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Title: Hexagonal-structured epsilon-NbN. Ultra-incompressibility, high shear rigidity, and a possible hard superconducting material

Abstract

Exploring the structural stability and elasticity of hexagonal ε-NbN helps discover correlations among its physical properties for scientific and technological applications. Here, for the first time, we measured the ultra-incompressibility and high shear rigidity of polycrystalline hexagonal ε-NbN using ultrasonic interferometry and in situ X-ray diffraction, complemented with first-principles density-functional theory calculations up to 30 GPa in pressure. Using a finite strain equation of state approach, the elastic bulk and shear moduli, as well as their pressure dependences are derived from the measured velocities and densities, yielding BS0 = 373.3(15) GPa, G0 = 200.5(8) GPa, ∂B S/∂P = 3.81(3) and ∂G/∂P = 1.67(1). The hexagonal ε-NbN possesses a very high bulk modulus, rivaling that of superhard material cBN (B0 = 381.1 GPa). The high shear rigidity is comparable to that for superhard γ-B (G 0 = 227.2 GPa). We found that the crystal structure of transition-metal nitrides and the outmost electrons of the corresponding metals may dominate their pressure dependences in bulk and shear moduli. In addition, the elastic moduli, Vickers hardness, Debye temperature, melting temperature and a possible superconductivity of hexagonal ε-NbN all increase with pressures, suggesting its exceptional suitability for applications under extreme conditions.

Authors:
 [1];  [2];  [2];  [2];  [2];  [3];  [4];  [4];  [4];  [2]
  1. State Univ. of New York (SUNY), Stony Brook, NY (United States); Jilin Univ., Changchun (China). State Key Lab. of Superhard Materials
  2. State Univ. of New York (SUNY), Stony Brook, NY (United States)
  3. Brookhaven National Lab. (BNL), Upton, NY (United States); State Univ. of New York (SUNY), Stony Brook, NY (United States)
  4. Jilin Univ., Changchun (China). State Key Lab. of Superhard Materials
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1226032
Report Number(s):
BNL-108266-2015-JA
Journal ID: ISSN 2045-2322; R&D Project: MA012MABA; KC0202050
Grant/Contract Number:
SC00112704
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Scientific Reports
Additional Journal Information:
Journal Volume: 5; Journal ID: ISSN 2045-2322
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY

Citation Formats

Zou, Y., Wang, X., Chen, T., Li, X., Qi, X, Welch, D., Zhu, P., Liu, B., Cui, T., and Li, B. Hexagonal-structured epsilon-NbN. Ultra-incompressibility, high shear rigidity, and a possible hard superconducting material. United States: N. p., 2015. Web. doi:10.1038/srep10811.
Zou, Y., Wang, X., Chen, T., Li, X., Qi, X, Welch, D., Zhu, P., Liu, B., Cui, T., & Li, B. Hexagonal-structured epsilon-NbN. Ultra-incompressibility, high shear rigidity, and a possible hard superconducting material. United States. doi:10.1038/srep10811.
Zou, Y., Wang, X., Chen, T., Li, X., Qi, X, Welch, D., Zhu, P., Liu, B., Cui, T., and Li, B. Mon . "Hexagonal-structured epsilon-NbN. Ultra-incompressibility, high shear rigidity, and a possible hard superconducting material". United States. doi:10.1038/srep10811. https://www.osti.gov/servlets/purl/1226032.
@article{osti_1226032,
title = {Hexagonal-structured epsilon-NbN. Ultra-incompressibility, high shear rigidity, and a possible hard superconducting material},
author = {Zou, Y. and Wang, X. and Chen, T. and Li, X. and Qi, X and Welch, D. and Zhu, P. and Liu, B. and Cui, T. and Li, B.},
abstractNote = {Exploring the structural stability and elasticity of hexagonal ε-NbN helps discover correlations among its physical properties for scientific and technological applications. Here, for the first time, we measured the ultra-incompressibility and high shear rigidity of polycrystalline hexagonal ε-NbN using ultrasonic interferometry and in situ X-ray diffraction, complemented with first-principles density-functional theory calculations up to 30 GPa in pressure. Using a finite strain equation of state approach, the elastic bulk and shear moduli, as well as their pressure dependences are derived from the measured velocities and densities, yielding BS0 = 373.3(15) GPa, G0 = 200.5(8) GPa, ∂BS/∂P = 3.81(3) and ∂G/∂P = 1.67(1). The hexagonal ε-NbN possesses a very high bulk modulus, rivaling that of superhard material cBN (B0 = 381.1 GPa). The high shear rigidity is comparable to that for superhard γ-B (G0 = 227.2 GPa). We found that the crystal structure of transition-metal nitrides and the outmost electrons of the corresponding metals may dominate their pressure dependences in bulk and shear moduli. In addition, the elastic moduli, Vickers hardness, Debye temperature, melting temperature and a possible superconductivity of hexagonal ε-NbN all increase with pressures, suggesting its exceptional suitability for applications under extreme conditions.},
doi = {10.1038/srep10811},
journal = {Scientific Reports},
number = ,
volume = 5,
place = {United States},
year = {Mon Jun 01 00:00:00 EDT 2015},
month = {Mon Jun 01 00:00:00 EDT 2015}
}

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Cited by: 8works
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  • Since the discovery of superconductivity in boron-doped diamond with a critical temperature (T C) 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 T C have been addressed by themore » 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). Furthermore, 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.« less
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  • We report compressibility measurements for three transition metal nitrides ({epsilon}-TaN, {delta}-MoN, Cr{sub 2}N) that have structures based on hexagonal arrangements of the metal atoms. The studies were performed using monochromatic synchrotron x-ray diffraction at high pressure in a diamond anvil cell. The three nitride compounds are well-known high hardness materials, and they are found to be highly incompressible. The bulk modulus values measured for {epsilon}-TaN, Cr{sub 2}N, and {delta}-MoN are K{sub 0}=288(6) GPa, 275(23) GPa, and 345(9) GPa, respectively. The data were analyzed using a linearized plot of reduced pressure (F) vs the Eulerian finite strain variable f within amore » third-order Birch-Murnaghan equation of state formulation. The K{sub 0}{sup '} values for {epsilon}-TaN and {delta}-MoN were 4.7(0.5) and 3.5(0.3), respectively, close to the value of K{sub 0}{sup '}=4 that is typically assumed in fitting compressibility data in equation of state studies using a Birch-Murnaghan equation. However, Cr{sub 2}N was determined to have a much smaller value, K{sub 0}{sup '}=2.0(2.0), indicating a significantly smaller degree of structural stiffening with increased pressure. We also present Raman data for {epsilon}-TaN and {delta}-MoN at high pressure in order to characterize the phonon behavior in these materials. All of the Raman active modes for {epsilon}-TaN were identified using polarized spectroscopy. Peaks at low frequency are due to Ta motions, whereas modes at higher wave number contain a large component of N motion. The high frequency modes associated with Ta-N stretching vibrations are more sensitive to compression than the metal displacements occurring at lower wave number. The mode assignments can be generally extended to {delta}-MoN, that has a much more complex Raman spectrum. The x-ray and Raman data for {epsilon}-TaN show evidence for structural disordering occurring above 20 GPa, whereas no such change is observed for {delta}-MoN.« less
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