Boron suboxide: As hard as cubic boron nitride

He, Duanwei; Zhao, Yusheng; Daemen, Luke L.; Qian, Jiang; Shen, Tong; Żerda, T. W.

doi:10.1063/1.1494860

Cited by 271 publications

(172 citation statements)

References 27 publications

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“…Another observation of our results is that the Vickers hardness decreases with the increase in load. Similar behavior has been reported for cubic boron nitride and Al 2 O 3 (25). Note that the cubic ␦-NbN superconducting phase has a the bulk modulus of 348 GPa, comparable to that of cubic boron nitride, and a Vickers hardness of 20 GPa, the same as sapphire.…”

Section: Resultssupporting

confidence: 62%

Hard superconducting nitrides

Chen

Struzhkin²,

Wu³

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

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276

137

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Detailed study of the equation of state, elasticity, and hardness of selected superconducting transition-metal nitrides reveals interesting correlations among their physical properties. Both the bulk modulus and Vickers hardness are found to decrease with increasing zero-pressure volume in NbN, HfN, and ZrN. The computed elastic constants from first principles satisfy c11 > c12 > c44 for NbN, but c11 > c44 > c12 for HfN and ZrN, which are in good agreement with the neutron scattering data. The cubic ␦-NbN superconducting phase possesses a bulk modulus of 348 GPa, comparable to that of cubic boron nitride, and a Vickers hardness of 20 GPa, which is close to sapphire. Theoretical calculations for NbN show that all elastic moduli increase monotonically with increasing pressure. These results suggest technological applications of such materials in extreme environments.elasticity ͉ elastic constants ͉ equations of state ͉ hardness ͉ binary compounds H ard superconducting materials are of considerable interest for specific electronic applications. Superconductivity has been discovered in diamond, generally believed to be the hardest material having very high shear and bulk moduli (1, 2), with a superconducting transition temperature (T c ) near 4 K when doped with boron (3). However, the transition-metal compounds having the sodium chloride (B1) structure (e.g., NbN, NbC, ZrN, or HfN) are also hard superconductors but with relatively higher T c s. The transition temperatures of solid solutions of NbN and NbC can reach a maximum value of 17.8 K, which is close to those found for the cubic A15-type compounds such as Nb 3 Sn and V 3 Si (4). The refractory characteristics of these transitionmetal nitrides and carbides have been applied as coatings to increase the wear resistance, for instance, in cutting tools as well as for magnetic storage devices. The unusual hardness enhancement in these materials has been theoretically shown to originate from a particular -band of bonding states between the nonmetal p orbitals and the metal d orbitals that strongly resists shearing strains (5). At the moment, there is a need to investigate elastic and mechanical properties of these superconductors under simulated extreme working conditions.Here, we report both experimental and theoretical studies of the equation of state, elasticity, and hardness of selected superconducting transition-metal nitrides. We find that the cubic ␦-NbN superconducting phase possesses a bulk modulus of 348 GPa, comparable to that of cubic boron nitride, and a Vickers hardness of 20 GPa, which is close to sapphire (Al 2 O 3 ) (6). The results indicate that these nitrides are good candidates for engineering hard superconducting materials. Experimental and Theoretical DetailsEquations of state studies were based on angle-dispersive synchrotron powder x-ray diffractometry with a diamond anvil cell. The diffraction experiments were carried out at the synchrotron beam line 16ID-B of the Advanced Photon Source High Pressure Collaborative Access Team. A 500 ϫ 500-m ...

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Section: Resultssupporting

confidence: 62%

Hard superconducting nitrides

Chen

Struzhkin²,

Wu³

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

276

137

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“…Broadly, two approaches are used to design and synthesize materials with high hardness. A first approach is to imitate natural diamond by combining light first row elements (B, C, N or O) to produce materials that maintain short bonds with high-covalency, such as c-BN, 1 B 6 O, 2 and BC 2 N. 3 A second route is to start with elemental metals that are intrinsically incompressible, but not hard, and try to improve their hardness by incorporating light elements into the metal structure to simultaneously optimize covalent bonding and valenceelectron density. 4 This class, which generally contains late, transition-metal borides, carbides, nitrides, and oxides contains many candidate hard materials.…”

Section: Introductionmentioning

confidence: 99%

Exploring the high-pressure behavior of superhard tungsten tetraboride

et al. 2012

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Abstract:In this work, we examine the high pressure behavior of superhard material candidate WB 4 using high-pressure synchrotron X-ray diffraction in a diamond anvil cell up to 58.4 GPa. The zero-pressure bulk modulus, K 0 , obtained from fitting the pressure-volume data using the second-order Birch-Murnaghan equation of state is 326 ± 3 GPa. A reversible, discontinuous change in slope in the c/a ratio is further observed at ~42 GPa, suggesting that lattice softening occurs in the c direction above this pressure. This softening is not observed in other superhard transition metal borides such as ReB 2 compressed to similar pressures. Speculation on the possible relationship between this softening and the orientation of boronboron bonds in the c direction in the WB 4 structure is included. Finally, the shear and Young's modulus values are calculated using an isotropic model based on the measured bulk modulus and an estimated Poisson's ratio for WB 4 .

