The intensity depends on the number of scatterers so it does not change if dislocations are present. You have anisotropic broadening and peculiar line shapes. I keep saying that "common crystals" is a definition that is just yours.. you should talk about single crystal versus powder and talk about crystals or about powers with or without defects
I agree with Matteo, In real life XRD peaks can be affected by stresses inside the material which are the effect of thermal or mechanical processing, or chemical contamination. Such effects can give rise to peak broadening (especially with grain size) and if residual stresses are present peak shifting.
The intensity of common, "real", or "defect" crystals is decribed by the square of the structure amplitude |F|². Ideal crystals are usually better described by |F| only. For powder XRD in general |F|² is used because of defects produced by milling. Electron diffraction often covers an area which can be called "defect-free" and shows dynamical diffraction effects, cf. EBSD. We usually esplain this be the mosaic model which describes phenomenologically lattice defects.
You guys are not worried about perfect crystals! But perfect crystals are really horror for single crystal crystallographers and I know that most of you are not. You are "powder guys". The name of the horror is "EXTINCTION". The intensity of X-ray diffraction from a perfect crystal is not given by the kinemetical theory which we all use normally. The strong reflections are mostly affected by the extinction effect and are reduced in intensity. There are two types of extinction: primary and secondary. For perfect crystals dynamical theory of X-ray diffraction has to be used and not the usual theory. Fortunately extinction effects are small in powder diffraction. So you are safe in most cases.
But I hope you will agree that the intensity is then linear dependent on |F| as I recommended before? Moreover I must admit that these poor "powder guys" perhaps have less extinction problems (what is by the way not correct for mutiphase materials) but much more challenges to solve like reflection or peak overlapping.
No I do not agree with that. The extinction due to perfect crystallinity is more complex than that. Intensity is still proportional to FF* where F* is the complex conjugate of F but has to be corrected due to extinction effect. This correction is rather complex and is difficult to explain here. But it is known very well and is well described in many text books of X-ray diffraction. If you wish to go more deeply then you have to read :
C.G. Darwin, Phil. Mag. 27, 315 (1914).
C.G. Darwin, Phil. Mag. 43,800 (1922).
W.H. Zachariasen 23, 558 (1967).
P. J. Becker and P. Coppens, Acta Cryst. A30, 129 (1974).
N. Kato, Acta Cryst. A32, 453 (1976).
One of the main reason for the popularity of powder diffraction is due to the fact that extinction effect is usually (you have to take care crystallite size) very small. I have no intention to belittle the powder diffraction technique. It is of great use for the material science and industrial problems.
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