Effect of demixing and coarsening on the energetics of poly(boro)silazane-derived amorphous Si–(B–)C–N ceramics

Novel poly(boro)silazane-derived Si–(B–)C–N ceramics pyrolyzed at 1100 and 1400 °C were analyzed by multinuclear magic-angle spinning nuclear magnetic resonance spectroscopy and high-temperature oxidative solution calorimetry to investigate the energetic effects of nanodomain structure evolution at two critical pyrolysis temperatures. Like other Si–B–C–N ceramics, increasing pyrolysis temperatures result in the demixing of SiCxN4−x mixed bond environments into SiC4 and SiN4 tetrahedra, interdomain bond cleavage and nanodomain coarsening. Concurrent demixing and domain coarsening, processes detrimental to these ceramics, were found to be energetically stabilizing.