Silicon-29 Magic-Angle Spinning Nuclear Magnetic Resonance Study of Some Lanthanum and Yttrium Silicon Oxynitride Phases

The preparation and Si-29 magic-angle spinning nuclear magnetic resonance spectra of the main phases in the LaSiON system and some related phases in the YSiON system are described. The silicon-29 chemical shifts for most of the LaSiON phases were found to fit well with expected values on the basis of silicon nearest-neighbor coordination, although in general they are more negative than those observed for the analogous YSiON phases. The N-apatite phase of expected composition La5Si3O12N is found to give a spectrum indistinguishable from that of the oxyapatite La9.33Si6O26, and therefore doubt is cast on the formulation of this phase. The phase LaSi3N5 is shown to give rise to an anomalously negative chemical shift when compared with values obtained from other silicon nitride phases.