Phase equilibrium in the system Ln-Mn-O V. Ln = Yb and Dy at 1100°C

Phase equilibrium was established in the Yb-Mn-O and Dy-Mn-O systems at 1100degreesC by varying the oxygen partial pressure from -log (P-O2/atm) = 0-13.00, allowing construction of phase diagrams at 1100degreesC for the systems Ln(2)O(3)-MnO-MnO2. Under experimental conditions, Yb2O3, MnO, Mn3O4, and YbMnO3 phases are found to be present in the Yb-Mn-O system, whereas Dy2O3, MnO, Mn3O4 DyMnO3, and DyMn2O5 phases are present in the Dy-Mn-O system. Ln(2)MnO(4), Mn2O3, and MnO are not stable in either system. Small nonstoichiometric ranges are found in the LnMnO(3) phase, with the nonstoichiometry represented by the equations, N-O/N-YbMnO3 = 1.00 x 10(-4)(log P-O2)(3) + 1.30 x 10(-3)(log P-O2)(2) + 7.20 x 10(-3)(log P-O2) + 5.00 x 10(-5) and N-O/N-DyMnO3 = 1.00 X 10(-4)(log PO2)(3) + 1.80 x 10(-3)(log P-O2)(2)+9.30 x 10(-3)(log PO2)+1.69 x 10(-2). Activities of the components in the solid solutions are calculated using these equations. LnMnO(3) may range Ln(2)O(3)-rich to Ln(2)O(3)-poor,while MnO is slightly nonstoichiometric to the oxygen-rich side. DyMn2O5 also seems to be nonstoichiometric. Lattice constants of LnMnO(3) under different oxygen partial pressures were determined, as well as lattice Constants of DyMn2O5 quenched in air. The standard Gibbs energy changes of reactions appearing in the phase diagrams were calculated. (C) 2003 Elsevier Inc. All rights reserved.