The Fe-Ti oxide system

There are structural analogues of a number of iron oxides in the Fe-H-O system. Under certain conditions, continuous solid solutions exist between the two members of a pair. The magnetite-ulvospinel and the hematite-ilmenite pairs are well-known examples. The principle in going from the Fe oxide to the Ti-containing phase is to replace two Fe by one Fe and one Ti , thereby increasing the unit cell size. 

A related system is that of the titanomaghemites, Fe2Ti05, which are formed by oxidation of the titanomagnetites. These are spinels with vacancies in some of the cation positions. The detailed distribution of cations and vacancies is not fully understood a discussion of the different models and possibilities is given by Lindsley (1976). A non-linear relationship between the unit cell size of titanomaghemite (a = 0.8483 nm) and that of maghemite (a = 0.835 nm) was matched by a non-linear increase in the Curie temperature from 80 to 450 °C (Dunlop Ozdemir, 1997). 

Another structure in the Fe-Ti-O system is that of pseudorutile Fe2Ti30g(0H)2. 

This mineral appears to consist of intergrowths of goethite and rutile with a unit cell with a = 0.2868 nm and c = 0.4607 nm (Grey et al., 1983). 

Interplanar spacings for the iron oxide crystal systems. 

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