[Ifeffit] Problem with large so2: Updated

[Raj kumar]

Dear all,


Earlier, I have posted few questions on large so2 value and got valuable
suggestions from Scott and Bruce. Here i am presenting my summary of
earlier emails and the present views. Could you please tell me whether am i
going in right direction.


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. First, I have modelled my reference (bulk
YbVO4) with two so2, N and R as free parameters. So2-1 is for first two
shell and so2-2 is for rest other shells. If I use single so2, the value is
obtained to be around 0.9 with unsatisfactory fit whereas second so2-2
incorporation leads to satisfied fit with large uncertainty on the obtained
number i.e., (2.04 +/- 0.9). Using the same strategy, I could successfully
fit the nanoparticles again with large so2-2 (1.79). From literature and
IFEFFIT earlier discussion, i understood that so2 should be between 0.8-1.2
value.  Further, so2-2 is found to well correlated with ss1 and delc (a
parameter to define the movement of atoms in c direction). Among two, the
former parameter (ss1) strongly correlate with so2 and take value of 0.8
and 1.9  for fixed and varying ss1, respectively, during the fit. This
large value of  so2 cannot be controlled with the used model. Also, I have
tried to fit the curve with fixed so2 i.e., below 1 but leads to
unsatisfactory fit. For your info, i have tabulated various strategy and
the resultant parameters. After considering Scott suggestions *(and
previous posts),* i have concluded the following: Since, so2 is used as a
normalization parameter and with the estimated uncertainty, i would
like to consider
the obtained number as reasonable value to normalize the unknown to
calculate the CN in other systems. Is this strategy good to calculate the
CN in unknown? and later to describe the trend on obtained parameters?

Regards,
Raj
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