Discordant nature of Cd in PbSe: Off-centering and core-shell nanoscale CdSe precipitates lead to high thermoelectric performance

Songting Cai, Shiqiang Hao, Zhong Zhen Luo, Xiang Li, Ido Hadar, Trevor P. Bailey, Xiaobing Hu, Ctirad Uher, Yan Yan Hu, Christopher Wolverton, Vinayak P. Dravid, Mercouri G. Kanatzidis

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Abstract

We report a novel hierarchical microstructure in the PbSe-CdSe system, which collectively contributes to significant enhancement in thermoelectric performance, with ZTave ∼ 0.83 across the 400-923 K temperature range, the highest reported for p-type, Te-free PbSe systems. We have investigated the local atomic structure as well as the microstructure of a series of PbSe-xCdSe materials, up to x = 10%. We find that the behavior of the Cd atoms in the octahedral rock salt sites is discordant and results in off-center displacement and distortion. Such off-centered Cd in the PbSe matrix creates (1) L-Σ electronic energy band convergence, (2) a flattened L band, both contributing to higher Seebeck coefficients, and (3) enhanced phonon scattering, which leads to lower thermal conductivity. These conclusions are supported by photoemission yield spectroscopy in air (PYSA), solid state 111Cd, 77Se NMR spectroscopy and DFT calculations. Above the solubility limit (>6%CdSe), we also observe endotaxial CdSe nano-precipitates with core-shell architecture formed in PbSe, whose size, distribution and structure gradually change with the Cd content. The nano-precipitates exhibit a zinc blende crystal structure and a tetrahedral shape with significant local strain, but are covered with a thin wurtzite layer along the precipitate/matrix interface, creating a core-shell structure embedded in PbSe. This newly discovered architecture causes a further reduction in lattice thermal conductivity. Moreover, potassium is found to be an effective p-type dopant in the PbSe-CdSe system, leading to an enhanced power factor, a maximum ZT of ∼1.4 at 923 K for Pb0.98K0.02Se-6%CdSe.

Original languageEnglish
Pages (from-to)200-211
Number of pages12
JournalEnergy and Environmental Science
Volume13
Issue number1
DOIs
Publication statusPublished - Jan 2020

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ASJC Scopus subject areas

  • Environmental Chemistry
  • Renewable Energy, Sustainability and the Environment
  • Nuclear Energy and Engineering
  • Pollution

Cite this

Cai, S., Hao, S., Luo, Z. Z., Li, X., Hadar, I., Bailey, T. P., Hu, X., Uher, C., Hu, Y. Y., Wolverton, C., Dravid, V. P., & Kanatzidis, M. G. (2020). Discordant nature of Cd in PbSe: Off-centering and core-shell nanoscale CdSe precipitates lead to high thermoelectric performance. Energy and Environmental Science, 13(1), 200-211. https://doi.org/10.1039/c9ee03087e