Exploratory Study of Substitutional Elements in Mg2Si for Inducing State of Negative Chemical Pressure

First-principles calculations were used to investigate the effects of substituting a Mg atom in Mg2Si with a foreign atom. The aim was to chemically induce a state of negative pressure for Mg2Si, which would theoretically increase its thermoelectric power factor. First, density of states (DOS) calculations were performed for Mg2Si with a Mg atom substituted with Group 3-12 elements (Sc to Zn). The results suggest that Group 3 and 4 elements are good candidates because the main features of the DOS curves for the substituted Mg2Si were the same as that of the undoped semiconductor. Structural optimization and energy calculations were then performed for Mg2Si substituted with Sc, Y, La, Ti, Z, and Hf. Only Sc and Y showed negative energy changes as a result of the substitutional reaction. The volume changes indicate that only Y is an appropriate substitutional element for inducing a state of negative pressure for Mg2Si.