Figure 5.

(A) An a_o/2[100] screw dislocation in MgO showing how the (100) plane is displaced by a_o/2 after one turn. The large dark spheres indicate O²⁻ anions, the smaller light spheres Mg²⁺ cations. (B) Projection of two idealized edge dislocations generated as part of a subgrain boundary in MgO by the insertion of two half-planes of Mg²⁺ and O²⁻. The arrows point at rows of Mg²⁺ cations that are under high compressive stress and therefore energetically unfavorable (after Harding et al., ref. 38).