Insight into structural, electronic, elastic and thermal properties of A15-type Nb3X (X = Si, Ge, Sn and Pb) compounds

https://doi.org/10.1016/j.mtcomm.2020.101410Get rights and content

Highlights

  • These Nb3X are thermodynamically and mechanically stable.

  • Nb-Nb and Nb-X bonds in Nb3X are ionic-covalent mixed bonds.

  • The sequence of elastic anisotropic is Nb3Si > Nb3Ge > Nb3Sn > Nb3Pb.

Abstract

Niobium-based compounds with the A15 structure have been widely applied in fusion engineering test reactor and superconducting materials. Hence, for a better understanding of the physical properties of A15-type Nb3X (X = Si, Ge, Sn and Pb) compounds, their structural, electronic, elastic and thermodynamic properties were investigated using the first-principles calculations. The calculated formation enthalpies indicated that these Nb3X compounds are energetically favorable and the sequence of thermodynamic stability is Nb3Si > Nb3Ge > Nb3Sn > Nb3Pb. Meanwhile, the phonon dispersions verified that these Nb3X compounds are dynamically stable. The electronic properties, such as the density of state, band structure, electron density difference and Mulliken population, suggested that these compounds are metallic, and Nb-Nb and Nb-X chemical bonds are ionic-covalent mixed bonds. The single-crystal and polycrystalline elastic properties were calculated. Moreover, the elastic anisotropy was discussed by elastic anisotropic indexes, three-dimensional surface construction and planar projections of elastic modulus, and the sequence of elastic anisotropy is Nb3Si > Nb3Ge > Nb3Sn > Nb3Pb. Finally, thermal properties such as Debye temperatures and sound velocities were analyzed based on elastic moduli.

Introduction

Recently, A3B compounds with A15-type structure, in which A is transition metal and B is an element on the right side of the periodic table [1], had been widely used as controllers of the plasma in fusion engineering test reactors due to good phase stabilities and excellent superconducting properties [[2], [3], [4], [5], [6], [7], [8], [9]]. The superconductivity of silicides and germanides of transition metals were measured, and the results showed that the transition temperature TC of V3Si is the highest (17.1 K) among all known binary compounds [10]. Moreover, it had been proved that the high TC and unusual electronically derived properties of V3Ga and V3Si are related to the sharp peak in electronic density of states near to the Fermi level [11]. Therefore, electronic properties are very important for superconducting materials.

Meanwhile, niobium-based A3B compounds with A15-type structure are also important superconducting materials [[12], [13], [14], [15], [16], [17], [18], [19]]. Niobium can form the wide Tc range superconducting compounds with other elements, such as Nb3Ge (23.6 K), Nb3Sn (18.9 K), Nb3Al (18.8 K) [20]. As early as the 1950s and 1960s, Nb3Ge was discovered, and the improvement of the structural order made it possible to increase Tc; meanwhile, it was also known as the compound with high upper critical field value in many A15 superconductors [21,22]. Due to the high Tc values, high critical magnetic fields and high critical current densities, the related properties of niobium-based A3B compounds have been extensively studied theoretically and experimentally [7,17,20,[23], [24], [25], [26]]. For example, the FP-LAPW method in WIEN2K code was used to investigate the electronic properties of Nb3X (X = Al, Ga, In, Ge, and Sn) compounds, the results indicated that Nb-d states can obviously hybridize with X-p states near the Fermi level, and Nb-X chemical bonds show the covalent characteristic [27]. In the investigations using first-principles calculations, there have been many reports about mechanical and electronic properties of Nb3Sn [[28], [29], [30], [31], [32]], mechanical properties of Nb3Ge [33] and Nb3Si [34,35]. However, at present, first-principles calculations of mechanical properties for Nb3Sn, Nb3Ge and Nb3Si are mainly concerned with elastic constants and moduli. Meanwhile, Nb3Pb, in which Pb is in the same group as Si, Ge and Sn, was discovered as a superconductor in 2004 [36], however, no first-principles calculations about Nb3Pb can be found so far. Besides, the discussions of elastic anisotropies and thermal properties of these Nb3X compounds are not deep and systematic.

