thermoelectrics

Thermoelectrics refers to technologies that convert heat to electricity and vice versa using thermoelectric effects. The Seebeck effect generates voltage from a temperature difference; the Peltier effect transfers heat when electric current flows. The Thomson effect relates to heating or cooling in a conductor with a temperature gradient.

A device's efficiency is described by the figure of merit ZT = S^2 σ T / κ. S is the Seebeck coefficient, σ electrical conductivity, κ total thermal conductivity, and T absolute temperature. Higher ZT generally means higher efficiency, but ZT varies with temperature and material.

Materials aim for large S and σ while small κ. Bi2Te3-based alloys dominate near room temperature; PbTe, skutterudites, half-Heuslers, and other complex compounds are used at higher temperatures. Nanostructuring and crystal engineering reduce κ by scattering phonons.

Thermoelectric devices assemble p-type and n-type legs in modules to create generators or coolers. They have no moving parts, are quiet, and are robust, but efficiencies are limited by ZT and temperature range.

Applications include waste heat recovery in vehicles and industry, remote power sources, space missions, and thermal management of electronics. Challenges include material cost and scarcity, long-term reliability under thermal cycling, and achieving high ZT across broad temperatures.

History: The Seebeck effect was discovered in 1821; the Peltier effect in 1834. Advances in materials and nanostructuring in recent decades have raised ZT values, enabling practical devices.