Temperature-driven phase transitions in SrBi$_2$Ta$_2$O$_9$ from first-principles calculations

TL;DR

This study uses first-principles calculations to explore temperature-induced phase transitions in SrBi$_2$Ta$_2$O$_9$, revealing an intermediate orthorhombic paraelectric phase driven by polar and nonpolar instabilities.

Contribution

It introduces a shell model fitted to first-principles data to predict complex phase transition sequences and intermediate phases in Aurivillius compounds.

Findings

Identification of two phase transitions in SrBi$_2$Ta$_2$O$_9$

Detection of an intermediate orthorhombic paraelectric phase

Correlation of phase transition with dielectric response

Abstract

The phase transition sequence of SrBi$_2$Ta$_2$O$_9$ is investigated using a shell model with parameters fitted to first-principles calculations. We show that the complex interplay between polar and nonpolar instabilities leads to the presence of two phase transitions, corroborating the existence of an intermediate orthorhombic paraelectric phase. This phase is characterized by the rotation of the TaO$_6$ octahedra around the a-axis. We show that this phase can be also detected from the dielectric response of the material. The present approach constitutes a powerful tool for a theoretical prediction of intermediate phases, not yet observed experimentally, in other Aurivillius compounds.