AFm phases containing iron

Iron(III) analogues of many of the phases described above have been obtained. Unless the anion imparts colour, AFm phases containing Fe are colourless, brown colours being due to iron(III) oxide or hydroxide impurity. They have a-axial lengths of approximately 0.589 nm (S57,K26). 

6 XRD patterns, thermal behaviour, optical properties and IR spectra 

Strong peaks in the XRD powder patterns of AFm phases normally include the first and second orders of the layer thickness, and the 1120 and 3030 

2885 nm and 0.1666 nm, respectively. In mixtures, it is sometimes difficult to distinguish between AFm phases of similar layer thickness, and in such cases, examination of the patterns of heated samples is often useful. 

As would be expected from their layer structures, AFm phases are optically negative. The AP phases typically have = 1.50-1.56, e = 1.49-1.54 for the Fe phases, is typically 1.56-1.61 and e is 1.54-1.60. 

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