FP-LMTO studies of hypothetical compounds with the beta$-SiAlON-like   structure in Si--(Mg,Al)--O--N systems
  The electronic and energy properties of beta-Si3N4 (a), Si{6-x}AlxOxN{8-x} (b) and the hypothetical ordered solid solutions Si{6-x}MgxO{2x}N{8-2x} (c), Si{6-x}MgxOxN{8-2x}Sx (d), Si{6-x}MgxOxN{8-x} (e), Si{6-x}Mg{x/2}Al{x/2}OxN{8-x} (f) are considered by the ab-initio band FP-LMTO method. The calculations show that the stability of the systems decreases in the order: (a) > (b) > (f) > (e) > (c) > (d). It is established that Si{6-x}MgxOxN{8-x} and Si{6-x}Mg{x/2}Al{x/2}OxN{8-x} possess non-zero values of the density of states at the Fermi energy, which consists mainly of localized O2p, N2p states, and the conductivity in those solid solutions is unlikely. It is found that the energy of the O2s,p states tends to shift depending on the coordination environment of oxygen atoms in the considered systems. The energy of ordering of Al and Mg atoms in Si{6-x}Mg{x/2}Al{x/2}OxN{8-x} is estimated to be 3.15 eV/56-atomic supercell. 
S.V.Okatov (Institute of Solid State Chemistry, UrD of RAS)