Controlled synthesis of the antiperovskite oxide superconductor Sr$_{3-x}$SnO

TL;DR

This paper presents an improved synthesis method for Sr$_{3-x}$SnO, a recently discovered antiperovskite oxide superconductor, enabling better control of strontium deficiency and revealing its effects on superconductivity.

Contribution

It introduces a controlled synthesis technique for Sr$_{3-x}$SnO, enhancing superconducting volume fraction and enabling detailed studies of its superconducting properties.

Findings

Superconductivity observed at T_c ~ 5 K in Sr$_{3-x}$SnO.

Superconducting volume fraction increased by 40% with improved synthesis.

Strontium raw material purity significantly affects superconductivity.

Abstract

A large variety of perovskite oxide superconductors are known, including some of the most prominent high-temperature and unconventional superconductors. However, superconductivity among the oxidation state inverted material class, the antiperovskite oxides, was reported just recently for the first time. In this superconductor, Sr$_{3-x}$SnO, the unconventional ionic state Sn$^{4-}$ is realized and possible unconventional superconductivity due to a band inversion has been discussed. Here, we discuss an improved facile synthesis method, making it possible to control the strontium deficiency in Sr$_{3-x}$SnO. Additionally, a synthesis method above the melting point of Sr$_{3}$SnO is presented. We show temperature dependence of magnetization and electrical resistivity for superconducting strontium deficient Sr$_{3-x}$SnO ($T_{\mathrm{c}}$ ~ 5 K) and for Sr$_{3}$SnO without a superconducting transition down to 0.15 K. Further, we reveal a significant effect of strontium raw material purity on the superconductivity and achieve 40% increased superconducting volume fraction (~100%) compared to the highest value reported so far. More detailed characterisation utilising powder X-ray diffraction and energy-dispersive X-ray spectroscopy show that a minor cubic phase, previously suggested to be a Sr$_{3-x}$SnO, is SrO. The improved characterization and controlled synthesis reported herein enable detailed investigations on the superconducting nature and its dependency on the strontium deficiency in Sr$_{3-x}$SnO.