Dear Dr Peter Stephens, Dr. Martin Fisch and Dr. Noberto Masciocchi, Many thanks for your reply and useful tips.In particularcomments from Dr. Noberto M. and for sparing time in rearranging my .INP file. Best regards, Dr Naveed Zafar Ali
Subject: Re: Site occupancies refinement Date: Mon, 28 Apr 2014 08:00:50 -0400 From: peter.steph...@stonybrook.edu To: naveed...@hotmail.com CC: rietveld_l@ill.fr You seem to be confusing beq (thermal parameter) with site occupancy. At a start, I would think that the site would have the same thermal parameter for either atom, and refine occupancies that sum to unity. For example, site A1 occ Fe feocc .9 x 0 y 0 z Az .055 beq Abeq 2site A2 occ Ru =1-feocc; x 0 y 0 z =Az; beq =Abeq;will put Fe and Ru in the same site, refine the iron occupancy (feocc), common z coordinate (Az), and give them the same isotropic thermal parameter (Abeq). You could imagine that the lighter atom could have a larger thermal parameter, but it would be very hard to determine that from powder data because it would be strongly correlated with site occupancy, etc. **************************Peter W. StephensProfessor, Department of Physics and AstronomyAssociate Dean for Curriculum, College of Arts and Sciences Stony Brook University(631) 632-8156http://mini.physics.sunysb.edu/~pstephensPlease update your records to my new email: peter.steph...@stonybrook.edu On Mon, Apr 28, 2014 at 7:39 AM, NAVEED ZAFAR <naveed...@hotmail.com> wrote: Dear Rietvelders, I was actually doing the site (occupancy) refinement using TOPAS 4.1 software.While studying the effect of doping on one crystallographic site. We normally refine the sites of interest employ the following methodology.Consider e.g., Pervoskite structure (ABO3) as an example.If we wish to dope the A site in ABO3, and to confirm whether doping was successful or not, we normally refinethe occupancies in the following way. For example.We refine occupancies like occupancy of original site A =beq1 occupancy of dopant site A` =1-beq1 If the refinemnent goes well, all the crystallogrhic occupancies should merge to a single constant value, those crystallographic sites which are fully occupied should give [occ=1] and those doped should yield net occupancies [occ (A + A`= 1]. Can anyone share or suggest,why the Beq (isotropic temperature factor) values are going to huge,?? at the end of such a refinement. Which otherwise should be around [ Beq=Uiso*8pi^2]. Also if possible share .pro file (GUI mode or Launch mode) of such a refinemnet or some literature. Best regards,Dr. Naveed Zafar Ali ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Please do NOT attach files to the whole list <alan.he...@neutronoptics.com> Send commands to <lists...@ill.fr> eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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