Study On The Electrical Property Of Tungsten Trioxide-Based Functional Materials By Tape Casting

As a kind of transition metal oxide, because of its multiphase and ferroelectricity, WO₃ (tungsten trioxide) have many special properties. As an important semiconductor material WO₃ is extensively used in fuel cells, electro chromic device, photocatalytic degradation, toxic gas sensor and others. In recent years, some authors reported studies on nonohmic behavior of sintered WO₃ ceramics indicating WO₃-based ceramics are potential varistor materials. However, the electrical properties of sintered WO₃ ceramics are instable, which is an obvious obstacle for practical application of WO₃ as a varistor material. In this work, single componen and functionally gradient materials(FGM) is prepared by the method of tape casting, and its electrical properties (current-voltage characteristic, resistivity , impedance),internal relations were discussed. The principal research contents include:The preparation of tape casting slurry is explored, through test to decide the optimized technology condition. The free cracks samples were fabricated. The microstructures of samples were observed by using a scanning electron microscope. Based on the study of the current-voltage characteristics, we find out that both the single componen and functionally gradient materials of Co₂O₃ doped WO₃ behaved negative differential resistance (NDR) characteristic. However, the NDR appears in nonlinear region and the property is correlated with the electric history of the samples. For functionally gradient materials, No delamination was observed in any case after high temperature sintering. Moreover, we also observed that the electric property of FGM exhibited anisotropy.The property different from traditional materials originates from heterogeneity of composition, and it is not determined by some layer of the sample.W_0.97-xCo_0.03Al_xO₃ polycrystalline ceramic bulks were fabricated by conventional ceramic technique. We found that the proper amounts of Al₂O₃ can reduce the resistivity of ceramics and improve the electrical stability of ceramics. In addition, the content of Al₂O₃ can adjust the resistivity and resistance-temperature properties of ceramics efficiently.This work systematically investigated the Fe₂O-3 doped WO₃ single componen and functionally gradient materials (FGM). FeWO₄ revealed by scanning electron microscope exist as low resistively phase. However, FeWO₄ can destruct the characteristics of grain boundary. Then, the leakage of samples current increase, nonlinear coefficient and breakdown voltage decrease.