Crystal structure studies on the garnet Y3Al5O12 by 27Al single-crystal NMR spectroscopy

The capability of single-crystal NMR to extract crystal structure information is demonstrated by a Al-27 single-crystal NMR study of the garnet Y3Al5O12 (YAG), By rotation of a YAG single crystal about three perpendicular axes 93 Al-27 spectra have been acquired, resulting in the observation of 3132 resonance frequencies; These have been assigned to three tetrahedral and four octahedral aluminum Sites. A thorough; analysis of the magnitudes and-relative orientations of the quadrupole coupling tensors for these seven aluminum; sites indicates the presence of a combination of symmetry elements that is unique to cubic crystal structures. Upper limits for the magnitudes of the anisotropic chemical shielding interaction are also determined for the seven aluminum sites and show that the geometrical arrangements of oxygen,ions in the first coordination sphere of all aluminum sites-must be nearly regular tetrahedra and octahedra, respectively.