Re: TOPAS Macro Language (peak shape broadening macros)
On 23 Jun 2015, at 22:22, Khalifah, Peter kp...@bnl.gov wrote: Preferred orientation results in the central assumption that the measured intensity is proportional to the reflection structure being violated, This is actually quite new to me as definition of preferred orientation or better texture. Until now I thought that in the case of preferred orientations the measured intensity is proportional to the volume fraction of grains oriented in a certain direction……. As many people will tell you, it is much more effective to eliminate preferred orientation (though improved sample preparation) than to try to model it. We actually use preferred orientation (texture) to help structure solution, and I found more easy to model them than to eliminate them. But may be is just me. Best regards, Luca Lutterotti ---Luca Lutterotti Dipartimento di Ingegneria Industriale, Universita' di Trento, via Sommarive 9, 38123 Trento, Italy Temporary address: Laboratoire CRISMAT-ENSICAEN, Université de Caen Basse-Normandie, Campus 2 6, Bd. M. Juin 14050 Caen, France e-mail address : luca.luttero...@unitn.it Home page : http://www5.unitn.it/People/en/Web/Persona/PER0004735 New Maud page : http://maud.radiographema.com Phone number :+39-0461-28-2414 Fax : +39-0461-28-1977--++ Please do NOT attach files to the whole list alan.he...@neutronoptics.com Send commands to 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/ ++
Re: TOPAS Macro Language (peak shape broadening macros)
Hi Alan, In the limiting case of orienting all crystals in 3D you get a mosaic single crystal (e.g. [1], or using an XFEL to measure 1 at a time). Then the refined the crystal structure has somewhat better accuracy than with a 1D Rietveld fit. Perhaps not the most popular idea for this mailing list :-) The intermediate case of multiple patterns with properly modelled texture should also be better even for refinement. Simplistically - you can add information about overlaps like 511/333 cubic overlap if you have a series of patterns. With only a single pattern you introduce extra texture parameters without adding the extra information to pay for this (which is why people tell us to get rid of it). With multiple patterns the story is different, but the price is figuring out the texture properly. Cheers, Jon === [1] Kimura et al, Langmuir, 2006, 22 (8), pp 3464–3466 DOI: 10.1021/la053479n http://pubs.acs.org/doi/abs/10.1021/la053479n On 24/06/2015 19:46, Alan Hewat wrote: Both Peter and Luca are correct :-) Preferred orientation can indeed be used to help SOLVE (unknown) structures, but when you want to REFINE structures you should try to eliminate systematic errors such as preferred orientation, if possible by better sample preparation. That may not be possible with highly oriented crystallites such as nanotubes, and as Naveed found, modelling peak broadening will not help. Search the program manual for texture or preferred orientation modelling. Pax. Alan. On 24 June 2015 at 17:44, Khalifah, Peter kp...@bnl.gov mailto:kp...@bnl.gov wrote: Yes, that is of course a more precise and correct answer. I did not mean to imply that diffraction physics work differently, just that the data processing resulted in some badly wrong assumptions about the data being used for Rietveld refinement. __ __ I tried to give a quick answer to a basic question from a basic point of view. If it was an expert question, I would have left it to the experts like you :-) __ __ -Peter __ __ *From:*Luca Lutterotti [mailto:luca.luttero...@ing.unitn.it mailto:luca.luttero...@ing.unitn.it] *Sent:* Wednesday, June 24, 2015 3:52 AM *To:* Khalifah, Peter *Cc:* rietveld_l@ill.fr mailto:rietveld_l@ill.fr *Subject:* Re: TOPAS Macro Language (peak shape broadening macros) __ __ __ __ On 23 Jun 2015, at 22:22, Khalifah, Peter kp...@bnl.gov mailto:kp...@bnl.gov wrote: __ __ Preferred orientation results in the central assumption that the measured intensity is proportional to the reflection structure being violated, __ __ This is actually quite new to me as definition of preferred orientation or better texture. Until now I thought that in the case of preferred orientations the measured intensity is proportional to the volume fraction of grains oriented in a certain direction……. __ __ As many people will tell you, it is much more effective to eliminate preferred orientation (though improved sample preparation) than to try to model it. __ __ We actually use preferred orientation (texture) to help structure solution, and I found more easy to model them than to eliminate them. But may be is just me. __ __ Best regards, __ __ Luca Lutterotti __ __ ---Luca Lutterotti Dipartimento di Ingegneria Industriale, Universita' di Trento, via Sommarive 9, 38123 Trento, Italy Temporary address: Laboratoire CRISMAT-ENSICAEN, Université de Caen Basse-Normandie, Campus 2 6, Bd. M. Juin 14050 Caen, France e-mail address : luca.luttero...@unitn.it mailto:luca.luttero...@unitn.it Home page : http://www5.unitn.it/People/en/Web/Persona/PER0004735 New Maud page : http://maud.radiographema.com Phone number :+39-0461-28-2414 Fax : +39-0461-28-1977-- ++ Please do NOT attach files to the whole list 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 Alan Hewat, NeutronOptics, Grenoble, FRANCE * alan.he...@neutronoptics.com +33.476.98.41.68 http://www.NeutronOptics.com/hewat __ ++ Please do NOT attach files to the whole list alan.he...@neutronoptics.com Send commands to lists...@ill.fr eg:
