Structural transition and large electric field-induced strain in BiAlO3-modified Bi0.5(Na0.8K0.2)0.5TiO3 lead-free piezoelectric ceramics

Lead-free perovskite solid solutions of (1−x)(Bi0.5(Na0.8K0.2)0.5TiO3)–xBiAlO3 (abbreviated as BNKT20–BA, x=0.00,0.025,0.050,0.075,0.100x=0.00,0.025,0.050,0.075,0.100) were synthesized by a conventional solid state reaction method. XRD patterns revealed that a pure perovskite phase was formed for x≤0.050x≤0.050. A structural transition from the coexistence of rhombohedral and tetragonal to pseudocubic phase was observed at x=0.050x=0.050. Polarization and strain hysteresis loops indicate that the ferroelectric order is disrupted significantly with the addition of BA. The destabilization of the ferroelectric order is accompanied by an enhancement of bipolar and unipolar strain. A large electric field-induced strain (S=0.30%S=0.30%) and a normalized strain (d33∗=Smax/Emax=391pm/V) were obtained at x=0.050x=0.050. These results provide evidence for the relation between the structural transition from the coexistence of rhombohedral and tetragonal into pseudocubic and the large electric field-induced strain in BNKT20–BA perovskite solid solutions.