Synthesis of YFeO3 by Thermal Decomposition of Mechanically Activated Mixtures Y(CH3COO)3•4H2O-FeC2O4•H2O

A mechanothermal synthesis of orthorhombic perovskite oxide (YFeO3) is proposed that starts from equimolar mixtures of Y(CH3COO)3·4H2O and FeC2O4·2H2O 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 (Y2O2CO3), leading to YFeO3 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 YFeO3 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 YFeO3 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 Y2O(CO3)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 CP 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 YFeO3 is only completed by a 250 h treatment at 1300 ◦C. What happens is that the phase Y3Fe5O12 forms at 1100 ◦C and such a phase only very slowly reacts (at T > 1100 ◦C) with Y2O3 to transform to YFeO3.