Thermogravimetric Study of the Ln_2O_3-Co-Co_2O_3 System Ln=Sm at 1000℃

概要

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Phase equilibrium is established in a system Sm-Co-O at 1000℃ by changing the oxygen partial pressure from 0 to 13.00 in-log (Po_2/atm), and a phase diagram is represented for a Sm_2O_3-Co-Co_2O_3 system. Under the experimental conditions, Sm_2O_3, CoO, Co, and SmCoO_3 phases are present. But Sm_2CoO_4 and Sm_4Co_3O_10 phases are not stable in the system. A slight nonstoichiometry is found in CoO and SmCoO_3 phases, and the nonstoichiometry of SmCoO_3 is discussed with respect to the oxygen partial pressure, and the activities of the components in the solid solutions are calculated using the composition-oxygen partial pressure relations obtained. Lattice constants of SmCoO_3, made in different oxygen partial pressures, are determined and compared with those values prepared at 1200℃. Standard Gibbs energy changes of the reactions in the phase diagram are calculated with the oxygen partial pressure in equilibrium with solids, and these are compared with previous values.
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