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 



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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 77811

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 between.

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 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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