Effects Of CuO, Nb₂O₅and Sb₂O₃Dopants On Microstructure And Electricity Properties Of ZnO Varistor Ceramics

Three series of ZnO varistor ceramic samples doped with CuO, Nb2O5and Sb2O3have been prepared by electronic ceramics preparation technology. The defects and the distribution of electron momemtum of the ZnO varistor ceramic samples have been studied by the measurements of positron annihilation lifetime spectrum and Doppler broadening spectrum of positron annihilation radiation; the microstructure of the samples have been studied by Scanning Electron Microscope and X-ray Diffraction; the varistor voltage, leakage current and nonlinear coefficient of ZnO varistor ceramics doped with different molar content of CuO, Nb2O5and Sb2O3have been measured. The effect of Cu ions, Nb ion and Sb ion dopant respectively on the microstructure and electrical properties of ZnO-based varistor ceramics have been discussed. The experimental results of this work are listed in the following:(1) For ZnO varistor ceramics doped with different molar ratio of CuO, with the increase of the content of CuO, the varistor voltage VlmA and nonlinear coefficient a first decreases and then rises, the varistor voltage VlmA reaches the lowest value of21.5V for the varistor doped with0.10mol%of CuO, and its grian size is the largest among this series of sample. However, with the increase of the content of CuO, the leakage current IL first increases and then decreases.(2) For ZnO varistor ceramics doped with different molar ratio of Nb2O5, with the increase of the content of Nb2O5, the grian size of ZnO and the leakage current IL of the varistor ceramics decreased first and then increased; the varistor voltage VlmA and nonlinear coefficient a of the varistor ceramics increased first and then decreased. For the varistor doped with1.5mol%Nb2O5, its varistor voltage VlmA reaches the lowest value of9.1V, while its leakage current IL reaches the largest value among this series of sample.(3) For ZnO varistor ceramics doped with different molar ratio of Sb2O3, with the increase of the content of Sb2O3, the ZnO grain size and the nonlinear coefficient a of the varistor ceramics first increases and then decreases, the varistor voltage VlmA decreased first and then increased. The leakage current IL of the varostor decreases with the increase of the content of Sb2O3. The varistor voltage VlmA of the varostor doped with0.05mol%Sb2O3reaches the lowest value of35.5V(among this series of sample), the leakage current IL and the nonlinear coefficient a of this sample reach45μA and10.3, respectively.(4) The electron density of ZnO varistor ceramics varies with the content of CuO. With the increase of the content of CuO, the mean positron lifetime of the varistor ceramics decreased first and then increased. The mean positron lifetime of the varostor doped with0.10mol%CuO reaches the smallest among this series of sample. The high of the peak of the ratio curve of the varistor ceramics first increased and then decreased with the increase of the content of CuO.(5) For ZnO varistor ceramics doped with different molar ratio of Nb2O5, with the increase of the content of Nb2O5, the amount of Zn-VZn complex increased, while the amount of VZn decreased, this give rise to the decrease of the mean positron lifetime.(6) For ZnO varistor ceramics doped with different molar ratio of Sb2O3, with the increase of the content of Sb2O3, the mean positron lifetime decreased first and then increased. The mean positron lifetime of the varostor doped with0.05mol%Sb2O3reaches199.02ps, and it is the smallest value among this series of sample.