From the latest issue of Acta Cryst B:

Cover illustration: The structure of remacemide nitrate (C17H21N2O+·NO3-)
solved from powder diffraction data using a global optimization approach
based on maximum likelihood. Only the remacemide molecule is optimized
while the nitrate ion is treated as an unknown blur.
[Markvardsen, David & Shankland, Acta Cryst. (2002), A58. Submitted]

Image produced by Dr A. Florence, University of Strathclyde, Scotland,
using POV-ray 3.1.


Regards,

Kenneth

>Image produced by Dr A. Florence, University of Strathclyde, Scotland,
>using POV-ray 3.1.

http://journals.iucr.org/b/issues/2002/01/00/isscontsbdy.html

Quite beautiful. But for SDPD untrained people, it looks like
an UFO over the North Sea spying terrestrial derricks ;-).
Unbelievable, the sea and the sky are too blue for being honest.

Armel

Powder diffraction concepts were soon introduced in China.
Late Prof. X. S. Lu was in England with the two Braggs (son
and father - inventors of crystal structure analysis) during
mid-1930 (?) and was back to China early 1940 (?) or late
1930 (?).

A list of papers (full text available) is kindly provided by
Xiaolong Chen (Institute of Physics, Academy of Sciences,
Beijing).

http://sdpd.univ-lemans.fr/iniref/china/early-structures.html

ALB

Hi!

     Could somedy provide me some informations about Powder Diffraction and
Rietveld Method
usage in pharmaceutical area, or a website containing some informations about
this application
of powder diffraction techniques and analysis??

Thanks a lot,

     Luca Mollica


[Non-text portions of this message have been removed]

>    Could somedy provide me some informations about Powder
>Diffraction and Rietveld Method usage in pharmaceutical area,
>or a website containing some informations about this application
>of powder diffraction techniques and analysis??

SDPD (Structure Determination by Powder diffractometry) is
more and more applied to pharmaceutical areas. Clues about
that can be seen at :

http://www.icdd.com/
Using the search option with "pharmaceutical" returns 44
entries among which you can find the PPXRD symposium.
This was a strong indication that ICDD felt recently more
concerned by pharmaceutical areas. If you intend to use
powder diffraction, the main ICDD product (the PDF) is for
you. However, be aware that among the 136895 powder
patterns in the PDF, there are only ~24000 organics. A very
curious fact, if you consider the number of organic and
organometallic crystal structures known (>220000).

http://sdpd.univ-lemans.fr/iniref.html
In the SDPD database, you may look at the increasing
number of structures of pharmaceutical compounds
determined, as well as at the increasing number of methods
specific to organic compounds (molecule location by
grid-search, Monte Carlo, simulated annealing, genetic
algorithm...).

My opinion is that Powder Diffraction is a tool for identification
and characterization still insufficiently in use in pharmaceutical
areas, by wrong tradition (alternative like NMR is preferred).

Which was first of the egg or the chicken, according to your
answer, you may decide if this underdevelopment is due
to ICDD and the small number of powder patterns from organic
compounds, not allowing easy identification, or if it is because
of too few experts in organic compounds involved in powder
diffraction so that the PDF had no data to enter. A third
explanation is of course the old bad ICDD politics about not
including systematically calculated powder patterns. Improvements
are expected this century, may be...

Best wishes,

ALB

PS - Of course, if you only want to refine a known structure,
the SDPD reduces to the final step (the Rietveld method).

At 02:39 PM 2/7/02 +0100, you wrote:
>
>>    Could somedy provide me some informations about Powder
>>Diffraction and Rietveld Method usage in pharmaceutical area,
>>or a website containing some informations about this application
>>of powder diffraction techniques and analysis??
>
>SDPD (Structure Determination by Powder diffractometry) is
>more and more applied to pharmaceutical areas. Clues about
>that can be seen at :
>
>http://www.icdd.com/
>Using the search option with "pharmaceutical" returns 44
>entries among which you can find the PPXRD symposium.
>This was a strong indication that ICDD felt recently more
>concerned by pharmaceutical areas.

