Nandini If you're using standard Bragg-Brentano the true fundamental parameters fitting from first principles will happily fit low angle asymmetry, as the mathematical basis for it is well known (look for some papers that Alan Coehlo and Bob Cheary did a while back, in J.Appl.Cryst I think). Axial divergence is dealt with through modelling the effect of Soller slits, source length, sample width and receiving slit length if my memory serves. Monochromators, etc, also have effects, but these have to be determined empirically.
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 4, 2004 9:46 AM To: [EMAIL PROTECTED] Thanks, Pam and Jon for the clarifications. Again, does this approach take care of low angle peak asymmetry better? thanks, nandini --- "Whitfield, Pamela" <[EMAIL PROTECTED]> wrote: > Nandini > > The best people to reply on behalf of fundamental > parameters would be Alan > Coehlo or Arnt Kern. > But until they do here goes.... > > The more general form is convolution-based profile > fitting. This can be > used for all peak profile types, whereas 'pure' > fundamental parameters has > only been inmplemented for the simple Bragg-Brentano > case (no > monochromators). Other geometries have to be > empirically modelled using a > standard and some sort of user-defined convolution > on top of the source > profile. Better fits can often be obtained using > this type of fitting than > the normal pseudo-Voigt or Pearson VII functions (in > my experience at > least). Where convolution-based fitting really > comes into its own in in > complex quantitative Rietveld analysis where the > number of refined variables > would become untenable for normal peak fitting. > Using convolution-based > fitting it is possible to cope with upwards of 10 > phases with severe peak > overlap and still get good results with good > stability. For example, > quantitative Rietveld analysis of cements is > becoming routine. > > 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 4, 2004 6:42 AM > To: [EMAIL PROTECTED] > > > Dear All, > > > Is the fundamental parameter approach better than > mathematical approach used in most of the Rietveld > refinement programs? Does that mean programs which > use > that approach are better? Any suggestions? > > Nandini > > > > > __________________________________ > Do you Yahoo!? > Friends. Fun. Try the all-new Yahoo! Messenger. > http://messenger.yahoo.com/ __________________________________ Do you Yahoo!? Friends. Fun. Try the all-new Yahoo! Messenger. http://messenger.yahoo.com/
