The influence of ball milling and subsequent sintering of a 3:1 molar mixture of SrCO3 and alpha-Fe2O3 on the formation of Sr3Fe2O7-delta double perovskite is investigated with different analytical techniques. Milling the mixture for 110 h leads to the formation of SrCO3-alpha-Fe2O3 nanocomposites and the structural deformation of alpha-Fe2O3 via the incorporation of Sr2+ ions. Subsequent sintering of the pre-milled reactants' mixture has led to the partial formation of an SrFeO3 perovskite-related phase in the temperature range 400-600 degrees C. This was followed by the progressive development of an Sr3Fe2O7-delta phase that continued to increase with increasing sintering temperature until a single-phased nanocrystalline Sr3Fe2P7-delta phase was attained at 950 degrees C (12 h). This temperature is similar to 350 degrees C lower than the temperature at which the material is prepared conventionally using the ceramic method. The evolution of different structural phases during the reaction process is discussed. Rietveld refinement of the X-ray diffraction data shows a value of 0.60 for the oxygen deficiency delta, in consistency with the Fe3+/Fe4+ ratio derived from the Fe-57 Mossbauer data recorded at both 300 K and 78 K. The Mossbauer data suggests that the Sr3Fe2O6.4 nanoparticles are superparamagnetic with blocking temperatures below 78 K. The surfaces of the Sr3Fe2O6.4 nanoparticles were shown to have a complex structure and composition relative to those of their cores with traces of SrCO3, SrO and SrFeO3-delta being detected. (C) 2015 Elsevier Ltd. All rights reserved.