Composite Transport Mechanism Enhancing Thermoelectric Performance Of Ag-Doped Mg3sb2

The first principle calculations are employed to investigate the Ag-doped Mg3Sb2. Comparing the formation energy and the bonds length between the Ag atom and its nearest Sb atoms, it is found that Ag atom is more favorable to substitute Mg atom in the anionic [Mg2Sb2](2?) layers. Comparing the electronic energy band structures between the un-doped and Ag-doped Mg3Sb2, the Femi level across the valence band through Ag doping. The double transport mechanism are induced by the doping, at low temperature, materials exhibit metallic properties, and when the temperature is higher than 422 K, the thermal excitation of electrons increases gradually, metallic and semiconductor transport mechanism coexist. As the temperature continue rising, the metallic conduction mechanism returns to dominant. The composite transport mechanism are verified in our calculations, and are found in temperature dependence of the electronic conduction and Seebeck coefficient. Our calculations explain the previous experiments.