Hi Shan,
Nothing at all surprising here. In fact, you're getting pretty good
results, in my opinion. Your CN insists on being "about" 4.8. When
you push the ss, with which CN is correlated, to the top of its
fitted range, the CN increases to about 5.2. To me, that says your CN
is 4.8 +/ 0.4. A 10% uncertainty in CN is quite good for EXAFS! Of
course, your real uncertainty is greater than that, because there are
some possible systematic errors (e.g. normalization, sample effects)
that might be present. But still, you're doing about as well as can
be expected.
Of course, that's assuming that CN's are what you're after. If
finding out whether it's Alumina or Yttria is what you're after, the
quality of fit and CN are not distinguishing between the two
possibilities. That leaves bond distance as the best EXAFS indicator
of which phase is present.
--Scott Calvin
Sarah Lawrence College
At 05:49 PM 12/20/2006, you wrote:
Thanks Carlo and Scott for ur response.
Some numbers from my fits in this regard and some more queries.
When I make a cluster based on the Alumina structure (replacing the
central Al with Y with relaxed lattice parameters) I get DW 0.0025 +-
0.002, without any restraint. While I restrain the DW to 0.005, my CN
jumps from 4.8 to 5.2.
When I make a cluster based on Yttria structure, I get DW factor of
0.008 +- 0.002, unrestrained. While I restrain the DW to 0.01, it
again jumps from 4.8 to 5.2.
First query...if you can pin down on the CN change (Carlo..you wanted
some numbers)
Second...what are ur comments on the above 2 models and the change in
DW factors.
I might add that ther is no appreciable difference with k=2, 3 or 2&3
fittings. All the fits produce red-chi-sqr less than 100 (~50-70), all
R-factors are <0.01 and no unphysical reports after the fit. And I
have only 1 peak to worry about, there is no second shell correlation
seen.
I would appreciate your 2 cents on this.
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