Since particles can consist of several crystals particles can be bigger than crystals but not vice versa. Therefore either the calibration of your TEM is incorrect (quite unusual) or the software deriving the crystal size from XRD data is incorrect. I would assume the last one since you need to input the instrumental broadening. If this influence is defined as too big the influence from the sample is underestimated an therefore the crystal size is assumed to be too big. On the other hand, about which difference we are talking? In TEM you usually have a very bad statistic. If you select a statistically underestimated part of our sample it might be in contrast to the crystal sizes derived from Scherrers equation. And...Scherrers equation is only a rough estimation. Do you have an anisotrop grain size?
Dear Dr. Harshit Mahandra
Good day and happy times.
X-ray diffraction usually gives more accurate results. You must take into consideration that, the crystallite size that is estimated from XRD analysis is dependent upon the evaluated broadening whether estimated using the integral breadth or the full width at half maximum (FWHM). Using Scherrer equation, and after estimating the FWHM broadening (of the pure sample in radians), the crystallite size is
D= [k*(lambda)]/[Beta* cos(theta)].
Warren Averbach Variance method can be used to determine the Crystallite size by using the evaluated Integral breadth. Warren suggests that, the method of using integral breadths gives an evaluation that is independent of the distribution in size and shape
The Scherrer equation is limited to nano-scale particles. It is not applicable in the most of metallographic and ceramographic microstructures.
Practically, there is a difference between the two ways. where, the broadening of the integral breadth is better than FWHM.
Good Luck
Yours,
Ahmed Saeed Hassanien
Both are different parameters , Particle size always greater than crystallite size. But You can determine 'd' spacing and crystallite size using SAED and HRTEM micrograph images
Dear Dr. Harshit Mahandra
Happy times
I agree with Dr. S.B. Deshmukh. What has measured by using XRD is really the crystallite size, but what has been measuring by TEM may be an agglomeration of several crystallites ( may be reach to more than 1000 unit cell). Therefore, there is a difference between what measured by XRD and TEM and no comparison between them.
Hence, the estimated dimension by XRD must be always less than that measured by TEM.
Yours,
A. S. Hassanien
Dear Dr. Harshit Mahandra
The attached Power point Presentation may help you
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