Effect of sintering condition on the microstructure and electrical properties of lead-free (Na0.5K0.5)NbO3- Bi0.5(Na0.82K0.18)0.5TiO3 ceramics

Abstract

In this work, the piezoelectric ceramic system of the (1-x)(Na0.5K0.5)NbO3-xBi(Na0.82K0.18)TiO3 with composition close to the morphotropic phase boundary is studied. (Na0.5K0.5)NbO3 with 0~5 mole% Bi(Na0.82K0.18)TiO3 has been prepared following the conventional mixed oxide process. From the results of X-ray diffraction and piezoelectric measurement, ceramics near x=0.03 are found at the MPB between the tetragonal and orthorhombic perovskite. The effect of sintering time on the properties of 0.97(Na0.5K0.5)NbO3-0.03Bi(Na0.82K0.18)TiO3 (0.97NKN-0.03BNKT) ceramics is discussed. For 0.97NKN-0.03BNKT ceramics, the electromechanical coupling coefficients of the planar mode kp and the thickness mode kt reach 0.31 and 0.47, respectively, at the sintering of 1100 oC for 3 h. Dielectric and piezoelectric properties have maximum values at the sintering temperature of 1100oC for 5 h. For 0.97NKN-0.03BNKT ceramics, the electromechanical coupling coefficients of the planar mode kp and the thickness mode kt reach 0.34 and 0.58, respectively, at the sintering of 1100 oC for 5 h. The effect of prolonging the sintering time to the 0.97NKN-0.03BNKT system is a helpful method on ceramic processing to improve densification and properties. With suitable concentration and sintering condition, good dielectric and piezoelectric properties were obtained.