Effect of the Crystal Deformation on the Lattice Vibration of Oxide Spinels

Infrared transmission of the powdered specimen of oxide spinels was measured from 20 to 200µ and at 100–400°K. The frequency of the longest wave length absorption decreases by the tetragonal deformation in NiCr 2 O 4 ( c / a >1) and FeV 2 O 4 ( c / a <1). In NiCr 2 O 4 , the shift is proportional to c / a -1, whereas the shift in FeV 2 O 4 starts from a temperature higher than Tc. The result on FeV 2 O 4 is consistent with the Mössbauer spectrum of Fe 57 . This frequency shift is explained by the change of the deformation magnitude of oxygen tetrahedra around the Jahn-Teller ions, which is induced by the short range ordering of the deformation of the tetrahedra. The line of FeV 2 O 4 shows a marked broadening at Tc. This is attributed to the critical relaxation of phonons.