BNH doping enhances the piezoelectric properties and temperature stability of KNN-based lead-free piezoelectric ceramics

KNN-based ceramics have gained considerable attention due to their excellent performances, cost-effectiveness, and potential applications in transducers. In order to accelerate the piezoelectric performances and temperature reliability of KNN-based ceramics, (1 − x)(K_0.48Na_0.52)(Nb_0.955Sb_0.045)O₃ − x(Bi_0.5Na_0.5)HfO₃ (abbreviated as KNNS-xBNH) ceramics were prepared. The study focused on investigating the impact of BNH components on their morphology, structure, piezoelectric performances, and temperature reliability of ceramics. This route is crucial for improving the overall performance of KNN-based ceramics. The synthetic piezoelectric ceramics have a typical perovskite structure, in which the optimized ceramic with x = 0.035 shows excellent piezoelectric properties: d₃₃ = 436 pC/N, k_p = 0.56, d₃₃^* = 604 pm/V, T_c = 253 °C, P_r = 14.75 μC/cm², E_c = 957 V/mm, and S_max = 0.18%. The co-occurrence of orthorhombic–tetragonal (O–T) phase, relaxation states, and their nanodomain structures contribute significantly to the excellent performance of ceramics with T_Fs < 0.8‰ and T_εr < 17‰. At the same time, it is verified that the presence of B-site defect dipoles in ceramics has an inactive effect on spontaneous polarization, which is evident in the decrease of d₃₃^* measured after polarization.