Bor – elementare Herausforderung für Experimentatoren und Theoretiker

Albert, Barbara; Hillebrecht, Harald

doi:10.1002/ange.200903246

Cited by 70 publications

(39 citation statements)

References 318 publications

(417 reference statements)

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“…[1] New properties also arise from alloying; a prime example is the superconductivity of magnesium diboride, which exhibits the highest critical temperature (39 K) among classical superconductors. [2] Hexaborides are also relevant because of their field emission properties [3] and their potential for thermoelectricity (CeB 6 ).…”

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confidence: 99%

A General Solution Route toward Metal Boride Nanocrystals

et al. 2011

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Metal-boron alloys contain a boron covalent framework providing typical high chemical, mechanical, and thermal stability, which allows important applications, for example, for diborides (NbB 2 ) and hexaborides (CaB 6 ) as refractory materials.[1] New properties also arise from alloying; a prime example is the superconductivity of magnesium diboride, which exhibits the highest critical temperature (39 K) among classical superconductors.[2] Hexaborides are also relevant because of their field emission properties [3] and their potential for thermoelectricity (CeB 6 ).[4] Moreover, transition-metal borides are drawing attention as efficient (de)hydrogenation catalysts that can accelerate, for instance, emission of hydrogen from ammonia-borane or borohydrides within energyharnessing devices based on hydrogen technology.[5] Applications in hyperthermia, information storage, thermoelectricity, and catalysis would benefit from scaling down to the nanometer range, which could bring, as for all nanomaterials, modified, enhanced, and even novel properties that arise from the finite particle size. To date, only a few nanostructured borides have been reported. This paucity arises mainly because M-B systems are typically synthesized at high temperatures above 1100 8C.[6] Nanoscale materials have been obtained at lower temperatures (25-100 8C), but at the expense of crystallinity and stability, and such approaches yield pyrophoric compounds without applicability.[7] The scarce reported procedures for nanostructured crystalline systems rely on physical [5,8] or chemical methods, [9] and none of them is demonstrated to be generally applicable to the wide and rich family of borides. Moreover, the majority of crystalline metal borides has not yet been approached at the nanoscale, such as hard (HfB 2 ) or ultrahard (MoB 4 ) materials, catalysts, and ferromagnetic compounds (FeB). The development of a reliable, versatile, and general synthesis procedure towards such systems is therefore still eagerly demanded.One requirement to obtain such nanostructures is the use of relatively mild temperatures, which are still high enough to trigger crystallization but low enough to avoid excessive grain growth, ideally in the range 500-900 8C. Then, development of a solution route instead of standard solid-state reactions may contribute to full kinetic accessibility of the reaction space, which includes control of nanocrystal size and shape. [10] Because of the thermal instability of organic solvents in such conditions, we turned to inorganic molten salts, which are readily available and safe to apply at the targeted temperatures.Herein we present the use of such salt melts for the first general synthesis of metal boride nanocrystals. The method is based on a one-pot ionothermal process which is simple and relies on medium temperature, atmospheric pressure, and environmentally friendly solvents. Applicability to a wide range of compounds, formation of novel nanostructures, and control over the nanocrystal size and the material texture are demons...

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A General Solution Route toward Metal Boride Nanocrystals

et al. 2011

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“…We exposed a vanadium wire (d = 1 mm) to a BCl 3 atmosphere at 1200°C for one hour. During this time, a layer of VB 2 4 (and probably VCl 3 ) in the gas phase. Additionally, the formation of solid VCl 3 could be proven by means of X-ray powder diffraction measurements.…”

Section: Resultsmentioning

confidence: 98%

“…Bulk metal borides are usually prepared from the elements by solid-state reaction at very high temperatures, even though this method has a lot of disadvantages. [4] The main problems are low reaction rates, side reactions and reactions with the crucible material. Therefore, alternative preparation methods at lower temperatures have been developed by using molten metals as solvents.…”

