STUDY OF THE ATOMIC-STRUCTURE AND PHASE-SEPARATION IN AMORPHOUS SI-C-N CERAMICS BY X-RAY AND NEUTRON-DIFFRACTION

Amorphous Si37C32N31 and Si37C29N34 ceramics were produced by pyrolysi s of a polyhydromethylsilazane precursor. Their structure was investig ated by X-ray and neutron diffraction. Wide angle diffraction showed t hat the Si-atoms are preferentially bonded to nitrogen atoms, but also bonding to carbon atoms was found. This suggests that the excess carb on atoms form an amorphous graphite-like phase. Small angle scattering revealed that the ceramics are inhomogeneous. The evolution of the ph ase separation during annealing was investigated and it was concluded that amorphous Si3N4 precipitates grow in the Si-C-N materials. The re sults are compared with previous results for amorphous Si24C43N33 prod uced from a polysilylcarbodiimide precursor [1 - 3].