Chapter

Boron Rich Solids

Part of the series NATO Science for Peace and Security Series B: Physics and Biophysics pp 115-130

Date:

Investigation of Hard Boron Rich Solids: Osmium Diboride and β-Rhombohedral Boron

  • M. HebbacheAffiliated withLaboratoire Matériaux et Phénomènes Quantiques (UMR 7162), Université Denis Diderot - Paris 7 Email author 
  • , D. ŽivkovićAffiliated withDepartment of Metallurgy, University of Belgrade

* Final gross prices may vary according to local VAT.

Get Access

Abstract

Recently, we succeeded in synthesizing three osmium borides, i.e., OsB1.1, Os2B3 and OsB2. Up to date, almost nothing is known about the physical properties of these materials. Microhardness measurements show that OsB2 is extremely hard. Ab initio calculations show that it is due to formation of covalent bonds between boron atoms. OsB2 is also a low compressibility material. It can be used for hard coatings. The β-rhombohedral polymorph of boron is the second hardest elemental crystal (H ≈ 33 GPa). It is also very light and a p-type semiconductor. In early 1970s, it has been shown that the doping of boron with 3d transition elements enhances its hardness by about 25%. We predict that, in general, heavily doped samples MBx, with x ≤ 31 or equivalently a dopant concentration larger than 3.2 at.%, should be ultrahard, i.e., H > 43 GPa. The relevant dopants M are Al, Cu, Sc, Mn, Mg and Li. In addition to these properties, boron-rich materials have a very low volatility, a high chemical inertness and high melting point. They are suitable for applications under extreme conditions and thermoelectric equipment.

Keywords

boron osmium diborides hard materials lightweight materials ab initio calculations