Effect of Ca doping on the superconducting properties of GdBaSrCu3O7−δ bulk samples

Gd1−xCaxBaSrCu3O7−δ samples (0⩽x⩽0.1) were prepared via solid-state reaction. Four-point probes method was used for resistance versus temperature measurements. Results show decrease in Tc by increasing x content. This variation is assumed to be irrelevant to the different phases or impurity effects since X-ray patterns show all samples are tetragonal single-phase. Ca doping decreases the oxygen content and lattice parameters of the samples. It is suggested that Ca prevents the dislocation of oxygen, and then disrupts the hole concentration of the system and antiferromagnetic correlation at CuO2 planes. Subsequently, destroys the superconductivity of the samples.