Changes in the burgers vector of perfect dislocation loops without contact with the external dislocations

We report the observations of a new type of changing process in the Burgers vector of dislocations by in situ transmission electron microscopy. Small interstitial-type perfect dislocation loops in bcc iron with diameters less than approximately 50 nm are transformed from a 1/2 < 111 > loop to another 1/2 < 111 > one or an energetically unfavorable < 100 > one; furthermore, a < 100 > loop is transformed to a 1/2 < 111 > one. These transformations occurred on high-energy electron irradiation or simple heating without contact with external dislocations. The origin of these phenomena is discussed.