Heat Transfer in Energy Materials: Study Elucidates Basic Microscopic Mechanisms

NOMAD lab researchers recently shed light on the fundamental microscopic mechanisms that help tailor materials for thermal insulation. This development promotes ongoing efforts to improve energy efficiency and sustainability.

The role of heat transport is crucial in various scientific and industrial applications, such as catalysis, turbine technologies, and thermoelectric heat converters that convert waste heat into electricity.

In particular, in the context of energy saving and the development of sustainable technologies, materials with high thermal insulation capabilities are very important. These materials allow us to store and use heat that would otherwise be wasted. Therefore, improving the design of highly insulating materials is a major research objective to enable energy efficient applications.

However, despite the fact that the basic physical laws have been known for almost a century, it is not important to design strong thermal insulators. At the microscopic level, heat transfer in semiconductors and insulators has been understood in terms of the collective oscillation of atoms around equilibrium positions in the crystal lattice. These oscillations, called “phonons” in the field, involve large numbers of atoms in solid materials and therefore span large, almost macroscopic length and time scales.

In a recently added edition Physical examination B and Physical Review Letters, researchers from the NOMAD laboratory at the Fritz Haber Institute have advanced computational capabilities to calculate thermal conductivities without experimental input with unprecedented accuracy. They showed that for strong thermal insulators the above-mentioned phononic picture does not hold.

Using massive calculations on supercomputers from the Max Planck Society, the North German Supercomputing Alliance and the Jülich Supercomputing Center, they scanned more than 465 crystalline materials whose thermal conductivity had not yet been measured. In addition to finding 28 strong thermal insulators, six of which have very low thermal conductivity comparable to wood, this study sheds light on a hitherto generally overlooked mechanism that allows systematic reductions in thermal conductivity.

Dr. Florian Knoop (now Linköping University), first author of both publications, says: “We have observed the transient formation of defect structures that have a massive effect on atomic motion in a very short period of time.”

“Such effects are usually ignored in thermal conductivity modeling, because these defects are very short-lived and microscopically localized compared to conventional heat transfer scales, so they are assumed to be insignificant. However, calculations have shown that they affect low thermal conductivities,” adds the senior author of the research. , Dr. Christian Carbogno.

These insights may offer new opportunities for fine-tuning and designing thermal insulators at the nanoscale through defect engineering, contributing to advances in energy-efficient technology.