NEUTRON-DIFFRACTION STUDY OF THE AMORPHOUS PHASE-STRUCTURE IN SILICON CARBONITRIDE CERAMICS OBTAINED BY PYROLYSIS OF A POLYVINYLSILAZANE

The atomic structure of silicon carbonitride ceramics derived from the pyrolysis of a polyvinylsilazane precursor has been studied by means of neutron diffraction. It is shown that the pair correlation function G(r) of the amorphous phase substituting up to 1400-degrees-C exhibits well defined peaks in the medium range order domain along the 0.3-2 nm range. This spectrum can be interpreted as a mixture of siliconcarbonitride phases with an average composition close to SiN0.98C0.25O0.06 and 1.25 free carbon. The local chemical and structural orders vary continuously in the material from pure aromatic carbon to nanocrystals of Si3N4, through the ternary SiCN solid solution which is believed to have a structure intermediate between the amorphous and crystalline states.