[Ifeffit] Crytallites AND polycrystalline - Artemis handling?
SCalvin at slc.edu
Mon Oct 20 08:15:02 CDT 2008
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 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
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
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)
S Calvin et al, Phys. Scr. T115 744-748 (2005).
The oxide amp entry is much simpler:
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
Sarah Lawrence College
On Oct 20, 2008, at 8:46 AM, Joseph Washington wrote:
> 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!
> 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!
>> 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
>>> is likely to be Ge-Te crystallites with some amorphous material at
>>> 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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