Jae-Ho Chung wrote:
Dear experts on Rietveld with x-ray,
When it comes to Rietveld, I have exclusively been working with
neutrons. Now I am just trying Rietveld with x-rays, and immediately
came up with a question. Since x-ray scatters from electrons, it seems
to me that we always have to use, for instance, O-2 instead of O, and so
on, for ionic compounds. But I have an impression that O is still used
in many examples, including certain example files given in GSAS, such as
Y2O3.EXP. Why is it?
I suggest that you plot the scattering curves for O and O-2, and then
decide how much difference it makes. In addition, you should also
postulate a theory concerning the differences. Hint: The electron
cloud is not a "point object".
As a naturally following question, since no material is perfectly ionic,
the oxidation numbers may become another “refinable” parameters. But I
suppose they are never refinable in GSAS or in FullProf. Therefore, I
suppose the fractional occupation may be compromised instead? Is this in
any way discussed among x-ray experts?
See above. What experiment would you propose to make the oxidation
number be refinable?
Larry
