Second phases of (La,Nb)-Codoped TiO2 varistor ceramic

Abstract

Crystal structure, chemical composition and phase transition of second phases in (La,Nb)-Codoped TiO2 varistor ceramics was investigated. SEM, XRD, XPS and EDS were carried out the analytic studies on the microstructure, chemical composition and crystal structure of TiO2 ceramics. The results showed that the second phases existed in (La,Nb) doped TiO2 varistors ceramics. With sintering temperature increasing, second phases will transit from LaNbO4 to LaNbTiO6. Ternary phase diagram of La2O3-Nb2O 5-TiO2 was plotted based on binary phase diagram of La2O3-Nb2O5, Nb2O 5-TiO2 and La2O3-TiO2. According to the ternary phase diagram, the relative content of second phases in TiO2 ceramics sintered at different temperature was estimated. It is suggested that increasing of both second phases and titanium vacancies V""Ti will result in a higher varistor voltage V1mA and nonlinear coefficient α. © 2009 IOP Publishing Ltd.