Dissemination of IT for the Promotion of Materials Science (DoITPoMS)



We have now gone over the foundation behind electrical and thermal conduction, as well as some of the more common applications. You should understand the role of electrons and phonons in thermal conduction, as well as how the interactions between them lead to changes in electrical conductivity with temperature. You should appreciate that metals have more heat transfer mechanisms than their non-metal counterparts, therefore explaining why they have higher thermal conductivity. Also, this TLP should have touched on some of the major applications of thermal and electrical conductors and insulators. Finally, the connections between thermal and electrical conductivity in metals have been made, including the Wiedemann-Franz Law.

To summarise the factors affecting conductivity:

  • Temperature – as temperature increases, the average energy per phonon increases, and by the umklapp scattering mechanism, thermal conductivity is decreased. Phonons also scatter electrons more.
  • Electron density (in metals) – if electrons are the conductors, more (valence) electrons usually leads to better conduction.
  • Alloying – interstitials scatter electrons, and decrease conductivity. Phase boundaries, impurities, dislocations, etc. decrease conductivity, even at low temperature.