%0 Journal Article
%A Ramamoorthy Ramesh
%A M.S Hegde
%A C.C Chang
%A J.M Tarascon
%A S.M Green
%A H.L Luo
%B Journal of Applied Physics
%D 1989
%G eng
%P 4878-4885
%R 10.1063/1.343806
%T Doping mechanism in Bi(Pb)-Sr-Ca-Cu-O superconductors
%V 66
%X A model that explains the doping mechanism in Bi(Pb)-Sr-Ca-Cu-O superconductor is presented. X-ray microanalysis reveals that the excess oxygen can be accounted for by the exact stoichiometry of the n=2 and 3 phases. We show that the presence of excess oxygen associated with the structural modulation in the compound is not sufficient to explain the hole concentration required by the transition temperature observed. Using a bond valence argument, we show that the effective valence of the Bi ion in the BiO bilayers is smaller than the expected value of +3, due to the incomplete oxygen coordination around the Bi ion. The model qualitatively explains the observations of lowering of T c with Er (or Tm) doping or oxygen annealing. The role of Pb addition is suggested to be one of altering the thermodynamics and kinetics of formation of the n=3 phase.