Thermodynamic Control of Phase Composition and Crystallization of Metal‐Modified Silicon Oxycarbides

Silicon oxycarbides modified with main group or transition metals ( Si MOC ) are usually synthesized via pyrolysis of sol‐gel precursors from suitable metal‐modified orthosilicates or polysiloxanes. In this study, the phase composition of different Si MOC systems (M = Sn , Fe , Mn , V , and Lu ) was investigated. Depending on the metal, different ceramic phases formed. For M = Mn and Lu , MO x / SiOC ceramic nanocomposites were formed, whereas other compositions revealed the formation of M/Si OC (M = Sn ), M Si x /Si OC (M = Fe) or MC x / SiOC (M = V) upon pyrolysis. The different phase compositions of the Si MOC materials are rationalized by a simple thermodynamic approach which generally correctly predicts which type of ceramic nanocomposite is expected upon ceramization of the metal‐modified precursors. Calculations show that the thermodynamic stability of the MO x phase with respect to that of the C – O system is the most important factor to predict phase formation in polymer‐derived Si MOC ceramic systems. A secondary factor is the relative stability of metal oxides, silicates, carbides, and silicides.