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

Research output: Contribution to journalArticlepeer-review

67 Scopus citations

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 (US)
Pages (from-to)200-211
Number of pages12
JournalEnergy and Environmental Science
Volume13
Issue number1
DOIs
StatePublished - Jan 2020

Funding

This work was primarily supported by the Department of Energy, Office of Science, Basic Energy Sciences under grant DE-SC0014520. This work made use of the EPIC facility of Northwestern University’s NUANCE Center, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205); the MRSEC program (NSF DMR-1720139) at the Materials Research Center; the International Institute for Nanotechnology (IIN); the Keck Foundation; and the State of Illinois, through the IIN. User Facilities are supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-06CH11357 and DE-AC02-05CH11231. Access to facilities of high performance computational resources at Northwestern University is acknowledged. PYSA measurements were carried out with equipment acquired by ONR grant N00014-18-1-2102. Y.-Y. Hu and X. Li acknowledge the support from the National Science Foundation (DMR-1847038). The solid-state NMR experiments were carried out at the NHMFL, which is supported by the National Science Foundation Cooperative Agreement (DMR-1644779) and the State of Florida. The research of T. P. B. and C. U. is supported by a grant from the U.S. Department of Energy under Award number DE-SC0018941.

ASJC Scopus subject areas

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

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