[sdpd] Re: random orientation in flat plates nanocrystallites

["Guilhem Dezanneau" <gdezano...@inpg.fr>]

Indeed, crystallites have been observed by TEM. my compound, synthesised by
spray pyrolisis consists
of spheric (Phi=0.4µm) shells with a thickness around 30nm and crystallite
contrast makes
them appear to be around 200nm in the other dimensions (shell surface).
diffraction was carried
out at the Swiss-Norvegian Beam Line(ESRF) on an 2D detector for which W is
around 0.0049
at Lambda=0.501909 angstroems. I am actually waiting for datas for U and V.
The structure can be refined in the R-3C space group but the point is that,
surprisingly, there are not
peaks that have larger widths i.e. the small dimension of my crystallites
seems not to be correlated to any
crystallographic direction. This has been partially confirmed by TEM dark
field images on which neighbour
crystallites are totally disoriented each other.




-----Message d'origine-----
De : Armel Le Bail <armel...@fluo.univ-lemans.fr>
À : sdpd...@egroups.com <sdpd...@egroups.com>
Date : mardi 15 février 2000 16:52
Objet : [sdpd] Re: random orientation in flat plates nanocrystallites


>If I understand well your 30*200*200nm (as seen by electron
>microscopy ?) nanocrystallites powder diffraction data are well
>fitted (Rietveld ?) by an isotropic grain size model ? Well, we
>need to know the resolution of your instrument (U, V, W values
>of your fit) because a bad resolution could give FWHM almost
>the same for 200 or 30nm crystallites. We need to know the
>crystal system. It is unusual to have platelets with a cubic
>symmetry, but if this is the case, then you may not see any
>anisotropic size broadening. If your compound is orthorhombic,
>you should see the h00 much broader than the 0k0 and 00l. But
>if there is a big preferred orientation effect, you will not see the
>0k0 and 00l...
>
>Tell us more.
>
>Best,
>
>
>Armel Le Bail - Universite du Maine, Laboratoire des Fluorures,
>CNRS ESA 6010, Av. O. Messiaen, 72085 Le Mans Cedex 9, France
>http://www.cristal.org/
>
>