Dear Armel (and others),

ICDD have had an agreement in place with the Cambridge Crystallographic
Data Centre for 3 years now, which allows ICDD to calculate and distribute
powder patterns from the entire Cambridge Structural Database (i.e. organic
and organometallic small molecule crystal structures). It has taken some
time to process the entire database (which is now over 250,000 entries in
size) as many have problems such as disorder etc. where decisions have had
to be made about how to handle this in pattern calculation. But this is now
essentially complete and ICDD will, all being well, be releasing a
relational database product, as yet unnamed, by the end of 2002, which will
include all the recorded organic patterns from the PDF alongside the
calculated patterns for the organic entries from the CSD.

ICDD are also planning a second PPXRD event for October or November this
year, to be held at their Newtown Square, PA, USA headquarters.

So, things are moving !

Cheers,

Steve Maginn,
CCDC, UK


=====================================================

Dr. Stephen J. Maginn,
Support and Marketing Manager,
Cambridge Crystallographic Data Centre (CCDC),
12 Union Road,
Cambridge CB2 1EZ, UK

phone +44 (0)1223 762534
FAX    +44 (0)1223 336033
e-mail   maginn@...

http://www.ccdc.cam.ac.uk

=====================================================

>Did you not know that powder patterns calculated from CSD entries will
>(finally) be available from ICDD later this year?  It does take a while, but
>we finally get there...

Yes. But it is a delight to sing that gospel song for the last time ;-).

  >So, things are moving !

A great welcome step. Alleluia and Amen !

Armel

Dear all,

if I may enter in the discussion raised by L. Mollica, to which Armel added
some provocative statement, I think the question here is not how many
powder pattern from organic compounds/drug substances are present or not in
the ICDD. Pharma industries don't use PXRD to identify known components,
known phases. They rather develop their own compounds, for which PXRD is
one of the main characterization tools in the solid state (despite what
Armel said), particularly when the drug substance is in development.

From my experience, the pharmaceutical sector is fully aware of what SDPD
can offer, because the crystallisation stage can be difficult, thus the
single crystal technique is not always viable for all the compounds, and
polymorphs and solvates present. This interest is so great that has
prompted, for instance,  'Consortia' like the one we belong to, promoted by
Accelrys, called Molecular Crystallisation, in which programs for SDPD like
PowderSolve are developed (I don't want to start any discussion on
commercial software etc., it's just an example).

The fact that few crystal structures of drug substances determined from
PXRD are available is understandable because industries do NOT want to
publish them, for obvious reasons, not necessarely because they are not
aware of SDPD.

Talking about the Rietveld technique, my impression is that it has not been
fully exploited in the pharmaceutical sector for quantitative issues like
limit of detection of polymorphic mixtures and amorphous determination , as
far as publications are concerned.

yours

Emilio Tedesco

Please if some one has to learn a Reitveld program
which one can be more appropriate for a beginner (we
have many Rietveld programs)
if some one can give some advice.
Thanks

__________________________________________________
Do You Yahoo!?
Send FREE Valentine eCards with Yahoo! Greetings!
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> Please if some one has to learn a Reitveld program
> which one can be more appropriate for a beginner (we
> have many Rietveld programs)
> if some one can give some advice.
> Thanks
>

Some good comments previously on the Rietveld Users Mailing
list mentioned the idea that using a DBW derivative Rietveld
such as Rietica or Fullprof makes a good teaching program -
due to the requirement of the user having to know about
general and special positions as well as other crystallography
required for a good understanding of crystallographic
refinement.

  http://www.ccp14.ac.uk/tutorial/lhpm-rietica/index.html

  http://www.ccp14.ac.uk/tutorial/fullprof/index.html


Though it can be problematic trying to use any Rietveld program
without an understanding of the crystallographic
fundamentals - no matter how good the Interface to the
Rietveld program is.  Some of the web courses such as offered
by Jeremy Cockcroft at Birkbeck or Armel Le Bail et al at
LeMans may be worth considering if crystallographic courses
cannot be offered locally.

