Hi, Seems everyone has beaten on this matter quite well. I humbly offer this paper: http://nvlpubs.nist.gov/nistpubs/jres/120/jres.120.013.pdf which discusses how you can experimentally determine (eliminate) the zero error with considerable certainly.
You should consider what you know the most, and least, about: you can never know the sample displacement or attenuation errors, you might know the lattice parameters, and you can eliminate the zero error if you want to. You can refine all parameters with high angle data; but you must be careful to inspect results for loss of physical plausibility. I do this only as an adventurous exercise. Regards, Jim James P. Cline Materials Measurement Science Division National Institute of Standards and Technology 100 Bureau Dr. stop 8520 [ B113 / Bldg 217 ] Gaithersburg, MD 20899-8523 USA james.cl...@nist.gov<mailto:james.cl...@nist.gov> (301) 975 5793 From: rietveld_l-requ...@ill.fr [mailto:rietveld_l-requ...@ill.fr] On Behalf Of David L. Bish Sent: Wednesday, March 29, 2017 9:41 AM To: rietveld_l@ill.fr Subject: Re: using Zero Hi Ana Isabel, Following up on Stan's comments, we always perform this type of calibration with a certified standard, e.g., an NIST standard (Si or LaB6). We then measure data from below the lowest-angle peak up the high-angle limit of the instrument (about 155 deg. in our case). If you use a certified standard, you can FIX the unit-cell parameter(s) and refine zero error and specimen displacement corrections. I typically obtain good refinements, with small esd's, when I follow this procedure. After all, the purpose is not to obtain the unit-cell parameter of your standard. If you have the ability to adjust the zero error of your instrument, you can then do that after doing your refinements. Ultimately you should be able to achieve a very small zero error. Make sure you then use that refined zero error in subsequent refinements, until you realign your instrument. The zero error should not be a function of your sample. Specimen displacement is a function of each sample (mount) and should always be refined to obtain more accurate (not precise) unit-cell parameters. Cheers, Dave On 3/29/2017 9:23 AM, Leopoldo Suescun wrote: Hola Ana Isabel, As Stan said, if you go high enough in 2theta you have enough data to de-correlate zero and sample displacement corrections and you can refine them together with lattice parameters, and have correct values for the three. The reason for thi si that delta(2theta) for each peak is a fixed amount with zero (for all 2theta), proportional to -Scos(theta) with S sample displacement and proportional to arcsin(lambda/2d) with change of lattice parameters. Since these three terms affecting peak positions have different behaviors with 2theta, zero is constant, displacement is maximum at low and high 2theta but null at 90 and lattice parameter increases the shift with 2theta (as does the separation of Kalfa1 and Kalfa2 peaks) then with a wide-enough patterns you will see the effects of the three affecting differently the low, mid and high 2theta peaks, making a refinement possible. But again, you need to go very high in 2theta to be able to de-correlate the three effects, collecting data from 10 to 80 degrees won´t allow you to refine more than one of the three with confidence (assuming the two you fix are correct). Of course, aligning your diffractometer correctly and placing the sample at the place where it should be is always the best choice... Good luck with your work Leo 2017-03-29 8:38 GMT-03:00 Julian Richard Tolchard <julianrichard.tolch...@sintef.no<mailto:julianrichard.tolch...@sintef.no>>: I would also suggest that it is easier to just check that your instrument zero is aligned than to mess around with long scans and fitting routines to separate correlated variables. Jools -----Original Message----- From: rietveld_l-requ...@ill.fr<mailto:rietveld_l-requ...@ill.fr> [mailto:rietveld_l-requ...@ill.fr<mailto:rietveld_l-requ...@ill.fr>] On Behalf Of "Lukasz Kruszewski" Sent: 29. mars 2017 13:25 To: Ana Isabel Becerro Nieto <ani...@icmse.csic.es<mailto:ani...@icmse.csic.es>> Cc: rietveld_l@ill.fr<mailto:rietveld_l@ill.fr> Subject: Re: using Zero Hi. You can do that, of course, but you have to choose: you can use Zero error OR sample displacement, but never use both (this induces some physical impossibilities). However, I assume your diffractometer is calibrated, and the zero position of the detector is fine; the sample displacement may (I suppose) be connected with preparation-derived errors, and I'd use the latter parameter instead of the zero error. Hope this helps anyhow. Good luck! Luke Kruszewski > 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 > > > > > > > > --- > El software de antivirus Avast ha analizado este correo electrónico en > busca de virus. > https://www.avast.com/antivirus > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > Please do NOT attach files to the whole list > <alan.he...@neutronoptics.com><mailto:alan.he...@neutronoptics.com> Send > commands to <lists...@ill.fr<mailto:lists...@ill.fr>> eg: > HELP as the subject with no body text The Rietveld_L list archive is > on http://www.mail-archive.com/rietveld_l@ill.fr/ > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > > -- Łukasz Kruszewski, Ph.D., adjunct Polish Academy of Sciences Institute of Geological Sciences Twarda 51/55 str. 00-818 Warsaw Poland ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Please do NOT attach files to the whole list <alan.he...@neutronoptics.com><mailto:alan.he...@neutronoptics.com> Send commands to <lists...@ill.fr<mailto:lists...@ill.fr>> eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -- Dr. Leopoldo Suescun Prof. Agr (Assoc. Prof.) de Física Tel: (+598) 29290705/29249859 Cryssmat-Lab./Cátedra de Fisica/DETEMA Fax: (+598) 29241906* e-mail: leopo...@fq.edu.uy/leopoldosues...@gmail.com<http://leopo...@fq.edu.uy/leopoldosues...@gmail.com> Facultad de Quimica, Universidad de la Republica. Montevideo, Uruguay Ahora la cristalografía importa más (www.iucr.org<http://www.iucr.org/>) Crystallography Matters more. ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Please do NOT attach files to the whole list <alan.he...@neutronoptics.com><mailto:alan.he...@neutronoptics.com> Send commands to <lists...@ill.fr><mailto:lists...@ill.fr> eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -- David L. Bish Department of Geological Sciences Indiana University 1001 E. 10th St. Bloomington, IN 47405 812-855-2039
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