The search for superhard materials: Doped boronM. Hebbache
Laboratoire Matériaux et Phénomènes Quantiques, Université Paris 7 - CNRS, UMR 7162 Bâtiment Condorcet, 75205 Paris Cedex 13, France, EU
received 2 June 2009; accepted in final form 22 June 2009; published July 2009
published online 15 July 2009
Superhard materials have numerous industrial applications and are then the subject of intense investigations. The -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 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.
61.82.Fk - Semiconductors.
85.40.Ry - Impurity doping, diffusion and ion implantation technology.
62.20.-x - Mechanical properties of solids.
© EPLA 2009