Issue
EPL
Volume 87, Number 1, July 2009
Article Number 16001
Number of page(s) 5
Section Condensed Matter: Structural, Mechanical and Thermal Properties
DOI http://dx.doi.org/10.1209/0295-5075/87/16001
Published online 15 July 2009
EPL, 87 (2009) 16001
DOI: 10.1209/0295-5075/87/16001

The search for superhard materials: Doped boron

M. Hebbache

Laboratoire Matériaux et Phénomènes Quantiques, Université Paris 7 - CNRS, UMR 7162 Bâtiment Condorcet, 75205 Paris Cedex 13, France, EU

mhe@univ-paris-diderot.fr

received 2 June 2009; accepted in final form 22 June 2009; published July 2009
published online 15 July 2009

Abstract
Superhard materials have numerous industrial applications and are then the subject of intense investigations. The $\beta $-rhombohedral polymorph of boron is the second hardest elemental crystal (HV ~ 34 GPa). It is also very light and a p-type semiconductor. In the early seventies, 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 $\leqslant$ 31 or equivalently a dopant concentration larger than 3.2 at.%, should be ultrahard, i.e., HV > 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 ( > 2400 °C). They are suitable for applications under extreme conditions and thermoelectric equipment.

PACS
61.82.Fk - Semiconductors.
85.40.Ry - Impurity doping, diffusion and ion implantation technology.
62.20.-x - Mechanical properties of solids.

© EPLA 2009