The Samson phase, β-Mg2Al3, revisited

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 SchaubGünter Krauss, Volker Gramlich, Jeppe Christensen, Sven Lidin, 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

    Research output: Contribution to journalReview articlepeer-review


    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.

    Original languageEnglish
    Pages (from-to)259-288
    Number of pages30
    JournalZeitschrift fur Kristallographie
    Issue number6
    Publication statusPublished - 2007 Jun 6

    Free keywords

    • CMA
    • Elastic parameters
    • Electron microscopy
    • Magnesium aluminides
    • Microstructure
    • Powder diffraction structure analysis
    • Samson phase
    • X-ray diffraction


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