What is the difference between XRD Data of polycrystalline and Single crystal?

For single crystalline material, the X-rays will be scattered only in certain directions. Which will cause high intensity peaks with a narrow width (not always true other variables can play a role in this). Whereas for polycrystalline, the material consists of so many single crystals oriented in so many directions causing the X-rays to be scattered among a wide range of 2-Theta instead of high intensity narrow width peaks. 

At first I have to say that it is possible from powder data to obtain structure solution. Take a look at Rietveld Method and software like:

But it is possible in general from relatively small molecules(10-20 non hydrogene atoms) and accuracy of data will be low comparison with single crystal method. And there are some restrictions like low quality of powder experimental data, hard to indexing for low simmetry and even space groups determination, overlapping of reflections, and also some impurities in sample.

Because in sample many small unoriented parts crystalline powder, diffraction from different reflections on the same theta angles (not only symmetry equivalent reflections) spreaded as circles with radius~2Tetha but non as separete spots like in single x-tal method. So you will get only set of circles instead of many diffraction spots. Moreover intensities of such circles low because diffraction power spreaded in big area but not in spots, so it is impossible to observe small intensity diffraction spots and to separate diffraction ones with close diffraction angles.

In case of single crystalline material, the XRD shows single peak. Whereas for polycrystalline, XRD shows several many peaks through a wide range of 2-Theta. instead of high intensity narrow width peaks.

In the case of new materials the only way to identifying the exact crystal system with their space group is the single crystal X-ray diffraction analysis.

For the known materials, we can go for the powder X-ray diffraction analysis and then we can compare with the existed xrd pattern to confirm the crystal system.

In fact, with modern computers it is often possible to determine the crystal structure having only the powder diffraction data. The solution will include a lot of the trial-and-error steps, but it can be done in reasonable time if the high quality powder diffraction pattern was obtained and the sample is free from the impurities. Please, refer to the modern textbooks such as V. K. Pecharsky, P. Y. Zavalij 'Fundamentals of Powder

Diffraction and Structural Characterization of Materials' for details and examples.

Mr. Thakur,

The simplest answer to your question would be that from polycrystalline sample you have collected set of reflections belonging to atoms from different unit cells.

Please pay attention to a discussion showing briefly the structural determination steps by single crystal XRD:

In spite of the fact that there are methods applicable to segregate each set of reflections to different unit cells allowing to obtain unit cell parameters even structural prediction, nevertheless that if you have polycrystalline objects of more than one polymorphs than this additionally reduced the applicability of powder XRD.

So that generally as an absolute method single crystal XRD has its strongly highlighted advantages for structiral determination over powder XRD.

It is harder to solve the structure of a material using data collected from a powder because powder data is 1 dimensional. Data from a single crystal is 3 dimensional. In both cases you see the same reflections but in the data from the powder there is more overlap.

There are many reasons why you may be unable to solve a structure with XRD data from a polycrystalline sample. If you provide more details about what you are trying to achieve it maybe more obvious why you are having trouble.

Dear Eduard Rusanov and Alexander B. Missyul, Could you please guide me a bit more about the solution of crystal structure from powder data? Please recommend me some studies to get step by step details and software used for it.

Which method is most appropriate for residual stress analysis in additive manufactured metal components consisting material of AlSi10Mg and SS316?

Good fundamental question! There appear to several components in the original question. 

It may be better to discuss these separately :-)

It is also important to discuss the method/optics used to obtain the "XRD Data" as well as the detector to record the intersection of the Ewald surface and the reciprocal space vectors.

Pranav! Good question! Post your question as a separate discussion and post the link right here for participants to contribute. You'd need to describe the mechanical processing history of the "manufactured metal components consisting material of AlSi10Mg and SS316" along with grain size and XRD equipment available.

Can I get atomic position from XRD data? 

Yes we can get the XRD data from atomic position but too complicated may be but not exactly....

For single crystalline material, the X-rays will be scattered only in certain directions. Which will cause high intensity peaks with a narrow width (not always true other variables can play a role in this). Whereas for polycrystalline, the material consists of so many single crystals oriented in so many directions causing the X-rays to be scattered among a wide range of 2-Theta instead of high intensity narrow width peaks.

In summary, Single crystal shows intense and sharp narrower peaks in XRD pattern but polycrystalline materials shows less intense and broad XRD peaks.

it is possible in general from relatively small molecules(10-20 non hydrogene atoms) and accuracy of data will be low comparison with single crystal method. And there are some restrictions like low quality of powder experimental data, hard to indexing for low simmetry and even space groups determination, overlapping of reflections, and also some impurities in sample.

Because in sample many small unoriented parts crystalline powder, diffraction from different reflections on the same theta angles (not only symmetry equivalent reflections) spreaded as circles with radius~2Tetha but non as separete spots like in single x-tal method. So you will get only set of circles instead of many diffraction spots. Moreover intensities of such circles low because diffraction power spreaded in big area but not in spots, so it is impossible to observe small intensity diffraction spots and to separate diffraction ones with close diffraction angles.

May this link help you

The XRD of poly crystalline material will result different sharp angular resolved peaks wihch position depends on crystal orientation. For example for poly Si film it will be 111, 220, orientations. For these crystal orientations the XRD intensity will have sharp peaks at 27 o, 43 o respectively. Each peaks coprresponds to each crystal rientation. The width of peak related to the crystal layers deviation. For thin films it can be used Scherrer's formula for estimations. But for the powder material it will be necessary use Voigt distribution,

The properties (mechanical, electrical, chemical, etc.) of a single-phase aggregate are determined by two factors: (1) the properties of a single crystal of the material, and (2) the way in which the single crystals are put together to form the composite mass.

In the polycrystalline materials we will be concerned with the second factor, namely, the structure of the aggregate, using this term in its broadest sense to mean the relative size, perfection, and orientation of the grains making up the aggregate. Whether these grains are large or small, strained or unstrained, oriented at random or in some preferred direction, frequently has very important effects on the properties of the material. If the aggregate contains more than one phase, its properties naturally depend on the properties of each phase considered separately and on the way these phases occur in the aggregate. Such a material offers wide structural possibilities since, in general, the size, perfection, and orientation of the grains of one phase may differ from those of the other phase or phases.

X-ray diffraction is a tool to investigate the role of these factors in material properties.

XRD from a single crystal results in sharp angular spectral peak, It depends on the physical process of reflection of x-rays from the crystal planes in crystal. But for polycrystaslline material x-rays reflects from different planes and will give several sharp peaks at different angular values of diffraction. Because various crystals with different crystal orientations results different sharp peaks in angular spectrasl distribution.