Details of a Researcher - Kamihara, Yoichi

Presentations -

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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

[International presentation] GCIM2025,

2025.06

Poster presentation, 済州、韓国

Transport properties of a mixed anion layered compound LaCu0.99Se0.99S0.01O as a wide-gap semiconductor

Yoichi KAMIHARA, Nobuhiko AZUMA, Tatsuhide FUJIOKA, Masanori MATOBA

[International presentation] GCIM2025,

2025.06

Oral presentation (general)

熱電変換材料（TEC）と技術は、300～600 Kでの性能向上が課題です。現在の主流はBi₂Te₃系材料ですが、新たな材料の開発が進められています。2000年代以降、混合アニオン層状化合物（MALCs）が電子材料として注目され、LaCuChO（Ch＝S, Se）やBiCuSeOが報告されました。2024年、我々はLaCuChOの熱電特性をJonkerプロットで評価しました。本会議では、Cu欠損や混合アニオン状態を持つLaCu₀.₉₉Se₀.₉₉S₀.₁Oの輸送特性について議論します。

Polycrystallic synthesis of SnPn layered compound EuSn2P2

Zihao LIU, Takamasa SHIMURA, Ryosuke SAKAGAMI, Yoichi KAMIHARA, Masanori MATOBA

[International presentation] GCIM2025,

2025.06

Oral presentation (general), 済州、韓国

Advancing oxygen evolution reaction through mixed-anion compounds

Hao HE, Rei KURAMOCHI, Michitaro YAMAGUCHI, Yoichi KAMIHARA

[International presentation] GCIM2025,

2025.06

Oral presentation (general), 済州、韓国

Synthesis of 21113V Fe-based superconductors, polycrystalline Sr2V1-xTixFeAsO3 samples

Aurélien ANTUNEZ, Haruyoshi SUZUKI, Yoichi KAMIHARA, Masanori MATOBA

[International presentation] GCIM2025,

2025.06

Poster presentation, 済州、韓国

2006年に鉄系混合アニオン層状化合物（MALC）超伝導体が発見されて以来、多くの研究が進められてきました。その中で、Sr₂VFeAsO₃−δ（21113系）が有望視され、Tconsetが37.2Kと報告されています。本研究では、Tiをドープした Sr₂V₁₋ₓTiₓFeAsO₃（Tiドープ21113V）を固相反応法で合成しました。SrO、FeAs、V、V₂O₅、Ti₂O₃ を 1050℃で40時間焼成し、粉末・バルクXRDで結晶相を解析しました。さらに、四端子法による電気抵抗測定とMPMSによる磁化測定を行いました。

Novel synthesis route of superconducting polycrystalline SmFeAsO1-xFx with Tc = 56 K

Y. Kamihara, Y. Kobayashi, R. Takeuchi, M. Matoba

[International presentation] TechConnect World Innovation 2025 (Austin, TX, USA) ,

2025.06

Oral presentation (general)

Ti-Doping of 21113V Fe-based superconductors, polycrystalline Sr2V1-xTixFeAsO3 samples

ANTUNEZ Aurelien, SUZUKI Haruyoshi, KAMIHARA Yoichi, MATOBA Masanori