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Dear Thanos, A few points concerning your question; I’ll assume you are looking at only the peak shapes and not attempting a Profile or Rietveld fit. 1) Ka2 peak stripping is not necessary; indeed - I'd suggest one should very much avoid altering</div>
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<meta charset="utf-8"></head><body><pre style="font-family: sans-serif; font-size: 100%; white-space: pre-wrap; word-wrap: break-word">Dear Thanos,
A few points concerning your question; I’ll assume you are looking at only the peak shapes and not attempting a Profile or Rietveld fit.
1) Ka2 peak stripping is not necessary; indeed - I'd suggest one should very much avoid altering the data.
2) Before determining the UVWXY terms, perhaps try fitting all the individual peaks for both sample, refining the sigma and gamma values independently for all peaks. Does the resulting trend of deltaQ/Q vs Q look similar for both samples? If not - you may have a data collection problem. You also might need to try different fixed values of the SH/L term at the beginning to get the asymmetry shape approximately close. Depending on the D2 resolution, you might see very slightly larger peak shapes for the Si.
3) Depending on the insutment profile, I find that it can sometimes be difficult to refine all UVWXY terms at once - at least at the start - for example if the shape is dominated by Lorentzian widths, then the Gaussian terms can be unstable when all are refined refined freely.
4) I don’t see why values would get diverge depending on the 2th range used. Do note however that with a Cu source, Si and LaB6 give no peaks < 20 deg 2th, so your instrument profile is not well determined for this low angle range.
In general, I can confirm that the procedure does work; I’ve used LaB6 660 data just this week to make an GSAS-II instparm file which works well for fitting of other reference samples like CeO2 and NAC.
best regards
Matthew
***
Matthew SUCHOMEL
Chargé de recherche
ICMCB - CNRS - Univ. de Bordeaux
***
> On 19 Dec 2024, at 19:00, gsas-ii-request@aps.anl.gov wrote:
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> 1. Inquiry reg setting up the instrument param file (Thanos Goulas)
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> ----------------------------------------------------------------------
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> Message: 1
> Date: Wed, 18 Dec 2024 23:49:18 +0000
> From: Thanos Goulas <A.Goulas@lboro.ac.uk>
> To: "gsas-ii@aps.anl.gov" <gsas-ii@aps.anl.gov>
> Subject: [GSAS-II] Inquiry reg setting up the instrument param file
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> Dear GSAS-II community,
>
> I have been working on setting up the instrument parameter file for a Bruker D2 in GSAS-II, using SRM 660 and 640 standards. However, I am encountering issues with peak identification, particularly with peak splitting at higher 2? angles.
>
> Given this, I was wondering if stripping the ka2 component is an absolutely necessary step for this process?
>
> When I limit my 2? range to 20?80?, I manage to obtain reasonable U, V, W, X, and Y parameters. However, these parameters go spammy when I attempt to refine them over a broader range, such as 5?140? (to get the D2's full profile)
>
> Finally, shouldn't I be getting the same parameters regardless of the standard I am using? LaB6 and Si produce completely different params.
>
> I would greatly appreciate your thoughts or suggestions on this.
>
> Looking forward to your insights.
>
> Thanos
>
> Dr Thanos Goulas, BEng MSc PhD
>
> Pronouns:<<a href="https://urldefense.us/v3/__https://www.mypronouns.org/__;!!G_uCfscf7eWS!Yq11gnqmg3M9-lh3tSzSV6QYuF1RAU_nfVcoSVmiiLRLWZUSOovRxbxHMf22yQ8Xcgau-y3QZLQuqTD66ep4j6E$">https://urldefense.us/v3/__https://www.mypronouns.org/__;!!G_uCfscf7eWS!Yq11gnqmg3M9-lh3tSzSV6QYuF1RAU_nfVcoSVmiiLRLWZUSOovRxbxHMf22yQ8Xcgau-y3QZLQuqTD66ep4j6E$</a>> he / him / his
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> School of Aeronautical, Automotive, Chemical and Materials Engineering
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> Department of Materials
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> Loughborough University, Loughborough, Leicestershire, LE11 3TU, UK
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