Thermoelectric figure of merit

Thermoelectric materials show the thermoelectric effect in a strong or convenient form.

The thermoelectric effect refers to phenomena by which either a temperature difference creates an electric potential or an electric potential creates a temperature difference. These phenomena are known more specifically as the Seebeck effect (converting temperature to current), Peltier effect (converting current to temperature), and Thomson effect (conductor heating/cooling). While all materials have a nonzero thermoelectric effect, in most materials it is too small to be useful. However, low-cost materials that have a sufficiently strong thermoelectric effect (and other required properties) could be used in applications including power generation and refrigeration. A commonly used thermoelectric material in such applications is bismuth telluride (Bi
2Te
3).

Thermoelectric materials are used in thermoelectric systems for cooling or heating in niche applications, and are being studied as a way to regenerate electricity from waste heat.

The usefulness of a material in thermoelectric systems is determined by the two factors device efficiency and power factor. These are determined by the material's electrical conductivity, thermal conductivity, Seebeck coefficient and behavior under changing temperatures.

The efficiency of a thermoelectric device for electricity generation is given by ${\displaystyle \eta }$, defined as

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