Short-range ordering in amorphous Si sub 3 B sub 3 N sub 7 as determined by multinuclear NMR spectroscopy

• Published in: Chemistry of materials 2000-08, Vol.12 (8), p.2341-2346
• Main Authors: Muller, U, Hoffbauer, W, Jansen, M
• Format: Article
• Language: English
• ISSN: 0897-4756

The ternary and quaternary amorphous networks of silicon boronitride and borocarbonitride are high-performance ceramics with extraordinary mechanical and thermal properties, e.g. excellent high temperature resistance. Even their resistance to oxidation, usually a drawback for non-oxide ceramics, is the best known so far. IR and exp 29 Si, exp 11 B, and exp 15 N NMR-spectroscopic data of exp 15 N-enriched samples of hexamethyl-disilazane, 1,1,1-trichloro-3,3,3- trimethyldisilazane (TTDS), 1,1,1-trichloro-3,3,3-trimethyl-disilazane (TTDS), ((trichlorosilyl)amino)dichloroborane (TADB), of the poly(borosilazane) Si sub 3 B sub 3 N sub 7.9 H sub 4.4 Cl sub 0.8 O sub 0.6 , and of the ceramical network Si sub 3 B sub 3 N sub 7 are given. The exp 15 N-substituted samples have been prepared using novel synthetic routes. The NMR data show that in the poly(borosilazane) Si sub 3 B sub 3 N sub 7.9 H sub 4.4 Cl sub 0.8 O sub 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 sub 3 B sub 3 N sub 7 . The local coordination of silicon and boron remains virtually unchanged. As confirmed by comparison of the NMR data of Si sub 3 B sub 3 N sub 7 with those of crystalline references (Si sub 3 N sub 4 , BN), nitrogen is now fully coordinated by three silicon and/or boron atoms.