[Ifeffit] Ifeffit Digest, Vol 167, Issue 2

Raj kumar rajrk37 at gmail.com
Wed Jan 4 05:38:05 CST 2017


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 <rajrk37 at gmail.com> 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, <ifeffit-request at millenia.cars.aps.anl.gov>
> wrote:
>
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>> Today's Topics:
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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 <dr.scott.calvin at gmail.com>
>> To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
>> Subject: Re: [Ifeffit] Problem with large so2
>> Message-ID: <3EF5E209-7681-49C6-9713-4BBF34C619A5 at 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 <rajrk37 at gmail.com> 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
>> >
>> > <YbVO4-bulk.fpj><YbVO4-nps.fpj>_____________________________
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>> End of Ifeffit Digest, Vol 167, Issue 2
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