Preparation And Electrical Properties Of Titanate-doped (K_0.5Na_0.5) NbO₃-based Ceramics

(K,Na)NbO3-based lead-free piezoelectric ceramics is considered to be one of most promising lead-free piezoelectric materials because of its excellent piezoelectric properties. However, it is difficult to obtain pure-KNN ceramics with high theoretical density due to the narrow sintering temperature and volatilization of alkali metals during calcinations process. The effect of GeO2on the structure and properties of (K,Na)NbO3-based piezoelectric ceramics doped by perovskite structure of titanate were studied in this thesis. Three kinds of lead-free piezoelectric ceramics,0.94(K0.5Na0.5)NbO3-0.06BaTiO3、0.95(K0.5Na0.5)NbO3-0.05SrTiO3and0.95(K0.5Na0.5)NbO3-0.05CaTiO3, were prepared by conventional solid-state reaction method. The effects of GeO2doping on the sintering of these three ceramics were investigated by X-ray diffraction analysis, scanning electronic microscopy observation and measurement of electrical performance. The results show that the phase structure is perovskite after titanate doping, It is a mixture of tetragonal and quadrature phase at room temperature. The GeO2doping does not change the structure and composition of the ceramics.. The shrinkage and density are increases with the increase of GeO2doping amount. They have a certain changes with the increase of sintering temperature but increased marginally. Scanning electron microscopy shows that the porosity is decreased and the fracture changes from intergranular fracture to transgranular fracture as GeO2doping increases. The dielectric and piezoelectric properties have been improved after the addition of doping sintering agents. Doping of calcium titanate has better performance on the dielectric properties and piezoelectric of ceramics than strontinm titanate and barium titanate doping. The piezoelectric constant value of ceramics can achieve121PC/N by doping of calcium titanate and sintering temperature range has been broadened, which may be due to the smaller grain size of KNN-BT and KNN-ST series ceramics. In conclusion, GeO2doping can promote the sintering of KNN-based ceramics, increase the density and decrease the sintering temperature. Meanwhile, the dielectric and piezolelctric properties were improved. The research has some significance to the research of improving the potassium sodium niobate based lead-free piezoelectric ceramics electrical properties through doping titanate and adding sintering agent.