Relating Local Structure to Thermoelectric Properties in Pb<sub>1–<i>x</i></sub>Ge<sub><i>x</i></sub>Bi<sub>2</sub>Te<sub>4</sub>
Jinfeng Dong, Yukun Liu, Jue Liu, Lei Hu, Yilin Jiang, Xian Yi Tan, Yuansheng Shi, Dongwang Yang, Kıvanç Sağlık, Ady Suwardi, Qian Li, Jing‐Feng Li, Vinayak P. Dravid, Qingyu Yan, Mercouri G. Kanatzidis
Abstract
Layered compounds have garnered widespread interest owing to their nontrivial physical properties, particularly their potential as thermoelectric materials. We systematically investigated PbBi 2 Te 4, a compound derived from Bi 2 Te 3 and PbTe. Synchrotron X-ray diffraction and transmission electron microscopy revealed that PbBi 2 Te 4 adopts and maintains the R 3̅ m 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 R 3̅ m structure. PbBi 2 Te 4 exhibits a negative Seebeck coefficient, indicating electron-dominated transport. It has a low lattice thermal conductivity (ca. 0.6 Wm –1 K –1 ) and a ZT value of 0.4 at 573 K. The effects of GeBi 2 Te 4 alloying in PbBi 2 Te 4 (Pb 1– x Ge x Bi 2 Te 4, 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 Ge 2+, the room-temperature lattice thermal conductivity decreased to 0.55 Wm –1 K –1 when x = 0.5. Combined with a maintained weighted mobility (ca. 60 cm 2 V –1 s –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 PbBi 2 Te 4 at 473 K, demonstrating its potential as a near-room-temperature thermoelectric system.