Binary dodecaborides

Placa, S. La; Binder, I.; Post, B.

doi:10.1016/0022-1902(61)80377-1

Cited by 61 publications

(40 citation statements)

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“…6. It can be rationalized that no higher tungsten boride having a "true" UB 12 structure exists by noting that the formation of dodecaborides containing well-ordered cuboctahedra depends strongly on the radius of the metal atom, with Y (1.80 Å) (43) and Zr (1.60 Å) (43) being respectively, the largest and smallest metals to do so under ambient pressure (44). In comparison, the radius of W is only 1.39 Å (43), which is too small to accommodate one cuboctahedral cage per metal atom, as would be required.…”

Section: Resultsmentioning

confidence: 99%

Structure of superhard tungsten tetraboride: A missing link between MB ₂ and MB ₁₂ higher borides

Lech

Turner

Mohammadi

et al. 2015

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

113

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Superhard metals are of interest as possible replacements with enhanced properties over the metal carbides commonly used in cutting, drilling, and wear-resistant tooling. Of the superhard metals, the highest boride of tungsten-often referred to as WB 4 and sometimes as W 1-x B 3 -is one of the most promising candidates. The structure of this boride, however, has never been fully resolved, despite the fact that it was discovered in 1961-a fact that severely limits our understanding of its structure-property relationships and has generated increasing controversy in the literature. Here, we present a new crystallographic model of this compound based on refinement against time-of-flight neutron diffraction data. Contrary to previous X-ray-only structural refinements, there is strong evidence for the presence of interstitial arrangements of boron atoms and polyhedral bonding. The formation of these polyhedra-slightly distorted boron cuboctahedra-appears to be dependent upon the defective nature of the tungsten-deficient metal sublattice. This previously unidentified structure type has an intermediary relationship between MB 2 and MB 12 type boride polymorphs. Manipulation of the fractionally occupied metal and boron sites may provide insight for the rational design of new superhard metals.A s demand increases for new superhard materials, the introduction of transition metal borides as candidate compounds has recently attracted a great deal of attention (1-4). This trend is at least partially driven by a need for greater efficiency in cutting tools compared with tungsten carbide (which is not superhard), as well as the shortcomings of the traditional superhard compounds-diamond (which is unusable for cutting ferrous materials) (5) and cubic boron nitride (which is very expensive to synthesize and difficult to shape) (6). Within the rapidly growing family of superhard borides, tungsten tetraboride (or WB 4 ) is of specific interest due to its excellent mechanical properties and its relatively lower cost compared with borides such as ReB 2 , OsB 2 , RuB 2 , and RhB 2 , which contain platinum group metals (3, 7-11). For instance, tungsten tetraboride demonstrates an extremely high indentation hardness of ∼43 GPa by the Vickers method (under an applied load of 0.49 N) (8) and ∼41.7 GPa by nanoindentation (maximum, at a penetration depth of 95.25 nm; Fig. 1), and can sustain a differential stress (a lower-bound estimate of compressive yield strength) of up to ∼19.7 GPa (12). More dramatically, it is like ReB 2 (2), capable of scratching natural diamond (11). We have, furthermore, previously shown that the hardness of this compound may be enhanced by the creation of solid solutions with other transition metals (9). However, to understand the underlying mechanisms for the hardness enhancements observed in WB 4 solid solutions, as well as to guide the design of new superhard borides with tailored mechanical properties, it is crucial to understand the crystal structure of this compound.Perhaps surprisingly for a simple binary ...

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Section: Resultsmentioning

confidence: 99%

Structure of superhard tungsten tetraboride: A missing link between MB ₂ and MB ₁₂ higher borides

Lech

Turner

Mohammadi

et al. 2015

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

113

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“…The primary requirement for the formation of the cubic-UB 12 structure is the radius of the metal in a 12 coordinate environment, with yttrium and zirconium being the largest and smallest metals, respectively, capable of accommodating a boron cuboctahedron cage, with slight size deviation rendering the metal dodecaboride unstable under ambient pressure. [102,133,134,306] Notable exceptions are HfB 12 , ThB 12 , and GdB 12 all of which in pure form can only be synthesized under high pressure, [96,134] or stabilized as a solid solution under ambient pressure: Y 1−x Hf x B 12 , [60] Th 1−x Zr x B 12 , [307] and Zr 1−x Gd x B 12.…”

