Crystallite size, if determined from XRD peak broadening measurements according to Scherrer method, and likewise from electron diffraction in TEM, can show different, values then the crystal domain size determined by direct view from TEM. In general, the first reason is that peak broadening accounts for two contributions: crystallite size and strain. If two contributions are not separated by for example, Williamson-Hall or Halder-Wagner method, and present strain in crystal structure is significant, this can account for higher peak broadening.

A more simpler reason for discrepancy could be the subjective nature of TEM measurements, as the local field of view at which the measurements are performed is very narrow and doesn't represent the true nature of the sample.

Marijan Marciuš Thank you for response sir. For one of my compound crystallite size is 70nm( XRD W-H) and particle size (TEM) is 10 nm. Is that possible?

Some information about correlation between TEM and XRD showed here Article Correlation between subgrains and coherently scattering domains

Dear colleague! May I add a question, please? What is about the shape of your particles/crystallites? Are they needles, cubes, plates? Is there any texture and orientation which you should take into account? Wkr, M. Herms.

Akash Kumar Sahu that is a huge discrepancy. Usually the crystallite size by Williamson-Hall method from XRD profile overestimates the size by a little bit, but not that much, while Halder-Wagner underestimates it. Bear in mind that XRD is a macroscopic analysis method, which gives you the "average" information on structural properties of particular crystal phase in your sample. On the other hand TEM is a microscopic and very subjective analysis method to the chosen field of view, as pointed out earlier. That means you would have to do measurement of at least several tens or maybe up to 100 field of views to get an average of the crystallite size by TEM and see how that correlates with your XRD measurement.

Given the fact that you have not specified any other details about the sample, we can only generally discuss the reasons for the discrepancy. There is also a number of issues that could be accounted for, apart from the TEM subjectivity issue mentioned above.

1. homogeneity of the sample at the microscopic level

2. particle size distribution (you should look into some light scattering methods to determine the particle size distribution).

3. particle morphology as Martin Herms pointed out.

4. XRD measurements - did you account for the instrumental profile broadening (measured on the well crystalline standard sample, like LaB6)?

5. which peaks and how many peaks did you take into account while doing W-H analysis,

6. significance of strain

7. agglomeration of the sample, etc.

Martin Herms Dear sir, particles are in rod-like shape confirmed by both SEM and TEM analysis.

Akash Kumar Sahu unfortunately in this case you cannot apply Williamson-Hall method to determine the crystallite size, since different crystal directions (Miller indices) will give you different peak broadening values.W-H and similar size-strain methods work only for nearly spherical particles.

Akash Kumar Sahu

You state above 2 points:

• 'For one of my compound crystallite size is 70nm( XRD W-H) and particle size (TEM) is 10 nm. Is that possible?'
• '...particles are in rod-like shape confirmed by both SEM and TEM analysis'

Can you see the contradiction in these statements? Take a look at the attached.

Dear colleagues! Please, allow a remark again. I do not know what material we do discuss here about? Particle size and size distribution in the range of several nanometers taking different shape into acount is a field where small angle scattering, either of X-rays or of neutrons, is well-established. Did you check this possibility? Wkr, M. Herms.