Transition from Single Crystalline FeCO3 to Layered and Ordered Nanostructured Α-Fe2o3

Layered and ordered nanostructured hematite rhombohedrons of submillimetric size were obtained by heating submillimeter single crystalline ferrous carbonate (FeCO3), at 600°C in air. The topotactic transformation and the increase of density led to the occurrence of internal porosity. The specific surface of the as-resulted hematite (α-Fe2O3) was found to be 14.5m2/g, unusually high for particles having submillimeter dimensions. Inside of the α-Fe2O3 crystals, a layered superstructure and 3D dendritic building blocks were observed. TEM imaging has revealed that the smallest subunits of this 3D architecture are crystallites with dimensions in the range of 70–80nm. To our knowledge, these findings, as well as the uniqueness of the resulting α-Fe2O3 crystals habit (rhombohedrons) have not been reported yet.