EFFECTIVE ATOMIC CHARGES AND CHARGE-TRANSPORT IN SUPERCONDUCTOR LATTICES

Effective atomic charges in RBa2Cu3O7 compounds (here R stands for ytt rium or a rare-earth metal), Tl2Ba2Ca2Cu3O10, and Bi1.6Pb0.4Sr2Ca2CU3O 10 have been determined. In RBa2Cu3O7, the holes are shown to be deloc alized primarily on the oxygen-chain sublattice. Two models of charge distribution within the lattices of Tl2Ba2Ca2Cu3O10 and Bi(1.6)Pb(0.4) Sr(2)Ca(2)CU3O(10) are proposed, which assume the presence of holes at oxygen sites in the Cu(2)-O plane but differ in the occupation of the 3d shell of Cu atoms at the nodes of Cu(1). The atomic charges of Tl, Bi, and Cu(1) on these two latter lattices are possibly controllable. The results obtained are shown to be qualitatively consistent with Ha ll measurements of the hole concentration and of its temperature depen dence in the compounds studied. (C) 1997 American Institute of Physics .