Re: [sdpd] Re: Welcome to sdpd

[Robin Shirley <R.Shirley...@surrey.ac.uk>]

> One factor to bear in mind is that better data generally helps.

A synchrotron is certainly nice, if you have easy access to one, or can
afford to wait for beamtime.

Otherwise, use a *modern* *focusing* laboratory powder diffractometer.
Seek time on someone else's instrument, if you don't have one in your own
lab.  The difference in data quality from a good modern laboratory
instrument over a routine one from say 10 or 15 years ago is quite
remarkable.  Failing that, a well-aligned Guinier-Hagg camera can also
work wonders.

Being able to index the pattern is quite useful too.  Controlling
systematic errors (as well as having the best available resolution) is
crucial here, considering that 0.02 degrees of zero error (or the
equivalent due to specimen displacement effects) can be too much.

Good luck (is also helpful).

Robin Shirley
University of Surrey, England

---------------------------------------

To:            sdpd...@yahoogroups.com
From:          Jonathan WRIGHT <wright...@esrf.fr>
Date:          Wed, 22 Aug 2001 19:43:08 +0200
Reply-to:      sdpd...@yahoogroups.com
Subject:       Re: [sdpd] Re: Welcome to sdpd

At 06:14 PM 8/22/01 +0200, alb...@cristal.org wrote:
>This mail was sent personnally to a new SDPD mailing list
>subscriber who asked :
>
>>I want to know, what I have to do now.
>[...]
>Other (general and informative) links to SDPD welcome.

One factor to bear in mind is that better data generally helps. In order of
preference for structure solution one might propose:

1. Grow a single crystal
(if it's very small you might try a microcrystal diffraction beamline at a
synchrotron)
2. Obtain a highly crystalline powder and collect powder data at a synchrotron
3. When crystallinity limits the peak widths then collect the best data you
can manage.

For certain problems (not too many hydrogen atoms?) neutron data will also
help. "Best" data and "better" data are both subjective concepts which
would depend on the sample and the structure you are trying to solve. For
indexing a difficult unit cell (and trying to solve a structure) it's
probably worth remembering that electron diffraction methods also exist.

Anyone who noted a recurring theme of synchrotrons above might be surprised
to find that I'm currently employed at one! So I should avoid impropriety
and not plug the esrf website or mention that applications deadlines are
(always) fast approaching (somewhere). Robert Dinnebier has collected a
useful list of various facilities where you might try to find "better" data:
http://www.pulverdiffraktometrie.de/Links/measurement/measurement.html
The site also contains a number of other links which may be of interest to
readers of this list.

Jon

[As always, these are my own opinions]



 

Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ 




------------------------ Yahoo! Groups Sponsor ---------------------~-->
Get your FREE credit report with a FREE CreditCheck
Monitoring Service trial
http://us.click.yahoo.com/M8mxkD/bQ8CAA/ySSFAA/UIYolB/TM
---------------------------------------------------------------------~->

 

Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/