powder sessions at the ACA
Afternoon all Tomorrow is the abstract deadline for the Toronto ACA meeting and there is a severe lack of abstracts for the powder/materials sessions. We have been trying hard to push the agenda of powder and materials diffraction within the ACA and more generally but if we don't get abstracts the number of sessions will go down rather than up. If you are attending the ACA meeting please consider submitting an abstract for one of the powder/materials sessions. Thanks Pam Chair - IUCr Commission for Powder Diffraction Chair - ACA Materials SIG Dr Pamela Whitfield CChem MRSC Energy Materials, ICPET, Building M12, National Research Council Canada, 1200 Montreal Road, Ottawa ON K1A 0R6 CANADA Tel: (613) 998 8462 Fax: (613) 991 2384 Email: pamela.whitfi...@nrc.gc.ca
new user to pdfgetN and PDFfit
Hello all, I am a new user to PDFgetN and PDFfit and have received a disc with a tutorial for ZnTe0.5Se0.5 with information to plug into PDFgetN. I have plugged in all the information from the CD given to me in the sample information and the experimental information, and I don't know what to enter for detector information with the bank number and the Q min and max. Under the plotting icon the only options that are highlighted are under the data file and plot options. I don't know what I have to do to generate a PDF for this data. Then after this I have to generate a model to fit the data and do not know how to do that in PDFfit. Is there anybody who can help me with this process? Thank you, Chad Ruschman Graduate Student
Re: Example of simultaneous fitting in TOPAS Academic
Hi Shishir. I am no expert in TOPAS so can't help directly. However I would recommend looking at a paper by Graham Stinton and John Evans (Journal of Applied Crystallography, 40, 87, (2007)). It provides a good intro to the reasons for parametric Rietveld refinement and some of the procedures they use (with TOPAS). I hope it is of some help. Adrian Hill sisir ray wrote: Hi, Does any body have an working example code for TOPAS Academic for simultaneous fitting of different diffractograms obtained at different temperatures or for different doping concentrations .I really appreciate your help. -- thankyou, Shishir Ray Graduate Student -- Adrian Hill +33 (0)4 76 38 1927 European Synchrotron Radiation Facility (ESRF) 6, rue Jules Horowitz 38043 Grenoble France
Re: Example of simultaneous fitting in TOPAS Academic
Hi Shishir, I'd like to help, but I am not exactly sure what you want. First, you are asking for "example code". Does this mean that you want to work in launch mode instead of using the GUI? If so, why? Second, it would be important to know why exactly you want to use simultaneous refinement. This option only makes sense if you have parameters which should be the same for different data sets. If, for example, you have measured the same sample at different temperatures, what would be the common refined parameters? The lattice parameters are of course different for different temperatures. If you are doing a Rietveld fit, will you refine the atomic coordinates? If not, there should be no need for simultaneous refinement. If yes, I would argue that the atomic coordinates should differ slightly with temperature. Again, no need for simultaneous refinement. The only parameter I could think of whould be some intrumental parameter which shouldn't change with temperature or the sample measured (e.g. zero shift). The same arguments would apply for a doping series. Simultaneous refinement makes sense if you have measured the same sample with different wavelengths or methods. Whether it is reasonable to refine a common structure model on a combination of neutron and XRD data simultaneously is open for discussion. Multiple wavelength synchrotron data might be a good example for simultaneous refinement. Another possibility would be a series of phase mixtures composed of the same phases. If you are interested in refining the structures of these phases and can't get them phase pure, you might try to correlate the peak shape and structure parameters to partially compensate the effects of peak overlap between the different phases. Best wishes, Frank sisir ray wrote: Hi, Does any body have an working example code for TOPAS Academic for simultaneous fitting of different diffractograms obtained at different temperatures or for different doping concentrations .I really appreciate your help. -- thankyou, Shishir Ray Graduate Student
