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Octahedral tilt twinning and compositional modulation in NaLaMgWO(6)
Graham King1, Susana Garcia-Martin, Patrick M Woodward
1The Department of Chemistry, The Ohio State University, 100 West 18th Ave, Columbus, OH 43210, USA. gking@chemistry.ohio-state.edu
Acta Crystallographica. Section B, Structural Science
|November 20, 2009
Summary
This study reveals a complex superstructure in the ordered perovskite NaLaMgWO(6) using advanced electron microscopy and diffraction techniques. The findings detail a unique arrangement of atoms and octahedral tilts, crucial for understanding material properties.
Area of Science:
- Materials Science
- Solid-State Chemistry
- Crystallography
Background:
- Perovskite materials exhibit diverse structures and properties.
- Ordered perovskites, such as NaLaMgWO(6), present opportunities for tailored functionalities.
- Understanding complex superstructures is key to predicting and controlling material behavior.
Purpose of the Study:
- To elucidate the complex superstructure of the ordered perovskite NaLaMgWO(6).
- To determine the unit-cell dimensions and structural characteristics.
- To investigate the interplay of atomic ordering, octahedral tilting, and compositional modulation.
Main Methods:
- Selected-area electron diffraction (SAED) for initial structural analysis.
- Neutron powder diffraction (NPD) for detailed crystallographic information.
- High-resolution transmission electron microscopy (HRTEM) for visualizing nanoscale features.
Main Results:
- A 12a(p) x 2a(p) x 2a(p) superstructure was identified, significantly larger than the simple perovskite unit cell.
- Layered ordering of Na/La and rock-salt ordering of Mg/W contribute to the superstructure.
- Octahedral tilting (a(-)a(-)c(0) tilt system) and compositional modulation are essential for the observed structure.
Conclusions:
- The complex superstructure arises from a combination of atomic ordering, octahedral tilting, and A-site cation modulation.
- HRTEM stripe contrasts are explained by both octahedral tilt twinning and compositional variations.
- This detailed structural understanding is vital for the design of novel perovskite-based materials.
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