Grain boundary motion was studied in situ at elevated temperatures by x-ray topography using synchrotron radiation. In addition to the position of grain boundary, other crystal defects that may interact with the moving boundary were observed simultaneously. Two types of bicrystals with the [001] rotation axis were selected for the experiments, the first one with a high coincidence Sigma5 misorientation of about 37degrees and the other one with no coincidence of two crystals for the misorientation of 45degrees. The geometrical differences between chosen bicrystals are examined and attention is also paid to faceting - local orientations of the boundary plane.