Yoichi KAMIHARA, Masanori MATOBA

[International presentation] 30th International Conference on Low Temperature Physics (LT30) (Bilbao, Spain) ,

2025.08

Poster presentation

LnFePnO (Ln: lanthanides. Pn: P, As.), a Fe-based mixed anion layered compound (MALC), exhibits a superconducting phase at low temperatures. The highest transition temperature (Tc) among Fe-based MALC is 58.1 K for SmFeAsO1-xFx [2]. On the other hand, La4Ni3O1−δ. a Ni-oxide superconductor, exhibits Tc of 30 K at 60 GPa [3]. LaNiPO, a Ni-based MALC, shows superconductivity at temperatures under 3 K [4]. The crystal structure is shown in Fig. 1. LaNiPO and related materials are candidates that have Tc as high as those of Fe-based MALC and Ni oxide superconductors. La, P, and Ni were heated at 700 deg. C for 10 h to obtain LaP-NiP-Ni2P (133 powder). Synthesis of LaNiPO samples was performed by heat-treating 133 powder and La2O3 at different temperatures.

Exploration of transparent semiconductor by synthesis of Sr2CuZnSO3-delta

D. Fujii, H. Suzuki, K. Fukuda, Y. Kamihara, M. Matoba

[International presentation] The 10th Japan-Korea International Symposium on Materials Science and Technology (JKMST2025) (東京) ,

2025.07

Poster presentation

Sr2CuZnSO3-delta, a mixed anion layer compound, is a member of both systems, 21113 system and Sr-CuM-O-S (M = Zn, Ga, In) system. 21113 system compounds are layered perovskite structures and reported to have oxygen deficiency. The amount of oxygen deficiency () affects electrical resistivity and lattice constants. Materials in Sr-Cu-M-O-S (M = Zn, Ga, In) system have CuS layers and SrMO3 layers. Sr2Cu2ZnS2O2 and Sr2CuMSO3 were reported to exhibit P-type transparent semiconducting properties. The electrical conductivity () increased with Na doping concentration in Sr sites and temperature. The electrical bandgap (Eg) of Sr2Cu2ZnS2O2 was 2.7 eV. We expect that Sr2CuZnSO3- exhibits P-type transparent semiconducting properties and controlling , we can optimize the electrical conductivity of the sample. Sr2CuZnSO3- is similar to Sr2CuMnSO3 in terms of the ionic radius of Zn and Mn, crystal system (tetragonal), and space group (P4/nmm). We referred to the crystal structure, lattice constants and X-ray diffraction (XRD) patterns of Sr2CuMnSO3. Sr2CuZnSO3- ( = 0.5) samples were synthesized in solid reaction method. Dehydration of Sr(OH)28H2O powder is performed by heating at 900℃ for 15 h to obtain SrO. Cu and S were heated at 300℃ for 40 h to obtain CuS. Stoichiometric amounts of SrO, ZnO, Zn and CuS powders were mixed in a agate mortar for 30 minutes and pressed into pellets. The pellets were heated at 900℃ for 40 h and we obtained Sr2CuZnSO3- samples. Weighing of powders was performed in a globe box filled with Ar (O2, H2O  1 ppm) and heat treatment was performed in a vacuumed silica tube. The samples were in the Alumina tube during heat treatment to prevent the reaction of Sr with the silica tube. The crystal phases were determined by the XRD measurement system (Rigaku Co. Ltd. Ultima IV, CuK alpha). Lattice constants of the samples were corrected using a Si standard sample. The surface of the samples was observed using a metallurgical microscope and the particle size was measured. The electrical resistivity of the samples was measured at room temperature and in the range of 50 to 400 K by the two-probe method using the Micro Probe System (MPS-CHL) while applying current in the range of 0.1 to 0.2 micro A.

Review on Thermoelectric properties of a mixed anion layered compound LaCu1-deltaS1-xSexO as a wide-gap semiconductor

Yoichi KAMIHARA

[International presentation] The 10th Japan-Korea International Symposium on Materials Science and Technology (JKMST2025) (東京) ,

2025.07

Oral presentation (invited, special)

Thermoelectric conversion materials (TEC) and technologies, which have been demonstrated at T = 300-600 K, are long-term fundamental problems for innovation. State-of-art thermoelectric materials are Bi2Te3-based materials. However the fundamental reports for the Bi2Te3-based materials had been demonstrated from 1954. New materials, which is NOT a Bi2Te3-based material, have been explored for innovation. Since the early 2000s, mixed anion layered compounds (MALCs) have been potential candidates for various electrical and electronic applications. A representative MALC LaCuChO (Ch = S, Se), which belongs to the tetragonal P4/nmm space group, exhibits a layered structure, with alternating layers of carrier blocking La2O2 and carrier conducting Cu2(S, Se)2 along to the c axis. On the other hand, BiCuSeO, which exhibits a layered structure as well as LaCuChO, was reported as a promising TEC material by Zhao et al., Appl. Phys. Lett. 97, 092118 (2010). In 2024, our group reported the thermoelectric properties of several LaCuChO in Jonker plot. (Azuma et al., Korean J. Mater. Res. 34, 464-474 (2024).). The Jonker plot helps us to evaluate previously reported transport properties of LaCuChO in thermal physics. In this JKMST2025, we will talk about thermoelectric properties for LaCu1−deltaS1−xSexO as a wide-gap semiconductor and a degenerated semiconductor due to Cu defect and mixed anion state in crystallographic chalcogenide site.

