An ab initio molecular dynamics study on Ti2AlN(0001) surfaces

Abstract

The structures, surface energies, electronic properties of Ti2AlN(0001) surfaces at 0 K-1273 K were systematically investigated by ab initio molecular dynamics and first-principles calculations. It is found that the structural relaxations of Ti(N)- and Ti(Al)-terminated surfaces at all temperatures are mainly confined between outermost two layers, and those of N(Ti)- and Al(Ti)-terminated surfaces with Ti atoms at second layer extends into third layer. N(Ti)-terminated surface experiences the largest relaxation, and Al(Ti)-terminated surface possesses the least relaxation and is the most stable surface at all temperatures. The structural shrinkage relaxation of outermost two layers and surface energy for N(Ti)- and Ti(N)- terminated surfaces keep relatively stable from 0 K to 933 K, whereas dramatically increase from 933 K to 1273 K. The relaxation of outermost two layers for Al(Ti)- and Ti(Al)-terminated surfaces changes owing to the thermal expansion of the d-spacing of Al-Ti layers. The larger thermal expansion coefficient of the d-spacing of Al-Ti layers and faster surface energy decline of Ti(Al)-terminated surface than those of Al(Ti)-terminated surface indicate stronger metallic properties. The influence of redistribution of Ti-3d, N-2p and Al-3p orbitals on the electronic properties and structural relaxations of different termination surfaces at all temperatures range is elucidated.