Temperature‐Insensitive High Strain in Lead‐Free Bi _0.5 (Na _0.84 K _0.16 ) _0.5 TiO ₃ –0.04SrTiO ₃ Ceramics for Actuator Applications

Abstract

Lead‐free piezoelectric ceramics, 0.96[{Bi 0.5 (Na 0.84 K 0.16 ) 0.5 } 1− x Li x (Ti 1− y Nb y )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 * = S max / E max = 800 pm/V). Furthermore, the temperature dependence of the field‐induced strain response showed temperature‐insensitivity up to 120°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 S max / 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.