Ferroelectricity in strained Ca$_{0.5}$Sr$_{0.5}$TiO$_3$ from first principles

TL;DR

This study uses density functional theory to explore how strain influences ferroelectricity in Ca$_{0.5}$Sr$_{0.5}$TiO$_3$, revealing most configurations are ferroelectric with varying polarization levels.

Contribution

First-principles calculations of strained Ca$_{0.5}$Sr$_{0.5}$TiO$_3$ structures showing widespread ferroelectricity and polarization dependence on atomic arrangements.

Findings

Most structures are ferroelectric with polarization up to 0.26 C/m$^2$

Larger polarization correlates with lower c/a ratios

Polarization driven by Ti-O displacements influenced by A-site cations

Abstract

We present a density functional theory investigation of strained Ca$_{0.5}$Sr$_{0.5}$TiO$_3$. We have determined the structure and polarization for a number of arrangements of Ca and Sr in a 2$\times$2$\times$2 supercell. The a and b lattice vectors are strained to match the lattice constants of the rotated Si(001) face. To set the context for the CSTO study, we also include simulations of the Si(001) constrained structures for CaTiO$_3$ and SrTiO$_3$. Our primary findings are that all Ca$_{0.5}$Sr$_{0.5}$TiO$_3$ structures examined except one are ferroelectric, exhibiting polarizations ranging from 0.08 C/m$^2$ for the lowest energy configuration to about 0.26 C/m$^2$ for the higher energy configurations. We find that the configurations with larger polarizations have lower c/a ratios. The net polarization of the cell is the result of Ti-O ferroelectric displacements regulated by A-site cations.