Low R value

ifenghan

While refining synchrotron data, I noticed that even when the fitting is poor, the R-value is usually very low, often between 2 and 3. I have tried normalization before, which seemed to resolve this issue, but recently, I encountered the same problem again. Can anyone help me with this? Attached are the and xy files.

run-358-evt-1-epix10kaquad3.txt

6kB

run-358-evt-1-epix10kaquad3.txt

61kB

johnsoevans

You're Rp is very low as you have a high background compared to the intensity of the diffraction peaks. If you look at tthe background-subtracted values (_dash) they are far higher (70%). This issue is discussed in most of the Rietveld text books.

Depending on what you're trying to extract from the data this may/may not be a problem.

Make sure you're being appropriately critical about the information content of your data. Refining coordinates, adps and spherical harmonic corrections simultaneously is pushing the limits of even the highest quality pxrd data.

ifenghan

johnsoevans

Can we do something in TOPAS to adjust this problem?

johnsoevans

There isnt really a problem here, it’s just the limits of the Rietveld method for this sample recorded under these conditions. All you can do is try and record better data with lower background and a higher q ramge to get more informatio.