Density functional theory calculations of mechanical and electronic properties of W1−xTaxN6, W1−xMoxN6, and Mo1−xTaxN6 (0 ≤ x ≤ 1) alloys in a hexagonal structure

Abstract

In this study, we report the structural, energetic, mechanical, electronic, thermal, and magnetic properties of W1−xTaxN6, W1−xMoxN6, and Mo1−xTaxN6 (0 ≤ x ≤ 1) alloys in a hexagonal structure (space group: R3¯m) determined using density functional theory–based first-principles calculations. These compounds are mechanically stable, whereas W0.33Ta0.66N6 is vibrationally unstable. Among both mechanically and vibrationally stable compounds, W0.66Ta0.33N6 and W0.66Mo0.33N6 have the highest hardness of 55 GPa, while the softest alloy (Mo0.33Ta0.66N6) exhibits 46 GPa, indicating new potential super hard materials. The high hardness in these materials is attributed to the combined effect of covalent N–N bonding of hexagonal rings and a metal to nitrogen charge transfer. Only two alloys, W0.33Mo0.66N6 and W0.66Mo0.33N6, are semiconducting alloys with electronic bandgaps of 1.82 and 1.92 eV, respectively. A significant magnetic moment of 0.82 μB per unit metal was calculated for W0.66Mo0.33N6.