Good luck with your project!

Cheers,
Artem

> Dear Artem,
>
>
> Thank you very much for pointing me to these resources. They have also
> been extremely useful.
>
> Have a wonderful holiday and a happy new year.
>
>
> Kind regards,
>
>
> Othman
>
> ________________________________
> From: baba...@univ.kiev.ua <baba...@univ.kiev.ua>
> Sent: Monday, 19 December 2016 9:31:29 PM
> To: Othman Al Bahri
> Subject: Re: Stoichiometry and occupancy fractions of solid solutions
>
> Dear Othman,
>
> General notes and precaution are concisely described in the
> Rietveld refnement guidelines "J. Appl. Cryst. (1999). 32, 36-50
> (paragraph 7).
> Then, you may refer to Madsen & Hill's Variable Counting Time concept,
> J. Appl. Cryst. (1994). 27, 385-392. Definitely, that's the solution
> for reliable refinement of site occupancies, when lab PXRD is utilized.
> Those considerations are simplified by condition of chemically averaged
> grain compositions, as Uwe has noted.
>
> Sincerely,
> Artem
>
>
>> 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
>> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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>> <alan.he...@neutronoptics.com>
>> Send commands to <lists...@ill.fr> eg: HELP as the subject with no body
>> text
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>>
>>
>
>
>


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