الفهرس 
acknowledgmentOnly 14 pages are availabe for public view
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Abstract
The effect of chemical substitution on improving the physical and mechanical properties of superconducting materials is of great importance. Many types of substitutions have been performed in different high-temperature superconductors and the results depend on the probable site occupancy. The substitution must be between ions of equivalent sizes. The substitution by the rare-earth elements in high-temperature superconductors has special
interest in the fields of basic and applied physics. Usually in the case of high-temperature superconductors, the rare-earth elements are substituted into Ca-sites. Praseodymium and lanthanum are rare-earth elements with valences 3+, which produced changes in both oxidation-states and flux pinning when substituted into Ca-sites. These changes could improve the superconducting properties such as the enhancement of the superconducting
transition temperature (Te) and critical current density (Je). The (Cuo.5Tlo.5)-1223 phase is known as a suitable phase for practical applications because of its high superconducting transition temperature, high critical current density and its low superconducting anisotropy.