Origin of Ultralow Thermal Conductivity in n-Type Cubic Bulk AgBiS 2: Soft Ag Vibrations and Local Structural Distortion Induced by the Bi 6s 2 Lone Pair

Ekashmi Rathore, Rinkle Juneja, Sean P. Culver, Nicolò Minafra, Abhishek K. Singh, Wolfgang G. Zeier, Kanishka Biswas

Research output: Contribution to journalArticlepeer-review

87 Scopus citations

Abstract

Crystalline materials with ultralow thermal conductivity are essential for thermal barrier coating and thermoelectric energy conversion. Nontoxic n-type bulk cubic AgBiS 2 exhibits exceptionally low lattice thermal conductivity (ΰ lat ) of 0.68-0.48 W/m K in the temperature range of 298-820 K, which is near the theoretical minimum (ΰ min ). The low ΰ lat is attributed to soft vibrations of predominantly Ag atoms and significant lattice anharmonicity because of local structural distortions along the [011] direction, arising because of the stereochemical activity of the 6s 2 lone pair of Bi, as suggested by pair distribution function analysis of the synchrotron X-ray scattering data. The low-temperature heat capacity of AgBiS 2 shows a broad hump because of the Ag-induced low-energy Einstein modes as also suggested from phonon dispersion calculated by first-principle density functional theory. Low-energy optical phonons contributed by Ag and Bi strongly scatter heat-carrying acoustic phonons, thereby decreasing the ΰ lat to a low value. A maximum thermoelectric figure of merit of â0.7 is attained at 820 K for bulk spark plasma-sintered n-type AgBiS 2 .

Original languageEnglish
Pages (from-to)2106-2113
Number of pages8
JournalChemistry of Materials
Volume31
Issue number6
DOIs
StatePublished - Mar 26 2019
Externally publishedYes

Funding

K.B. and W.G.Z. thank the DST-DAAD project. E.R. thanks JNCASR for a fellowship. R.J. acknowledges INSPIRE, DST for a fellowship. R.J. and A.K.S. acknowledge the support from DST Nanomission. S.P.C. and W.G.Z. thank beamline I15-1 of Diamond Light Source (EE17257-1). S.C. and W.G.Z. acknowledge the support by the Deutsche Forschungsgemein-schaft (DFG) (ZE 1010/5-1). S.P.C. acknowledges the Postdoctoral Fellowship from the Alexander von Humboldt Foundation.

Fingerprint

Dive into the research topics of 'Origin of Ultralow Thermal Conductivity in n-Type Cubic Bulk AgBiS 2: Soft Ag Vibrations and Local Structural Distortion Induced by the Bi 6s 2 Lone Pair'. Together they form a unique fingerprint.

Cite this