[GSAS-II] Calculating Particle size and Strain in GSAS2

[Shoaib Muhammad]

Hi,

 

This problem "Python.exe has stopped working" was becoming more frequent and
annoying. Recently I found its solution that I want to share:

 

I noticed that this problem happens only on my Windows 8 x64 machine. So
probably it was due to some problem with Python installation. I removed EPD
Canopy and installed Python 2.7.8 from https://www.python.org/downloads/

 

And then installed following Libs (most of these are available at
http://www.lfd.uci.edu/~gohlke/pythonlibs/) compatible with Python 2.7

 

WxPython

Matplotlib

NumPy

SciPy

PyOpenGL

Python Imaging Library

 

 

dateutil

pytz

pyparsing

six

 

last four libraries are probably required to run NumPy and Matplotlib
properly. 

 

Rerun the GSAS2 and problem solved :)

 

Regards,

/Shoaib

From: Robert Von Dreele [mailto:vondreele at aps.anl.gov] 
Sent: Friday, July 18, 2014 5:37 AM
To: Shoaib Muhammad
Subject: Re: RE: [GSAS-II] Calculating Particle size and Strain in GSAS2

 

Shoaib,
I can't seem to reproduce your error, but will keep trying. 
If you want to save the strain/size surface plot, use the Save button (looks
like an old diskette) at the bottom of the plot. The export/image is for 2-D
images.
Bob Von Dreele

On 7/17/2014 3:20 PM, Shoaib Muhammad wrote:

Thanks for your detailed reply. I am perusing to record HRPD pattern of LaB6
and will try to calculate "Instrument Parameters" from that pattern.

 

For question 5, I have performed a quick refinement in GSAS2 and attached
the gpx file. For simplicity I have selected isotropic size and strain
model. If I click on "Mustrain" or "Size" in Phases/Data tab, I can see a
nice sphere in Plot window. If I now run the refinement while "Mustrain" or
"Size" is selected, refinement will proceed but after refinement if I again
come to data tab after running refinement I will get error "Python has
stopped working" and this file will not open again. If I try to open it, I
will get the same error.

In the export menu if I select Export/Image Data as, I will get notice that,
"Project does not contain image" although isotropic strain model is visible
in plot window.

 

GPX file is attached and I am using Windows 8.1 64bit edition.

 

Thanks,

/Shoab

 

 

From: Toby, Brian H. [mailto:toby at anl.gov] 
Sent: Wednesday, July 16, 2014 3:20 AM
To: Shoaib Muhammad
Cc: gsas-ii at mailman.aps.anl.gov <mailto:gsas-ii at mailman.aps.anl.gov> 
Subject: Re: [GSAS-II] Calculating Particle size and Strain in GSAS2

 

Shoaib,  

 

Let me answer your e-mail as best as I can. 

 

First of all, you must accurately determine the instrument response terms
for the specific instrument that you used and as set up for your experiment
to get accurate site/microstress estimates. Remember that you are measuring
the extra broadening from your sample, so you must know what your instrument
is doing before you can know what broadening is "extra". 

 

On Jul 14, 2014, at 11:51 PM, Shoaib Muhammad <mshoaibce at gmail.com
<mailto:mshoaibce at gmail.com> > wrote:






it. Instrument parameter file was supposed to be used in Fullprof and has
the following text:

 

"Myresolution function

  0.000030   0.000050   0.000110 0 0 0"

 

I am not sure how to convert widths but I know this is covered in "Typical
values of Rietveld instrument profile coefficients" by James A. Kaduk and
Joel Reid, Powder Diffraction
<http://journals.cambridge.org/action/displayJournal?jid=PDJ>  / Volume 26 /
Issue 01 / March 2011, pp 88-93 (http://dx.doi.org/10.1154/1.3548128). I
would still recommend collecting and fitting data with a standard [NIST SRM
660(-,a,b) is a good choice, but anything with minimal broadening would do]
collected under the same conditions as your sample. 

 

 1-      In old GSAS there were couple of Peak profile function like "Pseudo
Voith" and may be Pearson VII also. How can I select/refine these peak
Profile functions in GSAS2?

 

GSAS-II has only one profile function and it works. It is a Pseudo-Voigt
(sum of Gaussian & Lorentzian; a real Voigt is the convolution, BTW). 

 

2-      Is it correct to fix U,V,W, X,Y in GSAS2 in-order to calculate
"Crystal Size" and "Microstrain"?

 

Yes, you must know the first 5 terms. 






3-      Can I refine "Crystal Size" and "Microstrain" together?

 

Yes, if needed and your range of data is large enough. Note that GSAS-II
allows for either or both to be anisotropic with either a preferred
direction (recommended) or a full expansion. 






4-      What does it mean by LGmin check box in Profile/Data tab?

 

Microstrain (aka residual stress) and crystallite broadening is usually
Lorentzian (LGmin = 1.0) but can have a Gaussian component (LGmin=0 is pure
Gaussian). You can refine this and see if the result is reasonable (0 <=
LGmin <= 1) and gives a better fit. 

 

5-      How to export the strain data to plot the image? I selected Mustrain
plot type, I can see the preview in plot window but can't export data. If
Mustrain is selected and I run the refinement, GSAS2 quits and I can't open
this file again. It always say "Python stopped working".

 

The strain data are the coefficients you get, but you should be able to
export the plot if you want. Please provide a lot more details on your
computer and exactly what you are doing, as well as a GPX file if you want
us to debug this. 

 

Brian

 






 

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