Charged Dislocations in Ionic Crystals

The paper aims to show that the charge clouds around dislocations are important for the mechanical properties of ionic crystals. The previous work of Eshelby, Newey, Pratt, and Lidiard is extended by solving the nonlinear equation giving the potential distribution and by obtaining the boundary condition appropriate at the dislocation core. Three typical examples are worked out in detail. Finally, a series of experimental phenomena are discussed and it is shown how the charge cloud model can be used to understand the experimental behavior. In particular, the minimum in the yield stress versus annealing temperature of NaCl doped with a known concentration of Pb${\mathrm{Cl}}_2$ is used to obtain the energy of formation of a positive ion vacancy in NaCl. One finds that ${E_F}^{+}=0.53\mathrm{}$ eV.