A new family of high temperature lead-free Na1/2Bi1/2TiO3-BiFeO3 piezoelectrics

The surge of interest in the search for lead-free alternatives in the past two decades has identified Na1/2Bi1/2TiO3-based materials to exhibit high strain, large mechanical quality factor, high temperature conductivity and temperature-stable permittivity. Nevertheless, the low depolarization temperature (Td) has been a major concern. This work reports the (1-x)Na1/2Bi1/2TiO3-xBiFeO3 solid solution processed using the quenching strategy to exhibit high Td that surpasses that of major Na1/2Bi1/2TiO3 class of materials. Upon quenching the sample, Td of Na1/2Bi1/2TiO3 with 60 mol% BiFeO3 considerably increases from 380 °C to 640 °C, while retaining the piezoelectric coefficient, d33z57 pC/N. The d33 value is nearly double that of traditional bismuth-layered high temperature piezoelectrics. The role of quenchinginduced thermal stability of d33 is substantiated by annealing investigations below 800 °C. The enhancement of Td is ascribed to the increased latticed distortion and enlarged domain size upon quenching. The practical feasibility of quenching is further substantiated by the similar hardness for the furnace cooled and quenched specimens, indicating comparable mechanical strength