Computational model boost for thermoelectric materials ...

Computational work from the laboratory of Theory and Simulation of Materials (THEOS) has focused on fundamental theories for thermoelectric conversion for faster, more cost-effective discoveries of improved materials.

Thermoelectric generators (TEG) can convert waste heat into sustainable electricity. The technology is increasingly looked towards for enhancing the sustainability of various energy-intensive industries, from transportation to power plants and manufacturing.

However there is a lack of theory underpinning the heat conduction in materials with poor thermal conductivity. For a material to be useful in a thermoelectric device, it needs to have a low heat transfer, or thermal conductivity, and a high electrical conductivity. The greater the difference between the two, the better suited the material. Some materials are known to be good candidates, but material scientists must rely on expensive testing as the underlying physical principles remain elusive.

The computational model uses simulations and modeling techniques on supercomputers to unravel the fundamental physical principles governing thermoelectric material behaviour and heat conduction.

The EPFL team research focused on a class of crystals known as skutterudites, which have a unique cage-like atomic structure and are known to be promising materials for thermoelectric conversion. They increase their thermoelectric efficiency when supplementary atoms, referred to as “rattlers,” are added into the atomic cages.

This showed that filler atoms can drive a crossover from the Boltzmann to the Wigner regimes of thermal transport from particlelike conduction to wavelike tunneling. At temperatures where the thermoelectric efficiency of skutterudites is largest, wavelike tunneling can become comparable to particlelike propagation.

With the new model developed at EPFL, the researchers observed the expected significant reduction in heat transfer and predicted the phenomenon with extreme precision without the need for any empirical data.

“Unlocking the theoretical secrets of thermoelectric materials brings us one step closer to a greener, more sustainable future,” says Enrico Di Lucente, researcher at THEOS, in collaboration with Michele Simoncelli, now at Cambridge University, and Professor Nicola Marzari, head of THEOS and director of the NCCR MARVEL.

The major scientific advance comes from how the computational model also sheds light onto an unexpected quantic mechanism at play.

“We found, for the first time, that these rattler atoms cause a transition in how heat is conducted within the crystals, switching from particle-like conduction to wave-like tunnelling,” says Di Lucente.

The new computational model opens the door to designing novel materials with ultralow thermal conductivity without the need for costly empirical trials, bringing us an important step closer to creating a more energy efficient economy.