Piezoelectric properties and thermal stability of (Na_0.53K_0.47−xAg_x)Nb_1−xSb_xO₃ ceramics

Abstract Many (K_1−xNa_x)NbO₃ (KNN)‐based ceramics with high piezoelectric performance exhibit undesirable strong temperature dependence due to the orthorhombic–tetragonal polymorphic phase transition near room temperature. In order to improve the temperature stability of the ceramics, many additives have been added into the KNN‐based ceramics to shift T_O–T down to below room temperature. Contrary to the previous approach (Na_0.53K_0.47−xAg_x)Nb_1−xSb_xO₃ (NKANS) ceramics with T_O–T well above room temperature have been prepared by a conventional solid‐state reaction method. The density and the electrical properties are effectively improved by the addition of AgSbO₃, and optimum piezoelectric properties are found in the ceramics with 0.05 ≤ x ≤ 0.07, with maximum k_p ∼ 0.46 for NKANS5 and maximum d₃₃ ∼ 199 pC/N for NKANS7. More importantly, k_p remains virtually almost unchanged up to the T_O–T temperature (≥100 °C), indicating that the NKANS ceramics exhibit a much improved piezoelectric thermal stability. The analyses suggest that both the high T_O–T value and diffuse orthorhombic–tetragonal phase transition should be responsible for the good temperature stability.