Dear Geetika This will not answer your question, buy maybe allows you change it.
As has been discussed several times in the Rietveld list, the only way to refine the occupancy of x cations in certain site is to have x or more independent determinations of the scattering power of that site. In your case it would be extremely difficult (if not impossible) to get four independent determinations (1 neutrons and 3 x-rays, 2 of them close to the absorption edge of two of you cations, at least). The result of one x-ray or neutron pattern is the average scattering power of the site, no matter how many cations you have spread in the same site. With only one average scattering power you can determine only one compositional variable for the site. So if you have cations A and B you can determine the partial occupancies of both only considering that they add up to one, so you are determining just one compositional variable with the constrain SOF(A)=1-SOF(B). Additionally, if you have 4 cations in the same site they are probably very similar in size, so also probably similar in scattering power, so x-rays will not allow you to determine the relative occupancies with accuracy. If you still want to determine the partial occupancy of the four cations in one site and don't have the four independent observations I suggest you to do a good chemical analysis that allows you deduce the site composition to a maximum of one variable. Hope this helps. Best regards Leo Dr. Leopoldo Suescun Argonne National Laboratory Materials Science Division Bldg 223 9700 S. Cass Ave. Argonne IL 60439 Phone: 1 (630) 252-9760 Fax: 1 (630) 252-7777 ----- Original Message ----- From: [EMAIL PROTECTED] Date: Saturday, February 24, 2007 1:20 am Subject: Occupancy Constraint... > Dear All, > > I am using FULLPROF 2006 for the analysis of my system. I am > having one > problem in defining the constraint. Actually I have 4 cations in > my system > and want to put a constraint as w+x+y+z=1. Is it possible to > define such > constraints using FULLPROF. > > > -- > "A successful man is one who can lay a firm foundation with the > bricks > others have thrown at him" > > Regards, > Geetika > Research Scholar, > C/o Prof. A. M. Umarji, > Materials Research Centre, > Indian Institute of Science, > Bangalore,Karnataka. > Pin Code-560012 > >
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