Improved superconducting properties by La addition in (Bi,Pb)-2212 bulk superconductor

Abstract

The effects of La addition on the structural and superconducting properties of (Bi,Pb)-2212 bulk superconductor prepared by solid state synthesis in the polycrystalline form were studied. The La content of the samples was varied from 0 to 0.5 on a general stoichiometry of Bi 1.7Pb 0.4Sr 2.0Ca 1.1Cu 2.1La x O y . Phase analysis by XRD, microstructural examination by SEM, measurements of density and superconducting properties were done to evaluate the relative performance of the samples. The critical temperature ( T C) and critical current density, in zero [ J C(0)] and applied field [ J C(H)], of La added samples were found to be much higher than those of the pure sample for optimum doping levels. A maximum T C-onset of 93.5 K ( x = 0.3) and a maximum J C(0) of 676 A/cm 2 ( x = 0.2) at 64 K were observed for the doped samples as against 76.7 K and 100.5 A/cm 2 at 64 K for the pure sample, respectively. At higher doping levels the T C and J C(0) decrease from the maximum values. The increase in T C and J C(0) and the improved J C-H characteristics are explained to be due to the substitution of La 3+ in place of Sr 2+ with a consequent change in the carrier (hole) concentration in the Cu–O 2 planes, and to be due to the flux pinning effect of structural defects and nanoscale precipitates brought about by La addition.