Understanding how heat travels through materials is important for a variety of technical applications. This includes thermoelectrics: materials that can generate electricity from the application of a temperature gradient, or vice versa.
A key requirement of a thermoelectric material is that it should achieve low thermal conductivity without compromising the electrical properties, limiting the flow of heat via lattice vibrations known as phonons.
In this study, published in Angewandte Chemie, the researchers from Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR) in Bangalore studied TlInTe2, a material with an incredibly low thermal conductivity. They hoped to understand what causes this, and use it to inform the design of new materials.
By using synchrotron X-ray Pair Distribution Function experiments (XPDF) and Inelastic Neutron Scattering (INS) measurements on MARI, they were able to study the structure and vibrations of the material as it underwent structural transitions at different temperatures.
Kanishka Biswas, an Associate Professor of JNCASR explains “fundamental understanding of the correlation between chemical bonding and lattice dynamics is extremely important to discover new low thermal conductive solids, which is possible here because of the excellent collaboration between JNCASR and ISIS."
They uncovered that the vibrations of weakly bound thallium (Tl) disrupts other vibrations as they travel through the lattice. This process, described as 'rattling', is why it has such a low thermal conductivity.
The INS results were the outcome of one of the first experiments to be done on MARI since it was upgraded. Beamline scientist David Voneshen explains; “I think it would have been almost impossible to see these results before the upgrade due to the rather absorbing sample and low energy of the Tl rattler."
The experimental time on MARI was funded through the neutron access program of Indian nanomission, Department of Science & Technology (DST), a five-year programme designed to develop collaborative links between ISIS, RAL and Indian researchers.
The full paper can be found online DOI: 10.1002/anie.202013923