Temperature dependence of the local Seebeck coefficient near the boundary in touching Cu/Bi–Te/Cu composites

The thermo-emf DV and temperature difference DT across the boundary were measured as functions of r and I for the touching p- and n-type Cu/Bi–Te/Cu composites composed of tBi–Te = 2.0 mm and tCu = 0.3 mm, where r is the distance from the boundary and I is a direct current producing DT which flows through two Peltier modules connected in series. The resultant Seebeck coefficient a across the boundary is obtained from the relation a = DV/DT. As a result, the resultant |a| of the touching pand n-type composites have a great local maximum value at r 0.03 mm and decrease rapidly with further increase of r to approach the intrinsic |aBi–Te|. The maximum resultant a of the p- and n-type composites reached great values of 1,043 and –1,187 lV/K at 303 K corresponding to I = 0.8 A and of 1,477 and –725 lV/K at 360 K corresponding to I = 2.0 A. Reflecting the temperature dependence of the intrinsic aBi–Te, the maximum a of the ptype composite increases with an increase of T, while that of the n-type one decrease with an increase of T. Surprisingly, the maximum a of the p- and n-type composites have great gradients of 8.36 and –7.15 lV/K2 in the range from 303 to 366 K, respectively, which are 21.8 and 134 times larger in absolute value than 0.383 and –0.0535 lV/K2 of the intrinsic p- and n-type aBi–Te, so that the maximum resultant a was thus found to be much more sensitive to temperature than the intrinsic aBi–Te. Moreover, the local Seebeck coefficient al(r) derived analytically from the resultant a(r) is enhanced significantly in the narrow region below r 0.05 mm and the maximum al values of the pand n-type composites were found to have extremely great values of approximately 1,800 lV/K at 360 K and –1,400 lV/K at 303 K, respectively, which are approximately 7.3 and 6.5 times higher in absolute value than the intrinsic p- and n-type aBi–Te at the corresponding temperatures.