Factors Influence on Electrophysical Parameters of the Composite Varistors

Abstract

Purpose. Evaluation influence structural state polymer phase on the response voltage and coefficient nonlinearity of a multilayer varistor based on zinc oxide. Methodology. Zinc oxide consisted of 97% zinc oxide and 3% total oxides of Bi2O3, Co3O4, MnO2, B2O3, SbO3, ZrO2, Al2O3. At a temperature of 1573°K, the synthesis of semiconductor ceramics based on Zinc oxide was carried out. For composite of thermoplastic polymers and Zinc oxide, non-polar and polar polymers, high pressure polyethylene and polyvinylidene fluoride were used. The composites were obtained by hot pressing at the melting temperature of the polymer phase and a pressure of 15 MPa. After that, using silver paste, measuring electrodes 10 mm in diameter were applied to the surface of the synthesized samples, and then current–voltage characteristics were measured. Modification of composites under action of gas-discharge plasma was carried out in a special cell that creates a dielectric-gas-composite system. The structure of the composites was studied by X-ray diffraction analysis and IR spectroscopy. Findings. The obtained experimental results show that the size of the particles of the inorganic phase significantly affects the current-voltage characteristics of the composite varistor: at a given thickness of the composite varistor, the operation voltage decreases markedly, and the nonlinearity coefficient increases. Numerous experimental results obtained by us show that the impact of electric discharge plasma on the polymer Zinc oxide-composite leads to a significant change in the permittivity and the concentration of local levels at the interface of the composite. The results research showed that  effect electrical plasma on the opening voltage depends on the polarity of polymer matrices. Moreover, plasma processing itself significantly changes the structure of the polymer phase at composite. Originality. The magnitude of the potential barrier at phase boundary is mainly determined by the volume fraction and size of the main structural element of ZnO ceramics. Changing the structural state of the polymer matrix allows the adjust response voltage and coefficient nonlinearity of volt-ampere characteristic of the multilayer varistor. Practical value. The discovered development of electron-ion processes at polymer phase of the varistor indicates the need to take into account change in its service characteristics from the duration and intensity of use. The result obtained has a certain practical significance, since it indicates not only the reason for the change in properties, but also the need to develop measures to increase the service life of the varistor.