Dear all,
I have a puzzle here. I have been learning GSAS for a while but still at a relatively low level. I am trying to calculate % of glass phase in a plasma sprayed alumina coating (eta alumina, ISCD #39104, space group Fd-3M, 227). The structure is copy-pasted as below:
Atom # OX SITE x y z SOF H ITF(B)
O 1 -2 32 e 0.37 0.37 0.37 1. 0 3.
Al 1 +3 8 a 0.25 0.25 0.25 0.503 0 3.
Al 2 +3 48 f 0.25 0 0 0.083 0 3.
Al 3 +3 16 d 0.625 0.625 0.625 0.564 0 3.
Al 4 +3 16 c 0.125 0.125 0.125 0.27 0 3.
However, when this CIF file is imported into GSAS (using EXPGUI), EXPGUI shows the following corresponding multiplicity
32
32
32
8
8
and GSAS-simulated XRD pattern is much different from the one generated from ICSD. Please help on this mismatch between ICSD and GSAS-EXPGUI.
Many thanks in advance
Don
Donald Wang
University of Connecticut
Dear Donald,
It must be pointed out that the space group generating software in GSAS always places the origin on a center of symmetry, a 1-bar site, if one exists. It will not generate the first setting in the International Tables for X-ray Crystallography for Fd3m or any of the several other centrosymmetric groups with 0,0,0 having a higher multiplicity at some other site.
Sincerely, Allen C. Larson
