Dear Kurt,
Xpert Pros are fantastic machines. Collections times are significantly reduced
with their new semi-conductor PSDs. The only snag with the machines is
that the
asymmetry at low angle is very stark - so much so that in effect you
are having
to model a multiple diffractometer situation. If you try and us fundamental
parameters to fit the date you run up against a commercial secret as to the
separation between each of the semi-conducting strips in the detector.
I don't know as yet, any Rietveld program that have profile functions that can
adequately model the low angle data from the new X'pert pro machines.
If anyone
does I'll be glad to know, and from a fundamental parameters approach what the
separation and/or width of the semi-conductor strips are?
Regards
William Bisson
Quoting Kurt Leinenweber <[EMAIL PROTECTED]>:
Hi All,
I am attempting to assist others to choose a new powder x-ray
diffractometer. We are currently looking at a Panalytical X'Pert Pro in
alpha-1 configuration, and I would like to know if anyone has any
experience with this for Rietveld refinements? For other reasons we
would like to keep the sample flat, but then we could not use the
alpha-1 configuration, so instead we would consider a "hybrid"
monochromator - I would like to ask if this monochromator makes it
impossible to do Rietveld? Also, any other insights and suggestions for
systems that are competitive with these would be welcome. We are at an
early stage and have time to think about this, will be looking at other
possibilities, and I would appreciate any suggestions.
Incidentally, I received some data on quartz (supplied by me) from the
alpha-1, and refined it using GSAS. The refined structural and thermal
parameters are fine, but I get strange r-factors, with wRp of 25% and
crystallographic R also near 25%, chi**2 of 0.5. Does anyone know why
this might happen? With my old Siemens D5000 I easily get down to 10%
or better in the r-factors right away, so something obvious must be
wrong.
Thank you,
- Kurt Leinenweber
William Bisson
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