Processing and study of the composite CdS/Bi-Pb-Sr-Ca-Cu-O
  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. 
E. D\'iaz-Vald\'es, G. S. Contreras-Puente, N. Campos-Rivera, C.   Falcony-Guajardo, and R. Baquero
cond-mat.supr-con