Anisotropy and dynamic thermal depolarization of 0.96(Bi0.5Na0.5)TiO3-0.04 BaTiO3 lead-free piezoceramics

Undoped (Bi0.5Na0.5)(0.96)Ba0.04TiO3 ceramics were prepared from mixed oxides and sol-gel autocombustion powder. Similar dielectric and electromechanical properties were found for both but sol-gel derived ceramics can be obtained with a lower thermal budget, which prevent losses of volatiles. Dielectric anisotropy is observed. All the features of the thermal evolution curves of epsilon(T)(11) are observed at temperatures clearly displaced towards higher values with respect to those of the epsilon(T)(33) curves. There is also anisotropy in the depoling process. When depoling is monitored in-situ using the shear mode of thickness poled plates, resonance is observed at T-d > 150 degrees C. Besides, hot in-situ measurements of time dependence of the resonaces of disks and plates at temperatures below Td showed that the depolarization of BNBT4 is a dynamical process.