First-principles molecular dynamics investigation of thermal and mechanical stability of the TiN(001)/AlN and ZrN(001)/AIN heterostructures

First-principles quantum molecular dynamics investigations of TiN(001)/AlN and ZrN(001)/AIN heterostructures with one and two monolayers (1 ML and 2 ML) of AIN interfacial layers were carried out in the temperature range of 0-1400 K with subsequent static relaxation. It is shown that the epitaxially stabilized cubic B1-AIN interfacial layers are preserved in all TiN(001)/AIN heterostructures over the whole temperature range. In the ZrN(001)/AlN heterostructures, the B1-AIN(001) interfacial layer exists at 0 K, but it transforms into a distorted one at 10 K consisting of tetrahedral AlN4, octahedral AIN6, and AIN5 units. The thermal stability of the interfaces was investigated by studying the phonon dynamic stability of the B1-AlN phase with different lattice parameters. The calculations showed that the B1-AIN interface should be unstable in ZrN(001)/AIN heterostructures and nanocomposites, and in those based on transition metal nitrides with lattice parameters larger than 4.4 A. Electronic band structure calculations showed that energy gap forms around the Fermi energy for all interfaces. The formation of the interfacial AIN layer in TiN and ZrN crystals reduces their ideal tensile and shear strengths. Upon tensile load, decohesion occurs between Ti (Zr) and N atoms adjacent to the 1 MLAIN interfacial layer, whereas in the case of 2 ML AIN it occurs inside the TiN and ZrN slabs. The experimentally reported strength enhancement in the TiN/AIN and ZrN/AlN heterostructures is attributed to impeding effect of the interfacial layer on the plastic flow. (C) 2014 Elsevier B.V. All rights reserved.