>... hints and further questions (since I'm trying to sort out things
>and I started to setup a site dedicated on diffraction profiles... and so
>instrumental contribution + sample broadening etc. etc...... by the
>way, volunteers are welcome to contribute.... just drop me an e-mail)...
Here is a contribution showing that there is a third approach, neither
fundamental nor empirical, just experimental ;-).
You probably know the most widely used method for extracting
microstructure sample effects from a powder pattern : the
Warren-Averbach method. In the more exact version of this method,
the profiles should never be modelled, but experimentally measured
(using two patterns, one from a defect-free sample and the other
from the defective sample) and then deconvoluted. No modelling
at all is the best approach...
In this sense, pretending that the fundamental approach is better than
the empirical is nonsense because none is as good as measuring profile
shapes. This third approach was also applied to the Rietveld method
in the so-called learnt-profile methods used in XRS-82 or ARIT1 (...).
Of course, the problem of these learnt-profiles is that they apply perfectly
only at the angular position from where they are parametrized. Models
come back for their extrapolation to the whole powder pattern.
Fundamental parameters and empirical are both approximated
approaches. The BGMN program uses another terminology which
is "Exact Peak Shape Model". Sorry, I don't like it anymore,
because a model is by definition not exact.
Anyway, I am ready to adopt the best model, including a model
based on "fundamental parameters", if this model provides the
best fit. As soon as empirical approaches will produce a better
fit, I will come back to them :-|.
Armel