Design of lead telluride based thermoelectric materials through incorporation of lead sulfide inclusions or ligand stripping of nanosized building block

Derak James, Xu Lu, Alexander Chi Nguyen, Donald Morelli, Stephanie L. Brock

Research output: Contribution to journalArticle

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Abstract

Design of thermoelectric materials focuses on the optimization of several unfavorably coupled factors: electrical conductivity, Seebeck coefficient, and thermal conductivity. Recent work in thermoelectrics has focused on decreasing lattice thermal conductivity by nanostructuring thermoelectric materials, while recent work in photovoltaics has demonstrated ligand stripping as a means to increased electron mobility in thin films of nanoparticles. In the present work, these two features are combined. A multigram scale synthesis of dispersible, lead telluride nanocrystals (25-50 nm) is developed using hot-injection methods in common organic solvents. These nanocrystals (NCs) are ligand stripped with sulfide (PbTe-S) or iodide (PbTe-I) sources to result in p-type or n-type materials with large Seebeck coefficients at room temperature of 520 or -540 μV·K-1, respectively. Sequential stripping with sulfide and then iodide (PbTe-SI) resulted in a small Seebeck due to counter doping. PbTe-S and PbTe-SI are found to generate nanostructured composites by growth of lead sulfide nanocrystals (∼50-60 nm) in situ upon annealing. However, the electrical conductivities are low (-1) due to excess doping during the ligand stripping. Intentional formation of a nanocomposite (PbTe-PbS) is achieved by combining PbTe NCs with 4-6 nm diameter lead sulfide particles via mixing by incipient wetness with a target of 8 mol % lead sulfide. The resulting nanocomposite is n-type with a Seebeck coefficient of -160 μV·K-1 and an electrical conductivity of 42 S·cm-1 at room temperature. The lattice thermal conductivities of all materials at room temperature are substantially lower than those of bulk lead telluride (2.0 W m-1·K-1). However, thermoelectric figure of merit (ZT) values are low for all samples (maximum ZT = 0.03 for PbTe-PbS), attributed primarily to the low electrical conductivities. This work underscores the importance of developing new methods for augmenting electrical conductivity if nanoparticle assemblies are to be practically employed in thermoelectrics.

LanguageEnglish (US)
Pages4635-4644
Number of pages10
JournalJournal of Physical Chemistry C
Volume119
Issue number9
DOIs
StatePublished - Mar 5 2015

Profile

lead tellurides
lead sulfides
thermoelectric materials
stripping
Lead
Nanocrystals
Ligands
inclusions
Seebeck coefficient
nanocrystals
Seebeck effect
ligands
electrical resistivity
Thermal conductivity
thermal conductivity
International System of Units
Iodides
Sulfides
iodides
sulfides

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Electronic, Optical and Magnetic Materials
  • Surfaces, Coatings and Films
  • Energy(all)

Cite this

Design of lead telluride based thermoelectric materials through incorporation of lead sulfide inclusions or ligand stripping of nanosized building block. / James, Derak; Lu, Xu; Nguyen, Alexander Chi; Morelli, Donald; Brock, Stephanie L.

In: Journal of Physical Chemistry C, Vol. 119, No. 9, 05.03.2015, p. 4635-4644.

Research output: Contribution to journalArticle

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abstract = "Design of thermoelectric materials focuses on the optimization of several unfavorably coupled factors: electrical conductivity, Seebeck coefficient, and thermal conductivity. Recent work in thermoelectrics has focused on decreasing lattice thermal conductivity by nanostructuring thermoelectric materials, while recent work in photovoltaics has demonstrated ligand stripping as a means to increased electron mobility in thin films of nanoparticles. In the present work, these two features are combined. A multigram scale synthesis of dispersible, lead telluride nanocrystals (25-50 nm) is developed using hot-injection methods in common organic solvents. These nanocrystals (NCs) are ligand stripped with sulfide (PbTe-S) or iodide (PbTe-I) sources to result in p-type or n-type materials with large Seebeck coefficients at room temperature of 520 or -540 μV·K-1, respectively. Sequential stripping with sulfide and then iodide (PbTe-SI) resulted in a small Seebeck due to counter doping. PbTe-S and PbTe-SI are found to generate nanostructured composites by growth of lead sulfide nanocrystals (∼50-60 nm) in situ upon annealing. However, the electrical conductivities are low (-1) due to excess doping during the ligand stripping. Intentional formation of a nanocomposite (PbTe-PbS) is achieved by combining PbTe NCs with 4-6 nm diameter lead sulfide particles via mixing by incipient wetness with a target of 8 mol {\%} lead sulfide. The resulting nanocomposite is n-type with a Seebeck coefficient of -160 μV·K-1 and an electrical conductivity of 42 S·cm-1 at room temperature. The lattice thermal conductivities of all materials at room temperature are substantially lower than those of bulk lead telluride (2.0 W m-1·K-1). However, thermoelectric figure of merit (ZT) values are low for all samples (maximum ZT = 0.03 for PbTe-PbS), attributed primarily to the low electrical conductivities. This work underscores the importance of developing new methods for augmenting electrical conductivity if nanoparticle assemblies are to be practically employed in thermoelectrics.",
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