[GSAS-II] GSAS-II Digest, Vol 143, Issue 1

[Viktor Zano]

Hi
Regarding " Issues with sequential refinement (Nick Weadock)", I also had
similar problem.
In May 15 2017 I wrote to gsas ii digest:

=========
Dear everyone
I try to do sequential refinement for Sc-doped TiO2 while in-situ heated at
25-1200C temperature range, total of 33 histograms.
As a function of temperature I have different lattice parameters, ratio of
anatase / rutile and crystallite size/microstrains.
I tried to refine them at that sequence usin GSAS-II.

 After working on lattice parameters (DXX, hydrostatic/elastic strain
terms) I tried to refine the ratio of anatase / rutile and/or crystallite
size/microstrains and got a "Sequential refinement error" message:

Invalid metric tensor
Cell/Dij refinement not advised


Sometimes I can't get the Sequential results, although I "see" that the DXX
have different values.
Even if I manage to get the results on table, I can't get them in graph as
lattice parameters (instead I get DXX)


Best regards,
Victor

=========

Eventually I had to restart the calculations in order to make them work
properly, not sure what went wrong.  In fact some of these 'sequential
refinement ' worked fine, some wasn't good. The problem was that I always
use the former values of the refinement to the next pattern's refinement.
I had 33 diffractions patterns from RT to 1200C. I divided them into 2
separate 'sequential refinement ', but eventually I repeated all  of them
manually.
I have to mention that I did these  'sequential refinements' 3-4 months
ago, using older versions of GSAS-II. Maybe it got better. Also I was less
experienced with GSAS-II :)

Hope it will help
Victor

2017-11-15 20:00 GMT+02:00 <gsas-ii-request at aps.anl.gov>:

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>    1. Issues with sequential refinement (Nick Weadock)
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> Message: 1
> Date: Tue, 14 Nov 2017 15:25:43 -0800
> From: Nick Weadock <nweadock at caltech.edu>
> To: gsas-ii at mailman.aps.anl.gov
> Subject: [GSAS-II] Issues with sequential refinement
> Message-ID:
>         <CAO0QVOqyfUmnPMTwp18VmbEaskxV-gssaC-hO_EAQzaybt77Jw at mail.
> gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Hi,
>
> I am having some issues with a sequential refinement in GSAS. I have been
> following along with the tutorial here:
> https://subversion.xray.aps.anl.gov/pyGSAS/Tutorials/
> SeqRefine/SequentialTutorial.htm
> to limited success.
>
> Previously, I had trouble getting the phase fractions to sum to 1. I would
> put the "wildcard" constraint in as stated in the tutorial, but the phase
> fractions still would not sum to 1 after the refinement. I re-did the
> tutorial and got it to work, however.
>
> I am trying the tutorial again, but have been running into the following
> exception: 'invalid metric tensor \n cell/Dij refinement not advised' I did
> not run into this problem previously.
>
> Has anyone had experience with similar issues in sequential refinement? I
> am trying to perform sequential refinement of my own data, but had the same
> issues with the phase fractions. A colleague performed a sequential
> refinement on the same data but the phase fractions worked out fine for
> them.
>
> I am using the most up to date version of GSAS-II. Any help would be
> greatly appreciated,
> --
> Nick Weadock
> PhD Candidate, Materials Science
> California Institute of Technology
> 1200 E California Blvd, Pasadena, CA 91125
> MC 138-78
> x2520
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