The thermodynamic and kinetic properties of mono- and di-vacancy defects in cubic (para-electric) barium titanate BaTiO3 were studied by means of density-functional theory calculations. It was determined which vacancy types prevail for given thermodynamic boundary conditions. The calculations confirm the established picture that vacancies occur in their nominal charge states almost over the entire band gap. For the dominating range of the band gap the di-vacancy binding energies were constant and negative. The system, therefore, strives to achieve a state in which, under metal-rich (O-rich) conditions, all metal (O) vacancies were bound in di-vacancy clusters. The migration barriers were calculated for mono-vacancies in different charge states. As O vacancies were found to readily migrate at typical growth temperatures, di-vacancies could be formed at ease. The key results of the present study with respect to the thermodynamic behavior of mono- and di-vacancies influence the initial defect distribution in the ferroelectric phases and therefore the conditions for aging.

Thermodynamics of Mono- and Di-Vacancies in Barium Titanate. P.Erhart, K.Albe: Journal of Applied Physics, 2007, 102[8], 084111