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Structural, Mechanical and Electronic Properties Study on Group VB Transition Metal Ternary Mononitrides from First-Principles Calculations

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Document pages: 43 pages

Abstract: The possible structures of the VB transition metal ternary mononitrides (V0.5Ta0.5N, V0.5Nb0.5N and Nb0.5Ta0.5N) are systematically explored in 0~300 GPa pressure rang through CALYPSO (Crystal structure Analysis by Particle Swarm Optimization) method. Three phases with Pmm2, Cmc21, and Fm-3m space group have been uncovered. The dynamical, mechanical and thermodynamic stabilities are determined from the phonon dispersion, elastic constants and formation enthalpy calculations. These mononitrides with Pmm2 and Cmc21 structures exhibit much more excellent mechanical property relative to VN, NbN and TaN with traditional B1 (NaCl-like) structure. The elastic anisotropy of these phases is fully investigated by the dependence of Young s, linear bulk and shear moduli along the crystal orientation. To further determine the mechanical strength, the compressive, tensile and indentation shear strength are systematically studied from the first-principles calculations. Our results revealed the Pmm2 and Cmc21 phases possess the excellent strength values up to 30 GPa under the Vickers indentation simulation calculations, which is comparable to well-known WB3, WB4 and ReB2 reported as the potential superhard transition-metal light-element compounds. The electronic structures of these mononitrides are also studied to explore the intrinsic chemical bonding nature, and a novel electronic property of the transition of semiconductor-to-conductor from V0.5Ta0.5N, V0.5Nb0.5N to Nb0.5Ta0.5N is exposed for the Fm-3m phase of these compounds.

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