Improvement of Low‐Temperature zT in a Mg3Sb2–Mg3Bi2 Solid Solution via Mg‐Vapor Annealing

Materials with high zT over a wide temperature range are essential for thermoelectric applications. n‐Type Mg3Sb2‐based compounds have been shown to achieve high zT at 700 K, but their performance at low temperatures (30 mm has a zT 0.8 at 300 K, which is comparable to commercial thermoelectric materials used at room temperature (n‐type Bi2Te3) while reaching zT 1.4 at 700 K, allowing applications over a wider temperature scale. By developing a novel annealing technique in Mg vapor, the high‐resistance grain boundaries of Mg3Sb1.49Bi0.5Te0.01 can be effectively eliminated. This increases the room‐temperature thermoelectric figure of merit, zT, from 0.3 to 0.8, making it the first real competitor to state‐of‐the‐art Bi2Te3‐based n‐type thermoelectric materials.