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Thermal conductivity 
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#1
Nov813, 03:20 AM

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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?



#2
Nov813, 03:52 AM

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What would you guess?



#3
Nov813, 06:54 AM

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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?



#4
Nov813, 07:41 AM

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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 socalled 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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