Comments on the interpretation of the infrared spectrum from MgAl2O4spinel

Abstract
The interpretation of the infrared spectrum from MgAl2O4 has been the subject of some controversy. Recent proposals by Striefler and Boldish (1978) contradict an earlier theoretical analysis of the vibrational spectrum according to which there are only nine translatory optic modes (3 longitudinal+3*2 transverse). Re-examination of the data derived from a Kramers-Kronig transformation of the single crystal reflectance spectrum shows that the latter is more consistent with experiment and with the Lyddane-Sachs-Teller relation. It is concluded that there can be, at most, three longitudinal mode-transverse mode splittings at zero wavevector, and that, of these, two are clearly associated with the strong infrared absorption peaks at 670 and 485 cm-1 respectively.

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