A MOSSBAUER SPECTROMETRY STUDY OF ELECTRONIC LOCALIZATION IN FERROSPINELS HAVING A TETRAHEDRAL MIXED-VALENCE SUBLATTICE

On the octahedral sublattice of the ferrospinels several cases of fast electron exchange have been studied with the Moessbauer effect, at a reference frequency close to 10**8 Hz. Very few similar cases have been investigated for the tetrahedral sublattice, where the jump distance and the orbital overlaps are less favorable for electron transfer. Different phases have been studied with the Moessbauer effect from room temperature up to 570 K as a function of their stability. For Fe//0//. //4//7**2** plus Fe//0//. //4//7**3** plus Cr//1//. //8//8**3** plus D'ALEMB //0//. //1//8O//4, the best interpretation corresponds to completely localized electrons at room temperature and to the possibility that at T greater than 440 K a small portion of iron (4 to 17%) displays a mixed valence character due to fast electron relaxation.