Substitution of different elements in the superconducto r compounds is one of the best ways to consider this question. Recent experiments have shown that substitution of magnetic elements such as Fe, Co and Ni in Y place in high superconductor YBa 2 Cu 3 O 7- ?? (YBCO) increases critical temperature . In this experiment , for the first time, to accurate investigate of increase in critical temperature caused by magnetic ions substitutio n, magnetic ion Co and non-magnetic ion Ca were substituted together in Y 0.98-x Co 0.02 Ca x Ba 2 Cu 3 O 7- ?? with 0 Ca 0.015, and non-magnetic ions Ca and Sr were separately substituted in Y 1-x (Ca/Sr) x Ba 2 Cu 3 O 7- ?? with 0 Ca 0.012$ and 0 Sr 0.012. All the samples were prepared by the conventional solid -state reaction. XRD data was analyzed by Rietveld refinment method and shows that there isn’t noticeable impurity in samples and all of them have an orthorhombic structure with pmmm symmetry. The AC Magnetic susceptibility analysis shows a reduction in critical temperature T c while the Ca and Sr content increase in all the samples. The critical resistance analysis of the samples is in agreement with the susceptibility results. According to SEM analysis results the grain size was increased and connections between grains were improved. At the end, we can say that because Ca and Sr have radiuses close to Y radius, reduction in critical temperature can attribute to holes reduction or non-magnetzation of these ions.