Lachlan.


--
-----------------------
Lachlan M. D. Cranswick

   1st Feb to 8th Feb - then 18th Feb to 17th March 2002
   CSIRO Division of Minerals
   PO Box 312, Clayton South,  Melbourne, Victoria,
   Australia, 3169.  Tel:  (613)  9545-8802
                     Fax:  (613)  9562 8919

Collaborative Computational Project No 14 (CCP14)
     for Single Crystal and Powder Diffraction
   Birkbeck University of London and Daresbury Laboratory
Postal Address: CCP14 - School of Crystallography,
                 Birkbeck College,
                 Malet Street, Bloomsbury,
                 WC1E 7HX, London,  UK
Tel: (+44) 020 7631 6850   Fax: (+44) 020 7631 6803
E-mail: l.m.d.cranswick@...    Room: B091
WWW: http://www.ccp14.ac.uk/

Hello,

No move towards a xtallography free archive ?
                http://www.eprints.org/

This cannot be expected from any xtallographer too
deeply involved inside the IUCr or ICDD (or etc) systems.

Professor Harnad's views about the fact that the paper
originally submitted is not the property of the editor
is interesting. The Editor's property is (only) the final revised
manuscript, then why not to make archives of original papers ?
http://cogsci.soton.ac.uk/~harnad/intpub.html
http://news.bbc.co.uk/hi/english/sci/tech/newsid_1818000/1818652.stm

ALB

I am in the process of replacing and old Philips diffractometer with a new
system. Currently the consideration is to replace it with a new Bruker D8, with
a primary beam monochromator (Ge) and  PSD detector. I have no experience with
the PSD detector and am wondering if there are any suggestions or comments as to
the optimization of this system (especially for collection of powder data to be
used in structure solution). Is this the best configuration and what advantages
does the PSD have over a solid state detector (other than speed)?

Thanks,
Michael Dicks

>Is this the best configuration and what advantages
>does the PSD have over a solid state detector (other than speed)?

According to Philips, the best configuration uses the X-celerator
detector... According to Bruker, or Rigaku, (or etc) the best configuration
may be different. Anyway, your configuration will certainly allow you to
be successful in SDPDs. Alpha-2 almost eliminated with low flux
consequence. Some problems with fluorescency are possible for 3d
elements (this is a disadvantage, but I cannot find any other advantage
than speed for a PSD).

Best

ALB
http://sdpd.univ-lemans.fr/powdif/low_fwhm_and_rp.html

>Is this the best configuration and what advantages
>does the PSD have over a solid state detector (other than speed)?

Armel covered it well.  Another thing that is worth mentioning is that
without collimation of the diffracted beam, it is impossible to study
anything that is on a single-crystal substrate, because of the many
secondary diffraction effects from the substrate at non-Bragg conditions.
If you are not doing any thin films, this will not be a problem.

				 - Kurt L.

>Is this the best configuration and what advantages
>does the PSD have over a solid state detector (other than speed)?

Sorry to use up bandwidth, but I thought of another problem with the PSD -
without soller slits, it cannot collect data below about 5 degrees two
theta, because of scattering from the primary beam.  If you are studying
clays or zeolites, this could be a limitation.

				 - K. Leinenweber

I'm not primarily concerned with structural solutions, so perhaps there
are other considerations, but with a primary beam monochromator  and a
PSD operating on a goniometer in transmission mode one can get down to
about 2 degrees.  This is still not ideal for clays but it is
considerably better than 5 degrees.  The situation improves further with
a longer wavelength tube such as cobalt in place of copper, which moves
the diffraction lines to higher angles, and may reduce fluorescence
background, depending on the sample.

