Advanced

The Samson phase, β-Mg2Al3, revisited

Feuerbacher, Michael ; Thomas, Carsten ; Makongo, Julien P.A. ; Hoffmann, Stefan ; Carrillo-Cabrera, Wilder ; Cardoso, Raul ; Grin, Yuri ; Kreiner, Guido ; Joubert, Jean Marc and Schenk, Thomas , et al. (2007) In Zeitschrift fur Kristallographie 222(6). p.259-288
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... (More)

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.

(Less)
Please use this url to cite or link to this publication:
author
; ; ; ; ; ; ; ; and , et al. (More)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; and (Less)
organization
publishing date
type
Contribution to journal
publication status
published
keywords
CMA, Elastic parameters, Electron microscopy, Magnesium aluminides, Microstructure, Powder diffraction structure analysis, Samson phase, X-ray diffraction
in
Zeitschrift fur Kristallographie
volume
222
issue
6
pages
30 pages
publisher
Oldenbourg Verlag
external identifiers
  • scopus:34249817074
ISSN
0044-2968
DOI
10.1524/zkri.2007.222.6.259
language
English
LU publication?
yes
id
cf365bca-6566-4406-8b94-1a6ab97e2e4b
date added to LUP
2019-04-08 15:16:25
date last changed
2020-12-27 05:46:29
@article{cf365bca-6566-4406-8b94-1a6ab97e2e4b,
  abstract     = {<p>The Al-Mg phase diagram has been reinvestigated in the vicinity of the stability range of the Samson phase, β-Mg<sub>2</sub>Al<sub>3</sub> (cF1168). For the composition Mg<sub>38.5</sub>Al<sub>61.5</sub>, this cubic phase, space group Fd3̄m (no 227), a = 28.242(1) Å, V = 22526(2) Å<sup>3</sup>, undergoes at 214°C a first-order phase transition to rhombohedral β′-Mg<sub>2</sub>Al<sub>3</sub>, (hR293), a = 19.968(1) Å, c = 48.9114(8) Å, V = 16889(2) Å<sup>3</sup>, (i.e. 22519 Å<sup>3</sup> 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 <sub>2</sub>Al<sub>3</sub> 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.</p>},
  author       = {Feuerbacher, Michael and Thomas, Carsten and Makongo, Julien P.A. and Hoffmann, Stefan and Carrillo-Cabrera, Wilder and Cardoso, Raul and Grin, Yuri and Kreiner, Guido and Joubert, Jean Marc and Schenk, Thomas and Gastaldi, Joseph and Nguyen-Thi, Henri and Mangelinck-Nöel, Nathalie and Billia, Bernard and Donnadieu, Patricia and Czyrska-Filemonowicz, Aleksandra and Zielinska-Lipiec, Anna and Dubiel, Beata and Weber, Thomas and Schaub, Philippe and Krauss, Günter and Gramlich, Volker and Christensen, Jeppe and Lidin, Sven and Fredrickson, Daniel and Mihalkovic, Marek and Sikora, Wieslawa and Malinowski, Janusz and Brühne, Stefan and Proffen, Thomas and Assmus, Wolf and De Boissieu, Marc and Bley, Francoise and Chemin, Jean Louis and Schreuer, Jürgen and Steurer, Walter},
  issn         = {0044-2968},
  language     = {eng},
  month        = {06},
  number       = {6},
  pages        = {259--288},
  publisher    = {Oldenbourg Verlag},
  series       = {Zeitschrift fur Kristallographie},
  title        = {The Samson phase, β-Mg<sub>2</sub>Al<sub>3</sub>, revisited},
  url          = {http://dx.doi.org/10.1524/zkri.2007.222.6.259},
  doi          = {10.1524/zkri.2007.222.6.259},
  volume       = {222},
  year         = {2007},
}