First-principles study of symmetry lowering in relaxed BaTiO3/SrTiO3 superlattices

TL;DR

This study uses first-principles calculations to analyze the structural and polarization properties of BaTiO3/SrTiO3 superlattices, revealing symmetry lowering and polarization distribution consistent with experimental observations.

Contribution

It provides a detailed first-principles analysis of symmetry lowering and polarization behavior in relaxed BaTiO3/SrTiO3 superlattices, which was not previously characterized.

Findings

Polarization in [110] direction develops only in SrTiO3 layers.

Polarization in [001] direction is uniform across the superlattice.

Symmetry is lowered to monoclinic space group Cm.

Abstract

The crystal structure and local spontaneous polarization of (BaTiO3)m/(SrTiO3)n superlattices is calculated using a first-principles density functional theory method. The in-plane lattice constant is 1% larger than the SrTiO3 substrate to imitate the relaxed superlattice structure and the symmetry is lowered to monoclinic space group Cm which allows polarization to develop along the [110] and [001] directions. The polarization component in the [110] direction is found to develop only in the SrTiO3 layers and falls to zero in the BaTiO3 layers, whereas the polarization in the [001] direction is approximately uniform throughout the superlattice. These findings are consistent with recent experimental data and first-principles results for epitaxially strained BT and ST.