Crystal Structure and Thermoelectric Properties of Pavonite Homologous Pb₄Sb_12–xBi_8+xSe₃₄

Abstract

The Pb 4 Sb 12−x Bi 8+x Se 34 (x = 0, 1, 2, 3, 4, and 5) crystals belong to pavonite homologues composed of thick NaCland thin GeS-type slabs which crystallize in the C2/m space group. Pb 4 Sb 12−x Bi 8+x Se 34 compounds exhibit n-type semiconductor transport behavior and demonstrate excellent thermodynamic stability. These intrinsic compounds have high carrier concentrations of ∼2.18 × 10 19 to 4.47 × 10 20 cm −3 , leading to high electrical conductivities. The two-band electronic structure results in a high Seebeck coefficient. Taking Pb 4 Sb 9 Bi 11 Se 34 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 Pb 4 Sb 9 Bi 11 Se 34 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 Pb 4 Sb 9 Bi 11 Se 34 is obtained at 723 K.