title: Hexagonal-structured ε-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, ∂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.affiliation: 1] Mineral Physics Institute, State University of New York, Stony Brook, N.Y. 11794, United States [2] State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun, 130012, China.
authors.forename: Yongtao
authors.initials: Y
authors.lastname: Zou
authors.affiliation: Department of Geosciences, State University of New York, Stony Brook, N.Y. 11794, United States.
authors.forename: Xuebing
authors.initials: X
authors.lastname: Wang
authors.affiliation: Department of Geosciences, State University of New York, Stony Brook, N.Y. 11794, United States.
authors.forename: Ting
authors.initials: T
authors.lastname: Chen
authors.affiliation: Mineral Physics Institute, State University of New York, Stony Brook, N.Y. 11794, United States.
authors.forename: Xuefei
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Geosciences, State University of New York, Stony Brook, N.Y. 11794, United States.
authors.forename: Xintong
authors.initials: X
authors.lastname: Qi
authors.affiliation: 1] Department of Materials Science and Engineering, State University of New York, N.Y. 11794, United States [2] Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, N.Y. 11973, United States.
authors.forename: David
authors.initials: D
authors.lastname: Welch
authors.affiliation: State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun, 130012, China.
authors.forename: Pinwen
authors.initials: P
authors.lastname: Zhu
authors.affiliation: State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun, 130012, China.
authors.forename: Bingbing
authors.initials: B
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun, 130012, China.
authors.forename: Tian
authors.initials: T
authors.lastname: Cui
authors.affiliation: Mineral Physics Institute, State University of New York, Stony Brook, N.Y. 11794, United States.
authors.forename: Baosheng
authors.initials: B
authors.lastname: Li