For our LaB6 sample (from local Russian authority) and with my machine (Rigaku Miniflex II) I found Y=0.0497 (with Fullprof); X refines to essentially zero.
Long ago I did the same with "Bruker D8 Advance" and NIST SRM 660a. What I dug out from my old files is that the picture was essentially the same: Y=0.0323 and X refines to zero. Maybe this helps... Sincerely, Maxim. -----Original Message----- From: Huy LE-QUOC [mailto:huy.le-q...@lpsc.in2p3.fr] Sent: Monday, February 08, 2010 1:51 PM To: Maxim V. Lobanov Subject: Re: What is a good sequence for refinement of (U,V,W) of a multiphase sample ? Maxim V. Lobanov a écrit : > Actually, V and W reflect instrumental broadening - so better to be refined > globally or fixed at the values refined with a standard (LaB6 or similar). > U is a mixture of instrumental contribution and Gaussian strain broadening > term - so, can de different for three phases. But practically for such > difficult multiphase situation maybe indeed it would be better to refine it > globally, at least for intermediate refinements. > Generally, it makes sense also to refine Gaussian size broadening > [~1/cos^2(theta)], usually denoted P or Z (software-dependent). > > Sincerely, > Maxim. > > ------------------------------------------- > Dr. Maxim Lobanov > Head of R&D Department > Huntsman-NMG > mailto: m_loba...@huntsman-nmg.com > > -----Original Message----- > From: gre...@unisi.it [mailto:gre...@unisi.it] > Sent: Wednesday, February 03, 2010 6:10 PM > To: rietveld_l@ill.fr > Subject: Re: What is a good sequence for refinement of (U,V,W) of a > multiphase sample ? > > you better refine uvw globally for the sample and then Lorentzian x and y > individually for each phase. uvw should be constant for a given > diffractometer setting and you might get it from an independent refinement > of a standard. > > best > > miguel > > > On 3 Feb 2010 at 15:41, Huy LE-QUOC wrote: > > >> Dear Rietvelders, >> >> I'm currently doing Rietveld refinements (with FullProf) for a >> multiphase sample whose 3 phases with space groups Fm3m, P63/m and >> I41a/md. The problem is the reflections of these 3 phases are very >> superposed and hence I have found that their (U,V,W) refined parameters >> seem to be very correlated. >> >> I have read somewhere that for each phase we should begin refine W, then >> V and finally U. But I don't know in my case whose 3 phases having their >> own (U, V, W) we should follow which sequence ? First refine (U, V, W) >> of the strongest phase and then for others phases? Or should we refine >> simultaneously W for all phases and then V and U for all phases? >> >> >> Do anyone of you have any experience on this case ? >> >> Thank you in advance for your kindly helps. >> >> Best regards, >> >> --- >> Huy LE-QUOC, >> Doctorant >> LPSC/CNRS - Centre de Recherche Plasmas-Matériaux-Nanostructures >> et Institut Néel/CNRS >> 53 rue des Martyrs, Grenoble 38026, FRANCE >> >> >> > > -- > Miguel Gregorkiewitz > Dip Scienze della Terra, Università > via Laterina 8, I-53100 Siena, Europe > fon +39'0577'233810 fax 233938 > email gre...@unisi.it > > > > > Dear Miguel, Thank you for your kindly help. In fact, I'm trying with the refinement of a LaB6 standard to find out the instrumental values of line profile. For this purpose, I have selected the Thompson-Cox-Hastings pseudo-Voigt peak shape (Npr = 7 in FulProf) but I'm a little confused with the fact that: should I refine just only 3 parameters (U, V, W) and let X and Y which corresponds to strain broadening and size broadening, respectively, equal zero (because we don't have these effects with LaB6 standard, I think) ? Or I still have to refine both (U, V, W) and then (X, Y) even for LaB6 standard ? Thanks in advance for your any help with this question. Best regards, Huy LE-QUOC,
