Point defect: also migration energy

Our present task is to build on the foundations laid in chap. 7, but now with special reference to the diffusive processes that take place at extended defects. The basic argument will be that by virtue of the more open atomic-level environments near extended defects, the activation energy both for point defect formation and migration will often be reduced relative to bulk values. We will build our case around a fundamental case study through the consideration of diffusion at surfaces. The surface diffusion example will illustrate not only how diffusive processes are amended at extended defects, but will also illustrate the shortcomings of the transition state formalism when the detailed atomic-level mechanisms are not known a priori. 

Point-defect migration energies can also be deduced from the growth or shrinkage of dislocation loops during or after irradiation in a HVTEM (see Chapter 22 by Veyssiere and Douin in this volume). 

The first-principles calculations also provide information on the mobility of point defects, that is, their ability to diffuse at certain temperature. The estimated annealing temperatures, above which point defects are mobile, and the energy migration barriers for the native defects in ZnO are listed in Table 3.5. It is evident... 

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