layered clay minerals
Dear Ana, Generally, as many of the contributors of this list said, smectites are only partly crystallised (sometimes turbostratic). Means you may observe nice 00L peaks, and diffusion bands along HK0 lines. These latters should be approached using appropriate formalism, actually I think not implemented in usual programs. You could find out how this formalism works, reading Dritz and Tchoubar books on the subject. On perfect powders, we (I and A. Manceau and B. Lanson in Grenoble, LGIT) could simulate diagrams like this using their formalism, taking account of bimodal compositional faults. Now on top of this, as in our case, a strong preferred orientation is also present in the sample. In these cases, we found useful to combine polarised EXAFS experiments with Quantitative Texture Analysis in order to sort out structural details. Please see on my personal web page, I have placed pdf files on this subject. daniel Quantitative Texture Analysis Internet Course: http://pecdc.univ-lemans.fr/qta/ -- Daniel Chateigner LPEC, UMR-CNRS 06087, Université du Maine-Le Mans http://pecdc.univ-lemans.fr/lpec.html av. O. Messiaen, BP535 72085 Le Mans cedex Tel prof: 33 (0) 243833268 Fax: 33 (0) 243833518 http://www.univ-lemans.fr/~dchat/danielc/daniel.htm --- --- World Directory of Crystallographers and concerned scientists - fill the form at: http://www.univ-lemans.fr/~dchat/wdc10/state.htm A web-based "Powder Structure Determination" course: http://sdpd.univ-lemans.fr/course/
Re: GSAS on layered clay minerals
> 2) Layered calys show a preferred orientation along the 001 planes due >the layered nature of the mineral. How should I use the "Preferred >orientation option" in GSAS? I cannot find any explanation in the GSAS >manual. EXPGUI Graphical User Interface for GSAS by Brian Toby provides a very easy in to using the Spherical Harmonics preferred orientation options within GSAS (as well as the March Dollase). This can handle very nasty preferred orientation problems (assuming it is preferred orientation that is causing the misfits) http://www.ccp14.ac.uk/solution/gsas/spher_harmonics_expgui.html (this includes both instructions for using EXPEDT and EXPGUI) EXPGUI information and download: http://www.ncnr.nist.gov/programs/crystallography/software/expgui/expgui_i ntro.html Mirrors: http://www.ccp14.ac.uk/ccp/web-mirrors/briantoby/programs/crystallography/ software/expgui/expgui_intro.html http://ccp14.sims.nrc.ca/ccp/web-mirrors/briantoby/programs/crystallograph y/software/expgui/expgui_intro.html Download FTP Site and Mirrors ftp://ftp.ncnr.nist.gov/pub/cryst/ Mirrors: http://www.ccp14.ac.uk/ccp/ccp14/ftp-mirror/briantoby/pub/cryst/ http://ccp14.sims.nrc.ca/ccp/ccp14/ftp-mirror/briantoby/pub/cryst/ I believe this pretty much assumes you have (or will) read the following paper to understand what is going on: Von Dreele, R. B. (1997). Quantitative texture analysis by Rietveld refinement. J. Appl. Cryst. 30, 517-525. Lachlan. --- Lachlan M. D. Cranswick Geochemistry - Lamont-Doherty Earth Observatory, Columbia University PO Box 1000, 61 Route 9W Palisades, New York 10964-1000 USA Tel: (845) 365-8662 Fax: (845) 365-8155 E-mail: [EMAIL PROTECTED] WWW: http://www.ldeo.columbia.edu CCP14 Xtal Software Website: http://www.ccp14.ac.uk
Re: GSAS on layered clay minerals
Are Wildfire and Diffax available via the web? Lachlan >the Rietveld-technique implies Bragg reflections. With clays you have a much more >complicated interference function and you should not use current day Rietveld >programs dealing with clays. It is not just the peak shape but also the peak positions >that are affected by disorder. See: D. L. Bish. Studies of Clays and Clay Minerals >Using X-Ray Powder Diffraction and the Rietveld Method, In: Computer Applications >to X-Ray Powder Diffraction Analysis of Clay Minerals; (eds R. C. J. Reynolds, J. R. >Walker) The Clay Mineral Society, Boulder, 1993; S.79-121. > >You can use codes like Wildfire (C.J. Reynolds) or Diffax (M. Treacy) to simulate the >diffraction patterns but you can not refine the structural model. To my knowledge Bish >and Reynolds are working on a code that will take the disorder into account. > >The above said relates to planar defects caused by disordered stacking of the very >same layers. Interstratification mentioned by Dragoe results from stacking layers of >different thickness along c*. This will additionally affect the positions of the 00l >reflections. > >Best wishes, > >Josef Breu --- Lachlan M. D. Cranswick Geochemistry - Lamont-Doherty Earth Observatory, Columbia University PO Box 1000, 61 Route 9W Palisades, New York 10964-1000 USA Tel: (845) 365-8662 Fax: (845) 365-8155 E-mail: [EMAIL PROTECTED] WWW: http://www.ldeo.columbia.edu CCP14 Xtal Software Website: http://www.ccp14.ac.uk
Re: GSAS on layered clay minerals
