Phase separation in Si–(B)–C–N polymer-derived ceramics

Details of phase separation in the microstructure of amorphous Si–(B)–C–N ceramics derived from polymers have been resolved using the recent results of structural investigations. The formation of an amorphous phase built of atomic compounds SiC and consequently located along the composition line between SiC and Si N4 in the ternary Si–C–N phase diagram demonstrates a generic feature of phase separation in all these materials. The amorphous carbon phase separates as a counterpart in the microstructure of Si–C–N ceramics, and in the case of Si–B–C–N ceramics such counterpart represents B–N–C domains of the composition (BN) located along the tie line C–BN in the ternary B–C–N phase diagram. The effect of phase separation has been also pondered as a source of exceptional material properties.