The materials scientists have now become used to identify and analyze crystal structures by the Rietveld analysis of limited-Q diffraction data collected by in-house X-ray diffractometer. Rarely they go to a synchrotron or neutron facilities to measure somewhat highe-Q better diffraction data and again analyze them by the Rietveld refinement often using Fullprof program (which is not fullproof by the way!). They usually throw away the important data hidden in the background of the diffraction pattern. Many of them however are aware that their samples are not perfectly crystalline and of suitable gain size. For such cases it would be better to measure diffraction data at a synchrotron or a spallation neutron source up to high-Q and use the total diffraction data including background diffuse scattering from the sample by the so-called PDF analysis. However if you have magnetic materials then the magnetic scattering intensities should be treated as well along with structural scattering. This is rarely or not at all done in the published PDF analysis. (For example, the CMR manganite materials.) Although PDF analysis can give extremely useful information about the local structure, in reality however we legitimately doubt the results at least in the case of magnetic materials. I would like to have your general opinion regarding PDF results. Do you do the PDF analysis very often and do you trust these results?
I am not an expert an PDF, but I feel that PDF could be very hard to interpret is you know or believe that there is a significant amount of local defects. For most materials, I would recommend some transmission electron microscopy (TEM) to understand what kind of defects you have, but that may be difficult on certain magnetic materials. If it is possible, TEM combined with PDF could give you a very strong understanding of local structure.
TEM is a fantastic and very powerful tool that I myself have not used much. Also electron diffraction that you can do with the same instrument can solve many materials science problems. Are you a specialist?
We have here now an workshop ADD2013 devoted to diffraction techniques and local structures. In fact you can also do PDF analysis of electron diffraction data.
The problem with the PDF of magnetic materials is of course the diffuse magnetic scattering coming from short range correlations of spins and the conventional PDF analysis do not take these into account.
Surely combined PDF and TEM will be very helpful!
PDF analysis is also becoming an established tool for investigating structures of nanoparticles. The structures of single nanoparticles should ideally be investigated by synchrotron X-ray and/or electron diffraction techniques, but so far we can only do that for realatively large nanoparticles, viz. 30 nm with synchrotron X-rays. My guess is that electron diffraction can do much better. What do you guys think?
The coherent diffraction from a single nanoparticle is the right technique for the determination of the structure of the nanoparticles. Only the manipulation and mounting of a single nanoparticle of size say 1-2 nm in the X-ray beam will not be trival! Also do we have necessary software to transform the diffraction data into atomic coordinates? In principle one has just to do Fourier transformation. This should be possible because the phase information can be extracted from the coherent diffraction data. Are there any other practical difficulties?
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