Thermal stability and elastic properties of Mg2X (X = Si, Ge, Sn, Pb) phases from first-principle calculations

Thermal stabilities, elastic properties and electronic structures of Mg2Si, Mg2Ge, Mg2Sn and Mg2Pb have been determined from first-principle calculations. The calculated heats of formation and cohesive energies show that Mg2Ge has the strongest alloying ability and Mg2Si has the highest structural stability. Gibbs free energy, heat capacity and Debye temperature are calculated and discussed. The elastic parameters are calculated, the bulk moduli, shear moduli, Young’s moduli and poisson ratio value are derived, the brittleness and plasticity of these phases are discussed, and the brittle behavior and structural stability mechanism are also explained through the densities of states (DOS) of these intermetallic compounds.

Predicted reduction of Gibbs free energy G/ and increase of heat capacity Cv of Mg2Si, Mg2Ge, Mg2Sn and Mg2Pb with the elevated temperature by the use of first-principle calculations.Figure optionsDownload as PowerPoint slideHighlights
► In this study we find that Mg2Ge has the strongest alloying ability and Mg2Si has the highest structural stability.
► The calculations of thermodynamic properties show that Gibbs free energy G’ of Mg2Si, Mg2Ge, Mg2Sn and Mg2Pb decreased, while heat capacity Cv increased with the elevated temperature.
► The calculated Debye temperature agrees well with the reported theoretical and experimental values.
► In this study we conclude that Mg2Si, Mg2Ge, Mg2Sn and Mg2Pb are all brittle, however, Mg2Pb is of good plasticity in the investigated compounds.