Atomistic calculations of charged point defects at grain boundaries in SrTiO$_3$

TL;DR

This study uses atomistic simulations to analyze the structures and formation energies of oxygen vacancies at specific grain boundaries in SrTiO$_3$, providing insights into defect behavior relevant to material growth.

Contribution

It introduces a continuum electrostatic model to accurately correct for artifacts in atomistic simulations of charged defects at grain boundaries in SrTiO$_3$.

Findings

Calculated oxygen vacancy formation energies vary across grain boundaries.

Electrostatic corrections improve accuracy of defect energy calculations.

Analysis links local charge densities to vacancy formation energies.

Abstract

Oxygen vacancies have been identified to play an important role in accelerating grain growth in polycrystalline perovskite-oxide ceramics. In order to advance the fundamental understanding of growth mechanisms at the atomic scale, classical atomistic simulations were carried out to investigate the atomistic structures and oxygen vacancy formation energies at grain boundaries in the prototypical perovskite-oxide material SrTiO$_3$. In this work, we focus on two symmetric tilt grain boundaries, namely $\Sigma$5(310)[001] and $\Sigma$5(210)[001]. A one-dimensional continuum model is adapted to determine the electrostatic potential induced by charged lattice planes in atomistic structure models containing grain boundaries and point defects. By means of this model, electrostatic artifacts, which are inherent to supercell models with periodic or open boundary conditions, can be taken into account and corrected properly. We report calculated formation energies of oxygen vacancies on all the oxygen sites across boundaries between two misoriented grains, and we analyze and discuss the formation-energy values with respect to local charge densities at the vacant sites.