Electronic band engineering of Mg 2 Si by isoelectronic impurity doping: a first-principles study for enhancing thermoelectric properties

Previous theoretical studies have suggested novel approaches for enhancing the thermoelectric performance of Mg 2 Si, i.e. electronic band engineering based on tensile strain to enhance the Seebeck coefficient and electrical conductivity simultaneously. To realise this approach, we investigated the doping with isoelectronic impurities (Ca, Sr, and Ba) substituted at Mg sites. We performed variable-cell relaxation calculations for Ca-doped, Sr-doped, and Ba-doped systems using first-principles calculations. The results showed that doping with Ca made the lowest and next-lowest conduction bands approach each other, which is advantageous for enhancing thermoelectric properties. Thermoelectric calculations showed that the distribution of Ca atoms would have a crucial effect on thermoelectric properties. Although Ca doping did not improve the n -type power factor for any structures examined in the present study, the Seebeck coefficient increased for the p -type, especially for a certain structure at 300 and 600 K, resulting in an improved power factor.