Diffraction by single crystals the theoretical basis

Within the unit cell we can define any point (termed a lattice point) by its fractional coordinates. Any two lattice points will be related by symmetry if they have the same three-dimensional surrounding of atoms. In the case of C-centering, for example, this means that every lattice point (which could represent an atom) is found again by translation along half the face diagonal defined by a and ft, so the lattice point (x , y, z) can also be found at (V2 + X, % + y, z). 

4 Three-dimensional periodic symmetry space groups 

The angle 9 is called the glancing (or Bragg) angle and n is an integer that assumes a value of one for primary diffraction and greater than one for higher-order diffraction. 

Constructive interference of X-rays reflected at two planes separated by a distance d (Bragg s Law). 

Equation 10.6 can then be recast for the three-dimensional, first-order diffraction case as 

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