Revisiting the zero-temperature phase diagram of stoichiometric SrCoO3 with first-principles methods

TL;DR

This study uses first-principles density functional theory to analyze the zero-temperature phase diagram of SrCoO3, revealing new stable phases and strain-induced transitions that challenge previous assumptions.

Contribution

It identifies a lower-energy tetragonal phase in bulk SrCoO3 and clarifies the nature of strain-induced phase transitions in thin films, revising earlier theoretical predictions.

Findings

Tetragonal P4/mbm phase is more stable than cubic Pm-3m in bulk.

Tensile strain causes an isostructural magnetic transition.

Large compressive strain induces combined structural, electronic, and magnetic changes.

Abstract

By using first-principles methods based on density functional theory we revisited the zero-temperature phase diagram of stoichiometric SrCoO3, a ferromagnetic metallic perovskite that undergoes significant structural, electronic, and magnetic changes as its content of oxygen is decreased. We considered both bulk and epitaxial thin film geometries. In the bulk case, we found that a tetragonal P4/mbm phase with moderate Jahn-Teller distortions and c/a ratio of ~1/sqrt{2} is consistently predicted to have a lower energy than the thus far assumed ground-state cubic Pm-3m phase. In thin films, we found two phase transitions occurring at compressive and tensile epitaxial strains. However, in contrast to previous theoretical predictions, our results show that: (i) the phase transition induced by tensile strain is isostructural and involves only a change in magnetic spin order (that is, not a metallic to insulator transformation), and (ii) the phase transition induced by compressive strain comprises simultaneous structural, electronic and magnetic spin order changes, but the required epitaxial stress is so large (<-6%) that is unlikely to be observed in practice. Our findings call for a revision of the crystallographic analysis performed in fully oxidised SrCoO3 samples at low temperatures, as well as of previous first-principles studies.