A comparison of the mixing thermodynamics of the antifluorite-structured Mg2Si1-xGex, Mg2Sn1-xGex and Mg2Si1-xSnx alloys from first principles

The mixing thermodynamics of the antifluorite-structured Mg2Si1-xGex is investigated using the first-principles calculations. We find that Mg2Si and Mg2Ge readily mix with each other leading to formation of a single-phase random solid solutions of Mg2Si1-xGex across the entire composition range from the temperature of about 50 K and above. At 0 K, Mg2Si1-xGex exhibits a weak energy preference toward local phase segregation into Mg2Si and Mg2Ge without forming any ordered patterns of Si and Ge atoms. Through a comparison with the mixing thermodynamics of Mg2Sn with Mg2Si or Mg2Ge, a small lattice misfit between Mg2Si and Mg2Ge of less than 1 % is responsible for the formation of stable Mg2Si1-xGex random solid solutions at such a low temperature. Besides their thermodynamic stability, our prediction reveals that the random solid solutions of Mg2Si1-xGex are dynamically and mechanically stable. These findings justify the uses of structural models of Mg2Si1-xGex, assuming a random distribution of Si and Ge atoms in the previous theoretical studies, and also provide an insight into the complete solubility of Mg2Ge in Mg2Si and vice versa at all temperature where the atomic diffusion is activated.

Automated summary

The mixing thermodynamics of antifluorite-structured Mg2Si1-xGex were investigated using first-principles calculations, revealing the ease of formation of single-phase random solid solutions of Mg2Si1-xGex from 50 K and above. At 0 K, there is a weak energy preference towards local phase segregation, while a small lattice misfit between Mg2Si and Mg2Ge contributes to the stable formation of Mg2Si1-xGex random solid solutions at low temperatures. These findings also suggest the thermodynamic and mechanical stability of these solid solutions, providing insight into the complete solubility of Mg2Ge in Mg2Si and vice versa at all temperatures where atomic diffusion is activated.