[GSAS-II] Le Bail with GSASII

Wed Apr 8 16:29:17 CDT 2020

Sergey,

The Le Bail refinement option with GSASII works really well, smoother than with the original GSAS...

Joel

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Today's Topics:

   1. Pawley refinemet question (Sergey Ushakov)
   2. Re: Pawley refinemet question (Toby, Brian H.)
   3. Re: Pawley refinemet question (Sergey Ushakov)

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Message: 1
Date: Wed, 8 Apr 2020 10:58:15 -0700
From: Sergey Ushakov <svushakov at ucdavis.edu>
To: gsas-ii at aps.anl.gov
Subject: [GSAS-II] Pawley refinemet question
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	<CAG1YaUPgKQpV-HkDRBMUDoFcZJEsLKD6YkvPAXryek+15Bu1Lw at mail.gmail.com>
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Greetings! I have a question maybe not specific to GSAS-II but more about Pawley vs Le Bail fitting of powder XRD data.
I work on high temperature data from laser-heated solid spheroids which rotate in a gas flow in aerodynamic levitator.
The data are collected in transmission geometry at 6-ID-D at APS.
The rotation is not well controlled since it depends on the shape of each bead formed by melt solidification, i.e., on surface tension, volume change on melting, etc.
So, sometimes data are very much powder-like and amenable to Rietveld refinement of the structure, but sometimes they are not, and in this case, I do Pawley fit for cell parameters.
I used to do Le Bail fitting for that in GSAS-I, but I understand that it was replaced by Pawley refinement (although there is an option for Le Bail extraction of intensities?).

To my surprise, Pawley fit in GSAS-II yield phase/weight fraction if one turns it on for refinement.
I thought phase fraction could be correctly refined only from Rietveld?

I would appreciate any comments on this!

Sergey

--
Sergey Ushakov PhD

Staff Research Associate

Peter A Rock Thermochemistry Laboratory and NEAT ORU Rm 4415, Chemistry Annex University of California, Davis Davis, CA 95616
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Message: 2
Date: Wed, 8 Apr 2020 18:14:35 +0000
From: "Toby, Brian H." <toby at anl.gov>
To: "Ushakov, Sergey V." <svushakov at ucdavis.edu>
Cc: "Von Dreele, Robert B. via GSAS-II" <gsas-ii at aps.anl.gov>
Subject: Re: [GSAS-II] Pawley refinemet question
Message-ID: <3609B7DE-29E9-4ECC-A06C-82CEE8EEE229 at anl.gov>
Content-Type: text/plain; charset="us-ascii"

Hi Sergey,

   Both LeBail and Pawley fits are not able to determine phase fractions because the scale factors are all arbitrary and thus the phase fractions cannot be refined. However, the reported mass/weight fractions are determined from the unrefined phase fractions and they are displayed even though meaningless.

Brian

On Apr 8, 2020, at 12:58 PM, Sergey Ushakov via GSAS-II <gsas-ii at aps.anl.gov<mailto:gsas-ii at aps.anl.gov>> wrote:

Greetings! I have a question maybe not specific to GSAS-II but more about Pawley vs Le Bail fitting of powder XRD data.
I work on high temperature data from laser-heated solid spheroids which rotate in a gas flow in aerodynamic levitator.
The data are collected in transmission geometry at 6-ID-D at APS.
The rotation is not well controlled since it depends on the shape of each bead formed by melt solidification, i.e., on surface tension, volume change on melting, etc.
So, sometimes data are very much powder-like and amenable to Rietveld refinement of the structure, but sometimes they are not, and in this case, I do Pawley fit for cell parameters.
I used to do Le Bail fitting for that in GSAS-I, but I understand that it was replaced by Pawley refinement (although there is an option for Le Bail extraction of intensities?).

To my surprise, Pawley fit in GSAS-II yield phase/weight fraction if one turns it on for refinement.
I thought phase fraction could be correctly refined only from Rietveld?

I would appreciate any comments on this!

Sergey

--
Sergey Ushakov PhD

Staff Research Associate

Peter A Rock Thermochemistry Laboratory and NEAT ORU Rm 4415, Chemistry Annex University of California, Davis Davis, CA 95616

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Message: 3
Date: Wed, 8 Apr 2020 11:21:07 -0700
From: Sergey Ushakov <svushakov at ucdavis.edu>
To: gsas-ii at aps.anl.gov
Subject: Re: [GSAS-II] Pawley refinemet question
Message-ID:
	<CAG1YaUOpCYzVGfa11Y6FoW4p+9dUfgah4a9C=27H=Nx-N0g3pQ at mail.gmail.com>
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Thank you, Brian, for clarifying this!

On Wed, Apr 8, 2020 at 11:14 AM Toby, Brian H. <toby at anl.gov> wrote:

> Hi Sergey,
>
>    Both LeBail and Pawley fits are not able to determine phase 
> fractions because the scale factors are all arbitrary and thus the 
> phase fractions cannot be refined. However, the reported mass/weight 
> fractions are determined from the unrefined phase fractions and they 
> are displayed even though meaningless.
>
> Brian
>
> On Apr 8, 2020, at 12:58 PM, Sergey Ushakov via GSAS-II < 
> gsas-ii at aps.anl.gov> wrote:
>
> Greetings! I have a question maybe not specific to GSAS-II but more 
> about Pawley vs Le Bail fitting of powder XRD data.
> I work on high temperature data from laser-heated solid spheroids 
> which rotate in a gas flow in aerodynamic levitator.
> The data are collected in transmission geometry at 6-ID-D at APS.
> The rotation is not well controlled since it depends on the shape of 
> each bead formed by melt solidification, i.e., on surface tension, 
> volume change on melting, etc.
> So, sometimes data are very much powder-like and amenable to Rietveld 
> refinement of the structure, but sometimes they are not, and in this 
> case, I do Pawley fit for cell parameters.
> I used to do Le Bail fitting for that in GSAS-I, but I understand that 
> it was replaced by Pawley refinement (although there is an option for 
> Le Bail extraction of intensities?).
>
> To my surprise, Pawley fit in GSAS-II yield phase/weight fraction if 
> one turns it on for refinement.
> I thought phase fraction could be correctly refined only from Rietveld?
>
> I would appreciate any comments on this!
>
> Sergey
>
> --
> Sergey Ushakov PhD
>
> Staff Research Associate
>
> Peter A Rock Thermochemistry Laboratory and NEAT ORU Rm 4415, 
> Chemistry Annex University of California, Davis Davis, CA 95616
>
> _______________________________________________
> GSAS-II mailing list
> GSAS-II at aps.anl.gov
> https://mailman.aps.anl.gov/mailman/listinfo/gsas-ii
>
>
>

--
--
Sergey Ushakov PhD

Staff Research Associate

Peter A Rock Thermochemistry Laboratory and NEAT ORU Rm 4415, Chemistry Annex University of California, Davis Davis, CA 95616 phone (530) 902-8185
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