Resolution of ambiguity between the depolarization and ferroelectric–relaxor transition temperature through dielectric studies in lead-free perovskite K0.5Bi0.5TiO3

Abstract

Lead-free relaxor K0.5Bi0.5TiO3 (KBT) has been selected to measure its depolarization temperature (Td) and to establish the difference between the Td and the normal ferroelectric to relaxor transition temperature (TF-R), which is still in a debatable stage for the relaxor ferroelectric system. These parameters are determined separately from the electrically poled specimen through the simple dielectric measurement instead of the pyroelectric measurement or other sophisticated techniques. Albeit, the electric field induces the normal ferroelectric behavior in the nonergodic relaxor state, the relaxor nature appears again through the heating above the freezing temperature. The difference between the frequencies of resonance and anti-resonance peaks in the real part of permittivity remains constant up tõ240 °C, and it reduces to almost zero at ∼285 °C, which has been considered as the Td of KBT. At the temperature higher than Td, an anomaly is noticed in the temperature dependent permittivity as well as in the dielectric loss graph of KBT; this temperature indicates the emergence of the relaxor nature from the normal ferroelectric (TF-R). The Td of the KBT is even higher than some of the lead-free ferroelectrics, which signifies its better suitability for the piezoelectric application. This easy method can be adopted undoubtedly to confirm the Td of the ferroelectric specimen, even for the material of higher Td (above 300 °C).