Domain size work is a bit of a can of worms. It's something I looked at more carefully a while back for nanoparticle work, and the deeper I got into it the worse it got. Peak broadening methods tend to give 'apparent' sizes, either area or volume weighted, and require corrections (usually not done) to a give a physically meaningful value, e.g. for a spherical particle D = 4/3<Dvol>. Langford and Louer published quite a bit on crystallite shape effects on peak broadening of nanoparticles. I've never quite looked at published crystallite size results in the same way again, especially direct comparisons to TEM data.
As far as size distributions (yet another can of wriggly things) are concerned there are people far more qualified than myself to comment. For the double-Voigt, Davor Balzar's various publications are worth looking at, if a little difficult to follow at times for a poor experimentalist like myself :-) There is a full chapter in IUCr monograph "Defect and Microstructure Analysis by Diffraction". You'll find it on Davor's publication page http://www.boulder.nist.gov/div853/balzar/selpublic.htm I can't remember where I got it from, but there is an Excel spreadsheet that will directly convert GSAS profile parameters to double-Voigt size-strain results. Pam Dr Pamela Whitfield CChem MRSC Energy Materials Group Institute for Chemical Process and Environmental Technology Building M12 National Research Council Canada 1200 Montreal Road Ottawa ON K1A 0R6 CANADA Tel: (613) 998 8462 Fax: (613) 991 2384 Email: <mailto:[EMAIL PROTECTED]> ICPET WWW: http://icpet-itpce.nrc-cnrc.gc.ca -----Original Message----- From: Nandini Devi Radhamonyamma [mailto:[EMAIL PROTECTED] Sent: June 7, 2004 11:33 AM To: [EMAIL PROTECTED] Dear All, Following the discussion about fundamental parameters approach (which was very helpful), I have a few more questions regarding the profile functions and their refining. I apologise if they seem very trivial (or plain stupid). We have a Philips PW3040 X'celerator running in a flat plate Bragg-Brentano geometry. My interest would be to calculate the domain size. The X'pert suit of programs includes a Scherrer calculator. Is it but better to use other programs like Breadth (double voigt) for more accurate results ? Or GSAS suit will do the job? While profile fitting, how does one choose which profile to fit? Is it by trial or does it in anyway depend on the instrument or geometry. For eg. while trying XFit, I could see that the options run to fundamental parameters also and previous discussions pointed to a dependency of fundamental parameters approach to the geometry. For using Double Voigt, how can I obtain the Lorentzian and Gaussian contributions? Any advice in this matter will be highly appreciated since I am in the woods so to speak in getting accurate size distributions in our samples. Thanks in advance, Nandini N. Radhamonyamma School of Chemistry Queen's University Belfast Belfast BT9 5AG __________________________________ Do you Yahoo!? Friends. Fun. Try the all-new Yahoo! Messenger. http://messenger.yahoo.com/
