18.104.22.168 Structure of defects and their agglomerates
This chapter discusses the structure of defects and their agglomerates. It provides an extensive literature on calculations of point defect structures, and also talks about face centered cubic lattice (fcc), body centered cubic lattice (bcc) and hexagonal close packed lattice (hcp). The alkali metals can be treated by the pseudo-potential theory, due to the simple electronic structure. The well-known geometrical transformation, which transforms the fcc lattice structure into bcc transforms also the (100) dumbbell of the former into the (110) dumbbell of the latter structure. The isotropy can be visualized even in a simple geometrical model as the nearest neighbors of a dumbbell atom form a ring of 4 atoms. The stable tri-interstitial consists of three mutually orthogonal dumbbells on nearest neighbor sites. Even for the “simple” hcp, the metal Mg can be treated by pseudopotentials, there is no consensus on the stable interstitial configuration. Experimental information on the structure of self-interstitial atom (SIA) and their small agglomerates has been obtained from diffuse scattering techniques or from the mechanical or magnetic relaxation behavior. The structure of the final large loops has been investigated extensively by transmission electron microscopy (TEM).