Probing Efficient N-Type Lanthanide Dopants for Mg3Sb2 Thermoelectrics.

The recent discovery of n-type Mg3Sb2 thermoelectrics has ignited intensive research activities on searching for potential n-type dopants for this material. Using first-principles defect calculations, here, a systematic computational screening of potential efficient n-type lanthanide dopants is conducted for Mg3Sb2. In addition to La, Ce, Pr, and Tm, it is found that high electron concentration (≳1020 cm-3 at the growth temperature of 900 K) can be achieved by doping on the Mg sites with Nd, Gd, Ho, and Lu, which are generally more efficient than other lanthanide dopants and the anion-site dopant Te. Experimentally, Nd and Tm are confirmed as effective n-type dopants for Mg3Sb2 since doping with Nd and Tm shows higher electron concentration and thermoelectric figure of merit zT than doping with Te. Through codoping with Nd (Tm) and Te, simultaneous power factor improvement and thermal conductivity reduction are achieved. As a result, high zT values of ≈1.65 and ≈1.75 at 775 K are obtained in n-type Mg3.5Nd0.04Sb1.97Te0.03 and Mg3.5Tm0.03Sb1.97Te0.03, respectively, which are among the highest values for n-type Mg3Sb2 without alloying with Mg3Bi2. This work sheds light on exploring promising n-type dopants for the design of Mg3Sb2 thermoelectrics.