Dear Franz, I'm sure there will be many opinions on this but here goes from me. The "sig" on the lattice parameters is only a measure of precision for the value and is not directly related to the microstrain broadening. It is more a measure of how well the peak positions can be collectively determined from the data by the lattice parameters. Broad peaks (from mustrain or small particles) are harder to position so can lead to poorer lattice parameter precision. The simple explanation for mustrain is that it describes a variation in unit cell dimensions due to either some external distorting force (stress) or some internal array of defects (e.g. substitutional disorder) that makes the crystallographic unit cells inequivalent & of slightly different dimensions from place to place within each microcrystalline particle. This smearing of the lattice dimensions in real space then (via Fourier transform) leads to a smearing of the reciprocal space, hence the Bragg peaks are no longer delta functions. The GSAS Manual has simple pictures that convey this idea and shows the different d-spacing dependence for mustrain vs particle size broadening. Hope this helps. Bob Von Dreele
________________________________ From: Franz Werner [mailto:[EMAIL PROTECTED] Sent: Wed 10/25/2006 8:48 AM To: rietveld_l@ill.fr Subject: GSAS: interpretation of strain broadening Dear All My question concerns the interpretation of the strain broadening percentage S as a result from GSAS refinements of CW X-ray data. I exclude Stephens' function here. Just the "simple" calculation from either the Gaussian (U) or Lorentzian (Y) component. Let's say one gets a value of 0.1% strain. Does it mean the lattice parameters vary by this amount? But on the other hand there are also the unit cell sigmas. How can one visualise this? Thank you for your comments. Kind regards Franz Werner Technische Universität Wien Austria -- Der GMX SmartSurfer hilft bis zu 70% Ihrer Onlinekosten zu sparen! Ideal für Modem und ISDN: http://www.gmx.net/de/go/smartsurfer
