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

 

[oswaler]

Hello,

Thank you for reaching out for assistance with your XRD data. It is not uncommon to observe an amorphous spectrum from crystalline samples when using XRD analysis. This can happen due to several reasons such as preferred orientation, sample preparation, or instrument calibration.

One possible explanation for your results could be the size of the crystals in your hydroxyapatite nanopowder. XRD analysis is sensitive to crystal size, with smaller crystals producing broader peaks and potentially overlapping with the amorphous background. This can make it difficult to distinguish between the two in your spectrum.

To confirm the presence of crystallinity in your sample, you may want to consider using additional techniques such as scanning electron microscopy (SEM) or transmission electron microscopy (TEM) to directly observe the crystal structure and size.

Additionally, it is important to ensure that your sample preparation is appropriate for XRD analysis. This includes grinding the powder to a fine, homogenous consistency and ensuring that the sample is well-packed in the instrument's sample holder.

I hope this helps in your interpretation of the XRD data for your hydroxyapatite nanopowder. If you have any further questions, please do not hesitate to ask. Best of luck with your research!