The Origin of Ultralow Thermal Conductivity in InTe: Lone-Pair-Induced Anharmonic Rattling

Understanding the origin of intrinsically low thermal conductivity is fundamentally important to the development of high‐performance thermoelectric materials, which can convert waste‐heat into electricity. Herein, we report an ultralow lattice thermal conductivity (ca. 0.4 W m−1 K−1) in mixed valent...

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Bibliographic Details
Published in:Angewandte Chemie (International ed.) 2016-06, Vol.55 (27), p.7792-7796
Main Authors: Jana, Manoj K., Pal, Koushik, Waghmare, Umesh V., Biswas, Kanishka
Format: Article
Language:English
Subjects:
Conductivity
Heat conductivity
indium telluride
lone pairs
rattling
thermoelectrics
ultralow thermal conductivity
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Summary:Understanding the origin of intrinsically low thermal conductivity is fundamentally important to the development of high‐performance thermoelectric materials, which can convert waste‐heat into electricity. Herein, we report an ultralow lattice thermal conductivity (ca. 0.4 W m−1 K−1) in mixed valent InTe (that is, In+In3+Te2), which exhibits an intrinsic bonding asymmetry with coexistent covalent and ionic substructures. The phonon dispersion of InTe exhibits, along with low‐energy flat branches, weak instabilities associated with the rattling vibrations of In+ atoms along the columnar ionic substructure. These weakly unstable phonons originate from the 5s2 lone pair of the In+ atom and are strongly anharmonic, which scatter the heat‐carrying acoustic phonons through strong anharmonic phonon–phonon interactions, as evident in anomalously high mode Grüneisen parameters. A maximum thermoelectric figure of merit (z T) of about 0.9 is achieved at 600 K for the 0.3 mol % In‐deficient sample, making InTe a promising material for mid‐temperature thermoelectric applications. It's in the rattle: An ultralow lattice thermal conductivity (ca. 0.4 W m−1 K−1) is found in mixed‐valent InTe, which has an intrinsic bonding asymmetry with coexistent covalent and ionic substructures. The phonon dispersion of InTe reveals the rattling vibrations of In+ cations along the columnar ionic substructure, which are strongly anharmonic and scatter the heat‐carrying acoustic phonons through strong anharmonic phonon–phonon interactions.
ISSN:1433-7851
1521-3773
DOI:10.1002/anie.201511737