Dear fellow Rietvelders,
Could anyone point me to some nice literature which critically discusses
the limitations of the Rietveld method when it comes to nano-crystalline
materials (specifically in the 1 to 3 nm range)?
As far as I'm aware, the core Rietveld literature seems to touch this
point only in the passing.
Background:
To the best of my knowledge, Rietveld-derived parameters (like lattice
constants or domain sizes) should not be trusted as being "physically
meaningful" anymore when you fit the powder pattern of a material in
the few nm range with standard Rietveld tools.
My naive understanding of this problem is that the physical principles
of diffraction (or rather the best way to model it) gradually change
when you go from long-range ordered to medium-/short-range ordered
materials.
Being a Rietveld practitioner rather than a theoretician, and having no
first-hand experience with WPPM and PDF methods, I am often confronted
with the problem to explain to my "customers" why I can't extract
trustworthy lattice constants or domain sizes from their
nano-crystalline samples, especially if it seems technically possible to
fit the pattern with a Rietveld program.
I think it would be nice if I could cite some critical discussion, or
overview article with further references, to put my finger on the problem.
Especially in the catalysis community literature, my impression is that
the applicability of the Rietveld method is sometimes overestimated,
leading to overinterpretation of the results.
Any suggestions?
Best wishes,
Frank Girgsdies
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