# Sr-induced dipole scatter in BST: Insights from MD simulations using a transferable bond valence-based interatomic potential

## TL;DR

This study extends a bond valence molecular dynamics approach to Ba$_x$Sr$_{1-x}$TiO$_3$ alloys, enabling atomistic insights into how Sr substitution affects ferroelectric properties and phase transitions, with results aligning with experiments.

## Contribution

The paper develops a transferable interatomic potential for BST alloys, allowing detailed MD simulations of composition-dependent ferroelectric behavior and phase transition mechanisms.

## Key findings

- Sr substitution scrambles dipoles and reduces polarization.
- Predictions match experimental and first-principles data.
- Enhanced understanding of disorder effects in BST alloys.

## Abstract

In order to design next-generation ferroelectrics, a microscopic understanding of their macroscopic properties is critical. One means to achieving an atomistic description of ferroelectric and dielectric phenomena is classical molecular dynamics simulations. Previously, we have shown that interatomic potentials based on the bond valence molecular dynamics (BVMD) method can be used to study structural phase transitions, ferroelectric domain nucleation, and domain wall migration in several perovskite oxides and fixed-composition binary and ternary alloys. Most modern devices, however, use variable-composition perovskite oxide alloys such as Ba$_x$Sr$_{1-x}$TiO$_3$ (BST). In this paper, we extend our bond valence approach to BST solid solutions and, in so doing, show that the potential parameters for each element are transferable between materials with different $x$. Using this potential, we perform BVMD simulations investigating the temperature and composition dependence of the lattice constants, Ti displacements, and ferroelectric polarization of BST and find that our predictions match experiments and first-principles theory. Additionally, based on a detailed analysis of local dipole distributions, we demonstrate that substitution of Sr for Ba scrambles dipoles, reduces global polarization, and enhances the order-disorder character of the ferroelectric-paraelectric phase transition.