John Twilley
Conservation Scientist


Kurt Leinenweber wrote:

>> Is this the best configuration and what advantages
>> does the PSD have over a solid state detector (other than speed)?
>
>
> Sorry to use up bandwidth, but I thought of another problem with the PSD -
> without soller slits, it cannot collect data below about 5 degrees two
> theta, because of scattering from the primary beam.  If you are studying
> clays or zeolites, this could be a limitation.
>
> 			 - K. Leinenweber
>
>
>
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>
>

Hi,

I am actually working on the Rietveld study of
Zirconia doped samples in which i would like to
extract the whole powder diff. pattern information
possible starting from cell parameters, till
microstructure, passing by amounts on different
phases.

The problem is that my samples are sintered pellets
which surprisingly (or not ?) leads to some problems :
It seems that diffractograms often show an important
sample displacement (maybe bad preparation ??)...which
would logically affect intensities.

My question is :
Is it reasonnable to work with sintered pellets
samples to perform Rietveld ?
If the answer is yes, is there a particular procedure
to prepare such samples...

precision:
- Unfortunately, these samples can hardly be milled
- and powders submitted to the same Heat-treatment
than pellets would surely lead to different structural
properties (in particular resp. amounts
tetra/monoclin. forms)
- orientation effects are surly not a problem since
samples are nanocrystalline

Thanks for your Help

Dr. G. Dezanneau
University of Barcelona
Dept. Electronica
Marti Franquès, 1
08026 Barcelona
Spain


___________________________________________________________
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Yahoo! Mail : http://fr.mail.yahoo.com

Hi,

	 As I have a couple instruments of both kinds, I'll add some general
comments, not only aimed at SDPD.

	 As Armel said, the primary beam monochromator+PSD does lead to data
stripped of Ka2 from the start, and you WILL get bad fluorescence background
problems if you use 1st row transition metals (but if you use this data
un-massaged, you can get beautifully low R's, which are absolutely
meaningless).  And yes, data collection is faster, at least from my
experience.



	 If you do not have diffracted beam Soller slits (you will probably
have to invent something of your own as I am currently doing) your low angle
peaks (and by that I mean below 15degrees or so) will look very strange and
anisotropic.  However, this does not limit you to above 5degrees two-theta,
it just gives you strange looking data.  I have gone down to 0.5 degrees for
normal scattered data, and below zero for thickness and roughness
measurements by reflectometry.

	 Low angle data from a conventional setup is usually pretty good, as
expected.



	 One advantage you have is that for regular powders, any crystal can
be used as a zero background sample holder - Just make sure that you do not
have an allowed reflection anywhere close to the scattering condition.  I
usually scavenge Si(111) wafers from old film depositions for sample
holders.  For high temperature work, old MgO or Al2O3 substrates are great
too.

	 For a conventional BB instrument, you have to buy specially cut
single crystals for your zero background sample holders.  They're really not
that expensive anyway.



	 Also, for thin film work, I find that having single crystal
substrates is not a problem - you may have a few weak and broad humps from
the substrate, which if you know they are there, you can easily remove.  In
fact, from my setup you can do a wonderful job of subtracting experimental
backgrounds to obtain "pure sample" diffractograms (e.g., you can remove
that annoying glass hump from your thin films data).

	 The same goes for the conventional instrument.



	 Finally, for thin film work, the instrument based on the PSD allows
you to collect data whose scattering vectors do not lie perpendicular to the
substrate.  This was the primary consideration for us when we designed/built
our thin films diffractometer.  The diffraction data is a lot richer and
looks more like what you would expect from a regular powder.  Also, you can
try to do a texture study from only a few diffraction patterns, rather than
having to collect a thousand intensities for several reflections.

	 On a conventional instrument with BB geometry data from a highly
oriented film usually ends up having one or two reflections, which also
gives you useful data.



	 Hope someone finds it useful, if only to decide what a misguided
fool I am.

