Enhanced piezoelectric properties of lead-free La and Nb co-modified Bi_0.5(Na_0.84K_0.16)_0.5TiO₃-SrTiO₃ Ceramics

New lead-free piezoelectric ceramics 0.96[{Bi_0.5(Na_0.84 K_0.16)_0.5}_1-xLa_x(Ti_1-y Nb_y)O₃]-0.04SrTiO₃ (BNKT-ST-LN, where x = y = 0.00 ≤ (x = y) ≤ 0.015) were synthesized using the conventional solid-state reaction method. Their crystal structure, microstructure, and electrical properties were investigated as a function of the La and Nb (LN) content. The X-ray diffraction patterns revealed the formation of a single-phase perovskite structure for all the LN-modified BNKT-ST ceramics in this study. The temperature dependence of the dielectric curves showed that the maximum dielectric constant temperature (T_m) shifted towards lower temperatures and the curves became more diffuse with an increasing LN content. At the optimum composition (LN 0.005), a maximum value of remnant polarization (33 C/cm²) with a relatively low coercive field (22 kV/cm) and high piezoelectric constant (215 pC/N) was observed. These results indicate that the LN co-modified BNKT-ST ceramic system is a promising candidate for lead-free piezoelectric materials.