Inversion of defect interactions due to ordering inSr1−3x∕2LaxTiO3perovskites: An atomistic simulation study

Abstract

${\mathrm{Sr}}_{1\ensuremath{-}3x∕2}{\mathrm{La}}_{x}{\mathrm{TiO}}_{3}$ perovskites exhibit large variations in radiation resistance and $A$-site vacancy ordering, depending on $x$ and thermal history. In this study we use a combination of ab initio and classical simulation techniques to characterize the energetics of $A$-site vacancy and cation interactions. We find that the $A$-site interactions follow intuitive electrostatic arguments at low concentrations of defects, promoting association of La ions with vacancies and dissociation of vacancy-vacancy pairs. However, when long-range $A$-site ordering is present, the defect interactions are inverted due to strain forces arising from cooperative atomic relaxations. To study the regime of partial ordering between these two extremes we use Monte Carlo simulations combined with lattice energy minimization. These show that in highly disordered configurations electrostatic defect interactions dominate, making it difficult for the thermodynamically stable (strain-stabilized) long-range order to nucleate. To quantify the critical nucleation volume we consider the balance of electrostatic and strain forces as a function of the size of the ordered region. These results provide a useful framework for understanding $A$-site ordering in experimental ${\mathrm{Sr}}_{1\ensuremath{-}3x∕2}{\mathrm{La}}_{x}{\mathrm{TiO}}_{3}$ samples, as well as shedding light on the implications of intrinsic defect ordering for radiation resistance.