7 The Crystalline Solid—Dislocations
59
Fig. 7.2 Laue pattern of a silicon crystal according to J. Washburn’s photograph in C. Kittel
[46], 1
Fig. 7.3 Model of a ‘minimal’ plastic deformation in a cubic lattice. The change in form when
compared with the initial state is visible. After the plastic deformation has taken place, all the
atoms once again occupy ideal lattice positions. It is therefore not possible to determine after the
deformation has taken place where the atoms in the ideal lattice were originally situated. The same
plastic deformation could also have been produced by a different suitable displacement of atoms.
In contrast to elastic deformations compare with Fig. 7.4
There are two characteristic completely different possible mechanical kinds of
lattice motion: elastic and the plastic deformations.
Simplified one can say that elastic deformations only occur when the involved
forces are small enough. If the mechanical influences on the solid (our hammering) increase, then plastic deformations also occur. Plastic deformations lead to a
permanent change of a solid, elastic deformations do not.