Substitution effects of Bi2Sr2Ca(Cu(1-x)M(x))(2)O-8+z (M=Co, Ni) single crystals

Single crystals of Bi2Sr2Ca(Cu(1-x)M(x))(2)O-8+z superconductors doped with Co and Ni have been prepared by the travelling-solvent-floating-zone (TSFZ) method. The measured concentration of M/Cu is 2.3%, 4.0%, 5.5% for M=Co and 2%, 5% for M=Ni. It is found that the c-axis shrinks with the increasing concentration of the doping element. The critical temperature T-c is sharply depressed by the substitution of both elements with an initial rate of about 5 K per percentage doping. The influence of the doping elements as impurities on the different pinning regimes of Bi-2212 single crystals is discussed.