Thermoelectric clathrates for waste heat recovery

Silke Bühler-Paschen

Institute of Solid State Physics, Vienna University of Technology, 1040 Vienna, Austria

Intermetallic clathrates are fascinating solids that offer multiple opportunities for both fundamental science and applications. Their crystallographic structure – invented by nature and first found for gas hydrates in arctic ice – is stabilized by two different types of chemical bonding: An essentially covalently bonded cavity-forming framework (host) encapsulates atoms via much weaker, predominantly ionic bonding (guests). This leads to a partial decoupling of some of the degrees of freedom of the resulting solid. For instance, distinctly different branches in the phonon spectrum (Debye- and Einstein-like modes) may be associated with the host and guest, respectively. Such decoupling, and a controlled interaction via materials design, is of great interest for thermoelectric applications, where a combination of materials properties is required that can hardly be met by simple solids. In this project affordable and highly tunable clathrates with potential for large scale use in waste heat recovery are at focus. With various new approaches we aim at reaching a level of understanding of the composition – structure – property relationship that will enable us to tailor these materials to distinctly higher thermoelectric figures-of-merit than achieved before. We expect this project to move clathrates a big step forward on the value chain, and to pave the way for their application in thermoelectric generators.