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“…cutting tools and wearresistant materials [66]. Diamond is known to be the hardest materials with H V ranging between 70 and 100 GPa, followed by cubic boron nitride (cBN) with H V of 45-50 GPa [67]. However, neither diamond nor cBN are indeed appropriate to the real applications as they require extreme conditions for their synthesis, resulting in extremely high cost of production and difficulty to obtain the materials with specific sizes and geometries [68].…”

Section: Boron Suboxidementioning

confidence: 99%

“…However, neither diamond nor cBN are indeed appropriate to the real applications as they require extreme conditions for their synthesis, resulting in extremely high cost of production and difficulty to obtain the materials with specific sizes and geometries [68]. Boron suboxide, often denoted by B 6 O, is also a material of choice for a superhard material, as it is suspected to be the hardest Introduction material after diamond and cBN [67]. Refined by the Rietveld method applied on x-ray powder diffraction data [69,70], the crystal structure of boron suboxide can be derived from α-boron (R3m), as already shown in Fig.…”

Section: Boron Suboxidementioning

confidence: 99%

First-principles study of configurational disorder in icosahedral boron-rich solids

Ektarawong¹

2015

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This thesis is a theoretical study of configurationally disordered icosahedral boronrich solids, in particular boron carbides, using density functional theory and alloy theory. The goal is to resolve discrepancies, regarding the properties of boron carbides, between experiments and previous theoretical calculations which have been a controversial issue in the field of icosahedral boron-rich solids. For instance, B 13 C 2 is observed experimentally to be a semiconductor, meanwhile electronic band structure calculations reveal a metallic character of B 13 C 2 due to its electron deficiency. In B 4 C, on the other hand, the experimentally observed band gap is unexpectedly smaller, not the usual larger, than that of standard DFT calculations. Another example is given by the existence of a small structural distortion in B 4 C, as predicted in theoretical calculations, which reduces the crystal symmetry from the experimentally observed rhombohedral (R3m) to the based-centered monoclinic (Cm). Since boron carbide is stable as a single-phase over a broad composition range (∼8-20 at.% C), substitution of boron and carbon atoms for one another is conceivable. For this reason, the discrepancies have been speculated in the literature, without a proof, to originate from configurational disorder induced by substitutional defects. However, owing to its complex atomic structure, represented by 12-atom icosahedra and 3-atom intericosahedral chains, a practical alloy theory method for direct calculations of the properties of the relevant configurations of disordered boron carbides, as well as for a thermodynamic assessment of their stability has been missing.In this thesis, a new approach, the superatom-special quasirandom structure (SA-SQS), has been developed. The approach allows one to model configurational disorder in boron carbide, induced by high concentrations of low-energy B/C substitutional defects. B 13 C 2 and B 4 C are the two stoichiometries, mainly considered in this study, as they are of particular importance and have been in focus in the literature. The results demonstrate that, from thermodynamic considerations, both B 13 C 2 and B 4 C configurationally disorder at high temperature. In the case of B 13 C 2 , the configurational disorder splits off some valence states into the band gap that in turn compensates the electron deficiency in ordered B 13 C 2 , thus resulting in a semiconducting character. As for B 4 C, the configurational disorder eliminates the monoclinic distortion, thus resulting in the restoration of the higher rhombohedral symmetry. Configurational disorder can also account for an exceliii iv lent agreement on elastic moduli of boron carbide between theory and experiment. Thus, several of the previous discrepancies between theory and experiments are resolved.Inspired by attempts to enhance the mechanical properties of boron suboxide by fabricating boron suboxide-boron carbide composites, as recently suggested in the literature, the SA-SQS approach is used for modeling mixtures of boron sub...

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Boron suboxide: As hard as cubic boron nitride

Cited by 271 publications

References 27 publications

Hard superconducting nitrides

Hard superconducting nitrides

Exploring the high-pressure behavior of superhard tungsten tetraboride

First-principles study of configurational disorder in icosahedral boron-rich solids

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