الفهرس | Only 14 pages are availabe for public view |
Abstract The thesis lies in three chapters; introduction, experimental techniques and results and discussion. It contains (114) pages, (52) figures and (19) tables. In the first chapter the history, development of the hightemperature superconductor, basic properties of superconductors, theories of the superconductivity, and literature review have been discussed. The second chapter contains the procedure used for preparation of the samples and the experimental techniques used to investigate the samples. The third chapter contains the discussion of the obtained results, in addition to the conclusion and the references. The co-precipitation method used for prepared nano metal oxides, and then doped to YBCO with concentrations from 0.1 to 0.5 wt%. The samples grounded by ball milling then pressed at 6 tons/cm2 and sintered at 920 oC and exposed to oxygen during cooling scheme. The obtained samples were studied via XRD, SEM, EDAX and resistivity measurements. XRD patterns revealed that the obtained samples have single phase perovskite structure YBCO with orthorhombic Pmmm symmetry and small differences in crystallinity. The lattice parameters a, b and c changed slightly with increasing the doping concentration. SEM -EDAX analysis shows that the grains are random in shape, orientation and linear dimension which equal (3-4) μm in average. The presence of nanoparticles affect on the creating of cooper pairs. Moreover, a gradual increase of grain size with the doping of nanooxides is also obvious in most samples. Most doped samples show high values of oxygenation which changes a little with the doping. Non magnetic doping of CuO and SnO2 decreased the critical transition temperature (Tc) and improved slightly as the doping increased accompanied by decrease in both of residual resistivity (ρ0) and ΔT but still below the pristine Y123 samples The behaviour of nano metal oxides changes form one doping to another according to their magnetic properties. Non magnetic doping SnO2 tends to accumulate on one point between YBCO grains, while other doping tends to distribute through the bulk of the samples. Resistivity dependence of temperature has been carried out for all the prepared samples and it is show that all doped YBCO samples show metallic behaviour at low values of doping(x) and semiconducting behaviour at higher x values. The superconductor parameters of YBCO (Tco, Tc, ΔT and ρ0) have been calculated. Comparison between magnetic and non magnetic nano doping declared that non magnetic doping leads to degradation of Tc for all concentration in contrast to low concentration of magnetic doping (Mn3O4). High values of magnetic doping concentration lead to degradation of Tc which refers to the possibility of cooper pair breaking and to the distortion of YBCO crystal. |