Effects of calcium substitution on the superconducting properties of R1−xCaxBa2Cu3Oz (R = Eu, Gd, Er; 0 ⩽ x ⩽ 0.3) polycrystalline samples

The influence of calcium substitution on the superconducting properties of polycrystalline R1−xCaxBa2Cu3Oz (R = Eu, Gd, Er; x = 0; 0.2; 0.25 and 0.3) samples has been studied by X-ray powder diffraction, AC susceptibility and DC magnetization measurements. The superconducting parameters such as critical temperature, inter- and intra-granular critical current and flux pinning are found to be strongly dependent both on Ca content and type of R element. The best combination of these parameters is found for the system Gd1−xCaxBa2Cu3Oz forming R1+yBa2−yCu3Oz clusters. The level of overdoping and the type of intergrain connection, were found to be influenced by the R element and the Ca concentration. Flux pinning in Gd1−xCaxBa2Cu3Oz is connected with the presence of R1+yBa2−yCu3Oz clusters.