Effect of Sr and Sr-Ca substitution on the superconductivity of (Er0.76Ca0.24)Ba2(Cu2.76Co0.24)Oz

The structural and superconducting properties of (Er1-xCax)Ba2-ySry(Cu2.76Co0.24)Oz are investigated using X-ray diffraction, resistivity, ac susceptibility, and oxygen content measurements. Increasing the Sr content in (Er0.76Ca0.24)Ba2-ySry(Cu2.76Co0.24)Oz lowers the oxygen content and decreases theT c, which is attributed to the rearrangement of oxygen atoms in the basal plane. This suppression ofT c aty =0.6 cannot be improved by appropriate hole doping with Ca in (Er1-xCax)Ba1.4Sr0.6(Cu2.76Co0.24)Oz forx = 0.24-0.48.