Composition and temperature dependence of structure and piezoelectricity in (1-x)(K1-yNay)NbO3-x(Bi1/2Na1/2)ZrO3 lead-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 (P-r=24C/cm(2)), piezoelectric coefficient (d(33)=320pC/N), effective piezocoefficient ({d_{33}<^>*}=420pm/V), coupling coefficient (k(p)=48%), and high strain (S=0.168%) were obtained at room temperature, but significant deterioration of P-r, {d_{33}<^>*}, and k(p) were observed by increasing from room temperature to 160 degrees C (17.5C/cm(2), 338pm/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.