Abstract
ABSTRACT The narrow-gap magnesium silicide semiconductor Mg2Si is a promising mid-temperature (600–900 K) thermoelectric material. It intrinsically possesses n-type conductivity, and n-type dopants are generally used for improving its thermoelectric performance; however, the synthesis of p-type Mg2Si is relatively difficult. In this work, the hole doping of Mg2Si with various impurity atoms is investigated by performing first principles calculations. It is found that the Ag-doped systems exhibit comparable formation energies ΔE calculated for different impurity sites (Mg, Si, and interstitial 4b ones), which may explain the experimental instability of their p-type conductivity. A similar phenomenon is observed for the systems incorporating alkali metals (Li, Na, and K) since their ΔE values determined for Mg (p-type) and 4b (n-type) sites are very close. Among boron group elements (Ga and B), Ga is found to be favorable for hole doping because it exhibits relatively small ΔE values for Si (p-type) sites. Furthermore, the interstitial insertion of Cl and F atoms into the crystal lattice leads to hole doping because of their high electronegativity.
Highlights
Thermoelectric generators that directly convert thermal energy into electric energy through the Seebeck effect can be potentially used for recovering waste heat energy to improve the energy efficiency of multiple applications, providing a possible solution to various environmental problems, such as global warming and limited energy resources.This article has been republished with minor changes
This table contains only the data obtained for the 2 Â 2 Â 2 cell incorporating an Ag atom, the values of a determined at other doping concentrations x are presented in Supplemental Material 1
These results show that the largest lattice constant was obtained for doping the 4b sites followed by the Si and Mg sites
Summary
Thermoelectric generators that directly convert thermal energy into electric energy through the Seebeck effect can be potentially used for recovering waste heat energy to improve the energy efficiency of multiple applications, providing a possible solution to various environmental problems, such as global warming and limited energy resources. According to the results of one experimental study [6], the Ag doping of Mg2Si results in p-type conductivity; the obtained systems exhibit the change in conductivity from p-type to n-type at temperatures above 650 K. This instability of p-type conductivity represents one of the obstacles to the successful development of Mg2Si-based thermoelectric power generators because the conventional thermoelectric modules have a π-shape structure consisting of both n-type and p-type semiconductors. The feasibility of achieving p-type conductivity through the interstitial insertion of impurities characterized by high electronegativity (F, Cl, and Br) has been evaluated
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