Actually most of the papers refer that it would shift to the higher 2 theta values.
well, one of the major problems of ResearchGate, and of the research community in general, is that people tend to write or to use some technique without knowing what they are talking about. And most editors and referees think they know diffraction but they act as if they don't or would not admit it.
With no offense, the most ridiculous thing I have read in this thread is "You can use Williamson–Hall method to calculate strain.". That's complete nonsense. The discussion about the XRD results in the attached paper is even more hilarious.. The works they cite confirms the fact that this is not an isolated case. I would love to see how they can justify a negative slope in the W-H plot or what tensile or compressive strains have to do with it. The method has serious issues, but one of the few correct features is that the microstrain broadening (if we believe that it is isotropic) is strictly non negative.
Moreover, to stress the fact that people are not aware of they are doing, there is no reference to the original Williamson-Hall paper and there is a self reference for the removal of the instrumental broadening.
Just as a side note:
- the W-H method is based on severe assumptions and hypotheses that are seldom verified. It should NOT be used for any quantitative analysis.
- the W-H method does not measure a "strain". a "microstrain" is what is obtained, a term simply indicating that there is a variation in d at the atomic level in the material (it is sqrt( and e is the distribution of atomic level strain in the specimen along the scattering vector).
- it can be easily demonstrated that the size part of the W-H method IS Scherrer equation... as it can also be verified by isolating bhkl in (3)...
- as I already commented a few times, it seems that in some parts of the world people still have to realize that quite long time ago the JCPDS has changed his name into ICDD (http://www.icdd.com/profile/history.htm)...
So just as a suggestion: before giving advices or support to people, think twice.. or perhaps more... and before using any formula, be sure you know the range of application and the result it gives.
Probably nothing will change (I already observed it as many people get offended when faced with reality or still think they are doing things right cause someone published the same nonsense), but letting those things pass, just turning the head on the other side, is definitely something unethical
the cobalt present in your sample has the same valence that in the papers? Depending on the valence and coordination of Co ion you will have different radius causing different effects on the crystal lattice or maybe the Co ion is in different forms (interstitial or substitutional)
what happens in case of interstitial and in case of substitutional????
The simplest answer will be, because the out of plane lattice of your materials is getting smaller after the doping. Try to check RSM to extract the in plane lattice constants and determine the associated change.
Please check the ionic radii of Co like whether it has higher or lower value as compare to Cd. Also, one more thing is, the shift may be due to stress or stain in the films..
that is may be due to the strain you can calculate the strain for example e=c-c0/c0*100
Then, you conclude that the shifting toward lower 2theta is due to strain or ionic radius of cation
If 2 theta shifts lower side it means your unit cell volume increasing. You can use Williamson–Hall method to calculate strain. It may be tensile or compressive strain depending on your results. Find attachment for more information. If you have any problem in calculating let me know. I will help you!
maybe you produce compressive stress in your film. Because the film is in-plane fixed on the substrate, the out-of plane lattice parameter is increased leading to a smaller 2theta value.
I suppose that Co may be include into lattice of CdS as defect of substitution of Cd and as a interstitial atom. In last case lattice parameter should increase and diffractions peaks should shift in small angles side.
For justification of this supposition you can anneal your material in sulfur vapour. At exsess of sulfur you obtaine material with Co in position of Cd becouse in this case relation metal/sulfur will shift in sulfur side while in case of Co as interstitial atom this relation will shift in metal side. So anneal in sulfur vapour should transfer Co from interstitial position into regular lattice position and lattice parameter should decrease and diffraction peacs should move to the high angle side.
Sorry to ask such an ingenuous question, but did you check that the zero was not shifted ? I remember having had this problem when I was studying CdS films in the 80's-90's.
I am comparing among a series of XRD and all the zeros r at same position
Is there any change in the integrated intensity of the peaks? If so you should try a structural refinement to see how the unit cell structure and contents have changed. It could also be residual strain, but in that case I would expect some reflections to shift in the opposite direction, as the compressive and tensile stresses must balance.
well, one of the major problems of ResearchGate, and of the research community in general, is that people tend to write or to use some technique without knowing what they are talking about. And most editors and referees think they know diffraction but they act as if they don't or would not admit it.
With no offense, the most ridiculous thing I have read in this thread is "You can use Williamson–Hall method to calculate strain.". That's complete nonsense. The discussion about the XRD results in the attached paper is even more hilarious.. The works they cite confirms the fact that this is not an isolated case. I would love to see how they can justify a negative slope in the W-H plot or what tensile or compressive strains have to do with it. The method has serious issues, but one of the few correct features is that the microstrain broadening (if we believe that it is isotropic) is strictly non negative.
Moreover, to stress the fact that people are not aware of they are doing, there is no reference to the original Williamson-Hall paper and there is a self reference for the removal of the instrumental broadening.
Just as a side note:
- the W-H method is based on severe assumptions and hypotheses that are seldom verified. It should NOT be used for any quantitative analysis.
- the W-H method does not measure a "strain". a "microstrain" is what is obtained, a term simply indicating that there is a variation in d at the atomic level in the material (it is sqrt( and e is the distribution of atomic level strain in the specimen along the scattering vector).
- it can be easily demonstrated that the size part of the W-H method IS Scherrer equation... as it can also be verified by isolating bhkl in (3)...
- as I already commented a few times, it seems that in some parts of the world people still have to realize that quite long time ago the JCPDS has changed his name into ICDD (http://www.icdd.com/profile/history.htm)...
So just as a suggestion: before giving advices or support to people, think twice.. or perhaps more... and before using any formula, be sure you know the range of application and the result it gives.
Probably nothing will change (I already observed it as many people get offended when faced with reality or still think they are doing things right cause someone published the same nonsense), but letting those things pass, just turning the head on the other side, is definitely something unethical
This doping is to substitute cadmium by cobalt. consideration of the ionic radius cademium is greater than cobalt, we attand lower lattice parameters and by following a shift of the Bragg angle to large values.
For a good explanation try to see the doping level in fact, if this level is great, in some condition, it leads to the formation of a ternary type CdxCoySz.
I think that when Co include into lattice of CdS as a interstitial atom.the lattice parameter should increase and diffractions peaks should shift in small angles side due to lattice strain due to the change of ionic radii of the Co and Cd. And its may also due to when the incident wave length on the crystal is not monochromatic, the peak position of the crystal planes shifted toward small angles. This occurs when the characteristic wavelengths of x-ray spectrum not well filtered.
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