ICT2014 Abstracts

Thermoelectric generators (TEG) consist of many thermocouples (pair of n- and p-type materials) which are switched electrically in series and thermally in parallel. During operation the materials are exposed to huge temperature gradients of sometimes several hundred Kelvin per centimetre and an electrical field. These factors can cause thermal degradation (Ludwig-Soret effect) and electromigration. Hitherto, influences on the thermoelectric properties have rarely been investigated, although module properties can significantly deteriorate, especially on a long-term scale. The applicability of new materials under specific thermal and electrical conditions can only be predicted knowing possible degradation effects. Therefore, a better understanding of the occurrent transport processes is essential for ensuring a successful development of future TEGs.

In the ongoing research project we intend to investigate segregation effects in thermoelectric materials caused by temperature gradients. Furthermore, local degradation due to interfacial reactions especially at contact surfaces is studied. For this reason, model systems of lead telluride (PbTe) films on different metal substrates (copper, iron) are produced and the chemical diffusion at varying temperatures is observed using Time of Flight-Secondary Ion Mass Spectrometry (ToF-SIMS). Sodium cobaltate (Na_xCoO₂) as a good sodium ion conductor is indicating a high tendency to segregation. By applying temperature gradients parallel to the layered structure of the samples, enrichment as well as depletion of sodium ions along the gradient should be observed.

Identifying materials whose thermoelectric properties diminish according to segregation effects as well as materials which show long-term stability against temperature gradients and electric fields is crucial for a purposeful development and improvement of promising systems.