Study of the Atomic Structure and Phase Separation in Amorphous Si-C-N Ceramics by X-Ray and Neutron Diffraction

Abstract

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