الفهرس 
Chapter 1Only 14 pages are availabe for public view
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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.