  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.