Section: Introductionmentioning

confidence: 99%

The Unexpected Formation of MB₂ Layers (M = Refractory Metal) on Metal Surfaces

2011

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The reactions between refractory metals (Ti, Zr, V, Nb, Ta, Mo, W) and BCl 3 vapour at high temperatures have been studied. For this purpose, the metal wires were heated up by an electrical current in a BCl 3 atmosphere for a couple of hours. Optical and X-ray diffraction methods were used to analyze the solid products, whereas mass spectrometry was used to study the gas phase composition. In the reactions

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“…[1] This complexity and uniqueness is connected to many open questions concerning bonding situation and even the real composition of the sample. [1] Boron-rich borides can serve as model compounds for elemental boron. [2] Furthermore they have interesting properties by themselves.…”

Section: Introductionmentioning

confidence: 98%

“…[3] A closer view on the structures of boron and boron-rich borides shows that there are three ways to solve the "problem of missing electrons"; that is, the formation of (condensed) boron polyhedra, additional electropositive metal atoms that are incorporated as cations and the uptake of more electronegative non-metal atoms with more valence electrons. [1,2] Little is known about phosphorous as an electron-donating non-metal in boron-rich borides. The only boron-rich phosphide known so far is the binary boron subphosphide with the ideal composition B 6 P, which has been well investigated due to its interesting properties for optoelectronic applications and as a refractory thermoelectric material.…”

Section: Introductionmentioning

confidence: 99%

LiB₁₂PC, the First Boron‐Rich Metal Boride with Phosphorus—Synthesis, Crystal Structure, Hardness, Spectroscopic Investigations

Vojteer

Sagawe

Stauffer

et al. 2011

Chemistry A European J

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We present synthesis, crystal structure, hardness, and IR/Raman and UV/Vis spectra of a new compound with the mean composition LiB(12)PC. Transparent single crystals were synthesised from Ga, Li, B, red phosphorus and C at 1500 °C in boron nitride crucibles welded in Ta ampoules. Depending on the type of boron used for the synthesis we obtained colourless, brown and red single crystals with slightly different P/C ratios. Colourless LiB(12)PC crystallizes orthorhombic in the space group Imma (No. 74) with a=10.188(2) Å, b=5.7689(11) Å, c=8.127(2) Å and Z=4. Brown LiB(12)P(0.89)C(1.11) is very similar, but with a lower P content. Red single crystals of LiB(12)P(1.13)C(0.87) have a larger unit cell with a=10.4097(18) Å, b=5.9029(7) Å, c=8.2044(12) Å. EDX measurements confirm that the red crystals contain more phosphorus than the other ones. The crystal structure is characterized by a covalent network of B(12) icosahedra connected by exohedral B-B bonds and P-P, P-C or C-C units. Li atoms are located in interstitials. The structure is closely related to MgB(7), LiB(13)C(2) and ScB(13)C. LiB(12)PC fulfils the electron counting rules of Wade and also Longuet-Higgins. Measurements of Vickers micro-hardness (H(V)=27 GPa) revealed that LiB(12)PC is a hard material. The optical band gaps obtained from UV/Vis spectra match the colours of the crystals. Furthermore we report on the IR and Raman spectra.

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Bor – elementare Herausforderung für Experimentatoren und Theoretiker

Cited by 70 publications

References 318 publications

A General Solution Route toward Metal Boride Nanocrystals

A General Solution Route toward Metal Boride Nanocrystals

The Unexpected Formation of MB₂ Layers (M = Refractory Metal) on Metal Surfaces

LiB₁₂PC, the First Boron‐Rich Metal Boride with Phosphorus—Synthesis, Crystal Structure, Hardness, Spectroscopic Investigations

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Bor – elementare Herausforderung für Experimentatoren und Theoretiker

Cited by 70 publications

References 318 publications

A General Solution Route toward Metal Boride Nanocrystals

A General Solution Route toward Metal Boride Nanocrystals

The Unexpected Formation of MB2 Layers (M = Refractory Metal) on Metal Surfaces

LiB12PC, the First Boron‐Rich Metal Boride with Phosphorus—Synthesis, Crystal Structure, Hardness, Spectroscopic Investigations

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The Unexpected Formation of MB₂ Layers (M = Refractory Metal) on Metal Surfaces

LiB₁₂PC, the First Boron‐Rich Metal Boride with Phosphorus—Synthesis, Crystal Structure, Hardness, Spectroscopic Investigations