Enhancement of the thermoelectric figure of merit in p- and n-type Cu/Bi-Te/Cu composites |
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Authors: | Osamu Yamashita Hirotaka Odahara |
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Affiliation: | (1) Faculty of Engineering, Ehime University, Bunkyocho, Matsuyama 790-8577, Japan;(2) Present address: 5-5-44, Minamikasugaoka, Ibaraki, Osaka 567-0046, Japan |
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Abstract: | The resultant thermoelectric properties of welded Cu/Bi-Te/Cu composites were measured at 298 K as a function of relative
thickness x of Bi-Te compound by changing the interval s between two thermocouples and compared with those calculated as a function of x by treating it as an electrical and thermal circuit. These composites were prepared by welding with eutectic solder of Pb-Sn,
after one end surface of the as-grown p- and n-type Bi-Te ingots were plated with Ni. It was found that the observed ZT of composites has a local maximum at an optimum x even when s was changed, as in the case of Cu/Bi-Sb/Cu and Ni/Bi-Sb/Ni composites with various relative thicknesses. Appearance of a
local maximum in ZT is owing to the barrier thermo-emf generated by a sharp temperature drop at the interface between Bi-Te compound and copper.
It may be caused by the separation of non-equilibrium carriers at the interface between them. The observed maximum ZT values at 298 K of the p- and n-type composites reached surprisingly great values of 1.53 and 1.66 at x=0.98, which correspond to about twice as large as those of commercially utilized Bi-Te compounds. This enhancement of ZT is available for generators, but may be not utilizable as a Peltier module. The composite materials were thus found to be
utilizable as useful means of further increase in ZT of macroscopic bulk materials. |
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