Pressure-Induced Stable Binary Compounds of Magnesium and Germanium

Motivated by the possibility to obtain unusual stoichiometric compounds (e.g., Na-Cl and Mg-O systems) with exotic properties at high pressures, we systematically investigated the high-pressure structures and chemical bonding of Mg-Ge systems by using a structure-searching method and first-principles calculations. Compared with the stable composition of Mg₂ Ge at ambient pressure, several stoichiometries (e.g., Mg₃ Ge, MgGe, and MgGe₂ ) were predicted to be stable under high pressures. The Pm $$ m Mg₃ Ge structure consists of a 12-fold-coordinated face-sharing GeMg₁₂ cuboctahedron, whereas the P4/mmm MgGe and Cmcm MgGe₂ phases form MgGe₈ hexahedrons and MgGe₄ polygons, respectively. All the stable phases of Mg-Ge compounds under high pressures exhibit metallic features owing to overlap between the conduction and valence bands. For Cmcm MgGe₂ , the projected density of states near the Fermi energy mainly derive from Ge s, Ge p, and Ge d, which are responsible for its metallicity. The calculated superconducting critical temperature values of Cmcm Mg₂ Ge and P4/mmm MgGe reach 10.3 and 9.07 K at 5 GPa, respectively.