The effect of intrinsic point defects on ferroelectric polarization behavior of SrTiO$_3$

TL;DR

This study uses density functional theory to explore how intrinsic point defects influence ferroelectric polarization and switching in SrTiO₃, revealing defect-specific effects on polarization magnitude and activation barriers.

Contribution

It provides detailed insights into how various intrinsic defects and defect clusters modulate ferroelectric behavior in SrTiO₃, highlighting defect engineering possibilities.

Findings

Ti_Sr antisite defects induce strong ferroelectric polarization.

Oxygen vacancies can enhance or reduce polarization depending on configuration.

Defect-induced polarization can be tuned by Sr/Ti nonstoichiometry.

Abstract

The effect of a variety of intrinsic defects and defect clusters in bulk and thin films of SrTiO$_3$ on ferroelectric polarization and switching mechanism is investigated by means of density-functional-theory (DFT) based calculations and the Berry phase approach. Our results show that both the titanium Ti$_\mathrm{Sr}^{\bullet \bullet}$ and strontium Sr$_\mathrm{Ti}^{"}$ antisite defects induce ferroelectric polarization in SrTiO$_3$, with the Ti$_\mathrm{Sr}^{\bullet \bullet}$ defect causing a more pronounced spontaneous polarization and higher activation barriers of polarization reversal than Sr$_\mathrm{Ti}^{"}$. The presence of oxygen vacancies bound to the antisite defects can either enhance or diminish polarization depending on the configuration of the defect pair, but it always leads to larger activation barriers of polarization switching as compared to the antisite defects with no oxygen vacancies. We also show that the magnitude of spontaneous polarization in SrTiO$_3$ can be tuned by controlling the degree of Sr/Ti nonstroichiometry. Other intrinsic point defects such as Frenkel defect pairs and electron small polarons also contribute to the emergence of ferroelectric polarization in SrTiO$_{3}$.