Origins of three‐dimensional charge and two‐dimensional phonon transports in Pnma phase PbSnSe2 thermoelectric crystal.

Recently, PbSnSe2 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 PbSnSe2 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 PbSnSe2 at a doping concentration of 7 × 1020 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 × 105 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 × 1019 cm−3, which represents a theoretical upper limit for an idealized PbSnSe2 crystal. This work interprets the origins of three‐dimensional charge and two‐dimensional phonon transport behavior in PbSnSe2 and demonstrates that such crystals are promising high‐performance thermoelectric semiconductors. [ABSTRACT FROM AUTHOR]