Neutron scattering experiments performed at ORNL show that lead telluride exhibits a strong anharmonic coupling between its optical and acoustic lattice vibrations, with a drop in thermal conductivity resembling a waterfall in this data image.
Neutron analysis of the atomic dynamics behind thermal conductivity is helping scientists at the Department of Energy's Oak Ridge National Laboratory (ORNL) gain a deeper understanding of how thermoelectric materials work. The analysis could spur the development of a broader range of products with the capability to transform heat to electricity.

Researchers performed experiments at both of ORNL's neutron facilities - the Spallation Neutron Source (SNS) and the High Flux Isotope Reactor - to learn why the material lead telluride, which has a similar molecular structure to common table salt, has very low thermal conductivity, or heat loss - a property that makes lead telluride a compelling thermoelectric material.

"The microscopic origin of the low thermal conductivity is not well understood. Once we do understand it better we can design materials that perform better at converting heat to electricity," said Olivier Delaire, a researcher and Clifford Shull Fellow in ORNL's Neutron Sciences Directorate.

Delaire's research shows that an unusual coupling of microscopic vibrational modes, called phonons, is responsible for the disruption of the dynamics that transport the thermal energy in lead telluride.