Potentiometric determination of the stability of $BaCu_2O_2$

The thermodynamic stability of the compound $BaCu_2O_2$ was determined using a solid-state galvanic cell: Pt, $Ar+O_2,Cu_2O+BaCu_2O_2+BaF_2 \mid BaF_2 \mid BaF_2+BaO,O_2+Ar,$ Pt as a function of temperature in the range 970-1170 K. Single crystal $BaF_2$ was used as the solid electrolyte. The partial pressure of oxygen in the argon gas flowing over the electrodes was 1.27 Pa. The reversible e.m.f. of the cell can be expressed by E = 224-0.016T($\pm$1.8)mV. The Gibbs free energy of formation of barium cuprite from component oxides according to the reaction $BaO(s) + Cu_2O(s) \rightarrow BaCu_2O_2(s)$ is \Delta G° = -43 230 + 3.09T(\pm350)$J mol^{-1}$