Beginer problems, difficulty charecterizing our diffractometer...
I am re-learning GSAS to bring Rietveld to my department (for the first time). We have an old Phillips Xpert. I am trying to refine a quartz standard to acquire my profile and instrument parameters for this instrument and have yet to get my Chi^2 below 500. The instrument is not in my direct control. I have caught and asked them to correct a few problems already (dwell time too low, aluminum sneaking into the beam, etc...) and this has helped. I would like not to annoy them any more than I have too. At this point I think my high Chi^2s are mainly due to low angle asymmetric peaks that my fit is not able to copy - the asym is not terrible but may be messing me up. I am getting better results with peak profile functions 3 and 4, but unable to get Chi^2 below 500. My scans go up to 70 degrees 2theta. I would like to tell the people caring for the instrument that my problem is on their end, but I am not confident in my own refining skills to say this. When I work with the tutorials or standard data from my graduate school experiment I am ok - I think I am proceeding in a reasonable way, although I can get stuck here and there. I would like to find out if I am doing something incorrectly or if the problem is instrument related. I hate to bug one of you but wonder if I could get someone to look at my work?? Is there a better forum for asking for this kind of help? Kindest regards to all of you, Blaise * * * * * * * * * * * * * Blaise Mibeck Research Scientist Energy Environmental Research Center University of North Dakota 15 North 23rd Street, Stop 9018 Grand Forks, ND 58202-9018 Phone: (701) 777-5077 Email: [EMAIL PROTECTED] mailto:[EMAIL PROTECTED]
Re: Beginer problems, difficulty charecterizing our diffractometer...
From what I have been told and led to believe, Chi^2 isn't the be all and end all. This will really depend upon your counting statistics. Pay more attention to your Rp, Rwp and what your fit actually looks like. Also, try performing a Le Bail fit to your data and see what Chi^2 you get. This should give you a bench mark to aim for. Best of luck Adrian Mibeck, Blaise wrote: I am re-learning GSAS to bring Rietveld to my department (for the first time). We have an old Phillips Xpert. I am trying to refine a quartz standard to acquire my profile and instrument parameters for this instrument and have yet to get my Chi^2 below 500. The instrument is not in my direct control. I have caught and asked them to correct a few problems already (dwell time too low, aluminum sneaking into the beam, etc…) and this has helped. I would like not to annoy them any more than I have too. At this point I think my high Chi^2s are mainly due to low angle asymmetric peaks that my fit is not able to copy – the asym is not terrible but may be messing me up. I am getting better results with peak profile functions 3 and 4, but unable to get Chi^2 below 500. My scans go up to 70 degrees 2theta. I would like to tell the people caring for the instrument that my problem is on their end, but I am not confident in my own refining skills to say this. When I work with the tutorials or standard data from my graduate school experiment I am ok – I think I am proceeding in a reasonable way, although I can get stuck here and there. I would like to find out if I am doing something incorrectly or if the problem is instrument related. I hate to bug one of you but wonder if I could get someone to look at my work?? Is there a better forum for asking for this kind of help? Kindest regards to all of you, Blaise * * * * * * * * * * * * * Blaise Mibeck Research Scientist Energy Environmental Research Center University of North Dakota 15 North 23rd Street, Stop 9018 Grand Forks, ND 58202-9018 Phone: (701) 777-5077 Email: [EMAIL PROTECTED] mailto:[EMAIL PROTECTED] -- Adrian Hill [EMAIL PROTECTED] Centre for Science at Extreme Conditions The University of Edinburgh Currently based at, The Institut Laue-Langevin ILL4 110 BP 156 6, rue Jules Horowitz 38042 Grenoble Cedex 9 France The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336.
RE: Beginer problems, difficulty charecterizing our diffractometer...
