Jagadesh Kopula Kesavan In XRD (yes, I know you're talking of EXAFS) then incomplete alloying is often indicated by peak distortion or the actual appearance of the separate phases if in sufficient quantity. I have experience in PdAu and PdAg alloys (both components completely miscible) in this area, so my comment is specific and not general.

XRD will indicate separate phase formation if present. Homogenized mixtures should obey Vegard’s rule.

Dear Jagadesh Kopula Kesavan ,

via EXAFS you should be able to distinguish these R distances; 2,44A for the Zn-Se and 2,6A for the Cd-Se distances.

However you should work at the Zn K-edge for gathering the Zn-Se distance and at the Cd K-edge for gathering the Cd-Se distance.

EXAFS measurements at the Se K-edge will make no sense, because you will be in trouble to separate/resolve the Se-Zn and the Se-Cd distances in that single EXAFS spectrum, but also the Se-Se distances you have in mind.

Reference measurements via ZnSe and CdSe with known bondlengths will help you to elaborate your distances without struggling with the EXAFS phases. Just compare the positions of the amplitudes of the Fouriertransforms*).

*) see for example the Fouriertransforms of ZnSe (at Zn-K-edge) as well as of CdSe (at Cd-K-edge) in:

https://www.researchgate.net/publication/338376779_EXAFS_study_of_the_temperature_dependence_of_the_Debye-Waller_factor_in_ZnSe_zincblende_compound

https://www.researchgate.net/publication/216025481_Surface_structure_of_cadmium_selenide_nanocrystallites

You will see that both R peaks (Zn-Se and Cd-Se) are 'stand-alone' peaks; so there is no reason for additional R shift via peak superpositions.

Good luck and

best regards

G.M.

Dear Gerhard Martens ,

Thank you for your detailed explanation. Yes, I know that we could clearly see the difference between Se-Cd and Se-Zn in the first coordination shell because of the back scattering amplitudes of Cd and Zn are different as well as the coordination distances are not same.This is clear. But what I want to know is, whether the Cd is diffused in the ZnSe phase and forming Zn1-xCdxS or staying in the CdSe phase. Is it sensitive to look from the Se K-edge?

It really make sense to see from the Zn K-edge where in the second coordination one should see Zn-Cd coordination if the Cd is diffused in ZnSe core and formed Zn1-xCdxS. Thank you once again for your kind explanation.

Dear Jagadesh Kopula Kesavan ,

thanks for feed back.

Looking from the Se K-edge, you will see the Zn at 2,44A and the Cd at 2,60A distance.

This 0,16A difference is to my opinion too close to seperate these two contributions via the Fouriertransform approach in order to have reliable a) distances and b) coodination numbers*).

However there is often fitting of EXAFS applied. You may try that. But you need a lot of fitting parmeters...(2 distances, 2 coordination numbers, 2? Debye-Wallerfactors).

Backscatteramplitudes and phases are known, but I have no experience about their quality for being reliably used in the EXFAS fitting approach**).

But there is a proverb: 'having enough parameters you are able to fit an elephant'.

So please be carefull when interpreting the fitting results...

*) Furthermore the concentration of Cd might be very low compared to Zn (you wrote about 'diffusion')

**) you may ask Dirk Luetzenkirchen-Hecht for that. He is still very active in the EXAFS area and is familiar with the today's software approaches. I am convinced that he will see this conversation at his next RG visit...

https://www.researchgate.net/profile/Dirk-Luetzenkirchen-Hecht

Best regards

G.M.

Dear Gerhard Martens

Thank you for your valuable suggestion.

Dear Alan F Rawle

Thank you for your suggestion. I absolutely agree with you. The main problem here is the concentration. The xrd only showed the CdS phase and did not show any peaks related to ZnSe/CdSe.