Crystal Structure and Thermoelectric Properties of Pavonite Homologous Pb₄Sb12–xBi8+xSe₃₄

The Pb4Sb12–xBi8+xSe34 (x = 0, 1, 2, 3, 4, and 5) crystals belong to pavonite homologues composed of thick NaCl- and thin GeS-type slabs which crystallize in the C2/m space group. Pb4Sb12–xBi8+xSe34 compounds exhibit n-type semiconductor transport behavior and demonstrate excellent thermodynamic stability. These intrinsic compounds have high carrier concentrations of ∼2.18 × 1019 to 4.47 × 1020 cm–3, leading to high electrical conductivities. The two-band electronic structure results in a high Seebeck coefficient. Taking Pb4Sb9Bi11Se34 as an example, it has a remarkable Seebeck coefficient of −149.1 μV K–1 and high electrical conductivity of ∼118 S cm–1. It is comparable with other pavonite at 723 K. On the other hand, due to mixed occupancies of cation sites and complex crystal structure, the Pb4Sb9Bi11Se34 features ultralow lattice thermal conductivity of ∼0.25 W m–1 K–1 at 723 K. The high figure of merit, ZT, of 0.48 for Pb4Sb9Bi11Se34 is obtained at 723 K.