Relating Local Structure to Thermoelectric Properties in Pb1–xGexBi2Te4

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 Bi2Te3and PbTe. Synchrotron X-ray diffraction and transmission electron microscopy revealed that PbBi2Te4adopts and maintains the R3̅mphase 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 R3̅mstructure. PbBi2Te4exhibits 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 GeBi2Te4alloying in PbBi2Te4(Pb1–xGexBi2Te4, where xranges 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–1when 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 PbBi2Te4at 473 K, demonstrating its potential as a near-room-temperature thermoelectric system.