Microscopic investigation of local structural and electronic properties of tungsten tetraboride: a superhard metallic material

Turner, Christopher L.; Žujović, Zoran D.; Koumoulis, Dimitrios; Taylor, Robert E.; Kaner, Richard B.

doi:10.1007/s10853-018-3078-6

Cited by 7 publications

(9 citation statements)

References 34 publications

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“…Our experimental valence-band spectrum shows five features denoted as A–E. The steep feature A that appeared near E F signifies a strong metallic character, which is in good agreement with the previous NMR results, thus excluding the possibility of a pseudogap in the DOSs at E F . The other features correspond to the specific electronic band structure in WB 4 sample.…”

Section: Resultssupporting

confidence: 91%

“…Specifically, although many electronic structure calculations have been reported for WB 4 , none of these have used the W deficiency and B 3 trimers as determined experimentally yet. More recently, by using nuclear magnetic resonance (NMR) spectroscopy, Turner et al 33 revealed a range of B sites and enhanced metallic character in WB 4 as compared to WB 2 and AlB 2 , which ruled out the possibility of a pseudogap existing in the density of states (DOSs) at the Fermi level (E F ) in this material, as predicted theoretically based on the pure WB 3 -and MoB 4 -type structures. Therefore, it is crucial to resolve the structural and bonding uncertainties in TM x B y compounds, which can promote in-depth understanding of the hardening mechanism in these promising materials.…”

Section: ■ Introductionmentioning

confidence: 69%

“…Similar multiple B binding states have been observed by Tao et al, 21 but they attributed all the lower binding energy states to the elemental boron. Actually, the 11 B NMR results by Turner et al also revealed a range of boron sites, 33 which can support the presence of different types of B states. Therefore, core-level XPS spectra suggest the existence of inhomogeneous charge transfers from two distinct W states as well as two distinct B states in WB 4 sample, which can be strongly correlated to the presence of W 2b vacancies and B 3 trimers.…”

Section: ■ Results and Discussionmentioning

confidence: 90%

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Nonrandomly Distributed Tungsten Vacancies and Interstitial Boron Trimers in Tungsten Tetraboride

Dong

Wang

et al. 2019

J. Phys. Chem. C

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Tungsten tetraboride (WB4) and its solid solutions represent one of the most promising candidates for superhard metals; however, the structural and bonding uncertainties regarding the fractionally occupied metal and boron sites have impeded an in-depth understanding of these compounds. Here, we examine the interstitial arrangements of boron atoms and polyhedral bonding in synthesized WB4 using W L-edge X-ray absorption spectroscopy and X-ray photoemission spectroscopy. We identify a nonrandom distribution of W vacancies and B3 trimers at the crystallographic W 2b site, instead of a full occupation. Furthermore, this peculiar structural arrangement is associated with two distinct sets of W and B binding states and a large value of density of states at the Fermi level (E F), which suggests an inhomogeneous charge transfer at different crystallographic W and B sites with a preferred metallic bonding. Theoretical calculations elucidate that, while the B3 trimers help form a three-dimensional covalent bonding network, the W vacancies are crucial to optimize the E F location and thus enhance the bonding strength. Our findings provide key insights into the hardening mechanism in WB4, which has broad implications for the rational design and synthesis of this class of materials.

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Section: Resultssupporting

confidence: 91%

Section: ■ Introductionmentioning

confidence: 69%

Section: ■ Results and Discussionmentioning

confidence: 90%

See 1 more Smart Citation

Nonrandomly Distributed Tungsten Vacancies and Interstitial Boron Trimers in Tungsten Tetraboride

Dong

Wang

et al. 2019

J. Phys. Chem. C

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“…The fact that these alloys are single phase not only makes it easier to study their properties, but also in the case of mechanical properties has the added benefit of solid-solution hardening resulting in enhanced hardness, i.e. 47.6 ± 1.7 GPa at 0.49 N load -a 17% increase in hardness over that of the parent phases (ZrB12 and YB12). Furthermore, we have studied the effects of the addition of carbon to the zirconiumyttrium dodecaboride system, as well as provide a possible explanation for the color in metal dodecaborides using diffuse-reflectance, XPS and solid-state NMR ( 10 B and 11 B) spectroscopy.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and Characterization of Single-Phase Metal Dodecaboride Solid Solutions: Zr_1–xY_xB₁₂ and Zr_1–xU_xB₁₂

