TY - JOUR
T1 - The Samson phase, β-Mg2Al3, revisited
AU - Feuerbacher, Michael
AU - Thomas, Carsten
AU - Makongo, Julien P.A.
AU - Hoffmann, Stefan
AU - Carrillo-Cabrera, Wilder
AU - Cardoso, Raul
AU - Grin, Yuri
AU - Kreiner, Guido
AU - Joubert, Jean Marc
AU - Schenk, Thomas
AU - Gastaldi, Joseph
AU - Nguyen-Thi, Henri
AU - Mangelinck-Nöel, Nathalie
AU - Billia, Bernard
AU - Donnadieu, Patricia
AU - Czyrska-Filemonowicz, Aleksandra
AU - Zielinska-Lipiec, Anna
AU - Dubiel, Beata
AU - Weber, Thomas
AU - Schaub, Philippe
AU - Krauss, Günter
AU - Gramlich, Volker
AU - Christensen, Jeppe
AU - Lidin, Sven
AU - Fredrickson, Daniel
AU - Mihalkovic, Marek
AU - Sikora, Wieslawa
AU - Malinowski, Janusz
AU - Brühne, Stefan
AU - Proffen, Thomas
AU - Assmus, Wolf
AU - De Boissieu, Marc
AU - Bley, Francoise
AU - Chemin, Jean Louis
AU - Schreuer, Jürgen
AU - Steurer, Walter
PY - 2007/6/6
Y1 - 2007/6/6
N2 - 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.
AB - 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.
KW - CMA
KW - Elastic parameters
KW - Electron microscopy
KW - Magnesium aluminides
KW - Microstructure
KW - Powder diffraction structure analysis
KW - Samson phase
KW - X-ray diffraction
U2 - 10.1524/zkri.2007.222.6.259
DO - 10.1524/zkri.2007.222.6.259
M3 - Review article
AN - SCOPUS:34249817074
SN - 0044-2968
VL - 222
SP - 259
EP - 288
JO - Zeitschrift fur Kristallographie
JF - Zeitschrift fur Kristallographie
IS - 6
ER -