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: [email protected] 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: [email protected] > 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]>
