Relating Local Structure to Thermoelectric Properties in Pb1–xGexBi2Te4

Abstract

Layered compounds have garnered widespread interest owing to their nontrivial physical properties, particularly their potential as thermoelectric materials. We systematically investigated PbBi₂Te₄, a compound derived from Bi₂Te₃ and PbTe. Synchrotron X-ray diffraction and transmission electron microscopy revealed that PbBi₂Te₄ adopts and maintains the R3̅m phase from 300 to 723 K, without any phase transition. Moreover, neutron pair distribution function analysis confirmed that the short-range local structure was consistent with the high-symmetry R3̅m structure. PbBi₂Te₄ exhibits a negative Seebeck coefficient, indicating electron-dominated transport. It has a low lattice thermal conductivity (ca. 0.6 Wm^–1K^–1) and a ZT value of 0.4 at 573 K. The effects of GeBi₂Te₄ alloying in PbBi₂Te₄ (Pb_1–xGe_xBi₂Te₄, where x ranges from 0.0 to 0.6) were also investigated. Due to alloying-induced point defect scattering and the off-centering effects of Ge²⁺, the room-temperature lattice thermal conductivity decreased to 0.55 Wm^–1K^–1 when x = 0.5. Combined with a maintained weighted mobility (ca. 60 cm²V^–1s^–2), the room-temperature ZT increased to 0.28. This value could further increase to 0.65 with a reduction in lattice thermal conductivity to its lower-limit value. A high ZT of 1.0 is also predicted for pristine PbBi₂Te₄ at 473 K, demonstrating its potential as a near-room-temperature thermoelectric system.