Atomistic Description for Temperature-Driven Phase Transitions in BaTiO$_3$

TL;DR

This study develops a first-principles-based atomistic model for BaTiO$_3$ that accurately simulates its temperature-driven phase transitions, revealing complex local atomic behaviors and challenging conventional views on bond-softening.

Contribution

The paper introduces a novel interatomic potential for BaTiO$_3$ derived from first-principles, enabling detailed MD simulations of phase transitions with atomic resolution.

Findings

Reproduces temperature-driven phase transitions in MD simulations.

Reveals mixed order-disorder and displacive transition characters.

Discovers bond-hardening behavior in the x polarization component during transition.

Abstract

Barium titanate (BaTiO$_3$) is a prototypical ferroelectric perovskite that undergoes the rhombohedral-orthorhombic-tetragonal-cubic phase transitions as the temperature increases. In this work, we develop a classical interatomic potential for BaTiO$_3$ within the framework of the bond-valence theory. The force field is parameterized from first-principles results, enabling accurate large-scale molecular dynamics (MD) simulations at finite temperatures. Our model potential for BaTiO$_3$ reproduces the temperature-driven phase transitions in isobaric-isothermal ensemble (NPT) MD simulations. This potential allows the analysis of BaTiO$_3$ structures with atomic resolution. By analyzing the local displacements of Ti atoms, we demonstrate that the phase transitions of BaTiO$_3$ exhibit a mix of order-disorder and displacive characters. Besides, from detailed observation of structural dynamics during phase transition, we discover that the global phase transition is associated with changes in the equilibrium value and fluctuations of each polarization component, including the ones already averaging to zero, Contrary to the conventional understanding that temperature increase generally causes bond-softening transition, the x polarization component exhibits a bond-hardening character during the orthorhombic to tetragonal transition. These results provide further insights about the temperature-driven phase transitions in BaTiO$_3$.