[GSAS-II] GSAS-II Digest, Vol 253, Issue 1

Wed Apr 8 14:20:49 CDT 2020

The Pawley refinement is superior to LeBail refinement in that it provides
the esd's. The problem of negative intensities may be mitigated by the
negative weight factor Brian implemented in GSAS-II.

Hooman

On Wed, Apr 8, 2020 at 1:22 PM <gsas-ii-request at aps.anl.gov> wrote:

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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)
>
>
> ----------------------------------------------------------------------
>
> 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
> Message-ID:
>         <
> CAG1YaUPgKQpV-HkDRBMUDoFcZJEsLKD6YkvPAXryek+15Bu1Lw at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> 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
>
> _______________________________________________
> GSAS-II mailing list
> GSAS-II at aps.anl.gov<mailto:GSAS-II at aps.anl.gov>
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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>
> Content-Type: text/plain; charset="utf-8"
>
> 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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> End of GSAS-II Digest, Vol 253, Issue 1
> ***************************************
>

-- 

*Hooman Yaghoobnejad AslPostdoctoral FellowTexas Materials Institute,
Cockrell School of Engineeringhooma at utexas.edu <hooma at utexas.edu>*

*204 E. Dean Keeton Street, C2200Austin, Texas 78712, USA*
*Office: ETC 8.112*
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