The effect of Co substitution for Cu in Bi2Sr2Ca1Cu2O8-delta

We have grown single crystal whiskers of Bi-2(SrCa)(n+1)(Cu1-xCox)(n)O8-del ta with 0 < x < 0.26, and measured their resistance R as a function of the temperature T. For x < 0.06, n = 2 in the majority of the sample and n = 3 in a small part. For both phases, the changes in T-c and in the extrapolate d residual resistance due to Co substitution are the same for Co as it is f or Zn and Ni, indicating that magnetic scattering is not important. For x a pproximate to 0.06, oxygenation can drive the sample from superconducting t o insulating, indicating that both the scattering of the carriers and the n umber of carriers affect the superconducting-insulating transition. This oc curs in samples in which the sheet resistance in a CuO plane is approximate ly h/(2e)(2). For x > 0.18, the samples are insulating and n = 1. (C) 1999 Elsevier Science B.V. All rights reserved.