Negative ionic states of tin in the oxide superconductor Sr$_{3-x}$SnO revealed by M\"{o}ssbauer spectroscopy

TL;DR

This study uses Mössbauer spectroscopy to reveal negative ionic states of tin in Sr$_{3-x}$SnO, showing coexistence of different Sn oxidation states and their relation to Sr deficiency and vibrational properties.

Contribution

It provides the first evidence of negative ionic tin states in an oxide superconductor and links local vibrational energies to specific Sn ionic states influenced by Sr deficiency.

Findings

Sn exhibits negative ionic states in Sr$_{3-x}$SnO.

Presence of multiple Sn ionic states correlates with Sr deficiency.

Vibrational energies of Sn ions depend on their ionic state.

Abstract

We report the temperature variation of the $^{119}$Sn-M\"{o}ssbauer spectra of the antiperovskite (inverse perovskite) oxide superconductor Sr$_{3-x}$SnO. Both superconductive (Sr-deficient) and non-superconductive (nearly stoichiometric) samples exhibit major $\gamma$-ray absorption with isomer shift similar to that of Mg$_2$Sn. This fact shows that Sr$_{3-x}$SnO contains the metallic anion Sn$^{4-}$, which is rare especially among oxides. In both samples, we observed another $\gamma$-ray absorption with a larger isomer shift, indicating that there is another ionic state of Sn with a higher oxidation number. The temperature dependence of the absorption intensities reveals that the Sn ions exhibiting larger isomer shifts have a lower energy of the local vibration. The larger isomer shift and lower vibration energy are consistent with the values estimated from the first-principles calculations for hypothetical structures with various Sr-deficiency arrangements. Therefore, we conclude that the additional $\gamma$-ray absorptions originate from the Sn atoms neighboring the Sr deficiency.