Ab initio study of the phase diagram of epitaxial BaTiO3

TL;DR

This study employs first-principles and effective-Hamiltonian methods to map the phase diagram of epitaxial BaTiO3, revealing differences from previous empirical models and providing insights relevant to thin film applications.

Contribution

It presents a new phase diagram of BaTiO3 under epitaxial constraints based on ab initio methods, contrasting prior empirical results.

Findings

Identification of a 'r phase' region at low temperature

Differences from previous empirical thermodynamic models

Relevance to low-temperature epitaxial thin films

Abstract

Using a combination of first-principles and effective-Hamiltonian approaches, we map out the structure of BaTiO3 under epitaxial constraints applicable to growth on perovskite substrates. We obtain a phase diagram in temperature and misfit strain that is qualitatively different from that reported by Pertsev et al. [Phys. Rev. Lett. 80, 1988 (1998)], who based their results on an empirical thermodynamic potential with parameters fitted at temperatures in the vicinity of the bulk phase transitions. In particular, we find a region of `r phase' at low temperature where Pertsev et al. have reported an `ac phase'. We expect our results to be relevant to thin epitaxial films of BaTiO3 at low temperatures and experimentally-achievable strains.