Lattice Relaxation in Epitaxial BaTiO$_3$ Thin Films

TL;DR

This study examines how epitaxial BaTiO$_3$ thin films undergo lattice and ferroelectric phase transitions under different strains, revealing strain-dependent transition temperatures and polarization orientations.

Contribution

It provides experimental evidence of strain-induced shifts in phase transition temperatures and domain orientations in BaTiO$_3$ thin films using synchrotron X-ray diffraction.

Findings

Transition temperature $T_C$ varies significantly with strain.

Polarization orientation depends on the type of strain.

Structural phase transitions are confirmed under different strain conditions.

Abstract

We have investigated the out-of-plane lattice relaxation related to the ferroelectric transitions in epitaxial BaTiO$_3$ (BTO) films using synchrotron X-ray diffraction. Under either compressive strain or tensile strain, there is evidence for two structural phase transitions as a function of temperature. The transition temperature $T_C$ is a strong function of strain, which can be as much as 100 K above the corresponding $T_C$ in bulk. Under compressive strain, the tetragonality of BTO unit cell implies that the polarization of the first ferroelectric phase is out-of-plane, while under tensile strain, the polarization is in-plane. The transitions at lower temperature may correspond to the $aa\to r$ or $c\to r$ transitions, following the notations by Pertsev \textit{et al}. The orientations of the domains are consistent with theoretical predictions.