Hi, I am going to be in the same boat soon, especially regarding obtaining instrument parameters for a new instrument. But one thing I do know, is that to get the polarization parameter, quartz is not a great standard. For polarization factors, you need something really simple, with heavy atoms and all atoms on centers of symmetry, and with thermal parameters very well constrained, so that you can REFINE the polarization parameters for your machine, particularly when incindent beam monochromators are used. The only problem is, I can't remember what the favorite standard is, or where it can be purchased. I will need to know myself, so I will ask, on behalf of Blaise and myself as well, what is the best standard for refining the polarization of an instrument with monochromatized beam? Thank you! - Kurt From: Mibeck, Blaise [mailto:[EMAIL PROTECTED] Sent: Wed 9/17/2008 12:22 PM To: rietveld_l@ill.fr Subject: Beginer problems, difficulty charecterizing our diffractometer... I am re-learning GSAS to bring Rietveld to my department (for the first time). We have an old Phillips Xpert. I am trying to refine a quartz standard to acquire my profile and instrument parameters for this instrument and have yet to get my Chi^2 below 500. The instrument is not in my direct control. I have caught and asked them to correct a few problems already (dwell time too low, aluminum sneaking into the beam, etc...) and this has helped. I would like not to annoy them any more than I have too. At this point I think my high Chi^2s are mainly due to low angle asymmetric peaks that my fit is not able to copy - the asym is not terrible but may be messing me up. I am getting better results with peak profile functions 3 and 4, but unable to get Chi^2 below 500. My scans go up to 70 degrees 2theta. I would like to tell the people caring for the instrument that my problem is on their end, but I am not confident in my own refining skills to say this. When I work with the tutorials or standard data from my graduate school experiment I am ok - I think I am proceeding in a reasonable way, although I can get stuck here and there. I would like to find out if I am doing something incorrectly or if the problem is instrument related. I hate to bug one of you but wonder if I could get someone to look at my work?? Is there a better forum for asking for this kind of help? Kindest regards to all of you, Blaise * * * * * * * * * * * * * Blaise Mibeck Research Scientist Energy Environmental Research Center University of North Dakota 15 North 23rd Street, Stop 9018 Grand Forks, ND 58202-9018 Phone: (701) 777-5077 Email: [EMAIL PROTECTED]
Re: Beginer problems, difficulty charecterizing our diffractometer...
Dear Blaise, The strong peak asymmetry may result from high-divergence Soller slits installed in your instrument. You may consider using sollers of lower divergence that normally allows easier peak shape approximation and, besides, increases the resolution (at the expense of intensity, of course). You also mentioned ‘aluminum sneaking into the beam’ which means that you don’t use the sample spinner. This may create additional problems related to poor particle statistics especially if the quarts powder is not fine enough. Many related problems are well discussed in ‘Rietveld refinement guidelines’ J. Appl. Cryst. (1999) 36. Best regards, Leonid *** Leonid A. Solovyov Institute of Chemistry and Chemical Technology K. Marx 42 660049, Krasnoyarsk Russia Email: [EMAIL PROTECTED] www.icct.ru/eng/content/persons/Sol_LA www.geocities.com/l_solovyov *** --- On Wed, 9/17/08, Mibeck, Blaise [EMAIL PROTECTED] wrote: From: Mibeck, Blaise [EMAIL PROTECTED] Subject: Beginer problems, difficulty charecterizing our diffractometer... To: rietveld_l@ill.fr Date: Wednesday, September 17, 2008, 8:22 PM I am re-learning GSAS to bring Rietveld to my department (for the first time). We have an old Phillips Xpert. I am trying to refine a quartz standard to acquire my profile and instrument parameters for this instrument and have yet to get my Chi^2 below 500. The instrument is not in my direct control. I have caught and asked them to correct a few problems already (dwell time too low, aluminum sneaking into the beam, etc...) and this has helped. I would like not to annoy them any more than I have too. At this point I think my high Chi^2s are mainly due to low angle asymmetric peaks that my fit is not able to copy - the asym is not terrible but may be messing me up. I am getting better results with peak profile functions 3 and 4, but unable to get Chi^2 below 500. My scans go up to 70 degrees 2theta. I would like to tell the people caring for the instrument that my problem is on their end, but I am not confident in my own refining skills to say this. When I work with the tutorials or standard data from my graduate school experiment I am ok - I think I am proceeding in a reasonable way, although I can get stuck here and there. I would like to find out if I am doing something incorrectly or if the problem is instrument related. I hate to bug one of you but wonder if I could get someone to look at my work?? Is there a better forum for asking for this kind of help? Kindest regards to all of you, Blaise * * * * * * * * * * * * * Blaise Mibeck Research Scientist Energy Environmental Research Center University of North Dakota 15 North 23rd Street, Stop 9018 Grand Forks, ND 58202-9018 Phone: (701) 777-5077 Email: [EMAIL PROTECTED] mailto:[EMAIL PROTECTED]
RE: Beginer problems, difficulty charecterizing our diffractometer...
