الفهرس 
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Abstract
Fabrication of ZnO varistors follows standard ceramic techniques. The components are mixed, for example by milling in a ballmill and spray drying afterwards. The mixed powder is dried and pressed to the desired shape. The resulting pellets are sintered at high temperature, typically 1000-1400 °C. Additives are usually added to improve the electric properties of varistors; increase the non linearity behavior or to improve the breakdown voltage of ZnO. X- ray diffraction analysis of sintered samples reveals no formation of new phases, but lattice constants of the phases were changed after sintering. Lattice constants of each sample were changed in different extents depending on the phases affinity to a particular ion and on overall varistor composition. the structure has a single phase with shift in the position of peaks (change in d-spacing). The present study reveals that the addition of CuO leads to a two phase microstructure; well crystalline ZnO grains in preferred orientation, ZnO crystallize in hexagonal system. It is characterized by perfect cleavage plane along 001 which was distinct in SEM of ZnO. CuO added was partly distributed in ZnO grains themselves, and SEM image of mix (M1) which containing ZnO + 0.3 mol٪ CuO, show that ZnO agglomerates of various size and shapes, some of these agglomerates are dissected and fine grains are in corporate within these lines of dissection. Also, there are a mass of solid solution of ZnO and CuO in some places are rich in Zn others in Cu showing a kind stereopticons (dark and light lines). The mass is dissected by parallel caveats perpendicular to the lines of stereotions, these was observed in mix (M6) which containing ZnO + 4 mol٪ CuO. SEM and AFM revealed the presence of inter-granular phase. Additives present in grain boundaries between ZnO grains. Additives concentration produce a decrease in the grain size by about 0.07 μm and also the surface roughness is increased by the factor of 0.09. The addition of CuO improve the nonlinear coefficient, also the irradiation with laser increase the values of it for almost all groups. Conductivity and dielectric constant are highly dependent on the microstructure of conducting grains surrounded by this insulating oxide barrier. Increasing the frequency was associated by a decrease in dielectric constant and an increase in conductivity, also the laser has a positive effect for some samples at both variables, The increase of electrical conductivity as a result of irradiating the samples with laser radiation is believed to be due to the generation of excess free carriers. The conduction mechanism found to be agree with Correlated Barrier Hopping model (CBH). Activation energy is highly affected by the presence of dopant and there are a decreasing in its value associated with CuO concentration and due to the laser effect. X ray Photoelectron spectrometer is used for element (0.1 at ٪) and chemical analysis, quantitative analysis and structure investigation . The binding energies of Zn 2p , Cu 2p , Cr 2p and O 1s core levels of ZnO varistor surfaces were determined by X-ray photoelectron spectroscopy (XPS). Other values, such as the full width at half maximum (FWHM) are useful indicators of chemical state changes and physical influences. That is, broadening of a peak may indicate: a change in the number of chemical bonds contributing a peak shape, a change in the sample condition. Sensitivity Factors (RSF) are used to scale the measured peak areas so variations in the peak areas are representative of the amount of material in the sample surface. The spectrum is dominated by two photoelectron peaks, corresponding to electrons originating in the 1s orbital’s of the carbon and oxygen atoms in the sample surface. Hydrogen and helium are missing from the table and are essentially impossible to detect by XPS. The atomic concentration ratio of elements measured by XPS is different than the one measured by EDS. Taking under consideration that, for EDS, the penetration depth is much greater than for XPS.