Ferroelectric Phase Transitions in Ultra-thin Films of BaTiO3

TL;DR

This study uses molecular dynamics simulations to explore how film thickness, strain, and electrode properties influence ferroelectric phase transitions in ultrathin BaTiO3 films, revealing complex behaviors including domain formation.

Contribution

It provides a detailed phase diagram and insights into the effects of electrodes and thickness on ferroelectric transitions in ultrathin BaTiO3 films.

Findings

Ferroelectric phase transitions depend on film thickness and strain.

Electrode quality influences domain structures and phase stability.

Depolarization effects are significant even with perfect electrodes.

Abstract

We present molecular dynamics simulations of a realistic model of an ultrathin film of BaTiO$_3$ sandwiched between short-circuited electrodes to determine and understand effects of film thickness, epitaxial strain and the nature of electrodes on its ferroelectric phase transitions as a function of temperature. We determine a full epitaxial strain-temperature phase diagram in the presence of perfect electrodes. Even with the vanishing depolarization field, we find that ferroelectric phase transitions to states with in-plane and out-of-plane components of polarization exhibit dependence on thickness; it arises from the interactions of local dipoles with their electrostatic images in the presence of electrodes. Secondly, in the presence of relatively bad metal electrodes which only partly compensate the surface charges and depolarization field, a qualitatively different phase with stripe-like domains is stabilized at low temperature.