Piezoelectric and Dielectric Properties in Bi_0.5(Na,K)_0.5TiO₃-x Ag₂O Lead-Free Piezoceramics

Lead-free piezoceramics of Bi_0.5(Na_0.825K_0.175)_0.5TiO₃ with varying concentrations of x mol% Ag₂O (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, denoted as BNKT-xA) were fabricated using the solid-state technique. An extensive investigation was undertaken to analyze the structural, piezoelectric, and dielectric properties of these piezoceramics in the presence of Ag ions. There is no evidence of any secondary solid solution in the BNKT-xA piezoceramics. The ceramics with x mol% Ag₂O in BNKT still demonstrate the presence of both rhombohedral (R) and tetragonal (T) phases. The addition of Ag⁺ is helpful to increase the relative density of the BNKT-xA piezoceramics. It is noteworthy that the BNKT-0.3 mol% A piezoceramics show remarkable improvements in their properties (d₃₃ = 147 pC/N, k_p = 29.6%, ε = 1199, tanδ = 0.063). These improvements may be ascribed to the denser microstructure and the preservation of morphotropic phase boundaries between R and T phases caused by the appropriate addition of Ag cations. The addition of Ag⁺ results in the relaxor behavior of the BNKT-xA ceramics, characterized by disorder among A-site cations. With the increase in temperature, the d₃₃ value of BNKT-xA ceramics does not vary significantly in the range of 25 to 125 °C, ranging from 127 to 147 pC/N (with a change of d₃₃ ≤ 13.6%). This finding shows that piezoelectric ceramics have a reliable performance over a certain operating temperature range.