Electron charge concentration diffraction

Clearly, the atoms, or electron densities in the unit cells, do not lie exactly on planes, any family of planes. In reality, they lie mostly in between. Why then should imaginary planes, which these planes are, scatter X rays at all The answer is that they don t. We can, however, make the assumption that all atoms do lie on nearby planes of each family, and then compensate for the fact that they are really displaced from the planes when we calculate the diffracted wave from those planes. This is somewhat analogous to assuming all of the mass of an object is concentrated at its center of mass, or representing a complicated charge distribution by a dipole moment. 

X-ray diffraction data. However, the observation by electron microscopy 12, 32) of twinned microcrystals in tin(IV) oxides containing a low concentration of antimony could be consistent with the accommodation of antimony(III) in more favorable sites and would be compatible with the observed migration of antimony away from the tin rich species and the formation of a mixed oxide with similar lattice parameters to tin(IV) oxide. However, the charge transfer spectrum would still require some Sb ions to occupy octahedral sites, and whether or not such accommodation could be achieved at or near the twin boundaries is not clear (32). 

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