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 1100°C by varying the oxygen partial pressure from −log ( P O 2 /atm)=0–13.00, allowing construction of phase diagrams at 1100°C for the systems Ln 2O 3–MnO–MnO 2. Under experimental conditions, Yb 2O 3, MnO, Mn 3O 4, and YbMnO 3 phases are found to be present in the Yb–Mn–O system, whereas Dy 2O 3, MnO, Mn 3O 4 DyMnO 3, and DyMn 2O 5 phases are present in the Dy–Mn–O system. Ln 2MnO 4, Mn 2O 3, and MnO 2 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 YbMnO 3 =1.00×10 −4(log P O 2 ) 3+1.30×10 −3(log P O 2 ) 2+7.20×10 −3(log P O 2 )+5.00×10 −5 and N O/ N DyMnO 3 =1.00×10 −4(log P O 2 ) 3+1.80×10 −3(log P O 2 ) 2+9.30×10 −3(log P O 2 )+1.69×10 −2. Activities of the components in the solid solutions are calculated using these equations. LnMnO 3 may range Ln 2O 3-rich to Ln 2O 3-poor, while MnO is slightly nonstoichiometric to the oxygen-rich side. DyMn 2O 5 also seems to be nonstoichiometric. Lattice constants of LnMnO 3 under different oxygen partial pressures were determined, as well as lattice constants of DyMn 2O 5 quenched in air. The standard Gibbs energy changes of reactions appearing in the phase diagrams were calculated.