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Valence changes and structural distortions in "charge ordered" manganites quantified by atomic-scale scanning
J C Loudon1, L Fitting Kourkoutis, J S Ahn
1School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA.
Physical Review Letters
|February 1, 2008
Summary
Researchers used scanning transmission electron microscopy to study charge ordering in manganites. They found a displacement wave modulation, not valence changes, in Bi0.5Sr0.4Ca0.1MnO3 stripes.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Solid-State Chemistry
Background:
- Mixed-valent manganites exhibit complex electronic properties, including charge ordering.
- Understanding the microscopic origins of charge ordering is crucial for developing advanced electronic materials.
Purpose of the Study:
- To investigate the real-space nature of charge ordering in Bi0.5Sr0.4Ca0.1MnO3.
- To determine if charge ordering involves valence fluctuations of manganese ions.
Main Methods:
- Scanning transmission electron microscopy (STEM) was employed to visualize the material's microstructure.
- High-angle annular dark-field (HAADF) imaging revealed periodic stripe-like modulations.
- Geometric phase analysis (GPA) quantified the atomic displacements associated with the modulation.
- Electron energy loss spectroscopy (EELS) was used to probe valence states across the observed stripes.
Main Results:
- STEM-HAADF imaging showed uniform, stripe-like modulations in Bi0.5Sr0.4Ca0.1MnO3.
- GPA analysis identified the modulation as a displacement wave with specific transverse and longitudinal amplitudes.
- EELS measurements across the stripes indicated no significant periodic valence changes in Mn ions, with an upper bound of +/-0.04.
Conclusions:
- The charge ordering modulation in Bi0.5Sr0.4Ca0.1MnO3 is primarily a structural displacement wave, not a consequence of significant Mn valence changes.
- This finding provides critical real-space insights into the microscopic mechanisms governing charge ordering in mixed-valent manganites.
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