الفهرس 
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Abstract
In this thesis work, four groups of CuO-doped ZnO varistor samples were prepared; each group consists of 9 samples with different concentrations of CuO in the range (0-6) mol٪. The samples were prepared by solid-state reaction from the Calcined Oxides with CuO concentrations, the method of preparation of samples is by mixing, drying, pressing and sintering each of the four groups at different temperatures, namely; 900°C, 1000°C, 1100°C, 1200°C for 2 hours. Three samples of group (III), sintered at 1100°C were used to investigate the effects of laser irradiation for 2 min. by exposure to pulsed picosecond Nd: YAG laser beam of a spot size of 5 mm and having pulse width of 20 picosecond and output energy 80 mJ per shot; the laser system was operated at a repetition rate of 5 shots per sec., and 1064 nm wavelength. V-I characteristics of the samples in group (III), sintered at 1100°C show that they exhibit nonlinear relationship depending on the concentration of CuO inclusions in the ZnO, and this is demonstrated by values obtained for the nonlinearity coefficient (). The calculated values of () for group (III), sintered at 1100°C, was in the range (10-65), achieving maximum value of 65, and it occurred at CuO content of 4 mol٪. These values of the nonlinearity coefficient indicate that the ZnO ceramic varistor samples are clearly varistors, because each value of them is > 5. The different proportions of the dopant constituents gave rise to different threshold voltages, nonlinearity coefficients, and leakage currents. Other electrical characteristics of the samples were measured before and after laser irradiation by covering it with a layer of silver suspension. AC frequency range (0-100) kHz at temperature range (20-170)°C was applied to investigate the electrical properties. XPS through a depth of about 10 nm from the surface after Argon ion laser reveals Zinc, Carbon, Oxygen, and Copper, EDS results indicate that Carbon element exists in the three samples, before laser irradiation, with different concentrations, probably some of it is coming from the vacuum chamber of SEM, and the highest content was in sample (2), this resulted in the increase of conductivity, the conductivity of sample (2) highly increased than those of samples (1) and (3), the iron component was found in sample (3) only in a very small concentration, so its effect on the conductivity of this sample is thought to be negligible with respect to the effect of Carbon. The XRD shows ZnO hexagonal structure before laser exposure and the average crystallite size increased after laser irradiation. The surface structure and morphology were investigated before and after laser exposure using SEM and AFM. SEM images show CuO concentrations are found in the corners between the hexagonal ZnO granules prior to laser irradiation, while the crystalline structure is varied from one sample to another after laser irradiation. ِAlso, production of many pores, increase in number of cracks and particulates of dimensions in the submicron range is noticed after the laser irradiation. The laser-induced grain-melting along with these formations highly increased the surface roughness. The large increase in roughness is clearly observed in AFM images and data after laser irradiation and varies depending on the nature of the plasma formed above the material by the powerful laser pulses. This plasma imparts heat energy to the surface leading to surface melting, as noticed also in SEM images.