Effects of A-site non-stoichiometry on the structural and electrical properties of 0.96K_0.5Na_0.5NbO₃ - 0.04LiSbO₃ lead-free piezoelectric ceramics

Effects of A-site non-stoichiometry on the structural and electrical properties of 0.96K_0.5+xNa_0.5+xNbO₃ ^-0.04LiSbO₃ lead-free piezoelectric ceramics were examined for 0 ≤ x ≤ 0.02. The piezoelectric coefficients exhibited a maximum, d₃₃ = 187 pC/N at x = 0.0075, coinciding with the maximum of the grain size and the apparent density at x = 0.0075. The apparent density and the piezoelectric coefficients decreased with increasing x at higher x which was likely due to the crystal geometrical distortion of 0.96K_0.5+xNa _0.5+xNbO₃^-0.04LiSbO₃. In addition, super-large grains were found and this may be due to liquid phase sintering. Excess (K⁺+Na⁺) attracted a sum of space charges to keep the charge neutral, resulting in charge leakage during the course of ceramic polarization, influencing the piezoelectric and ferroelectric properties. These findings are of importance for guiding the design of K_0.5Na _0.5NbO₃-based lead-free ceramics with enhanced electrical properties.