Re: [Ifeffit] Ifeffit Digest, Vol 167, Issue 2

[Raj kumar]

Hi Scott,

I would like to add an extra point to the previous message. Yes, i am
getting a large uncertainty for the second so2 (2.04 +/- 1.36).

Regards,
Raj

On 3 January 2017 at 21:32, Raj kumar  wrote:

> Hi Scott,
>
> Thank you very much for your prompt response. EXAFS measurement was done
> after the XRD characterization. From XRD, it is confirmed that there is no
> side phase formation and contamination. Hence, i guess the heavier element
> role could be avoided here.
>
> Split distances could be the reason??. The following is the method, i have
> opted for modelling the obtained curve. Since YbVO4 is zircon structure, i
> have constrained distance in paths 3, 8 and 9 with the pre-structural info
> and let other distances vary with regular mathematical expression
> alpha*Reff. am i doing wrong here? Before this, I have tried alpha*Reff for
> all paths but fit failed miserably for multi-shells.
>
> Regards,
> Raj
>
> On 3 January 2017 at 19:00, 
> wrote:
>
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>>
>>1. Re: Problem with large so2 (Scott Calvin)
>>
>>
>> --
>>
>> Message: 1
>> Date: Tue, 3 Jan 2017 09:59:18 -0600
>> From: Scott Calvin 
>> To: XAFS Analysis using Ifeffit 
>> Subject: Re: [Ifeffit] Problem with large so2
>> Message-ID: <3ef5e209-7681-49c6-9713-4bbf34c61...@gmail.edu>
>> Content-Type: text/plain; charset="utf-8"
>>
>> Hi Raj,
>>
>> I haven?t looked at your files, but the kinds of results you are
>> describing often indicate the model you are using beyond the first shell is
>> incorrect. It may be that it has the wrong elements (e.g., heavier elements
>> are present than what you modelled) or that the model includes split
>> distances when in reality the compound is more symmetric.
>>
>> In short, no, the high second S02 does not make sense (although it would
>> be good to know the uncertainties).
>>
>> Best,
>> Scott Calvin
>> Lehman College of the City University of New York
>>
>> > On Jan 3, 2017, at 9:38 AM, Raj kumar  wrote:
>> >
>> > Dear All,
>> >
>> >
>> >
>> > I have been trying to fit EXAFS signal of YbVO4 both in bulk and
>> nanoparticles form. Here, I would like to estimate so2 from bulk
>> (reference) and subsequently use the number, as normalization parameter, to
>> calculate the co-ordination number in all nanoparticles. Nanoparticles were
>> synthesized by solution route. From our earlier understanding on the
>> synthesis, in some cases, Yb may or may not completely involve in reaction.
>> Therefore, I except Yb in two environments, one surrounded by mere oxygen
>> (in precise oxygen-Hydrogen; due to disorder one may expect a single peak)
>> and another one in YbVO4 environment. With this info and for reasonable
>> fit, I have used two so2 as free parameters for N: one for first shell
>> (oxygen at two distances) and another for rest other shells.  If I use
>> single so2, I obtain the value of around 0.92 with unsatisfactory fit
>> whereas the fit seems plausible with two so2 i.e., 0.75 and 2.2,
>> respectively. Using the same strategy, I could successfully fi!
>>  t the nanoparticles again with large second so2 (1.79). From literature
>> and IFEFFIT earlier discussion, i understood that so2 should be between
>> 0.8-1.2 value. Here, I would like to know, does this huge second so2 value
>> makes sense? is the obtained so2 value can be used to calculated
>> coordination number for unknown? Further, i have attached my worked files
>> with this message.
>> >
>> >
>> >
>> > Regards,
>> >
>> > Raj
>> >
>> > _
>> __
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>> > Ifeffit@millenia.cars.aps.anl.gov
>> > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
>> > Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/options/ifeffit
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>> End of Ifeffit Digest, Vol 167, Issue 2
>> 

Re: [Ifeffit] Ifeffit Digest, Vol 167, Issue 2

[Bruce Ravel]

On 01/03/2017 03:32 PM, Raj kumar wrote:

From XRD, it is confirmed that there is no side phase formation and
contamination. Hence, i guess the heavier element role could be avoided
here.


Raj,

While this might be true for your sample, in general, a statement like 
this always concerns me.


From XRD, you can say is that there is no /crystalline/ side phase 
formation and that there is no contamination in the /diffracting/ 
/portion/ of the sample.


