INFLUENCE OF Ca DOPING ON THE SUPERCONDUCTIVITY OF Y1-xCaxBa2Cu3O7-δ

Abstract

Here, we report the effect of Ca doping on the superconducting transition temperature (T_c), crystal structure and microstructural properties of Y_1-xCa_xBa₂Cu₃O_7-δ (0 ≤ x ≤ 0.05). It was found that the variation of c-axis lattice parameter remains almost constant. However, a slight decrease in both a and b axes are noticeable leading to the reduction of orthorhombicity of Y-123 phase. The superconducting transition temperature decreases with Ca²⁺ substitution at the Y3+. The T_c of YBa₂Cu₃O_7-δ (Y-123) was reduced from 91 K for x = 0.00 to 84 K for x = 0.05. The degradation of T_c is attributed to the decrease in oxygen content in the CuO chains. The superconducting transition breadth, ΔT, increases with Ca substitution indicating the degradation of crystallinity or the presence of inhomogeneity. Changes in grain size and grain boundary were also observed by SEM. As the concentration of Ca increases, the grain size becomes larger giving rise to the reduction of porosity in the system.