Hi,

First of all thank you for all the comments and suggestions for my first
email. About the internal standard, my purpose is to consider the
instrumental effect (e.g. peak broadening). I do not know whether this
effect can shift the peak positions. Can somebody give me information about
this?. The available diffractometer in my institute is a little bit old
therefore I have to make sure that the results are reliable enough.



Thanks and best wishes



Gumelar Pritosiwi


On Thu, May 14, 2009 at 3:45 PM, Leopoldo Suescun <leopo...@fq.edu.uy>wrote:

>  Dear Gumelar Pritosiwi,
>
>
>
> There are two independent topics in your question. If you are using a well
> calibrated conventional diffractometer to determine your cell parameters
> then you don’t need an internal standard. That would be useful if you,
> additionally, need to do a quantitative phase analysis.
>
>
>
> In a conventional machine with sealed tube source the cell parameters
> determination can be done easily in the case of cubic magnetite, because you
> already know the incident wavelength and d-spacings for the observed maxima
> are linearly related to “a” cell parameter by d(hkl)=a/sqrt(h^2+k^2+l^2).
>
>
>
> Programs such as FULLPROF, GSAS, TOPAS, etc. are meant for Rietveld
> refinement, that is something a little bit more complex than cell parameters
> determination, although most of these programs have additional routines
> (peak search and indexing in Winplotr) that can help determine cell
> parameters of an unknown phase, or in your case, of the magnetite you are
> studying. You can also try full profile fit (LeBail or Pawley methods) to
> extract best possible cell parameters provided your data is of enough
> quality and you are willing to cope with profile shapes, background
> modeling, etc. (too complicated to start with in my opinion).
>
>
>
> If you use data with internal standard for lattice parameters determination
> you may choose to ignore the internal standard peaks or just collect new
> data on the raw material where you just see your magnetite peaks (be
> careful, if your sample contains other crystalline materials you will need
> to identify the extra peaks and avoid using them for the cell parameters
> determination).
>
>
>
> Free programs like checkcell will allow you to determine your cell
> parameters by refinement of previously determined peak positions, other
> programs like Winplotr, PowderX, etc will allow you to perform a peak search
> and extract a peak list, other programs like CMPR can fit individual peaks
> and output a list of fit results. Any of these (and many more) you can then
> fit to obtain “a” using the abovementioned equation. There are probably many
> more free programs to do either thing more or less automatically so you
> should check the www or ccp14 site for information.
>
>
>
> If your magnetite show any kind of structural distortion this may be a bit
> more complex, but in that case you’ll need to check some crystallography
> book to get a better idea of what can you do with your powder diffraction
> data and how can you do it. A good book for beginners that gets all the way
> up to complex stuff is “Fundamentals of Powder Diffraction and Structural
> Characterization of Materials” by V.K. Pecharsky and P.Y. Zavalij edited by
> Springer.
>
>
>
> Hope this helps.
>
> Leo
>
>
>
>
>
>
>
>
>
> Dr. Leopoldo Suescun
>
> Prof. Agr (Assoc. Prof.) de Física       Tel: (+598 2) 9290648/9249859
>
> Cryssmat-Lab./DETEMA                             Fax: (+598 2) 9241906
>
> Facultad de Quimica, Universidad de la Republica
>
>   ,_.
>
>   |  \
>
>   |   v-
>
>  ,'     \
>
>  |      (
>
>  \__Montevideo, Uruguay
>
>
>
> *From:* Gumelar Pritosiwi [mailto:pritos...@gmail.com]
> *Sent:* Thursday, May 14, 2009 8:30 AM
> *To:* rietveld_l@ill.fr
> *Subject:* Introduction and Unit cell parameter determination
>
>
>
> Dear all,
>
> I am a new member of this mailing list. My background is environmental
> engineer. At the moment I am conducting a research related to the
> crystalline iron oxide magnetite. One of the analyses that I have to do is
> the determination the unit cell dimension (lattice parameter) of the crystal
> from X-ray powder diffraction data. So far, for the XRD analysis I have
> mixed my sample with an internal standard. Because I am a beginner in the
> crystallography, I would like to hear opinions on two things:
>
> - Is using an internal standard a good way of sample preparation for the
> determination of unit cell?. Can anybody give me an example of a good
> internal standard that can be used for XRD analysis?.
>
> - Can anybody give me a suggestion which free software can be used for the
> determination of unit cell parameter from XRD powder diffraction data (with
> internal standard)?. I have learned a little about FullProf but I don?t know
> whether this program can handle XRD data with internal standard or not. My
> knowledge about FullProf is very limited, therefore if some hints about this
> program are more than welcome. Is perhaps FullProf too complicated for me as
> a beginner?.
>
> ?
>
> Thanks a lot and best regards
>
> ?
>
> Gumelar Pritosiwi
>
>
> --
> Gumelar Pritosiwi
> Institute of Environmental Technology and Energy Economics
> Hamburg University of Technology
> Eissendorfer Str. 40
> 21073 Hamburg
> Tel ?+49 40 42878 3319
> Fax ?+49 40 42878 2315
>
>
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