Cesar Pay Gomez

Complexity of hexagonal approximants in the RE13Zn~58 system (RE = Ce, Pr, Nd, Sm, Gd, Tb and Dy)

Abstract For the RE13Zn58quasi crystal approximants (RE = Ce, Pr, Nd, Sm, Gd, Tb, Dy), single crystals were prepared from the elements and their structures were refined from single-crystal X-ray diffraction data. They are derived from the Gd13Cd58type structure and crystallize in the space group P63/mmc or its subgroups. The crystal structures of Ce and Pr compounds are identical to that of the archetype, in the Nd compound a pair exchange disorder changes the composition and for Sm a further, partially occupied interstitial position lowers the symmetry to P63mc. For the compounds with Gd, Tb and Dy, the occupancy may order, lowering the symmetry further. For the case of Tb13Zn59 high quality single crystals allowed us to refine the fully ordered orthorhombic super structure.

Structure of Dy13Zn57 a binary quasicrystal approximant

Abstract The title compound Dy13Zn57, crystallizes in the orthorhombic space group Pnma (No.xa062) with the cell parameters a=14.060(5), b=14.260(5) and c=24.700(3)xa0A. The structure has formerly been described as Dy13Zn58 with the hexagonal type structure of Gd13Zn58. Single-crystal X-ray diffraction measurements however, show extra reflections breaking the C-centering of the corresponding orthorhombic cell with the parameters ao≈ch, bo≈ah and c o ≈ 3 ×a h and thereby making it primitive. The title compound is comprised of structural building units that also are encountered in the other RE13Zn58 (RE=rare earth) compounds, the related RE13Cd58, the RECd6 phases and the newly found binary quasicrystal YbCd5.7.