I have an XRD pattern of malachite phase in a range of 5-50 degree in 2 theta. After that, I use MID-JADE software to refine the pattern and it shows a good refinement with low R-value and GOF < 2. I also attached the file here (File Refined by MID-JADE).
Later, I try to use Fullprof to refine this observed pattern, however, the obtained result is not good (File Refine.PNG). I follow the following procedure to refine the pattern:
1. I use Chebychev polynomial with 12 coefficient as MID-JADE for the background.
2. I refined scale factor.
3. Cell parameters
4. FWHM parameters
5. Shape parameters.
6. Atom position and etc.
Can anyone please help me to solve the problem? I also attach the observed data, CIF file of reference for you to check.
Thank you very much!!!
Dear Canh Nguyen ,
The start point's Fullprof sensitive parameter is the scale factor; I'll suggest to fit it initially by hand, and so as a free fitting procedure.
It is necessary to consider that the asymmetric peak profile may be responsible for the fitting result. Have you used a profile with divergent axial asymmetry?
FullProf Suite can handle it, asymmetric peak profile.
I am considering the material is stoichiometric.
Even in the MDI-JADE fitting some issues of peak intensities may be better addressed, try occupancy, divergent axial asymmetry, particle size distribution, and stack fault.
Best regards,
WNM
Canh Nguyen @ The first step should be adjusting the scale factor. By default, Fullprof shows a scale factor of 10^-2, you need to adjust this to say 10^-7. Then refine the scale factor and ensure that all the peaks are picking well. Ensure that scale factor is refiining.
Better to use the, "Linear interpolation between a set of background points with refinable heights" as back ground and manually select background points, say 50-100 (100 is the maximum).
If you don't select proper background, you can't fit the data at all. The refining of backgrounds you can do even at later stage.
Then refine lattice constant, one by one (if it is lower symmetry structure), then together.
Then W, then U, V, eta and X. The peak shape is mostly decided by W
Then asymetry parameter, Wyckoff positions, thermal parameter
Good luck
Dear, Wagner Da Nova Mussel and Sorb Yesudhas ,
Thank you very much for answering my question.
From your suggestion, I applied it to refine the pattern and now I have better refinement but its still not good.
I try to find these problems, but it's still not clear for me. Would you mind explaining more details about some issues:
1. Wagner Da Nova Mussel As you said, I try to refine asymmetry parameters. I put 50 to AsyLim in prc file as recommended by other guys on ResearchGate. Do we need to refine it manually or is it a reference value for it?
2. Sorb Yesudhas In Fullprof softwear, I do not see the Y value of peak shape. Do I need to change this value in pcr file? and what value is good?
3. One more thing is that the thermal parameters can not be negative, but I'm wondering that there is a upper limit for these value?
I also attach my file here. I think the peak shape is not good.
Thank you for taking your time.
Best regards,
Canh Nguyen
Canh Nguyen @In Fullprof, the width parameters are U, V, W, eta and X. The eta and X will have only minor roles. Could you please share me your pcr file and also data file, let me have a look into it.
Dear Canh Nguyen ,
I didn't mean only refine asymmetric parameters;
Please, use a divergent axial asymmetric peak function description.
Please, check the reference:
A Correction for Powder Diffraction Peak Asymmetry Due to Axial Divergence, Journal of Applied Crystallography 27(6):892-900 DOI: 10.1107/S0021889894004218.
Please see the figure attached.
Best regards,
WNM
Sorb Yesudhas Here is pcr file and data file. I try to fit atom position and thermal parameters but they seem to be not good.
Wagner Da Nova Mussel thank you very much for your recommendation. I've just tried to use it but it seems to work as good as pseudo-Voigt. But I will read through the papers.
Canh
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