Ab Initio study of the crystal structure and the elastic properties of the Mo 0.85 Nb 0.15 B 3 compound under pressure
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.420
Ab Initio study of the crystal structure and the elastic properties of the Mo0.85Nb0.15B3 compound under pressure. J. León-Flores1, M. Romero2, J. Rosas-Huerta1, R. Escamilla1. 1 Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Ciudad de México, 04510.
2
Facultad de Ciencias, Universidad Nacional Autónoma de México, Ciudad de México, 04510.
ABSTRACT
The elastic constants, elastic modulus, anisotropy, Debye temperature, and sound velocity properties of Mo0.85Nb0.15B3 were investigated by first-principles calculations under pressure based on the generalized gradient approximation (GGA) proposed by Perdew–BurkeErnzerhof (PBE). Employing the stress-strain method and the Voigt-Reuss-Hill approximations， were calculated the elastic properties of single and polycrystalline crystals; Bulk modulus (B), Young modulus (E), Poisson ratio (ν), Pugh ratio (G/B), Debye temperature and the Cauchy pressure terms. The calculated ν, Cauchy pressure, and Pugh ratio G/B values indicate that Mo0.85Nb0.15B3 shows a transition from brittle to ductile under pressure. Finally, the Density of States decreases as pressure increases.
INTRODUCTION Molybdenum Triboride (MoB3) has been recently studied because it is a potential hard material. As far as we know, there are few reports on the replacement of transition metals at the Mo sites in the MoB 3 compound. One of them related to the improvement of the hardness of the material through substitution group IV transition metals in the Mo sites with an enhancement of the hardness of the 15 percent approximately [1]. Moreover, it was reported that the Nb 15 percent substitution in the Mo sites induces superconductivity in the Mo 1-xNbxB3 compound [2]. It is remarkable to notice that Simonson et al. in 2009 [2] denotes the MoB 3 compounds as MoB4 since at
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that time, there was a controversy related to the crystalline structure of the molybdenum triboride compound. Years later, in 2012, Zhang et al. [3] suggested the stability of the crystalline structure of the MoB3 compound over the MoB4 compound through Density Functional Theory (DFT) studies. Consequently, it was well accepted that the MoB 3 and the Mo0.85Nb0.15B3 compound have a hexagonal crystal structure described by the P6 3/mmc space group (No. 197, Z=1) with two non-equivalent Wyckoff positions 2b (0, 0, 1/4) and 2c (1/3, 2/3, 1/4) for the molybdenum-niobium atoms; while, the boron atoms are occupying, just one crystallographic site described by the 12i (x, 0, 0) Wyckoff position forming a kind of honey-comb boron layer (figure 1). One of the main contributions of exploring the elastic behavior of the materials under pressure is to provide suitable information for the possible manufacturing p
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