X-Ray diffraction questions
Didn't know where to post this
Most of these questions sound very basic in nature and the answers are often given for granted, but as of recently a few doubts are arising.
0) This is very basic: the phenomenon of light diffusion when the X-ray hits the atom: is it simple light scattering where the incident light
preferably travels in the incident direction or is it something more? I've always thought of it as similar to Rayleigh scattering of light.
1) x-ray diffraction supposedly lets me identify the structure of crystaline solids because when the light hits the sample, it is diffracted at a
certain angle and you can find out the distance between planes from Bragg's equation from which you can further make out the reciprocal lattice (from
which you can furter obtain your spectra). This said, the sample has to have a certain % of cristallinity, because amorphous materials give a broad
band instead of narrow peaks and you can't understand anything from that. Is that right? Did I mess something up? Correct me, please.
2) Why it isn't possible to analyse the structure of elements which are present <2%? Often I am told that they are too much dispersed and very fine
and so you can't see them in the XRD pattern. But why? Couldn't they be seen just like powders?
3) powder vs single crystal: In my experience I've always worked with powders and I've also came to understand how you can derive the crystaline
structure despite all the orientations. What if I didn't have fine powders but bigger grains (hot pressed powders)? Can I analyse the bigger pieces or
do I have to crush them until I obtain a fine powder?
4) What happens exactly in the instrument? Nowadays, you just put the sample inside and it will give out the spectra with all those good looking
peaks, but how did it obtain them? I know that the first raw information it should receive is the points that make out the reciprocal lattice. Also,
there are many people who call them peaks, other who call them reflections and each of them says that the other way around is wrong because they
aren't peaks/reflections. Which is it then?
5) Which are the requisites for a decent XRD quantitive analysis that makes sense? In which cases you should be wary of the results? In which cases
you cannot carry out a quantitative analysis (common limits)?
Thanks for your time and attention
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