α-Mg3Sb2 is an excellent thermoelectric material through excess-Mg addition and n-type impurity doping to overcome its persistent p-type behavior. It is generally believed that the role of excess-Mg is to compensate the single Mg vacancy to realize n-type carrier conduction. In contrary to this belief, the present work indicates that the role of excess-Mg is to compensate the electronic charge of defect complex (VMg(2) + MgI)1-. The Mg solubility in α-Mg3+xSb2 is quite small when only considering a single defect, but it enlarged up to x = 0.011 with the defect complex (VMg(2) + MgI)1-, which is more reasonable as supported by experiments. Under Mg-poor conditions, VMg(1)2- and VMg(2)2- are the dominant defects, and their concentrations can reach (1.05-1.18) × 1019 cm-3 at 1200 K. Under Mg-rich conditions, (VMg(2) + MgI)1- is found to be the dominant reason for strong p-type behavior, and their concentrations can reach as high as 3.5 × 1020 cm-3, which shifts the Fermi level closer to the valence band maximum. The predicted carrier concentrations in the range 1017-1020 cm-3 are in the same range found experimentally for pure p-type α-Mg3Sb2.
All Science Journal Classification (ASJC) codes
- Chemical Engineering (miscellaneous)
- Energy Engineering and Power Technology
- Materials Chemistry
- Electrical and Electronic Engineering