Effective atomic charges in YBa2Cu3O7 determined by emission Moessbauer spectroscopy on 67Cu(67Zn)

A comparison has been made of experimentally determined (by emission Mossbauer spectroscopy on 67Cu(67Zn)) and calculated (in the point charge model) parameters of the electric field gradient (EFG) tensor at the Cu(1) and Cu(2) sites of YBa2Co3O7 and YBa2Cu3O6 lattices. There is no quantitative agreement between the experimental and theoretical values of the principal component of the EFG tensor because of ambiguity in the Sternheimer antiscreening factor for Zn2+ and the atomic charge scaling. The comparison of these values for the Cu(1) and Cu(2) sites in YBa2Cu(1)Cu(2)2O(1)2O(2)2O(3)2O(4) makes it possible to overcome the problem and determine the possible charge states of the atoms at the lattice sites. The conclusion has been drawn that the hole is localized at the O(4) site, although it is partially transferred to the O(2) and O(3) sites. (author)