Effects of the addition of Li_0.8Ni_0.2Nb_0.96O₃ on the structure and electrical properties of K_0.48Na_0.52NbO₃ lead-free piezoceramics

Highlights: • A new solid solution system of K_0.48Na_0.52NbO₃–Li_0.8Ni_0.2Nb_0.96O₃ was investigated. • Li_0.8Ni_0.2Nb_0.96O₃ was found to act as a sintering aid. • The Ni²⁺ ions were confirmed to enter the B-sites and lead to the formation of the secondary phase. • Q_m was improved significantly by increasing Li_0.8Ni_0.2Nb_0.96O₃ content. - Abstract: Lead-free K_0.48Na_0.52NbO₃ (KNN) ceramics doped with Li_0.8Ni_0.2Nb_0.96O₃ (LNN) were prepared by the mixed oxide method. The structure, microstructure, and electrical properties of the ceramics were investigated systematically. All the samples exhibited the main orthorhombic perovskite phase structure, and the secondary phase K_5.75Nb_10.85O₃₀ was detected when x ≥ 0.010. Our work revealed that the Ni²⁺ ions entered into the B-site and lead to the formation of small amounts of the secondary phase. Moreover, the addition of LNN increased the density of the KNN ceramics. With increasing addition of LNN, the T_C increased while the T_O-T decreased, respectively. The ceramic doped with 2 mol% LNN exhibited optimum electrical properties with P_r of 23.92 μC/cm², d₃₃ of 110 ± 3 pC/N, k_p of 27.15% and k_t of 27.75%. The Q_m increased significantly with increasing LNN content, and the maximum value of 195 is obtained at x = 0.035