Bismuth-telluride/iron-disilicide segmented thermoelectric elements: Patterning, preparation and properties

We report on the development of a stacked thermogenerator element consisting of Bi-Te based materials for the low temperature and FeSi2 for the high temperature stage. In order to determine the optimum segment length, a new numerical method was applied which maximizes the differential, i.e. local electrical power output. The resulting segment length for the Bi-Te stage is smaller than predicted by locally maximizing the figure of merit. For the practical preparation of the anticipated structure, powdered semiconductors and metals were consolidated by means of a uniaxial hot-pressing method, i.e. so-called plasma activated sintering (PAS). It was also employed in directly forming the material junctions. Due to the large differences in thermophysical and mechanical properties, Bi-Te and FeSi2 cannot be directly joined in a single processing step. We employed Ni as a suitable common interface material with intermediate coefficient of thermal expansion. The joint to the low yield strength FeSi2 requires however an additional layer, for which NiFe alloys were identified to be applicable. From the standpoint of electrical and thermal transport, all junctions exhibit reliable properties. Problems occur at the FeSi2 / NiFe interface under high atmospheric temperatures due to the development of corrosion products and mechanical mismatch of the reaction layer.