A model was proposed for the variable O content of this oxide. It was based upon the assumption that the above was the stoichiometric composition of a highly acceptor-doped version of the prototype compound, Cu3Ba2YO7. The acceptor centers, BaY’, were compensated by O vacancies at the stoichiometric composition. Oxidation then involved the filling of extrinsic O vacancies, and the creation of holes. A mass-action analysis led to the expression:

(6+y)y2/(1-y) = 0.0003594 exp[0.83(eV)/kT] PO2½

where y was the deviation from stoichiometry in Cu3Ba2YO6+y, and -0.83eV was the enthalpy of oxidation per added O atom. This expression was in excellent agreement with thermogravimetric data for temperatures of between 300 and 900C, and O partial pressures of between 0.00001 and 1atm. Corrections for the effect of intrinsic ionization improved the fit at high temperatures and low y-values.

A.Mehta, D.M.Smyth: Physical Review B, 1995, 51[21], 15382-7