Misorientated domains, crystal

However, this relation is not exactly trae. The crystals are not comprised of perfect crystal planes they show domains slightly misoriented with respect to one another. These crystal domains usually extend over a few tens of cells and their misorientation are characteristic of the crystal in question, something referred to as the crystal s mosaicity. A qualitative illustration of this mosaidty is shown in Figure... 

In order for the dynamical theory of X-ray diffraction to hold, successive reflecting planes would have to be parallel to each other to within a few seconds of arc. This is the case within the mosaic blocks which comprise the crystal. Imperfections produce a warping of the lattice which causes different mosaic blocks to have a misorientation of the order of minutes of arc. The boundaries of these mosaic blocks can be interpreted as consisting of arrays of dislocations. The various ways in which arrays of dislocations can form boundaries are illustrated in the article by Hirsch. The average thickness of the mosaic blocks measured in a particular direction is referred to as the coherently diffracting domain size. 

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