In-situ high-resolution transmission electron microscopy with a time resolution of 1/60 s performed on electron-irradiation-induced grain-boundary migration of a MgO[001] Sigma = 5 tilt boundary. Atomic processes of the migration were elucidated for the first time. The non-periodic boundary, which was composed of several structural units; migrated and became a periodic structure along the (310)(A)-(3 (1) over bar 0)(B) planes after the units transformed into the units surrounded by the (310)(A)-(3 (1) over bar 0)(B) facets. Subsequently, the units surrounded by the (120)(A)-(210)(B) facets grew and aligned along the (120)(A)-(210)(B) planes. It was found firstly that the present migration proceeds at every translation and transformation of three kinds of structural unit of the boundary and secondly that the migration speed is controlled by the intervals of the time of translation or transformation of the units. It was shown that the atomic arrangement of the boundary during the translation and transformation can be predicted from the coincidence-site lattice model when the boundary is composed of stable structural units. [References: 22]
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