Phase Transition, Electrical Properties, and Temperature‐Insensitive Large Strain in <scp> BiAlO ₃ </scp> ‐Modified <scp> Bi _0.5 (Na _0.75 K _0.25 ) _0.5 TiO ₃ </scp> Lead‐Free Piezoelectric Ceramics

Abstract

Lead‐free piezoelectric (1– x )( Bi 0.5 (Na 0.75 K 0.25 ) 0.5 TiO 3 )‐ x BiAlO 3 ( BNKT25 ‐ x BA, 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 ~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 0.025 x BA is fairly temperature‐insensitive up to 150°C, even at 130°C the d * 33 is as large as ~415 pm/V.