Skip to main content
U.S. Department of Energy
Office of Scientific and Technical Information

Crystal structures and formation mechanisms of boron-rich tungsten borides

Journal Article · · Physical Review B

Boron-rich tungsten borides tend to adopt mechanically unfavorable layered structures but experimentally exhibit excellent mechanical properties rivalling traditional superhard solids. Unravelling the contraindicated structure-property relationship, however, has been impeded by their structural ambiguities because of the difficulty in probing boron and atomic deficiency of these borides. Here, we study crystal structures of boron-rich tungsten borides WB3+x and WB2+x by neutron diffraction based on high-quality samples prepared by a high-pressure method, leading to definitive structural resolutions for both borides with unique compositions of WB5.14 and WB2.34. Combined with theoretical calculations, their structural stability is revealed to be closely related to atomic deficiency, which is governed by the valence-band filling with an optimal valence-electron concentration of ~10 per cell. The presence of interstitial boron trimers at the vacant W : 2b sites in WB5.14 alters the crystal symmetry, making the Wyckoff 2d site more favorably occupied by W, rather than the 2c site, as previously misassigned. Here, the staggered planar boron layers and wrinkled boron bonding in WB2.34 are identified to be crucial for stabilizing its structure. These findings unveil the longstanding structural mysteries of boron-rich tungsten borides and offer powerful insights for rational design of borides by defect chemistry.

Research Organization:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Organization:
USDOE
Grant/Contract Number:
AC05-00OR22725
OSTI ID:
1818658
Journal Information:
Physical Review B, Journal Name: Physical Review B Journal Issue: 1 Vol. 104; ISSN 2469-9950
Publisher:
American Physical Society (APS)Copyright Statement
Country of Publication:
United States
Language:
English

References (57)

Advancements in the Search for Superhard Ultra-Incompressible Metal Borides journal November 2009
Transition Metal Borides: Superhard versus Ultra-incompressible journal October 2008
WB 5− x : Synthesis, Properties, and Crystal Structure—New Insights into the Long‐Debated Compound journal July 2020
A General Solution Route toward Metal Boride Nanocrystals journal February 2011
Bor-reiche Wolframboride journal May 1967
Critical assessment and thermodynamic calculation of the binary system boron-tungsten (B-W) journal April 1995
Crystal Structure of W1−x B3 and Phase Equilibria in the Boron-Rich Part of the Systems Mo-Rh-B and W-{Ru,Os,Rh,Ir,Ni,Pd,Pt}-B journal March 2014
Structure of poorly crystalline MoS2 — A modeling study journal February 1986
The crystal structure of the molybdenum boride Mo1−xB3 journal February 1973
Lattice constants and nonstoichiometry of WB2-x journal April 1995
Unexpectedly hard and highly stable WB3 with a noncompact structure journal August 2013
Sulfur-catalyzed phase transition in MoS2 under high pressure and temperature journal January 2014
A facile one-step route to nanocrystalline TiB2 powders journal April 2004
Boron-Rich Molybdenum Boride with Unusual Short-Range Vacancy Ordering, Anisotropic Hardness, and Superconductivity journal December 2019
Nonrandomly Distributed Tungsten Vacancies and Interstitial Boron Trimers in Tungsten Tetraboride journal November 2019
New Tungsten Borides, Their Stability and Outstanding Mechanical Properties journal June 2018
Superhard Tungsten Tetraboride Films Prepared by Pulsed Laser Deposition Method journal August 2011
Exploring Hardness and the Distorted sp 2 Hybridization of B–B Bonds in WB 3 journal September 2014
Electronic structure of transition-metal borides with the AlB2 structure journal October 1986
Toward Inexpensive Superhard Materials: Tungsten Tetraboride-Based Solid Solutions journal December 2012
A New Molybdenum Nitride Catalyst with Rhombohedral MoS 2 Structure for Hydrogenation Applications journal April 2015
Icosahedral packing of B12 icosahedra in boron suboxide (B6O) journal January 1998
Ionic high-pressure form of elemental boron journal January 2009
Polyphony in B flat journal April 2016
Polytypism in superhard transition-metal triborides journal May 2014
Discovery of elusive structures of multifunctional transition-metal borides journal January 2016
Unexpected stable phases of tungsten borides journal January 2018
Phase stability and mechanical properties of tungsten borides from first principles calculations journal January 2010
Origin of hardness in WB4 and its implications for ReB4, TaB4, MoB4, TcB4, and OsB4 journal September 2008
Peculiar structure and tensile strength of WB 4 : nonstoichiometric origin journal March 2012
Radial x-ray diffraction of tungsten tetraboride to 86 GPa under nonhydrostatic compression journal January 2013
Interstitial-boron solution strengthened WB 3+ x journal October 2013
Unexpected structural softening of interstitial boron solid solution WB3+x journal November 2014
Large-volume cubic press produces high temperatures above 4000 Kelvin for study of the refractory materials at pressures journal January 2020
Tungsten tetraboride, an inexpensive superhard material journal June 2011
Structure of superhard tungsten tetraboride: A missing link between MB 2 and MB 12 higher borides journal March 2015
Low-compressibility of tungsten tetraboride: a high pressure X-ray diffraction study journal June 2011
Neutron scattering lengths and cross sections journal January 1992
Unravelling the structure and strength of the highest boride of tungsten WB 4.2 journal December 2019
Projector augmented-wave method journal December 1994
Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set journal October 1996
Low-compressibility and hard materials Re B 2 and W B 2 : Prediction from first-principles study journal December 2006
Thermodynamic identification of tungsten borides journal June 2011
Exploring the high-pressure behavior of superhard tungsten tetraboride journal February 2012
Unexpectedly low indentation strength of WB 3 and MoB 3 from first principles journal November 2012
Electronic and Structural Origin of Ultraincompressibility of 5 d Transition-Metal Diborides M B 2 ( M = W , Re, Os) journal May 2008
Stability and Strength of Transition-Metal Tetraborides and Triborides journal June 2012
Global Structural Optimization of Tungsten Borides journal March 2013
Anomalous Stress Response of Ultrahard WB n Compounds journal October 2015
Generalized Gradient Approximation Made Simple journal October 1996
EXPGUI , a graphical user interface for GSAS journal April 2001
Composition and crystallographic data for the highest boride of tungsten journal February 1966
Computational materials discovery: the case of the W–B system journal January 2014
Synthesis of group IV and V metal diboride nanocrystals via borothermal reduction with sodium borohydride journal January 2018
Tungsten Diboride: Preparation and Structure journal January 1966
An unexpected softening from WB 3 to WB 4 journal June 2012
The Crystal Structures of Molybdenum and Tungsten Borides. journal January 1947