Composition and temperature dependence of structure and piezoelectricity in (1−x)(K 1−y Na y )NbO ₃ ‐x(Bi 1/2 Na 1/2 )ZrO ₃ lead‐free ceramics

Lead‐free piezoceramics with the composition (1−x)(K 1− y N a y )NbO 3 ‐x(Bi 1/2 Na 1/2 )ZrO 3 ( KN yN‐ 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 =24 μC/cm 2 ), piezoelectric coefficient ( d 33 =320 pC /N), effective piezocoefficient ({d₃₃^*}=420 pm/V), coupling coefficient ( k p =48%), and high strain ( S =0.168%) were obtained at room temperature, but significant deterioration of P r , {d₃₃^*}, and k p were observed by increasing from room temperature to 160°C (17.5 μC/cm 2 , 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.