I am refining the high resolution XRD data of LiFeSnO4. Fe and Sn are present at two crystallographically distinct sites in oredered form. I would like to refine the occupancies of Fe and Sn at these two different sites to map the disorder of Fe/Sn distribution in crystal. I am using Fullprof software. I need help for input command where I can introduce the chemical constraints on the occupancy of these two? Where can I introduce this input command? Thanking you in advnace...
To refine cationic distribution within the same crystallographic site, you have to add a "minus sign" into the flag. E.g. below, gallium and iron are in the same position (i.e. 0.15, 0, 0.1751).
!Atom Typ X Y Z Biso Occ In Fin N_t Spc /Codes
Ga1 GA 0.1500 0.000 0.1751 0.575 0.8600 0 0 0 0
0.00 0.00 0.00 0.00 11.00
Fe1 FE 0.1500 0.000 0.1751 0.575 0.1400 0 0 0 0
0.00 0.00 0.00 0.00 -11.00
To keep constant the occupancy of the site during refinement of cationic distribution, there is a flag “11.00” on the first occupancy and “-11.00” on the second one. Thus when the occupancy of gallium changes, the iron occupancy has an opposite evolution keeping the whole occupancy equal to one.
Go to phases and select the structural method: Rietveld refinement at 1. png.
Select the refinement and click atoms in phase 1 at 2.png. Then the below window will appear for you to fill it.
Dear Profs, Lefevre and Sertkol Thank you for your informative explainations and time you have given to clarify my problems regarding usage of fullprof software. I have followed the explaination and is working well. Now I have one more question in my mind that can we put overall constraint on the chemical composition of single element present at 2 or more than 2 crystallographical distinct sites. If it is yes then, where should I enter the command of it... Thanking you once again...
Dear Sir,
What do u fill in the B column and Occ. could you explain those two symbols please.
Dear Sir,
you can link different occupancies and different elements in FullProf using Non Linear Integers (NLI).
I´ve attached an exemplary file linking 2 elements mixed on two positions.
The elements on each position are linked to be 1 (two NLIs, lower two lines)
and they are fixed to be 2 together on both positions (one NLI, first line).
Maybe you have to update your Fullprof as it´s a newer funktion.
Good look for your research
Markus
Dear @Christophe Lefevre
Much thanks for the answer. If an element occupies two different sites, for example Zn atom occupying both 4c and 8d sites in the lattice, which means for each 1 increment of occupation at 4c site comes along with 0.5 reduction of occupation at 8d site, how should I edit the prc codes?
Much thanks in advance.
Fangzhou Song Did you find a way to edit the pcr flags based on your question?
Shruti Chakravarty You can open .pcr file in notepad and write it manually. After that save it and open from the Fullprof software.
Christophe Lefevre Thank you for the information. Do you have any idea about the significance of the number 11.00? I have put 21 and -21 and it is also refining the occupancies correctly .
you can use any flag value like 11.00 and -11.00 for constraint or 21.00 with -21.00 for constraint...
this link may be helpful:
https://www.researchgate.net/post/Full_Proff_how_to_encode_constraint_relations_for_refining_the_occupation_rate_of_the_Wyckoff_position_when_there_are_more_than_3_atoms_in_this_site/1
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