Preparation And Electrical Properties Of Tungsten Trioxide-Polymer Composite

In this thesis, WO₃-Ultra High Molecular Weight Polyethylene (UHMWPE) composite has been designed according to principles of designing the functional compound materials. And the samples of this kind material have been prepared with UHMWPE as substrate, and respectively with nanometer size grain and micrometer size grain of WO₃ as functional particle.Firstly, the processes of preparing samples have been chosen; and the samples have been prepared. The fragile samples and the insulated samples have been rejecting; the others are keeping for the following experiments.Secondly, Voltage-Current characteristics, Impedance Spectrum and Dielectric Spectrum of these collected samples have been measured. Scanning Electron Microscopy (SEM) and X-Ray Analysis have been made on the typical samples. The differences between the samples possessing high nonlinear coefficient and possessing low one, as well as the differences between the samples of (nanometer size grain of WO₃)-UHMWPE composite and (micrometer size grain of WO₃)-UHMWPE composite have been discussed.Thirdly, potential barrier value of the samples possessing high nonlinear coefficient has been calculated, which has the same change trend as that of nonlinear coefficient. Potential Barrier is a physical quantity which exists widely in varistor; but the sources of potential barrier can be different. In the studies on ZnO, the potential barrier is commonly thought come from grain boundary defects. But the grain boundary defects aren't fit to explain the nonlinearity in the samples in this thesis.In our experiments, electrical nonlinear phenomenon of samples has close relationship with the phase transition from the high conductivity phase to the low one. The two sets impedance spectrum curves obtained respectively with bias on and off show that the resistance of grain boundary has no obvious change under two conditions, which also show the source of potential barrier isn't the grain boundary defects. Similarly, the reason that the samples of (nanometer size grain of WO₃)-UHMWPE composite have low nonlinear coefficient and high conductivity is that there exists high conductivity phase mainly and little low conductivity, and therefore exists little phase transition.