Evolution of Superconductivity with Sr-Deficiency in Antiperovskite Oxide Sr_3-xSnO

Bulk superconductivity was recently reported in the antiperovskite oxide Sr_3-xSnO, with a possibility of hosting topological superconductivity. We investigated the evolution of superconducting properties such as the transition temperature T_c and the size of the diamagnetic signal, as well as normal-state electronic and crystalline properties, with varying the nominal Sr deficiency x₀. Polycrystalline Sr_3-xSnO was obtained up to x₀ = 0:6 with a small amount of SrO impurities. The amount of impurities increases for x₀ > 0.6, suggesting phase instability for high deficiency. Mössbauer spectroscopy reveals an unusual Sn^4- ionic state in both stoichiometric and deficient samples. By objectively analyzing superconducting diamagnetism data obtained from a large number of samples, we conclude that the optimal x₀ lies in the range 0.5 < x₀ < 0.6. In all superconducting samples, two superconducting phases appear concurrently that originate from Sr_3-xSnO but with varying intensities. These results clarify the Sr deficiency dependence of the normal and superconducting properties of the antiperovskite oxide Sr_3-xSnO will ignite future work on this class of materials.