| Institution: | 1. Center for Integrated Materials Research, Department of Chemistry and iNANO, Aarhus University, Langelandsgade 140, 8000 Aarhus, Denmark;2. Materials Dynamics Laboratory, RIKEN SPring-8 Center, Sayo, 679-5148 Hyogo, Japan
Precision Spectroscopy Division, SPring-8/JASRI, 1-1-1 Kouto, Sayo, 679-5198 Hyogo, Japan;3. Institut Laue Langevin, 71 avenue des Martyrs, 38042 Grenoble, France;4. Faculty of Pure and Applied Sciences and Tsukuba Research Center for Energy Materials Science (TREMS), University of Tsukuba, Tsukuba, 305-8571 Japan;5. Materials Dynamics Laboratory, RIKEN SPring-8 Center, Sayo, 679-5148 Hyogo, Japan |
| Abstract: | Loosely bonded (“rattling”) atoms with s2 lone pair electrons are usually associated with strong anharmonicity and unexpectedly low thermal conductivity, yet their detailed correlation remains largely unknown. Here we resolve this correlation in thermoelectric InTe by combining chemical bonding analysis, inelastic X-ray and neutron scattering, and first principles phonon calculations. We successfully probe soft low-lying transverse phonons dominated by large In1+ z-axis motions, and their giant anharmonicity. We show that the highly anharmonic phonons arise from the dynamic lone pair expression with unstable occupied antibonding states induced by the covalency between delocalized In1+ 5s2 lone pair electrons and Te 5p states. This work pinpoints the microscopic origin of strong anharmonicity driven by rattling atoms with stereochemical lone pair activity, important for designing efficient materials for thermoelectric energy conversion. |
