A DFT-Study of Structure and Properties of Amorphous SiCN

摘要

Structures and properties oi amorphous silicon carbonitride (a-SiCN) materials are stud-ied using density funetional methods. Topologically different models of a-SiCN with 112-156 atoms each were generated from continuous alternating random networks. The networks have distinct topologies which result in a different chemical bonding in the investigated structural models. A lirst model consists o( Si-N and Si-C bonds only, For such materials with "anionic" carbon we found the highest bulk modulus. However, the network strain is largely due to the high SiC content, resulting in bond rupture and redistribution in the amorphous structure. A second model consists of Si-N and C-N bonds only. We found that a tetrahedral coordination of "cationic'' carbon in such a compound is unstable at elevated temperatures. as indicated by Car-Parrinello molecular dynamic (CPMD) simulations. A third model consists of amorphous Si_3N_4 as host structure and a segregation of graphitic C inside a pore. Such a model, although low in density, has an enlarged bulk modulus, comparable to the "anionic" model.