Sr-induced dipole scatter in BaxSr1-xTiO3: Insights from a transferable- bond valence-based interatomic potential
RB Wexler and YB Qi and AM Rappe, PHYSICAL REVIEW B, 100, 174109 (2019).
In order to design next-generation ferroelectrics, a microscopic understanding of their macroscopic properties is critical. One means to achieve 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 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 BaxSr1-xTiO3 (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 bond valence molecular dynamics 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 in rhombohedral BST, 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.
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