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

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
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Grégory Geneste, Hichem Dammak, Marc Hayoun, Mickael Thiercelin. Low-temperature anharmonicity of barium titanate: A path-integral molecular-dynamics study. Physical Review B : Condensed matter and materials physics, American Physical Society, 2013, 87 (1), ⟨10.1103/PhysRevB.87.014113⟩. ⟨hal-01932719⟩

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