Electric field-induced strain of lead-free Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3 ceramics modified with LiTaO3

The phase diagram of ternary (1−x−y) Bi0.5Na0.5TiO3−x Bi0.5K0.5TiO3−yLiTaO3 (BNT−BKT−LT) ceramics was investigated within the range of x = 0–0.4 and y = 0–0.1 via analyses on their crystal structure, dielectric and field-induced strain properties. BNT-rich compositions revealed ferroelectric rhombohedral symmetry (FER: x < 0.18 and y < 0.04) while BKT modified BNT ceramics transformed into ferroelectric tetragonal symmetry (FET; x > 0.18 and y < 0.02). However, LT modification of BNT–BKT ceramics induced a phase transition to nonpolar pseudocubic symmetry (NPPC; x = 0–0.4 and y > 0.04). At phase boundaries between these three regions, the coexistence of two or three phases was observed. Interestingly, the electric field-induced strain was markedly enhanced at the ferroelectric-nonpolar phase boundary.