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Complex Materials

Dumbbell Rattling and Nanostructured Thermoelectrics


Investigations have been undertaken into the behaviour of Zn4Sb3 thermoelectric materials using inelastic neutron scattering and specific heat measurements, with the aim of establishing the connection between lattice dynamics and thermal transport properties. Our measurements reveal the dumbbell rattling behaviour of Sb dimers. The thermal conductivity obtained from the line-broadening observed in inelastic neutron scattering is in very good agreement with earlier thermal transport measurements.

Following the suggestion that phonon and electron confinement effects could lead to a substantial enhancement of thermoelectric properties in nanostructured materials, we aim to pursue our research on different materials, including, for example, Zn4Sb3, Bi2Te3, in order to achieve a better understanding of phonon transport on the nanoscale.

Raphaël Hermann, Werner Schweika


Guest Tunneling and Rattling in Thermoelectric Materials


Materials for thermoelectric applications typically have large and complex unit cells that favour low lattice thermal conductivity. A prominent feature in the lattice dynamics of such materials is the existence of soft localized vibrational modes. Particularly in cage-like structures, the incoherent rattling of the atoms trapped in the cages gives rise to low energy Einstein modes. In more complex cages, the trapped guests may be located off-center and then exhibit fascinating translational quantum tunneling behavior. This allows for the highly unusual observation of the tunneling of heavy atoms in a crystalline material. Inelastic and quasi-elastic neutron scattering, nuclear resonance scattering and Mossbauer spectroscopy all offer insights into the dynamics of the trapped guests in the µeV to meV range.

Raphaël Hermann