Phase Relationships in the Si_3N_4-SiO_2-Lu_2O_3 System

摘要

Phase relationships in the Si_3N_4-SiO_2-Lu_2O_3 system were investigated at 1850℃ in 1 MPa N_2. Only J-phase, Lu_4Si_2O_7N_2 (monoclinic, space group P2_1/c, a = 0.74235(8) nm, b -1.02649(10) nm, c = 1.06595(12) nm, and p = 109.793(6)°) exists as a lutetium silicon oxynitride phase in the Si_3N_4-SiO_2-Lu_2O_3 system. The Si_3N_4/Lu_2O_3 ratio is 1, corresponding to the M-phase composition, resulted in a mixture of Lu-J-phase, β-Si_3N_4, and a new phase of Lu_3Si_5ON_9, having orthorhombic symmetry, space group Pbcm (No. 57), with a = 0.49361(5) nm, b = 1.60622(16) nm, and c = 1.05143(11) nm. The new phase is best represented in the new Si_3N_4-LuN-Lu_2O_3 system. The phase diagram suggests that Lu_4Si_2O_7N_2 is an excellent grain-boundary phase of silicon nitride ceramics for high-temperature applications.