It is very common when preparing nanoparticulate matter for there to be 
non- or poorly-diffracting content in the sample.  If that content 
contains the absorbing element, then it will have an impact on the XAS data.


B



--
 Bruce Ravel   bra...@bnl.gov

 National Institute of Standards and Technology
 Synchrotron Science Group at NSLS-II
 Building 743, Room 114
 Upton NY, 11973

 Homepage:http://bruceravel.github.io/home/
 Software:https://github.com/bruceravel
 Demeter: http://bruceravel.github.io/demeter/
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Re: [Ifeffit] Ifeffit Digest, Vol 167, Issue 2

[Raj kumar]

Hi Scott,

Thank you very much for your prompt response. EXAFS measurement was done
after the XRD characterization. From XRD, it is confirmed that there is no
side phase formation and contamination. Hence, i guess the heavier element
role could be avoided here.

Split distances could be the reason??. The following is the method, i have
opted for modelling the obtained curve. Since YbVO4 is zircon structure, i
have constrained distance in paths 3, 8 and 9 with the pre-structural info
and let other distances vary with regular mathematical expression
alpha*Reff. am i doing wrong here? Before this, I have tried alpha*Reff for
all paths but fit failed miserably for multi-shells.

Regards,
Raj

On 3 January 2017 at 19:00, 
wrote:

> Send Ifeffit mailing list submissions to
> ifeffit@millenia.cars.aps.anl.gov
>
> To subscribe or unsubscribe via the World Wide Web, visit
> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
> or, via email, send a message with subject or body 'help' to
> ifeffit-requ...@millenia.cars.aps.anl.gov
>
> You can reach the person managing the list at
> ifeffit-ow...@millenia.cars.aps.anl.gov
>
> When replying, please edit your Subject line so it is more specific
> than "Re: Contents of Ifeffit digest..."
>
>
> Today's Topics:
>
>1. Re: Problem with large so2 (Scott Calvin)
>
>
> --
>
> Message: 1
> Date: Tue, 3 Jan 2017 09:59:18 -0600
> From: Scott Calvin 
> To: XAFS Analysis using Ifeffit 
> Subject: Re: [Ifeffit] Problem with large so2
> Message-ID: <3ef5e209-7681-49c6-9713-4bbf34c61...@gmail.edu>
> Content-Type: text/plain; charset="utf-8"
>
> Hi Raj,
>
> I haven?t looked at your files, but the kinds of results you are
> describing often indicate the model you are using beyond the first shell is
> incorrect. It may be that it has the wrong elements (e.g., heavier elements
> are present than what you modelled) or that the model includes split
> distances when in reality the compound is more symmetric.
>
> In short, no, the high second S02 does not make sense (although it would
> be good to know the uncertainties).
>
> Best,
> Scott Calvin
> Lehman College of the City University of New York
>
> > On Jan 3, 2017, at 9:38 AM, Raj kumar  wrote:
> >
> > Dear All,
> >
> >
> >
> > I have been trying to fit EXAFS signal of YbVO4 both in bulk and
> nanoparticles form. Here, I would like to estimate so2 from bulk
> (reference) and subsequently use the number, as normalization parameter, to
> calculate the co-ordination number in all nanoparticles. Nanoparticles were
> synthesized by solution route. From our earlier understanding on the
> synthesis, in some cases, Yb may or may not completely involve in reaction.
> Therefore, I except Yb in two environments, one surrounded by mere oxygen
> (in precise oxygen-Hydrogen; due to disorder one may expect a single peak)
> and another one in YbVO4 environment. With this info and for reasonable
> fit, I have used two so2 as free parameters for N: one for first shell
> (oxygen at two distances) and another for rest other shells.  If I use
> single so2, I obtain the value of around 0.92 with unsatisfactory fit
> whereas the fit seems plausible with two so2 i.e., 0.75 and 2.2,
> respectively. Using the same strategy, I could successfully fi!
>  t the nanoparticles again with large second so2 (1.79). From literature
> and IFEFFIT earlier discussion, i understood that so2 should be between
> 0.8-1.2 value. Here, I would like to know, does this huge second so2 value
> makes sense? is the obtained so2 value can be used to calculated
> coordination number for unknown? Further, i have attached my worked files
> with this message.
> >
> >
> >
> > Regards,
> >
> > Raj
> >
> > _
> __
> > Ifeffit mailing list
> > Ifeffit@millenia.cars.aps.anl.gov
> > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
> > Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/options/ifeffit
>
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> End of Ifeffit Digest, Vol 167, Issue 2
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>
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