Origins of three‐dimensional charge and two‐dimensional phonon transports in <i>Pnma</i> phase <scp>PbSnSe<sub>2</sub></scp> thermoelectric crystal
Tianyu Wang, Xinlei Duan, Hao Zhang, Jinlong Ma, Hangtian Zhu, Xin Qian, Jia‐Yue Yang, Te‐Huan Liu, Ronggui Yang
Abstract
Abstract Recently, PbSnSe 2 alloy was found to exhibit a large hysteresis effect on transport properties, demonstrating its significant potential for thermoelectric applications. Using ab initio approaches, we studied the carrier transport properties of PbSnSe 2 crystal, which is a special case of the alloy with the shortest‐range order. A peak power factor of 134.2 μW cm −1 K −2 was found along the cross‐plane direction in the n ‐type PbSnSe 2 at a doping concentration of 7 × 10 20 cm −3 at 700 K. This high power factor originates from delocalized p electrons between intra‐plane Pb–Se pairs and between cross‐plane Sn–Se pairs that can build up transport channels for conducting electrons, leading to a high electrical conductivity of 5.9 × 10 5 S m −1 . Introducing Pb atoms into Pnma phase SnSe can decrease the phonon group velocities and enhance the phonon–phonon scatterings, leading to a low thermal conductivity of 0.53 W m −1 K −1 at 700 K along the cross‐plane direction. The calculated peak ZT of ~3 along the cross‐plane direction at an n ‐type doping concentration of around 5 × 10 19 cm −3 , which represents a theoretical upper limit for an idealized PbSnSe 2 crystal. This work interprets the origins of three‐dimensional charge and two‐dimensional phonon transport behavior in PbSnSe 2 and demonstrates that such crystals are promising high‐performance thermoelectric semiconductors.