I am trying to refine my data in full prof and my chi2 is 0,834E11 and everytime i try to refine the data the plot deviates further from the actual data and the chi2 doesnt change. The first image is with the parameters found in literature and the second is after refinement, in some cases the peaks from the refinement disapear
Hello Eliana Fuentes
Fullprof is a very complete refinement software, and it can make refinements in more than one method. As I can see, your calculated pattern has some asymmetry, and it may be caused by the parameters of peaks broadening. Your chi2 less than 1 means that there is something very wrong with the parameters. You might have to start again, or to look for errors in refinement. I can help you with this.
Best regards,
Ricardo Tadeu
Hello，Because your XRD patterns of raw data shows a second phase (for example, at 6.6 degree), so when you refine this data, it has some difference from .cif file firstly. Then, I suggest you learning the process of Fullprof. In your PCR file, there are many parameters(like, lattice constant a, b, c; peak shape factor: H, V,W, and et.,.....) needed to be refine. sometimes, your refinement route is important and it leads a different result.
Hello, In your given image it is evident that the second phase around 7 degrees is also present, so during refinement use the appropriate .cif file and go to the profile section tick the scale firstly in the pcr file then run, it reduces the value of chi2 and makes attention on other parameters also.
Apart a phase that lacks, the main problem of the refinement is about the FWHM of the peaks, the calculated ones are too large. You should reduce their starting values and also reduce the asymmetry parameter (see the broad peak tail at the left of the calculated peaks)
Dear Eliana Fuentes
When you mention that "the data the plot deviates further from the actual data", refer to how, for example, the maxima at 2θ 5° is not displayed, or this maxima is not included in the Fullprof refinement, or both.
In principle, the boundaries of the diffraction pattern to take into account to be "refined" and "displayed" in the Rietveld refinement with Fullprof (shown in the image) should be changed. There are two different concepts, the first is the most important because it directly affects the refinement. The second has to do with the aesthetic aspect, to visualise the fit in the moment.
In the first case, if the refinement does not take into account important regions of the pattern, it could be solved by changing the 2θ boundaries of the pattern to take into account to be refined.
In the other case, you can simply edit the PCR file with a text editor to change the 2θ boundaries displayed during refinement. It should also not affect the refinement itself, which does not happen. This means that this case does not occur. Moreover, chi2 does not improve.
However, there is not enough information to be sure that the first option is happening. It could also be an incorrect parameter or condition in the .PCR file. To help you better it would be good if we could visualise the whole pattern and also check the .PCR file with its powder data.
Furthermore, it is not defined whether it is a Le Bail or a Rietveld refinement. I assume that it is a Rietveld refinement.
I would recommend that you do a Le Bail refinement first as a first step to check the accuracy of the models used. You will also have a very good starting point for the Rietveld refinement.
Kind regards
Analio Dugarte
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