Elastic properties ofMg(1−x)AlxB2 have been studied from first principles. The
elastic constants (c11, c12, c13, c33 and c55) have been calculated, in the regime
of x = 0 to 0.25. From these calculations the ratio between the bulk modulus
and shear modulus (B/G) as well as the ratio between the two directional
bulk moduli (Ba/Bc) have been evaluated. Our calculations show that the
ratio Ba/Bc decreases monotonically as the aluminium content is increased,
whereas the ratio B/G is well below the empirical ductility limit, 1.75, for all
concentrations. In addition, we analyse the electronic structure and the nature
of the chemical bonding, using the balanced crystal orbital overlap population
(BCOOP) (Grechnev et al 2003 J. Phys.: Condens. Matter 15 7751) and the
charge densities. Our analysis suggests that, while aluminium doping decreases
the elastic anisotropy of MgB2 in the a and c directions, it will not change the
brittle behaviour of the material considerably.
(Some figures in this article are in colour only in the electronic version)
2004. Vol. 16, no 29, 5241–5250- p.