Valence disproportionation of GeS in the PbS matrix forms Pb₅Ge₅S₁₂ inclusions with conduction band alignment leading to high n-type thermoelectric performance

• Main Authors: Luo, Zhong-Zhen, Cai, Songting, Hao, Shiqiang, Bailey, Trevor P., Xie, Hongyao, Slade, Tyler J., Liu, Yukun, Luo, Yubo, Chen, Zixuan, Xu, Jianwei, Luo, Wenjun, Yu, Yan, Uher, Ctirad, Wolverton, Christopher, Dravid, Vinayak P., Zou, Zhigang, Yan, Qingyu, Kanatzidis, Mercouri G.
• Other Authors: School of Materials Science and Engineering
• Format: Article
• Language: English
• Published: 2022
• Subjects: Engineering::Materials; Thermoelectric Material; Thermoelectric Performance
• Online Access: https://hdl.handle.net/10356/161744
• Institution: Nanyang Technological University

Converting waste heat into useful electricity using solid-state thermoelectrics has a potential for enormous global energy savings. Lead chalcogenides are among the most prominent thermoelectric materials, whose performance decreases with an increase in chalcogen amounts (e.g., PbTe > PbSe > PbS). Herein, we demonstrate the simultaneous optimization of the electrical and thermal transport properties of PbS-based compounds by alloying with GeS. The addition of GeS triggers a complex cascade of beneficial events as follows: Ge2+ substitution in Pb2+ and discordant off-center behavior; formation of Pb5Ge5S12 as stable second-phase inclusions through valence disproportionation of Ge2+ to Ge0 and Ge4+. PbS and Pb5Ge5S12 exhibit good conduction band energy alignment that preserves the high electron mobility; the formation of Pb5Ge5S12 increases the electron carrier concentration by introducing S vacancies. Sb doping as the electron donor produces a large power factor and low lattice thermal conductivity (κlat) of ∼0.61 W m-1 K-1. The highest performance was obtained for the 14% GeS-alloyed samples, which exhibited an increased room-temperature electron mobility of ∼121 cm2 V-1 s-1 for 3 × 1019 cm-3 carrier density and a ZT of 1.32 at 923 K. This is ∼55% greater than the corresponding Sb-doped PbS sample and is one of the highest reported for the n-type PbS system. Moreover, the average ZT (ZTavg) of ∼0.76 from 400 to 923 K is the highest for PbS-based systems.