Refinement problem

Watcharaporn Keankeo ( watchara@geology.anu.edu.au )
Fri, 24 Jul 1998 10:41:42 +1000

Dear Rietvelders
I am refining a structure of natural andradite-Ca3(Fe,Al)2Si3O12 and
encounter some difficulty. The isothermal parameter of Ca-atom is very high
(2.9) whereas the others are all negative. I check the positions of all
atoms are correct; and the R-factors are good. I wonder what causes this
strange behaviour of Ca- the instrument problem or its own andradite
structure? I tried to replace some of Ca-atoms with another possible cations
but did not help much.
Could anybody help me to understand this phenomenon?
Thank you very much.
Watchara