Structure evolution of h.c.p./c.c.p. metal oxide interfaces in solid-state reactions

Area of Science:

• Materials Science
• Solid-State Chemistry
• Crystallography

Background:

• Crystalline interface structure is crucial for solid-state reactions.
• The Al2O3/MgAl2O4/MgO system serves as a model for interface reaction mechanisms.
• Understanding interface migration is key to controlling material properties.

Purpose of the Study:

• To investigate the atomic structure and migration mechanisms of Al2O3/MgAl2O4 interfaces.
• To characterize the role of dislocations in interface progression during different growth stages.
• To elucidate the crystallographic orientations and grain boundary formation in MgAl2O4.

Main Methods:

• Growth of MgAl2O4 layers between Al2O3 and MgO.
• Characterization of atomic structure using aberration-corrected scanning transmission electron microscopy (STEM).
• Analysis of oxygen sublattice stacking transitions (h.c.p. to c.c.p.).

Main Results:

• Observed transformation of oxygen sublattice stacking from hexagonal close-packed (h.c.p.) in Al2O3 to cubic close-packed (c.c.p.) in MgAl2O4.
• Identified partial dislocations associated with steps at the interface, dominating in later diffusion-controlled stages.
• Demonstrated interface progression via partial dislocation glide with Al3+/Mg2+ cation exchange, resembling zipper-like motion.

Conclusions:

• Interface migration in this system is accomplished by partial dislocation glide, facilitating cation exchange.
• MgAl2O4 grains grow via oppositely gliding dislocations, forming twin and grain boundaries.
• The findings provide a framework for understanding interface reactions and phase transformations in materials with h.c.p./c.c.p. transitions.