Kurt, It looks like incorrect step size (difference between actual step size and one that is written in the file) or incorrect distance to the detector. The later may incorrect step size if detector is PSD.
I have similar situation with much smaller difference in peak position but the shift (difference between actual and written step size) varies from measurement to measurement. Bruker is working on this but so far no solution/cause is known. Your case may be simpler if the difference is constant. Perhaps calibration of detector or its distance to the sample is needed. Best, Peter Zavalij X-ray Crystallographic Center University of Maryland College Park, MD Office: (301)405-1861 Lab: (301)405-3230 Fax: (301)314-9121 From: Kurt Leinenweber [mailto:ku...@asu.edu] Sent: Thursday, January 08, 2009 6:09 PM To: Rietveld_l@ill.fr Subject: error in peak positions that is linear in theta Dear Rietvelders, (I hope this list is appropriate for this question). I am trying to set up a new D8 diffractometer from Bruker, and have it set up with a Vario monochromator focusing on a sample in a capillary. Of course I hope to do Rietveld refinement on the samples eventually. But there is an error in two theta of the peak positions on all samples, and the error is linear in two theta. At 40 degrees the error (measured minus expected) is about 0.020 degrees, at 80 degrees the error is about 0.040 degrees, etcetera. Has anyone ever seen anything like this and do you know where it could come from? Thank you very much, - Kurt ********* Kurt Leinenweber Dept. of Chemistry and Biochemistry Arizona State University Tempe, AZ 85287-1604 phone (480)-965-8853 fax (480)-965-2747 ***********
