Re: [Ifeffit] Ifeffit Digest, Vol 167, Issue 3

4 Jan 2017

      Hi Bruce,

I agree with your comments. Side phase with less than 5% in total
composition cannot be easily detected using regular XRD but comprehensively
using EXAFS.  Here, i have also recorded bulk sample, similar to
nanoparticles composition, which is completely free from contamination.
...
From this data, i have ruled out the presence of heavy metals.
Regards,
Raj

On 4 January 2017 at 12:38, 
wrote:
...
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Today's Topics:
1. Re: Ifeffit Digest, Vol 167, Issue 2 (Raj kumar)
   2. Re: Ifeffit Digest, Vol 167, Issue 2 (Bruce Ravel)
   3. Re: Ifeffit Digest, Vol 167, Issue 2 (Raj kumar)
----------------------------------------------------------------------
Message: 1
Date: Tue, 3 Jan 2017 21:32:51 +0100
From: Raj kumar 
To: ifeffit@millenia.cars.aps.anl.gov
Subject: Re: [Ifeffit] Ifeffit Digest, Vol 167, Issue 2
Message-ID:

Content-Type: text/plain; charset="utf-8"
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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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: <3EF5E209-7681-49C6-9713-4BBF34C619A5@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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