The change in particle size is resulting in change in unit cell lattice paramaters in manganites. Please explain it in terms of crystallography and why is it so.
Dear Ms.Swain,
I hope you can describe your inquiry somehow in details. I believe you mean Lattice parameters and coherent domain size. What is your method of synthesis?, are you doping a host material? milling or .... . What kind of fitting you use? have you correct the instrumental broadening?. Furthermore, introducing defects or other factors will change the coherent domain size and lattice parameters due to the change of peaks broadening. Many reliable papers discuss this behavior for different compounds and methods of synthesis.
Good luck
The particle size should be effecting the width of the peaks within your XRD spectra, not so much the lattice parameters. It is possible that the widening of the peaks is effecting your refinement results. A couple of very rough rules of thumb; powder particles around 10 micron will give good spectra (i.e. minimising issues with preferred orientation), smaller particles give broader peaks, particles 5 nm or smaller may be outside of the x-ray coherence length and will be missed in the spectra.
Having said that particle size will have an effect on surface area to volume ratio and atoms pack differently closer to the surface than within the bulk.
I hope some of this helps, do you know what sort of particle sizes you are dealing with?
Hi Anupama ,
Ignoring other affecting factors (synthesis routes, residual stresses, impurity, porosity, etc) the relation between particle size and lattice parameters can be explained as following:
At macro, micro, and sub-micron sizes there are no effects on lattice parameters.
At nano sizes (mostly less than 10 nano meter, depending on alloy type) the equilibrium spacing between atoms will be smaller than the
equilibrium spacing between atoms in bulk material of the same element.
The atoms at the surface of a particle (indeed at any free surface) perceive an environment that is distinctly different from that perceived by atoms within the bulk of the crystal (since there are no atoms to interact with on the outside of the free surface).
The result is an effective surface tension on the surface of these particles, which implies that the atoms within the particles are under an effective force.
As a consequence, the atoms within the nanoparticles should have different equilibrium spacing than the atoms within bulk single crystals.
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