Effect of Al Substitution on Structural and Electrical Properties of Bi1.6Pb0.4Sr2CaCu2−xMxO8+δ Superconducting Ceramics

In this work we study the effect on structural and electrical properties of superconducting compound Bi1.6Pb0.4Sr2CaCu2−yMyO8+δ were M=Al (with y=0–0.6). The samples were prepared by the solid-state reaction method. The samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), direct current (DC) resistivity versus temperature ρ(T) and alternative current (AC) susceptibility measurements. Structural analysis shows that the crystalline lattice structure of the prepared sample belongs, mainly, to the superconductive tetragonal phase Bi(Pb)2212. The SEM micrographs show that in the undoped sample the grain size has a random distribution with few grains greater than 5 μm. The grains are very dense and well connected. A quite different microstructure is obtained for the doped samples of which grains are more connected with a flat characteristic shape of Bi(Pb)2212 superconductors. All samples exhibit a superconducting character and Tc and the superconducting volume fraction decrease with increasing rate of aluminum.