Re: Quantitative analysis
[EMAIL PROTECTED] a écrit : Hi Blaise In Bragg-Brentano mode, sample spinning does nothin for PO. This is because the diffraction vector is normal to the sample surface, and sample spinning rotates along this vector. That's wrong! As I have already written, the empirical PO corrections like March-Dollase and Rietveld-Toraya suppose that the PO is fibre-like (axial symmetry). If your sample does not have fibre-like PO, you can create it by sample spinning. Radovan Spinning does increase your particle statistics, which almost always helps. If you're looking at a capillary, spinning the capillary does help with PO, but just being in a capillary helps PO. As to spinning speeds, a good guide is one revolution per data point. Cheers Matthew Matthew Rowles CSIRO Minerals Box 312 Clayton South, Victoria AUSTRALIA 3169 Ph: +61 3 9545 8892 Fax: +61 3 9562 8919 (site) Email: [EMAIL PROTECTED] -- Radovan Cerny Laboratoire de Cristallographie 24, quai Ernest-Ansermet CH-1211 Geneva 4, Switzerland Phone : [+[41] 22] 37 964 50, FAX : [+[41] 22] 37 961 08 mailto : [EMAIL PROTECTED] URL: http://www.unige.ch/sciences/crystal/cerny/rcerny.htm
RE: Quantitative analysis
hi all, not only fibre like, but single component fibre, and with the fibre axis parrallel to the sample normal (i.e. cyclic fibre. this is very restrictive and generally does not correspond to the real texture. Contrarilly to what has been said here or there, the March-Dollase does not ensure PO normalisation, but only the normalisation of this single component, there is then no physical restriction between all hkl lines in terms of crystal angles, which gives rise to a lot of fitting space with unreasonable solutions either in terms of QTA or QPA. A physically based correction for PO needs the calculation of the ODF, and more than a single pattern to be measured. But this is the price to pay for a corect estimate of phase amounts in textured samples. daniel -- Daniel Chateigner Professeur CRISMAT-ENSICAEN Bd. M. Juin 14050 Caen, France http://www.ecole.ensicaen.fr/~chateign/danielc/
RIET: availability of Golden Book of Phase Transitions, Wroclaw (2002)
A quick query for people A few of the ICSD crystal structure entries (such as [Metathenardite] Disodium sulfate(VI)) have references to: Golden Book of Phase Transitions, Wroclaw (2002) Does anyone know if this book really exists and where it can be obtained from? Even http://www.abebooks.com/ does not seem to know about it. Thanks in advance, Lachlan --- Lachlan M. D. Cranswick Contact outside working hours / Coordonnees en dehors des heures de travail: NEW E-mail / courriel: lachlanc *at* magma.ca Home Tel: (613) 584-4226 ; Cell/mobile: (613) 401-6254 WWW: http://lachlan.bluehaze.com.au/ P.O. Box 2057, Deep River, Ontario, Canada, K0J 1P0 (please use clear titles in any Email - otherwise messages might accidentally get put in the SPAM list due to large amount of junk Email being received. If you don't get an expected reply to any messages, please try again.) (Essayez d'utiliser des titres explicites - sans quoi vos messages pourraient aboutir dans un dossier de rebuts, du fait de la quantite tres importante de pourriels recue. Si vous n'obtenez pas la reponse attendue, merci de bien vouloir renvoyer un message.)
RE: Anisotropic peak broadening with TOPAS
Sorry, pressed the wrong button... If you just want to try fitting the peaks, you could try something like this: str phase_name Metal_oxide local broad 100 'crys size for hk0 and hkl local sharp 2000 'crys size for 00l local csL = IF (And(H == 0, K == 0, L 0)) THEN sharp ELSE broad ENDIF; CS_L(csL) 'insert remainder of structure... I don't know much about Lvol, but isn't an average crystallite size for a highly asymmetric crystal not all that meaningful? I am willing to be educated here, as I haven't had much need to get accurate crystallite size from diffraction data before Cheers Matthew Matthew Rowles CSIRO Minerals Box 312 Clayton South, Victoria AUSTRALIA 3169 Ph: +61 3 9545 8892 Fax: +61 3 9562 8919 (site) Email: [EMAIL PROTECTED] -Original Message- From: Frank Girgsdies [mailto:[EMAIL PROTECTED] Sent: Wednesday, 29 October 2008 22:05 To: Rietveld_l@ill.fr Subject: Anisotropic peak broadening with TOPAS Dear Topas experts, C) One could leave the spherical harmonics approach and go to a user defined model, which refines different Cry Size parameters for different crystal directions. In my case, two parameters would probably be sufficient, one for the c-direction, and a common one for the a- and b-direction. The Topas Technical Reference, section 7.6.3. gives a similar example of a user defined peak broadening function, depending on the value of l in hkl. I could probably come up with an analogous solution which has a 1/cos(theta) dependence and two parameters, one for the 00l and one for the hk0 case. My problem with this approach is how to treat the mixed reflections hkl. I suppose they should be scaled with a somehow weighted mix of the two parameters, where the weighting depends on the angle between the specific hkl and the c-axis. However, I no idea how a physically reasonable weighting scheme (and the corresponding Topas syntax) should look like. -- Frank Girgsdies Department of Inorganic Chemistry Fritz Haber Institute (Max Planck Society) --
