Phase Transition, Electrical Properties, and Temperature-Insensitive Large Strain in BiAlO3-Modified Bi0.5(Na0.75K0.25)0.5TiO3 Lead-Free Piezoelectric Ceramics

Lead-free piezoelectric (1-x)(Bi-0.5(Na0.75K0.25)(0.5)TiO3)-xBiAlO(3) (BNKT25-xBA, x = 0-0.100) ceramics were synthesized using a conventional solid-state reaction method. The effect of BA addition into the BNKT25 ceramics was investigated by X-ray diffraction, dielectric and ferroelectric characterizations, and electric field-induced strain. X-ray diffraction revealed a phase transition from a tetragonal to a pseudocubic phase at x = 0.050. As the BA content increased, the maximum dielectric constant as well as the depolarization temperature (T-d) decreased. The polarization and strain hysteresis loops indicate that the addition of BA significantly disrupts the ferroelectric order of the BNKT25 ceramics leading to a degradation of the remanent polarization and coercive field. However, the destabilization of the ferroelectric order is accompanied by a significant enhancement in the unipolar strain which peaks at x = 0.025 with a value of similar to 0.29%, which corresponds to a normalized strain, d*(33) (=S-max/E-max) of 484 pm/V. It was observed that the unipolar strain of 0.025xBA is fairly temperature-insensitive up to 150 degrees C, even at 130 degrees C the d*(33) is as large as similar to 415 pm/V.