Neutron diffraction study of nanocrystalline oxycarbide glasses prepared by sol-gel

Two series of three specimens for a total of six compositions were prepared by the sol-gel method and the precursors were pyrolised at 1000 degreesC under inert atmosphere of Argon after the hydrolysis/condensation process. The Neutron Diffraction patterns of these products are typical of amorphous materials. The radial distribution function (RDF) of these glasses suggests that the main network is composed, as in silica glass, of inter-connected tetrahedral units where some of the di-valent oxygen atoms have been substituted for tetravalent carbon atoms. A concomitant structural study was conducted on the same specimens after pyrolysis at 1200, 1400 and 1500 degreesC respectively, in order to follow phase separation phenomena induced at high temperature. After pyrolysis at 1500 degreesC the patterns show the formation of beta-SiC and, additionally, for the composition with low carbon content, the appearance of microcrystalline cubic silicon, with a consistent fraction of the matrix still amorphous. The specimens with high carbon content display clearly in the RDF the C-C distances typical of graphitic-like structures.