There are some differences between hexagonal and hexagonal closed packed crystal structures. ow to identify and differentiate them?
Ralph Huebner
The hcp exhibit the space group P6(3)/mmc and can be discripted as dihexagonal dipyramidal. The hexagonal crystal structure (a = b and alpha = beta = 90°, gamma = 120°) includes 27 space groups and one of them is P6(3)/mmc.
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Ralph Huebner
So how to identify and differentiate them? F.e. By indexing of a diffraction pattern (x-ray)
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Yasir Idrees
Thanks for help Ralph. I was a little confused with both of them. thats why my Omega phase (hexagonal) SAEDP are slightly different than zirconium (HCP) :)
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Abhishek Kumar
Omega phase SAED pattern shows a diffraction spot at 1/3 and 2/3 of bcc direction along bcc zone axis, which is also true for zone axis analysis. Whereas, for hcp phase you will have a different arrangement of diffraction spots along bcc. The perfect C(32) omega belongs to P6(3)/mmm space group, whereas hcp belongs to P6(3)/mmc.
Talking for Zr or Ti alloy systems:
3. The packing fraction of omega is 0.57 whereas that of hcp is 0.74.
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