Oxygen/Nitrogen Ordering in Lanthanum New Phase (La3Si8N11O4)

Abstract

High-resolution 17O NMR spectra have been collected for crystalline samples of lanthanum new phase, La<inf>3</inf>Si<inf>8</inf>N <inf>11</inf>O<inf>4</inf>. In conjunction with previously published 29Si and 15N 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 17O spectrum at 188ppm; the remaining oxygens, occupying bridging sites shared with nitrogen, show up only weakly on the 17O spectrum as a broad diffuse band centered around zero ppm. The peak at -57.3ppm on the 29Si spectrum is believed to correspond to an overlap of [SiN<inf>4</inf>] and [SiON<inf>3</inf>] environments, with the -68.2ppm peak corresponding to an [SiO<inf>2</inf>N <inf>2</inf>] environment. © 2004 Published by Elsevier Inc.