[sdpd] impurities

[Jon Wright <wright...@esrf.fr>]

Jon Wright wrote:
> Armel Le Bail wrote:
>>  An unknown impurity representing less than 1% of the bulk
>>  cannot be treated by other means than excluded zones.
> 
> Sorry to be pedantic, but after all, that's what the internet is here
> for :-) Impurities can be treated via the Bayesian formalism:
> 
> W. I. F. David, J. Appl. Cryst. (2001). 34, 691-698
> [ doi:10.1107/S0021889801011396 ]
> "Robust Rietveld refinement in the presence of impurity phases"
> 
> Since no one has programmed this yet in a mainstream Rietveld package,
> it seems like a bit of a missed opportunity. 

...and now this magic is available for everyone. Nice paper for anyone 
concerned about un-modelled impurities:

J. Appl. Cryst. (2009). 42, 385-391  [ doi:10.1107/S0021889809008450 ]
http://journals.iucr.org/j/issues/2009/03/00/db5058/index.html
"Implementation and use of robust refinement in powder diffraction in 
the presence of impurities"
K. H. Stone, S. H. Lapidus and P. W. Stephens

Synopsis: A modification to the usual least-squares analysis is 
implemented, to refine structural parameters from powder diffraction 
data containing an unmodeled impurity. The method is characterized using 
known materials, and two new structures are refined using the method.





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