Hi! It is my experience, that if you want to refine all three: zero, sample displacement and the lattice parameter of silicon you need to bind to the very last peak of Si that appears about 157deg for Cu anode. So. if Ana doesn't use NIST standard silicon but her own powder the procedure would be the following: 1. Measure pure Si sample up to 160deg accurate enough to have a nice 444 peak at 157deg. If you can't go that far have at least 533 at 137deg. 2. Refine. 3. Visually examine the fit of the very last peak at you pattern. It's weak anyway, so the effect on least squares will be small and the software may just ignore some misfit there. But your eye will catch it. 4. Once you are done use the obtained zero and lattice parameter in your real sample and fix them both. 5. As the very last step of the refinement, release zero. If it stays within say 0.01deg you did your job! Cheers Stan
> of course you should, Ana! > > The coordinate of the origin depends on goniometer alignment which may > change from one diffraction to the next although, in my experience, > deviations from 0 are mostly the same. > > What should be fixed is the unit cell parameter of Si, but there is > considerable discussion in the literature about the exact value to be used. > If you have a sufficiently wide 2th interval (e.g. 0-140 deg), it > does not correlate too much with the origin coordinate, so I usu refine the > cell parameter as well. Accordance with lit values can then be discussed > to see if they make sense. > > BTW, what instrument are you using? > > > Best > > > Miguel > > > > Il 2017-03-29 10:55 Ana Isabel Becerro Nieto ha scritto: > >> Dear all, >> >> >> I am using Si as internal standard to calibrate my pattern. Should I >> refine the "Zero error" of the diffractometer if I am using the >> calibrated pattern? >> >> Thanks a lot, >> >> >> Ana >> >> >> DRA. ANA ISABEL BECERRO >> >> >> INSTITUTO DE CIENCIA DE MATERIALES DE SEVILLA >> >> >> CSIC-US >> >> >> [1] >> Libre de virus. www.avast.com [1] >> >> >> >> >> Links: >> ------ >> [1] >> https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_cam >> paign=sig-email&utm_content=emailclient >> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ >> Please do NOT attach files to the whole list >> <[email protected]> >> Send commands to <[email protected]> eg: HELP as the subject with no body >> text The Rietveld_L list archive is on >> http://www.mail-archive.com/[email protected]/ >> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ >> > > --- > michele gregorkiewitz Dip Scienze Fisiche, della Terra e dell'Ambiente > Universitďż˝ di Siena > via Laterina 8, I-53100 Siena [email protected], +39'0577'233810 > > > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > Please do NOT attach files to the whole list > <[email protected]> > Send commands to <[email protected]> eg: HELP as the subject with no body > text The Rietveld_L list archive is on > http://www.mail-archive.com/[email protected]/ > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > > >
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