[Ifeffit] How to input atoms in solid solution for Artemis

Scott Calvin dr.scott.calvin at gmail.com
Thu Jun 23 15:23:36 CDT 2016


One additional thought:

Distinguishing Ni-Ni and Ni-Fe by creating two different feff paths and fitting the spectrum as a mixture of the two is very difficult, to put it mildly, as both Anatoly and Matt indicated.

But the bond length determined by your fit may be able to give you a clue, particularly when compared to appropriate standards. Depending on the details of your structure, the average bond length may depend on the fraction of sites occupied by iron to a degree which is measurable by EXAFS. Even if you simply use a nickel-nickel scattering path in feff to model your structure, differences in bond length could be indicative of changes in site occupancy.

Ideally, this could be done by creating a series of standards with known iron-nickel ratios, fitting the bond length for each, and then comparing a fit of a sample with a similar structure but unknown iron-nickel ratio to the results for the standards.

—Scott Calvin
Sarah Lawrence College

> On Jun 23, 2016, at 3:41 PM, Fuxiang Zhang <zhangfx at umich.edu> wrote:
> 
> Hi, Matt and Anayoly,
> Thank you very much for the help.
> 
> Fuxiang
> 
> On Thu, Jun 23, 2016 at 1:51 PM, Anatoly I Frenkel <afrenke2 at yu.edu <mailto:afrenke2 at yu.edu>> wrote:
> Whatever you decide to do, remember that Ni Ni and Ni Fe pairs look very similar by EXAFS, so it does not matter how you end up doing it.
> You can as well use pure Ni but you may want to consider both fcc and bcc structure for making the model because the alloy may end up to be either that or that, especially if it is a nanoalloy.
> 
> Anayoly
> 
> 
> 
> Sent from my Verizon Wireless 4G LTE Tablet
> 
> 
> -------- Original message --------
> From: Fuxiang Zhang <zhangfx at umich.edu <mailto:zhangfx at umich.edu>> 
> Date: 6/23/2016 12:51 PM (GMT-05:00) 
> To: ifeffit at millenia.cars.aps.anl.gov <mailto:ifeffit at millenia.cars.aps.anl.gov> 
> Subject: [Ifeffit] How to input atoms in solid solution for Artemis 
> 
> Hi, All,
> I am new in using EXAFS techniques. Just wondering how to input atomic structure of NiFe solid solution to Artemis. It has a simple Ni-structure, but both Ni and Fe occupy the same site. If I use partial occupancy, Artemis program does not allow. Anyone can give me an ideal?
> Also the coordination number N cannot be refined in this simple system (12), is that right? In fact I just want to get the N through the fitting of EXAFS because of the partial occupancy.
> Thank you very much
> 
> Fuxiang Zhang 
> 
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