A new thermodynamic model of lithium niobate that is based on the use of the sixth-degree Landau potential is proposed. 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. (Mon,) studied this question.
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