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.

High-quality polycrystalline samples of LaO0.5F0.5BiS2 were obtained using high-pressure synthesis technique. The LaO0.5F0.5BiS2 sample prepared by heating at 700 ºC under 2 GPa showed superconductivity with superconducting transition temperatures (Tc) of Tc onset = 11.1 and Tc zero = 8.5 K in the electrical resistivity measurements and Tc onset = 11.5 and Tc irr = 9.4 K in the magnetic susceptibility measurements, which are obviously higher than those of the LaO0.5F0.5BiS2 polycrystalline samples obtained using conventional solid-state reaction. It was found that the high-Tc phase can be stabilized under high pressure and relatively-low annealing temperature. X-ray diffraction analysis revealed that the high-Tc phase possessed a small ratio of lattice constants of a and c, c/a.

We have systematically investigated the crystal structure, magnetic susceptibility, and electrical resistivity of the BiS 2 -based superconductor

We have systematically investigated the crystal structure and the magnetic properties of BiS 2 -based superconductor Ce 1-x Nd x O 1-y F y BiS 2 (x = 0 -1.0, y = 0.3 , 0.5 and 0.7) and Nd 1-z Sm z O 1-y F y BiS 2 (x = 0 -0.8, y = 0.3 , 0.5 and 0.7) . In the REOBiS 2 system, both crystal structure and physical properties are tunable by substituting with the different RE (RE = rare earth) elements, having a different ionic radius, such as Ce, Nd and Sm.In the Ce 1-x Nd x O 1-y F y BiS 2 system, bulk superconductivity is observed for

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 W/cmK 2 at around 470 ºC for LaOBiS1.2Se0.8. The obtained dimensionless figure-of-merit (ZT) was 0.17 at around 470 ºC in LaOBiS1.2Se0.8.