Phase Relationships in the Si3N4–SiO2–Lu2O3 System |
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Authors: | Naoto Hirosaki Yoshinobu Yamamoto Toshiyuki Nishimura Mamoru Mitomo Junichi Takahashi Hisanori Yamane Masahiko Shimada |
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Affiliation: | National Institute for Materials Science, Tsukuba, Ibaraki 305-0044 Japan;Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Aoba, Sendai 980–8577, Japan |
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Abstract: | Phase relationships in the Si3N4–SiO2–Lu2O3 system were investigated at 1850°C in 1 MPa N2. Only J-phase, Lu4Si2O7N2 (monoclinic, space group P 21/ 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 = 1.60622(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. |
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Keywords: | silicon nitride grain boundaries oxynitride |
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