INFRARED REFLECTIVITY STUDY OF THE METASTABLE SOLID-SOLUTION Y2O3-AL2O3 ON BOTH SIDES OF THE YTTRIUM-ALUMINUM-GARNET Y3AL5O12 COMPOSITION

Infrared reflection spectra of compacted powdered samples of yttrium a luminium 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 met astable solid solution Y2O3-Al2O3 on both sides of the Y3Al5O12 compos ition with a molar percentage of Y2O3, varying from 28.5% to 46.4%. Th e structure is shown to remain cubic la3d over the whole composition r ange since the 17 modes allowed by group symmetry analysis are observe d for all compositions. No local mode is observed, and the increase of intensities of low frequency modes in yttrium-rich compositions is fo und to be consistent with the substitution of heavy yttrium onto octah edral aluminium sites.