Thermodynamically stable Si _wC _xN _yO _z polymer-like, amorphous ceramics made from organic precursors

This communication reports new results on the enthalpy of formation of pseudo-amorphous ceramic compounds constituted from silicon, carbon, oxygen, and nitrogen (SiCNO), made from the polymer route. Again, like the SiCO materials, although with one exception, the enthalpy of formation from crystalline components (SiO ₂ cristobalite, β-Si ₃N ₄, SiC, and excess C) is negative. Some of the alloyed oxygen-nitrogen compositions yield enthalpies that are much more negative (̃100 kJ/g . atom) in comparison with compositions that contain mainly oxygen or nitrogen (̃20 kJ/g×atom). The exception, having a N/O ratio near 2, has a positive value for the enthalpy. This may reflect the presence of nanoclusters of stoichiometric Si ₂N ₂O instead of the pseudo-amorphous nanodomain structure seen for the other samples.