Large R_exp and Wt% Rietweld errors

marekgocnik

Hello everyone,

I am working on Rietveld refinement of steel samples, where the data was obtained by synchrotrone radiation.

After refining the parameters the fit looks in very good agreement with measured data. But, when I check the R_exp and Wt% Rietweld errors the values are
R_exp = 100.45
GOF = 0.05
Wt% Rietveld = 71.706

I have found another threat with recomendation to read "Rietveld refinement guidelines" by McCusker, unfortunatelly it did not help.
I have inclueded a picture from TOPAS. Any ideas/suggestions are welcome.

Have a nice day, Marek

rowlesmr

Your GOF is very much less than one, so i'm guessing that the intensity errors are not properly set in your data file.

What does the diffraction data file look like?

marekgocnik

rowlesmr
Hi, thank you for your response.

I am not exactly sure about your question, I will try to answwer it. I have .xy diffraction dile (2Theta @ Intensity) without an error collum.
When the data is examined even in log scale in Origin, there is no background, very high quality meassurements.

Have a nice day,
Marek

johnsoevans

Now the data image has appeared the numbers you quote look surprising, espectially if you mean Rwp by Wt% Rietveld. Are you showing the entire fit in the image? Is your Rp value sensible (it looks like it should be <10% from the plot)?

If you have .xy data then TOPAS will be assuming esds of (yobs)⁰.5 and weighting accordingly unless you've applied a specific weighting scheme.

Is there anything odd in the data like a 0.0 intensity which might be throwing things?