X-ray, neutron and electron diffraction techniques can all be used to probe structure of materials. They are complimentary to each other. X-ray diffraction was used first historically, electron and neutron diffraction came much later. The basic principles of structural study were firmly established before the other two techniques slowly became mature. The popularity of X-ray diffraction technique is not hard to understand. Any home laboratory can afford an X-ray source and a few diffractometers whereas electron diffraction instruments are too expensive for home laboratories. Only a luck few can afford that. You cannot have a neutron source at home for useful neutron diffraction investigations. You have travel to a national (if you are lucky) or an international laboratory. You have to write research proposals and convince the committees that your problem cannot be solved by X-ray diffraction, you have done all you could do at your home laboratory. Only then you may get some beam time for your investigation. All these process will cost you about six months or more.

Now let us discuss why you should more than one of these diffraction techniques for your investigation. X-ray diffraction is in fact more versatile and of more general use for structural research. You can study relatively small amount of sample especially with synchrotron X-rays (problematic as neutron for availability). In electron diffraction you can use even smaller samples. But neutron diffraction needs relatively much larger amount of sample. But if you have to study magnetic structure you do not have any choice, you have to use neutron diffraction. For crystal structures you are quite well off with X-ray and electron diffraction but there are some cases where neutron diffraction may be necessary. If you have samples with hydrogen or other light elements with other heavy elements then X-ray and electron diffraction will not be able to locate them, you may have to use neutron diffraction. This is because neutron scattering length is not directly related with the atomic number whereas for X-ray and electron the scattering is more for elements with higher atomic number. Also the neighboring atoms in the periodic tables are hard to be distinguished by X-ray and electron diffraction whereas neutron diffraction can do this job very easily. Again if you wish to study dynamics of atomic motion (phonons) then neutron scattering is the best tool. You can now understand that you must consider very carefully which diffraction/scattering technique is appropriate for your specific investigation. Sometimes you may have to use more than one technique. There are specialists for each of these techniques and you should consult before you wish to use a particular technique. For neutron diffraction for example you can contact the instrument responsible and ask his opinion before you write a proposal. India is lucky to have a  nation neutron source at Trombay. In addition India is a member country (small member though) of Institut Laue-Langevin which has the high flux neutron reactor and excellent neutron spectrometers a diffractometers. So you can write proposal at ILL and get neutron beam time. But mind that in order to be successful you have to write a very good proposal because the competition is very high for ILL proposals.

One reason is the efficiency of scattering depending on element and isotope. In general, the heavier the element, the higher the scattering efficiency for X-ray and electron. Scattering efficiency of neutron is totally different. For example, hydrogen and deuterium can be distinguished by neutron diffraction.

Another reason is the degree of damage. Many organic material is sensitive to electron beam and the original structure is easily modified. Compared to electron beam, damage by X-ray is very small.

I would say the main reason is coat and availability. Xrd is widely available and affordable, neutron scattering on the other hand requires a high energy neutron source. Those are found in national Labs and such where availability is an issue. 

Sample preparation is very simple for XRD and instrumentation is readily available as it is relatively cheap and any university involved in research has such equipment available in Materials Science and Physics departments. Electron diffraction requires a transmission electron microscope and more complicated sample preparation, to reduce the thickness for electron transmission. Also the volume analyzed is much smaller than in XRD, of course that can be good if you are studying small phases in multiphase materials.

X-ray, neutron and electron diffraction techniques can all be used to probe structure of materials. They are complimentary to each other. X-ray diffraction was used first historically, electron and neutron diffraction came much later. The basic principles of structural study were firmly established before the other two techniques slowly became mature. The popularity of X-ray diffraction technique is not hard to understand. Any home laboratory can afford an X-ray source and a few diffractometers whereas electron diffraction instruments are too expensive for home laboratories. Only a luck few can afford that. You cannot have a neutron source at home for useful neutron diffraction investigations. You have travel to a national (if you are lucky) or an international laboratory. You have to write research proposals and convince the committees that your problem cannot be solved by X-ray diffraction, you have done all you could do at your home laboratory. Only then you may get some beam time for your investigation. All these process will cost you about six months or more.

