Low-temperature anharmonicity of barium titanate: a path-integral molecular dynamics study

TL;DR

This study uses path-integral molecular dynamics to reveal that quantum effects significantly enhance dielectric and piezoelectric properties of barium titanate at low temperatures, highlighting its strong anharmonicity.

Contribution

It demonstrates the importance of quantum fluctuations in low-temperature properties of barium titanate through advanced simulations.

Findings

Quantum effects double the dielectric susceptibility.

Piezoelectric constants are significantly increased by quantum fluctuations.

Dielectric properties evolve slowly below 100 K due to zero-point energy.

Abstract

We investigate the influence of quantum effects on the dielectric and piezoelectric properties of barium titanate in its (low-temperature) rhombohedral phase, and show the strongly anharmonic character of this system even at low temperature. For this purpose, we perform path-integral molecular-dynamics simulations under fixed pressure and fixed temperature, using an efficient Langevin thermostat-barostat, and an effective hamiltonian derived from first-principles calculations. The quantum fluctuations are shown to significantly enhance the static dielectric susceptibility (~ by a factor 2) and the piezoelectric constants, reflecting the strong anharmonicity of this ferroelectric system even at very low temperature. The slow temperature-evolution of the dielectric properties observed below ~ 100 K is attributed (i) to zero-point energy contributions and (ii) to harmonic behavior if quantum effects are turned off.