Why Does XRD Show Amorphous Spectrum in Crystalline Hydroxyapatite Nanopowder?

[Msl]

Hello!

I would like to ask your help in the interpretation of Xrd data from hydroxyapatite nanopowder.
I know from the start that powders which I am analysing are already crystalline (another techniques were used to confirme that) but I keep having a characteristic spectrum of amorphous hydroxyapatite.
Why does this happen? What´s the influence of crystal size during in XRD procedure?

Thank you !

 

[Dave_H]

Hello,
A small crystal size will induce a broadening effect of the Debye rings. This relationship is discribed by:

B=0.9\lambda/tcos(\theta)

B = broadening of diffraction line measure at FWHM
t = crystal size diameter

B is the broadening of the peak due to grain size alone, therefore you must correct for the specific machine, do this using a large grained standard (of the same material).

B² = B_M² - B_s²
Where B_M is the measured breadth of the diffraction line and B_s is the measured breadth of the of the standard line.

I hope this helps, all this info can be found with much better explanation in:

Elements of X-Ray Diffraction, 2nd Edition, B.D. Cullity