Advanced research in thermoelectrics

C. Linseis1

1Linseis Messgeräte GmbH Selb, Germany

Keywords: Seebeck effect, laser flash
property: thermal conductivity, electric resistivity, thermal expansion
material: solids

Thermoelectricity is the study of the direct conversion between thermal and electrical energy through the Seebeck and Peltier effects. The Seebeck effect is used to supply power in thermolectric generators (TEG) for a couple of decades and is of current interest to automobile manufacturers to supply additional power through waste heat recovery. The Peltier effect can be used for electronic spot cooling of computer processors and has widely been used to thermally manage optoelectronic devices such as communication lasers and infra-red detectors. A more common use is in portable heaters/coolers that can be purchased inexpensively at many local stores.

While wider use of thermoelectrics in more mainstream applications holds great promise because of their high reliability, the low efficiency with which they operate has restricted their usage. Recently, there has been a resurgence of activity in this field to find novel materials that can operate with higher efficiency to provide alternative power generation options and competition with conventional refrigeration technology.

The efficiency of a thermoelectric material is directly related to the figure of merit ZT. The current state of the art thermoelectric materials have maximum ZT values of around 1 at their respective optimum temperatures. Although this value has been the maximum for over 40 years, there exist no theoretical reason for this to be the absolute limit. Several recent reports have indicated that much higher ZTs are possible both in thin film superlattices and in bulk materials. A ZT of 3 to 4 would indicate an efficiency great enough to allow direct competition with conventional refrigeration devices.

To enable advanced research in thermoelectrics, LINSEIS offers a complete range of instruments. The instruments available involve Seebeck and Electric Resistivity- LSR, Thermal Diffusivity and Thermal Conductivity- LFA, Thermal Expansion and Density- Dilatometer and Specific Heat- DSC. All these data can be measured with high accuracy and reproducibility in a broad temperature range. From these data the thermoelectric figure of merit ZT can be calculated to characterize thermoelectric materials.

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