Electrooptical properties of ferroelectric Gd2(MoO4)3

On the basis of the symmetry of the free energy function describing properly the transition of gadolinium molybdate into the ferroelectric state, macroscopic relations are derived for the spontaneous birefringence and for the temperature dependence of the electrooptic coefficientsz _ij . Since the transition parameters correspond to lattice vibrational modes with finitek, the resulting formulae differ considerably from those for classical ferroelectrics with transition parameterP. Experimental data are presented for the temperature dependence of freez ₆₃ andz ₄₁, clampedz ₆₃ and free permittivity for a multidomain and single domain crystal. These results and earlier data on spontaneous birefringence compare well with theory.