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Surface Reconstruction with a Fractional Hole: (sqrt[5] x sqrt[5])R26.6 degrees LaAlO3 (001)
C H Lanier1, J M Rondinelli, B Deng
1Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA.
Physical Review Letters
|March 16, 2007
Summary
The surface structure of lanthanum aluminate (LaAlO3) was determined, revealing a lanthanum oxide termination with vacancies. Charge compensation occurs via delocalized holes, not oxygen vacancies, driven by cation expulsion and increased covalency.
Area of Science:
- Materials Science
- Surface Science
- Solid State Chemistry
Background:
- Understanding the surface structure of complex oxides like LaAlO3 is crucial for their electronic properties.
- The (sqrt[5] x sqrt[5])R26.6 degrees reconstruction on LaAlO3 (001) surfaces presents unique structural and electronic challenges.
Purpose of the Study:
- To determine the precise atomic structure of the reconstructed LaAlO3 (001) surface.
- To elucidate the mechanism of charge compensation in this reconstructed surface.
Main Methods:
- Transmission electron diffraction (TED) was employed to analyze the surface structure.
- Direct methods were used in conjunction with TED data.
- Density functional theory (DFT) calculations were performed to investigate electronic properties and bonding.
Main Results:
- The LaAlO3 (001) surface exhibits a (sqrt[5] x sqrt[5])R26.6 degrees reconstruction with a lanthanum oxide termination.
- A lanthanum vacancy exists within each surface unit cell.
- Charge compensation is achieved through delocalized holes, with no oxygen vacancies or hydrogen filling.
- DFT calculations support these findings, indicating increased covalency and cation expulsion.
Conclusions:
- The reconstructed LaAlO3 surface is terminated with lanthanum oxide and features lanthanum vacancies.
- Delocalized holes are responsible for charge compensation, highlighting a unique surface electronic state.
- The reconstruction is driven by the tendency of electropositive cations to leave the surface, leading to enhanced covalency.
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