[sdpd] superstructure and GSAS...

[Marco Sommariva <marco.sommariva...@mater.unimib.it>]

Dear all,
I have a question about GSAS:
my TOF neutron diffraction profile exhibits a broadening of some low
intense superstructure peaks where the index l is =2n+1 (tetragonal I
cell). I'd like to do a refinement where this effect is taken in
account. The superstructure is probably due to an ordering of vacancies
in planes perpendicular to z-axis.
I tried to use  Stephens's function n°4 in GSAS, setting the anisotropic
broadening axis to 0 0 2, and the other two vectors as 1 0 0 and 0 1 0
(because I should describe with three vectors the sub-lattice with sharp
peaks, which has index l=2n, while the others are general); but my
refinement doesn't work: the calculated profile presents very sharp
peaks for all experimental peaks.
What is my mistake?
Thanks in advance,
Marco Sommariva



-- 
Marco Sommariva
Department of Materials Science
University of Milano - Bicocca
Via R. Cozzi 53 - 20125 MILAN, ITALY
Phone +39.02.6448.5141 (5142)
Fax   +39.02.6448.5400
e-mail: marco.sommariva...@mater.unimib.it



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