High temperature segmenting for increased specific output

Enhanced performance of thermoelectric modules can be obtained by operation over an extended temperature range and by segmenting the individual legs with different thermoelectric materials so that each is held in a temperature range over which it shows its highest figure of merit. A computer code has been developed to calculate the performance of thermoelectric couples with each leg containing up to three segments; using measured material properties this code has been used to calculate the geometry of the legs (ratio of areas and ratio of segment lengths) which yields optimum efficiency. Initial segmenting studies have been carried out between a variety of pairs of materials which have the potential for use in segmented legs. Special emphasis has been placed initially on bonding Zn/sub 4/Sb/sub 3/ to p-(Bi,Sb)/sub 2/(Te,Se)/sub 3/ using Fe as an interface barrier and measuring the properties of this bond, since this combination has potential for early use as the p leg in thermoelectric modules similar to the present bismuth-telluride-based modules manufactured and sold by Hi-Z but operating at higher temperature with an accompanying increase in efficiency. Also the zinc-antimony system of compounds has been studied in order to determine which has the best properties for thermoelectric use. Experimental results on these materials and on segmented legs are discussed.