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The defect distribution in an ionic crystal is calculated for both pure crystals and crystals containing divalent cationic impurities. By taking the electrostatic energy into account explicitly, it is shown that bulk electrical neutrality and space-charge regions surrounding the vacancy sources are an inherent aspect of thermal equilibrium. Interactions among defects of the opposite charge are taken into account using the nearest-neighbor-binding model. Inclusion of the long-range eBects of the Coulomb interaction and the question of the sign of charged dislocations are discussed.Eshelby, Newey, Pratt, and Lidiard' noted that edge dislocations, being sources and sinks for vacancies, would also give rise to such charging e8ects, the analog of the surface charge being a charge on the dislocation line itself with the space charge distributed with cylindrical symmetry around the dislocation line.When a crystal contains a small concentration of impurities which possess an absolute value of charge different from that of the host ions of the crystal, there also arises a space-charge region near the surface and around edge dislocations. ' Consider a NaCl crystal containing divalent cations. At temperatures where the t Extracted from a thesis submitted to the Graduate College by K. L.

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