AL-27 AND SI-29 SOLID-STATE NUCLEAR-MAGNETIC-RESONANCE STUDY OF SILICON-CARBIDE ALUMINUM NITRIDE SYSTEMS - EFFECT OF SILICON ALUMINUM RATIOAND PYROLYSIS TEMPERATURE/

Three series of SiC/AlN samples were prepared by pyrolysis of ''poly(a luminosilazane)'', the product of the reaction between hexamethylcyclo trisilazane and triethylaluminum. The Si/Al ratio was varied for one s eries (with constant pyrolysis temperature) and the pyrolysis temperat ure was varied for the other two series, with Si/Al = 1 and 3. Al-27 a nd Si-29 magic angle spinning NMR were used to analyze these samples i n terms of coordination number, nearest neighbor atoms, and crystallin ity. NMR results indicate that higher crystallinity and phase separati on into discrete SiC and AlN crystallites accompany an increase in pyr olysis temperature. Disorder and increased heterogeneity in connectivi ty are observed with increasing Si/Al ratio of the initial reactants.