Standard Gibbs' energies of formation of BaCuO₂, Y₂Cu₂O₅ and Y₂BaCuO₅

Abstract

The Gibbs' energies of formation of BaCuO₂, Y₂Cu₂O₅ and Y₂BaCuO₅ from component oxides have been measured using solid state galvanic cells incorporating CaF₂ as the solid electrolyte under pure oxygen at a pressure of 1.01×10⁵ Pa 〈BaO〉 + 〈CuO〉→〈BaCuO₂〉 ΔG°_f,ox(± 0.3) (kJ mol⁻¹)=−63.4−0.0525T(K) 〈Y₂O₃〉 + 2〈CuO〉→〈Y₂Cu₂O₂〉 ΔG°_f,ox(± 0.3) (kJ mol⁻¹)=18.47−0.0219T(K) 〈Y₂O₃〉 + 〈BaO〉 + 〈CuO〉→〈Y₂BaCuO₅〉 ΔG°_f,ox(± 0.7) (kJ mol⁻¹)=−72.5−0.0793T(K) Because the superconducting compound YBa₂Cu₃O_7−δ coexists with any two of the phases CuO, BaCuO₂ and Y₂BaCuO₅, the data on BaCuO₂ and Y2BaCuO5 obtained in this study provide the basis for the evaluation of the Gibbs' energy of formation of the 1-2-3 compound at high temperatures.