Tungsten Diboride: Preparation and Structure

Woods, Hannah; Wawner, F. E.; Fox, B.G.

doi:10.1126/science.151.3706.75

Cited by 91 publications

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“…Transition metal borides with different boron contents have been studied experimentally and/or theoretically, such as ReB 2 [1][2][3][4], ReB 4 [5], WB 2 [6][7][8], WB 4 (WB 3 ) [9,10], MnB 3 [11], MnB 4 [11][12][13], TaB 2 [14][15][16][17] etc.. These compounds have excellent mechanical, as well as thermal and chemical properties.…”

Section: Introductionmentioning

confidence: 98%

Prediction of new high pressure phase of TaB3: First-principles

Zhang

Zhao

2015

Journal of Alloys and Compounds

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Section: Introductionmentioning

confidence: 98%

Prediction of new high pressure phase of TaB3: First-principles

Zhang

Zhao

2015

Journal of Alloys and Compounds

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“…Although the hypothetical oP8-WB is more stable than the two experimentally observed phases (tI16-WB and oC8-WB) at T>2879 K, a phonon dispersion calculation shows dynamical instability of oP8-WB with a small imaginary frequency for a -point phonon. In addition, the assumed hP4-WB has the extremely high relative formation energy and should be thermodynamically unstable.At 1:2 composition, the experimentally reported hP3-WB 2 [12] has by far the highest relative formation energy (-83 meV/atom) and thus it seems unlikely that it occurs at ambient condition.Unexpectedly, a phonon dispersion calculation shows that it is also dynamically unstable with imaginary frequencies. Interestingly, hP6-WB 2 has the lowest formation energy (-366 meV/atom) and becomes a thermodynamic ground state, which accords with the recent first-principles calculations [13,14,20].…”

mentioning

confidence: 94%

“…At 1:2 composition, the experimentally reported hP3-WB 2 [12] has by far the highest relative formation energy (-83 meV/atom) and thus it seems unlikely that it occurs at ambient condition.…”

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confidence: 94%

“…The early established hP14-W 2 B 5 [9] was recently identified as hP12-WB 2 [10], which has a maximum measured hardness of 42.2 GPa [11]. First-principles calculations suggested that hP6-WB 2 was energetically more stable than the experimentally reported hP3-WB 2 [12] and could have the high hardness with a value of 43.8-47.4 GPa [13,14]. It was once accepted that the claimed hP20-WB 4 [15] was an inexpensive superhard material (Vickers hardness 43.3-46.2 GPa under the load of 0.49 N) [16][17][18][19].…”

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confidence: 97%

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Unexpectedly hard and highly stable WB3 with a noncompact structure

Liang

Gou

Yuan

et al. 2013

Chemical Physics Letters

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A highly stable tungsten triboride with the Pearson symbol hP24 (hP24-WB 3 ) is identified by using density functional theory calculations. This new structure can be derived from the well-known hP3 configuration by removing one third of tungsten atoms systematically so that the remaining tungsten atoms form three cycled layers of open hexagons with each a layer displaced by one atom. Such a porous and metallic system has an unexpectedly high Vickers hardness of 38.3 GPa. It is revealed that a three-dimensional covalent framework composed of hexagonal boron planes interconnected with strong zigzag W-B bonds is responsible for its unusual high hardness.The synthesis and prediction of new transition-metal borides (TMBs) possessing exceptional properties are the subject of an intense research activity since their unique characteristics confer a considerable technological interest to them. For example, following the discovery of a famous superconductor [5] were found to be display appealing superconductivity. Strikingly, a large TMB 6 family attracts much attentions for they exhibit valence fluctuations (SmB 6 ) and Kondo (CeB 6 ) effects or have low work functions and low volatility at high temperature (LaB 6 , CeB 6 ) allowing their use as high performance thermionic emitters [6]. Moreover, FeB 2 was predicted to be the first metal diboride semiconductor [3]. Recently, the boron incorporation into TMs forming dense TMBs ensures high valence electron density and strong covalent bonding resulting in high hardness [7]. Applying this principle, a series of promising superhard TMBs were experimentally synthesized or theoretically predicted [8]. In the following, we demonstrate that a novel TMB with unusual behaviors can be found in such a well-known and accessible binary system as W-B.A great interest is currently focused on tungsten borides, not only because they can form rich phases, but also because of their high potentials to serve as relatively inexpensive superhard In this Letter, we present a comprehensive study of the phase stability, crystal structure and electronic properties for the W-B system. We find a brand new hP24-WB 3 that can be obtained from the well-known hP3-WB 2 by removing one third of tungsten atoms systematically. This noncompact and conductive hP24-WB 3 not only is the highest boride of tungsten with the thermodynamic stability but also has an unexpectedly high hardness of 38.3 GPa. Furthermore, we reveal that such an anomalous hardness has its electronic origin. This newly identified compound strongly challenges the common strategy only pursuing dense TMBs for superhard materials.The calculations were carried out using the density functional theory within the generalized gradient approximation (GGA) [24] as implemented in the Vienna ab initio simulation package (VASP) [25]. The chosen cutoff energy of 500 eV and dense k-point meshes ensure numerical convergence of energy differences to typically ~1 meV/atom. All considered structures were optimized with respect to both lattice parameters and ...

