Joe Kajitani

In-plane chemical pressure essential for superconductivity in BiCh2-based (Ch: S, Se) layered structure.

BiCh2-based compounds (Ch: S, Se) are a new series of layered superconductors, and the mechanisms for the emergence of superconductivity in these materials have not yet been elucidated. In this study, we investigate the relationship between crystal structure and superconducting properties of the BiCh2-based superconductor family, specifically, optimally doped Ce1−xNdxO0.5F0.5BiS2 and LaO0.5F0.5Bi(S1−ySey)2. We use powder synchrotron X-ray diffraction to determine the crystal structures. We show that the structure parameter essential for the emergence of bulk superconductivity in both systems is the in-plane chemical pressure, rather than Bi-Ch bond lengths or in-plane Ch-Bi-Ch bond angle. Furthermore, we show that the superconducting transition temperature for all REO0.5F0.5BiCh2 superconductors can be determined from the in-plane chemical pressure.

Correlation between crystal structure and superconductivity in LaO0.5F0.5BiS2

Abstract Correlation between crystal structure and superconducting properties of the BiS2-based superconductor LaO0.5F0.5BiS2 was investigated. We have prepared LaO0.5F0.5BiS2 polycrystalline samples with various lattice constants. It was found that high-pressure annealing generated uniaxial strain along the c axis. Further, the highly-strained sample showed higher superconducting properties. We concluded that the uniaxial strain along the c axis was positively linked with the enhancement of superconductivity in the LaO1−xFxBiS2 system.

Enhancement of Tc by Uniaxial Lattice Contraction in BiS2-Based Superconductor PrO0.5F0.5BiS2

We investigated the crystal structure and superconducting properties of As-grown and high-pressure-annealed PrO0.5F0.5BiS2. We found that the high-pressure annealing generates uniaxial lattice contraction along the c axis. Both As-grown and high-pressure-annealed PrO0.5F0.5BiS2 show bulk superconductivity. The Tc of PrO0.5F0.5BiS2 is clearly enhanced from Tczero = 3.6 K to Tczero = 5.5 K by high-pressure annealing. Unexpectedly, the semiconducting characteristics is relatively enhanced by high-pressure annealing. Namely, we assume that the enhancement of Tc can not be understood by an increase of electron carriers. Having considered these facts, we conclude that the enhancement of Tc correlates with uniaxial lattice contraction along the c axis in PrO0.5F0.5BiS2.

Enhancement of thermoelectric properties by Se substitution in layered bismuth-chalcogenide LaOBiS2-xSex

We have investigated the thermoelectric properties of the novel layered bismuth chalcogenides LaOBiS2-xSex. The partial substitution of S by Se produced the enhancement of electrical conductivity (metallic characteristics) in LaOBiS2-xSex. The power factor largely increased with increasing Se concentration. The highest power factor was 4.5 μW/cmK2 at around 470 °C for LaOBiS1.2Se0.8. The obtained dimensionless figure-of-merit (ZT) was 0.17 at around 470 °C in LaOBiS1.2Se0.8.

High-temperature thermoelectric properties of novel layered bismuth-sulfide LaO1−xFxBiS2

We have investigated the high-temperature thermoelectric properties of the layered compound LaO1−xFxBiS2. The electrical resistivity of LaOBiS2 showed an anomalous behavior; a metal-semiconductor transition was observed around 270 K. It was found that the value of the electrical resistivity decreased with F substitution. The Seebeck coefficient decreased with increasing F concentration. The highest power factor of 1.9 μW/cm K2 at 480 °C was obtained for LaOBiS2.

Effect of high-pressure annealing on the normal-state transport of LaO 0.5 F 0.5 BiS 2

We study normal state electrical, thermoelectrical, and thermal transport in polycrystalline

Electrical and thermal transport of layered bismuth-sulfide EuBiS 2 F at temperatures between 300 and 623 K

{\mathrm{BiS}}_{2}

Increase in Tc and Change of Crystal Structure by High-Pressure Annealing in BiS2-Based Superconductor CeO0.3F0.7BiS2

-based compounds, which become superconducting by F doping on the O site. In particular, we explore undoped

Anisotropic upper critical field of theBiS2-based superconductorLaO0.5F0.5BiS2

{\mathrm{LaOBiS}}_{2}

The effect of RE substitution in layered REO0.5F0.5BiS2: chemical pressure, local disorder and superconductivity

and doped