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

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 TiN(111)/SixNy/TiN(111) interfaces, which form in the highly thermally stable nc-TiN/a-SixNy 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 Ti-Si-N, and predominantly octahedral Ti-Si-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 Si3N4, TiN, and TiSi2.