Magnesium based Si-Ge alloys under pressure: DFT evolutionary search results

The search of minimal enthalpy structures of ternary magnesium alloys of different stoichiometry MgxSiyGez under pressure P ≤ 6 GPa has been performed using the software suite USPEX implementing the evolution algorithm combined with the density functional theory (DFT) approach. The evolutionary search has yielded new possible ternary compounds of the stoichiometries Mg₁₂Ge₃Si, Mg₆Ge₄Si₃, Mg₆Ge₃Si₄, Mg₆GeSi₃, Mg₄Ge₃Si₂, Mg₄Ge₃Si₂, Mg₄SiGe, and Mg₂GeSi, which have negative enthalpy of formation at pressures in the range of 0 to 10 GPa and which are not substitution solutions of Ge on Mg₂Si matrix (or Si on Mg₂Ge matrix). These compounds have metallic properties and formation enthalpies comparable to those of binary silicides Mg₂Si. Phonon spectra investigations indicate that only first five of them are stable showing no imaginary frequencies.