The XRD patterns recorded form the SrCO3 and α-Fe2O3 mixture following milling for the times indicated are shown in Fig. 1. Only the reflection peaks corresponding to the corundum-related α-Fe2O3 are indexed. The reflection peaks for both reactants are broadened relative to those of the non-milled materials as milling proceeds. This indicates a continuous decrease in the crystallite size. After 90 h of milling, the average crystallite size of both reactants was estimated to be ∼17 nm and remained almost the same on further milling up to 110 h. The presence of all reflection peaks of both SrCO3 and α-Fe2O3 throughout the milling process is clearly implicative that mechanical milling alone does not induce the reaction leading to the formation of a single-phased Sr3Fe2O7−δ. However, it is interesting to note that with increasing milling time the intensities of the 104 and 110 reflection peaks of α-Fe2O3 (at ca. 33° and 36° respectively) change in a similar way to that observed when tin(IV) and lithium were incorporated within α-Fe2O3[19] and [20]. This indicates that milling induces the progressive incorporation of the strontium ions (Sr2+) within the nanocrystalline α-Fe2O3 structure.