Couldn't the Al in the beam be due to beam spilling over the sample holder, irrespective of a spinning sample? . I'd also like to echo Lachlan's comment about Y2O3. It's what we use in our lab - if you can refine the thermal parameters to sensible values, you know you've got all of your intensity corrections done right. 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: Leonid Solovyov [mailto:[EMAIL PROTECTED] Sent: Thursday, 18 September 2008 14:34 To: rietveld_l@ill.fr Subject: Re: Beginer problems, difficulty charecterizing our diffractometer... Dear Blaise, The strong peak asymmetry may result from high-divergence Soller slits installed in your instrument. You may consider using sollers of lower divergence that normally allows easier peak shape approximation and, besides, increases the resolution (at the expense of intensity, of course). You also mentioned 'aluminum sneaking into the beam' which means that you don't use the sample spinner. This may create additional problems related to poor particle statistics especially if the quarts powder is not fine enough. Many related problems are well discussed in 'Rietveld refinement guidelines' J. Appl. Cryst. (1999) 36. Best regards, Leonid *** Leonid A. Solovyov Institute of Chemistry and Chemical Technology K. Marx 42 660049, Krasnoyarsk Russia Email: [EMAIL PROTECTED] www.icct.ru/eng/content/persons/Sol_LA www.geocities.com/l_solovyov *** --- On Wed, 9/17/08, Mibeck, Blaise [EMAIL PROTECTED] wrote: From: Mibeck, Blaise [EMAIL PROTECTED] Subject: Beginer problems, difficulty charecterizing our diffractometer... To: rietveld_l@ill.fr Date: Wednesday, September 17, 2008, 8:22 PM I am re-learning GSAS to bring Rietveld to my department (for the first time). We have an old Phillips Xpert. I am trying to refine a quartz standard to acquire my profile and instrument parameters for this instrument and have yet to get my Chi^2 below 500. The instrument is not in my direct control. I have caught and asked them to correct a few problems already (dwell time too low, aluminum sneaking into the beam, etc...) and this has helped. I would like not to annoy them any more than I have too. At this point I think my high Chi^2s are mainly due to low angle asymmetric peaks that my fit is not able to copy - the asym is not terrible but may be messing me up. I am getting better results with peak profile functions 3 and 4, but unable to get Chi^2 below 500. My scans go up to 70 degrees 2theta. I would like to tell the people caring for the instrument that my problem is on their end, but I am not confident in my own refining skills to say this. When I work with the tutorials or standard data from my graduate school experiment I am ok - I think I am proceeding in a reasonable way, although I can get stuck here and there. I would like to find out if I am doing something incorrectly or if the problem is instrument related. I hate to bug one of you but wonder if I could get someone to look at my work?? Is there a better forum for asking for this kind of help? Kindest regards to all of you, Blaise * * * * * * * * * * * * * Blaise Mibeck Research Scientist Energy Environmental Research Center University of North Dakota 15 North 23rd Street, Stop 9018 Grand Forks, ND 58202-9018 Phone: (701) 777-5077 Email: [EMAIL PROTECTED] mailto:[EMAIL PROTECTED]
