The elastic properties of Mg1-xAlxB2 were studied from first principles. The constants (c11, c12, c13, c33, c55) were calculated for x = 0 to 0.25. From these calculations, the ratio of the bulk to the shear modulus (B/G) as well as the ratio between the 2 directional bulk moduli (Ba/BC) were evaluated. The calculations showed that the Ba/BC ratio decreased monotonically as the Al content was increased, whereas the B/G ratio was well below the empirical ductility limit, 1.75, for all concentrations. In addition, the electronic structure and the nature of the chemical bonding was analyzed by using the balanced crystal orbital overlap population and the charge densities. The analysis suggested that, while Al doping decreased the elastic anisotropy in the a and c directions, it would not appreciably change the brittle behavior of the material.

Elastic Properties of Mg1-xAlxB2 from First Principles Theory. P.Souvatzis, J.M.Osorio-Guillén, R.Ahuja, A.Grechnev, O.Eriksson: Journal of Physics - Condensed Matter, 2004, 16, 5241-50