Effect of KNN substitution on the structural, electrical, and piezo characteristics of lead-free 0.94NBT–0.06SrTiO₃ ceramics

The conventional solid-state reaction approach was employed to develop 0.94NBT–0.06SrTiO₃ and 0.94NBT–0.06SrTiO₃–KNN lead free electro ceramics. Both ceramics coexist in the rhombohedral structural phase (R3c) and tetragonal structural phase (P4mm) regions. When K_0.5Na_0.5NbO₃ (KNN) is introduced to 0.94Na_0.5Bi_0.5TiO₃–0.06SrTiO₃, the structure grows more symmetric without compromising electrical polarization. The surface morphology of both ceramics is measured by the average grain size, which is reduced somewhat from 3 to 2.6 μm, resulting in the influence of KNN. The composition-induced local structural transition—i.e., the change from order to disorder-occurs when KNN is added to the 0.94NBT–0.06SrTiO₃ binary system. Additionally, the depolarization temperature (T_d) increases substantially with the inclusion of KNN. When KNN is present, the coercive field (E_c) dramatically reduces from 32 to 21 kV/cm (~ ΔE = 11 kV/cm), without impairing the remaining remnant polarization (P_r). When compared to 0.94NBT–0.06SrTiO₃, the substitution of KNN produces a high strain response of roughly 0.25% (under a mild field of 60 kV/cm). The longitudinal strain value of 140pC/N was determined parallelly. As a result, both of these lead-free ceramics are attractive prospects for next-generation electro ceramic applications.