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We investigate grain boundary motion and grain rotation in a body-centered cubic bicrystal composed of a spherical grain embedded in a single crystal matrix by three-dimensional phase-field crystal simulations. Structure and time evolution of dislocation networks formed on the grain boundary during the capillarity-driven grain shrinkage are examined. The results for initially spherical grains rotated about the [110] or [111] axes of the matrix grain reveal the formation of hexagonal dislocation networks (HDNs) on the grain boundary. We demonstrate that the anisotropic distribution of the HDNs is responsible for asymmetric shrinkage of the embedded grain. Through a detailed analysis of the HDNs, we clarify the mechanisms of dislocation reactions during the grain shrinkage in three dimensions, which include dissociation and recombination of a/2<111> and a<100> dislocations. The configuration of the HDNs is …