Synthesis and characterization of new lead-free ferroelectric (1 - x)AgNbO_3-xK_0.5Na_0.5NbO₃ solid solution

A new lead-free solid solution of(1 - x)AgNbO₃-xK _0.5Na_0.5NbO₃ [AN-KNN] (with x = 0-0.50) has been prepared by solid state reaction in oxygen atmosphere in the form of ceramics. The substitution of (K_0.5Na_0.5)⁺ for Ag⁺ greatly enhances both the dielectric and ferroelectric properties of AN which initially is a weak ferroelectric. With increasing KNN content, the maximum dielectric constant increases significantly, i.e. ∼ 8.5 times higher for x = 0.12 than for the pure AN, and the Curie temperature decreases from 345°C in x = 0 to 250°C in x = 0.10 and then increases again from 250 to 295°C for x = 0.12-0.50. It is found that the addition of KNN introduces a normal ferroelectric behavior in the solid solution possibly by suppressing the octahedral tilting in AN, giving rise to a dramatic increase in the remnant polarization (P_r), which reaches a value of P_r = 6.5 μC/cm² atx = 0.30.