Si and N K-XANES spectroscopic study of novel Si-C-N ceramics

X-ray absorption near edge structure (XANES) measurements at the Si and N K-edges of ternary Si-C-N compounds are applied to analyze the changes of structural units owing to the thermally induced ceramization of silicon dicarbodiimide Si(N=C=N)(2) at temperatures up to 1600 degrees C. Samples synthesized below 800 degrees C show an environment of silicon consisting of carbodiimide (N=C=N) groups. Further annealing leads to a crystalline phase, Si2CN4, which combines the structural units (Si-N-Si) and (Si-N=C=N). Recorded spectra of samples annealed at temperatures higher than 1200 degrees C show the decomposition of Si2CN4 The material then transforms to a Si3N4-SiC composite material through an intermediate amorphous Si-C-N phase. (C) 1998 Elsevier Science B.V. All rights reserved.