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Origin of ultra-low thermal conductivity in n-type cubic bulk AgBiS2: Soft Ag vibrations and local structural distortion induced by Bi 6s2 lone pair

DOI: 10.1021/acs.chemmater.9b00001 DOI Help

Authors: Ekashmi Rathore (Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR)) , Rinkle Juneja (Indian Institute of Science,) , Sean P. Culver (Justus-Liebig-Universität Giessen) , Nicolὸ Minafra (Justus-Liebig-Universität Giessen) , Abhishek K. Singh (Indian Institute of Science) , Wolfgang Zeier (Justus-Liebig-Universität Giessen) , Kanishka Biswas (Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR))
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Chemistry Of Materials

State: Published (Approved)
Published: March 2019
Diamond Proposal Number(s): 17257

Abstract: Crystalline materials with ultralow thermal conductivity are essential for thermal barrier coating and thermoelectric energy conversion. Nontoxic n-type bulk cubic AgBiS2 exhibits exceptionally low lattice thermal conductivity (κlat) of 0.68-0.48 W/mK in the temperature range 298-820 K, which is near to the theoretical minimum (κmin). The low κlat is attributed to soft vibrations of predominantly Ag atoms and significant lattice anharmonicity due to local structural distortions along the [011] direction, arising due to the stereochemical activity of the 6s2 lone pair of Bi, as suggested by pair distribution function (PDF) analysis of the synchrotron X-ray scattering data. Low temperature heat capacity of AgBiS2 shows a broad hump due to the Ag-induced low energy Einstein modes as also suggested from phonon dispersion calculated by first principle density functional theory (DFT). Low energy optical phonons contributed by Ag and Bi strongly scatter heat carrying acoustic phonons, thereby decreasing the κlat to a low value. A maximum thermoelectric figure of merit of ~0.7 is attained at 820 K for bulk spark plasma sintered n-type AgBiS2.

Journal Keywords: Thermal conductivity; Phonons; Lattices; Oscillation; Chemical structure

Subject Areas: Materials, Chemistry, Energy

Instruments: I15-1-X-ray Pair Distribution Function (XPDF)

Added On: 05/03/2019 11:04

Discipline Tags:

Physical Chemistry Materials Science Energy Materials Quantum Materials Thermoelectrics Chemistry

Technical Tags:

Scattering Pair Distribution Function (PDF)