Piezoelectric properties and thermal stability of (Na _0.53K _0.47-xAg _x)Nb _1-xSb _xO ₃ ceramics

Many (K _1-xNa _x)NbO ₃ (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 _xO ₃ (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 AgSbO ₃, 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 d ₃₃ ∼ 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.