The formation of various types of extended defects by deuteron and/or He bombardment was studied by means of transmission electron microscopy. It was assumed that a fraction of the implanted gas atoms remained in metastable states and were easily dissociated and precipitated to form planar agglomerates upon heating to 500K. The habit planes were determined by minimizing the total strain energy, the surface energy and chemical bonding energy. On the other hand, irradiation at high temperatures produced secondary extended defects of interstitial type. A novel structure on the {100} planes was found only in the case of deuteron bombardment. The proposed structural model contained no D atoms as building blocks, although D must have played an essential role in the formation of the defect.

S.Muto, S.Takeda, M.Hirata: Materials Science Forum, 1995, 196-201, 1171-6