The Technology of Discovery

6A Primer on the Underlying Physics in Thermoelectrics

Hsin Wang

Oak Ridge National Laboratory, Oak Ridge, Tennessee

6.1 Underlying Physics in Thermoelectric Materials

The discovery of the thermoelectric effect [1–3] was almost 200 years ago. Today, solid‐state refrigeration and power generation equipment use thermoelectric materials and devices. The history of the development of radioisotope thermoelectric generators presented in previous chapters shines a light on one of the outstanding achievements in thermoelectric technology. In addition, theories on thermoelectricity and the underlying physics have been improved over the past 60–70 years and are well documented. [4–10] This chapter presents a primer of the fundamental physics to help readers understand the essentials of past and current theories on thermoelectric materials related to RTGs.

All solid materials have charge carriers (electrons or holes), which are free to move when subjected to an internal or external potential field. Similarly, when a material, for example, a small bar, is subjected to a temperature gradient, the average energy of the free carriers at the hotter end of the bar increases, thus creating a carrier concentration gradient. However, the diffusion of the free carriers is counterbalanced by the development of an electric field, where the potential difference is known as Seebeck voltage. For a metal, the Seebeck coefficient, or thermal power, S is small, a few micro‐volts per K. Equation 6.1 defines ...