Re: [sdpd] Question

[Tay Yee Yan <one_twinklestar...@yahoo.com.sg>]

Dr Armel:
 
Thanks a lot! I will take note of these strategies!!
 
Regards,
Yee Yan

Armel Le Bail <alb...@cristal.org> wrote:

>May I know if a particular powder sample is in nano size and suspected to 
>be coupled with strain effect, defects like stacking faults and vacaccies 
>and finally with a known impurity. What is the best strategies to identify 
>those factors above using current XRD or other techniques? What if an 
>unknown impurity is present? Is there any good references that you can 
>recommend? Would like to hear advices from all of you!

Very short advices...:

Size effect - Identifying that your sample present domains of coherent
diffraction smaller that 100 Angstroms is easy: the FWHM become of
the order of one degree (2-theta) or more.

Strain effect on the broadening is order-dependent, size effect is not.
But this is hard to see immediately on the powder pattern if your sample
is not very simple (very simple meaning that diffraction peaks are
not overlapping too much at large angle).

Stacking fault generally affect some reflection families. So, having
many reflections narrow, and a few reflections broad is a good
clue.

Oxygen vacancies can be "seen" in general better by neutron
diffraction than by XRD (much efficient on heavy atoms vacancies).
The Rietveld method is necessary for a structure refinement.
Be cautious with the conclusions, data have to be perfect.
You may conclude erroneously to some vacancies effect if
preferred orientation is present, etc.

Identifying a known impurity is the affair of a search-match
software coupled with the PDF2 or 4. Then apply a multiphase
Riietveld software.

What if an unknown impurity is present ? Try to influence
the synthesis so as to obtain that new compound as a pure
phase and then index, solve the structure (the subject of this SDPD
mailing list) and refine it by using the Rietveld method.

A few references :
CCP14 : http://www.ccp14.ac.uk/
Search-Match Round Robin : http://www.cristal.org/SMRR/
Size Strain Round Robin : http://www.boulder.nist.gov/div853/balzar/s-s_rr.htm
SDPD Round Robin : http://www.cristal.org/sdpdrr2/
Rietveld Mailing List new archive : 
http://www.mail-archive.com/rietveld_l...@ill.fr/
     and the old ones : http://www.cristal.org/forum/rietveld_l/index.html
SDPD Mailing List archive : http://groups.yahoo.com/group/sdpd/
SDPD-Database : http://www.cristal.org/iniref.html
SDPD Internet Course : http://www.cristal.org/DU-SDPD/
Journals : http://journals.iucr.org/
Books :
B1- Introduction to X-ray Powder Diffractometry
by Ron Jenkins and Robert L. Snyder
Volume 138 of Chemical Analysis, Ed. J.D. Winefordner
Wiley-Interscience, 1996.
B2 - Modern Powder Diffraction
Reviews in Mineralogy, Volume 20
D.L. Bish and J.E. Post, Editors
Mineralogical Society of America, 1989.
B3 - The Rietveld Method
IUCr Monographs on Crystallography - 5
R.A. Young, Editor
Oxford Science Publication, 1993.
B4 - Fundamentals of Crystallography
IUCr Texts on Crystallography -2
C. Giacovazzo, Editor
Oxford Science Publication, 1992.
B5 - X-ray Diffraction Procedures for Polycrystalline and Amorphous Materials
H.P Klug and L.E. Alexander
Wiley-Interscience, 1974, 2nd edition.
B6- Defects and Microstructure Analysis by Diffraction
R.L. Snyder, J. Fiala and H.J. Bunge,
IUCr Monographs on Crystallography, Vol 10,
Oxford Science Publications, 1999.
B7- Structure Determination from Powder Diffraction Data
W.I.F. David, K. Shankland, L.B. McCusker, and Ch Baerlocher,
IUCr Monographs on Crystallography, Vol 13,
Oxford Science Publications, 2002.

Etc, etc, etc

Best wishes,

Armel


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