The cation-deficient layered perovskite oxide Ba5Nb4O15 is one of the functional materials that exhibits a microwave-responsive dielectric property and an ultraviolet-active photocatalytic property. Although systematic control of the morphology of Ba5Nb4O15 is beneficial for improving these properties, synthesized Ba5Nb4O15 usually has a plate-like shape owing to its crystal structure, with a particle size less than 5 μm. For systematic morphological control of Ba5Nb4O15, the crystal growth was studied by using a chloride-based flux method. Idiomorphic plate-like Ba5Nb4O15 crystals up to 50 μm in size and polyhedron ones ∼10 μm in size were obtained using a BaCl2 flux by changing the solute concentration to 5-20 mol % and 50 mol %, respectively. The growth of the Ba5Nb4O15 crystals was investigated by thermogravimetric and differential thermal analysis and in situ X-ray diffraction analysis. These analyses revealed the flux-growth manner of Ba5Nb4O15 as follows: (I) Ba5Nb4O15 was formed by a solid-state reaction above ∼650 °C. (II) After the melting of BaCl2 above ∼962 °C, the Ba5Nb4O15 crystals became larger and assumed idiomorphic shapes, indicating that they were somewhat dissolved in the flux and that the crystal growth was promoted. Increasing the holding time yielded an increased number of crystals larger than 28 μm. This indicates that Ostwald ripening effectively yields Ba5Nb4O15 crystals up to 50 μm in size. Chloride fluxes with different alkaline or alkaline earth cation fluxes did not produce such large crystals. It is assumed that the common ion effect of Ba2+ in the solute and flux provides an effective reaction field to facilitate Ostwald ripening.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics