Re: Help for analysis strain using GSAS？

[Daxu Liu]

Because my mathematics background is very weak, maybe it is difficult for me to 
understand on those functions describing the strain.
Thanks everyone, and I will try my best to catch it. Thanks all again!  Happy 
new year!
Best regards, Daxu 

  From: Daxu Liu 
 To: RIETVELD_L Distribution List  
 Sent: Monday, December 19, 2016 8:45 PM
 Subject: Help for analysis strain using GSAS？
   
Hi, everyone,
Someone can supply some information on analyzing strain using GSAS?  Because 
one of the reviewers asked me to determine the stain of biogenic calcite, 
however I don't know how to analyze the refinement data to obtain the strain. I 
wonder whether the resolution of conventional Bragg-Brentano X-ray 
diffratometer is able to determine the strain. I know GSAS does describe the 
strain using some functions for conventional XRPD data. How to output the 
corresponding data to calculate the strain.

Best regrads, Daxu 

   ++
Please do NOT attach files to the whole list 
Send commands to  eg: HELP as the subject with no body text
The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/
++

Re: Stoichiometry and occupancy fractions of solid solutions

[Leopoldo Suescun]

Dear Othman,

I agree with previous comments and warnings from colleagues.

But regarding your specific question, you need to check the manuals for
GSAS II or FULLPROF on how to setup the constraints on the site occupancies
of all the atoms and sites involved.

It is not sufficient to constrain the occupancies of each site add up to 1.

You also need to cross-constrain occupancies in such a way that the sum of
occupancy*multiplicity for each element equals your known chemical
composition.

For example, if you have 2 sites a and b for B/C, the two sites have
multiplicities MULTa and MULTb (as defined in the International Tables Vol.
A), your composition is B0.5C2.5 and the number of formula units A2B/C3O12
is Z, your constrains should look something like this: (I will call SOF-Ba
and SOF-Bb the fractional occupancies of B in a and b sites respectively
and SOF-Ca and SOF-Cb the fractional occupancies of C in a and b sites
respectively):

SOF-Ba+SOF-Ca=1
SOF-Bb+SOF-Cb=1
(you said you already set up these two and those make sure you don´t have
more or less than 3*Z atoms in the sites)

SOF-Ba*MULTa+SOF-Bb*MULTb=0.5*Z
SOF-Ca*MULTa+SOF-Cb*MULTb=2.5*Z
these constraints keep your B and C composition in the expected values.

Be careful with the number of formula units per unit cell or your constrain
will be wrong. If you have more than two sites you need to proceed
accordingly adding a third constraint for the total occupancy of the third
site and adding the corresponding term in the two sum constraints.

Depending on the specific software this will be written differently but the
idea should be to keep these relations.

Best luck with your refinement,
Leo


2016-12-19 5:54 GMT-03:00 Othman Al Bahri :

> Dear all,
>
>
> I've made a series of solid solution powders using a solid state reaction
> in the form A2B3-xCxO12 at x= 0.5 steps. A2B3O12 is orthorhombic while A2C
> 3O12 is monoclinic. I'm refining the XRD data to find the atomic
> distribution of the solute.
>
>
> I've constrained the sum of the occupancy fractions for each relevant
> site to equal 1. At low concentrations of the solute, I initially set the
> solute's occupancy fractions to 0 and keep the solvent's occupancy at 1
> then refine the fractions (after following the usual Rietveld refinement
> steps). This seems to give reasonable occupancy fraction values (no big
> numbers or negative values) but the stoichiometry is way off. This is
> probably because each site has different Wykoff multiplicities so
> constraining the sum of each site's fractions to 1 is insufficient.
>
>
> Let's assume that I knew the stoichiometry from Mass Spectroscopy or XPS -
> is there a way to constrain the stiochiometry in a Rietveld refinement? I'm
> using GSAS-II and comfortable with FullProf but feel free to give advice
> for any other open-source software.
>
>
> I've seen a few papers where the authors mention, typically in the
> supplementary info, that their refinements' stoichiometry was off and that
> it should be ignored. However I'm not comfortable with this approach and
> would appreciate your advice.
>
>
> This is my first time working with solid solutions so please feel free to
> offer any general advice on what I should be careful with. I've tested for
> phase mixtures (insolubility) by visually comparing my XRD patterns with
> the sum of simulated XRD patterns of molar mixtures and through Rietveld 
> refinements
> with two phases. The system I'm working with has been reported but the
> original authors didn't do Rietveld refinements - they were interested in
> physical property measurements.
>
>
> Kind Regards,
>
>
> Othman
>
> ++
> Please do NOT attach files to the whole list  >
> Send commands to  eg: HELP as the subject with no body
> text
> The Rietveld_L list archive is on http://www.mail-archive.com/
> rietveld_l@ill.fr/
> ++
>
>
>


-- 
Dr. Leopoldo Suescun
Prof. Agr (Assoc. Prof.) de Física  Tel: (+598) 29290705/29249859
Cryssmat-Lab./Cátedra de Fisica/DETEMA  Fax: (+598) 29241906*
Facultad de Quimica, Universidad de la Republica. Montevideo, Uruguay

Ahora la cristalografía importa más (www.iucr.org) Crystallography Matters
more.
++
Please do NOT attach files to the whole list 
Send commands to  eg: HELP as the subject with no body text
The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/
++

APS Powder Diffraction Educational Content, APS 100 Years of Powder Diffraction Minisymposium

[Toby, Brian H.]

Due to the wonders of web page management, our web content on powder 
diffraction, which includes quite a few on-line lectures, has moved to a new 
location: 
https://www1.aps.anl.gov/Education/Powder-Diffraction-Educational-Materials. 
This URL is hard to find at present, so this is worthwhile to bookmark.

This page contains some new content that may be of interest: On November 11, 
2016 we held a half-day symposium on historical developments in powder 
diffraction as well as contemporary APS work to commemorate the 100th 
anniversary of powder diffraction. Speakers were: David Cox (Brookhaven 
National Laboratory, retired), Tim Fawcett (International Centre for 
Diffraction Data) Pete Chupas (APS), Andrey Yakovenko (APS), Saul Lapidus 
(APS), Olaf J. Borkiewicz (APS) and Robert B. Von Dreele (APS). Recorded 
versions (slides/audio) of all lectures are now available on-line here: 
https://www1.aps.anl.gov/Education/Powder-Diffraction-Century-Symposium.

Brian++
Please do NOT attach files to the whole list 
Send commands to  eg: HELP as the subject with no body text
The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/
++

Re: Stoichiometry and occupancy fractions of solid solutions

[Larry Finger]

On 12/19/2016 09:29 AM, Cline, James Dr. (Fed) wrote:

Your data is from where?  I wouldn’t trust numbers from refinements as these
from lab data.



Jim





James P. Cline
Materials Measurement Science Division
National Institute of Standards and Technology
100 Bureau Dr. stop 8520 [ B113 / Bldg 217 ]
Gaithersburg, MD 20899-8523USA
jcl...@nist.gov 
(301) 975 5793
FAX (301) 975 5334



*From:*rietveld_l-requ...@ill.fr [mailto:rietveld_l-requ...@ill.fr] *On Behalf
Of *Othman Al Bahri
*Sent:* Monday, December 19, 2016 3:54 AM
*To:* rietveld_l@ill.fr
*Subject:* Stoichiometry and occupancy fractions of solid solutions



Dear all,



I've made a series of solid solution powders using a solid state reaction in the
form A_2 B_3-x C_x O_12 at_x= 0.5 steps. A_2 B_3 O_12 is orthorhombic while A_2
C_3 O_12 is monoclinic. I'm refining the XRD data to find the atomic
distribution of the solute.



I've constrained the sum of the occupancy fractions for each relevant site to
equal 1. At low concentrations of the solute, I initially set the solute's
occupancy fractions to 0 and keep the solvent's occupancy at 1 then refine the
fractions (after following the usual Rietveld refinement steps). This seems to
give reasonable occupancy fraction values (no big numbers or negative values)
but the stoichiometry is way off. This is probably because each site has
different Wykoff multiplicities so constraining the sum of each site's fractions
to 1 is insufficient.



Let's assume that I knew the stoichiometry from Mass Spectroscopy or XPS - is
there a way to constrain the stiochiometry in a Rietveld refinement? I'm using
GSAS-II and comfortable with FullProf but feel free to give advice for any other
open-source software.



I've seen a few papers where the authors mention, typically in the supplementary
info, that their refinements' stoichiometry was off and that it should be
ignored. However I'm not comfortable with this approach and would appreciate
your advice.



This is my first time working with solid solutions so please feel free to offer
any general advice on what I should be careful with. I've tested for phase
mixtures (insolubility) by visually comparing my XRD patterns with the sum of
simulated XRD patterns of molar mixtures and through Rietveld refinements with
two phases. The system I'm working with has been reported but the original
authors didn't do Rietveld refinements - they were interested in physical
property measurements.



Kind Regards,



Othman


I am showing my age, but in my PhD thesis, I demonstrated that even when using 
single-crystal data to refine distributions of such favorable species as Fe vs 
Mg, constraining full occupancy was not sufficient. A stoichiometry constraint 
was also needed. The reference is Finger, Larry W (1969) The crystal structure 
and cation distribution of a grunerite, Mineral. Soc. Am. Spec. Paper, 2, 95-100.


If you know the overall chemical composition from electron microprobe data as in 
my case, or from the chemicals used in the synthesis, use that information to 
constrain the refinement!


Larry

++
Please do NOT attach files to the whole list 
Send commands to  eg: HELP as the subject with no body text
The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/
++

RE: Stoichiometry and occupancy fractions of solid solutions

[Cline, James Dr. (Fed)]

Your data is from where?  I wouldn't trust numbers from refinements as these 
from lab data.

Jim


James P. Cline
Materials Measurement Science Division
National Institute of Standards and Technology
100 Bureau Dr. stop 8520 [ B113 / Bldg 217 ]
Gaithersburg, MD 20899-8523USA
jcl...@nist.gov
(301) 975 5793
FAX (301) 975 5334

From: rietveld_l-requ...@ill.fr [mailto:rietveld_l-requ...@ill.fr] On Behalf Of 
Othman Al Bahri
Sent: Monday, December 19, 2016 3:54 AM
To: rietveld_l@ill.fr
Subject: Stoichiometry and occupancy fractions of solid solutions


Dear all,



I've made a series of solid solution powders using a solid state reaction in 
the form A2B3-xCxO12 at x= 0.5 steps. A2B3O12 is orthorhombic while A2C3O12 is 
monoclinic. I'm refining the XRD data to find the atomic distribution of the 
solute.



I've constrained the sum of the occupancy fractions for each relevant site to 
equal 1. At low concentrations of the solute, I initially set the solute's 
occupancy fractions to 0 and keep the solvent's occupancy at 1 then refine the 
fractions (after following the usual Rietveld refinement steps). This seems to 
give reasonable occupancy fraction values (no big numbers or negative values) 
but the stoichiometry is way off. This is probably because each site has 
different Wykoff multiplicities so constraining the sum of each site's 
fractions to 1 is insufficient.



Let's assume that I knew the stoichiometry from Mass Spectroscopy or XPS - is 
there a way to constrain the stiochiometry in a Rietveld refinement? I'm using 
GSAS-II and comfortable with FullProf but feel free to give advice for any 
other open-source software.



I've seen a few papers where the authors mention, typically in the 
supplementary info, that their refinements' stoichiometry was off and that it 
should be ignored. However I'm not comfortable with this approach and would 
appreciate your advice.



This is my first time working with solid solutions so please feel free to offer 
any general advice on what I should be careful with. I've tested for phase 
mixtures (insolubility) by visually comparing my XRD patterns with the sum of 
simulated XRD patterns of molar mixtures and through Rietveld refinements with 
two phases. The system I'm working with has been reported but the original 
authors didn't do Rietveld refinements - they were interested in physical 
property measurements.



Kind Regards,



Othman
++
Please do NOT attach files to the whole list 
Send commands to  eg: HELP as the subject with no body text
The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/
++

Re: Help for analysis strain using GSAS？

[Leopoldo Suescun]

Dear Daxu,
You can find this information in GSAS Manual (the file GSAS Manual.pdf is
included in the distribution of GSAS and should be available for download
from APS web site that is currently not available, at least from my place,
I can e-mail it privately if you don´t have it).

In short, both U in Cagliotti's Gaussian FWHM or Y in Lorentzian broadening
equations have a behavior with 2theta compatible with strain broadening.
You'll need a decent quality powder pattern to refine one or both of the
parameters, substract the instrumental contribution to U and/or Y and
calculate the sample contribution.

But, as the many experts in the list will warn, this is just a simple and
possibly inadequate approximation of your sample that should have
complexities not necessarily accountable by the model in the software, so
care should be taken in making strong assumption based on these numbers.

There are other Rietveld refinement software pieces that are devoted to
modelling these kind of sample contributions that you may explore. But the
results will also depend a lot on your data and the complexity of the
sample so you should be careful.

Best luck
Leo

2016-12-19 9:45 GMT-03:00 Daxu Liu :

> Hi, everyone,
>
> Someone can supply some information on analyzing strain using GSAS?
> Because one of the reviewers asked me to determine the stain of biogenic
> calcite, however I don't know how to analyze the refinement data to obtain
> the strain. I wonder whether the resolution of conventional Bragg-Brentano
> X-ray diffratometer is able to determine the strain. I know GSAS does
> describe the strain using some functions for conventional XRPD data. How to
> output the corresponding data to calculate the strain.
>
>
> Best regrads, Daxu
>
> ++
> Please do NOT attach files to the whole list  >
> Send commands to  eg: HELP as the subject with no body
> text
> The Rietveld_L list archive is on http://www.mail-archive.com/
> rietveld_l@ill.fr/
> ++
>
>
>


-- 
Dr. Leopoldo Suescun
Prof. Agr (Assoc. Prof.) de Física  Tel: (+598) 29290705/29249859
Cryssmat-Lab./Cátedra de Fisica/DETEMA  Fax: (+598) 29241906*
Facultad de Quimica, Universidad de la Republica. Montevideo, Uruguay

Ahora la cristalografía importa más (www.iucr.org) Crystallography Matters
more.
++
Please do NOT attach files to the whole list 
Send commands to  eg: HELP as the subject with no body text
The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/
++

Help for analysis strain using GSAS？

[Daxu Liu]

Hi, everyone,
Someone can supply some information on analyzing strain using GSAS?  Because 
one of the reviewers asked me to determine the stain of biogenic calcite, 
however I don't know how to analyze the refinement data to obtain the strain. I 
wonder whether the resolution of conventional Bragg-Brentano X-ray 
diffratometer is able to determine the strain. I know GSAS does describe the 
strain using some functions for conventional XRPD data. How to output the 
corresponding data to calculate the strain.

Best regrads, Daxu ++
Please do NOT attach files to the whole list 
Send commands to  eg: HELP as the subject with no body text
The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/
++

AW: Stoichiometry and occupancy fractions of solid solutions

[Uwe Kolitsch]

Dear Othman,

You should check if the synthesised grains in your powder are chemically
homogeneous of if they show any zonation due to growth processes. Variable
chemistry will cause broadened and/or asymmetric peaks

Are vacancies known to occur in this class of compounds? The conditions of
preparation might be important (synthesis in air or something else?).

 

Uwe

 

 

Von: rietveld_l-requ...@ill.fr [mailto:rietveld_l-requ...@ill.fr] Im Auftrag
von Othman Al Bahri
Gesendet: Montag, 19. Dezember 2016 09:54
An: rietveld_l@ill.fr
Betreff: Stoichiometry and occupancy fractions of solid solutions

 

Dear all,

 

I've made a series of solid solution powders using a solid state reaction in
the form A2B3-xCxO12 at x= 0.5 steps. A2B3O12 is orthorhombic while A2C3O12
is monoclinic. I'm refining the XRD data to find the atomic distribution of
the solute. 

 

I've constrained the sum of the occupancy fractions for each relevant site
to equal 1. At low concentrations of the solute, I initially set the
solute's occupancy fractions to 0 and keep the solvent's occupancy at 1 then
refine the fractions (after following the usual Rietveld refinement steps).
This seems to give reasonable occupancy fraction values (no big numbers or
negative values) but the stoichiometry is way off. This is probably because
each site has different Wykoff multiplicities so constraining the sum of
each site's fractions to 1 is insufficient.

 

Let's assume that I knew the stoichiometry from Mass Spectroscopy or XPS -
is there a way to constrain the stiochiometry in a Rietveld refinement? I'm
using GSAS-II and comfortable with FullProf but feel free to give advice for
any other open-source software.

 

I've seen a few papers where the authors mention, typically in the
supplementary info, that their refinements' stoichiometry was off and that
it should be ignored. However I'm not comfortable with this approach and
would appreciate your advice.

 

This is my first time working with solid solutions so please feel free to
offer any general advice on what I should be careful with. I've tested for
phase mixtures (insolubility) by visually comparing my XRD patterns with the
sum of simulated XRD patterns of molar mixtures and through Rietveld
refinements with two phases. The system I'm working with has been reported
but the original authors didn't do Rietveld refinements - they were
interested in physical property measurements.

 

Kind Regards,

 

Othman

++
Please do NOT attach files to the whole list 
Send commands to  eg: HELP as the subject with no body text
The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/
++

Stoichiometry and occupancy fractions of solid solutions

[Othman Al Bahri]

Dear all,


I've made a series of solid solution powders using a solid state reaction in 
the form A2B3-xCxO12 at x= 0.5 steps. A2B3O12 is orthorhombic while A2C3O12 is 
monoclinic. I'm refining the XRD data to find the atomic distribution of the 
solute.


I've constrained the sum of the occupancy fractions for each relevant site to 
equal 1. At low concentrations of the solute, I initially set the solute's 
occupancy fractions to 0 and keep the solvent's occupancy at 1 then refine the 
fractions (after following the usual Rietveld refinement steps). This seems to 
give reasonable occupancy fraction values (no big numbers or negative values) 
but the stoichiometry is way off. This is probably because each site has 
different Wykoff multiplicities so constraining the sum of each site's 
fractions to 1 is insufficient.


Let's assume that I knew the stoichiometry from Mass Spectroscopy or XPS - is 
there a way to constrain the stiochiometry in a Rietveld refinement? I'm using 
GSAS-II and comfortable with FullProf but feel free to give advice for any 
other open-source software.


I've seen a few papers where the authors mention, typically in the 
supplementary info, that their refinements' stoichiometry was off and that it 
should be ignored. However I'm not comfortable with this approach and would 
appreciate your advice.


This is my first time working with solid solutions so please feel free to offer 
any general advice on what I should be careful with. I've tested for phase 
mixtures (insolubility) by visually comparing my XRD patterns with the sum of 
simulated XRD patterns of molar mixtures and through Rietveld refinements with 
two phases. The system I'm working with has been reported but the original 
authors didn't do Rietveld refinements - they were interested in physical 
property measurements.


Kind Regards,


Othman
++
Please do NOT attach files to the whole list 
Send commands to  eg: HELP as the subject with no body text
The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/
++