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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
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Crystal structures
are the periodic arrangement of atoms in a crystal
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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).
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Unit cells
are used to describe the smallest
repeating structure in a lattice of
a crystalline material
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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.
Celeste Morris, Bradley Sieve and Heather Bullen, Department of Chemistry, Northern Kentucky University, Highland Heights, KY 41099