Sure, Joseph.
These were nanoparticles made with a reverse micellar method. Past
experience has shown that this synthesis produces a passivating oxide
layer on an iron core; the passivating layer is usually amorphous,
which is a good thing; hematite has a lattice mismatch and thus
doesn't passivate. Linear combination analysis suggested this samples
was 75% metal and 25 +/- 5% oxide.
A typical amp entry is:
S02_Fe*Frac_bcc*(1-3/4*reff/R_Fe+1/16*(reff/R_Fe)^3)
S02_Fe is just the usual S02 factor, and "should" be from 0.70 to 1.0.
It's lower than that in the fit I've sent you; that's one of the
indications the fit may not yet be done. (I've actually gone much
further with this fit, but that would have made for a more confusing
file.)
Frac_bcc is the fraction of iron atoms in an ordinary bcc metal
environment. In the fit I sent you, it optimizes to 34 +/ 9%. Notice
that's consistent with the linear combination analysis. That makes me
happy.
R_Fe is the radius of the core, modeled as a sphere. The formula in
which it appears accounts for the reduction in average coordination
number due to surface termination, and is discussed in several of my
papers, including my articles:
S. Calvin et al., Appl. Phys. Lett. 87, 233102 (2005)
and
S Calvin et al, Phys. Scr. T115 744-748 (2005).
The oxide amp entry is much simpler:
S02_Fe*Frac_Ox*2
Frac_Ox is 1-Frac_Bcc; i.e. what's not metal is oxide.
The factor of 2 is just because I was working with a path from
hematite that had coordination number of 3 (there's some splitting in
hematite); I multipled by 2 to get an assumed coordination number of
6. Much of my subsequent fitting has been using bond valence theory to
try to distinguish between coordination of 4 or 6 for the amorphous
oxide.
--Scott Calvin
Sarah Lawrence College
On Oct 20, 2008, at 8:46 AM, Joseph Washington wrote:
Scott,
Thank you very much. I am looking at this file and I understand
everything as far as the isotropic expansion terms in the delr and
the debye term. Can you clarify the amp math expression? Also, just
so we're on the same page, tell me a little about this system?
Thank you again for your help!
Joseph
Scott Calvin wrote:
Hi Joe,
Here's an in-progress Artemis file for a system with some broad
similarities to the one your describe. Perhaps it will help.
Disclaimer: This is /not/ a final fit!
--Scott
------------------------------------------------------------------------
On Oct 17, 2008, at 2:15 PM, Joseph Washington wrote:
Hello all,
I am working on analyzing Ge edge EXAFS data of an annealed sample
which
is likely to be Ge-Te crystallites with some amorphous material at
the
grain boundary (or perhaps, just Ge-N crystal material at the
interface). I do not have any information about the grain size, only
possible constituents for the grain and the boundary. Can anyone
give me
some examples of how Artemis might handle this?
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