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 (Cu_4−nCr_n)O_x (n 4 0 to 0.20) type glassy precursors become high-T_c superconductors by annealing at 840 °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 Tc 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.