	 AlexY


Dr. Alexandre F. T. Yokochi
Assistant Professor (Senior Research)
Director, X-ray Crystallographic Facilities
Department of Chemistry
Oregon State University
Corvallis, OR 97331-4003

Ph#  (541) 737-6724 Email: alex.yokochi@...
Fax# (541) 737-2062 Web Page: www.chem.orst.edu/yokochi

Hi again,

About the Philips X'celerator. A gain in speed of up to 99 is claimed.
http://www.analytical.philips.com/products/xrd/xpertpro/x_celerator/
It is also claimed that the large reduction in data collection
time can of course also be used to increase the resolution
of the diffractogram. In order to prove that, the NIST corundum
plate SRM1976 was measured overnight :
http://www.analytical.philips.com/news/press/content/file_133.pdf

I should state that we obtain that resolution and statistics quality
by using a proportional counter in 10 nights, not in 99 nights (but
not stripping alpha-2 with an incident beam monochromator...).

So, is there not some exaggeration with the X'celerator ?-). Do
users can confirm ?

I suppose that this new type of detector (Real Time Multiple Strip)
will be proposed soon by the other manufacturers, or is there
an exclusive Philips licence ?

ALB

Hello all,

I have been following this discussion with interest.  We have been X'Cellerator
users of the first hour and we have only had positive experiences with it. To
give you an idea of the gain in speed : we had a program defined for regular use
(phase identification) in which we measure a powder specimen from 8° to 100° in
4 hours with 0.04 Sollers (incident and diffracted).  Since the arrival of the
X'Cellerator, we do our phase identification runs from 5° to 120° in 45 minutes
with 0.02 Sollers.

Doing this, not only have we got much better statistics, but the peak shapes are
also much easier to fit.  Although they are somewhat broader than the peaks
obtained with a proportional counter (for the same Soller slits), their shape is
much more regular.  This results in BETTER determinations of lattice parameters
and quantitative analysis, because of an easier peak shape description.  To see
an example, take a look at
http://www3.sckcen.be/microstructure/Infrastructure/Infrastructure_XRD_XPert_Pow\
der_UO2%20lattice%20param.htm. The website is in full development, but it will
give you an idea.  If there's enough interest, I could provide this forum with
some spectra (for instance LaB6) taken in several configurations.

The background is different from what one obtaines with a proportional counter,
but smooth and, except for a broad bump at low angles, relatively flat.

We have been using a Ni filter to get rid of the Kb, because there was no back
monochromator available yet and we don't have a primary monochromator.  In a few
weeks, we will also have the new back monochromator available and I'll be able
to tell you more on that subject.

We have also done measurements with a capillary spinner and there also, great
results were obtained in much shorter times
(http://www3.sckcen.be/microstructure/Infrastructure/Infrastructure_XRD_XPert_Ca\
pillaries_UO2%2Bx.htm).  In the future, we are planning on doing some high
temperature diffraction (Buhler furnace), where I expect to see large gains in
speed too.  Considering the loss of 2 times 15% of the signal because of the Be
windows, I think the X'Cellerator will be very useful.

Has anyone ever considered applying signal theory as known in electronics to
diffraction patterns ?  Because of the recent improvements in resolution in the
diffractometers, a lot of effects such as axial divergence have become a rather
annoying problem in the description of diffraction peak shapes (at least in my
experience).  The combination of a high resolution goniometer with a fast, but
lower resolution detector may ultimately prove to be the best combination.  To
demonstrate this, it would be necessary to do the math.

Kind regards,

Sven Van den Berghe

****************************************************************
Dr. Sven Van den Berghe
Microstructure Research
Reactor Materials Research Department (RMO)
Laboratory for High and Medium Activity (LHMA)
Boeretang 200
B-2400 Mol
Belgium
Tel. : +32 14 33 30 64
Fax : +32 14 32 12 16
E-mail : svdbergh@... <mailto:svdbergh@...>
****************************************************************


