Analysis of Nanoprecipitates in a Na-Doped PbTe-SrTe Thermoelectric Material with a High Figure of Merit

Yoon Jun Kim, Li Dong Zhao, Mercouri G Kanatzidis, David N. Seidman

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

The dimensionless figure of merit, ZT, of bulk thermoelectric materials depends mainly on the transport properties of charge carriers and heat-carrying phonons. PbTe-4 mol % SrTe doped with 2 mol % Na (Pb0.94Na0.02Sr0.04Te) is a nanostructured material system that exhibits a ZT higher than 2. The precipitate size distribution of SrTe precipitates is believed to play a key role. This raises the question of whether its performance is limited by precipitate coarsening (Ostwald ripening) at elevated temperatures. Herein, we utilize an atom-probe tomography (APT) to study the number density and mean radii of precipitates in concert with partial radial distribution functions (RDFs) of individual atoms. We find that the SrTe precipitates actually contain oxygen: SrTe1-xOx. We correlate this information with the overall ZT performance, specifically focusing on the electrical and lattice thermal conductivities after isothermal heat treatments at 300 and 400 °C for 7 days, followed by furnace cooling. Comparison of the samples annealed at 400 and 300 °C demonstrates significant coarsening of SrTe1-xOx precipitates as well as strong segregation of oxygen impurities in the SrTe1-xOx precipitates. Additionally, on the basis of the partial RDFs, the Na dopant atoms cluster with other Na atoms as well as with Pb, Te, and Sr atoms; clustering depends strongly on the annealing temperature and concomitantly affects the overall ZT values. We found that the coarsening slightly increases the lattice thermal conductivity and also increases the electrical conductivity, thereby having little or even a beneficial effect on the ZT values. Importantly, these findings demonstrate that APT enables quantitative analyses in three dimensions of the PbTe-4 mol % SrTe samples in addition to correlation of their properties with the thermoelectric performance.

Original languageEnglish
Pages (from-to)21791-21797
Number of pages7
JournalACS Applied Materials and Interfaces
Volume9
Issue number26
DOIs
Publication statusPublished - Jul 5 2017

Fingerprint

Precipitates
Atoms
Coarsening
Distribution functions
Tomography
Thermal conductivity
Oxygen
Ostwald ripening
Phonons
Charge carriers
Nanostructured materials
Transport properties
Furnaces
Heat treatment
Doping (additives)
Annealing
Impurities
Cooling
Temperature

Keywords

  • atom-probe tomography
  • partial radial distribution functions
  • PbTe-SrTe
  • precipitate coarsening
  • thermoelectric materials

ASJC Scopus subject areas

  • Materials Science(all)

Cite this

Analysis of Nanoprecipitates in a Na-Doped PbTe-SrTe Thermoelectric Material with a High Figure of Merit. / Kim, Yoon Jun; Zhao, Li Dong; Kanatzidis, Mercouri G; Seidman, David N.

In: ACS Applied Materials and Interfaces, Vol. 9, No. 26, 05.07.2017, p. 21791-21797.

Research output: Contribution to journalArticle

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T1 - Analysis of Nanoprecipitates in a Na-Doped PbTe-SrTe Thermoelectric Material with a High Figure of Merit

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AU - Kanatzidis, Mercouri G

AU - Seidman, David N.

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AB - The dimensionless figure of merit, ZT, of bulk thermoelectric materials depends mainly on the transport properties of charge carriers and heat-carrying phonons. PbTe-4 mol % SrTe doped with 2 mol % Na (Pb0.94Na0.02Sr0.04Te) is a nanostructured material system that exhibits a ZT higher than 2. The precipitate size distribution of SrTe precipitates is believed to play a key role. This raises the question of whether its performance is limited by precipitate coarsening (Ostwald ripening) at elevated temperatures. Herein, we utilize an atom-probe tomography (APT) to study the number density and mean radii of precipitates in concert with partial radial distribution functions (RDFs) of individual atoms. We find that the SrTe precipitates actually contain oxygen: SrTe1-xOx. We correlate this information with the overall ZT performance, specifically focusing on the electrical and lattice thermal conductivities after isothermal heat treatments at 300 and 400 °C for 7 days, followed by furnace cooling. Comparison of the samples annealed at 400 and 300 °C demonstrates significant coarsening of SrTe1-xOx precipitates as well as strong segregation of oxygen impurities in the SrTe1-xOx precipitates. Additionally, on the basis of the partial RDFs, the Na dopant atoms cluster with other Na atoms as well as with Pb, Te, and Sr atoms; clustering depends strongly on the annealing temperature and concomitantly affects the overall ZT values. We found that the coarsening slightly increases the lattice thermal conductivity and also increases the electrical conductivity, thereby having little or even a beneficial effect on the ZT values. Importantly, these findings demonstrate that APT enables quantitative analyses in three dimensions of the PbTe-4 mol % SrTe samples in addition to correlation of their properties with the thermoelectric performance.

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