First principles study of structural, elastic, electronic and optical properties of Nb₂N and Ta₂N compounds

Abstract

Structural, elastic, electronic and optical properties of hexagonal b-Nb 2 N and b-Ta 2 N compounds are studied for different pressures. The computational technique is based on a plane wave pseudo potential (PWPP) method. The exchange correlation is treated using a generalized gradient approximation (GGA). We evaluate ground state quantities such as lattice parameter, bulk modulus and its pressure derivative, as well as elastic constants. The calculated equilibrium lattice is in rather good agreement with experimental data. Elastic constants and their pressure dependence are calculated using a static finite strain technique. We derive bulk and shear moduli, Young's modulus and Poisson's ratio for ideal polycrystalline b-Nb 2 N and b-Ta 2 N aggregates. Also, we present results of densities of states. Furthermore, starting from dynamical optical properties, the static dielectric constant e(v ¼ 0) is calculated for both compounds, along with the corresponding static refractive index n(0). The present results are a pioneer quantitative theoretical prediction of elastic, electronic and optical properties in the case of b-Nb 2 N and b-Ta 2 N compounds.

Phase diagram, mechanical properties, and electronic structure of Nb–N compounds under pressure

“…Inspired by Ta 2 N 3 compound stabilized at high-pressure, Jiang et al 35 first proposed that U 2 S 3 type Nb 2 N 3 may be stable at wide pressures, and is a potential candidate for hard material. Hexagonal and trigonal structured Nb 2 N materials have also been studied by Chihi et al 37 and Yu et al 38 In addition, much attentions have been focused on the mononitride of Nb since it is proposed that δ-NbN is a superconducting phase with a high transition temperature of 17.8 K. 33 The δ-NbN is a high temperature phase and can be stable at above 1070 -1225 °C. Hexagonal and trigonal structured Nb 2 N materials have also been studied by Chihi et al 37 and Yu et al 38 In addition, much attentions have been focused on the mononitride of Nb since it is proposed that δ-NbN is a superconducting phase with a high transition temperature of 17.8 K. 33 The δ-NbN is a high temperature phase and can be stable at above 1070 -1225 °C.…”

“…Chihi et al 36 investigated the crystal structures and elastic properties of Nb 4 N 5 and Nb 5 N 6 compounds. Hexagonal and trigonal structured Nb 2 N materials have also been studied by Chihi et al 37 and Yu et al 38 In addition, much attention has been focused on the mononitride of Nb since it is proposed that d-NbN is a superconducting phase with a high transition temperature of 17.8 K. 33 d-NbN is a high temperature phase and can be stable at above 1070-1225 1C. First-principles studies showed that the cubic phase is unstable at low temperature, 39,40 and the ground state of NbN is stabilized in the hexagonal CW type structure.…”

Mechanical and metallic properties of tantalum nitrides from first-principles calculations

“…The a-Ta 2 N is an amorphous phase of Ta 2 N. 9 b-Ta 2 N adopts the Fe 2 N-type structure. 10 The TaN exists in three forms: q-TaN (WC-type structure), d-TaN (NaCl-type structure), and 3-TaN (CoSn-type structure). 11,12 The rst principle calculations indicate that the presence of Ta vacancies can reduce the density of state (DOS) around the Fermi level and result in a metal-to-insulator transition in d-TaN.…”

Characterization of molecular beam epitaxy grown β-Nb2N films and AlN/β-Nb2N heterojunctions on 6H-SiC substrates

“…where C ij are the stiffness coefficients of the β-Nb 2 N (C 11 = 533 GPa, C 12 = 238 GPa, C 13 = 179 GPa, C 33 = 568 GPa). 17) The estimated in-plane tensile biaxial stress of the β-Nb 2 N on 6H-SiC is 0.2 GPa, and its component along c-direction is zero. Thus, the film is partially strained.…”