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 > > > > > > -- UTS CRICOS Provider Code: 00099F DISCLAIMER: This email message and any accompanying attachments may contain confidential information. If you are not the intended recipient, do not read, use, disseminate, distribute or copy this message or attachments. If you have received this message in error, please notify the sender immediately and delete this message. Any views expressed in this message are those of the individual sender, except where the sender expressly, and with authority, states them to be the views the University of Technology Sydney. Before opening any attachments, please check them for viruses and defects.
