Measuring particle size by coordination number
Hi all, Sorry, I may be asking a question already asked in the mailing list, but I am unable to get it from the earlier discussions. I am reading one of the research article ´´ Determination of crystallite size in a magnetic nanocomposite using extended x-ray absorption fine structure´´ .J. Appl. Phys,. vol 94, page 778, 2003 In this paper there is a formula N_nano = [1-3/4(r/R)+1/16(r/R)^3]N_bulk, which you said can be used in the Artemis for extracting the particle size. I am trying to use this formula for determination of size of Ni particles in an Ni / Al2O3 catalyst. From TEM the size determined is around 4 nm. So, I am trying to fit the theoretical model of Ni metal to the sample data in the Artemis I defined a guessed parameter R and then put the whole formula for S02 = amp*(1-(0.75*(Reff/R))+(0.063*(Reff*Reff*Reff/(R*R*R)))). The value of R I am getting is 0.81 (0.05) which is quite small. Is there something I am missing in the formula or I have to define the N seprately for sample cooridnation number. Currently, I am using only the first path in the fitting. With thanks Abhijeet Gaur -- *Dr. Abhijeet Gaur* *Post doctoral fellow in the Institute for Chemical Technology and Polymer Chemistry * *Karlsruher Institut für Technologie (KIT), Karlsruhe Germany.*
Hi Abhijeet,
The formula looks poorly when it is only applied with one path.
The strength of this approach, and of Anatoly Frenkel’s alternative strategy for finding particle sizes, is that it compares coordination numbers for different shells, helping to break the correlations between N, S02, and sigma2.
Even then, it tends to report sizes that are small compared to those provided by other techniques, but compares sizes between different samples quite well.
—Scott Calvin
Sarah Lawrence College
On Aug 3, 2015, at 4:41 AM, Abhijeet Gaur
Oops—too early in the morning for me! I meant "The formula works poorly when it is only applied with one path”
—Scott Calvin
Sarah Lawrence College
On Aug 3, 2015, at 7:11 AM, Scott Calvin
An additional reason for the discrepancy in particle sizes between EXAFS and TEM may be that TEM detects only particles above a cut-off size, whereas particles of all sizes (including single ion complexes) contribute to the EXAFS signal. Assuming that EXAFS is 100% accurate in determining particle size ;-), this would result in smaller sizes reported by EXAFS and will be noticeable if a significant fraction of the atoms are in particles with sizes below the detection limit of TEM.
-Max
From: ifeffit-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit-bounces@millenia.cars.aps.anl.gov] On Behalf Of Scott Calvin
Sent: Monday, August 3, 2015 6:12 AM
To: XAFS Analysis using Ifeffit
Subject: Re: [Ifeffit] Measuring particle size by coordination number
Hi Abhijeet,
The formula looks poorly when it is only applied with one path.
The strength of this approach, and of Anatoly Frenkel’s alternative strategy for finding particle sizes, is that it compares coordination numbers for different shells, helping to break the correlations between N, S02, and sigma2.
Even then, it tends to report sizes that are small compared to those provided by other techniques, but compares sizes between different samples quite well.
—Scott Calvin
Sarah Lawrence College
On Aug 3, 2015, at 4:41 AM, Abhijeet Gaur
As an illustration of the very good comment that Max just made, here is a recent paper that explains this discrepancy in detail, and proposes a remedy.
Anatoly
Sent from my mobile phone, please forgive typos
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From: "Maxim Boyanov"
participants (4)
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Abhijeet Gaur -
Anatoly I Frenkel -
Maxim Boyanov -
Scott Calvin