Enhancement of the thermoelectric power factor in Ag/Bi-Te/Ag composite devices

The resultant thermoelectric properties of the p- and n-type Ag/Bi-Te/Ag composite devices welded with pure Bi were measured at 298 K as a function of relative thickness of x, where x is the ratio of thickness of Bi-Te compound to the interval between two thermocouples and the chemical compositions of the p- and n-type Bi-Te compounds used here are (Bi0.25Sb0.75)2Te3 and Bi2(Te0.94Se0.06)3, respectively. Consequently, the electrical resistivities ρ of the p- and n-type Ag/Bi-Te/Ag devices increased linearly with an increase of x, while the Seebeck coefficients α were enhanced significantly in the range from x = 0.03 to 0.10, so that their observed P values have a large local maximum at x = 0.06. The x-dependence of P values was found to be explained roughly with the simple model proposed here when some reduction in the thermal conductivity κ of Ag and Bi was taken into the calculation. The maximum P of the p- and n-type Ag/Bi-Te/Ag devices reached extremely large values of 27.8 and 88.3 mW/K2m, which are higher than 25.7 mW/K2m obtained for the previous n-type Ni/Bi/Cu device. C 2006 Springer Science+Business Media, Inc