Hello Iftakhar Bin Elius !

Difraction Methods Diffraction X-ray Neutron Electron Different radiation source of neutron or electron can also be used in diffraction experiments. The physical basis for the diffraction of electron and neutron beams is the same as that for the diffraction of X rays, the only difference being in the mechanism of scattering

Advantages and disadvantages of X-rays Advantages; X-ray is the cheapest, the most convenient and widely used method. X-rays are not absorbed very much by air, so the specimen need not be in an evacuated chamber. Disadvantage; They do not interact very strongly with lighter elements.

Reference: https://www.slideshare.net/Ouniyeh/x-ray-diff-lecture-3

Answer from DaSilva is explaining the difraction condition in a good way but if the grain size dependenc case of neutron difraction is similar to that of the x-ray, I say yes since the difraction angle depends on the d-spacing of the crystals. In the Nanoscal grains the lattice (d-spacing) depends on size In more details in this size the grain(crystal) will have seires of d-spacing which gives a seires of difraction angle, that we see a wide angle for difraction. A smaller grains gives a wider angle while large grains give a sharper angle

to understand more about the size dependence on nanoscal size crystals I recommend to read the title power point

I am afraid I have to contradict, neutrons interact with the electron cloud. Interaction of neutrons with electrons is due to the magnetic field produced by the electronic currents within the atom, acting on the magnetic moments of the neutron.

My query was can I use Sherrer equation to get an estimation of the crystallinity/grain size, because a peak from chemical structure may also have a magnetic peak nearby which may effect its breadth. Resulting an error. Thanks for your answer Oreci Escobar Da Silva.

Dear Iftakhar Bin Elius, in several cases I succeded in determining the coherent diffraction domain ('particle size') of nanoparticles using neutron diffraction. the best way is to use a Rietveld refinement software (Fullprof, Gsas, ...); the software calculates the magnetic and neutron scattering contribution to each diffraction line. Moreover, it calculates the size-broadening contribution to each nuclear peak in the diffraction pattern, whereas in the classical Sherrer method you apply the equation to only one single peak. In that way the calculation is much more precise. Conversely, if you don't want to use one of these software, I suggest to you to select a peak in the neutron diffraction pattern that has a rather high intensity and it is located at a medium or at a high diffraction angle. In fact, magnetic scattering in this angular region is very low or totally suppressed due to form factor. so in this angular region of the neutron diffraction pattern, the peak is totally originated by nuclear scattering and you can apply the Sherrer equation without worrying about magnetic contribution.

As Da Silva explained, different sources for scattering experiments exist, but (as also already mentioned) the mechanism of broadening of reflections by crystallite size is similar. Broadening from n scattering and XRD experiments is (nearly) equivalent. But in ALL cases the instrumental broadening must be taken into account if a reliabal value is desired. Depending on the instrument the line width of n scattering scans often (but not generally for all different instruments) show a more significant instrumental broadening than XRPD scans. The higher the index / 2theta position / k-value of a reflection is, the more also strain will cause significant broadening. Due to this behaviour a low indexed peak should be preferred to skip this influence. Therefore decomposition of a scan by programs taking Bragg scattering and magnetic scattering into account should be preferred (as Martinelli suggested). If the structure of the compound(s) is unknown or drastically modified by texture, then evaluation of a single peak (or a low number of individual peaks, WH-plot) may be used as a compromise. Assuming the Bragg peak shows a high intensity and the magnetic reflection only a low intensity the error due to overlap should be tolerable. Perhaps you may have anisotropic line broadening. Check the line width of other peaks, too. Again, an intelligent software for evaluation should be preferred.