Fwd: from Rui Si at SSRF: help needed
Hi Rui,
I am CCing my answer to you and to the Ifeffit Mailing List. It's
always a good idea to use the mailing list as it greatly increases the
number of eyes that get to look at your question. If you reply to
this, please do so via the mailing list.
In the PDF file you attached, you asked these two questions:
(1) Why the second peak (ca. 3 Å) in experimental data is missing in
the Co3O4 model?
I do not know anything about your sample, so this is a tough question.
Are you certain of its phase purity? Could there be another form of
cobalt oxide present in the sample?
(2) Why need to add the “shift vector” suggested by Artemis?
Actually, no action is required and the software change the Co
core from 0.125, 0.125, 0.125 to 0.5 0.5 0.5, and keep the shift
vector as 0 0 0.
The purpose of the shift vector is explained here:
http://bruceravel.github.io/demeter/artug/atoms/space.html#multipleoriginsan...
In the case of the CIF file you attached, the shift vecotr does not
seem required. The list of atomic coordinates without the shift
vecotr looks right to me.
B
-------- Original Message --------
Subject: from Rui Si at SSRF: help needed
Date: Tue, 15 Jul 2014 07:33:31 +0000
From: 司锐
Hi Bruce,
Thank you very much for your help.
For the phase purity, we have used XRD to confirm that only Co3O4 structure was present in the sample (no other crystallized phase). So, I am pretty curious about this. I will also ask my colleague to identify the model structure in related software.
Best,
Rui
----------------------------------------------------------
Dr. Rui Si
Shanghai Institute of Applied Physics, Chinese Academy Sciences
Shanghai Synchrotron Radiation Facility
Address:
239 Zhangheng Rd, Pudong District
Shanghai 201204, China
E-mail: sirui@sinap.ac.cn
Tel: (86)21-33932079
Cell:(86)13301753969
________________________________________
发件人: Bruce Ravel [bravel@bnl.gov]
发送时间: 2014年7月15日 20:25
到: XAFS Analysis using Ifeffit; 司锐
主题: Fwd: from Rui Si at SSRF: help needed
Hi Rui,
I am CCing my answer to you and to the Ifeffit Mailing List. It's
always a good idea to use the mailing list as it greatly increases the
number of eyes that get to look at your question. If you reply to
this, please do so via the mailing list.
In the PDF file you attached, you asked these two questions:
(1) Why the second peak (ca. 3 Å) in experimental data is missing in
the Co3O4 model?
I do not know anything about your sample, so this is a tough question.
Are you certain of its phase purity? Could there be another form of
cobalt oxide present in the sample?
(2) Why need to add the “shift vector” suggested by Artemis?
Actually, no action is required and the software change the Co
core from 0.125, 0.125, 0.125 to 0.5 0.5 0.5, and keep the shift
vector as 0 0 0.
The purpose of the shift vector is explained here:
http://bruceravel.github.io/demeter/artug/atoms/space.html#multipleoriginsan...
In the case of the CIF file you attached, the shift vecotr does not
seem required. The list of atomic coordinates without the shift
vecotr looks right to me.
B
-------- Original Message --------
Subject: from Rui Si at SSRF: help needed
Date: Tue, 15 Jul 2014 07:33:31 +0000
From: 司锐
Hi Rui,
Since XRD indicates your material is phase pure, I can think of three likely contributors as to why the 3 angstrom peak is "missing."
First is that you never actually plotted the model. You plotted the magnitude of individual paths from the model, but you did not sum the paths and plot the magnitude of the result. Your paths 2, 3, and 4 all show considerable amplitude around 3 angstroms, but the magnitude plot does not show phase. It is quite possible for those paths to add out of phase, and thus partially cancel. You should try summing the paths and plotting the result.
Second, Co3O4 is a spinel, and has two different absorbing sites for cobalt (the tetraehdrally and octahedrally coordinated ones). It very much looks to me like you only did a feff calculation for one of those sites. You need to calculate for both sites. Since there are two octahedral sites for every tetrahedral one, you need to weight the octahedral sites twice as heavily when you do the sum (you can use the S02 path parameter to affect weighting).
Finally, you didn't include any multiple-scattering paths. Multiple-scattering paths are significant contributors to spinel spectra in that region of the Fourier transform.
--Scott Calvin
Sarah Lawrence College
On Jul 15, 2014, at 5:25 AM, Bruce Ravel
(1) Why the second peak (ca. 3 Å) in experimental data is missing in the Co3O4 model?
participants (3)
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Bruce Ravel -
Scott Calvin -
司锐