et al. 2019

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Single-phase metal dodecaboride solid solutions, Zr0.5Y0.5B12 and Zr0.5U0.5B12, were prepared by arc melting from pure elements. The phase purity and composition were established by powder X-ray diffraction (PXRD), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and 10B and 11B solid-state nuclear magnetic resonance (NMR) spectroscopy. The effects of carbon addition to Zr1-xYxB12 were studied and it was found that carbon causes fast cooling and as a result rapid nucleation of grains, as well as "templating" and patterning effects of the surface morphology. The hardness of the Zr0.5Y0.5B12 phase is 47.6 ± 1.7 GPa at 0.49 N load, which is ∼17% higher than that of its parent compounds, ZrB12 and YB12, with hardness values of 41.6 ± 2.6 and 37.5 ± 4.3 GPa, respectively. The hardness of Zr0.5U0.5B12 is ∼54% higher than that of its UB12 parent. The dodecaborides were confirmed to be metallic by band structure calculations, diffuse reflectance UV-vis, and solid-state NMR spectroscopies. The nature of the dodecaboride colors-violet for ZrB12 and blue for YB12-can be attributed to chargetransfer. XPS indicates that the metals are in the following oxidation states: Y3+, Zr4+, and U5+/6+. The superconducting transition temperatures (Tc) of the dodecaborides were determined to be 4.5 and 6.0 K for YB12 and ZrB12, respectively, as shown by resistivity and superconducting quantum interference device (SQUID) measurements. The Tc of the Zr0.5Y0.5B12 solid solution was suppressed to 2.5 K.

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“…Recent studies using solid-state nuclear magnetic resonance (SSNMR) spectroscopy on crystalline (β-) and amorphous boron as well as on the metal borides ReB 2 , AlB 2 , and WB 4 show that this analytical technique has the capability to study structural and electronic properties, for example, bonding situations and (spin–lattice) dynamics, on an atomic scale for solids containing boron. − Furthermore, it may help to clarify ambiguities and overcome limitations of the conventional X-ray diffraction (XRD) investigations. Combined with theoretical methods, SSNMR experiments may even provide an understanding of (unexpected) observed effects.…”

Section: Introductionmentioning

confidence: 99%

GIAO versus GIPAW: Comparison of Methods To Calculate ¹¹B NMR Shifts of Icosahedral Closo-Heteroboranes toward Boron-Rich Borides

2020

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In this work, we perform first-principle density functional theory calculations with the Perdew−Burke−Ernzerhof (PBE) exchange correlation functional to compare the results of the gauge-including atomic orbital (GIAO) method with the gauge-including projector-augmented wave (GIPAW) approach for isotropic 11 B nuclear magnetic resonance shifts. GIPAW had been used successfully for the theoretical calculation of nuclear magnetic parameters of 11 B species in strong ionic solid-phase compounds such as borates but had been applied very rarely to structures where boron is mainly involved in complex covalent bonding situations, for example, in icosahedra of boron-rich borides. Thus, we investigate the accuracy of both well-known methods and reliability of the effective treatment of core electrons on a test set containing 16 experimentally known closo-(hetero)dodecaboranes. In general, we find very good agreement between GIAO and GIPAW when compared to experimental observations. However, accidental degeneracies of the shift values are better predicted by GIPAW. The optimized molecular geometries on the PBE level agree well with gaseous electron diffraction data and lead to theoretical isotropic chemical 11 B shifts with root-mean-square errors of 2.1 and 1.0 ppm depending on the used model of converting absolute shieldings to chemical shifts. The comparison with results from hybrid functionals (B3LYP, B3LYP-D2, and PBE0) shows a minor improvement in accuracy, which is in agreement with 13 C shifts of sp 3 -hybridized species. In order to prove the reliability of the conversion parameters obtained by PBE, we report the calculated 11 B shifts of 1,2-, 1,7-, and 1,12-PCB 10 H 11 with GIAO and GIPAW to our knowledge for the first time. Additionally, Bader's analysis is carried out on the converged electron density for all boron species within the molecular test set, yielding no simple direct relation between charge and isotropic shifts.

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Microscopic investigation of local structural and electronic properties of tungsten tetraboride: a superhard metallic material

Cited by 7 publications

References 34 publications

Nonrandomly Distributed Tungsten Vacancies and Interstitial Boron Trimers in Tungsten Tetraboride

Nonrandomly Distributed Tungsten Vacancies and Interstitial Boron Trimers in Tungsten Tetraboride

Synthesis and Characterization of Single-Phase Metal Dodecaboride Solid Solutions: Zr_1–xY_xB₁₂ and Zr_1–xU_xB₁₂

GIAO versus GIPAW: Comparison of Methods To Calculate ¹¹B NMR Shifts of Icosahedral Closo-Heteroboranes toward Boron-Rich Borides

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Microscopic investigation of local structural and electronic properties of tungsten tetraboride: a superhard metallic material

Cited by 7 publications

References 34 publications

Nonrandomly Distributed Tungsten Vacancies and Interstitial Boron Trimers in Tungsten Tetraboride

Nonrandomly Distributed Tungsten Vacancies and Interstitial Boron Trimers in Tungsten Tetraboride

Synthesis and Characterization of Single-Phase Metal Dodecaboride Solid Solutions: Zr1–xYxB12 and Zr1–xUxB12

GIAO versus GIPAW: Comparison of Methods To Calculate 11B NMR Shifts of Icosahedral Closo-Heteroboranes toward Boron-Rich Borides

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Resources

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Synthesis and Characterization of Single-Phase Metal Dodecaboride Solid Solutions: Zr_1–xY_xB₁₂ and Zr_1–xU_xB₁₂

GIAO versus GIPAW: Comparison of Methods To Calculate ¹¹B NMR Shifts of Icosahedral Closo-Heteroboranes toward Boron-Rich Borides