Reversal of the lattice structure in SrCoOx epitaxial thin films studied by real-time optical spectroscopy and first-principles calculations

TL;DR

This study demonstrates reversible lattice and electronic structure changes in SrCoOx thin films driven by oxygen content, using real-time optical spectroscopy and first-principles calculations, revealing a controllable phase transition between brownmillerite and perovskite structures.

Contribution

It introduces a method to reversibly switch lattice and electronic phases in SrCoOx films via ambient pressure changes at low temperatures, combining spectroscopy and computational insights.

Findings

Reversible phase transition between brownmillerite and perovskite structures.

Identification of a metal-insulator transition linked to oxygen content.

Real-time spectroscopic ellipsometry effectively monitors structural changes.

Abstract

Using real-time spectroscopic ellipsometry, we directly observed a reversible lattice and electronic structure evolution in SrCoOx (x = 2.5 - 3) epitaxial thin films. Drastically different electronic ground states, which are extremely susceptible to the oxygen content x, are found in the two topotactic phases, i.e. the brownmillerite SrCoO2.5 and the perovskite SrCoO3. First principles calculations confirmed substantial differences in the electronic structure, including a metal-insulator transition, which originates from the modification in the Co valence states and crystallographic structures. More interestingly, the two phases can be reversibly controlled by changing the ambient pressure at greatly reduced temperatures. Our finding provides an important pathway to understanding the novel oxygen-content-dependent phase transition uniquely found in multivalent transition metal oxides.