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Soft Phonon Modes Leading to Ultralow Thermal Conductivity and High Thermoelectric Performance in AgCuTe
Author(s) -
Roychowdhury Subhajit,
Jana Manoj K.,
Pan Jaysree,
Guin Satya N.,
Sanyal Dirtha,
Waghmare Umesh V.,
Biswas Kanishka
Publication year - 2018
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201801491
Subject(s) - thermal conductivity , phonon , thermoelectric effect , materials science , thermoelectric materials , condensed matter physics , thermal , engineering physics , optoelectronics , physics , composite material , thermodynamics
Crystalline solids with intrinsically low lattice thermal conductivity (κ L ) are crucial to realizing high‐performance thermoelectric (TE) materials. Herein, we show an ultralow κ L of 0.35 Wm −1 K −1 in AgCuTe, which has a remarkable TE figure‐of‐merit, zT of 1.6 at 670 K when alloyed with 10 mol % Se. First‐principles DFT calculation reveals several soft phonon modes in its room‐temperature hexagonal phase, which are also evident from low‐temperature heat‐capacity measurement. These phonon modes, dominated by Ag vibrations, soften further with temperature giving a dynamic cation disorder and driving the superionic transition. Intrinsic factors cause an ultralow κ L in the room‐temperature hexagonal phase, while the dynamic disorder of Ag/Cu cations leads to reduced phonon frequencies and mean free paths in the high‐temperature rocksalt phase. Despite the cation disorder at elevated temperatures, the crystalline conduits of the rigid anion sublattice give a high power factor.