Oxygen/nitrogen ordering in lanthanum new phase (La3Si8N11O4)

Abstract

High-resolution O-17 NMR spectra have been collected for crystalline samples of lanthanum new phase, La3Si8N11O4. In conjunction with previously published Si-29 and N-15 spectra obtained for this phase, and in the light of the high-quality crystal structure data reported recently, a more detailed interpretation of the NMR spectra is presented than was possible in previous studies. The non-bridging oxygens in the structure are responsible for the single sharp peak seen in the 170 spectrum at 188 ppm; the remaining oxygens, occupying bridging sites shared with nitrogen, show up only weakly on the 170 spectrum as a broad diffuse band centered around zero ppm. The peak at -57.3 ppm on the Si-29 spectrum is believed to correspond to an overlap of [SiN4] and [SiON3] environments, with the -68.2 ppm peak corresponding to an [SiO2N2] environment. (C) 2004 Published by Elsevier Inc.