| Stacking
fault are local regions of incorrect stacking of crystal planes associated
with the presence of partial dislocations. This is shown for an hcp crystal
for which the normal packing sequence is: ABABABAB..... A dislocation loop
added to this structure (a) must be compatible with the planes on either
side of the loop addition and is shown in the C location that is compatible
with both A and B. Lattice relaxation (b) around the dislocation loop yields
a region of high energy stacking fault. A lattice shear (c) above the added
plane can create a lower energy stacking fault that has fewer next nearest
neighbors in incorrect order for the hcp structure.
The
transmission electron microscope photograph shows a top view of dislocation
loops in a cadmium crystal produced by the aggregation of interstitial
cadmium atoms. These are of the type corresponding to (c).
Stacking faults are also produced by the dissociation of unit dislocations
to reduce the elastic strain energy of a crystal. |
