NANOMETRIC SI C/N POWDERS - EXAFS STUDY AT THE SILICON K EDGE/

Preceramic nanosized Si/C/N powders with a variable C/N ratio have bee n investigated by X-ray absorption spectroscopy at the silicon K edge. By combining XANES and EXAFS analysis results, we have proposed a mod el for the local structure of the as-prepared powders. This structural amorphous model has been tested through multiple scattering calculati ons using the FEFF code calculations. The evolution during the pyrolys is process is followed, specially for intermediate C/N values for whic h a delay in the crystallisation temperature occurs. Before the format ion of very small crystallites, one can observe a reorganisation of th e short range atomic structure.