The Peculiarities of DC and AC-Field Dependent Relaxor/Ferroelectric Properties of Some Disordered Crystals

The detailed study of transition processes between normal and relaxor behaviors under DC and AC external electric fields has been carried out in the stoichiometric PbSc 1/2 Ta 1/2 O 3 (PST) and PbSc 12/ Nb 1/2 O 3 (PSN) crystals with different degree of ions ordering. The methods used are the measurements of the dielectric permittivity(e), optical transmission(OT) and small-angle light scattering (SALS) as a function of temperature at different amplitudes of electric field application. The spontaneous phase transition occurring in these crystals is shown to be accompanied by a sharp SALS intensity peak indicating the percolation nature of this transition. Applying an dc electric field reduces the temperature interval of existence of the relaxor state. Two different types of nonlinearities with respect to the amplitude of the ac drive are revealed in intermediate relaxor state between ferroelectric and paraelectric phases.