Hi all Thanks to those that have replied off-list.
I've managed to jiggle things around and get various answers. If you want an answer between -14 and +6 wt% amorphous, I can make it happen. I can either use charged atoms or not, or use thermal parameters or not. Combining those between the corundum and Si3N4, you get the following: [image: image.png] This is using the scattering factors defined with 11 gaussians. If you use the ones defined by 9 gaussians, you get [image: image.png] The structures I used are below. In the certificate for 656, the structures are referenced, but those structures have no thermal parameters. Does anyone know what was used in the NIST determination? phase_name "Aluminium_oxide_alpha_10425_icsd" Hexagonal( 4.759355, 12.99231) space_group "R -3 c H" site Al1 num_posns 12 x 0 y 0 z 0.14772 occ Al+3 1. beq 0.318 site O1 num_posns 18 x 0.3064 y 0 z 0.25 occ O-2 1. beq 0.334 phase_name "ALPHA_Marchand_ICSD_26191" Hexagonal( 7.75411, 5.62034) space_group "P31c" 'atom positions from Marchand. Thermals from ICSD 77811 site Si1 num_posns 6 x 0.0806 y 0.5095 z 0.3020 occ Si+4 1 beq 0.25 site Si2 num_posns 6 x 0.1675 y 0.2560 z 0.0070 occ Si+4 1 beq 0.29 site N1 num_posns 2 x 0 y 0 z 0 occ N 1. beq 0.88 site N2 num_posns 2 x =1/3; y =2/3; z 0.3500 occ N 1. beq 0.46 site N3 num_posns 6 x 0.0390 y 0.3860 z 0.0310 occ N 1. beq 1.06 site N4 num_posns 6 x 0.3190 y 0.3210 z 0.2660 occ N 1. beq 0.17 phase_name "BETA_Billy_ICSD_35566" Hexagonal( 7.60633, 2.90778) space_group "P 63/m" ' structure from Billy, thermals from ICSD 170004 site Si1 num_posns 6 x 0.2323 y 0.4096 z 0.25 occ Si+4 1 beq 0.231 site N1 num_posns 2 x =1/3; y =2/3; z 0.25 occ N 1 beq 0.326 site N2 num_posns 6 x 0.3337 y 0.0323 z 0.25 occ N 1 beq 0.314 On Tue, 12 Apr 2022 at 17:13, 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 >> >
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