Analysis of phase changes during synthesis of Sr₂Fe_1.2Mo_0.8O_6-δ solid solution by the solid-phase reaction method

Phase transformations during crystallization of the magnetic metal-oxide compound Sr₂Fe_1.2Mo_0.8O_6-δ by the solid-phase reactions method from a mixture of simple reagents 2SrCO₃ + 0.6Fe₂O₃ + 0.8MoO₃ have been analyzed. By means of differential-thermal and thermogravimetric analyses it was found that the synthesis of strontium ferromolybdate of the Sr₂Fe_1.2Mo_0.8O_6-δ composition proceeds through a series of successive-parallel stages. In this way, when considering the dynamics of phase transformations, it has been found that the main accompanying compounds during the crystallization of the solid solution of double perovskite Sr₂Fe_1.2Mo_0.8O_6-δ are Fe₂O₃, SrCO₃, SrMoO₄ and SrFeO₃. When analyzing the phase composition of the batch consisting of a mixture of initial reagents of stoichiometric composition: 2SrCO₃ + 0.6Fe₂O₃ + 0.8MoO₃, it was noted that with an increase in temperature, complex compounds SrMoO₄, SrFeO₃, and then Sr₂Fe_1.2Mo_0.8O_6-δ as well, appear almost simultaneously. This circumstance indicates that the compounds SrMoO₄ and SrFeO₃ are the structure-forming ones for the solid solution of ferromolybdate – strontium. With a subsequent increase in temperature to 1470 K, it was found that the dissolution of SrFeO₃ with the formation of double perovskite Sr₂Fe_1.2Mo_0.8O_6-δ occurs faster than the dissolution of strontium molybdate SrMoO₄. The results of the analysis indicate the difficult nature of the dynamics of solid-phase reactions during the formation of Sr₂Fe_1.2Mo_0.8O_6-δ.