Point defect engineering and machinability in n-type Mg3Sb2-based materials

Approaching practical thermoelectric devices require high-performance and machinable thermoelectric materials . However, the currently available materials are usually brittle. In this work, Nd-doped Mg 3 Sb 2 -based compounds exhibit not only excellent thermoelectric performance but also superior machinability . Mg 3.2 Nd 0.03 Sb 1.5 Bi 0.5 exhibits a high power factor of 20.6 μW cm −1  K −2 at 725 K and a peak zT of 1.8, which mainly originates from the increased n of ~8 × 10 19  cm −3 by Nd/Mg substitutional defects. Defect calculations predict that other rare earth elements (Sm, Gd, Tb, Dy and Ho) have the same effect as Nd on Mg 3 Sb 2 and the predicted highest achievable electron concentrations at 700 K are ~10 20  cm −3 . The measured hardness, Young's modulus and fracture toughness of Mg 3.2 Nd 0.03 Sb 1.5 Bi 0.5 are 1.1 GPa, 49.8 GPa and 1.4 MPa m 1/2 , respectively. In addition, the sample can be easily machined into the dog-bone shape with external thread at both ends, indicating the excellent machinability of Mg 3 Sb 2 -based materials. This work suggests a bright future of Mg 3 Sb 2 -based thermoelectric materials for practical applications and device fabrication .