On Thu, 19 Apr 2001, N. Dragoe wrote: > Hi, > > In clay minerals sometimes you have some interstratification, >this is a problem because I am not aware of any Rietveld program to model >this (I hope I am wrong..). BGMN has no "built-in" clay mineral features. But using its structure interpreter language, you may create some more complex code in a structure describing *.str file (specific to BGMN). See the table at www.bgmn.de/download-structures.html at the entry chloritfxbg. Of course, this is not primary for structure refinement, this try was for quant analysis. As I hope, there will be further progress in design of clay mineral specific *.str files for quant analysis. J"org Bergmann, Dresden, Germany [EMAIL PROTECTED]
Re: GSAS on layered clay minerals
Ana, in Gsas you can choose two types of correction methods: March-Dollase and Spherical Harmonics ones. They are based on different physical description of the texture in the powder, so before clicking blindy gsas keys, read the papers on the physical approximation of each model: March-Dollase model: Dollase, J. Appl. Cryst.(1986) 19, 267-272 Sph. Harmonics: Von Dreel, J.Appl. Cryst(1997) 30, 517-525 and Texture in general: Matthies, Wenk, Vinel J. Appl. Cryst. (1988) 21, 285-304 I think you can find something on GSAS manual as well, my old GSAS manual lists, at page 140, "Preferred orientation of powders" Anyway, your mail suggests that preferred orientation corrections and how they reflects on quantitative analyses of powder should ask for another round robin. Ciao mattia -- *** Mattia Dugnani Universita' degli Studi di Milano Dipartimento di Scienze della Terra via Botticelli 23 20133 Milano (Italy) Tel. +39-02-23698340 FAX. +39-02-70638681 ***
Re: GSAS on layered clay minerals
Dear Mrs. Becerro, the Rietveld-technique implies Bragg reflections. With clays you have a much more complicated interference function and you should not use current day Rietveld programs dealing with clays. It is not just the peak shape but also the peak positions that are affected by disorder. See: D. L. Bish. Studies of Clays and Clay Minerals Using X-Ray Powder Diffraction and the Rietveld Method, In: Computer Applications to X-Ray Powder Diffraction Analysis of Clay Minerals; (eds R. C. J. Reynolds, J. R. Walker) The Clay Mineral Society, Boulder, 1993; S.79-121. You can use codes like Wildfire (C.J. Reynolds) or Diffax (M. Treacy) to simulate the diffraction patterns but you can not refine the structural model. To my knowledge Bish and Reynolds are working on a code that will take the disorder into account. The above said relates to planar defects caused by disordered stacking of the very same layers. Interstratification mentioned by Dragoe results from stacking layers of different thickness along c*. This will additionally affect the positions of the 00l reflections. Best wishes, Josef Breu Priv. Doz. Dr. Josef Breu Institut fuer Anorganische Chemie Universitaet Regensburg D-93040 REGENSBURG Phone: (+) 49 941 943 4523 Fax: (+) 49 941 943 3261 e.mail: [EMAIL PROTECTED] http://www.chemie.uni-regensburg.de/Anorganische_Chemie/Breu/index.html
Re: GSAS on layered clay minerals
Hi, In clay minerals sometimes you have some interstratification, this is a problem because I am not aware of any Rietveld program to model this (I hope I am wrong..). The effect is well described by Bish and Post in a book published in the '90s. I can dig up the reference if you need it, Regards, http://www.chem.t.u-tokyo.ac.jp/appchem/labs/kitazawa/dragoe/ - Original Message - From: Ana Isabel Becerro <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Thursday, 19 April 2001 6:48 PM Subject: GSAS on layered clay minerals Dear All, I am a new user of this Rietveld e-mail list. I have started working on the refinement of clay structures with GSAS from conventional X-ray powder diffraction patterns and I have found two problems in the very beginning:
GSAS on layered clay minerals
Dear All, I am a new user of this Rietveld e-mail list. I have started working on the refinement of clay structures with GSAS from conventional X-ray powder diffraction patterns and I have found two problems in the very beginning: 1) The diffraction pattern of a layered clay (any smectite, for example) shows two types of reflections: symmetrical lines coming from the basal 00l (l for list) reflections (due to the layered nature of the smectite) and also asymmetrical lines coming from hk0 reflections which I am unable to reproduce in GSAS. 2) Layered calys show a preferred orientation along the 001 planes due the layered nature of the mineral. How should I use the "Preferred orientation option" in GSAS? I cannot find any explanation in the GSAS manual. Thank you very much and greetings from Sevilla, ana -- Ana Isabel Becerro ICMSE (CSIC) Avda. Américo Vespucio s/n 41092 Sevilla (Spain) Tel: 34-95 4489576 Fax: 34 95 4460665
