Can we trust the temperature - misfit strain thin film phase diagrams?

TL;DR

This paper examines the accuracy of thermodynamic phase diagrams for ferroelectric thin films, emphasizing the importance of high-order electromechanical interactions, demonstrated through a BaTiO3 example.

Contribution

It highlights the significance of including high-order electromechanical couplings for accurate phase diagram predictions in ferroelectric thin films.

Findings

High-order electromechanical interactions significantly affect phase diagrams.

Standard methods may be inaccurate without these high-order terms.

First-principles calculations reveal the impact on BaTiO3 thin films.

Abstract

Currently used methods for the description of thermodynamics of ferroelectric thin films (Landau theory or ab initio based Monte-Carlo simulations) are based on an energy expansion in terms of internal degrees of freedom. It was shown that these methods can suffer from a substantial inaccuracy unless higher-order electromechanical interactions are not taken into account. The high-order electromechanical couplings strongly renormalize the sixth-power polarization terms of the thermodynamic energy expansion. In this paper, apart from the general statement, we illustrate it with an example of a temperature - misfit strain phase diagram of a BaTiO3 thin film derived with high-order electromechanical interactions evaluated using first principles calculations.