What factors affect the thermal conductivity of solids?

[Niles]

Hi all

Am I correct to say that - in general - the thermal conductivity of metals is higher than that of semiconductors, because metals have more free electrons to help conduct the heat?

And is it correct that phonon-contribution to heat conductivy is more or less the same for all solids, regardless of the solid being an insulator, semiconductor or metal?

 

[Bob S]

Here is a list of the thermal conductivity of various metals and insulators:
http://en.wikipedia.org/wiki/List_of_thermal_conductivities
Note in particular that the thermal conductivity of beryllium oxide (an insulator) is better than brass (a metal).
Bob S

 

[kanato]

The phonon contribution to thermal conductivity can definitely vary. IIRC the relation involves the group velocity of the phonons which is usually quite large in systems with light atoms like beryllium oxide or strong bonds like diamond. Carbon is a good example of how changes in phonon and electronic structure change the thermal conductivity. Diamond (insulating carbon) is about 2000, but graphite (conducting carbon) is about 50-250.

The general trend that you mention is true; electrons often dominate the thermal conductivity, which you notice from the table if you ignore the few exceptional insulating materials. But it's good to remember that there are some interesting exceptions.