Dear Rietvelders, I am a PhD student working at UCL (UK) and was wondering if anyone out there could help me with a diffraction related problem:
I am attempting to refine some neutron diffraction data on a powder sample that has a very laminar structure. The refinement is acceptable but close inspection shows that some peaks are modelled poorly compared to others. The relative intensity of each peak appears to be a good fit but some peaks are sharper than others whilst some are noticably broadened. The instrument responsible suggested using anisotropic strain within Fullprof to attempt to model the peak shape anisotropies (as an ILL instrument was used to collect the data). This worked quite well and when considering the crystallite morphologies it seems physically reasonable. I have also been using TOPAS to refine the some of the data for comparison and as a new user have not found a way of including this kind of anisotropic strain into the refinement. Is it possible? If so does anybody have an example? Many thanks for your help Ross Colman p.s If it helps in the discussion, I am analysing a crystal structure with P -3 m 1 symmetry and so the refinable parameters within Fullprof are s_400, s_004 and s_112. From a chemical point of view the c direction is only weekly hydrogen bonded and so the laminar structure seen in SEM should be within the a-b plane. ________________________________ Ross Colman G19 Christopher Ingold Laboratories University College London Department of Chemistry 20 Gordon Street London WC1H 0AJ Phone: +44 (0)20 7679 4636 Internal: 24636 Email: ross.col...@ucl.ac.uk <mailto:ross.col...@ucl.ac.uk>
