One of the fundamental methods in determining the structure of crystals is the x-ray diffraction. The x-ray magnitude is proportional to the spacing between atoms in crystals (1A) which makes x-ray the preferred crystallography tool.
In a perfect diffraction the incident angle equals the angel of the diffraction, and the distance between two diffractions can be determined by Bragg's law:
2 d sin ϴ = n λ
Different crystals have different densities of electrons, consequently, the scattering of the x-ray beam will differ as the beam diffracts by the planes in the crystal. A three-dimensional picture of the density of electrons within the crystal can be made by the angles and directions of the scattered beams. But as the crystal structure becomes more complex, the picture that is given by the x-ray diffraction becomes less clear. However, it has worked for crystals with hundreds of thousands of atoms. Besides, x -ray diffraction has been used to determine the structure of over 99% of the Cambridge Structural Database, which contains over 500,000 structures. So, although the basics of this method are quite simple, it is still the master method in studying crystal structures. (Fig. ref=http://www.chem.ufl.edu/~itl/2045_s99/lectures/lec_h.html)
For this reason how amazing to consider and learn about crystal structure,especially when X-rays could help to see inside the crystal and know all detailes of crystal structure and unite cell.
ReplyDeleteIt is a surprisingly powerful method, underpinned by such a simple law. Even though, it would still be quite tricky to fully understand the structure of more complex crystals.
ReplyDeleteIt's also interesting to quickly google x-ray diffraction and see the immense number of applications of this one method. X-ray diffraction is yet another example of the basic premise of the majority of experimental physics.... bang "stuff" into other "stuff" and see what happens. It's amazing how much you can learn with this simple approach.
it is interesting that with the help of crystallography we can make a 3D picture of the density of electrons inside the crystal. but we have to know the angle and intensities of the diffracted beams.
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