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

Undoped (Bi_0.5Na_0.5)_0.96Ba_0.04TiO₃ 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 ε^T₁₁ are observed at temperatures clearly displaced towards higher values with respect to those of the ε^T₃₃ 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°C. Besides, hot in-situ measurements of time dependence of the resonaces of disks and plates at temperatures below T_d showed that the depolarization of BNBT4 is a dynamical process.