The distinct effects of isomorphous substitution of various divalence trace metals on hematite structure

To provide a better knowledge of the mechanisms by which trace metals associate with and affect the structure of hematite, series of Mn-, Cu-, Ni-substituted hematite samples were synthesized and characterized by Powder X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS). The results show that the incorporation of Mn, Ni, Cu into the structure of hematite changes the cell parameters of hematite due to the different radii between these trace metals and Fe3+. The isomorphous substitution of trace metal ions with different radius from Fe3+, either larger or smaller than Fe3+, will both cause increase in the ratio of the face-sharing Fe-Fe coordination distance to edge-sharing Fe-Fe distance, but through the distinct underlying mechanisms.