부산대학교 도서관

Phase diagram studies of the system SrO-Fe3O4-MoO3 were undertaken in Ar/l% H2 at 1200°C with particular emphasis on the region near Sr2FeMoO6 (SFMO). We find that Sr2FeMoO6 is not a point compound but is part of the Sr2+zFe2-xMoxOy solid solution region. The oxygen stoichiometry, y, in Sr2Fe2-xMoxOy was also determined across the solid solution region. Using the experimental data and by invoking a substitution model based on preferential substitution of similar ionic radii for Mo ions on the Fe ion sites, it was possible, for the first time, to calculate the individual Fe and Mo valence states in the substituted samples. In Ar/1% H2 at 1200°C, Fe2+/Fe3+ and Mo5+/Mo6+ are present in Sr2Fe2-xMoxOy. With increasing Mo substitution, the amount of Fe3+ decreases. In the ideal Sr2FeMoO6 composition, we predict the amounts of Fe2+, Fe3+, Mo5+, and Mo6+ to be equal. In Ar/1% H2 at 1200°C, there is a predominance of Mo5+ in Sr2FeMoOy because the oxygen stoichiometry, y, in SFMO has a value of only 5.8. Hence such processing conditions are too reducing. The work predicts the processing conditions for optimizing film and bulk properties, as well as explaining why there is a wide variability of reported sample properties in the literature. To optimize the magnetoresistive properties of Sr2FeMoO6, it is critical (a) to carefully select the correct annealing atmosphere to obtain oxygen stoichiometric Sr2FeMoO6 and (b) to control cation composition; otherwise nonstoichiometric Sr2Fe2-xMoxOy will form instead of Sr2FeMoO6. [ABSTRACT FROM AUTHOR]