The role of Cu in the thermoelectric transport properties of Mg3Sb2-based materials

Elemental doping plays a crucial role in optimizing carrier concentration and suppressing lattice thermal conductivity in thermoelectric materials. In this study, Cu atoms were doped in both n- and p-type Mg 3 Sb 2 -based thermoelectric compounds. The results indicate that the incorporation of Cu effectively improves the electrical transport properties of Mg 3 Sb 2 -based thermoelectric compounds while simultaneously suppressing their thermal transport, ultimately achieving enhanced thermoelectric properties: (a) For p-type Mg 3 Sb 2 , a small quantity of Cu atoms provides electrons in the lattice interstitial and thus compensates holes, leading to a decreased carrier concentration and electrical conductivity. However, with increasing Cu content, Cu atoms preferentially occupy Mg2 sites, thereby increasing hole concentration, and thus improving electrical conductivity. Further increasing Cu content, an MgCuSb secondary phase forms, which is unfavorable for overall p-type thermoelectric performance of the Mg 3 Sb 2 -based matrix due to the n-type transport of the MgCuSb compound. (b) For n-type Mg 3 Sb 2 , no such secondary phase was observed despite the same Cu-doping content, which involves a distinct doping mechanism from the p-type one. Consequently, the zT values of p-type Mg 3 Sb 2 materials are improved by 17%–33% over the whole temperature range. And regarding the n-type Mg 3 Sb 2 materials, the highest peak zT value of ~1.4 and average zT avg of ~1.04 are achieved. Therefore, the doping of the Cu element proves to be an effective way in optimizing thermoelectric properties of both p-type and n-type Mg 3 Sb 2 -based materials.