Characterisation of the free-carbon phase in precursor-derived SiCN ceramics

Different polymeric precursors with varying carbon contents were prepared by ammonolysis of functionalised chlorosilanes. Pyrolysis under inert atmospheres at 1000 °C led to amorphous Si–C–N–(H) ceramics. Further heat treatment caused the transformation into the thermodynamically stable crystalline phase assemblage. The structural changes, especially those of the excess carbon, were studied by characterising the solid intermediates via solid state magic angle spinning (MAS) nuclear magnetic resonance spectroscopy (NMR). In addition, Raman spectroscopy, electron spin resonance spectroscopy (ESR), microwave conductivity measurements and chemical analysis were employed. Combination of all these methods provides a comprehensive picture of the formation and of the behaviour of the free-carbon phase present in the polymer-derived ceramics.