Short-Range Ordering in Amorphous Si3B3N7 As Determined by Multinuclear NMR Spectroscopy

IR and 29 Si, 11 B, and 15 N NMR-spectroscopic data of 15 N-enriched samples of hexamethyldisilazane, 1,1,1-trichloro-3,3,3-trimethyldisilazane (TTDS), 1,1,1-trichloro-3,3,3-trimethyldisilazane (TTDS), ((trichlorosilyl)amino)dichloroborane (TADB), of the poly(borosilazane) Si 3 B 3 N 7.9 H 4.4 Cl 0.8 O 0.6, and of the ceramical network Si 3 B 3 N 7 are given. The 15 N-substituted samples have been prepared using novel synthetic routes. The NMR data show that in the poly(borosilazane) Si 3 B 3 N 7.9 H 4.4 Cl 0.8 O 0.6 silicon is coordinated tetrahedrally by nitrogen in the first coordination sphere and boron is coordinated trigonally planar by nitrogen atoms. In this partially polymerized network, a small fraction of the nitrogen coordination is blocked by hydrogen, as verified by IR spectroscopy. Calcination of the poly(borosilazane) results in the fully polymerized network Si 3 B 3 N 7 . The local coordination of silicon and boron remains virtually unchanged. As confirmed by comparison of the NMR data of Si 3 B 3 N 7 with those of crystalline references (Si 3 N 4, BN), nitrogen is now fully coordinated by three silicon and/or boron atoms.