Chemistry - Thermopower

The thermopower, thermoelectric power, or Seebeck coefficient of a material describes how it functions thermoelectrically.

The Seebeck coefficients, represented as $S$ , are non-linear, and depend on the conductors' absolute temperature, material, and molecular structure.

If the temperature difference between the two nodes of a thermocouple is small,

$T_2 = T_1 + \Delta T \,$

and a voltage ΔV is seen at the terminals, then the thermopower of the entire thermocouple is defined as:

$S_{AB} = S_B-S_A = \lim_{\Delta T \to 0} {\Delta V \over \Delta T}$

This can also be written in relation to the electric field $E$ and the temperature gradient $\nabla T$ , by the equation

$S = {E \over \left | \nabla T \right |}$

Superconductors have zero thermopower, and can be used to make thermocouples. This allows a direct measurement of the thermopower of the other material, since it is the thermopower of the entire thermocouple as well. In addition, a measurement of the Thompson coefficient, $μ$ , of a material can also yield the thermopower through the relation: $S = \int {\mu \over T} dT$

In semiconductors the sign of the thermopower is used to determine whether the charge carriers are electrons or holes.