BiFeO₃-modified (Li, K, Na)(Nb, Ta)O₃ lead-free piezoelectric ceramics with temperature-stable piezoelectric property and enhanced mechanical strength

BiFeO₃-modified lead-free piezoceramics Li_0.05(Na_0.515K_0.485)_0.95Nb_0.8Ta_0.2O₃ (LKNNT) were successfully fabricated by conventional method to investigate its influences on phase structure and electricity as well as mechanical properties. A tiny amount of BiFeO₃ (BF) changes the phase structure of LKNNT to tetragonal and further to pseudocubic, and also effectively improves the sintering ability and densification of LKNNT which enhances the mechanical property. The LKNNT piezoceramics with the addition of 1 mol% BF has the bulk density of 5.02 g/cm³ and an enhanced fracture strength of 142 MPa which is even higher than that of the sample of similar composition prepared by spark plasma sintering, also possesses room temperature electric properties of d ₃₃* ~ 225 pm/V, k _p ~ 36.3%, ε _r ~ 1140, tgδ ~ 0.018, T _c ~ 305 °C and Q _m ~ 80. The d ₃₃* remains constant up to 150 °C and the change ratio of dielectric property largely decreases over the temperature range of −50–150 °C, which can be attributed to the temperature-independent phase structure of LKNNT piezoceramics, making the ceramics as a promising candidate for actual applications.