Structure refinement of the icosahedral AlPdMn quasicrystal using quantitativeconvergent beam electron diffraction and symmetry-adapted parameters

Abstract

The atomic structure of the perfect AlPdMn icosahedral phase has been studiedon a single-crystal specimen using the quantitative convergent beam electrondiffraction (QCBED) technique combined with a description of the shapes ofatomic surfaces using a symmetry-adapted series of surface harmonics. Thespherical model (Boudard et al 1992 J. Phys.: Condens. Matter 4 10149) was usedas a starting point for the refinement. By fitting the calculated electrondiffraction intensities in the CBED line profile to the experimental electrondiffraction intensities, the coefficients in the surface harmonic expansion of theatomic surfaces’ boundaries are refined. The refined parameters show thatthe fluctuations of the external boundary of atomic surface for Pd atn0can be as large as 0.2 nm. The boundaries of the atomic surfaces for Mn show littlefluctuation. Compared to the spherical model, in the present model the number ofunphysically short interatomic distances is reduced significantly. The three-dimensionalatomic clusters with centres located successively at the six-dimensional lattice nodesn0,n1 andbc1are generated by means of the cut method.