Influence of electric fields on dielectric properties of GPI ferroelectric

Using modified microscopic model of GPI by taking into account the piezoelectric coupling with strains ${\epsilon }_i$ in the frames of two-particle cluster approximation, the components of polarization vector and static dielectric permittivity tensor of the crystal at applying the external transverse electric fields $E_1$ and $E_3$ are calculated. An analysis of the influence of these fields on thermodynamic characteristics of GPI is carried out. A satisfactory quantitative description of the available experimental data for these characteristics has been obtained at a proper choice of the model parameters.