Effect of Cr doping on the electrical conductivity and Seebeck coefficient in the superconductors obtained from the Bi-Pb-Sr-Ca-Cu-Cr-O-type glassy precursors by annealing

Homogenous (Bi3Pb)Sr3Ca3(Cu4-nCrn)O-x (n = 0 to 0.20) type glassy precursors become high-T-c superconductors by annealing at 840 degrees C. The suppression of T-c with increase of Cr concentration supports the pair-breaking mechanism. The feeble semiconducting behavior shown by the doped samples above their respective T-c values followed Mott's variable range hopping conduction mechanism. Like Ti- and Fe-doped samples, studied earlier, the thermoelectric power (TEP) of the present Cr-containing sample showed small positive peak above T-c, which was considered to be associated with the phonon-drag effect. The linear part of the temperature-dependent TEP (above T-c) well fitted the two-band model.