Searching insight into the atomistic structure of SiCO ceramics

We investigate elements comprising the atomistic structure of amorphous silicon oxycarbide ceramics: glassy SiCO, free'' carbon, and the interface between them. Using a network modeling approach we generate a wide variety of structure models, incorporating different hypotheses of atomic arrangements. The models are subsequently treated within density functional theory including ab initio molecular dynamic simulations. Analyzing the structure and energy of optimized models, we find that enthalpy of formation of glassy SiCO increases with increasing phase content of SiC. Models with high SiC content show a preference for precipitation of SiC clusters embedded in amorphous silica. Addressing a possible interface between SiCO glass and free'' carbon, we find no support for a favorably bonded interface. Instead, the two phases are separated completely even at the expense of dangling bonds within the carbon phase. This separation is driven by the low surface tension of silica glass.