The structure of a propagating MgAl2O4/MgO interface

Author(s)
Chen Li, Thomas Griffiths, Timothy Pennycook, Clemens Mangler, Petr Jerabek, Jannik C. Meyer, Gerlinde Habler, Rainer Abart
Abstract

To understand how a new phase forms between two reactant layers, MgAl

2O

4 (spinel) has been grown between MgO (periclase) and Al

2O

3 (corundum) single crystals under defined temperature and load. Electron backscatter diffraction data show a topotaxial relationship between the MgO reactant and the MgAl

2O

4 reaction product. These MgAl

2O

4 grains are misoriented from perfect alignment with the MgO substrate by ~2–4°, with misorientation axes concentrated in the interface plane. Further study using atomic resolution scanning transmission electron microscopy shows that in 2D the MgAl

2O

4/MgO interface has a periodic configuration consisting of curved segments (convex towards MgO) joined by regularly spaced misfit dislocations occurring every ~4.5 nm (~23 atomic planes). This configuration is observed along the two equivalent [1 0 0] directions parallel to the MgAl

2O

4/MgO interface, indicating that the 3D geometry of the interface is a grid of convex protrusions of MgAl

2O

4 into MgO. At each minimum between the protrusions is a misfit dislocation. This geometry results from the coupling between long-range diffusion, which supplies Al

3+ to and removes Mg

2+ from the reaction interface, and interface reaction, in which climb of the misfit dislocations is the rate-limiting process. The extra oxygen atoms required for dislocation climb were likely derived from the reactant MgO, leaving behind oxygen vacancies that eventually form pores at the interface. The pores are dragged along by the propagating reaction interface, providing additional resistance to interface motion. The pinning effect of the pores leads to doming of the interface on the scale of individual grains.

Organisation(s)
Department of Lithospheric Research, Physics of Nanostructured Materials
External organisation(s)
Charles University Prague
Journal
Philosophical Magazine
Volume
96
Pages
2488-2503
No. of pages
16
ISSN
1478-6435
DOI
https://doi.org/10.1080/14786435.2016.1205233
Publication date
2016
Peer reviewed
Yes
Austrian Fields of Science 2012
105120 Petrology
Keywords
ASJC Scopus subject areas
Condensed Matter Physics
Portal url
https://ucris.univie.ac.at/portal/en/publications/the-structure-of-a-propagating-mgal2o4mgo-interface(25641d1c-2a2d-49ad-9423-749c74ac9c96).html