Phase equilibria in the Ln2O3-V2O3-V2O5 (Ln=Eu and Yb) systems at 12000C

Phase equilibria in the systems, Eu2O3-V2O3-V2O5 and Yb2O3-V2O3-V2O5, were established at 12000C by changing the oxygen partial pressure from -0.68 (air) to -13.00 atm in terms of log Po2. In the Eu2O3-V2O3-V2O5 system, 0.81Eu2O3.0.19V2O5 (Eusub(1.62)Vsub(0.38)Osub(3.38)) was stable; in the Yb2O3-V2O3-V2O5 system, a new compound Yb7V3O16 was stable; and in both systems Ln2O3, LnVO4, LnVO3, Vsub(n)Osub(2n-1) (n=2-7), and VO2 were stable under the present experimental conditions. On the basis of the established phase diagrams, Gibbs energies of these reactions, 31/50 Eu2O3+19/50EuVO3+19/100O2=Eusub(1.62)Vsub(0.38)Osub(3.38), EuVO3+1/2O2= EuVO4, 2Yb2O3+3YbVO3+1/2O2=Yb7V3O16, Yb7V3O16+O2=2Yb2O3+3YbVO4, and YbVO3+1/2O2= YbVO4, were determined to be -58.9, -126.0, -134.0, -210.0, and -117.7 kJ respectively. EuVO4, Eusub(1.62)Vsub(0.38)Osub(3.38), YbVO4, Yb7V3O16, V2O3, and VO2 have nonstoichiometric compositions. (author)