Models of the Interfaces in Superhard TiN-Based Heterostructures and Nanocomposites from First-Principles

Abstract

This chapter reviews structures and properties of various TiN-based heterostructures. The study of such systems is of vital importance in development of new materials with desired optimum properties. After discussion of the current literature, the recently published results of first-principles quantum molecular dynamics (QMD) calculations of heterostructures consisting of one monolayer of interfacial SiNx, SiC, BN and AlN inserted between several monolayers thick slabs of B1(NaCl)-TiN (001) and (111) in the temperature range of 0–1,400 K are reviewed in some detail. The results revealed that SiN(001) exists as pseudomorphic B1-SiN interfacial layer only at 0 K. At finite temperature, this heterostructure transforms into distorted octahedral SiN6 and tetrahedral SiN4 units aligned along the {110} directions. At 300 K, the aggregates of the SiNx units are close to a disordered, essentially amorphous SiN. After heating to 1,400 K and subsequent relaxation at 300 K, the interfacial layer corresponds to a strongly distorted Si3N4-like structure. The B1-SiN, Si3N4-like SiN and Si3N4-like Si2N3 interfaces between the TiN(111) slabs are stable in the whole temperature range considered here. The B1-Si3N4-like interfaces derived from SiN by the formation of Si-vacancies are unstable at finite temperatures. An estimate of interfacial formation energies showed that the most favorable configurations of the (111) interfaces are silicon atoms tetrahedrally coordinated to nitrogen. The most stable (001) B1-derived heterostructure with Si0.75 N interface consist of both tetrahedrally and octahedrally coordinated silicon atoms. The TiN(001)/B1-SiC/TiN(001) interface exists as pseudo-morphic B1-SiC layer between 0 K and 600 K. After heating to 900–1,400 K and subsequent static relaxations, the interfacial layer corresponds to a strongly distorted 3C-SiC-like structure oriented in the (111) direction in which the Si and C atoms are located in the same interfacial plane. The Si atoms form fourfold coordinated N-Si ≡ C3 configurations, whereas the C atoms are located in the Ti2 = C ≡ Si3 surrounding. All the (111) interfaces simulated at 0, 300, and 1,400 K have the same atomic configurations. For these interfaces, the Si and C layers correspond to the Si-C network in the (111) direction of 3C-SiC. The Si and C atoms are located in N-Si ≡ C3 and Ti3 ≡ C ≡ Si3 configurations, respectively. The BN(001) interfacial layer forms a disordered h-BN-like structure consisting of BN3 units in the whole temperature range considered here. Finally, the B1-AlN(001) interface is found to be stable within the whole temperature range.