First-principles calculations on the mechanical properties of niobium nitrides

Wang, Chao; Wen, Mao; Su, Yanqing; Xu, Liqiang; Qu, Chao; Zhang, Y.J.; Qiao, Liang; Yu, Shansheng; Zheng, Weitao; Jiang, Q.

doi:10.1016/j.ssc.2009.02.004

Cited by 23 publications

(9 citation statements)

References 31 publications

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“…It is seen that the electronic spectra of the NaCl-and WC-based structures of V In the case of NaCl-type VN, the Fermi level is located below the DOS minimum that separates these sub-bands, whereas in WC-type VN, E F is located right in this local minimum of the DOS. The calculated PDOSs of VN are consistent with those of stoichiometric transition metal nitrides 19,20 . The substitution of nitrogen by carbon leads to an appearance of additional carbon states below the Fermi level (E F ).…”

Section: Resultssupporting

confidence: 72%

First-principles study of phase stability of stoichiometric vanadium nitrides

et al. 2011

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First-principles pseudo-potential total-energy and phonon spectrum calculations of various phases of stoichiometric vanadium nitrides with a small number of vanadium and nitrogen vacancies, as well with small carbon and oxygen admixtures were carried out. It was found that the stoichiometric hexagonal and tetragonal vanadium nitrides (VN) were dynamically stable. The NaCl-type VN exhibited lattice instability. The total energy for the computed ground-state phases of VN increased in the sequence: hexagonal (WC-type, P6m2) -hexagonal (AsNi-type, P 63/mmc) -tetragonal (P 42/mcm) -cubic (NaCl-type, F m3m) -cubic (ZnS-type, F43m) -cubic (CsCl-type, P m3m). At low temperatures, the vacancies in both sublattices stabilize the triclinic phases of VxNx, for x < 0.94, which is consistent with tetragonal symmetry. At high temperatures, the stability of the NaCl-and WC-type VN structures was estimated using an approach based on band energy smearing. The results obtained indicate that the cubic structure of VN with the fully occupied sublattices will be stable only at high temperatures. The small carbon and oxygen admixtures do not stabilize the cubic phase compared to the hexagonal one. The phase stability of the cubic and hexagonal structures of VxNx was explained on the basis of the peculiarities of their electronic densities of states near the Fermi level. The predicted structural transformations in stoichiometric vanadium nitrides are compatible with those observed in experimentally.

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Section: Resultssupporting

confidence: 72%

First-principles study of phase stability of stoichiometric vanadium nitrides

et al. 2011

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“…Haglund et al 14–16 investigated the cohesive properties and enthalpies of formation of 3d, 4d, and 5d TMNs and discussed the bonding mechanism by using the linear muffin‐tin orbital (LMTO) method. Wang et al 17 calculated the mechanical properties of cubic δ ‐NbN and hexagonal δ ′ ‐NbN with density functional theory (DFT) and found that the calculated ideal strength of δ ′ ‐NbN was higher than that of δ ‐NbN. Puska et al 18 have predicted the first‐principle electronic structure and positron‐state calculations for carbides as well as nitrides of transition metals and determined their positron affinities and lifetimes.…”

Section: Introductionmentioning

confidence: 99%

Pressure induced phase transitions in transition metal nitrides: Ab initio study

Srivastava

Chauhan

Singh

2011

Physica Status Solidi (b)

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We have analyzed the stability of transition metal nitrides (TMNs) XN (X ¼ Ti, Zr, Hf, V, Nb, Ta) in their original rocksalt (B1) and hypothetical CsCl (B2) type phases under high compression. The ground state total energy calculation approach of the system has been used through the generalized gradient approximation (GGA) with the Perdew-BurkeErnzerhof (PBE) type parameterization as exchange correlation functional. In the whole series of nitrides taken into consideration, tantalum nitride is found to be the most stable. We have observed that under compression the original B1-type phase of these nitrides transforms to a B2-type phase. We have also discussed the computation of ground state properties, like the lattice constant (a), bulk modulus (B 0 ) and first order pressure derivative of the bulk modulus (B' 0 ) of the TMNs and their host elements.

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“…It is known that rock-salt structured δ -NbN possesses the highest transition temperature among transition-metal nitrides (∼17 K), and has several polymorphs 4 8 20 21 22 23 such as WC-type NbN, δ -NbN (NiAs-type) and hexagonal ε -NbN (#194, P 6 3 / mmc ), but only cubic δ -NbN has been extensively investigated 1 2 4 8 . Recent first-principles theoretical calculations of the thermodynamic properties and structural stability in NbN polymorphs 22 23 ( e.g. NaCl-, NiAs- and WC-type NbN) predicted that the hexagonal-structured NbN ( e.g.…”

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confidence: 99%

Discovery of Superconductivity in Hard Hexagonal ε-NbN

Zou

Zhang

et al. 2016

Sci Rep

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Since the discovery of superconductivity in boron-doped diamond with a critical temperature (TC) near 4 K, great interest has been attracted in hard superconductors such as transition-metal nitrides and carbides. Here we report the new discovery of superconductivity in polycrystalline hexagonal ε-NbN synthesized at high pressure and high temperature. Direct magnetization and electrical resistivity measurements demonstrate that the superconductivity in bulk polycrystalline hexagonal ε-NbN is below ∼11.6 K, which is significantly higher than that for boron-doped diamond. The nature of superconductivity in hexagonal ε-NbN and the physical mechanism for the relatively lower TC have been addressed by the weaker bonding in the Nb-N network, the co-planarity of Nb-N layer as well as its relatively weaker electron-phonon coupling, as compared with the cubic δ-NbN counterpart. Moreover, the newly discovered ε-NbN superconductor remains stable at pressures up to ∼20 GPa and is significantly harder than cubic δ-NbN; it is as hard as sapphire, ultra-incompressible and has a high shear rigidity of 201 GPa to rival hard/superhard material γ-B (∼227 GPa). This exploration opens a new class of highly desirable materials combining the outstanding mechanical/elastic properties with superconductivity, which may be particularly attractive for its technological and engineering applications in extreme environments.

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First-principles calculations on the mechanical properties of niobium nitrides

Cited by 23 publications

References 31 publications

First-principles study of phase stability of stoichiometric vanadium nitrides

First-principles study of phase stability of stoichiometric vanadium nitrides

Pressure induced phase transitions in transition metal nitrides: Ab initio study

Discovery of Superconductivity in Hard Hexagonal ε-NbN

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