Department Of The Titanium Dioxide Semiconductor Functional Materials

TiO₂ ceramic varistors, a kind of semiconductor with double function, have low breakdown voltage, excellent non-linear coefficient and high dielectric constant. They are widely utilized, mainly being used as transient high-voltage protector and surge arrestor. TiO₂ ceramic varistors have a great potential application in market.The properties of TiO₂ ceramic varistors were studied in this paper. These were no-additive, only Nb₂O₅ additive, double additive of Nb₂O₅ and La₂O₃, nano-TiO₂ additive and rare earth CeO₂ additive sample. The microstructure of low-voltage TiO₂ ceramic varistors, with different compositions and process, were tested systematically. Last, grain boundary segregation driving force of different sample were researched. Some experimental results were obtained.Through many experiments, the best comprehensive properties with repeated and stable experiment were proved to be the nano-TiO₂ doping in all series samples. In nano-TiO₂ doping series, the properties of [ 98.7 mol % TiO₂ (6wt % nano-TiO₂) ] +0.6mol %Nb₂O₅+0.4 mol%La₂O₃+0.3 mol%SiO₂ composition was best in sintering 1360℃. The properties include: breakdown voltage of 4.36V/mm, nonlinear coefficient of 6.3, dielectric dissipation of 0.22 and comparative dielectric of 9.7×10⁴. In nano-TiO₂ doping series, sample properties of breakdown voltage deduced and nonlinear coefficient rised with the sintering temperature going high. In the rare earth doping series, sample with good properties sintering temperature can be deduced to 1240℃, but with no repeatful and stable experiment.In addition, through the analysis of grain boundary segregation driving force, the grain boundary segregation driving force factors benefit the analysis of relation with composite and microstructure. The photography of SEM implies, the microstructure of TiO₂ ceramic varistors are composed of grains, less second phase and gas hole, which are various of composite. The analysis of second phase with XRD indicates it is composed of TiO₂ with little LaNbTiO₆, La₄Ti₉O₂₄ and NbO₂.Finally, TiO₂ Varistors resistence is designed and made compared with related technology parameters of round SrTiO₃ ring varistor resistence. Module size is Φ_out of 15mm, Φ_in of 9mm,d of 1.2～1.5mm.