Introduction
to
X-ray Diffraction (XRD)

 

 

 

 

 

Basic Theory: Crystallography
 

What are some of the key crystallography concepts?

The emphasis of this learning module is not on obtaining a detailed understanding of crystal structures.  However a few key concepts are useful in understanding crystallography and results obtained using XRD.

Key Concepts  

  • Crystal structures are the periodic arrangement of atoms in a crystal
     
  • Structures are defined using lattices (infinite array of points in space)
     
    • Common lattices are shown below

                (note the spheres represent lattice points, NOT atoms)

  • Unit cells are used to describe the smallest repeating structure in a lattice of a crystalline material.
  • These repetitions are what give rise to the constructive interference defined by Bragg’s Law

Image of common lattices.  Google Images. http://www.chem.ox.ac.uk/icl/heyes/structure_of_solids/Lecture1/Lec1.html#anchor2 (Accessed 12/12//07).
 

  • Unit cells are used to describe the smallest repeating structure in a lattice of a crystalline material
     
  • These repetitions are what give rise to the constructive interference defined by Bragg’s Law

 Note: It is important to recognize that simple examples shown in this module have atoms existing within lattice sites.  This is rarely the case beyond metals and simple salts. 

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Contact

Celeste Morris, Bradley Sieve and Heather Bullen, Department of Chemistry, Northern Kentucky University, Highland Heights, KY 41099