Elastic and electronic properties of the alkali pnictide compounds Li3Sb, Li3Bi, Li2NaSb and Li2NaBi

First principles calculations, by means of the full potential linearized augmented plane wave method within the density functional theory, were carried out for the electronic and elastic properties of the alkali pnictide compounds Li3Sb, Li3Bi, Li2NaSb and Li2NaBi. The exchange and correlation effects have been treated using the local density and the generalized gradient approximations. The calculated lattice parameters and bulk moduli are in good agreement with the available data. The ternaries are softer than the binaries. The calculated elastic constants show that the studied compounds satisfy the stability criteria and the binary compounds are more anisotropic than the ternaries. The elastic moduli and the Debye temperature of polycrystalline samples are also calculated, and the predicted Debye temperatures for the antimonide compounds are higher than those for the bismuthide ones. The calculated bandgaps are indirect with the top of the valence band at Γ, and they decrease in this order Li3Sb–Li2NaSb–Li3Bi– Li2NaBi.