NMR INVESTIGATION OF THE STRUCTURE OF ALUMINUM-CONTAINING NITROGEN MELILITE (M'(SS))

Replacement of silicon and nitrogen by aluminum and oxygen, respectively, in yttrium N-melilite (Y2Si3O3N4) forms an extensive solid solution M'(ss). M'(ss) samples formed in the yttrium system are often phase mixtures. Si-29 and Al-27 magic-angle spinning MMR spectra can consequently be complex, but combined with X-ray diffraction, resonances associated with M'(ss) can be identified and have elucidated possible atomic arrangements in M'(ss). The proposed yttrium M'(ss) structure based on NMR results consists of AlO4 and SiO2N2 coordinations only, with aluminum occupying the MgO4 sites in the analogous akermanite structure and accounts far the apparent limit of aluminum solubility in N-melilite.