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The Origin of Ultralow Thermal Conductivity in InTe: Lone‐Pair‐Induced Anharmonic Rattling
Author(s) -
Jana Manoj K.,
Pal Koushik,
Waghmare Umesh V.,
Biswas Kanishka
Publication year - 2016
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201511737
Subject(s) - anharmonicity , phonon , condensed matter physics , thermal conductivity , thermoelectric effect , lone pair , materials science , thermoelectric materials , ionic bonding , chemistry , physics , thermodynamics , ion , molecule , composite material , organic chemistry
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 + In 3+ Te 2 ), 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 5s 2 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.