Thermoelectric properties of the welded Cu/Bi_0.88 Sb_0.12 /Cu composites in the temperature region from 193 K to 298 K

Abstract

The resultant thermoelectric properties of Cu/T/Cu composites welded with ${\hbox{T}=\hbox{Bi}_{0.88}\hbox{Sb}_{0.12}}$ alloy were measured in the temperature range from T = 193 K to 298 K and compared with those calculated as a function of x by treating these composites as an electrical and thermal circuit, where x is the ratio of thickness of Bi–Sb alloy to the interval between two thermocouples. Consequently, the resultant electrical resistivities ρ of composites coincided closely with the calculated ρ values as a function of x, while the resultant Seebeck coefficients α were enhanced significantly in the range from x=0.076 to 0.61. In the x range from 0.16 to 1.0, the x-dependence of the resultant thermoelectric power factor P was found to be explained roughly at every temperature by the simple model proposed here when an enhancement factor in α was taken into the calculation. However, the maximum resultant P appeared at a small x of 0.076. The resultant P at x = 0.076 increases with a decrease of T and reached a surprisingly great value of 128.3 mW/K² m at 193 K, which is 15.5 times larger than 8.29 mW/K² m obtained for Bi_0.88Sb_0.12 alloy. On the other hand, its resultant ZT also increases monotonically with a decrease of T and has a great value of 0.54 at 193 K, which is 31% higher than 0.41 at 193 K for Bi–Sb alloy. The significant enhancement in the resultants P and ZT at low temperatures is owing predominantly to the increase in α due to the boundary effect.