Hi,
At the moment there is development of a NIST Nanocrystallite Size Standard 
Reference Material (SRM1979).

Jim Cline and I are working on this SRM. It will include two materials:
(1) CeO2 with spherical crystallite shape and size distribution in the ~20nm 
size range (isotropic shape);
(2) ZnO with cylindrical or hexagonal prismatic crystallite shape with height 
in the, H~60-80nm and diameter, D~20-30nm range (anisotropic shape).

This outlined in introduction of Armstrong et al (2004b) chapt.8, in 
"Diffraction analysis of the microstructure of materials", Springer-Verlag, 
pp.187--227.

In both cases the Bayesian/MaxEnt method will be used to determine the 
*physical* size distribution and shape. For example in the case of (1), the 
method tests the model for a spherical crystallite shape, while also testing 
various size distribution models i.e lognormal, gamma etc. For this case a 
lognormal size distribution has found to be the appropriate distribution. In 
the case of (2) the distributions are for H and D, respectively, while testing 
different shape models can also be carried out. This presently being developed.

The Bayesian/MaxEnt method is a general formulation which tests the underlying 
assumption of various models and determines the most probable size distribution 
and crystallite shape.

There is lots of working/development going on!!
Regards, Nicholas


----- Original Message -----
From: Nicolae Popa <[EMAIL PROTECTED]>
Date: Monday, November 22, 2004 7:12 pm

> 
> >
> > It is also true that no development has been done for anisotropy. 
> Not yet!
> >
> > Well, if all previous works about trying to take account of 
> size/strain> anisotropy in the Rietveld method are nothing yet, 
> this allows to
> > close the discussion. Let us wait for really serious developments to
> > come.
> 
> You not correctly understood me (I would like to believe that not
> ill-disposed).
> I said that no development for size anisotropy has been done including
> "physical" size distributions (like lognormal, etc.) as were done 
> for the
> isotropic case.
> For example: Langford, Louer & Scardi, JAC (2000) 33, 964-974 and 
> Popa &
> Balzar JAC (2002) 35, 338-346.
> Concerning previous (phenomenological) works trying to take account of
> strain/size anisotropy in the Rietveld method, I have myself a 
> contribution:"The (hkl) dependence of diffraction-line broadening 
> caused by strain and
> size for all Laue groups in Rietveld refinement, N. C. Popa, J. 
> Appl. Cryst.
> (1998) 31, 176-180."
> Could I be so stupid to say that such kind of works, including 
> mine, are
> nothing?
> 
> Best wishes,
> Nicolae Popa
> 
> 
> 
> 
> 
> 


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