Phenomenological description of the diffuse phase transition in ferroelectrics

Features of the diffuse phase transition in lead magnesium niobate and strontium barium niobate, typical relaxor ferroelectric materials, were studied as a function of temperature and frequency. A new empirical equation for a phenomenological description of the temperature dependence of the dielectric permittivity (epsilon') peak is proposed. In fact, the proposed equation provides an excellent fitting of the experimental curves at temperatures into and above the dielectric dispersion region, enabling us to calculate some characteristic parameters of the phase transitions in ferroelectric materials.