Дислокации

Дислокации concern to linear defects of a lattice, т. е. To imperfections covering in a crystal area, which extent in one direction considerably surpasses the size of atoms or ions. On character of distortions of a lattice дислокации are divided in the pure state on regional (linear) and screw. In real crystals дислокации often represent a combination regional and screw дислокаций. Such дислокации are called mixed. Дислокации are a source of internal pressure(voltage) in crystal bodies, they create even in free from external loadings a crystal a field of deformations and pressure(voltage).

One of the basic concepts of the theory дислокаций is the concept of a line дислокации. As a line дислокации that imagined line in a crystal is called, along which (in its(her) small vicinity) the maximal distortions of a lattice concentrate. Actually at occurrence дислокации the crystal lattice remains undistorted everywhere, except for area directly environmental a line дислокации. The line дислокации not necessarily should be a straight line, and can have excesses, step, т. е. Any form. The feature of this line consists that she never comes to an end (breaks) in a crystal, and leaves on his(its) surface, becomes isolated on itself, forming a loop, or becomes isolated on other lines дислокации.

Regional дислокация. An attribute regional дислокации is the presence in one part of a crystal superfluous ("torn off" or "unfinished") nuclear plane (полуплоскости or экстраплоскости), not having continuations in other part of a crystal (fig. 12, экстраплоскость is specified by an arrow(pointer)).

The maximal distortions and pressure(voltage) in a lattice concentrate at presence regional дислокации along edges(territory) of a superfluous nuclear plane. This zone of the maximal pressure(voltage) limited to a dashed line in a fig. 13, is called as a nucleus дислокации.

Screw дислокация. An attribute screw дислокации is the transformation of parallel nuclear planes (in бездефектном a crystal) in a uniform nuclear plane as геликоидальной of a surface (like a screw plane) and presence on a surface of a crystal original дислокационной nuclear ступеньки (уступа).

1 .

Fig. 12. Model regional дислокации a Fig. 13. The circuit of education кра-

In a crystal евой дислокации

The schematic image screw дислокации is given in a fig. 16. Its(her) education can be imagined if mentally to make in a crystal a cut(section) (on a plane АВСD), and then at the expense of force Р to move one part of a crystal in this plane in relation to other part on one internuclear distance downwards so that one cut off edge(territory) of each nuclear plane of a lattice, perpendicular planes среза, has coincided with other cut off edge(territory) нижележащей of a plane of a lattice. The cut off surfaces can thus be connected absolutely precisely, then it is impossible to distinguish, on what plane inside кри сталла the cut(section) was made.

Fig. 14. The circuit of education screw дисло- a Fig. 15. The schematic image nuclear

кации of planes at screw дислокации

In other words, at presence screw дислокации nuclear planes of a lattice, as it was already marked, turn to similarity спиралевидной of a screw surface, whence and name - screw дислокация (fig. 15).

Questions:

1. What such defects of a crystal lattice?

2. What such firm solutions and what conditions of education of firm solutions of replacement and introduction?

3. Characterize defects on Я.И.Френкелю and In. Шоттки and why defects on Шоттки and Френкелю concern to термодинамически to equilibrium defects, in what the reason of their education and what factors render influence on their concentration in a crystal lattice?

4. Name kinds of linear defects.

5. What is a structural attribute of presence in a crystal lattice regional both screw дислокации and their qualitative and quantitative characteristic?

6. Describe the reasons of education and property дислокаций, methods of definition of their density and result meanings(importance) of this density in the perfect and deformed crystals.

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