Dielectric properties in lead-free piezoelectric (Bi0.5Na0.5)TiO3–BaTiO3 single crystals and ceramics

The 0.93(Bi0.5Na0.5)TiO3–0.07BaTiO3 (BNB7T) piezoelectric single crystals and ceramics have been grown respectively by using the self-flux and solid-state-reaction methods. The real (ε′) and imaginary (ε″) parts of the dielectric permittivity of BNB7T crystals and ceramics were investigated with and without an electric (E) poling as functions of temperature and frequency. The BNB7T crystal shows a stronger dielectric maximum at Tm~240°C than the ceramic at Tm~300°C. The dielectric permittivity of BNB7T ceramic shows an extra peak after poling at an electric field E=40kV/cm in the region of 80–100°C designated as the depolarization temperature (Td). A wide-range dielectric thermal hysteresis was observed in BNB7T crystal and ceramic, suggesting a first-order-like phase transition. The dielectric permittivity ε′ obeys the Curie–Weiss equation, ε′=C/(T−To), above 500°C, which is considered as the Burns temperature (TB), below which polar nanoregions begin to develop and attenuate dielectric responses.