Phases occurring in the Si3N4–YN system

Abstract

A method is described for synthesising complex silicon lanthanide nitrides by carbothermal reduction and nitridation (CRN) of both SiO ₂ –Ln ₂ O ₃ mixtures and elemental Si–Ln ₂ O ₃ mixtures at 1400–1450 °C. Syntheses in the Si ₃ N ₄ –YN system confirm the existence of the compounds YSi ₃ N ₅ and Y ₂ Si ₃ N ₆ , which can be prepared virtually free of oxygenated impurity phases from mixtures containing SiO ₂ rather than from mixtures containing elemental Si. A third compound was also prepared in this system, with an XRD pattern corresponding to that reported for Y ₆ Si ₃ N ₁₀ ; mass change data and EDX analyses suggest, however, that this phase is much less Y-rich than Y ₆ Si ₃ N ₁₀ , with an apparent composition nearer Y ₃ Si ₆ N ₁₁ . X-Ray powder diffraction data and ²⁹ Si and ⁸⁹ Y solid-state MAS NMR spectra are reported for all three phases. The NMR results suggest the presence of at least three Si sites in each phase, and at least two types of Y site, one of which, characterised by a resonance at δ 490–510 (ref. YCl ₃ ), is common to all three compounds.