Electrostrain optimization of Bi0.5Na0.5TiO3-based lead-free piezoceramics by CaZrO3 modifying

Bi0.5Na0.5TiO3 (BNT)-based ceramics with excellent electrostrain properties are considered to be one of the most promising lead-free alternative systems. In this work, appropriately deviating from the morphotropic phase boundary (MPB) range, the ceramics of (1−x)(0.75Bi0.5Na0.5TiO3-0.25Bi0.5K0.5TiO3)-xCaZrO3 (abbreviated as 0.75BNT-0.25BKT-xCZ, x = 0, 0.01, 0.03, 0.05) were synthesized by the solid-state reaction method. The phase structure combined with the dielectric, ferroelectric, and field-induced strain properties was systematically analyzed. The X-ray diffraction patterns showed that CZ was well incorporated into the 0.75BNT-0.25BKT structure to form a single-solid solution. As CZ content increases, the phase structure constructed by the coexistence of rhombohedral and tetragonal phases gradually transforms into the pseudocubic phase. Meanwhile, the dielectric temperature spectra demonstrated the coexistence of ferroelectric and relaxor phases during the phase transition with the formation of the weakly coupled relaxor, implying the presence of nanodomains which were further confirmed by the high-resolution transmission electron microscopy image. Interestingly, the maximum unipolar strain of 0.34% with a prominent increase of 70% and the hysteresis of 33% with a moderate increase of 26% were obtained simultaneously at x = 0.03 as compared to those at x = 0 (0.75BNT-0.25BKT). Further to this, this study investigated the origin of the large strain together with hysteresis variation and considered that reversible phase transition combined with relaxation behavior helps realize a tradeoff between large strain and low hysteresis, which provides an effective path for the further development of high-performance lead-free piezoelectric ceramics.