Amorphous State OD order

However, there is no real reflecting plane. To solve this problem, it is necessary to find an equivalent by considering the lattice of a single crystal. 

Amorphous substances (e.g., Ga, Se, Ge, Si02, C) are mostly derived from face-centered cubic crystals or hexagonal ones. The law of Donnay and Marker [4] allows one to connect the diffraction pattern to the external shape of a crystal. The more developed face of a crystal is the one where the atomic density is maximum (i.e., when the atoms are in contact). Correspondingly, electrostatic 

FIGURE 1.4 Representation of linear order (ID) in real space and in reciprocal space. (Adapted from A. Guinier. Theorie et techniques de la radiocristallographie. 2nd ed. Dunod, Paris, 1956, 736 p. X-ray diffraction in crystals, imperfect crystals and amorphous bodies, Dover ed. translation (1994). With permission.) 

FIGURE 1.5 Calculus of the adjustment factor X (a) face-centered cubic (fee) crystal (b) hexagonal crystal. 

In amorphous substances deriving from fee crystals, the first halo could thus be used without too much error with X 1.23. In amorphous substances deriving from hexagonal crystals, however, the error is too large and X is not reliable. 

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