Maybe a silly question: are you assuming you have the data on an absolute scale in order to do these calculations? Do things like surface roughness somehow not matter?



On 13/04/2022 11:56, Matthew Rowles wrote:
Thanks Tony

When I add the absorption edge correction to the silicon nitride model (and add beta-silicon nitride), it becomes -2.8 wt% amorphous; up a little due to the added correction and down a little due to the extra phase.

If I change your al-SN thermals from 1 to those given in ICSD 77811, I get +4.8 wt% amorphous. Your atoms were already neutral, so I left them as-is.

If I make all the Si-nitride phases' thermal parameters == 0, then I can get up to 8.5 wt% amorphous.

In all of this, corundum is staying as charged atoms, with Al and O beqs fixed at 0.334 and 0.278.

I'll have to have a go at applying the absorption edge correction; I always forget which parameter is which thing and have to rederive my understanding of it everytime...



On Wed, 13 Apr 2022 at 13:58, iangie < <>> 

    Dear Matthew,

    I tried your data and get ~-1% amorphous. My .pro is in below link.

    I normally do not refine Beq, which I believe gives biggest source of error
    in QPA...



    *Dr. Xiaodong (Tony) Wang*
    *Senior Research Infrastructure Specialist (XRD)*
    Central Analytical Research Facility (CARF)   |  Queensland University of
    *Address:* Level 6, P Block, Gardens Point campus, 2 George St Brisbane QLD 
    *Tel:*+61 7 3138 1904  | *Mob:*0452 571 680
    *Email:* tony <>.
    <>   | *Web:*

    At 2022-04-13 13:00:44, "Matthew Rowles" <
    <>> wrote:

        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:

        This is using the scattering factors defined with 11 gaussians.

        If you use the ones defined by 9 gaussians, you get

        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  12x 0      y 0 z 0.14772 occ Al+3 1. beq  0.318
        site O1  num_posns  18x 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 
        site Si1 num_posns  6x 0.0806 y 0.5095 z 0.3020 occ Si+4 1   beq 0.25
        site Si2 num_posns  6x 0.1675 y 0.2560 z 0.0070 occ Si+4 1   beq 0.29
        site N1  num_posns  2x 0      y 0      z 0      occ N    1.  beq 0.88
        site N2  num_posns  2x =1/3;  y =2/3;  z 0.3500 occ N    1.  beq 0.46
        site N3  num_posns  6x 0.0390 y 0.3860 z 0.0310 occ N    1.  beq 1.06
        site N4  num_posns  6x 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  6x 0.2323 y 0.4096 z 0.25 occ Si+4   1  beq 0.231
        site N1  num_posns  2x =1/3;  y =2/3;  z 0.25 occ N      1  beq 0.326
        site N2  num_posns  6x 0.3337 y 0.0323 z 0.25 occ N      1  beq 0.314

        On Tue, 12 Apr 2022 at 17:13, Matthew Rowles <
        <>> 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

            Does anybody want to have a look at the data and see what I'm doing
            wrong? Data available at:




            On Wed, 16 Mar 2022 at 21:13, Matthew Rowles <
            <>> 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

                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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