Spinel oxides AB

It will be convenient to summarise some of the general results before discussing specific compounds in more detail. Taking iron(II) spinels first in the paramagnetic region normal 2,3 spinels Fe My 04 with Fe in the 

With iron(IIl) spinels it is not possible to have a normal spinel structure with Fe + on the A sites because the cationic charge is an odd number but a disordered spinel such as Fe [M Mb ]04 can have the tetrahedral sites occupied by Fe disorder in the B sites generates a small electric field gradient at the A site and a small quadrupole splitting is observed. Normal 

3 spinels M Fe2 04 with Fe on the trigonally distorted B sites show a similar spectrum because the electric field gradient acting on the spherical ion gives a smaller quadrupole splitting than that observed with the Fe + ion on the B sites. Most inverse 2,3 iron(III) spinels are magnetically ordered even above room temperature and the Fe occupancy of both A and B sites leads to two superimposed six-line spectra in which only the B site shows a quadrupole hyperfine interaction. 

These general remarks will now be illustrated by reference to individual oxide spinel phases. Sulphide spinels are discussed on p. 285. 

Feo 7Alo. 3[Feo 3Alf. 5 7]04, although the degree of inversion is Ukely to depend on the sample preparation. There are signs of spin ordering at 

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