High Thermoelectric Performance in the Wide Band-Gap AgGa1- xTe2 Compounds

Directional Negative Thermal Expansion and Intrinsically Low Thermal Conductivity

Xianli Su, Na Zhao, Shiqiang Hao, Constantinos C. Stoumpos, Mengyuan Liu, Haijie Chen, Hongyao Xie, Qingjie Zhang, Chris Wolverton, Xinfeng Tang, Mercouri G Kanatzidis

Research output: Contribution to journalArticle

Abstract

A deficiency of Ga in wide band-gap AgGa1- xTe2 semiconductors (1.2 eV) can be used to optimize the electrical transport properties and reduce the thermal conductivity to achieve ZT > 1 at 873 K. First-principles density functional theory calculations and a Boson peak observed in the low temperature heat capacity data indicate the presence of strong coupling between optical phonons with low frequency and heat carrying acoustical phonons, resulting in a depressed maximum of Debye frequency in the first Brillouin zone and low phonon velocities. Moreover, the AgTe bond lengths and TeAgTe bond angles increase with rising temperature, leading to a significant distortion of the [AgTe4]7− tetrahedra, but an almost unmodified [GaTe4]5− tetrahedra. This behavior results in lattice expansion in the ab-plane and contraction along the c-axis, corresponding to the positive and negative Gruneisen parameters in the phonon spectral calculations. This effect gives rise to the large anharmonic behavior of the lattice. These factors together with the low frequency vibrations of Ag and Te atoms in the structure lead to an ultralow thermal conductivity of 0.18 W m−1 K−1 at 873 K.

Original languageEnglish
Article number1806534
JournalAdvanced Functional Materials
DOIs
Publication statusAccepted/In press - Jan 1 2018

Fingerprint

Phonons
tetrahedrons
thermal expansion
Thermal conductivity
phonons
Energy gap
thermal conductivity
low frequencies
broadband
Bosons
Bond length
Brillouin zones
Transport properties
contraction
Specific heat
Density functional theory
bosons
transport properties
specific heat
Semiconductor materials

Keywords

  • directional negative thermal expansion
  • intrinsically low thermal conductivity
  • phonon spectrum
  • thermoelectric properties
  • vacancy

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics

Cite this

High Thermoelectric Performance in the Wide Band-Gap AgGa1- xTe2 Compounds : Directional Negative Thermal Expansion and Intrinsically Low Thermal Conductivity. / Su, Xianli; Zhao, Na; Hao, Shiqiang; Stoumpos, Constantinos C.; Liu, Mengyuan; Chen, Haijie; Xie, Hongyao; Zhang, Qingjie; Wolverton, Chris; Tang, Xinfeng; Kanatzidis, Mercouri G.

In: Advanced Functional Materials, 01.01.2018.

Research output: Contribution to journalArticle

Su, Xianli ; Zhao, Na ; Hao, Shiqiang ; Stoumpos, Constantinos C. ; Liu, Mengyuan ; Chen, Haijie ; Xie, Hongyao ; Zhang, Qingjie ; Wolverton, Chris ; Tang, Xinfeng ; Kanatzidis, Mercouri G. / High Thermoelectric Performance in the Wide Band-Gap AgGa1- xTe2 Compounds : Directional Negative Thermal Expansion and Intrinsically Low Thermal Conductivity. In: Advanced Functional Materials. 2018.
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abstract = "A deficiency of Ga in wide band-gap AgGa1- xTe2 semiconductors (1.2 eV) can be used to optimize the electrical transport properties and reduce the thermal conductivity to achieve ZT > 1 at 873 K. First-principles density functional theory calculations and a Boson peak observed in the low temperature heat capacity data indicate the presence of strong coupling between optical phonons with low frequency and heat carrying acoustical phonons, resulting in a depressed maximum of Debye frequency in the first Brillouin zone and low phonon velocities. Moreover, the AgTe bond lengths and TeAgTe bond angles increase with rising temperature, leading to a significant distortion of the [AgTe4]7− tetrahedra, but an almost unmodified [GaTe4]5− tetrahedra. This behavior results in lattice expansion in the ab-plane and contraction along the c-axis, corresponding to the positive and negative Gruneisen parameters in the phonon spectral calculations. This effect gives rise to the large anharmonic behavior of the lattice. These factors together with the low frequency vibrations of Ag and Te atoms in the structure lead to an ultralow thermal conductivity of 0.18 W m−1 K−1 at 873 K.",
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