Anharmonicity of BaTiO_3 single crystals

TL;DR

This paper investigates the anharmonicity in BaTiO_3 single crystals, demonstrating the critical role of eighth order terms in phase transition modeling and revealing unexpected polarization anharmonicity.

Contribution

It introduces a straightforward method to evaluate the significance of eighth order terms in dielectric non-linearity analysis, emphasizing their importance in phase transition description.

Findings

Eighth order term is essential for BaTiO_3 phase transition modeling.

The quartic coefficient etahanges sign above 165B0C.

BaTiO_3 exhibits strong polarization anharmonicity.

Abstract

By analyzing the dielectric non-linearity with the Landau thermodynamic expansion, we find a simple and direct way to assess the importance of the eighth order term. Following this approach, it is demonstrated that the eighth order term is essential for the adequate description of the para/ferroelectric phase transition of BaTiO_3. The temperature dependence of the quartic coefficient \beta is accordingly reconsidered and is strongly evidenced by the change of its sign above 165 C. All these findings attest to the strong polarization anharmonicity of this material, which is unexpected for classical displacive ferroelectrics.