Element Substitution Effect on Superconductivity in BiS 2 -Based NdO1−x F x BiS 2

Abstract

Recently, new layered superconductors having a BiS2-type conduction layer have been discovered. NdO1−x F x BiS2 is a typical BiS2-based superconductor with a maximum T c of 5.4 K. In this study, the effect of element substitution within the superconducting layer of BiS2-based NdO0.5 F 0.5BiS2 was investigated. We systematically synthesized two kinds of polycrystalline samples of NdO0.5 F 0.5Bi(S1−x Se x )2and NdO0.5 F 0.5Bi1−y Sb y S 2 by a two-step solid-state reaction method. The phase purity and the changes in lattice constants were investigated by X-ray diffraction. The superconducting properties were investigated by magnetic susceptibility and electrical resistivity measurements. It was found that the partial substitution of S by Se resulted in the uniaxial lattice expansion along the a-axis. The superconducting transition temperature were gradually degraded with increasing Se concentration in NdO0.5 F 0.5Bi(S1−x Se x )2. When Bi was partially substituted by Sb, the uniaxial lattice contraction along the c-axis was observed in NdO0.5 F 0.5Bi1−y Sb y S 2. In the Sb-substituted system, a metal-insulator transition was observed with increasing Sb concentration.