Section: Borides With a Skeleton/backbone Of Boron Atomsmentioning

confidence: 99%

“…[268,305] The cubic-UB 12 ( Figure 17) structure type consists of a face-centered cubic lattice of 24 boron atom cuboctahedra, with the metal atoms at the center of each of the boron cages. [133] In this arrangement, each boron atom is bonded to five other boron atoms and two metal atoms. The metal atoms inside of the boron cuboctahedron are equidistant from the centers of the twelve boron-boron bonds, therefore, they can be considered twelve coordinate.…”

Section: Borides With a Skeleton/backbone Of Boron Atomsmentioning

confidence: 99%

“…[410] Binary transition and lanthanide metal dodecaborides have been prepared using a borothermal reduction method with appropriate metal oxides (M 2 O 3 ) and amorphous boron in an induction or high-temperature furnace at 1400-1500 °C. [46,52,54,61,133,411,412] In addition, solid solutions of transition metal dodecaborides (UB 12 12 ) covering a wide range of compositions can be prepared using this method. [52,305,413] …”

Section: ) Carbothermal Reduction (Reduction Of Metal Oxides and Bormentioning

confidence: 99%

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Rediscovering the Crystal Chemistry of Borides

2017

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For decades, borides have been primarily studied as crystallographic oddities. With such a wide variety of structures (a quick survey of the Inorganic Crystal Structure Database counts 1253 entries for binary boron compounds!), it is surprising that the applications of borides have been quite limited despite a great deal of fundamental research. If anything, the rich crystal chemistry found in borides could well provide the right tool for almost any application. The interplay between metals and the boron results in even more varied material's properties, many of which can be tuned via chemistry. Thus, the aim of this review is to reintroduce to the scientific community the developments in boride crystal chemistry over the past 60 years. We tie structures to material properties, and furthermore, elaborate on convenient synthetic routes toward preparing borides.

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“…Among these are tetragonal boron (Hoard, Hughes & Sands, 1958), simple rhombohedral boron (Decker & Kasper, 1959), rhombohedral boron phosphides and silicides (Matkovich, 1960(Matkovich, , 1961a, rhombohedral boron oxide and arsenide (La Placa & Post, 1961), C4A1B24 (Matkovich, Economy & Giese, 1964), A1B10 (Will, 1967), BeB12 (Becker, 1960), B12C2A1 (Economy, Matkovich & Giese, 1965), cornplex rhombohedral boron (Hughes, Kennard, Sullenger, Weaklien, Sands & Hoard, 1963) and YB-70 (Richards & Kasper, 1965). Derivative similarities between various higher borides were first reported by Matkovich (1961b) who noted that compounds of different stoichiometries may be derived from the same icosahedral framework and that differences are due to substitution or degree of occupancy of extraicosahedral atoms in interstitial holes.…”

Section: Introductionmentioning

confidence: 99%

Structure of MgAlB₁₄ and a brief critique of structural relationships in higher borides

Matkovich¹,

Economy²

1970

Acta Crystallogr B Struct Sci

122

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Binary dodecaborides

Cited by 61 publications

References 1 publication

Structure of superhard tungsten tetraboride: A missing link between MB ₂ and MB ₁₂ higher borides

Structure of superhard tungsten tetraboride: A missing link between MB ₂ and MB ₁₂ higher borides

Rediscovering the Crystal Chemistry of Borides

Structure of MgAlB₁₄ and a brief critique of structural relationships in higher borides

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Binary dodecaborides

Cited by 61 publications

References 1 publication

Structure of superhard tungsten tetraboride: A missing link between MB 2 and MB 12 higher borides

Structure of superhard tungsten tetraboride: A missing link between MB 2 and MB 12 higher borides

Rediscovering the Crystal Chemistry of Borides

Structure of MgAlB14 and a brief critique of structural relationships in higher borides

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Product

Resources

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Structure of superhard tungsten tetraboride: A missing link between MB ₂ and MB ₁₂ higher borides

Structure of superhard tungsten tetraboride: A missing link between MB ₂ and MB ₁₂ higher borides

Structure of MgAlB₁₄ and a brief critique of structural relationships in higher borides