First-Principles DFT Study of Imide and Fluoride Analogs of Silicon Oxide, Silicon Oxynitride, and Their Alloys

The potential of designing silicon-based oxide/nitride with new properties through nanostructure and chemical tuning continues to captivate researchers. In this context, while oxynitrides of Si, Ge and Si/Ge are being actively explored, N-rich alternatives to the ubiquitous Si3N4 end member are far less known or studied. Recently, the imide-based Si2N2(NH) was synthesized and found to adopt a crystalline structure analogous to that of Si2N2O. Therefore, in this thesis, a density functional theory (DFT) study of the thermochemistry of Si-N-H compounds including Si2N2(NH) and Si(NH)2 is undertaken, focusing on their relative stability and structural polymorphism. Analogies in the polymorphism in these oxide/imide systems are also elucidated using on ab initio DFT thermochemistry. In the case of silicon diimide, Si(NH)2, several potential synthesis routes involving ammonia and/or ether-like NH(SiH3)2 molecular sources are proposed.Despite the structural analogy of beryllium fluoride with silica, its detailed phase diagram has yet to be established experimentally. In this case, both the static and thermally corrected phase ordering of BeF2 polymorphs using ab initio phonon-based thermochemistry are investigated. The compression behavior and mechanical instabilities of a dozen BeF2 crystalline polymorphs is also compared studied, leading to the development of a methodology to construct a BeF2 (P-T) phase diagram.