Phase transition, dielectric and piezoelectric properties of K_0.5Na_0.5NbO₃–CaTi_0.9Zr_0.1O₃ lead-free ceramics

Lead-free (1 − x)K_0.5Na_0.5NbO₃–xCaTi_0.9Zr_0.1O₃ + 0.75 mol%MnO₂ piezoelectric ceramics have been prepared by an ordinary sintering technique and their phase transition, dielectric and piezoelectric properties have been studied. The results of X-ray diffraction show that CaTi_0.9Zr_0.1O₃ diffuse into K_0.5Na_0.5NbO₃ lattices to form a solid solution with a perovskite structure. After the addition of CaTi_0.9Zr_0.1O₃, both the cubic–tetragonal and tetragonal–orthorhombic phase transition temperatures decrease, and a relaxor behavior is induced. Coexistence of the orthorhombic and tetragonal phases is formed in the ceramics with 0.03 < x < 0.07 at room temperature. Owing to the higher number of possible polarization states resulting from the coexistence of the two phases, the piezoelectric properties of the ceramics are enhanced significantly. The ceramic with x = 0.05 exhibits the following optimum properties: d ₃₃ = 203 pC/N, k _p = 45.0%, and T _C = 342 °C.