Hi everyone,
I’m using FullProf to perform Rietveld analysis on Portland cement pastes. I’m a beginner with this technique. My χ², Rp and Rwp seem to stall around χ² ≈ 1.46, Rp = 14.6%, and Rwp = 19.0%. I’ve tried multiple refinement attempts, but the fitting doesn’t improve.
Questions:
- Are these Rp/Rwp/χ² values reasonable for cement pastes?
- What would you check first to improve the fit in such systems? (e.g., background function, peak asymmetry...)
- Do you have typical ranges for Rp/Rwp that you consider acceptable for well-modeled cement paste datasets?
Regards,
Hello Marcelo Miranda Farias
Answering your questions:
1 - The values of Rp/Rwp/X2 are very good, but these are not the only things you check to confirm that your refinement is good. It´s much more about visual checking. There will be cases which X2 of 2.5 is already a good result, as long as the model fits well the obtained data. So, if you want our help, we have to see what you got. Send message privately if it suits you better, I am totally willing to help.
2 - We have to actually see the whole refinement to make any suggestion. It´s not possible to make any suggestions without seeing what you made.
3 - As I said, depends on the visual matching of Rietveld model and your data.
Feel free to reply if you need help.
Best regards,
Dr. Ricardo Tadeu.
-No such criteria to decide as "very good" on the basis of Rp/Rwp/X2.
-The model is said to be good only when the difference line is flat.
-As per my knowledge, you should check the difference line visually and then the cell parameters, atomic parameters, and importantly the density, if these parameters are in physical limit then your model is fitted good.
Your agreement indices values are certainly good, but there are no reference values for these data and particualrly for a peculiar class of materials. Cements are complex systems, containing many times a lot of phases, so it is possible that something is missing. If you upload the result of your refinement maybe we can help you with some more specific comment.
El cemento es una mezcla de fases compleja, por lo tanto, lo primero es garantizar una buena estadística de tus polvos (granos menores a 10 micras para una buena colección de datos), después es conveniente conocer los dominios de homogeneidad cristalina y tener cuidado con las reflexiones a bajos ángulos, donde puede haber superposición de picos, una vez que se cumplan estas condiciones, lo importante es no sobreparametrizar el problema, recuerda que el programa FullProf Rietveld a diferencia de otros, no toma decisiones por ti, por lo tanto los parámetros que tu uses en base al conocimiento de la muestra te darán una máxima verosimilitud de las fases conocidas.
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