Defect Clustering in Rare-Earth-Doped BaTiO₃ and SrTiO₃ and Its Influence on Dopant Incorporation

Abstract

Rare-earth (RE) doping of BaTiO 3 and SrTiO 3 has received tremendous research attention in recent decades. Although RE doping has been a particularly popular topic, little or no attention has been given to the contribution from different defect arrangements. In this study, we use a proven interatomic potential model to calculate the binding energies of different RE donor defect (Ba/Sr site doping) configurations in BaTiO 3 and SrTiO 3 . We consider two standard donor defect mechanisms, namely, charge compensation from Ba/Sr vacancies or Ti vacancies. Consistently stronger negative binding energies are calculated for SrTiO 3 compared to BaTiO 3 . We also show that SrTiO 3 can accept a larger range of RE ion sizes at the divalent cation site than BaTiO 3 . This is highlighted by the simple trend of increasing binding energy with decreasing RE ion size found for the defect configurations with a Ti vacancy in SrTiO 3 . Conversely, defect clustering in BaTiO 3 can cause significant strain on the lattice, resulting in positive binding energies. Our results show that one standard defect arrangement per incorporation mechanism cannot be applied to all dopants. We clearly show that the lowest energy defect configuration is dependent on both the dopant and host material. The consequences of these findings for the overall defect incorporation energetics in BaTiO 3 and SrTiO 3 are also presented.