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

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.
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:
OSTI Identifier:
1226032
Report Number(s):
BNL--108266-2015-JA
Journal ID: ISSN 2045-2322; R&D Project: MA012MABA; KC0202050
Grant/Contract Number:
SC00112704
Type:
Accepted Manuscript
Journal Name:
Scientific Reports
Additional Journal Information:
Journal Volume: 5; Journal ID: ISSN 2045-2322
Publisher:
Nature Publishing Group
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY