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Journal of Materials Science

, Volume 54, Issue 4, pp 3547–3557 | Cite as

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

  • Christopher L. Turner
  • Zoran Zujovic
  • Dimitrios KoumoulisEmail author
  • R. E. TaylorEmail author
  • Richard B. Kaner
Metals
  • 112 Downloads

Abstract

Tungsten borides, such as tungsten tetraboride (WB4) exhibit a wide range of appealing physical properties, including superhardness, chemical inertness and electronic conductivity. Among the various tungsten borides, the most puzzling remains WB4, with its crystal structure to linger in question for over half a century (Lech et al. in Proc Natl Acad Sci USA 112:3223–3228, 2015). In the present investigation, polycrystalline WB4 samples have been synthesized with two different methods and characterized at the atomic level by combining X-ray diffraction, scanning electron microscopy and nuclear magnetic resonance spectroscopy. The 11B multiple quantum MAS experiment revealed a range of boron sites that were not resolved within the experiment. This result is in contrast to the 11B MAS spectrum of WB2 with four resolved, discernible boron resonances. However, despite the structural complexity and boron-site variety in WB4, the detection of a single exponential of 11B spin–lattice relaxation recovery suggested that all of the boron sites relaxed with a single time constant. The Knight shift (K) was found to be independent of temperature while the \( T_{1}^{ - 1} \) was governed by the Korringa law with a Korringa product T1T = 350 sK across the entire temperature range (168–437 K) of this study. The measured Korringa product was small, indicating substantial spin–lattice relaxation resulting from coupling with the conduction carriers. The abovementioned experimental results not only clearly rule out structures, such as the “MoB4-type phase” of WB4, with the resulting Fermi level in the pseudo-gap as has previously been predicted theoretically; but they also provide a comprehensible and valuable insight into the structural and electronic properties of WB4 at the atomic level.

Notes

Acknowledgements

This research is supported by the National Science Foundation MRI program Grant No. 1532232 (R.E.T., R.B.K.) and DMR-1506860 (R.B.K.).

Compliance with ethical standards

Conflict of interest

C.L.T. works with SuperMetalix, Inc., a company who is developing products based on superhard metals using patents licensed from UCLA. R.B.K. also has a financial interest in SuperMetalix, Inc. The authors Z.Z, D.K. and R.E.T. declare no conflict of interest.

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© Springer Science+Business Media, LLC, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Department of Chemistry and BiochemistryUniversity of California, Los AngelesLos AngelesUSA
  2. 2.NMR Centre and the Biocide Toolbox Research Programme, School of Chemical SciencesUniversity of AucklandAucklandNew Zealand
  3. 3.School of Physical Science and TechnologyShanghaiTech UniversityPudong, ShanghaiChina
  4. 4.Department of Materials Science and Engineering and California NanoSystems InstituteUniversity of California, Los AngelesLos AngelesUSA
  5. 5.Department of PhysicsUniversity at Buffalo, SUNYBuffaloUSA

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