Structure and properties ofTiN(111)∕SixNy∕TiN(111)interfaces in superhard nanocomposites: First-principles investigations

Abstract

We perform first-principles calculations based on density-functional theory to investigate the role of interfaces in superhard nanocomposites. A prerequisite is clearly knowledge of the detailed atomic structure, which is addressed in the present paper. In particular, we study the relative stability of $\mathrm{TiN}(111)∕{\mathrm{Si}}_{x}{\mathrm{N}}_{\mathrm{y}}∕\mathrm{TiN}(111)$ interfaces, which form in the highly thermally stable $nc\text{\ensuremath{-}}\mathrm{TiN}∕a\text{\ensuremath{-}}{\mathrm{Si}}_{x}{\mathrm{N}}_{y}$ nanocomposites. For nitrogen-rich conditions, the most favorable configurations involve very thin layers of Si, which are purely nitrogen coordinated and tetrahedrally bonded. For increasingly nitrogen-poor conditions, interfaces involving $\mathrm{Ti}\text{\ensuremath{-}}\mathrm{Si}\text{\ensuremath{-}}\mathrm{N}$, and predominantly octahedral $\mathrm{Ti}\text{\ensuremath{-}}\mathrm{Si}\text{\ensuremath{-}}\mathrm{Ti}$, bonding are preferred. The atomic geometry and associated electronic structure are discussed for these interfaces, as well as properties of the bulk $\ensuremath{\alpha}$, $\ensuremath{\beta}$, and $\ensuremath{\gamma}$ phases of ${\mathrm{Si}}_{3}{\mathrm{N}}_{4}$, $\mathrm{TiN}$, and ${\mathrm{TiSi}}_{2}$.