Subgrain Boundaries in MgO

The structure of subgrain boundaries in as‐grown MgO was characterized by transmission electron microscopy. The types of subboundaries which occur quite frequently are (1) a pure tilt boundary consisting only of ½ [101]‐type dislocations ( A set); (2) a tilt boundary consisting mainly of ½ [101] ( A set) and ½ [011] ( B set) dislocations; and (3) a mixed boundary with ½ [101] ( A set), ½ [011] ( B set), and ½ [01] ( C set) dislocations. At the nodes the following dislocation reactions occur: ½ [011]+½ [10] =½ [110] and ½ [10]+½ [101] = [100]. The precipitation of impurities at the subboundaries and their role in pinning the subboundaries are discussed.