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 <[email protected]> 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:[email protected]] > *Sent:* Wednesday, June 24, 2015 3:52 AM > *To:* Khalifah, Peter > *Cc:* [email protected] > *Subject:* Re: TOPAS Macro Language (peak shape broadening macros) > > > > > > On 23 Jun 2015, at 22:22, Khalifah, Peter <[email protected]> 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 : [email protected] > 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 <[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]/ > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > > > -- ______________________________________________ * Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE * <[email protected]> +33.476.98.41.68 http://www.NeutronOptics.com/hewat ______________________________________________
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