First-principles modeling of polysilazane derived SiCNH ceramics: insights into the organization of the free carbon phase

Abstract

The atomic-scale structure of a Si 32 C 25 N 24 H 19 composition made from a polysilazane and assimilated to a silicon carbo-nitride ceramic, is studied by resorting to first-principles molecular dynamics simulations. The initial configurations used for molecular dynamics were generated by applying various conditions on the atomic local environments and coordination numbers. Specifically, seven models with different organisation of the free-carbon phase (C) were generated, which allowed rationalizing the organizations of the C phase in the material. To validate our models, we compared the calculated pair distribution functions to the experimental one and investigated the various local environments of the proposed models. Our results indicate that, for the Si 32 C 25 N 24 H 19 composition, the free carbon phase is essentially made of poorly spatially correlated carbon layers instead of highly organised layers or percolation networks.