Is the imperfect crystal in fact the best?

Two factors lie behind the importance of X-ray diffraction by crystals: the atoms are arranged in a regular fashion; and the X-ray's wavelength is the same order as the distances between neighbouring atoms in the crystal. Natural or synthetic crystals are known to exist perfect in a volume of the order of mm3. On the other hand, there are other crystals that contain many local distortions in a similar volume. These two types of structure provide rays diffracted along the same directions for the same crystals but the intensity of a given diffraction can be strongly decreased for the perfect crystal, up to 30-50% for the most intense, small-angle reflections. Whether an imperfect crystal is indeed best for X-ray diffraction is discussed.