Amplitude dependences of dielectric permittivity and dielectric losses in a mixed K0.88(NH4)0.12H2PO4 crystal

Amplitude dependences of dielectric permittivity ? and dielectric losses tanδ in K_0.88(NH₄)_0.12H₂PO₄ mixed crystal near the ferroelectric phase transition temperature T _C are investigated. At measurement fields E _～ exceeding some critical value, dependence tanδ(E _～) can be described within a model that includes the depinning of domain walls from point lattice defects. The activation field is found to grow appreciably when approaching T _C from below, due to the presence of nonpolar regions.