DIELECTRIC AND STRUCTURAL RELAXATION PHENOMENA IN NA0.5BI0.5TIO3 SINGLE-CRYSTAL

Dielectric permittivity studies of Na0.5Bi0.5TiO3 Single crystals in a broad range of frequency up to 10 MHz and temperature 300-823 K are r eported. In this temperature range dielectric dispersion below 1 MHz h as been found. The obtained data were fitted to the Cole-Cole relation . The mean relaxation time tau is strongly temperature dependent (0.04 -2.6 x 10(-5) s). A remarkable hysteresis effect in the values of tau on cooling and heating took place. The Delta epsilon(T) dependence (th e maximal value of Delta epsilon similar to 400) is similar to the glo bal epsilon'(T) response at low frequency. An isothermal structural tr ansformation in Na0.5Bi0.5TiO3 was observed by X-ray measurements. The order of the time in which the transformation takes place (similar to 300 minutes) corresponds to the time in which the strongest time evol ution of electric permittivity and time changes of dielectric dispersi on were detected.