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Control of polymorphism in NaNbO(3) by hydrothermal synthesis
Deena R Modeshia1, Richard J Darton, Sharon E Ashbrook
1Department of Chemistry, University of Warwick, Coventry, UKCV4 7AL.
Chemical Communications (Cambridge, England)
|December 17, 2008
Summary
Researchers synthesized a metastable ilmenite polymorph of sodium niobate (NaNbO3) under mild hydrothermal conditions. This one-step process achieved the desired ilmenite structure, deviating from the typically expected perovskite form.
Area of Science:
- Materials Science
- Inorganic Chemistry
- Crystallography
Background:
- Sodium niobate (NaNbO3) is typically synthesized in the perovskite polymorph.
- Achieving alternative polymorphs like ilmenite often requires complex or harsh synthesis conditions.
Purpose of the Study:
- To develop a direct, one-step synthesis method for the metastable ilmenite polymorph of NaNbO3.
- To investigate the crystallization pathway under mild hydrothermal conditions.
Main Methods:
- Mild hydrothermal synthesis with controlled pH.
- Use of near-stoichiometric metal precursor amounts.
- In situ energy-dispersive X-ray diffraction (EDXRD) for real-time crystallization monitoring.
Main Results:
- Direct formation of the ilmenite polymorph of NaNbO3 was achieved, bypassing the expected perovskite structure.
- Crystallization proceeded rapidly through a series of intermediate crystalline phases.
- The process was optimized by lowering pH and using stoichiometric precursors.
Conclusions:
- Mild hydrothermal conditions, with precise control over pH and precursor stoichiometry, enable the direct synthesis of metastable NaNbO3 ilmenite.
- Understanding the intermediate phases provides insights into the crystallization mechanism of NaNbO3 polymorphs.
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