  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.
