DEGREE OF PHASE TRANSFORMATIONS AND CRYSTALLIZATION MECHANISM OF THE METAL OXIDE COMPOUND Sr2FeMoO6–δ

Abstract

Polythermic dependences of the phase transformation degree during Sr₂FeMoO_6–d crystallization by the solid phase method have been studied for powders synthesized from the stoichiometric mixture of the oxides SrCO₃ Fe₂O₃, MoO₃ and from the partially reduced precursors SrFeO_3–x and SrMoO_4–y. It is found that the general rule for all samples is a transition from the kinetic mode of interaction to the diffusion one. In this case, the reaction product layer is formed and is increased with its blocking action. However, it should be mentioned that for the samples synthesized from a mixture of simple oxides, the kinetic stage of solid-phase interactions is mixed with the presence of some fraction of the diffusion part due to the formation of intermediate reaction products. When α is increased, the fraction of the diffusion part grows. The use of the partially reduced precursors SrFeO_3–x and SrMoO_4–y with submicron grains allows one to synthesize the single-phase compound Sr₂FeMoO_6–d with the superstructure ordering of Fe³⁺/Mo⁺⁵ cations. In this case, the kinetic difficulties of the Sr₂FeMoO_6–d phase formation are significantly reduced by increase in the diffusion mobility of Fe³⁺ and Mo⁺⁵ cations and by decrease in the distance of their motion to the reaction zone.