Abstract
The transverse thermoelectric effect is generally found in a material system with anisotropic electrical/thermal properties. Herein, we reported a simple way of forming thermoelectric anisotropy in a single piece of Bi-Sb-Te compound by partially doping of Ag elements. A transverse Seebeck effect is experimentally observed on the asymmetrically doped Bi-Sb-Te pellet. We show that the optimized aspect ratio of the pellet (length/thickness = 2.6) for maximum transverse Seebeck performance is associated with the distribution of eddy thermoelectric current in the pellet according to the FlexPDE simulation results, and the simulated results indicated that the optimized aspect ratio is proportional to the difference of Seebeck coefficient at the two regions. Besides, a potential redistributor was applied on the non-uniform Bi-Sb-Te pellet to enhance the transverse Seebeck voltage, which raises the effective Seebeck coefficient from 105 to 216 μV/K at the cold side. A two-dimensional distribution of electrical potential and temperatures in the pellet is modeled numerically. The size dependence of thermoelectric power and electrical resistance for the asymmetrically doped Bi-Sb-Te compounds is also investigated. The transverse modules made of the pellets with a dimension of length : thickness : electrode length = 2.6 : 1: 1.74 shows a maximum power density of 1150 W/m2 at a temperature difference of △T = 85℃. Finally, the electrical transport behavior of the non-uniform Bi-Sb-Te compounds is investigated, which shows an asymmetrical I-V characteristics when applying a current sweep through the gradient doped Bi-Sb-Te compound. The thermally induced voltage in the longitudinal direction of the gradient doped pellet is strongly dependent on the thermal isolation condition during the scanning Seebeck measurement. A numerical simulation analysis has been conducted to explain the abnormal Seebeck measurement results.