First-principle study of hidden phases in oxygen-deficient La_1-xSr_xCoO_3-δ perovskites

La_1-xSr_xCoO_3-δ (LSCO) is a promising material for neuromorphic devices, as its topotactic phase transitions from perovskite to oxygen-deficient phases are accompanied by dramatic changes in electronic properties. Such changes originate from a subtle dependence of orbital filling on the geometric environment created by the presence of oxygen vacancies, when an electric bias is applied to the material. Interestingly, in LSCO the threshold voltage required to initiate a transition exhibits a non-monotonic behavior as a function of Sr-concentration and biaxial strain [1]. Using DFT+U calculations and the Quantum Espresso code, we show that the variation in the threshold voltage in LSCO films can be explained by the presence of Grenier phases during a topotactic phase transition. We find that the electronic structure of Grenier phases depends on the Sr-concentration and strain conditions, and that metallic and insulating phases are obtained for x = 0.33 and 0.67, respectively. Given that in LSCO insulating domains give rise to barriers for the topotactic phase transitions, our findings provide a guideline to control the electronic properties in LSCO and attain desired phase transitions.

[1] Chaturvedi et al. ACS Appl. Mater. Interfaces 13, 51205 (2021)