Just curious, is the sample as prepared in the holder wider than the beam width at 10 degrees where you start the scan? This is a common issue that not many realize that for quantitative analysis the diffracting volume is constant provided the sample is larger than the beam in the tube and detector plane. If the beam is larger than the sample at these angles you no longer have a constant diffracting volume and hence errors in the analysis. I am not sure many of the manufactures realize this based on personal experience with default settings of optics for some instruments being much too large. Additionally, background is a major issue as I have found especially with amorphous materials present background algorithms do not do a very good job and often create the background by hand.
Regards, Ed On Tue, Apr 12, 2022 at 5:14 AM Matthew Rowles <rowle...@gmail.com> wrote: > Hi all > > I've collected some more data, and am still getting spurious results, and > by spurious, I mean -5 wt% amorphous in SRM-alpha-656 when quantified by > the external method against SRM 676a. > > We had some SRM-656alpha (couldn't find any of the beta) stored in a > drying oven, and some SRM676a stored in a cupboard. I collected some data > using a D8 with Ni-filtered Cu and a lynx-eye detector (0.25° fixed > divergence, 250 mm radius, 2x2.5° sollers). The patterns were collected > consecutively (using the same program), with a single peak from SRM1976 (b, > I think), acting as an intensity calibrant (the intensity didn't > appreciably change), collected before, after, and between. > > Does anybody want to have a look at the data and see what I'm doing wrong? > Data available at: > > https://raw.githubusercontent.com/rowlesmr/pdCIFplotter/changing-str-to-float-conversion/data/row_Cu_676a.xy > > > https://raw.githubusercontent.com/rowlesmr/pdCIFplotter/changing-str-to-float-conversion/data/row_Cu_al656.xy > > > Thanks > > Matthew > > > > > > On Wed, 16 Mar 2022 at 21:13, Matthew Rowles <rowle...@gmail.com> wrote: > >> Hi List People >> >> Do any of you use NIST SRM656 in your quantitative analysis quality >> control? >> >> I've recently started at a new lab, and am finding it impossible to make >> a physically realistic model (in Topas) that gives results anywhere near >> correct (or at least, close to the certificate values). >> >> As an example, using the external std approach with SRM676, I've managed >> to calculate there is -11 wt% amorphous in the beta-656 standard. >> >> I've tried using the silicon nitride structures given in the SRM >> certificate, but the papers and the ICSD entries don't list any thermal >> parameters. >> >> I can get the same results as given on the certificate using a siroquant >> model, but I don't know the provenance of the HKL files used in the >> analysis. >> >> >> Thanks in advance >> >> >> Matthew Rowles >> > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > Please do NOT attach files to the whole list <alan.he...@neutronoptics.com > > > Send commands to <lists...@ill.fr> eg: HELP as the subject with no body > text > The Rietveld_L list archive is on > http://firstname.lastname@example.org/ > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > > -- Dr. Edward A. Laitila Senior Research Engineer/Scientist II/Adjunct Assistant Professor Michigan Technological University Dept. of MSE Room 628 M&M Building (906) 369-2041
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