Gibbs free energy of formation of LnBa(2)Cu(3)O(7-x) phases determined by the EMF method (Ln = Yb, Tm, Er, Ho, Dy)

Employing electrochemical cells with calcium fluoride solid electrolyte po( 2), CaO + CaF2//CaF2//CuO + LnBa(2)Cu(2)O(7-x) + Ln(2)CuBaO(5) + BaF2, p(o2 ), for Ln = Yb, Er, Tm, Ho, Dy, and Gd, the Gibbs free energy change of the reaction of formation of the solid LnBa(2)Cu(3)O(7-x) phases for subsequen t lanthanide elements was determined. Either an air or argon and oxygen gas mixture was used to fix oxygen potential over the reference and working el ectrodes. Next, the obtained results were used to derive the Gibbs free ene rgy change of reactions of formation of the investigated LnBa(2)Cu(3)O(7-x) phases, except for that of the gadolinium compound, In this particular cas e, the side reaction made the reproducible cell performance impossible. (C) 1999 Academic Press.