SnO*

We recently reported bulk superconductivity in the antiperovskite oxide Sr_3-xSnO, with a possibility of topological nature. We investigate the evolution of superconducting properties with the nominal Sr deficiency x₀. In all superconducting samples, two superconducting phases with T_c ≈ 5 K and 1 K appear concurrently that originate from Sr_3-xSnO. Mössbauer spectroscopy reveals an unusual Sn^4- ionic state in both stoichiometric and superconductive samples. In addition to the main absorption peak, we observe a satellite peak attributable to the Sn sites with nearest-neighbor Sr deficiencies. The intensities of these two peaks exhibit a rather different temperature dependence, possibly reflecting different environment of the lattice vibrations. These results clarifying the Sr deficiency dependence of the normal and superconducting properties of the antiperovskite oxide Sr_3-xSnO will promote future work on this class of materials.