Generally, the elastic anisotropy of compounds can introduce microcracks under stress due to the relatively large brittleness of compounds. Moreover, thermal properties, such as the sound velocity and Debye temperature, are undoubtedly important for the applications of solids. Furthermore, mechanical properties are related to the bonding characteristics in the compound, and the charge transfer and bonding behavior between atoms can be explored deeply by Mulliken population analysis. Therefore, in this work, the structural, electronic, elastic and thermal properties of Nb3X (X = Si, Ge, Sn and Pb) compounds were investigated using the first-principles calculations. Thess will provide a theoretical basis for future related work on the related compounds.

Section snippets

Computational methods

The CASTEP code [37] based on the density functional theory (DFT) [38] was employed to perform the first-principles calculations to investigate electronic structures, elastic properties, and Debye temperatures of Nb3X (X = Si, Ge, Sn and Pb) compounds. The OTFG ultrasoft pseudo-potentials were used to describe the interactions between ionic-core and valence-electrons. The generalized gradient approximation (GGA) within the Perdew-Burke-Ernzerhof (PBE) program was employed to treat the

Structural properties and phase stabilities

Fig. 1 shows the three-dimensional and top views of A15-type Nb3X (X = Si, Ge, Sn and Pb) compounds with the space group of Pm 3¯ n (No. 223). Each Nb3X unit cell has six Nb atoms and two X atoms. The structural parameters were optimized firstly before the calculations of elastic and thermal properties, and the optimized parameters, as well as the experimental parameters [40], are listed in Table 1. As can be seen from Table 1, the symmetry of all Nb3X compounds is unchanged after the geometry

Conclusions

In summary, the calculated formation enthalpies, phonon dispersion curves and elastic constants indicate that these Nb3X compounds are thermodynamically, dynamically and mechanically stable. According to electronic properties, Nb-Nb and Nb-X bonds in Nb3X are ionic-covalent mixed bonds. Nb3Si has the largest B, G and E due to the strongest bond strength of chemical bonds in Nb3Si. Poisson's ratio ν, GH/BH, and Cauchy pressure (C12-C44) values ​​indicate that all of these Nb3X are ductile. The

Declaration of Competing Interest

We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the submitted manuscript entitled “Insight into structural, electronic, elastic and thermal properties of A15-type Nb3X (X = Si, Ge, Sn and Pb) compounds”.

Acknowledgments

This work was supported by the Yunnan Ten Thousand Talents Plan Young & Elite Talents Project under Grant no. YNWR-QNBJ-2018-044, the Candidate Talents Training Fund of Yunnan Province under Grant no. 2015HB019, and the National Natural Science Foundation of China under Grant no. 51761023.

References (79)

  • I. Papadimitriou et al.

    Ab initio investigation of the intermetallics in the Nb-Sn binary system

    Acta Mater.

    (2015)
  • X. Zhang et al.

    First-principles prediction of the physical properties of ThM2Al20 (M= Ti, V, Cr) intermetallics

    Solid State Commun.

    (2018)
  • X. Zhang et al.

    Insight into the elastic and anisotropic properties of BiMg2MO6 (M= P, As and V) ceramics from the first-principles calculations

    Ceram. Int.

    (2019)
  • J. Chen et al.

    Elastic anisotropy and thermodynamics properties of BiCu2PO6, BiZn2PO6 and BiPb2PO6 ceramics materials from first-principles calculations

    Ceram. Int.

    (2020)
  • X.D. Zhang et al.

    A first principles investigation on the influence of transition-metal elements on the structural, mechanical, and anisotropic properties of CaM2Al20 intermetallics

    J. Mol. Graph. Model.

    (2020)
  • J.Y. Chen et al.

    The influence of vacancy defects on elastic and electronic properties of TaSi (5/3) desilicides from a first-principles calculations

    Ceram. Int.

