Energetic consideration of the conduction type of Mg2Si doped with Cu, Ag, or Au using first-principle calculations

Highlights: ► Energetic consideration of Cu-, Ag-, and Au-doped Mg2Si has been performed using first-principle calculations. ► Cu will be inserted into 4b site of Mg2Si, resulting in making a p-type compound. ► Au will substitute Si of the Mg2Si lattice, resulting in making an n-type compound. ► Difference in number of sites to be substituted or inserted by Ag causes p-type conduction of Ag-doped Mg2Si. - Abstract: Electronic energy calculations of Cu-, Ag-, or Au-doped Mg2Si, expected thermoelectric energy conversion materials, have been performed using a density-functional theory assuming that doped elements will work as either (1), substitutional impurities of Mg or Si sites of the Mg2Si lattice, or (2), inserted impurities into its 4b sites. From the energetic point of view, it was found that Cu will be most favorably inserted into the 4b site of Mg2Si, resulting in making a p-type compound. Au will substitute Si of Mg2Si lattice to make an n-type compound. Ag will make both of an interstitial compound and a substitutional compound where Mg and Si are almost equally replaced, but the overall conduction type would be p-type. These predictions agrees well to the observed facts for Ag- and Au- doped Mg2Si but does not for Cu-doped Mg2Si, perhaps because of insufficient solubility of Cu into Mg2Si to compensate the n-type carriers of undoped Mg2Si.