I would advise the article from Brian H. Toby, 2006: "R factors in Rietveld analysis: How good is good enough?", Powder Diffr., Vol. 21, No. 1
This is in agreement with the previous answers! With some details/ context.
In the Rietveld refinement there aren't values of reference for these agreement indices due to their strict dependence on the conditions of the data collection (in house X-ray powder diffraction or synchrotron, the time per step..., the wavelenght of radiation and the composition of your sample). Sometimes you can find also values lower than 1, but are not particularly significant. In many cases, for Rwp, values lower than 10% are considered good. However, I think that the only way do decide if the fit is good is a visual judgement, always better than the agreement indices.
The point of doing a Rietveld refinement is not to get an excellent fit but to get the correct solution. For the later, Rp and Rwp values are of little use. You can easily get a smaller Rp or Rwp for an incorrect solution, although it will still be an excellent fit.
I agree with the answers of Marcelia and Lawrence. Visual judgement is the best way of ascertaining the fitting. If data quality is not good then with even a moderate fit your chi2 for fitting will be low. So please dont go for any statistical value.
I would advise the article from Brian H. Toby, 2006: "R factors in Rietveld analysis: How good is good enough?", Powder Diffr., Vol. 21, No. 1
This is in agreement with the previous answers! With some details/ context.
Hello
Rwp2/Rexp2=less than 4 this means your fitting process was good. Actually profile fitting is very important step to match your data. So please dont forget after your fittin every time check those numbers ratio.
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