Effective charges of atoms in lattices YBa2Cu4O8 AND Y2Ba4Cu7O15
On the basis of comparison of experimental and calculated parameters of tenzor of the lattice electric field gradient it is shown, that the holes in YBa2Cu4O8 and Y2Ba4Cu7O15 are localized around of ions Cu in CuO3-chains on ions of oxygen. These results are in the consent with the model assuming that the mechanism responsible for high-temperature superconductivity is the interaction of electrons with the two-nuclear two-electronic centers with negative correlation energy.