Transport properties and ac susceptibility of (Bi_1.6Pb_0.4)Sr₂ Ca₂Cu_1-xCo_x)₃O_y superconductors

We have investigated the effect of the partial substitution of Cu by Co in the stabilized 108 K phase Bi:2223, prepared by conventional solid state reaction method, by using electrical resistivity, Hall coefficient and ac susceptibility measurements. The critical temperatures and Hall concentration depend strongly on the Co content of the samples. Up to Co concentration of x=0.025 the bending of the p(T) curves, above T_c, can be described in the terms of the Lawrence-Doniach theory. The intergrain and intragrain critical transition temperatures decrease by ΔT_CG=8.5 K and ΔT_j=11.2 K, respectively, as a result of the substitution of Co for Cu in Cu-O pyramids.