Scherrer equation can be helpful in gaining an estimation of the nano size. The method relies on the FWHM of the diffraction peaks. For micron size and above, the results should be handled with care as other factors, e.g. lattice imperfections, can contribute to the peak width in the XRD diagram. It is always better to rely on TEM or SEM characterization for your purpose.

Talal- I know the modified scherrer equation to find the crystal size. Is there any possible way to find the particle size from crystal size? I also admit with you that TEM and SEM are the characterization techniques to find the approximate particle size. But I want to know particle size from crystal size which is obtained from XRD data.

The simple answer to your question is "No". A particle can be viewed as an agglomerate of crystallites or crystalline domains, and only in the limiting case the particle size will be equal to the crystallite size. The particle size can be determined using e.g. light scattering or even X-ray scattering (using Small Angle X-ray Scattering -SAXS). This requires however synchrotron radiation.

Eric-Thanks for your valuable opinion. But you said that in some limiting case,we assumed that the particle size will be equal to crystal size. I want to know that what is that limiting case?

You can't find out particle size with XRD data. It's not easy to determine the particle size since FE-SEM or even TEM are just "local examination".

For your 2nd question "we assumed that the particle size will be equal to crystal size. I want to know that what is that limiting case": in my opinion, there is no relationship between particle size and crystal size.

BR,

Le Phuc Nguyen- It's ok. But based on eric answer, I asked him that question. I want to the limiting case from Eric. Thanks for your suggestion Le Phuc.

as Mr Eric Van Steen said: A particle can be viewed as an agglomerate of crystallites or crystalline domains. So if your sample were well treated, for ex: using ultrasonic to avoid the agglomeration..., then, particle size could be equal to crystal size.

It's not always evident.

By the way, you can take a look at this thread "https://www.researchgate.net/post/Can_anyone_explain_the_terms_particle_size_grain_size_crystal_size_and_crystallite_size_of_nanomaterials?exp_tc=tprc"

BR,

When the particle contains one crystallite