Structure, ferroelectric properties, and electric field-induced large strain in lead-free Bi0.5(Na,K)0.5TiO3–(Bi0.5La0.5)AlO3 piezoelectric ceramics

Lead-free (1 − x)Bi0.5(Na0.78K0.22)0.5TiO3–x(Bi0.5La0.5)AlO3 (BNKT–BLA) piezoelectric ceramics with x ranging from 0 to 0.030 were synthesized by a conventional solid state reaction method. The effect of (Bi0.5La0.5)AlO3 addition on the structure, ferroelectric properties, and electric field-induced strain were investigated. In the studied composition range, the XRD patterns revealed a single perovskite phase with tetragonal symmetry. However, the tetragonality (c/a) of the BNKT ceramics significantly decreased as the BLA content was increased. The polarization and strain hysteresis loops indicate that the ferroelectric order of the BNKT ceramics was significantly disrupted by the addition of BLA, leading to degradation in the remnant polarization and coercive field. However, the destabilization of the ferroelectric order is accompanied by significant enhancements in the bipolar and unipolar strains. A large electric field-induced strain (S = 0.40%) and a corresponding normalized strain (image) were observed under 70 kV/cm at a composition of x = 0.010.