Elastic constants of binary Mg compounds from first-principles calculations

Elastic constants (C_ij's) of 25 compounds in the Mg–X (X = As, Ba, Ca, Cd, Cu, Ga, Ge, La, Ni, P, Si, Sn, and Y) systems have been predicted by first-principles calculations with the generalized gradient approximation and compared with the available experimental data. Ductility and the type of bonding in these compounds are further analyzed based on their bulk modulus/shear modulus ratios (B/G), Cauchy pressures (C₁₂–C₄₄), and electronic structure calculations. It is found that MgNi₂ and MgCu₂ have very high elastic moduli. Mg compounds containing Si, Ge, Pb, Sn, and Y, based on their B/G ratios, are inferred as being brittle. A metallic bonding in MgCu₂ and a mixture of covalent/ionic bond character in Mg₂Si, as inferred from their electronic structures, further explain the corresponding mechanical properties of these compounds.