Composition and Temperature Dependence of Structure and Piezoelectricity in (1−x)(K1−yNay)NbO3-x(Bi1/2Na1/2)ZrO3Lead-Free Ceramics

Lead-free piezoceramics with the composition (1-x)(K1-yNay)NbO3-x(Bi1/2Na1/2)ZrO3 (KNyN-xBNZ) were prepared using a conventional solid-state route. X-ray diffraction, Raman spectroscopy, and dielectric measurements as a function of temperature indicated the coexistence of rhombohedral (R) and tetragonal (T) phase, typical of a morphotropic phase boundary (MPB) as the BNZ concentration increased and by adjusting the K/Na ratio. High remnant polarization (Pr = 24 μC/cm2), piezoelectric coefficient (d33 = 320 pC/N), effective piezocoefficient (d33* = 420 pm/V), coupling coefficient (kp = 48%), and high strain (S = 0.168%) were obtained at room temperature, but significant deterioration of Pr, d33*, and kp were observed by increasing from room temperature to 160°C (17.5 μC/cm2, 338 pm/V, and 32%, respectively) associated with a transition to a purely T phase. Despite these compositions showing promise for room-temperature applications, the deterioration in properties as a function of increasing temperature poses challenges for device design and remains to be resolved.