Presentations

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.

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.

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.

複合アニオン層状化合物半導体LaCuChO (Ch = S, Se)はおよそ 3 eV の光学禁制帯を示す絶縁体である。LaCuChO (Ch = S, Se)は1 at.%程度の銅欠陥により生じる正孔ドープにより、そのp型のキャリアの極性が生じる。LaCuChO (Ch = S, Se)の熱電変換性能について、Jonker plot に即して報告する。

Mixed anion layered compounds (MALCs), which contain several different anions in crystallographic sites, are novel functional materials. Indeed, high-Tc superconductors [1], high-efficient thermoelectric conversion materials [2], transparent semiconductor [3], and electrical catalyst for oxygen evolution reaction [4] have been found in MALCs. In the conference, we demonstrate a review on the MALCs and magnetic properties of a representative MALC, Sr2VFeAsO3-δ. Sr2VFeAsO3-δ is a mixed anion layered compound with a thick-blocking layer composed by a perovskite-related vanadium oxide layer. In 2019, an electric and magnetic phase diagram as a function of oxygen deficiency (δ) on superconducting Sr2VFeAsO3-δ was experimentally demonstrated. In this study, the magnetic stability of V and Fe in Sr2VFeAsO3-δ (δ = 0, 0.25, 0.50) was theoretically verified based on the density functional theory. Stable magnetic phases of the V are antiferromagnetic ordered phase between two ferromagnetic V magnetic layers (so-called A-AFM) for δ = 0. And the stable magnetic phases of V are ferrimagnetic ordered phase (Ferri.) for δ = 0.25, 0.50. Magnetic phases of Fe are a stripe-type antiferromagnetic ordered phase (s-AFM) in δ = 0, 0.25, 0.50, although the magnetic phases of the Fe with δ = 0.25 shows almost the same formation energy between s-AFM and paramagnetic (PM) ordered phases. Theoretical magnetic ordered phases are qualitatively consistent with the experimental electronic and magnetic phase diagrams for Sr2VFeAsO3-δ, although quantitative differences appear between measured for amounts of element specific magnetic moments and theoretical ones. I wiil talk on "Mixed anion compound iron-based superconducting wire and its manufacturing method" in the conference.[5] [1] Y. Kamihara, et al, J. Am. Chem. Soc. 130, 3296-3297 (2008). Iron-based layered superconductor La[O1-xFx]FeAs (x = 0.05-0.12) with Tc = 26 K [2] M. Ishizawa, et al, J. Appl. Phys. 123, 245104 (2018). [3] K. Ueda, et al, Phys. Rev. B 69, 155305_1-4 (2004). Single-atomic-layered quantum wells built in wide-gap semiconductors LnCuOCh (Ln=lanthanide, Ch=chalcogen). [4] S. Hirai, et al, J. Mater. Chem. A 6, 15102-15109 (2018). Oxygen vacancy-originated highly active electrocatalysts for the oxygen evolution reaction [5] Y. Tojo, S. Iwasaki, M. Matoba, and Y. Kamihara, Japanese Patent No. 6814007 (2020). Mixed anion compound iron-based superconducting wire and its manufacturing method (in Japanese)

層状オキシセレン化合物 BiCuSeO は、導電層と絶縁層が交互に積層された構造を持つため、低い熱伝導率を示し、中間温度域での p 型熱電材料として期待されています。本研究の目的は、ほぼ単相の多結晶 BiCuSeO の熱電特性を評価することです。

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。

Bi2Te3系材料の開発以来、実用化を目的とした熱電変換の研究は、デバイスやモジュールに焦点を当てて進められてきました。EuSn2P2は、Bi2Te3結晶と共通の特徴を持っています。

Cr系ペロブスカイト関連複合アニオン層状化合物の酸素発生反応電気化学触媒機能を新たに報告する。

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。

SmFeAsO1-xFxは、複合アニオン層状化合物の内、鉄系高温超伝導体として知られる。SmFeAsO1-xFx の 超伝導転移温度 56 Kを示す試料を作製するための新たな合成ルートについて報告する。

複合アニオン層状化合物であるSr2Mg0.3Ti0.7FeAsO3-delta多結晶の合成方法と、得られた試料の超伝導体積について報告する。