Doping effect of Sr or Ca on single phased YBa2Cu3O7−y

Abstract

Abstract The relation between superconductivity and phase structure in YBa2Cu3O7−y doped with Sr and Ca has been studied systematically by the measurements of superconductivity, phase structure and thermal analysis. It is found that, for series of YBa2−xCaxCu3O7−y as 0⩽x⩽0.25, the samples are of single phase, and their Tc decrease linearly with content of Ca; for series of YBa2−xSrxCu3O7−y as 0⩽x⩽1.25, the samples are of single phase, but their Tc can change with the content of Sr either monotonously or non-monotonously, depending on the preparation conditions. A strong correlation exists between Tc and the crystal structure of the samples. The results obtained suggest strongly that the intensity of the coupling between Cu-O planes and Cu-O chains is very important to the high-Tc superconductivity of YBa2Cu3O7−y.