RE: TOPAS Macro Language (peak shape broadening macros)
Yes, that is of course a more precise and correct answer. I did not mean to imply that diffraction physics work differently, just that the data processing resulted in some badly wrong assumptions about the data being used for Rietveld refinement. I tried to give a quick answer to a basic question from a basic point of view. If it was an expert question, I would have left it to the experts like you :-) -Peter From: Luca Lutterotti [mailto:luca.luttero...@ing.unitn.it] Sent: Wednesday, June 24, 2015 3:52 AM To: Khalifah, Peter Cc: rietveld_l@ill.fr Subject: Re: TOPAS Macro Language (peak shape broadening macros) On 23 Jun 2015, at 22:22, Khalifah, Peter kp...@bnl.govmailto:kp...@bnl.gov wrote: Preferred orientation results in the central assumption that the measured intensity is proportional to the reflection structure being violated, This is actually quite new to me as definition of preferred orientation or better texture. Until now I thought that in the case of preferred orientations the measured intensity is proportional to the volume fraction of grains oriented in a certain direction……. As many people will tell you, it is much more effective to eliminate preferred orientation (though improved sample preparation) than to try to model it. We actually use preferred orientation (texture) to help structure solution, and I found more easy to model them than to eliminate them. But may be is just me. Best regards, Luca Lutterotti ---Luca Lutterotti Dipartimento di Ingegneria Industriale, Universita' di Trento, via Sommarive 9, 38123 Trento, Italy Temporary address: Laboratoire CRISMAT-ENSICAEN, Université de Caen Basse-Normandie, Campus 2 6, Bd. M. Juin 14050 Caen, France e-mail address : luca.luttero...@unitn.itmailto:luca.luttero...@unitn.it Home page : http://www5.unitn.it/People/en/Web/Persona/PER0004735 New Maud page : http://maud.radiographema.com Phone number :+39-0461-28-2414 Fax : +39-0461-28-1977-- ++ Please do NOT attach files to the whole list alan.he...@neutronoptics.com Send commands to 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/ ++
Re: TOPAS Macro Language (peak shape broadening macros)
Both Peter and Luca are correct :-) Preferred orientation can indeed be used to help SOLVE (unknown) structures, but when you want to REFINE structures you should try to eliminate systematic errors such as preferred orientation, if possible by better sample preparation. That may not be possible with highly oriented crystallites such as nanotubes, and as Naveed found, modelling peak broadening will not help. Search the program manual for texture or preferred orientation modelling. Pax. Alan. On 24 June 2015 at 17:44, Khalifah, Peter kp...@bnl.gov wrote: Yes, that is of course a more precise and correct answer. I did not mean to imply that diffraction physics work differently, just that the data processing resulted in some badly wrong assumptions about the data being used for Rietveld refinement. I tried to give a quick answer to a basic question from a basic point of view. If it was an expert question, I would have left it to the experts like you :-) -Peter *From:* Luca Lutterotti [mailto:luca.luttero...@ing.unitn.it] *Sent:* Wednesday, June 24, 2015 3:52 AM *To:* Khalifah, Peter *Cc:* rietveld_l@ill.fr *Subject:* Re: TOPAS Macro Language (peak shape broadening macros) On 23 Jun 2015, at 22:22, Khalifah, Peter kp...@bnl.gov wrote: Preferred orientation results in the central assumption that the measured intensity is proportional to the reflection structure being violated, This is actually quite new to me as definition of preferred orientation or better texture. Until now I thought that in the case of preferred orientations the measured intensity is proportional to the volume fraction of grains oriented in a certain direction……. As many people will tell you, it is much more effective to eliminate preferred orientation (though improved sample preparation) than to try to model it. We actually use preferred orientation (texture) to help structure solution, and I found more easy to model them than to eliminate them. But may be is just me. Best regards, Luca Lutterotti ---Luca Lutterotti Dipartimento di Ingegneria Industriale, Universita' di Trento, via Sommarive 9, 38123 Trento, Italy Temporary address: Laboratoire CRISMAT-ENSICAEN, Université de Caen Basse-Normandie, Campus 2 6, Bd. M. Juin 14050 Caen, France e-mail address : luca.luttero...@unitn.it Home page : http://www5.unitn.it/People/en/Web/Persona/PER0004735 New Maud page : http://maud.radiographema.com Phone number :+39-0461-28-2414 Fax : +39-0461-28-1977-- ++ Please do NOT attach files to the whole list alan.he...@neutronoptics.com Send commands to 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 Alan Hewat, NeutronOptics, Grenoble, FRANCE * alan.he...@neutronoptics.com +33.476.98.41.68 http://www.NeutronOptics.com/hewat __ ++ Please do NOT attach files to the whole list alan.he...@neutronoptics.com Send commands to 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/ ++
