Dear All,Many thanks for the useful TIPS and tricks about the factors effecting both peak shape broadening and peak intensities (PO).Am grateful to Jon Wright, Alan Hewat, and Luca Lutterotti for also shraing their views on the issue.Eva McCabe: Topas Wiki, really is awesome for users like me. Normally, I copy paste the relevant macro and found reasonabledecrease in Rwp value. But I would request the user to place an example file relevant to each contributed macro. That would be beneficial I presume. Moreover, I am also thankful to Peter Khalifah for writing in detail about the stuff, and for sharing the useful tutorial written by Arnt Kern and Pamela Whitfield (MMRRSA). As a novice user with basic experience in diffraction, I really wish to join such a useful workshop (MMRRSA) on Modern Methods in Rietveld Refinement and Structural Analysis, in future. Please also share such an event on this mailing list. With my best regards, Dr. Naveed Zafar Ali ___________________________________________________________________________________________________________
> Subject: Re: TOPAS Macro Language (peak shape broadening macros) > Date: Wed, 24 Jun 2015 22:16:56 +0200 > From: wri...@esrf.fr > To: rietveld_l@ill.fr > > 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: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
