  We have fabricated and characterized samples of the superconducting-
semiconducting Bi-Pb-Sb-Sr-Ca-Cu-O/CdS composite. Nano-size particles of CdS
were deposited and introduced into the porosities of the Bi-Pb-Sb-Sr-Ca-Cu-O
material by the spray pyrolysis technique. The morphology and hollow size in
the porous superconducting material as well as the grain size in CdS and the
morphology of the surface of the composite were obtained by Scanning Electron
Microscopy. We obtained the critical superconducting temperature of both the
Bi-Pb-Sb-Sr-Ca-Cu-O and the Bi-Pb-Sb-Sr-Ca-Cu-O/CdS composite measuring the
resistivity. Both show a metallic behaviour just above the superconducting
transition. For the superconductor alone, resistivity starts falling at Tc,on
sup = 99,9 K and reaches zero at Tc,sup=76,3 K. The behaviour of the composite
is different. The transition starts at Tc,on comp = 65,3 K and reaches zero
resistance at Tc,comp = 56,5 K. This seems to indicate that the semiconductor
penetrates the whole superconducting Bi-Pb-Sb-Sr-Ca-Cu-O sample so that there
is no region of pure superconducting material left. Since the materials do not
actually mix (see text) the behaviour might be attributable to the interface.
Also the resistivity curves present a very interesting feature, i.e., below the
temperature at which the composite attains zero-resistivity, a re-entrant
behaviour manifests itself and a finite resistivity peak appears. It increases
to a certain value to drop back to zero at some temperature below. We comment
further on this feature in the text.
