Infrared reflectivity study of the metastable solid solution Y2O3Al2O3 on both sides of the yttrium aluminium garnet Y3Al5O12 composition

Infrared reflection spectra of compacted powdered samples of yttrium aluminium garnet are shown to provide essentially the same information as the more conventional measurements performed upon the surface of a single crystal. The method is applied to the infrared study of the metastable solid solution Y2O3Al2O3 on both sides of the Y3Al5O12 composition with a molar percentage of Y2O3 varying from 28.5% to 46.4%. The structure is shown to remain cubic Ia3d over the whole composition range since the 17 modes allowed by group symmetry analysis are observed for all compositions. No local mode is observed, and the increase of intensities of low frequency modes in yttrium-rich compositions is found to be consistent with the substitution of heavy yttrium onto octahedral aluminium sites.