Phase transition, dielectric and piezoelectric properties of K0.5Na0.5NbO3–CaTi0.9Zr0.1O3 lead-free ceramics

Abstract

Lead-free (1 − x)K0.5Na0.5NbO3–xCaTi0.9Zr0.1O3 + 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 CaTi0.9Zr0.1O3 diffuse into K0.5Na0.5NbO3 lattices to form a solid solution with a perovskite structure. After the addition of CaTi0.9Zr0.1O3, 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: d33 = 203 pC/N, kp = 45.0%, and TC = 342 °C.