Presentations

Fe置換したYBCOの水素下熱処理による超伝導転移温度を測定し、反応経路に依存することが明らかになった。

複合アニオン層状化合物(Mixed anion layered compound, MALC) RETMPnO (RE : 希土類遷移金属. TM : Fe, Ni. Pn : P, As.) は低温下で超伝導を示す. TM=Ni であるNi 系MALC 超伝導体LaNiPO はLa-O 層とNi-P 層の積層構造をもち, 低温下で超伝導を示す. 一方で, 超伝導を示さない鉄系MALC であるLaFeAsO は, 57Fe のメスバウワ分光測定において130 K 以下で磁気分裂を示す. 61Ni のメスバウワ分光測定は線源である61Co の半減期は100 分であり, 測定例が少ない. 我々は多結晶LaNiPO試料の合成を行い, 試料中の61Ni についてメスバウワ分光測定を行う.

Bi-2212 layered cuprate samples were synthesized using the sol–gel method, and their structures were identified by X‑ray diffraction (XRD) analysis. In addition, the oxygen vacancy formation tendencies under thermal treatment were quantitatively determined through computational experiments.

多結晶SmFeAsO1-xHxの高圧合成と水素濃度決定基準と低温での磁性を報告する。

Hole-doping effects in REFeAsO (1111) were demonstrated by substituting Eu2+ for La3+. Unlike typical electron-doped superconductors, Eu-doped LaFeAsO exhibited normal conducting behavior with structural transitions near 150 K. By co-doping with fluorine, we (A.S and Y. K., et al) successfully induced superconductivity at Tc ~ 30 K. These findings clarify the bipolar electronic phase diagram of 1111-type iron-based superconductors through diverse chemical substitutions.

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.

Synthesis and procedures and transport properties of 21113V Fe-based Superconductors, polycrystalline Sr2V1-xTixFeAsO3 Samples are demonstrated.

鉄系高温超伝導体の母相であるLaFeAsOのLaサイトにEuを置換した化合物の電気的性質を報告する。

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)]

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.

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.

The magnetic flux density (Bz) distribution under magnetic field (Hz) of surface on polycrystalline H-doped SmFeAsO0 sample was observed and quantified using magneto-optical (MO) imaging method.

The surface energy of Bi2Sr2CaCu2O8+x (Bi-2212) was calculated by first-principles calculations using a slab model of Bi-2212, and the stability was evaluated. A correlation between surface energy and catalytic capacity has also been reported, so there is room for further study.

新規n型Zintl相化合物 Rb(Cd,Zn)4As3の高温輸送現象について報告する。

143-Zintl相化合物Rb(Cd,Zn)4As3多結晶体の結晶構造と熱電変換性能の組成制御による向上を報告する。

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.

鉄系高温超伝導体 H-doped SmFeAsO (Sm1111) のデバイ温度をメスバウワ分光測定でも求まるアイソマーシフトの温度変化より求めた。

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.