Local valence balance in the structure of a high-temperature superconductor

Hitherto superconductivity of complex oxides has been observed only if the metal is present in a mixed (nonintegral) degree of oxidation. It is of interest to verify the statement that in YBa2Cu3Ox there is no copper in a degree of oxidation above 2+; instead of this, part of the oxygen is in the degree of oxidation 1-. Thus, the calculations of the valence forces tell against the presence of copper in a mixed degree of oxidation between 2+ and 3+ in high-temperature superconductors of the stoichiometric composition RBa2Cu3O7. In two-dimensional layers, copper is in the degree of oxidation 2+ (or even lower), while the electron holes are concentrated in one-dimensional chains - either in the form Cu(3+) or in the form O(1-)