New Nitrogen-Rich Phases in the Lu-Si-O-N System

Abstract

Phase relationships in the quaternary Lu-Si-O-N system have been studied by the solid-state reaction method using LuN powder obtained by nitridation of Lu metal. New nitrogen-rich compounds of Lu₃Si₅ON₉ and Lu₆Si₁₁ON₂₀ were found in the sample prepared at 2123 K under 0.92 MPa of high purity N₂ gas. It was confirmed that the Lu₃Si₅ON₉ coexists with Si₃N₄ and Lu₄Si₂O₇N₂. This result implies that a pseudo-quaternary Si₃N₄-SiO₂-Lu₂O₃-LuN diagram, not the conventional Si₃N₄-SiO₂-Lu₂O₃ and/or Si₃N₄-Lu₂O₃-LuN pseudo-ternary one, can express properly the phase relationships in the Lu-Si-O-N system. The Rietveld analysis of the X-ray powder diffraction data measured at room temperature refined the crystal structures of Lu₃Si₅ON₉ (orthorhombic, space group Pbcm, A-57) and Lu₆Si₁₁ON₂₀ (trigonal, P31c, A-159).