  Grain rotation in crystals often results in coarsening or refinement of the
grains that modify the mechanical and thermal properties of materials. While
many studies have explored how externally applied stress and temperature drive
grain structure dynamics in nano-polycrystalline materials, the analogous
studies on colossal grains have been limited, especially in the absence of
external force. In this work, we used X-ray free electron laser pulses to
irradiate single-crystalline bismuth selenide (Bi2Se3) and observed grain
boundary formation and subsequent grain rotation in response to the X-ray
radiation. Our observations with simultaneous X-ray diffraction and
transmission X-ray microscopy demonstrate how intense X-ray radiation can
rapidly change grain morphologies of initially single-crystalline material.
