No abstract

No abstract

We simultaneously measured the Seebeck coefficient and thermal diffusivity of a rectangular parallelepiped bulk thermoelectric material. We used one-dimensional heat conduction equation to show that a periodic heat cycle produces not only the thermoelectromotive force but also a certain phase shift angle between the edge and intermediate points of a sample along the length of the material. Based on the equation of the modified Angström method, an experiment at 300 K was performed using NIST standard material (SRM 3451, Bi2Te3 material) to measure the Seebeck coefficient and thermal diffusivity. The measured Seebeck coefficient was −231 ± 3 µV/K, which corresponds to the published value. Using the same experimental setup as that for the thermal diffusivity measurement, the dependence of the phase shift angle on frequency was measured from 5 mHz to 10 Hz for the phase shift angle from −8.2 to −450°. The estimated thermal diffusivity was (1.53 ± 0.05) × 10−6 m2/s. We conclude that the modified Angström method can be used to measure the Seebeck coefficient and thermal diffusivity simultaneously.

The thermal diffusivity of two bulk thermoelectric elements and a thermoelectric module was measured by an infrared camera using a thermographic method without any contact in air at room temperature. The estimated values for the elements (3.45 × 10−6 m2/s for a BiSb sample and 1.60 × 10−6 m2/s for a BiTe sample) were slightly larger than those measured in vacuum. The difference was explained as the effect of heat convection on the surface of the samples by solving the one-dimensional heat conduction equation numerically. The thermal diffusivity of thermoelectric elements in a thermoelectric module was also estimated using the thermographic method, and values of (1.1–1.7) × 10−6 m2/s in air were obtained, depending on the element. On the basis of the measurement results, the performance of the module was estimated using impedance spectroscopy, which can estimate not only the dimensionless figure of merit but also the thermal loss and response. The thermal response and thermal loss in air were similar to those in vacuum; however, the dimensionless figure of merit was 0.82 in vacuum and 0.70 in air.

No abstract