Strain effects on oxygen migration in perovskites

Abstract

Fast oxygen transport materials are necessary for a range of technologies, including efficient and cost-effective solid oxide fuel cells, gas separation membranes, oxygen sensors, chemical looping devices, and memristors. Strain is often proposed as a method to enhance the performance of oxygen transport materials, but the magnitude of its effect and its underlying mechanisms are not well-understood, particularly in the widely-used perovskite-structured oxygen conductors. This work reports on an ab initio prediction of strain effects on migration energetics for nine perovskite systems of the form LaBO3, where B = [Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga]. Biaxial strain, as might be easily produced in epitaxial systems, is predicted to lead to approximately linear changes in migration energy. We find that tensile biaxial strain reduces the oxygen vacancy migration barrier across the systems studied by an average of 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 systems. The estimated range for the change in migration barrier within each system is ±25 meV per percent strain when considering all hops. These results suggest that strain can significantly impact transport in these materials, e.g., a 2% tensile strain can increase the diffusion coefficient by about three orders of magnitude at 300 K (one order of magnitude at 500 °C or 773 K) for one of the most strain-responsive materials calculated here (LaCrO3). We show that a simple elasticity model, which assumes only dilative or compressive strain in a cubic environment and a fixed migration volume, can qualitatively but not quantitatively model the strain dependence of the migration energy, suggesting that factors not captured by continuum elasticity play a significant role in the strain response.

Direct observation of oxygen vacancy-driven structural and resistive phase transitions in La2/3Sr1/3MnO3

“…Another effect that could contribute to the elongated shape of structural domains is migration anisotropy within LSMO. Lattice strains in perovskite oxides are known to affect the diffusion coefficient via a change of interatomic bond lengths2728, favouring oxygen migration perpendicular to the elongated unit cell29. Elongation of the out-of-plane lattice spacing in an oxygen-deficient LSMO film would thus favour horizontal oxygen vacancy migration.…”

Strain control of oxygen kinetics in the Ruddlesden-Popper oxide La1.85Sr0.15CuO4

“…The range of approximate estimated k * values for the different strain states were obtained using the estimate of 89 meV/(% strain) variation in the activation barrier for k *. This estimate was based on the maximum difference in the calculated activation barriers for O migration with strain for an array of perovskite materials 32 (additional details on how k * was approximated can be found Supplementary Note 3). It is important to note that the as-grown state was used as the reference for the calculations of k *; thus, the computed lattice response times are all relative to the initial, equilibrium as-grown state.…”

Roles of Bulk and Surface Chemistry in the Oxygen Exchange Kinetics and Related Properties of Mixed Conducting Perovskite Oxide Electrodes

“…Oxygen vacancy mobility may also be enhanced by more facile reduction of B site cations since transfer of some electron density from oxygen makes it smaller and more able to pass through the A-A-B cation triangle [39,40]; in this sense migration enthalpies may scale with oxygen vacancy formation enthalpies. Tensile strain has also been calculated to decrease the migration barrier for oxygen hopping in perovskites [41]. The presence of cation vacancies and their induced disorder has additionally been suggested to increase the ionic mobility [42].…”

“…Again epitaxial thin film model electrodes, such as deposited by PLD, are an asset in performing fundamental studies, as strain can be induced by the energetic growth process and/or by coherent lattice mismatch with the substrate or adjacent layers (accounting for thermal and chemical expansion). Beyond enhancements in oxide ion mobility [41] or incorporation kinetics that may be derived by stretching the lattice through which the ion passes, there is also a chemo-mechanical coupling in many systems, whereby the applied strain can lead to changes in point defect chemistry [93]. Both of these effects could, in principle, alter surface oxygen incorporation/excorporation energetics.…”