Phase equilibrium in the system Ln-Mn-O IV.: Ln=Sm at 1100°C

Phase equilibrium in a Sm-Mn-O system has been established at 1100degreesC while changing the oxygen partial pressure from 0 to 13.00 in -log(P-O2/atm), and a phase diagram at 1100degreesC is presented for a Sm2O3-MnO-MnO2 system. Under the experimental conditions, Sm2O3, MnO, Mn3O4, SmMnO3, and SmMn2O5 phases are present at 1100degreesC, but Sm2MnO4, Mn2O3, and MnO2 are unstable in the system. LnMn(2)O(5)- type phase is stable under the present experimental conditions differing from the previously reported La-Mn-O and Nd-Mn-O systems. A wide range of nonstoichiometry has been found in the SmMnO3 phase which coexisted with Sm2O3, X ranges from -0.010 at log P-O2 = -10.00 to 0.098 at log P-O2 = 0 in the molecular formula of SmMnO3+x. The nonstoichiometry is represented by an equation, NO/N-SmMnO3 = 3.00 x 10(-4) (log P-O2)(3) +6.20 x 10(-3) (log P-O2)(2) + 4.28 x 10(-2) (log P-O2) + 0.0979, and the activities of the components in the solid solution are calculated using the equation. SmMnO3 seems to vary in composition in the Sm2O3-rich or Sm2O3-poor side as it was with LaMnO3. SmMn2O5 is slightly nonstoichiometric. Lattice constants of SmMnO3 made under different oxygen partial pressures and those of SmMn2O5 prepared in air were determined, along with spacings and relative intensities of SmMn2O5. Standard Gibbs energies of reactions shown in the system were calculated and compared with previously reported values. (C) 2002 Elsecier Science (USA).