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Nonstoichiometric dislocation cores in alpha-alumina
N Shibata1, M F Chisholm, A Nakamura
1Institute of Engineering Innovation, University of Tokyo, 2-11-16, Yayoi, Bunkyo, Tokyo 113-8656, Japan. shibata@sigma.t.u-tokyo.ac.jp
Science (New York, N.Y.)
|April 7, 2007
Summary
Dislocation core structures in alumina (alpha-Al2O3) were resolved using atomic-resolution imaging. Researchers found that dislocation cores are locally nonstoichiometric, challenging previous assumptions.
Area of Science:
- Materials Science
- Solid-State Physics
- Crystallography
Background:
- Dislocation core structures in oxides are crucial for material properties but remain poorly understood.
- Previous assumptions, based on charge balance, suggested nonstoichiometric cores were impossible.
Purpose of the Study:
- To directly resolve the atomic structure of dislocation cores in alumina (alpha-Al2O3).
- To investigate the stoichiometry and configuration of dislocation cores and their implications for material behavior.
Main Methods:
- Atomic-resolution imaging techniques were employed to visualize cation and anion sublattices.
- Direct observation of dissociated basal edge dislocations in alpha-Al2O3.
Main Results:
- Direct atomic-resolution images revealed the cation and anion sublattices within dislocation cores.
- A dissociated basal edge dislocation was observed to comprise two cores, with aluminum and oxygen columns terminating each partial.
- Each partial core was found to be locally nonstoichiometric due to excesses of aluminum or oxygen.
Conclusions:
- The mobile, high-temperature dislocation core structure in alumina consists of two closely spaced partial dislocations.
- Synchronized motion of these partials on adjacent planes is necessary for basal slip.
- These findings challenge prior assumptions about nonstoichiometric dislocation cores in oxides.
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