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“…Tungsten is one of the few transition metals that is known for its ability to form higher boron content borides. In addition to tungsten diboride (WB 2 ), which is not superhard (22,23), tungsten is able to form tungsten tetraboride (WB 4 ), the highest boride of tungsten that exists under equilibrium conditions (24)(25)(26). The advantage of this material over other borides are: (i) Both tungsten and boron are relatively inexpensive, (ii) the lower metal content in the higher borides reduces the overall cost of production because the more costly transition metal is being replaced by less expensive boron thus reducing the cost per unit volume, and (iii) the higher boron content lowers the overall density of the structure, which could be beneficial in applications where lighter weight is an asset.…”

mentioning

confidence: 99%

Tungsten tetraboride, an inexpensive superhard material

Mohammadi

Lech

Xie

et al. 2011

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

310

281

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Tungsten tetraboride (WB 4 ) is an interesting candidate as a less expensive member of the growing group of superhard transition metal borides. WB 4 was successfully synthesized by arc melting from the elements. Characterization using powder X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX) indicates that the as-synthesized material is phase pure. The zeropressure bulk modulus, as measured by high-pressure X-ray diffraction for WB 4 , is 339 GPa. Mechanical testing using microindentation gives a Vickers hardness of 43.3 AE 2.9 GPa under an applied load of 0.49 N. Various ratios of rhenium were added to WB 4 in an attempt to increase hardness. With the addition of 1 at.% Re, the Vickers hardness increased to approximately 50 GPa at 0.49 N. Powders of tungsten tetraboride with and without 1 at.% Re addition are thermally stable up to approximately 400°C in air as measured by thermal gravimetric analysis.dispersion hardening | indentation hardness | intrinsic hardness | nano-indentation hardness | solid solutions I n many manufacturing processes, materials must be cut, formed, or drilled, and their surfaces protected with wearresistant coatings. Diamond has traditionally been the material of choice for these shaping operations, due to its superior mechanical properties (e.g., hardness > 70 GPa) (1, 2). However, diamond is rare in nature and difficult to synthesize artificially due to the need for a combination of high temperature and high pressure. Industrial applications of diamond are thus generally limited by cost. Moreover, diamond is not a good option for high-speed cutting of ferrous alloys due to its graphitization on the material's surface and formation of brittle carbides, which leads to poor cutting performance (3). Other hard or superhard (hardness ≥ 40 GPa) substitutes for diamond include compounds of light elements such as cubic boron nitride (4) and BC 2 N (5) or transition metals combined with light elements such as WC (6), HfN (7), and TiN (8). Although the compounds of the first group (B, C, or N) possess high hardness, their synthesis requires high pressure and high temperature and is thus nontrivial (9, 10). On the other hand, most of the compounds of the second group (transition metal-light elements) are not superhard although their synthesis is more straightforward.To overcome the shortcomings of diamond and its substitutes, we have been pursuing the synthesis of dense transition metal borides, which combine high hardness with synthetic conditions that do not require high pressure (11,12). For example, arc melting and metathesis reactions have been used to synthesize the transition metal diborides OsB 2 (13, 14), RuB 2 (15), and ReB 2 (16-20). Among these, rhenium diboride (ReB 2 ) with a hardness of approximately 48 GPa under a load of 0.49 N has proven to be the hardest (16, 21). The boron atoms are needed to build the strong covalent metal-boron and boron-boron bonds that are responsible for the high hardness of these materials (12). Because of this, it is expected th...

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Tungsten Diboride: Preparation and Structure

Cited by 91 publications

References 0 publications

Prediction of new high pressure phase of TaB3: First-principles

Prediction of new high pressure phase of TaB3: First-principles

Unexpectedly hard and highly stable WB3 with a noncompact structure

Tungsten tetraboride, an inexpensive superhard material

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