First principles study of Mg₂X (X=Si, Ge, Sn, Pb): elastic, optoelectronic and thermoelectric properties

Abstract Full potential linearized augmented plane wave method within the framework of density functional theory was applied to calculate the structural, elastic, electronic, thermoelectric and optical properties of Mg₂X (X=Si, Ge, Sn, Pb) compounds. Exchange-correlation effects were treated using generalized gradient approximation and modified Becke-Johnson technique. Calculated structural parameters were found in good agreement to the experimental data. With the pressure application, the lattice constant decreased while the bulk modulus increased. Brittleness and ductility of these compounds were interpreted via the calculated elastic constants. The optical properties like complex dielectric function, refractive index, reflectivity, and optical conductivity were investigated in the pressure range 0-10 GPa. Very high reflectivity in a wide energy range indicates the usefulness of these materials as a shield from high energy radiations. In addition, the thermopower of the materials was calculated as a function of the chemical potential at various temperatures. These materials are suitable for applications in optoelectronic and thermoelectric devices due to their high thermopower and narrow bandgap.