First-principles study of the temperature-pressure phase diagram of BaTiO3

TL;DR

This study uses first-principles calculations to explore how zero-point ionic motions influence the temperature-pressure phase diagram of BaTiO3, revealing that quantum fluctuations stabilize all polar phases down to 0 K.

Contribution

It demonstrates the significant impact of zero-point motion on the phase stability of BaTiO3, confirming and extending previous phase diagram models.

Findings

Zero-point motion stabilizes all polar phases down to 0 K.

Including quantum fluctuations alters the phase diagram dramatically.

Results support the phase diagram proposed by Ishidate et al.

Abstract

We investigate the temperature-pressure phase diagram of BaTiO_3 using a first-principles effective-Hamiltonian approach. We find that the zero-point motion of the ions affects the form of the phase diagram dramatically. Specifically, when the zero-point fluctuations are included in the calculations, all the polar (tetragonal, orthorhombic, and rhombohedral) phases of BaTiO_3 survive down to 0 K, while only the rhombohedral phase does otherwise. We provide a simple explanation for this behavior. Our results confirm the essential correctness of the phase diagram proposed by Ishidate et al. (Phys. Rev. Lett. 78, 2397 (1997)).