Cation ordering and oxygen transport behaviour in Sr_1−3x/2La_xTiO₃perovskites

Abstract

Molecular dynamics and genetic algorithm simulations are used to identify the mechanisms by which oxygen is transported through the Sr 1−3x/2 La x TiO 3 family of perovskites as a function of x. Across this compositional range the relative stability of ordered structures and random arrangements of A cation sublattice ions and vacancies is established. O and Ti Frenkel pair formation is then predicted. This shows that Ti defects are more favourable for all La-containing compositions, but have a larger defect volume than O defects for low x. Oxygen diffusion at high temperature is determined using Molecular Dynamics simulations. Two types of oxygen transport mechanisms are identified, that each contribute to oxygen diffusion in ordered structures. These mechanism involve transient O and Ti defects respectively, and provide means for O ions to swap positions. Depending on cation ordering, they can be correlated in space, which causes different diffusion patterns depending on composition.