A general introduction of the disclination is given. Many micrographic examples and bubble raft models of disclinations are used as illustrations.
Definitions and historical aspects of the subject are reviewed in the first section. Disclination is defined as a line defect in the rotational symmetry element of the crystal lattice. It is an old brother of dislocation only recently drawing attention.
As discussed in section 2, disclination occurs in (1) small or thin crystals, (2) crystals with unquantized elements, (3) the pattern with weak interaction force. It also occurs as (4) imperfect disclination or (5) dipole of disclinations.
Structure of disclinations is described in section 3 using bubble raft model and electron micrographs. Stresses of the disclinations calculated by linear elastic approximation are presented.
Various configuration of disclinations are considered in section 4. Growing tip of a deformation twin are approximated by a dipole of partial disclinations, while an array of the disclination dipoles are proposed by Li as a model of grain boundary structure in metals. A densely packed state of disclinations may correspond to the liquid state.
The motion of disclinations are analysed in section 5. A wedge disclination moves by generating or absorbing dislocations, and a disclination dipole moves by exchanging dislocations between the two. A grain boundary consisting of an array of disclination dipoles migrates by the same process.
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