There is no easy answer to this question (it is still subject of current research) and it would be hard to explain all differences just in a few lines. However I can give you a couple hints to show you that the two things are quite different:
- to calculate a strain you need a reference, as you calculate (d-d0)/d0). So you have to define your reference d0 also here for both cases (perhaps the value in a perfect ideal macroscopic bulk (perfect and unstrained lattice)
- if you look for strain you have to decide which type of strain you talk about (I, II or III type). Type I is averaged over the whole specimen, type II over a grain and type III is local variation in a grain with respect to the average.
- Type I strain is called residual strain. in the thin film the type I strain is associated to a (residual) stress (e.g. due to the coupling between grains or to adhesion film/substrate or differential thermal expansion etc.). The lattice would show your d0 if you would be able to remove this residual stress. In the powder the type I strain is apparent and is just caused by the change in the stability conditions of the bonds. If you want to remove this apparent strain, you have to destroy the whole specimen.
This strain of type I mostly causes peak shift
- in powders you usually see a lot of type III strain. Actually is see the root mean strain i.e. sqrt() often termed microstrain (I don't like the definition as the root mean strain is technically not a strain, but just the variance of the strain distribution). This type III strain is related to the presence of defects and non homogeneous strain distribution in the particles and causes mostly peak broadening.
- the methods you can use for films (that are considered as a bulky beam) are different from those of powders. For the film you use Poisson effect to measure the residual strain: for the powder this is not possible (and you have to rely to absolute lattice parameter evaluation, prone to large errors)
That's why I say you cannot easily compare the changes in cell parameter of a nanoparticle (single object) with the residual strain in a film (polycrystalline aggregate).
There is no easy answer to this question (it is still subject of current research) and it would be hard to explain all differences just in a few lines. However I can give you a couple hints to show you that the two things are quite different:
- to calculate a strain you need a reference, as you calculate (d-d0)/d0). So you have to define your reference d0 also here for both cases (perhaps the value in a perfect ideal macroscopic bulk (perfect and unstrained lattice)
- if you look for strain you have to decide which type of strain you talk about (I, II or III type). Type I is averaged over the whole specimen, type II over a grain and type III is local variation in a grain with respect to the average.
- Type I strain is called residual strain. in the thin film the type I strain is associated to a (residual) stress (e.g. due to the coupling between grains or to adhesion film/substrate or differential thermal expansion etc.). The lattice would show your d0 if you would be able to remove this residual stress. In the powder the type I strain is apparent and is just caused by the change in the stability conditions of the bonds. If you want to remove this apparent strain, you have to destroy the whole specimen.
This strain of type I mostly causes peak shift
- in powders you usually see a lot of type III strain. Actually is see the root mean strain i.e. sqrt() often termed microstrain (I don't like the definition as the root mean strain is technically not a strain, but just the variance of the strain distribution). This type III strain is related to the presence of defects and non homogeneous strain distribution in the particles and causes mostly peak broadening.
- the methods you can use for films (that are considered as a bulky beam) are different from those of powders. For the film you use Poisson effect to measure the residual strain: for the powder this is not possible (and you have to rely to absolute lattice parameter evaluation, prone to large errors)
That's why I say you cannot easily compare the changes in cell parameter of a nanoparticle (single object) with the residual strain in a film (polycrystalline aggregate).
The answer isn`t easy to explain. You can use Poisson effect to measure the residual strain for thin films but for the powder this is not possible unless you define the absolute lattice parameter of the nanocrystalline lattice.
The method to calculate strain (microstress level, dislocation density) in CdTe thin films based on XRD measurements described in our paper, which attached.
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