Dear Varadarian, I didn't look at your attachments, but have you considered that there might be some Cd-Ca in the second shell? I didn't see what value of x you had in Cd(1-x)CaxO, but if the oxides form a solid solution one might naively expect the second shell to have (1-x) Cd and x Ca coordination. Ca and Cd scatter photoelectrons differently enough to be distinguishable in the EXAFS. It might be that there is extra disorder too, say if the typical Cd-Ca distance was different from the typical Cd-Cd distance.
Cheers, --Matt On Tue, Jul 6, 2010 at 7:29 AM, Varadarajan Sridharan <varadu.sr...@gmail.com> wrote: > Greetings to all > > I am a beginner to EXAFS. > > Recently I had carried out Cd K-edge EXAFS measurements on Cd1-xCaxO > solid solution. The end members CdO and CaO belong to same crystal structure > Fm-3m. > > I had analysed the spectrum with Atthena and fitted with Arthemis. I am > attaching the Athena project file (***.prj) and that of Arthemis project > file (***.apr) for your reference. > > Athena: > > As per the crystal structure of CdO, the first nearest neighbour is at > 2.345 A corresponding to Cd-O1 inter atomic distance and 2nn distance is > 3.3.16 A corresponding to Cd-Cd1 inter atomic distance. Though I am able get > the first peak in chi(R) plot at expected position, I am having some > problems for the second peak. The second peak has features; main one and a > shoulder. The main peak itself appears at lower R compared to expected one. > Intensity of the shoulder increases with Ca substitution at the expense of > main peak itself. > > Can any one comment on this? > > My predicament: If I associate, based on the structure of second peak, > bimodal distribution for the Cd-Cd1 interatomic distance, the difference of > 0.4 A is 11%. This value gives me an uneasy feeling. Is it possible to > accommodate this difference within the setting of F m-3m? > > OR > > It is due the multi scattering is the > problem? > > Arthemis: > > For CdO: The k^3 weighted chi fitting, I agree is far from satisfaction. > Std of delR is a bothering point. I had included 20 paths. Even for the CdO > with F m-3m, the calculated second peak has a shoulder at lower R. I could > see a small contribution from path 4. But I am not sure if that is all. > > How to float the individual GDS parameter for each and every path? What can > be done to improve the fitting? > > Thanking you all in advance > > Varadarajan Sridharan > > ---------------------------------- > > Condensed matter Physics Division > > Materials Science division > > Indira Gandhi Centre for Atomic Research > > Kalpakkam 603 102 > > India > > _______________________________________________ > Ifeffit mailing list > Ifeffit@millenia.cars.aps.anl.gov > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit > > _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit