Phase relationships in the Si3N4-SiO2-Lu2O3 system were investigated at 1850°C in 1 MPa N2. Only J-phase, Lu4Si2O7N2 (monoclinic, space group P21/c, a = 0.74235(8) nm, b = 1.02649(10) nm, c = 1.06595(12) nm, and β = 109.793(6)°) exists as a lutetium silicon oxynitride phase in the Si3N4-SiO2-Lu2O3 system. The Si3N4/Lu2O3 ratio is 1, corresponding to the M-phase composition, resulted in a mixture of Lu-J-phase, β-Si3N4, and a new phase of Lu3Si5ON9, having orthorhombic symmetry, space group Pbcm (No. 57), with a = 0.49361(5) nm, b = 1.606222(16) nm, and c = 1.05143(11) nm. The new phase is best represented in the new Si3N4-LuN-Lu2O3 system. The phase diagram suggests that Lu4Si2O7N2 is an excellent grain-boundary phase of silicon nitride ceramics for high-temperature applications.
|Number of pages||3|
|Journal||Journal of the American Ceramic Society|
|Publication status||Published - 2002 Nov|