Boron: Elementary Challenge for Experimenters and Theoreticians

Abstract

Many of the fundamental questions regarding the solid-state chemistry of boron are still unsolved, more than 200 years after its discovery. Recently, theoretical work on the existence and stability of known and new modifications of the element combined with high-pressure and high-temperature experiments have revealed new aspects. A lot has also happened over the last few years in the field of reactions between boron and main group elements. Binary compounds such as B(6)O, MgB(2), LiB(1-x), Na(3)B(20), and CaB(6) have caused much excitement, but the electron-precise, colorless boride carbides Li(2)B(12)C(2), LiB(13)C(2), and MgB(12)C(2) as well as the graphite analogue BeB(2)C(2) also deserve special attention. Physical properties such as hardness, superconductivity, neutron scattering length, and thermoelectricity have also made boron-rich compounds attractive to materials research and for applications. The greatest challenges to boron chemistry, however, are still the synthesis of monophasic products in macroscopic quantities and in the form of single crystals, the unequivocal identification and determination of crystal structures, and a thorough understanding of their electronic situation. Linked polyhedra are the dominating structural elements of the boron-rich compounds of the main group elements. In many cases, their structures can be derived from those that have been assigned to modifications of the element. Again, even these require a critical revision and discussion.

Generalized evolutionary metadynamics for sampling the energy landscapes and its applications

“…The most striking feature in all the discovered boron allotropes is that boron atoms form icosahedral clusters [20,21]. Such clusters are also found in boron-rich solids [21]. The simplest structure containning icosahedron is α-boron, which is based on a distorted cubic packing of icosahedra.…”

Thermal conductivity of PrRh4.8B2, a layered boride compound

“…[1][2][3][4][5][6][7] Regarding properties, many studies have been carried out into the magnetism of borides, [7][8][9][10][11][12][13][14] and recent especial efforts have been made to develop the high temperature thermoelectric properties of novel borides. [15][16][17][18][19][20] Being refractory materials, thermoelectric borides have the potential to be used in high impact energy-saving applications like topping cycles for power plants and waste heat power generation in industry.…”

Stoichiometric Boron-Based Nanostructures

“…The elemental boron and boron-containing compounds hold a unique place in chemistry, physics, and materials science (Greenwood, 1973;Donohue, 1974;Matkovich, 1977;Emin, 1987;Albert & Hillebrecht, 2009). In general, they are composed of various multi-atom boron clusters, such as graphitic layer, octahedral B 6 and icosahedral B 12 , among which the 12-atom B 12 icosahedral cluster is the most common form (Greenwood, 1973;Donohue, 1974;Matkovich, 1977;Emin, 1987;Albert & Hillebrecht, 2009).…”

“…In general, they are composed of various multi-atom boron clusters, such as graphitic layer, octahedral B 6 and icosahedral B 12 , among which the 12-atom B 12 icosahedral cluster is the most common form (Greenwood, 1973;Donohue, 1974;Matkovich, 1977;Emin, 1987;Albert & Hillebrecht, 2009). The electronic properties of these boron clusters are characterized by the three-center electron-deficient bond, which presents some analogy with metallic bonding because electron deficiency forces electrons to be shared at the cluster surface (Greenwood, 1973;Donohue, 1974;Emin, 1987).…”

“…The elemental boron has a low density but a high melting point around 2300°C as well as a hardness close to that of diamond. Moreover, boron is one of the very few elements that can be used in nuclear engineering, high temperature semiconductor devices, thermoelectric power conversion applications, or as a lightweight protective armor for space shuttles (Greenwood, 1973;Donohue, 1974;Matkovich, 1977;Emin, 1987;Albert & Hillebrecht, 2009). The semiconductor boron becomes a superconductor at temperatures 6-12 K under high pressures above 160 GPa (Erements et al, 2001), but the structure and transition mechanism of superconducting boron is still unkown.…”