Growth and transport properties of Mg3X2(X = Sb, Bi) single crystals

The discovery of high thermoelectric performance in n-type polycrystalline Mg-3(Sb,Bi)(2)-based Zintl compounds has ignited intensive research interest. However, some fundamental questions concerning the anisotropic transport properties and the origin of intrinsically low thermal conductivity are still elusive, requiring the investigation of single crystals. In this work, high-quality p-type Mg3Sb2 and Mg3Bi2 single crystals have been grown by using a self-flux method. The electrical resistivity rho of Mg3Bi2 single crystal displays an anisotropy with rho in-plane twice larger than out-of-plane. The low-temperature heat capacity and lattice thermal conductivity of Mg3Sb2 and Mg3Sb2 single crystals have been investigated by using the Debye-Callaway model, from which the existence of low-lying vibration mode could be concluded. Large Gruneisen parameters and strong anharmonicity are found responsible for the intrinsically low thermal conductivity. Moreover, grain boundary scattering does not contribute significantly to suppress the lattice thermal conductivity of polycrystalline Mg3Sb2. Our results provide in-sights into the intrinsic transport properties of Mg3X2 and could pave a way to realize enhanced thermoelectric performance in single-crystalline Mg3X2-based Zintl compounds. (C) 2018 Elsevier Ltd. All rights reserved.