I guess it is obvoius from the following that I am a big fan of Variable
Count Time (VCT) data collection which comes with the riet7/sr5 software which
has been modified to use data format -
ftp.minerals.csiro.au/pub/xtallography/sr5.
Generally, using variable count time allows you have time effective data
collections,
more stable and more accurate structure refinement and to go further than
normal fixed count time allows by having all the reflections roughly of equal
intensity over the whole range of the pattern (Hill and Madsen).
Though if you note from the second IUCr Rietveld Refinement Round Robin
(Hill and
Cranswick), there was no difference in the result in refining m-ZrO2 from the
participant using both fixed and variable count time data. Thus whether
Variable Count Time makes a difference can depend on the sample you are
dealing with.
Many substituted phases I have encountered seem to refine to more sensible
results
with VCT data. Fouriers can also look a lot cleaner with less background
noise.
You can also use the variable count time in GSAS by converting the VCT data
to GSAS ESD data using Mark Bowdens Convert for DOS.
ftp://ftp.minerals.csiro.au/pub/xtallography/convert-dos-cri
Thus any program that can take an ESD format can use VCT style data.
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The XRDTIME software has the option to generate a Philips 1710 output that
can automatically collect both fixed (conventional) and variable count time
data.
In theory, the source code also allows it to be adapted to other types of
diffractometers.
The program flow for collecting data:-
XRDTIME - generate XRD data collection commands
USE Philips Sendcomm.exe program to collect data (or any program
that can send a list of commands to the diffractometer and
collect the counts)
SPLIT - to separate the resulting datasets.
REFRMVAR - REFRMFIX - reformat the data into riet7/sr5 Rietveld format.
CONVERT for DOS - to convert VCT data into GSAS ESD format.
(not a GUI but it works OK)
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If anyone needs a hand with the XRDTIME program and VCT, either post to
the list or give me an email.
Cheers,
Lachlan.
Lachlan Cranswick _--_|\
Phone/Fax : (613) 9455-1345 / \
E-mail : lachlan@melbpc.org.au \_.--._/
Mobile Phone/Voice Mail : 0412-1141-31 v
Crystallographic WWW : http://www.unige.ch/crystal/stxnews/stx/volnteer.htm