Electron microscopy
 
Determination of Crystal Structures using HRTEM Technique
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Two ways are normally used to determine unknown crystal structures:
         i) Use electron diffraction intensities, similar to X-ray diffraction,
         ii) Combine electron diffraction and HRTEM.

Electron diffraction technique normally is the first choice used for determining unknown crystal structures. However, when the phase determination using electron diffraction only is difficult due to its relatively poor and incomplete intensity data, e.g. for very complex structures, HRTEM technique becomes more powerful. For instance, when the crystals contains defects, disorders, crystals of only a few unit cells large, and surface structures which play important role for catalytic properties, then the HRTEM technique provides direct observation of structure projections for understanding the crystal structures.

Silicate IM-5 [1] contains 24 unique Si-atoms in the framework and was too complicated to be solved by PXRD alone due to the serious reflection overlapping. This IM-5 was actually the most complex zeolite solved by HRTEM. However, note that this IM-5 could also be solved by electron crystallography alone with a tilt series of electron diffraction patterns. [2]

 

 

 

 

 

 

[1] J. L. Sun, Z. B. He, S.Hovm¨ oller, X.D. Zou, F. Gramm, Ch. Baerlocher and L. B. McCusker, Z. Kristallogr., 2010, 225, 77.
[2] Junliang Sun and Xiaodong Zou, Structure determination of zeolites and ordered mesoporous materials by electron crystallography, DOI: 10.1039/c0dt00666a.

 

 

 

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