Oxygen active materials are capable of rapidly transporting oxygen and exchanging it with the environment and have a wide range of applications, including solid oxide fuel cells, gas separation membranes, oxygen sensors, chemical looping devices, and memristors.  Recent work has shown that epitaxial strain can play a significant role in altering the transport of oxygen through oxygen active materials, particularly in fluorite structured compounds.  However, transition metal perovskites are an important class of oxygen active materials that have received only limited attention.  In this work we use ab initio methods to model the coupling of biaxial epitaxial strain with oxygen vacancy formation and migration energetics in a range of transition metal perovskites.  We focus on materials of the form LaBO₃, where B = [Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga].  We predict the formation volume and strain response of oxygen vacancy formation energy, demonstrating that non-linear coupling of strain and vacancy formation can yield responses qualitatively different than those expected from simple elasticity arguments.  In particular, as first observed in Ref. [1], we show that in some cases the vacancy can weaken the bonding and lower the elastic constants, which allows the formation of a vacancy to reduce the strain energy.  This effect leads to stabilization of the vacancy under both compressive and tensile strain, even though the vacancy has positive formation volume.

We also predict the migration volume and the strain response of oxygen migration energetics, here finding that values are quite consistent with a simple elastic strain model.[2]  We find that tensile (compressive) biaxial strain reduces (enhances) the oxygen vacancy migration barrier approximately linearly across the systems studied (Figure 1).  The average decrease in migration energy is 66 meV per percent strain for a single selected hop, with a low of 36 and a high of 89 meV decrease in migration barrier per percent strain across all the systems studied.  In general we find that the oxygen transport kinetics can be altered by orders of magnitude in perovskites through strain effects on both vacancy content and migration energetics.  These effects could play a significant role on materials performance at interfaces and in thin-film devices.

[1] W. Donner, C. L. Chen, M. Liu, A. J. Jacobson, Y. L. Lee, M. Gadre, and D. Morgan, Epitaxial Strain-Induced Chemical Ordering in La0.5Sr0.5CoO3-delta Films on SrTiO3, Chemistry of Materials 23, p. 984-988 (2011).

[2] T. Mayeshiba and D. Morgan, Strain Effects on Oxygen Migration in Perovskites, Phys. Chem. Chem. Phys. 17, p. 2715-2721 (2015 ).