Investigation of Aging Effects on Superconducting Properties of BiS₂-based Compounds: First 12-Year Restudy

Decomposition of superconductors sometimes becomes crucial when studying essential physical properties of the superconductors. For example, the cuprate superconductor YBa₂Cu₃O_7-d decomposes by long-time air exposure. In this study, we investigate the aging effects on superconducting properties of BiS₂-based superconductors Bi₄O₄S₃ and LaO_0.5F_0.5BiS₂; both were first synthesized in 2012, using their polycrystalline samples synthesized several years ago. We find that 12-year-old Bi₄O₄S₃ samples exhibit bulk superconductivity with a slight degradation of the superconducting transition temperature (T_c) of 0.2 K. For a high-pressure-synthesized LaO_0.5F_0.5BiS₂ sample, clear decrease in T_c is observed, which suggests that high-pressure strain is reduced by aging.