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 > > > No virus found in this incoming message. > Checked by AVG - www.avg.com > Version: 8.5.325 / Virus Database: 270.12.29/2114 - Release Date: 05/14/09 > 06:28:00 >
