At first glance it looks like a classic microabsorption problem, but I don't have the linear absorption coefficients to hand. Using an internal standard with a too small absorption will tend to over-estimate the amorphous content. Ce versus Zn is a pretty big contrast for CuKa, even if the particle sizes are small enough. The whole point of that NIST series (674 I think) is that they were to be used as appropriate contrast matching standards for quant analysis, and were supposed to be quite different from each other.
Changing the wavelength to reduce the contrast (e.g. Mo) may help for that particular mix but probably won't completely solve it. Pam From: Peter Y. Zavalij [mailto:[EMAIL PROTECTED] Sent: November 15, 2007 9:07 PM To: rietveld_l@ill.fr Subject: Amorphous content Hi, I am trying to determine amorphous content using Rietveld refinement and internal standard. However resulting content of amorphous phase is really unrealistic. Moreover testing the method using standards with known amorphous content does not clarify the situation. For example ZnO (NIST, 95% crystallinity) used as standard to determine amorphous content in CeO2 (also NIST standard with 91% crystallinity) yield 25% of amorphous phase which is a little bit too much comparing with expected 9%. We tested several different standards, mixtures and preparations, different diffractometers and software without much luck... Seems like something simple is missing... Any clues? Many thanks, Peter Zavalij X-ray Crystallographic Laboratory Department of Chemistry & Biochemistry 091 Chemistry Building University of Maryland College Park, MD 20742-4454 Phone: (301)405-1861 Fax: (301)314-9121 E-mail: [EMAIL PROTECTED] http://www.chem.umd.edu/facility/xray/
