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
Bi1.7Pb0.4Sr2.0Ca1.1Cu2.1LaxOy. 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 (TC) and critical current density, in zero [JC(0)]
and applied field [JC(H)], of La added samples were found to be much higher than those of the pure sample for optimum doping levels. A maximum
TC-onset of 93.5K (x = 0.3) and a maximum JC(0) of 676 A/cm2 (x = 0.2) at 64K were observed for the doped samples as against 76.7K and
100.5 A/cm2 at 64K for the pure sample, respectively. At higher doping levels the TC and JC(0) decrease from the maximum values. The increase
in TC and JC(0) and the improved JC-H characteristics are explained to be due to the substitution of La3+ in place of Sr2+ with a consequent change
in the carrier (hole) concentration in the Cu–O2 planes, and to be due to the flux pinning effect of structural defects and nanoscale precipitates
brought about by La addition.
