PHASE TRANSFORMATIONS DURING CRYSTALLIZATION OF A SOLID SOLUTION OF STRONTIUM-SUBSTITUTED DOUBLE PEROVSKITE

The kinetics of phase contents modification in the process of SrBaFeMoO_6–δ crystallization from a stoichiometric mixture of SrCO₃ + BaCO₃ + 0,5Fe₂O₃ + MoO₃ simple oxides using the solid phase method has been investigated. In the temperature region of 300–1200°С, a number of endotermic effects have been detected. Herewith, the first one (with maximum around 552°С) and the third one (with maximum around 743°С) are accompanying by the significant decrease of the mass of specimen. In the temperature range of 946–1200°С, the mass change of specimen is practically not observable, while the thermal effect is still present, and the specimen remains not single-phase one. This indicates the difficulty of the flow of solid phase reactions with the formation of solid solution of barium-strontium ferromolybdate. During analysis of the change of the phase composition consisting of a mixture of initial reagents of stoichiometric relation SrCO₃ + BaCO₃ + 0,5Fe₂O₃ + MoO₃, it has been observed that with increasing temperature, complex compounds BaMoO₄, SrFeO₃ appear almost simultaneously, then SrBaFeMoO_6–δ appears consequently. Thus, the compounds BaMoO₄ и SrFeO₃, are structure forming for the solid solution of barium-strontium ferromolybdate. With further temperature increase up to 770°С the formation of new compound ВаFeO₃ with disappearing SrFeO₃ was detected. In this case, the amount of double perovskite increases faster than that of barium molybdate. The main accompanying compounds at the crystallization of the SrBaFeMoO_6–δ double perovskite solid solution are BaMoO₄ and SrFeO₃. It was established that at the initial stage of the interaction, the resulting solid solution of barium-strontium ferromolybdate is enriched with iron and its composition changes during the reaction in the direction of an increase of the molybdenum content, as in the case of other precursor combinations.

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