First-principles study of the deformation and migration mechanisms of Li–La–Ti–O perovskite under uniaxial stress

Abstract

We have investigated the deformation of and Li-ion migration in Li–La–Ti–O (LLTiO) under various uniaxial stresses by first-principles calculations. Structural analysis showed after relaxation, LLTiO without stress possesses a distorted lattice with the displacement of Li ion and tilting of the TiO₆ octahedrons. Migration analysis without stress showed that the Li ion can migrate via its equivalent sites with an energy barrier of 0.31–0.37 eV. In addition, the energy becomes high when the Li ion migrates through bottlenecks, and also when the migration is accompanied by significant changes in the tilt angles of the octahedrons. Mechanical and migration analyses under uniaxial stresses along the z axis showed that the tensile stress reduces the lattice distortion, which remarkably affects the Li-ion migration, while the effect of stress on the Li-ion migration varies depending on the path. The current results suggest that an appropriate configuration of the ions and controlling the stress could possibly improve the Li-ion migration in LLTiO, but stress could also have a detrimental effect on the Li-ion migration.