The Effect of Resonant Energy Levels on the Thermoelectric Power and Thermoelectric Power Factor

Authored by: Joseph P. Heremans

Thermoelectrics and its Energy Harvesting

Print publication date:  April  2012
Online publication date:  April  2016

Print ISBN: 9781439874707
eBook ISBN: 9781439874714
Adobe ISBN:

10.1201/b11891-14

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Abstract

Most of the recent work aimed at increasing the thermoelectric (TE) figure of merit zT of modern materials has focused on reducing the lattice thermal conductivity using phonon scattering mechanisms, such as nanostructures or localized phonon modes. This approach has been very successful, leading to a ­doubling of zT, but further progress along these lines promises to come more slowly: Slack1 teaches us that the phonon conductivity is limited in most bulk systems to what is known as the amorphous limit, that is, where the phonon mean free path is of the order of one interatomic distance. Comparatively less research effort has been aimed at increasing the thermoelectric power factor P = S2σ, where S denotes the thermopower or Seebeck coefficient and σ the electrical conductivity. The quantity that needs optimization here is more specifically the product (S2n), where n is the charge carrier concentration, because in doped semiconductors and metals, the thermopower S(n) decreases with increasing n, a relation attributed to Pisarenko2 and illustrated for p-type PbTe at room temperature as a full line in Figure 12.1. Combined with the electrical conductivity which is given to the first order by 12.1 σ=nqμ

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