X-ray Diffraction (XRD)






Basic Theory: Crystallography

From diffraction patterns one can find the crystal structure of an unknown material.  In addition one can also determine factors such as the orientation of single crystals, or measure the size and shape of crystalline regions.

There are several X-ray diffraction techniques.  Two of the most common are:

Single crystal X-ray diffraction: used to solve structure of crystalline materials ranging from inorganic compounds to complex macromolecules such as proteins or polymers.  You can learn everything about a crystal structure, but requires a single crystal.  Although obtaining single crystals is difficult, single crystal X-ray crystallography is a primary method for determining the molecular conformations of biological interest such as DNA, RNA and proteins. 

Power X-ray diffraction: used to characterize crystallographic structure, grain size, and preferred orientation in polycrystalline or powder solid samples.  This is a preferred method of analysis for characterization of unknown crystalline materials.  Compounds are identified by comparing diffraction data against a database of known materials.   It can be used to follow phase changes as a function of variable such as temperature, pressure.  

This module focuses on providing and introduction to X-ray diffraction Powder X-ray analysis to identify crystalline materials.  

Let’s examine in the next section how different unit cells and atoms influence diffraction using a program called Powdercell.

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