ehsan
Hi,
I am trying to to do a full refinement of a solid solution sample. Due to changes in lattice constant and peak shifts, I can not get a good fit using predefined CIF files. Is it possible to modify the input file and consider the presence of solid solution phase?
Regards,
Ehsan
johnsoevans
If the .cifs you're using are correct you ought to be able to get a good fit of the end members. You should then be able to use the outputs of these refinements as input for other members of the solid solution. The refinements ought to converge readily, with just small peak shifts due to cell parameter changes and minor intensity changes due to site occupancy changes. If the refinements don't converge readily it suggests something else may be wrong.
ehsan
Dear Prof. John,
What is the meaning of "end members"?
Is it possible to change the coordinates of atoms in the unit cell in order to fit them into the shifted peaks? I indexed my sample and determined the best space group. However, it did not helped the fitting comparing to standard CiF data.
Thanks for your efforts.
Regards,
Ehsan
mfisch
Imagine Na_(1-x) K_x Cl. with 0 < x < 1 as solid solution series. KCl and NaCl are the end members.
Maybe, you should first play a bit around and see what changing atomic positions, occupancies and lattice parameters does to the calculated diffraction pattern. I suggest using a well known sample for this, e.g. rutile?
There are many examples that you can use on John's webpage...
ehsan
Hi,
Many thanks for the explanation.
I wonder if anybody has access to “cif” file for Iron Tungsten Carbide, C Fe2 W2, PDF Number 01-072-1987. Is it possible to obtain the Cif file from TOPAS. I fitted its peaks using Pawley refinement but the atomic positions are not available.