The effects of sintering temperatures on dielectric, ferroelectric and electric field-induced strain of lead-free Bi0.5(Na0.78K0.22)0.5TiO3 piezoelectric ceramics synthesized by the sol–gel technique

Lead-free Bi0.5(Na0.78K0.22)0.5TiO3 (BNKT) piezoelectric ceramics were synthesized by the sol–gel technique. The effects of sintering temperatures on the crystal structure, microstructure, densification, dielectric, ferroelectric and electric field-induced strain behaviors of the BNKT ceramics were investigated. X-ray diffraction patterns exhibited a pure perovskite structure from 1075 to 1150 °C. A scanning electron microscopy study revealed an increase in grain size with increasing sintering temperature. The density of the ceramics sintered at 1150 °C reaches a maximum value of 5.55 g/cm3, which is 96% of the theoretical density. BNKT ceramics sintered at an optimum temperature of 1150 °C exhibited a high remnant polarization of 18.5 μC/cm2, a high electric field-induced strain of 0.20% and dynamic piezoelectric coefficient d33∗ = (Smax/Emax) of 247 pm/V.