Structure, dielectric and piezoelectric properties of K0.5Na0.5NbO3–Bi0.5(Na0.7K0.2Li0.1)0.5TiO3 ceramics

Abstract

(1−x)K0.5Na0.5NbO3−xBi0.5(Na0.7K0.2Li0.1)0.5TiO3+1mol% MnO2 lead-free ceramics were prepared by an ordinary sintering method and their structure, dielectric and piezoelectric properties were investigated. A K0.5Na0.5NbO3-based solid solution with perovskite structure is formed after the addition of Bi0.5(Na0.7K0.2Li0.1)0.5TiO3 to K0.5Na0.5NbO3. A small amount of Bi0.5(Na0.7K0.2Li0.1)0.5TiO3 retards the grain growth, induces a diffuse phase transition at TC, decreases Curie temperature and weakens the ferroelectricity of the ceramics. The ferroelectric orthorhombic-ferroelectric tetragonal phase at TO–T is shifted to low temperature after the addition of (Na0.7K0.2Li0.1)0.5TiO3, leading to the formation of the coexistence of orthorhombic and tetragonal phases near room temperature at 0.015<x<0.035. Because of the more possible polarization states resulting from the coexistence of the two phases, enhanced piezoelectric properties are obtained in the ceramics situated near the coexistence zone of two phases. The ceramic with x=0.030 possesses the relatively high TC of 372°C and large d33 of 183pC/N.