Synthesis of YFeO 3 by thermal decomposition of mechanically activated mixtures Y(CH 3COO) 3·4H 2O–FeC 2O 4·2H 2O

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A mechanothermal synthesis of orthorhombic perovskite oxide (YFeO 3) is proposed that starts from equimolar mixtures of Y(CH 3COO) 3·4H 2O and FeC 2O 4·2H 2O subjected to mechanical activation by high energy milling. The course of the decomposition process has been studied by thermoanalysis (TG/DSC) showing that, after dehydration, the decomposition occurs, through the formation of an intermediate carbonaceous phase (Y 2O 2CO 3), leading to YFeO 3 only when starting from the milled mixtures. Annealing in air the activated mixture in the temperature range between 400 and 900 °C shows that crystalline YFeO 3 is obtained only for annealing temperatures T ≥ 650 °C: this has been confirmed both by XRD and FT-IR measurements. On the other hand TG/DSC experiments performed on YFeO 3 obtained by annealing at T ≥ 400 °C show a slight mass loss accompanied by an exothermic DSC peak, very likely due to the decomposition of the intermediate Y 2O(CO 3) 2, for all the samples annealed at T ≤ 600 °C. All the heat capacity data derived from measurements of temperature modulated DSC show the Neel temperature. However reproducible C P data have been obtained only for the samples annealed 8 h at T ≥ 750 °C. As a matter of fact XRPD of samples of physical mixture show that the formation of YFeO 3 is only completed by a 250 h treatment at 1300 °C. What happens is that the phase Y 3Fe 5O 12 forms at 1100 °C and such a phase only very slowly reacts (at T > 1100 °C) with Y 2O 3 to transform to YFeO 3.