Improved figure of merit (z) at low temperatures for superior thermoelectric cooling in Mg(3)(Bi,Sb)(2)

The low-temperature thermoelectric performance of Bi-rich n-type Mg(3)(Bi,Sb)(2) was limited by the electron transport scattering at grain boundaries, while removing grain boundaries and bulk crystal growth of Mg-based Zintl phases are challenging due to the volatilities of elemental reactants and their severe corrosions to crucibles at elevated temperatures. Herein, for the first time, we reported a facile growth of coarse-grained Mg(3)Bi(2-x)Sb(x) crystals with an average grain size of ~800 μm, leading to a high carrier mobility of 210 cm(2) · V(−1) · s(−1) and a high z of 2.9 × 10(−3 )K(−1) at 300 K. A [Formula: see text] T of 68 K at T(h) of 300 K, and a power generation efficiency of 5.8% below 450 K have been demonstrated for Mg(3)Bi(1.5)Sb(0.5)- and Mg(3)Bi(1.25)Sb(0.75)-based thermoelectric modules, respectively, which represent the cutting-edge advances in the near-room temperature thermoelectrics. In addition, the developed grain growth approach can be potentially extended to broad Zintl phases and other Mg-based alloys and compounds.