Structural vacancies in (Ti,Al)N: An ab initio study

Axel Forslund,Andrei V Ruban

doi:10.1103/physrevmaterials.6.013803

Abstract

The zero K formation energies of metal and nitrogen vacancies in several (Ti,Al)N alloys and at the (001) (Ti,Al)N/AlN interface are obtained in ab initio supercell calculations. The dependence of the formation energies of metal vacancies on their local environment and type are analyzed and explained in terms of effective cluster interactions for unrelaxed calculations. The common trend for all investigated types of vacancies is that their formation energy increases with the number of Al nearest neighbors if local lattice relaxations are not allowed. However, local lattice relaxations produce a dramatic effect especially in the case of metal vacancies leading to a complicated nonlinear dependence on the local environment indicating the existence of strong multisite strain-induced interactions.

Highlights

Titanium nitride and titanium-aluminum nitride films are used as hard coatings for cutting tools due to their exceptional mechanical and tribological properties [1,2,3]
The electronic structure and total energy calculations were done by the projector augmented wave (PAW) method [11] as implemented in the Vienna ab initio simulation package (VASP) [12,13,14]
The vacancy formation energy has been calculated as the energy difference between the supercell with and without vacancy plus the energy of the vacant element in its ground state structure: Eviac = Etiot − Et0ot + Ei

Summary

INTRODUCTION

Titanium nitride and titanium-aluminum nitride films are used as hard coatings for cutting tools due to their exceptional mechanical and tribological properties [1,2,3] They are produced using either physical or chemical vapor deposition (PVD or CVD) and the growth process strongly affects their composition and structure at the atomic level. Structural vacancies are present on the nitrogen or carbide sublattice, where at low temperatures they form ordered structures at different temperatures and compositions [8]. This is the case of B1-TiNx with nitrogen deficient compositions where several B1-TiN based ordered alloys (Ti2N3, Ti4N3, and Ti6N5) are stable according to an ab initio investigation by Yu et al [9].

DETAILS OF AB INITIO CALCULATIONS

Effective interactions calculations

Structural vacancy formation energies

Configurational dependence of the formation energies of metal vacancies

E Al niAl

SUMMARY