Dear Mr Bhowmik,
do not expect a massive metal ingot to be necessarily free of preferred
orientation, in particular in presence of a dendritic microstucture.
Thus it should be no surprise to observe wrong reflection intensities.
Or did you manage to make a "powder" from your Cr based material?
Another nasty effect that may affect your expected intensities is that a
pattern may look like to be originated from the C14 polytype but it is
in fact from layer-faulted C36. This was recently reported by Aufrecht
et al. /Mater. Res. Soc. Symp. Proc./ *1128* (2009) U08-07.
Note furthermore, that Laves phases can exhibit a large variety of
polytypes (as you will know), which are even more intergrown and can
contain stacking faults. Thus often the powder-diffraction pattern
exhibited by a Laves phase (or of another layered structure) is often
not simply the superposition of the patterns expected for the observed
(e.g. by TEM) stacked polytype blocks but the situation can become very
complex.
Best regards
A. Leineweber, J. Aufrecht
A. Bhowmik wrote:
Hello, I am studying a refractory metal Laves phase (Cr-Cr2X-based)
system. My alloys arc arc melted an annealed. Hence it has a typical
dendritic microstructure. The two phases in the material are Cr-rich
and the intermetallic Cr2X. The Cr phase has a bcc and the
intermetallic has a complex C14 (Strukturbericht designation) crystal
structures.
Now I am a GSAS user. In doing structure refinement of my system using
Rietveld method, the problem that I am having, currently, is that I am
not able to fit the intensities of all the peaks present, particularly
the strongest relections from the Cr-peaks and some peaks of the other
Laves phase, which is why I am only reading off the lattice parameters
from my fit and nothing else apart from that. I have not tried
imposing any 'preferred orientation' on the material, however, since
mine one is simply as-cast and annealed.
Can you suggest a way out to make this work, please?
kind regards
--
Dr. Andreas Leineweber
Max-Planck-Institut fuer Metallforschung
Heisenbergstrasse 3
70569 Stuttgart
Germany
Tel. +49 711 689 3365
Fax. +49 711 689 3312
e-mail: a.leinewe...@mf.mpg.de
home page of department:
http://www.mf.mpg.de/de/abteilungen/mittemeijer/english/index_english.htm
