Papers by Keyword: J-Phase

Abstract: Oxidation behavior of R4Si2O7N2 (J-phase; R = Y and rare-earth element) has been investigated by thermometric measurements in air. All R4Si2O7N2, of which the powder samples are prepared by gas-pressured sintering method under 1 MPa of N2 gas, are oxidized to R2SiO5 with an exothermic reaction in air under an ambient pressure. The oxidation temperature to produce the final oxide increases from c.a. 930 to 1060 °C with decreasing the ionic radii of the rare earth elements.

Abstract: Oxygen/nitrogen (O/N) configuration in RE-J-phase, RE4Si2O7N2 (RE = rare earth element), was simulated by the Monte Carlo method applied to O/N distribution models. Proportion of local structures of Si2(O,N)7 ditetrahedra and Si(O,N)4 tetrahedra in the J-phase was quantitatively assessed. For the Lu-J-phase model with the bridging site between two Si atoms being occupied by nitrogen atom, the Si2(O,N)7 ditetrahedra composed of O3≡Si–N–Si≡O2N (> 40 %), O3≡Si–N–Si≡O3 (c.a. 30 %), and O2N≡Si–N–Si≡O2N(c.a. 15 %). Tetrahedra of SiO3N and SiO2N2 were dominant and small amount of SiON3 tetrahedra coexisted. For La-J-phase model with the O/N occupancy of 0.1/0.9 at the bridging site, configurations of O3≡Si–O–Si≡O2N (c.a. 5%), O3≡Si–O–Si≡O3 (c.a. 3%), and O2N≡Si–O–Si≡O2N (c.a. 2%) were demonstrated in addition to the three configurations of ditretrahedra recognized in the Lu-J-phase. In La-J-phase coexistence of SiO4 tetrahedra was presented.