Composition- And temperature-dependent large strain in (1 - x) (0.8Bi0.5Na0.5TiO3-0.2Bi0.5K0.5TiO3)- x NaNbO3 ceramics

Ternary solid solutions of (1 - x)(0.8Bi_0.5Na_0.5TiO₃- 0.2Bi_0.5K_0.5TiO₃)- xNaNbO₃ (BNKT-xNN) lead-free piezoceramics were fabricated using a conventional solid-state reaction method. Pure BNKT composition exhibited an electric-field-induced irreversible structural transition from pseudocubic to ferroelectric rhombohedral phase at room temperature. Accompanied with the ferroelectric-to-relaxor temperature T_F-Rshifted down below room temperature as the substitution of NN, a compositionally induced nonergodic-to-ergodic relaxor transition was presented, which featured the pinched-shape polarization and sprout-shape strain hysteresis loops. A strain value of ∼0.445% (under a driving field of 55 kV/cm) with large normalized strain of ∼810 pm/V was obtained for the composition of BNKT-0.04NN, and the large strain was attributed to the reversible electric-field-induced transition between ergodic relaxor and ferroelectric phase.