|On Nov 14, 11:09am, patrizia canton wrote:
|> Subject: Solid solution
|> hello
|> I have a problem:two ions randomly distributed with the same atomic position
|> into the same cell, one ion is predominant, the other one is in minor
|> quantity (at the moment I don't know exactly this quantity). Is it possible
|> to consider these two atoms simultaneously? If it is, how can I do it?
|> thanks
|>-- End of excerpt from patrizia canton
|
|If you have any decent Rietveld software this should be straightforward
|enough. Give the atomic positions for the two ions the same codewords so
|that when these are refined they will stay the same. Refine the ionic
|occupancies and temperature factors for the two ions with separate codewords.
|You should then be able to find out the quantities of your two ions.
|--
|tony bell A.M.T.Bell@dl.ac.uk
|crystallographer and marathon runner (but not necessarily in that order :-))
|engineering and physical science research council
|daresbury laboratory, daresbury, warrington, cheshire, UK. WA4 4AD.
It is not going to be straightforward if your solid solutions is consisting of
elements with similar scatering factors for particular radiation.
One example:
Mn and Fe in garnet (50:50 according to microprobe data);
XRD data, Cu-radiation;
GSAS on VAX/VMS;
constrain for both atoms for atomic position; and
for the sum of both atoms to total 1;
Results after fractional occupancy refinement are something like
Fe = 1.7 and Mn = -0.7 ...
Solutions:
A. Don't try to refine site occupancies 8-( or
B. Find a very good friend with synchrotron radiation source and
go to radiation length that will give you distinctive scattering
factors. (BTW I am looking for such person)
Regards
Alex Haralampiev, haralaag@ucbeh.san.uc.edu
Dept. of Geology
Univ. of Cincinnati
P.S. If you are willing to help with one or two data collections on synthetic
products consisting of tourmaline, garnet, albite etc. and have available
synchrotrone x-ray source (or at least Fe-radiation tube) please let me know