A new thermodynamic model of lithium niobate is proposed, based on the use of the sixth-degree Landau potential. Its feature is the nonlinear dependence of the coefficient at the square of polarization along the polar direction on temperature. In contrast to the previously used fourth-degree potential, this ensures good agreement between the behavior of spontaneous polarization and deformation calculated on its basis and the results of experimental studies. Using the proposed thermodynamic potential, a complete set of material constants determining the thermomechanical properties of lithium niobate, as well as constants of the electro-optical and acousto-optical effects in a wide range of temperature changes, is constructed. Independence of the elastic moduli of lithium niobate from temperature is confirmed, in contrast to piezoelectric, acousto-optical and electro-optical constants, some of which undergo significant changes. The results are of interest when choosing the orientation of the crystal cut in the process of developing micro- and nanoscale acousto- and optoelectronic devices.
Shirokov et al. (Wed,) studied this question.