Regarding XRD the crystallite size is a measure of the "size" of coherent scattering domains. SEM will give a picture of grains that may or may not consist of different sub domains. TEM eventually will give a picture of those possible sub domains and will be roughly comparable with the crystallite sizes of XRD.

You may have a look at the appended link. Also a wast amount of similar questions are discussed on RG.

Regards

http://old.vscht.cz/sil/keramika/Characterization_of_particles/CPPS%20_English%20version_.pdf

Similar topic was discussed before. I suggest you to read it. Replies are helpful.

Regards.

https://www.researchgate.net/post/What_is_the_difference_between_crystallite_size_grain_size_and_particle_size

Dear colleague Kumar,

Crystallite Size is Different than Particle Size. A particle may be made up of several different crystallites or just one crystallite so in this case (particle size = crystallite size)

Crystallite size often matches grain size, but there are exceptions

Crystallites are coherent diffraction domains in X-ray diffraction.

Particles are chunks/pieces (usually very small, below 1 mm) of solid matter, ensembles of atoms. Particles can be as small as two atoms (the nitrogen particle for example, N2)

Grains are volumes, inside crystalline materials, with a specific orientation.

Particles can be polycrystalline, single crystal or amorphous. A 100 nanometer particle of gold, for instance, can be made of:

a single gold crystal,

many grains with a grain size