Phase transitions and large electric field-induced strain in BiAlO3-modified Bi0.5(Na, K)0.5TiO3 lead-free piezoelectric ceramics

Lead-free piezoelectric (1 − x)(Bi0.5(Na0.78K0.22)0.5TiO3)–xBiAlO3 (abbreviated BNKT22–BA, x = 0.00–0.100) ceramics were synthesized using a conventional sintering technique. The incorporation of BA into the BNKT22 lattice was investigated by X-ray diffraction (XRD), and the dielectric and ferroelectric characterizations and electric field-induced strain behavior. We found that the structural and electrical properties of BNKT22 ceramics are significantly influenced by the presence of BA content. X-ray diffraction revealed a pure perovskite phase for x ⩽ 0.050. A phase transformation from tetragonal to pseudocubic was observed at x = 0.050. As BA content increased, the maximum dielectric constant continuously decreased, and the depolarization temperature (Td) shifted towards lower temperatures. The polarization and strain hysteresis loops indicate that the addition of BA significantly disrupts the ferroelectric order. The destabilization of the ferroelectric order is accompanied by an enhancement of bipolar and unipolar strains. In particular, a very large electric field-induced strain (S = 0.35%) and a normalized strain (d33∗ = Smax/Emax = 592 pm/V) were observed at x = 0.030, near the tetragonal–pseudocubic phase boundary. These results suggested that the BNKT22–BA system is a promising candidate for high performance, lead-free electromechanical applications.