Details of a Researcher - Kamihara, Yoichi

Presentations -

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Synthesis and analysis of 21113V Fe-based Superconductors, Polycrystalline Sr2V1-xTixFeAsO3 Samples

Aurelien ANTUNEZ, Haruyoshi SUZUKI, Takato UENO, Masanori MATOBA, Yoichi KAMIHARA

[International presentation] International symposium on advanced magnetic materials and applications (ISAMMA) 2026 (釜山, 大韓民国) ,

2026.06

2026.07

Poster presentation

Estimation of oxygen deficiency in Bi2Sr2CaCu2O8+x based on first-principles calculations and XRD analysis

Ryotaro Taniguchi, Taisuke KAIZUKA, Haruyoshi Suzuki, Yoichi Kamihara

[International presentation] GCIM2026&MRS-K Spring Meeting,

2026.05

2026.06

Poster presentation

Two type trends in a Jonker plot for polycrystalline mixed anion layered compounds Cu-defected LaCu(S, Se)O

Yoichi KAMIHARA, Tatsuhide FUJIOKA, Nobuhiko AZUMA

[International presentation] GCIM2026&MRS-K Spring Meeting,

2026.05

2026.06

Oral presentation (general)

The performance of Thermoelectric conversion (TEC) materials is evaluated by the dimensionless figure of merit, ZT = Seebeck coefficient (S)^2 thermal conductivity (kappa)^-1 resistivity (rho) ^-1.　ZT > 1 is a benchmark for practical application. Among LnCuChO (Ln:Lanthanide, Ch:Chalcogen), Goto et al.　clarified that the p-type conduction in LaCuSO originates from Cu defects, reporting that a 1% Cu deficiency decreased the electrical resistivity by six orders of magnitude. In contrast, Kato et al. reported that the electrical resistivity of LaCuSeO did not decrease, despite attempts to introduce Cu defects. In 2024, we reported the first Jonker plot for LnCuChO [Korean J. Materials Research 34, 464 (2024).]. Present report is a proceeding for updated Jonker plot for LnCuChO. Polycrystalline LaCu1-delta S1-xSexO (x=0.5 - 0.99) bulk samples were prepared by solid-state reaction and characterized by XRD. Transport properties and optical band gap (Eg) were evaluated. For x = 0.5, the temperature dependence of rho was semiconducting for delta = 0 and delta~0.02, but metallic for delta ~0.01. The delta~0.01 sample exhibited a maximum ZT of 6.4 x 10-4 at 673 K, with rho = 1.3 x 10-3 Ohm m, kappa = 6.0 Wm−1K−1, and S = 87 micro VK−1. The band gaps were 2.92 eV (delta=0), 2.67 eV (delta~0.01), and 2.84 eV (delta~0.02). In-gap states were observed around 2.1 eV for the delta~0.01 sample. For x = 0.99, 17 samples of delta~0.01 were prepared. Among the prepared samples the one with the lowest electrical resistance exhibited a maximum ZT of 8.6 x 10-5 at 673 K, with rho = 7.4 x 10-3 Ohm m, kappa = 8.7 Wm−1K−1, and S = 91 micro VK−1. Plotting these results on a Jonker plot revealed the existence of two linear mechanisms in the transport properties.

拡張単位胞を考慮した複合アニオン層状化合物LaFeAsOのFeスピン分極の定量評価

伊藤颯大, 鈴木温義, 谷口遼太郎, 神原陽一

[Domestic presentation] 一般社団法人日本材料科学会主催 2026年度学術講演大会プログラム (東海大学湘南キャンパス12号館) ,

2026.05

Oral presentation (general)

複合アニオン層状化合物LaCu1-deltaS0.02Se0.98O (delta = 0.01)の熱電性能評価

佐藤優里子, 東伸彦, 藤岡達英, 的場正憲, 神原陽一

[Domestic presentation] 一般社団法人日本材料科学会主催 2026年度学術講演大会プログラム (東海大学湘南キャンパス12号館) ,

2026.05

Oral presentation (general)

多結晶SmFeAsO1-xHx (x ~ 0.1)の超伝導相図およびメスバウアー分光による研究

何浩, 神原陽一

[Domestic presentation] 第25回メスバウアー分光研究会シンポジウム,

2026.05

Oral presentation (general)

鉄系高温超伝導体 Eu-doped 1111の磁性

神原陽一

[Domestic presentation] 第25回メスバウアー分光研究会シンポジウム,

2026.05

Oral presentation (general)

Crystal Structure Dependence of Oxygen Evolution Reaction for YBa2Cu3O7-delta as Electrochemical Catalyst

Yoichi Kamihara

[International presentation] TechConnect World Innovation Conference and Expo (ローリー, ノースカロライナ州, 米国) ,

2026.03

Oral presentation (general)

Oxygen evolution reaction (OER) is an essential part of the electrolysis of water in the fields of renewable energy, and rechargeable metal–air batteries. However, since the large overpotential of OER causes an energy loss in electrolysis of water, an appropriate OER electrocatalyst is required. The OER requires an electrode as the catalyst to enhance its reaction efficiency. Practical, existing OER catalysts are metal oxides of noble metals like Iridium (Ir) and Ruthenium (Ru). The practical OER catalysts are expensive, and their introduction into large-scale industrial facilities and infrastructure requires high costs, which presents a barrier to smart society. The search for alternative materials that are both cheaper and possess high catalytic activity is required to remove the barrier. One approach for an inexpensive OER catalyst is research on transition metal layered oxides with oxygen vacancies. Indeed, Hirai et al., in [S. Hirai, et al., J. Mater. Chem. A 6, 15102-15109 (2018). Oxygen vacancy-originated highly active electrocatalysts for the oxygen evolution reaction], reported that an layered perovskite-related compound with oxygen vacancies Sr2VFeAsO3-delta (delta >= 0.5) exhibits the lower OER overpotential and the larger reaction rate than those of conventional OER catalyst. Thus, layered perovskite-related compounds possess functionality as electrochemical catalysts. A representative layered perovskite-related compound is the orthorhombic YBa2Cu3O7-delta (YBCO), known as a high-critical-temperature superconductor. As the delta increases in YBCO, superconducting phase disappears, it becomes an insulator, and its crystal structure becomes tetragonal. The functionality of tetragonal YBCO that does not exhibit a superconducting phase is still unknown. In this report, the function of tetragonal YBa2Cu3O7-delta (YBCO) was investigated as a new OER catalyst, which enhances the activity because of the reaction mechanism caused by oxygen deficiency. YBCO samples were synthesized via a sol-gel reaction and calcined at 760, 820 and 920 deg. C. Crystal structures were determined by powder X-ray Diffraction (XRD). The overpotentials of YBCO as an OER catalyst were measured by Rotating Ring Disk Electrodes (RRDE). OER activity of YBCO is superior to a bare glassy carbon and carbon black with regards to OER overpotential and Tafel slope. Moreover, the crystal structure of YBCO may play a role in the enhancement of OER activity. Tetragonal YBCO exhibits better OER catalyst activity than that of orthorhombic YBCO. [N. Takehara, R. Kuramochi, Y. Kamihara et al. Mater. Sci. Tech. Jpn., accepted for publication, (in Japanese)]

鉄系高温超伝導体 Eu-doped 1111 の電子磁気状態相図

神原陽一

[Domestic presentation] 第5回メスバウアー産業利用研究会,

2026.03

Oral presentation (general)

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.

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