The approach you use describes anisotropy of the peak broadening in ellipsoidal approximation and it is not strange that fit is improved. The question is how adequate the model is. You may also try PSF #4. There was a lot of discussion recently on this list about the anisotropic broadening and perhaps someone will more details in response to this part. Question 3 about preferred orientation. GSAS has spherical harmonic approach in which you can specify shape of the sample (cylinder is one of the choices available), its orientation and maximum order of the harmonic you want to employ. The details can be found in the GSAS manual and the corresponding paper (J. Appl. Cryst. (1997). 30, 517-525) Good luck,
Peter Y. Zavalij University Crystallographer Institute for Materials Research and Chemistry Department Binghamton University, SUNY, Vestal Pkwy, East Binghamton, NY 13902-6000, USA Tel: (607)777-4298 Fax: (607)777-4623 E-mail:[EMAIL PROTECTED] http://materials.binghamton.edu/zavalij -----Original Message----- From: Darin Hoffman [mailto:[EMAIL PROTECTED] Sent: Monday, May 03, 2004 11:39 AM To: [EMAIL PROTECTED] To any one that can help: I am performing a rietveld refinement using GSAS on x-ray data of a rod material. I have thus far been able to make a good fit by simply attaining the Particle size and strain broadening. The data so far matches close to what I expect. I am using the type 2 pseudo-Voigt profile and have been trying to refine my fit with as few variables as possible. I have just recently started using the GSAS program so I have tried to use only the variables I know well. Mainly the size and strain parameters. I tried for my own curiosity to refine the Gamma variables (Gamma11,22,33,12,13,23). This has improved my refinement to a Rwp=0.14 rather than a Rwp=0.3. Since this has improved my fit I think I am using the variables correctly. So my question is: 1) What is the physical representation of these variables the gamma variable? The GSAS manual describes them as the empirical extension of the microstrain anisotropy. I know that they put weighting on the (h,k,l) coordinates to deal with line broadening but how do I know they are weighting them correctly for my hexagonal lattice? 2)From the GSAS manual (gamma=y): yl=y11(h^2)+y22(k^2)+y33(l^2)+2*y12(hk)+2*y13(hl)+2*y23(kl) What does this equation mean? 3) This question is on a slightly different subject: I know my material is cylindrical in shape is there a way to input this orientation into GSAS? Can someone give me a good reference in how to use either the March-Dollase Preferred Orientation or the Spherical Orientation? Thank you to who ever can help me solve these problems. -Darin Hoffman ################################################# Darin Hoffman Research Intern, NPDF Lujan Neutron Scattering Center Los Alamos National Laboratory e-mail: [EMAIL PROTECTED] PH: 505-667-8704 #####################################################
