Abstract

Lead-free (1-x)(K_0.48Na_0.48Li_0.04)(Nb_0.95Sb_0.05)O₃-xBi_0.50Na_0.50HfO₃  ((1-x)KNLNS−xBNH, x = 0–0.035) ceramics were fabricated through a combined strategy of phase-structure modification and a two-step sintering technique, achieved by adjusting the different contents of Bi_0.50Na_0.50HfO₃ (BNH) impurities. Experimental results showed that the crystal structure of KNLNS−BNH ceramics gradually evolved from an orthorhombic Amm2 phase to a rhombohedral R3m phase through a coexistence of rhombohedral R3m and tetragonal P4mm phases. This structural transformation was associated with a marked improvement in the electrical properties of the KNLNS−BNH ceramics. At an optimal BNH content of 0.025 mol, the 0.975KNNST–0.025BNH ceramic exhibited excellent electrical properties. Specifically, high electromechanical coupling factors were achieved (k_p = 0.37 and k_t = 0.39), along with a large piezoelectric constant (d₃₃ = 230 pC/N) and an enhanced dielectric constant (ε_r = 1137 and e_max = 6274). In addition, a high remnant polarization (P_r = 15.6 μC/cm²) was obtained at x = 0.015. With increasing BNH content, the Curie temperature (T_c) decreased gradually from 364 °C to 318 °C, while the orthorhombic−tetragonal phase transition temperature (T_O−T) decreased from 110 °C to 60 °C. Meanwhile, the diffuseness parameter (γ) exhibited a slight increase from 1.34 to 1.56. Overall, the favorable electrical properties of ceramics indicate strong potential for future practical applications.