The Tio <sub> 2 </ Sub> A Preliminary Study Of The Pressure-sensitive Ceramic Grain Boundary Segregation

As a new type double functions material, the TiO₂ varistor ceramic has excellent nonlinear voltage current and high capacitors characteristics. Because of it's low breakdown voltage, high permittivity dielectrics and simple technological production process, the TiO₂ varistor ceramic broadly use in the matter of over voltage protectors, noise absorptors and surge arrestors of middle and low voltage electronic circuits, and instrumental in the development of the miniature electric machine. At present, the TiO₂ varistor ceramic is a better electric function material for low voltage varistor ceramics under 20V.This paper intended to explore the research work from two aspects, the first part, on the basis of the preliminary research work of TiO₂ varistor ceramic grain boundaries segregation's thermodynamics and defect chemistry, we simulate the grain boundaries segregation under the conditions of undoped nonstoichiometry, undoped reductive air, Nb₂O₅ acceptor doped and Al₂O₃ donor doped, and proved it by experimentation. The second part, we observed the grain boundaries segregation of TiO₂ varistor ceramic by transmission electron microscope (TEM) and atomic force microscopy(AFM),then analysised and discussed it. Eventually, we derived the grain boundaries energy formula by high resolution transmission electron microscopy (HREM).First of all, we surveyed the grain boundaries segregation of the TiO₂ varistor ceramic in this article, then discussed the TiO₂ varistor ceramic grain boundaries segregation's thermodynamics and defect chemistry, and then simulated the grain boundaries segregation under the conditions of undoped nonstoichiometry, undoped reductive air, Nb₂O₅ acceptor doped and Al₂O₃ donor doped, finally, we proved it by experimentation. We found that the results from the experimentation have a little bit difference from the simulator,because the simulator is based on the ideal nonstoichiometry materials, the experimentation tested by us is using the chemistry materials, so we thought the result of simulator is reasonable.Furthermore, we observed the grain boundaries segregation of TiO₂ varistor ceramic by TEM and AFM, and investigated the atomic scale grain boundaries structure of the TiO₂ varistor ceramic by HREM, and preliminary certain that (110) plane is the leading forms of the TiO₂ varistor ceramic grains, and derivatived the grain boundary energy formula of the TiO₂ varistor ceramic.In the meantime, Some experiences about preparing TEM specimen of the TiO₂ varistor ceramic grain boundaries were gotten. After the TEM observed, we found some grain boundaries phenomenon and explained it.In brief, the research work for this paper has brought the investigations of grain boundaries segregation simulation, verification and grain boundaries structure into one and laid some foundations on the TiO₂ varistor's development for future researches, the result of which will have an important reference value in its further research.