Behaviour of Na0.5Bi0.5TiO3 ceramics in the ac electric field

The dielectric dispersion and influence of a.c. electric field strength on electric permittivity as well as the hysteresis loops for Na0.5Bi0.5TiO3 ceramics were investigated. The dipolar relaxation of Cole-Cole type below 1 MHz is observed. This relaxation significantly evolves with temperature and is connected with dynamics of polar regions. The increasing strength of a.c. electric field shifts the electric permittivity characteristic towards lower temperatures. This effect can be associated with the reactivation and reversal of the polar regions and mechanical stresses rising because of external field action. Examination of the low-frequency hysteresis loops reveals the occurrence of usual ferroelectric properties below 200 degrees C. The occurrence of deformed hysteresis loops above 200 degrees C is discussed in terms of electro-mechanical interaction between polar regions and nonpolar matrix.