الفهرس 
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Abstract
The new HTc-ceramic superconductors are very important for their useful applications in magnets, power transmission, computer interconnections, Josephson devices and other instrumentations. The success of these applications being depend on many interlocking factors, including critical c.d., critical fields, allowable processing temperatures, mechanical properties and chemical stability for the intended superconductors. Thus, YBa Cu 0 z HTc-superconductors is a class of 3 7-6 solid state compounds which generally have a deficient perovskite orthorhombic crystal structure. Additives have been employed to improve the properties of HTcsuperconductors. Foreign atoms can produce changes in superconductors properties by increasing the critical-transition temperature (Tc) and enhanc ing densification of the compact as well as controlling their grain growth. Some minor additions are often quite effective as sintering aids or microstructure regulators accelerating or inhibiting grain growth or may promote oxidation or reduction of their grain boundaries. The objective of the present thesis was, therefore, to follow up the effects of dopant cations and their concentrations on the physicochemical and superconducting properties of YBa HTc- 2 ceramic superconductors.