If you just want to try fitting the peaks, you could try something like this:
str phase_name "Metal_oxide" local broad 100 'crys size for hk0 and hkl local sharp 2000 'crys size for 00l local cs = IF (And(H == 0, K == 0, L > 0)) THEN sharp ELSE broad ENDIF; CS_L(cs) 'insert remainder of structure... Cheers Matthew ________________ Matthew Rowles CSIRO Minerals Box 312 Clayton South, Victoria AUSTRALIA 3169 Ph: +61 3 9545 8892 Fax: +61 3 9562 8919 (site) Email: [EMAIL PROTECTED] -----Original Message----- From: Frank Girgsdies [mailto:[EMAIL PROTECTED] Sent: Wednesday, 29 October 2008 22:05 To: Rietveld_l@ill.fr Subject: Anisotropic peak broadening with TOPAS Dear Topas experts, C) One could leave the spherical harmonics approach and go to a user defined model, which refines different Cry Size parameters for different crystal directions. In my case, two parameters would probably be sufficient, one for the c-direction, and a common one for the a- and b-direction. The Topas Technical Reference, section 7.6.3. gives a similar example of a user defined peak broadening function, depending on the value of l in hkl. I could probably come up with an analogous solution which has a 1/cos(theta) dependence and two parameters, one for the 00l and one for the hk0 case. My problem with this approach is how to treat the mixed reflections hkl. I suppose they should be scaled with a somehow weighted mix of the two parameters, where the weighting depends on the angle between the specific hkl and the c-axis. However, I no idea how a physically reasonable weighting scheme (and the corresponding Topas syntax) should look like.