Temperature Dependent Piezoelectric Properties of Lead-Free (1-x)K0.6Na0.4NbO3-xBiFeO3Ceramics

(1-x)K0.4Na0.6NbO3-xBiFeO(3)lead-free piezoelectric ceramics were successfully prepared in a single perovskite phase using the conventional solid-state synthesis. Relative permittivity (epsilon(r)) as a function of temperature indicated that small additions of BiFeO(3)not only broadened and lowered the cubic to tetragonal phase transition (T-C) but also shifted the tetragonal to orthorhombic phase transition (TO-T) toward room temperature (RT). Ceramics withx= 1 mol.% showed optimum properties with small and large signal piezoelectric coefficient,d(33)= 182 pC/N andd*(33)= 250 pm/V, respectively, electromechanical coupling coefficient,k(p)= 50%, andT(C)= 355 degrees C.k(p)varied by similar to 5% from RT to 90 degrees C, whiled*(33)showed a variation of similar to 15% from RT to 75 degrees C, indicating that piezoelectric properties were stable with temperature in the orthorhombic phase field. However, above the onset ofT(O-T), the properties monotonically degraded in the tetragonal phase field asT(C)was approached.