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 $\mathrm{TiN}\left(111\right)∕{\mathrm{Si}}_x{\mathrm{N}}_{\mathrm{y}}∕\mathrm{TiN}\left(111\right)$ interfaces, which form in the highly thermally stable $nc\text{−}\mathrm{TiN}∕a\text{−}{\mathrm{Si}}_x{\mathrm{N}}_y$ 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 $\mathrm{Ti}\text{−}\mathrm{Si}\text{−}\mathrm{N}$, and predominantly octahedral $\mathrm{Ti}\text{−}\mathrm{Si}\text{−}\mathrm{Ti}$, bonding are preferred. The atomic geometry and associated electronic structure are discussed for these interfaces, as well as properties of the bulk $\alpha$, $\beta$, and $\gamma$ phases of ${\mathrm{Si}}_3{\mathrm{N}}_4$, $\mathrm{TiN}$, and ${\mathrm{TiSi}}_2$.

• Received 25 September 2005

DOI:https://doi.org/10.1103/PhysRevB.74.035402