Now let us discuss why you should more than one of these diffraction techniques for your investigation. X-ray diffraction is in fact more versatile and of more general use for structural research. You can study relatively small amount of sample especially with synchrotron X-rays (problematic as neutron for availability). In electron diffraction you can use even smaller samples. But neutron diffraction needs relatively much larger amount of sample. But if you have to study magnetic structure you do not have any choice, you have to use neutron diffraction. For crystal structures you are quite well off with X-ray and electron diffraction but there are some cases where neutron diffraction may be necessary. If you have samples with hydrogen or other light elements with other heavy elements then X-ray and electron diffraction will not be able to locate them, you may have to use neutron diffraction. This is because neutron scattering length is not directly related with the atomic number whereas for X-ray and electron the scattering is more for elements with higher atomic number. Also the neighboring atoms in the periodic tables are hard to be distinguished by X-ray and electron diffraction whereas neutron diffraction can do this job very easily. Again if you wish to study dynamics of atomic motion (phonons) then neutron scattering is the best tool. You can now understand that you must consider very carefully which diffraction/scattering technique is appropriate for your specific investigation. Sometimes you may have to use more than one technique. There are specialists for each of these techniques and you should consult before you wish to use a particular technique. For neutron diffraction for example you can contact the instrument responsible and ask his opinion before you write a proposal. India is lucky to have a  nation neutron source at Trombay. In addition India is a member country (small member though) of Institut Laue-Langevin which has the high flux neutron reactor and excellent neutron spectrometers a diffractometers. So you can write proposal at ILL and get neutron beam time. But mind that in order to be successful you have to write a very good proposal because the competition is very high for ILL proposals.

@thanks to all of you making my doubt clear .

As I think that neutron scattering will help in case of isotopes to find clear structure , But then we need a reactor for this to produce neutron beams, Is such ?

High intensity neutron beams require either a reactor or accelerator (spallation) source. A reasonably complete list of such facilities can be found here:

http://en.wikipedia.org/wiki/Neutron_research_facility

As others have indicated, each technique provides similar information from slightly different perspectives.   From my own experience,  XRD basically looks a variation in electron density and is useful in probing general lattice parameters for a wide variety of materials in different formats(bulk, thin film, powder, fiber, etc...). 

Neutron scattering can give similar information but here the information originates from differences in the atomic nucleus.  This makes it a good technique for looking at materials tagged with isotopes, such as  mixture containing a deuterated version of a polymer. 

Electron diffraction, like XRD is looking at variations in electron density, however, you are examining a sample on a much smaller scale.  XRD is basically a bulk measurement, where electron diffraction can directly correlate atomic packing to localized regions in a sample. 

Each of these tools are very powerful and can produce a very detailed description of material structure on the atomic scale  when used together. 

JMD

I am not an expert of any of these XRD, neutron and electron, but soild-state NMR. I heard neutron needs 10 gram of sample to get a spectrum so it is some restriction other than its high price esp. in Korea. Solid-state NMR can be a cross-checking technique for X-ray, electron, neutron spectroscopy but its drawback is poor sensitivity and it requires about 50-100 mg. BUT it can also characterize some atomic dynamics. I don't know whether x-ray etc. can detect any atomic dynamics.

X-ray and electrons are scattered from electrons. Neutron scattering is of two types: nuclear scattering in which neutrons are scattered from the nuclei and magnetic scattering in which neutrons are scattered from unpaired electrons. So X-ray and electron scattering can be used to determine electron density distribution whereas neutron scattering can be used to determine nuclear density distribution and also magnetization distribution. So for structural studies all these three scattering techniques can be used. But for magnetic structure determination neutron scattering is the most useful technique. However X-rays are electromagnetic radiation and therefore are also  scattering by unpaired electrons but this scattering is very small and difficult to measure. The electron has a spin and therefore can in principle also be used to study magnetic structure but has hardly been used due to practical difficulties. So neutron scattering is the only tool for determining magnetic structures. Thermal neutrons have energies in the range of meV which is of the same order of magnitude as the elementary excitations viz. phonons and magnons in solids. So neutrons can be used to study the phonon and magnon dispersions in a solid. Dynamical studies with synchrotron X-rays are also possible but more difficult. So neutron scattering is unique for studying magnetic structure and dynamics. Yes NMR can also be used to study dynamics but the study is limited to momentum transfer Q=0 like all other local probes. Neutron scattering is practically the only tool to study wave vector dependent susceptibility of the system by mapping completely the scattering function S(Q,\omega).

Another important aspect of neutron scattering is that the neutron scattering length varies from isotope to isotope of the same atom. This makes neutron very useful for structural studies using isotope substitution. By doing neutron diffraction experiments on  samples without and with isotope substitution you can determine the scattering contributed purely from the particular isotope-substituted atom only.  

Do you know exchange 1D/2D technique in NMR? NMR can identify atomic sites determined by its surrounding electron orbitals which is referred as the chemical shift, and NMR can detect the jumping rate between those sites. In practical sense, XRD and NMR is easy to use and complement with each other very well. Neutron is strong for light atom site assigment where XRD cannot deliver a firm result? But neutron require so much sample quantity which is the limiting factor and also pretty expensice since you need a nucleus reactor. Am I wrong?

Dear Tapan, BTW Do you have neutron reactor? We may need it in the future. I am working on H-bonded ferroelectrics. Nice to talk with you. 

because diffractometers are readily available? and easier to work with?

Institut Laue-Langevin has the most powerful reactor neutron source of the world. But Korea has a reactor too for neutron research. It is called High-Flux Advanced Neutron Application Reactor (HANARO). You can contact instrument scientist there.