Local Structures of Ditetrahedra in Rare-Earth Silicon-Oxynitride J-Phases

抄録

The rare-earth silicon-oxynitride J-phases, La₄Si₂O₇N₂ and Lu₄Si₂O₇N₂, contain ditetrahedra of Si₂(O,N)₇. The mean composition of the ditetrahedra in both compounds is Si₂O_5.0N_2.0 which was calculated with the oxygen/nitrogen occupancies determined by the Rietveld analysis using the neutron powder diffraction data. Six configurations of O and N atoms are specified in the ditetrahedra of La₄Si₂O₇N₂: (1) O₃Si-N-SiO₃, (2) O₂NSi-N-SiO₃, (3) O₂NSi-N-SiO₂N, (4) O₂NSi-O-SiO₂N, (5) ON₂Si-O-SiO₂N, and (6) ON₂Si-O-SiON₂. In the case of Lu₄Si₂O₇N₂, the former three configurations (1), (2), and (3) can be present because of the full occupation of the N atom at the bridging site between two Si atoms.