I am doing Rietveld refinement of catalyst which have two phase NiO and CeO2 respectively. I am using using MATCH software. However, MATCH is not letting me to select Atomic Co-ordinate checkbox for refinement.
I also tried to refine it with Fullprof manually. In this case it automatically got deselected after refinement while showing no changes in their values.
However, when I replaced NiO with other phase like SnO, La2O3 just for checking, the Atomic co-ordinate checkbox became available for use in MATCH.
I am unable to understand the reason behind this.
CeO2 atomic co-ordinate: Ce : X=0, Y=O, Z=0
O : X=0.25, Y=O.25, Z=0.25
NiO atomic co-ordinate: O: X=0.5, Y=O.5, Z=0.5
Ni : X=0, Y=O, Z=0
In these structures all atoms are in the special positions. Their coordinates are constrained by symmetry. See International Tables, Vol. A.
In these structures all atoms are in the special positions. Their coordinates are constrained by symmetry. See International Tables, Vol. A.
I wonder what do you want to do with software like MAUD or Fullprof? Unfortunately, software is not immediately dangerous for other people like cars, however, I would wish that for some software (except of programming languages) a qualification for its use should be required. You also cannot simply bye a car and (try to) drive around. Software misleads people to make any calculations, and then the resulting numbers will be published somewhere and possibly implemented in databases. Please note: A good software does not crash if wrong input data or settings are selected. A very good software tries to prevent or recognize any meaningless setting. Imagine in your case, the software would enable a refinement of atoms: the software would certainly get a result...and I would bet a wager, even a better fit (less constraints -> better fit but possibly less accurate or even wrong. That is the reason why constraints are implemented!).
What does this tell you? You should never use a software which you do not fully understand. And even then you should worry that there is no mistake in the software. My tipp: read some fundamental books about crystallography. I am sure you do not like it, but the only serious alternative is: Don't touch such software! The results you are generating are highly risky for anybody else (and finally may kill people). And in publications practically nobody has the time to test your results. The maximum is to find out, whether there are fundamental errors recognizable. However, I doubt, that there is a big number of reviewers who have the time for this very valuable job.
Based on Wykoff symbol (dictated by symmetry), atomic coordinated are restricted for refinements.
BTW, Have you tried HighScore Plus?
Malvern Panalytical's HighScore Plus is a graphical based easy to use option for Rieteld refinement.
You can request a demo version which works for 2 weeks from website: https://www.malvernpanalytical.com/en/products/category/software/x-ray-diffraction-software/highscore-with-plus-option
Some useful webinars:
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W20200529XRD
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W20200611XRD
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W20200702XRD?
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W20200728XRD.html
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