Synthesis of nickel deficient hexagonal perovskite BaNi1-xO3-y and its oxygen evolution reaction activity

Taisuke KAIZUKA, Yoichi KAMIHARA

[International presentation] The 10th Japan-Korea International Symposium on Materials Science and Technology (JKMST2025) (東京) ,

2025.07

Oral presentation (general)

Synthesis of polycrystalline hexagonal perovskite BaNi1-xO3-y featured by nickel deficiency has been succeeded, which contains very little impurity phases. The sample was synthesized by Sol-gel method, using dextran. Ba(NO3)2 and Ni(NO3)2 6(H2O) were dissolved into water with metal atom ratio of 1:0.7. Then the solution was mixed with dextran. After drying in air at least 1 day, the gel-like precursor was calcined, then sample of black powder, nominal polycrystalline BaNi0.7O3-y, was obtained. XRD analysis indicated Bragg diffraction of the sample were assigned to hexagonal BaNiO3 lattice with space group “P 63/m m c”. There were very little impurity phases of NiO and BaNi0.83O2.5. Very weak unknown reflections were also detected, which were of other phases. Lattice constants were value of a = 0.5582 nm and c = 0.4861 nm, different from any reported one. Because there were no measure unknown reflections, this sample seems to have disorganized nickel vacancies which is as much as 30% of ideal nickel amount. The ratio of Ba and Ni was investigated by SEM-EDX analysis and it was found that the ratio was corresponded to that of initial mixture approximately. The measure of catalytic activity of oxygen evolution reaction (OER) was applied to BaNi1-xO3-y. The current density and overpotential could not be determined because there was large polarization between upward and downward voltage sweeping in cyclic voltammetry (CV). This polarization indicates changes of crystalline phase and composition of sample. This polarization is observed until at least 50 cycle of CV, thus the changes of sample state is considered partly reversible.

Seebeck coefficient and electrical conductivity of mixed anion layered compounds Cu-deficient LaCuChO (Ch = S, Se) in Jonker plot

Y. Kamihara

[International presentation] Asia Pacific Society for Materials Research 2025 Annual Meeting (APSMR 2025 Annual Meeting) (Sapporo, Hokkaido, Japan) ,

2025.07

Oral presentation (invited, special)

Since the early 2000s, mixed anion layered compounds (MALCs) have attracted considerable attention as promising materials exhibiting a wide range of electrical, electronic, magnetic, superconducting, and catalytic functionalities. A representative example of MALCs is LaCuChO (Ch = S, Se), which crystallizes in the tetragonal P4/nmm space group and consists of alternating carrier-blocking La2O2 layers and carrier-conducting Cu2Ch2 layers stacked along the c-axis. A structurally analogous layered compound, BiCuSeO, in which La is replaced by Bi, was reported by Zhao et al. to be a promising thermoelectric material (Appl. Phys. Lett. 97, 092118 (2010)).
LaCuChO (Ch = S, Se) is a wide band gap insulator with an optical band gap of approximately 3 eV. Due to copper deficiency on the order of 1 at.%, hole doping occurs, resulting in p-type carrier polarity. In a polycrystalline sample of LaCu0.99S0.5Se0.5O, where S and Se are each solid-solution at 50% on the Ch site and ~1 at.% Cu deficiency (delta) is introduced, impurity levels within the optical band gap have been observed—attributed to gap states induced by the defects. The electrical properties of LaCu0.99S0.5Se0.5O exhibit temperature dependence indicative of a degenerate semiconductor above room temperature. However, in a sample with 2 at.% Cu deficiency (delta = 0.02), despite the persistence of gap states, the resistivity at room temperature reached approximately 0.1 MΩ·cm, indicative of insulating behavior. This suggests that, in addition to Cu vacancies, other compensating defects at crystallographic sites may arise that neutralize the carriers. In this presentation, we report an evaluation of the thermoelectric performance of LaCuChO (Ch = S, Se) using Jonker plots.

Synthesis and thermoelectric performance evaluation of a layered oxyselenide BiCuSeO for future copper deficiency introduction

Jo OTAKE, Nobuhiko AZUMA, Masanori Matoba, Yoichi KAMIHARA