Temperature-Insensitive High Strain in Lead-Free Bi0.5(Na0.84K0.16)0.5 TiO3-0.04SrTiO3 Ceramics for Actuator Applications

Lead-free piezoelectric ceramics, 0.96[{Bi-0.5(Na0.84K0.16)(0.5)}(1-x) Li-x(Ti1-yNby)O-3]-0.04SrTiO(3) (BNKLiTN-ST) with x, y = 0-0.030, were synthesized by solid-state reaction method. X-ray diffraction patterns indicated that Li and Nb successfully diffused into the BNKT-ST lattice and formed a pure perovskite structure with x, y <= 0.025. Increasing the Li and Nb contents (x, y = 0.020) induced a phase transformation from the coexistent rhombohedral-tetragonal phases for pure BNKT-ST ceramics to a pseudocubic phase, resulting in degradation of the remnant polarization and coercive field. However, the field-induced strain was markedly enhanced at x, y = 0.020, giving rise to a giant dynamic piezoelectric constant (d(33)(star) = S-max/E-max = 800 pm/V). Furthermore, the temperature dependence of the field-induced strain response showed temperature-insensitivity up to 120 degrees C. To explore its potential for device applications, a 10-layered stack-type multilayer actuator was fabricated from the optimal composition (x, y = 0.020). This actuator showed a large SmaxSmax/E-max of 600 pm/V at a relatively low driving field of 4.5 kV/mm suggesting highly promising results in lead-free BNT-based ceramics.