Enhancing the thermoelectric power factor of Mg3Sb2 with Sn doping on electronegative sites of Sb: Effects of reducing the electronegativity difference

The weighted mobility is a better descriptor of the optimal performance of electronic transport for thermoelectric materials. The smaller the electronegativity difference between two atoms, the more covalent the bonding character between these two atoms. A series of p-type Sn-doped Mg3Sb2 was prepared by mixing and grinding Mg, Sb, and wet chemically synthesized Sn powders, followed by cold pressing and heating in an evacuated-and -encapsulated ampoule at 500 degrees C. Both the electronic and thermal transport of p-Mg3Sb2-xSnx (x = 0, 0.02, 0.04, and 0.06) are investigated at temperatures ranging from 325 to 700 K. Sn doping on the electronegative Sb site lowered the electrical resistivity to 161 m Omega-cm at 325 K for x = 0.04, which is 91% lower than the pristine Mg3Sb2. The power factor is enhanced upon Sn doping as a result of increased weighted mobility peaking at x = 0.04. The highest power factor of the Mg3Sb1.96Sn0.04 alloy is 2.55 mu W/cm-K-2 having 16 times enhancement as compared to the pristine Mg3Sb2 at 700 K. As a result, Mg3Sb1.96Sn0.04 has a maximum zT of similar to 0.30 at 700 K. The strategy of reducing the difference of electronegativity between electropositive cations and electronegative an-ions by partial replacement of Sn on electronegative Sb site is effective to increase the weighted mobility and hence enhance the power factor of p-Mg3Sb2.