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Residual Resistivity


I saw that the graph of resistivity to temperature of alloys like nichrome is like soenter image description here

Meaning that even at 0 K it has some resistivity just like copper :

enter image description here

I read some where "It is the residual resistivity due to defect scattering" Is this related to the defects that i studied in solid state chemistry about lattice defects.Can some body elaborate?

  • An alloy is a mixture of metals and a temperature coefficient of resistivity comparable to metals then why is its graph more linear than metals.
  • Is this because of the lattice structure of an alloy?
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The residual resistivity can be due to any kind of imperfection which destroys the complete periodicity of the lattice; most famous kinds are structural defects (provided that they happen in a disordered manner) as you correctly mention and impurities (again they should be distribited in a disordered manner). The way alloys are made, their lattice structure is certainly disordered since people don't make them by manipulating the lattice to make it perfect, and this disorder introduces a mean-free-path of order of the microscopic inhomogenities (the spatial fluctuation of the density of the different metals composing the alloy) of the alloy to the electric transport. This disorder has a small temperature dependence (at least at low temperatures) compared to the contribution from Phonons and I guess it usually remains the main source of resistivity. Now as to why the trend is more linear in the case of alloys, your graphs are not on the same scale to be used for the comparison and I wasn't able to find a good collection of graphs either, so let's wait for a better collection of graphs before the final conclusion; maybe that's not always the case.

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@The-Ever-Kid: also, I'd imagine that at low temperatures the resistivity depends quite strongly on the microstructure, i.e. grains. In fact, I'd say that one could approximate it as a network of resistors representing the grain boundaries, since a single grain will have a much smaller resistance --- the grains might be small enough that electrons remain coherent over them. –  genneth May 22 '12 at 10:45
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