Re: [sdpd] Reference materials for calibration and indexing

[Armel Le Bail <armel...@fluo.univ-lemans.fr>]

>What is the average size/strain results determined on the In2O3 or
>is this what the round robin will give?

It is not determined. Moreover, CeO2 is part of this Round Robin,
but In2O3 is not yet. The Round Robin is only at its first stage :
recording patterns of selected compounds, to my knowledge.

>Can the raw, uncorrected for intensity data for In2O3
>be put on the site or Emailed to those who are
>interested?  (me for starters)  

It would have been sufficient to multiply the intensities
back by sin(theta). But, yes, the original uncorrected data
set can be also found into PowBase now:
    http://www.cristal.org/powbase/
Use "In2O3" as keyword (without quotes) in the search engine,
the entry number is 169b.

>It would be interesting to test out these new computer
>controlled ADS slits vs fixed slits for Rietveld work
>given the old mechanical ones used to come in for
>criticism as being not as good as fixed slits for providing
>reliable intensities (and used to be far more painful
>to install and align compared to fixed slits).

Such a comparison exists already for a NAC sample
at : http://www.cristal.org/powdif/low_fwhm_and_rp.html
and the In2O3 data set adds a new convincing example that
it works sufficiently well, with the advantage of better statistics
at large angle without degrading resolution.

Let me recall that WinMProf is able to treat directly the
variable slit data without the need of any correction (the Rietveld
approach just includes the sin(theta) term, which is less
terrific than a LP correction, after all)

>I remember having an offline (verbal)
>discussion around two years ago where it was claimed the 
>standard modelling/correction of ADS intensity data using
>the 1/(sin theta) correction as being only approximately
>correct.  

This is very probably true : the correction is only approximately
correct. In my experience, the error is entirely reported on
the thermal parameters - which are knowingly the largest dustbin
in powder diffraction analysis - so that I am not sure if the B
values are degraded or improved by the process (they become
slightly smaller ;-)).

Best,


Armel Le Bail - Université du Maine, Laboratoire des Fluorures,
CNRS ESA 6010, Av. O. Messiaen, 72085 Le Mans Cedex 9, France
http://www.cristal.org/