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

Replacement of silicon and nitrogen by aluminum and oxygen, respective ly, in yttrium N-melilite (Y2Si3O3N4) forms an extensive solid solutio n 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 consequ ently be complex, but combined with X-ray diffraction, resonances asso ciated with M'(ss) can be identified and have elucidated possible atom ic arrangements in M'(ss). The proposed yttrium M'(ss) structure based on NMR results consists of AlO4 and SiO2N2 coordinations only, with a luminum occupying the MgO4 sites in the analogous akermanite structure and accounts far the apparent limit of aluminum solubility in N-melil ite.