Enhancement of the generating power in Cu/Bi–Te/Cu composite thermoelectric devices

The voltage DV and electric current DI of the p- and n-type Cu/Bi–Te/Cu composite thermoelectric devices were measured as a function of DT for four regions of the intrinsic Bi–Te compound, Cu/Bi–Te and Bi–Te/Cu interfaces and Cu/Bi–Te/Cu composite using thermocouples set at intervals of s = 2 and 6 mm, where the lengths of Bi–Te compound and copper are 4 and 5 mm, respectively. DV and DI of all regions tended to increase linearly with an increase of DT. The resultant a was obtained from the relation DV/DT. The resultant a values of regions including the interface are much higher in absolute value than those of the intrinsic Bi–Te compounds, so that the barrier thermo- emf is found to occur in the forward-bias direction. It indicates that the barrier thermo-emf appears even in the semiconductor-metal junction, as in the case of the p–n junctions. The resultant a of Cu(TH)/Bi–Te interface rich in the heat flow increases with an increase of DT, while that of Bi–Te/Cu(TC) interface poor in the heat flow decreases with an increase of DT. The DT-dependence of a of the interfaces is entirely opposite at the hot and cold sides. As a result, the resultant a of the p- and n-type Cu/Bi–Te/Cu composites remained little varied with changes of DT, so that the present composites have a thermal stability superior to the intrinsic Bi–Te compounds.The generating powers DWBi-Te and DWCu/Bi-Te/Cu for the p- and n-type intrinsic Bi–Te compounds and Cu/Bi–Te/Cu composites increased parabolalically with an increase of DT, and the ratios of DWCu/Bi–Te/Cu to DWBi–Te reached great values of 1.41 and 1.45 for the p- and n-type composites, respectively. It was thus found that the enhancement in the resultant a of the composite materials results in a significant improvement in the conversion efficiency for generators