Dislocation decoration

The early work on dislocation decoration in silver halides is described in ... 

Figure 3-4. Dislocation decoration in an AgBr-NaCl interdiffusion zone. Dislocations formed by self-stress due to lattice parameter changes. The decoration density indicates the dislocation density [after H. Haefke, H. Stenzel (1989)].

The dislocation microstructures that develop during creep with stresses in the range 15 < a < 110 MPa at temperatures from 1,400 to 1,600°C were studied in detail by Darot and Gueguen (1981) on the optical microscope scale using the dislocation decoration technique as modified by Jaoul et al. (1979). However, TEM was used to determine Burgers vectors by application of the g-b = 0 and g-bxu = 0 invisibility criteria (Section 5.6). 

Figure 1.13. Dark-field TEM images of single-crystal calcite shocked to 85 GPa, displaying (a) the crossing of multiple twins, a large number of perfect dislocations and (b) numerous partial dislocations decorating the twin planes, (c) Secondary electron image of compacted calcite powder shocked to 85 GPa. The recovered specimen is composed of numerous foamy aggregates containing bubbles, voids, and crater-shaped objects.

Figure 3.14. Optical micrograph of a dislocation source in silicon, decorated with copper...

Figure 3.1 Electron micrograph showing a dislocation in silver, imaged as a dark line. The small triangular features that decorate the dislocation are stacking faults formed by the aggregation of point defects. [From W. Sigle, M. L. Jenkins, and J. L. Hutchison, Phil. Mag. Lett., 57 267 (1988). Reproduced by permission of Taylor and Francis, http //www.informa world.com.]...

This is one mechanism by which dislocations can become decorated (Section 3.7.3). A classic example is the decoration of dislocations in potassium chloride,... 

Since dislocations are linear strain fields, if a crystal is treated in an appropriate atmosphere, impurity ions selectively precipitate along the dislocation. These can be detected by infra-red microscopes, and so the method was used to prove the presence of dislocations during the early period of dislocation studies. If a dislocation is decorated by metallic elements, the dislocations act as a resistance against etching, and only the portion apart from dislocations is etched, and decorated dislocations remain as protrusions. The resulting protrusions are etch hillocks. 

Figure 15-2. Decoration of dislocations in olivine by internal oxidation. Precipitates are Fe304 [by courtesy of D. Kohlstedt, University of Minnesota].

It was at that time that Franck and Seitz proposed mechanisms for the multiplication and generation of vacancies by intersection of dislocations88 explaining the observed softness of crystals and providing models that were subsequently verified by the technique of decoration of dislocations.89... 

Small extrinsic dislocation loops which are not connected with stacking faults were also found in the crystals (FIGURE 8(a)). Sometimes they appear in high density in the central part of the crystal, often also decorated by Ga precipitates. They also were interstitial type with Burgers vector <2203> (FIGURE 8(b)). 

For the detection of dislocations by electroetching as well as by chemical etching, it is frequently necessary to "decorate " the dislocations by means of one or more impurities in the base metal. The impurity atoms interact with the dislocations. This idea was first put forward by Wyon and Laeombe (11) in the case of the Al. The same approach has also been extended to Fe (12), Si-Fe alloys (13), Zn (14), Cu (15), and others. 

Jaoul, O., Gueguen, Y., Michaut, M., Ricoult, D. (1979). A technique for decorating dislocations in forsterite. Phys. Chem. Minerals, 5, 15-19. 

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