Effect of substitution for Cu in Bi2Sr2Ca(Cu1-xMx)(2)O-y (M=Fe, Co) on thermopower and band spectrum in the normal state

Systematic study of the thermopower, S, and resistivity, rho, for four series of Fe and Co doped Bi2Sr2CaCu2Oy ceramic samples with different oxygen content has been carried out. By means of analysis of the obtained results on the basis of a narrow-band model, the main parameters of the band spectrum in the normal state have been determined. The concentration dependences of all parameters defined both experimentally and by calculations have a critical point of dopant content (x(c)-0.08 and 0.06 for Fe and Co doped samples, respectively). This fact suggests the type of substitution to change after x(c). We have also concluded that annealing in oxygen-deficit atmosphere and doping by Fe or Co affect oxygen atoms located in different positions.