[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [sdpd] ADS and In2O3 data - XFIT Tutorial
>However, if varying slits widths are used, a progressive angular-dependent defocusing occurs and the quality of the data deteriorates. Furthermore, if the measured intensities are to be used in a Rietveld refinement, the slits opening needs to have a precision of at least 1% or, in other words, be reproducible to a few microns over the entire 2theta range. For these reasons, the use of such slits for a Rietveld refinement is not recommended."
Well, are all the variable slit systems identical ? Probably not.
The CeO2 pattern was also recorded with the Bruker variable slits
system (using 400 steps over the whole angular range, if I
remember well). I have now a series of patterns to which the
Rietveld method was applied, in spite of this being not recommended.
Let me ask you to show me on these patterns, most in PowBase
(NAC, In2O3, CeO2, NIST SRM 1976...) where is the big problem ?
The minimal FWHM is in the range 0.045-0.060°2-theta. The Rp
values (in the original Rietveld definition : background subtracted,
and peak-only) are in the range 5-10%. The atomic coordinates are
very close to the expected ones. The B are maybe slightly too small.
The cell parameters are OK. This is fine for me.
Some recommendations are made for being transgressed ;-).
Best,
Armel Le Bail
http://www.cristal.org/course/