> -----Original Message-----
> From: Armel Le Bail [mailto:alb@...]
> Sent: dinsdag 19 februari 2002 10:12
> To: sdpd@yahoogroups.com
> Subject: RE: [sdpd] Optimal instrument configuration
>
>
> Hi again,
>
> About the Philips X'celerator. A gain in speed of up to 99 is claimed.
> http://www.analytical.philips.com/products/xrd/xpertpro/x_celerator/
> It is also claimed that the large reduction in data collection
> time can of course also be used to increase the resolution
> of the diffractogram. In order to prove that, the NIST corundum
> plate SRM1976 was measured overnight :
> http://www.analytical.philips.com/news/press/content/file_133.pdf
>
> I should state that we obtain that resolution and statistics quality
> by using a proportional counter in 10 nights, not in 99 nights (but
> not stripping alpha-2 with an incident beam monochromator...).
>
> So, is there not some exaggeration with the X'celerator ?-). Do
> users can confirm ?
>
> I suppose that this new type of detector (Real Time Multiple Strip)
> will be proposed soon by the other manufacturers, or is there
> an exclusive Philips licence ?
>
> ALB
>
>
>
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>
>
> Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/

Hi,

As far as I have seen with my own eyes - measurements performed on my own
samples in Almelo in the Philips factory - there is no exxageration with
this 99 gain in speed. Using a secondary monochromator the speed gain is
about 16, but with a conventional detector you loose perhaps also a factor
of 6 when inserting a monochromator in the diffracted beam.
The design of this monochromator is very special, since it takes
(partially?) the diffracted beam out of the diffracting plane, because of
the special design of the X'celerator. For the moment the polarisation
factor of this monochromator is not known and have not been measured; they
say that they are working on  it.
The signal/noise ratio and the resolution are indeed comparable with those
of a traditional counter. For those who want to have a significant lower
signal/noise ratio the new Bruker Sol'X detector may be a better choice,
but that one is only slightly faster than a conventional one.
I will be able to do some more tests in a few weeks or so.

Don't know  if other manufacturers are working on this new technique. They
better do so.

Arie van der Lee

An addition to what I have said before on the X'celerator:
the configuration that is proposed by Philips does not give the possibility
to place a Ni-filter in the diffracted beam, so as to suppress fluorescence
without using a monochromator. So the Ni-filter can only be used in the
primary beam and is thus only useful for suppressing K-beta. In order to
suppress fluorescence the secondary monochromator is unavoidable.

Arie

Hello,

I remember a discussion about the fact that locating
molecules methods would need to be included in a
crystallography sub-topic. Well, this seems to be
done for the next IUCr congress :

http://www.kenes.com/iucr/main_topics.htm

02 Methods for Structure Determination

                  1. Difficult Structures
                  2. Direct Methods of Phase Determination
                  3. Maximum Entropy Methods
                  4. Anomalous Dispersion/MAD/MIR Phasing
                  5. Laue Time Resolved Methods
                  6. Incommensurate Structure Solution
                  7. EXAFS and XANES
                  8. High Resolution NMR and Macromolecules
                  9. Liquid Structure Determination
                  10. Structure Prediction: Computational Methods
                  11. Ab initio Powder Diffraction Solutions: Molecular
Compounds
                  12. Ab initio Powder Diffraction Solutions: Inorganic
Compounds
                  13. Ab initio Powder Diffraction Solutions: Electron
Diffraction
                  14. Ab initio Low Resolution Macromolecular Phasing
                  15. X-ray and Neutron Complementarity
                  16. Rietveld Refinement Methods

SDPD is gaining more place ;-).

I find their abstract system a bit curious, not allowing
sub or superscript. Chemical formulae will be strange
in the book of abstracts. Deadline March 1, 2002...

Armel

Hello,

I am updating (not finished yet) the SDPD-D for 2001 and was surprise
by the finding of a paper giving directly the SDPD-D classification in the
abstract. First time I see that... Even me, I don't do it.

Thanks a lot !

