Strain Control of Oxygen Vacancies in Epitaxial Strontium Cobaltite Films

TL;DR

This study demonstrates that applying epitaxial strain to strontium cobaltite films effectively controls oxygen vacancy concentration at low temperatures, enabling tailored electronic and magnetic properties for energy and device applications.

Contribution

The paper introduces strain engineering as a novel method to manipulate oxygen vacancies in epitaxial oxides at low temperatures, independent of environmental conditions.

Findings

A 2% biaxial tensile strain reduces oxygen activation energy by ~30%.

Strain induces a transition from ferromagnetic metal to antiferromagnetic insulator.

Oxygen vacancy concentration can be tuned independently of ambient environment.

Abstract

The ability to manipulate oxygen anion defects rather than metal cations in complex oxides can facilitate creating new functionalities critical for emerging energy and device technologies. However, the difficulty in activating oxygen at reduced temperatures hinders the deliberate control of important defects, oxygen vacancies. Here, strontium cobaltite (SrCoOx) is used to demonstrate that epitaxial strain is a powerful tool for manipulating the oxygen vacancy concentration even under highly oxidizing environments and at annealing temperatures as low as 300 C. By applying a small biaxial tensile strain (2%), the oxygen activation energy barrier decreases by ~30%, resulting in a tunable oxygen deficient steady-state under conditions that would normally fully oxidize unstrained cobaltite. These strain-induced changes in oxygen stoichiometry drive the cobaltite from a ferromagnetic metal towards an antiferromagnetic insulator. The ability to decouple the oxygen vacancy concentration from its typical dependence on the operational environment is useful for effectively designing oxides materials with a specific oxygen stoichiometry.