Element Substitution Effect on Superconductivity in BiS2-Based NdO_(1-x)F_xBiS₂

Recently, new layered superconductors having a BiS2-type conduction layer have been discovered. NdO1-xFxBiS2 is a typical BiS2-based superconductor with a maximum Tc of 5.4 K. In this study, the effect of element substitution within the superconducting layer of BiS2-based NdO0.5F0.5BiS2 was investigated. We systematically synthesized two kinds of polycrystalline samples of NdO0.5F0.5Bi(S1-xSex)2 and NdO0.5F0.5Bi1-ySbyS2 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 NdO0.5F0.5Bi(S1-xSex)2. When Bi was partially substituted by Sb, the uniaxial lattice contraction along the c axis was observed in NdO0.5F0.5Bi1-ySbyS2. In the Sb-substituted system, a metal-insulator transition was observed with increasing Sb concentration.