Excellent piezoelectric properties of (K, Na)(Nb, Sb)O₃-CaZrO₃-(Bi, Ag)ZrO₃ lead-free piezoceramics

Fe₂O₃-containing 0.96(K_0.5Na_0.5)(Nb_0.93Sb_0.07)-(0.04-x)CaZrO₃-x(Bi, Ag)ZrO₃ piezoceramics with 0.0 ≤ x ≤ 0.04 fabricated at 1090 °C show a dense microstructure without any secondary phases. The piezoceramic with x = 0.03 has an ideal rhombohedral–orthorhombic–tetragonal (R-O-T) multi-structure because its constituent structure proportions are similar. Its R-O-T phase transition temperature (T_R-O-T) increases with increasing measuring frequency, indicating that this piezoceramic exhibits relaxor properties which develop near its ferroelectric-to-ferroelectric phase transition temperature, that is, its T_R-O-T. This piezoceramic has nanodomains that are approximately 3 nm × 20 nm in size. The associated low boundary energies of these domains are expected to facilitate domain rotation. Furthermore, the piezoceramic has an extremely high piezoelectric constant (d₃₃) of 680 ± 10 pC/N, which exceeds the maximum d₃₃ reported in the literature for similar materials. This high d₃₃ is attributed to the existence of an ideal R-O-T multi-structure and nanodomains.