That paper is :

Structure determination and refinement of acid strontium oxalate from X-ray
and neutron powder diffraction
Vanhoyland G; Bouree F; Van Bael MK; Mullens J; Van Poucke LC
JOURNAL OF SOLID STATE CHEMISTRY 2001, Vol 157, Iss 2, pp 283-288
Sr(HC2O4)-1/2(C2O4)-H2O, P2(1)/n, C1=14, Nc = 42, C2 = 11, XC1 + N /
TREOR-97 and DICVOL-91, EXTRA, EQUI, SIRPOW-92 (DM), GFOURIER, FULLPROF

An example to follow ?

Armel

http://sdpd.univ-lemans.fr/iniref.html

Hello,

I survey changes at the ICDD Web site by the Tracerlock
system (at http://www.tracerlock.com/ ), because, if not,
there are few chances that announcements would be made
here about interesting SDPD events organized by ICDD (though
this is the only mailing list about SDPD).

Anyway, the PPXRD-2 is coming :

http://www.icdd.com/ppxrd/default.htm

       PPXRD-2
       Pharmaceutical Powder X-ray Diffraction Symposium
       December 9-12, 2002
       Philadelphia, PA, U.S.A.

Best,

Armel

Hi,

I just received the last IUCr Newsletter Volume 9, Number 3,
2001. There is an Accelrys advertisement inside telling :

"Powder diffraction problems ? Choose the easier way..."

And below that text is shown an old project of flying bicycle.
And more text : "Science, faster".

I conclude that Accelrys means by the "..." above that all which
is not Reflex plus corresponds to a more complex way...

Well, I am not the guy on the bicycle on their picture, are you ? ;-).

The easier way remains to be demonstrated. I can say too,
easily, that my way is the easier, and that Reflex Plus is a
submarine bicycle, this is just auto-advertisement (as usual
for commercial advertisement). Do company advisors believe
such declarations without questioning (I am afraid yes) ?

Best,

Armel

> "Powder diffraction problems ? Choose the easier way..."

i.e. single crystal diffraction.

Cheers,

Kenneth

>> "Powder diffraction problems ? Choose the easier way..."

> i.e. single crystal diffraction.

Yes indeed.

Though that does require some co-operation from your sample (or access to
special techniques, such as diffraction from individual microcrystals.)

Robin Shirley

To:            sdpd@yahoogroups.com
From:          "Shankland, K (Kenneth) " <k.shankland@...>
Date:          Thu, 7 Mar 2002 18:29:24 -0000
Subject:       [sdpd] Laugh?  I nearly started...
Reply-to:      sdpd@yahoogroups.com

> "Powder diffraction problems ? Choose the easier way..."

i.e. single crystal diffraction.

Cheers,

Kenneth





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

> >> "Powder diffraction problems ? Choose the easier way..."
>
> > i.e. single crystal diffraction.
>
>Yes indeed.

For those having not received the IUCr Newsletter and wanting
to laugh too (unless they recognize themselve as running the
flying bicycle ;-), the advertisement is distributed for free at :
http://sdpd.univ-lemans.fr/flying-bicycle.jpg

Best,

Armel

Hello,

In the long series of powder diffraction problems there
is a challenging one. Because the mineral in question is
a zeolite, I am sure that a lot of people would be interested
in solving its structure. Everybody can find it in most zeolite
review papers. Of course it has not been attributed a
framework code, since the framework is unknown. The name
is cowlesite, Ca6[Al12Si18O60].33H2O. JCPDS-ICDD 29-0286
and 46-1405. Micromounts of samples can be afforded for 3 US$.
A search in Google gives a lot about it.

Well, if you have a good synchrotron powder pattern, or even a
good conventional X-ray powder pattern, I would be curious to see it.
You may organize an interesting Round Robin. Solving the cowlesite
crystal structure is clearly a challenge for any SDPD package,
including those which "help you to solve crystal structure faster".

Best,

Armel

PS- 1 : SDPD thought of the day which may apply to cowlesite:
"A proposed cell without a crystal structure is highly dubious,
even if the cell comes from 'single crystal' data".

PS- 2 : The SDPD Mailing list will be unattainable from March 15,
evening to March 18, because of YahooGroups maintaining.