Phases occurring in the Si3N4-YN system

A method is described for synthesising complex silicon lanthanide nitrides by carbothermal reduction and nitridation (CRN) of both SiO2-Ln(2)O(3) mixtures and elemental Si-Ln(2)O(3) mixtures at 1400-1450 degrees C. Syntheses in the Si3N4-YN system confirm the existence of the compounds YSi3N5 and Y2Si3N6, which can be prepared virtually free of oxygenated impurity phases from mixtures containing SiO2 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 Y6S3N10; mass change data and EDX analyses suggest, however, that this phase is much less Y-rich than Y6Si3N10, with an apparent composition nearer Y3Si6N11. X-Ray powder diffraction data and Si-29 and Y-89 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 delta 490-510 (ref. YCl3), is common to all three compounds.