**3. Microstructural stability**

**Figure 2.** Equilibrium bicrystal interface structures of <1 1 0> symmetric tilt boundaries and two perfect crystal orientation [18]. The structures are viewed along the tilt axis [1 1 0], with the open and filled circles indicating atomic

**Figure 3.** HRTEM images of [0 0 0 1]-tilt grain boundaries in ZnO bicrystals. (a) 10.6 ± 0.1° boundary composed of a dislocation array. (b) 20.1 ± 0.2° near Σ = 7 boundary having a facet structure. (c) 20.0 ± 0.2° near Σ = 7 boundary with a symmetric structure. (d) Higher magnification image of (c) with the boundary core structural units represented by quadrilaterals [19].

positions in alternate (2 2 0) planes [18].

146 Study of Grain Boundary Character
