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Thermal conductivity

by aaaa202
Tags: conductivity, thermal
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aaaa202
#1
Nov8-13, 03:20 AM
P: 1,005
For a nonmetal what determines thermal conductivity is the propagation of lattice vibrations. As T increases these lattice vibrations collide with each other more often. Does this mean that the thermal conductivity will de- or increase?
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DrDu
#2
Nov8-13, 03:52 AM
Sci Advisor
P: 3,555
What would you guess?
aaaa202
#3
Nov8-13, 06:54 AM
P: 1,005
Im guessing the phonon collisions act as a sort of resistance, so the conductivity drops with increasing temperature. But on the other hand, what if there were no collisions? What would then transmit heat?

DrDu
#4
Nov8-13, 07:41 AM
Sci Advisor
P: 3,555
Thermal conductivity

If there are no collisions, e.g. at very low temperatures, you have ballistic transport which is very rapid.
I think that only so-called Umklapp scattering processes actually can reduce the heat transport and this requires the sum of the crystal momenta of the two phonons to be larger than a reciprocal lattice vector. So it is only important at relatively high energies ~ Debye energy. Whether this includes room temperature depends on the material.


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