    (2020)
  • V.H. Mankad et al.

    Thermodynamical and phonon properties of rare-earth REBi (RE = Ce and La) bismuthidies

    Comp. Mater. Sci.

    (2012)
  • C.B. Zhang et al.

    First-principles calculations of phase transition, elasticity, phonon spectra, and thermodynamic properties for hafnium

    Comp. Mater. Sci.

    (2019)
  • D.Z. Li et al.

    The mechanism of elastic and electronic properties of Tungsten Silicide (5/3) with vacancy defect from the first-principles calculations

    Vacuum

    (2020)
  • Y. Pan et al.

    Influence of transition metal on the mechanical and thermodynamic properties of IrAl thermal barrier coating

    Vacuum

    (2020)
  • M.H. Palmer

    On the charge distribution in ethanes and disilanes and correlations with equilibrium bond lengths; an ab initio study

    J. Mol. Struct.

    (2000)
  • S. Azhagiri et al.

    Molecular structure, Mulliken charge, frontier molecular orbital and first hyperpolarizability analysis on 2-nitroaniline and 4-methoxy-2-nitroaniline using density functional theory

    Spectrochim. Acta A.

    (2014)
  • D.Z. Li et al.

    Insight into the pressure effect on the structural stability and physical properties of cubic sesquioxides X2O3 (X = Sc, Y and In)

    Vacuum

    (2019)
  • Y. Pan et al.

    The structure, mechanical and electronic properties of WSi2 from first-principles investigations

    Vacuum

    (2019)
  • X. Zhang et al.

    Phase stability, elastic, anisotropic and thermodynamic properties of GdT2Al20 (T = Ti, V, Cr) compounds: a first-principles study

    Vacuum

    (2018)
  • Y. Pan et al.

    Influence of Mo concentration on the structure, mechanical and thermodynamic properties of Mo–Al compounds from first-principles calculations

    Vacuum

    (2020)
  • J.Y. Chen et al.

    Insight into the vacancy effects on mechanical and electronic properties of Tantalum Silicide

    Ceram. Int.

    (2020)
  • X.D. Zhang et al.

    Insight into the vacancy effects on mechanical and electronic properties of V5Si3 silicides from first-principles calculations

    J. Mol. Graph. Model.

    (2020)
  • Y. Tian et al.

    Microscopic theory of hardness and design of novel superhard crystals

    Int. J. Refract. Metals Hard Mater.

    (2012)
  • S. Chen et al.

    Phase stability, structural and elastic properties of C15-type Laves transition-metal compounds MCo2 from first-principles calculations

    J. Alloys. Compd.

    (2015)
  • M.E. Fine et al.

    Elastic constants versus melting temperature in metals

    Scr. Metall. Mater.

    (1984)
  • J. Yang et al.

    Anisotropy in elasticity, sound velocities and minimum thermal conductivity of zirconia from first-principles calculations

    J. Eur. Ceram. Soc.

    (2017)
  • J. Michel

    Leger, Pressure and temperature formation of A3B compounds

    J. Less-Common Met.

    (1973)
  • M. Kim et al.

    Topological states in A15 superconductors

    Phys. Rev. B

    (2019)
  • Y. Ding et al.

    A multi-scale point of view on the structure-property relationships of A15 superconductors

    J. Mod. Trans.

    (2014)
  • C. Zhang et al.

    Representation of A15 composition and TC in internal-Sn Nb3Sn superconducting strands

    Sci. China Tech. Sci.

    (2010)
  • B.A. Glowacki

    Pinning improvement of A15 applied superconducting materials

    Acta. Phys. Pol. A

    (2016)
  • G.F. Hardy et al.

    The Superconductivity of some transition metal compounds

    Phys. Rev.

    (1954)
  • B.M. Klein et al.

    Self-consistent augmented-plane-wave electronic-structure calculations for the A15 compounds V3X and Nb3X, X = Al, Ga, Si, Ge, and Sn

    Phys. Rev. B

    (1978)
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