Abstract
Meta stable embedded nano-sized -particles within a single grain extracted from an alloy having the nominal composition
have been examined with X-ray diffraction. By applying the orientational and metric relationships that exist between the hexagonal unit cell of the
-particles and the cubic unit cell of the Al-matrix, it has been proven possible to directly collect diffracted intensity data from the
-particle ensemble. This has been done using synchrotron radiation and a
-diffractometer having a scintillator point detector setup. The approach has resulted in improved data quality compared to previous experiments. The interpretation of the data set, based on a combination of Patterson syntheses, direct methods and geometrical restraints, yielded two possible average structural representations: one Al-rich with the approximate stoichiometric composition
and one Al-depleted with approximate stoichiometric composition
. Both structures are realized in the same space group,
, and are most probably superimposed in the crystalline system examined. The geometries are discussed within the atomic environment approach where icosahedral or near-icosahedral configurations are encountered. Comparison with previous published models and the equilibrium structure reveals a main difference related to the distribution of the Zn-sites in the unit cell. A possible transformation path is also suggested. Various aspects and challenges regarding data collection, data reduction and data quality are specifically addressed.
Acknowledgments
The authors wish to express their thanks to dr. Atle Sjølyst-Kverneland and prof. Vidar Hansen for providing the material used in this investigation and for stimulating discussions. Furthermore we are grateful to the Swiss-Norwegian beamline consortium for providing synchrotron beamtime and general support during the experiment.