Transport by defects

In metals the conductivity decreases with temperature according to the Wiedeman-Franz law. 

The quotient of electrical conductivity a and thermal conductivity X is inversely proportional to the temperature. The ionic conductivity of solids depends on the lattice type and the type of the defects. The conductivity increases with temperature. This property is used to distinguish the ion conductor from the electron conductor. For vacancies and interstitials in the ion lattice, conductivity depends on the formation enthalpy for vacancy-interstitial pairs, Afo v. 

With increasing temperature the number of vacancies and atoms on interstitials will increase. Increasing temperature will also activate the motion of vacancies and interstitials through the crystal, the activation energy is E. The temperature dependence of the conductivity (7 is given by the equation 

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Figure 2. Schematic representation of surface transport processes (A) unrolling-carpet mechanism (B) transport by defect diffusion.

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