Thermoelectrics and Energy Materials

The discovery of the new class of coinage metal polychalcogenide halides uncovered a new set of materials with promising properties. An extremely low thermal diffusivity in combination with high mobility and redox activity of structure units in the solid state are common features of this compounds. A linear and mobile chalcogen chain is responsible for a reversible switching of the electric properties from a p-conducting via an n-conducting state back to p-conduction by a simple change of temperature in one compound. Such a reversible redox-reaction (formation and breaking of covalently-bonded Te dumbells) within the chalcogenide substructure can have a certain impact in data storage applications due to its local resistivity switch in the sub-nano regime. The high mobility of the coinage metal and the polychalcogenide substructure lead to an highly efficient scattering of phonons and therefore an extremely low thermal diffusivity and thermal conductivity. Some compounds reach the thermal conductivity of nanostructured materials and superlattices known to be the best available thermoelectrics at the moment. Our activities will be focused on the optimization of the thermoelectric properties to challenge the problems in energy production in the future. There are still major aspects in terms of the efficiency and the stability of thermoelectrics, especially in bulk samples without nano-structuring, which need to be solved soon.