INFRARED OPTICAL-PROPERTIES OF COBALT(II) SPINELS

Experimental results of optical measurements on cobalt (II) spinel thi n films (Co3O4, CoFe2O4, CoMnFeO4) are compared to the infrared lattic e vibrational spectra determined by Kramers Kronig analysis and oscill ator fit calculations. The ionic character of cobalt (II) spinels is d iscussed in connection with the TO-LO splitting and found to follow th e trend: aluminate and ferrite > chromite > cobaltite. The study of th e band ionicity in the series of spinels MFe(2)O(4) and MCr(2)O(4) (M= Co, Ni, Cu and Zn) shows that the TO-LO splitting may be correlated wi th the classical parameters deduced from the ligand-field and X-ray sp ectroscopies.