Selection and optimization of Sb and Ta co-doped (K0.41Na0.59)(Nb1-x-ySbxTay)O3 lead-free ceramics

Lead-(K_0.41Na_0.59)(Nb_1-x-ySb_xTa_y)O₃ (abbreviated as KNNST) ceramics with x = 0.0–0.15 and y = 0.0–0.2 were successfully synthesized and thoroughly investigated. The analysis of the XRD patterns recorded for KNNST ceramics revealed the presence of orthorhombic, tetragonal, and rhombohedral perovskite phases. The nature of the phase formed was influenced by the concentration of Sb or Ta. Good physical, dielectric, ferroelectric, and piezoelectric properties were recorded for the Sb-doped (K_0.41Na_0.59)NbO₃ ceramics when the Sb content was 0.06 M (ε_r = 945, k_p = 0.33, k_t = 0.39, d₃₃ = 145 pC/N, and tanδ = 0.15). The co-doping of KNN ceramics with Sb and Ta significantly affects the structure, density, and electromechanical properties of the materials. When the rhombohedral and tetragonal (R–T) phases of (K_0.41Na_0.59)(Nb_0.79Sb_0.06Ta_0.15)O₃ coexisted, the ceramics exhibited improved electrical characteristics with d₃₃ = 170 pC/N, k_p = 0.47, k_t = 0.41, T_C = 315 °C, and P_r = 12.6 μC/cm². Additionally, with the Ta content was 0.15 M and the Sb content was 0.06 M, the value of S_max (0.086%) and d₃₃^* (356 pm/V) increased significantly.