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Polymorphism in NaSbO3: structure and bonding in metal oxides
Hiroshi Mizoguchi1, Patrick M Woodward, Song-Ho Byeon
1Department of Chemistry, Ohio State University, Columbus, Ohio 43210-1185, USA.
Journal of the American Chemical Society
|March 12, 2004
Summary
A new sodium antimonate (NaSbO(3)) polymorph with a perovskite structure was synthesized under high pressure. This discovery sheds light on the complex bonding and structural preferences in ternary antimonate compounds.
Area of Science:
- Solid-state chemistry
- Materials science
- Crystallography
Background:
- Ternary perovskites are crucial in materials science, but their structural diversity and stability under pressure are not fully understood.
- Sodium antimonate (NaSbO(3)) is known to exist in an ilmenite polymorph under ambient conditions.
Purpose of the Study:
- To synthesize and characterize a new high-pressure polymorph of NaSbO(3).
- To investigate the structural, electronic, and bonding properties of this novel material.
- To understand the factors governing the stability of different NaSbO(3) polymorphs.
Main Methods:
- High-pressure synthesis using a uniaxial split sphere anvil type press (USSA-2000) at 10.5 GPa and 1150 degrees C.
- X-ray diffraction for crystal structure determination.
- Optical measurements to determine the band gap.
Main Results:
- A new orthorhombically distorted perovskite polymorph of NaSbO(3) was successfully synthesized and recovered to ambient conditions.
- The structure (space group Pnma) exhibits significant octahedral tilting distortion, larger than predicted by ionic radii.
- The compound is a white insulator with an optical band gap of 3.4 eV, representing the first ternary perovskite with Sb(5+) on the octahedral site.
Conclusions:
- The observed distortion is attributed to a second-order Jahn-Teller effect on oxygen, driven by strong Sb-O covalent bonding.
- A conflict between Sb-O covalent bonding and Na-O repulsive interactions destabilizes the perovskite structure at ambient conditions, favoring the ilmenite polymorph.
- Analysis of bonding explains the prevalence of structures violating Pauling's rules in ASbO(3) and ABiO(3) compounds.
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