A mechanothermal synthesis of orthorhombic perovskite oxide (YFeO3) is proposed that starts from equimolar mixtures of Y(CH3COO)(3)center dot 4H(2)O and FeC2O4 center dot 2H(2)O 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 degrees C shows that crystalline YFeO3 is obtained only for annealing temperatures T >= 650 degrees 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 degrees 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 degrees 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 degrees 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 degrees C. What happens is that the phase Y-3 Fe5O12 forms at 1100 degrees C and such a phase only very slowly reacts (at T > 1100 degrees C) with Y2O3 to transform to YFeO3. (C) 2011 Elsevier B.V. All rights reserved.