The Samson phase, β-Mg2Al3, revisited

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Abstract

The Al-Mg phase diagram has been reinvestigated in the vicinity of the stability range of the Samson phase, β-Mg2Al3 (cF1168). For the composition Mg38.5Al61.5, this cubic phase, space group Fd3̄m (no 227), a = 28.242(1) Å, V = 22526(2) Å3, undergoes at 214°C a first-order phase transition to rhombohedral β′-Mg2Al3, (hR293), a = 19.968(1) Å, c = 48.9114(8) Å, V = 16889(2) Å3, (i.e. 22519 Å3 for the equivalent cubic unit cell) space group R3m (no 160), a subgroup of index four of Fd3̄m. The structure of the β-phase has been redetermined at ambient temperature as well as in situ at 400°C. It essentially agrees with Samson's model, even in most of the many partially occupied and split positions. The structure of β′-Mg 2Al3 is closely related to that of the β-phase. Its atomic sites can be derived from those of the β-phase by group-theoretical considerations. The main difference between the two structures is that all atomic sites are fully occupied in case of the β′-phase. The reciprocal space, Bragg as well as diffuse scattering, has been explored as function of temperature and the β- to β′-phase transition was studied in detail. The microstructures of both phases have been analyzed by electron microscopy and X-ray topography showing them highly defective. Finally, the thermal expansion coefficients and elastic parameters have been determined. Their values are somewhere in between those of Al and Mg.

Detaljer

Författare
  • Michael Feuerbacher
  • Carsten Thomas
  • Julien P.A. Makongo
  • Stefan Hoffmann
  • Wilder Carrillo-Cabrera
  • Raul Cardoso
  • Yuri Grin
  • Guido Kreiner
  • Jean Marc Joubert
  • Thomas Schenk
  • Joseph Gastaldi
  • Henri Nguyen-Thi
  • Nathalie Mangelinck-Nöel
  • Bernard Billia
  • Patricia Donnadieu
  • Aleksandra Czyrska-Filemonowicz
  • Anna Zielinska-Lipiec
  • Beata Dubiel
  • Thomas Weber
  • Philippe Schaub
  • Günter Krauss
  • Volker Gramlich
  • Jeppe Christensen
  • Daniel Fredrickson
  • Marek Mihalkovic
  • Wieslawa Sikora
  • Janusz Malinowski
  • Stefan Brühne
  • Thomas Proffen
  • Wolf Assmus
  • Marc De Boissieu
  • Francoise Bley
  • Jean Louis Chemin
  • Jürgen Schreuer
  • Walter Steurer
Externa organisationer
  • Jülich Research Centre
  • Max Planck Institute for Chemical Physics of Solids
  • Versailles Saint-Quentin-en-Yvelines University
  • Ecole des Mines de Nantes
  • Aix-Marseille University
  • Institut National Polytechnique De Grenoble (ENSEEG - INP Grenoble)
  • AGH University of Science and Technology
  • ETH Zürich
  • Stockholms universitet
  • Institute of Physics, Slovak Academy of Sciences
  • Goethe University
  • Los Alamos National Laboratory
Forskningsområden

Nyckelord

Originalspråkengelska
Sidor (från-till)259-288
Antal sidor30
TidskriftZeitschrift fur Kristallographie
Volym222
Utgåva nummer6
StatusPublished - 2007 jun 6
PublikationskategoriForskning
Peer review utfördJa