Epitaxial growth of anisotropically shaped, single-crystal particles of cubic SrTiO 3
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Shang-Cong Cheng Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802 (Received 11 October 1999; accepted 16 December 1999)
A novel method for synthesizing anisotropically shaped particles of materials having cubic symmetry is reported. Anisotropically shaped single-crystal particles of cubic SrTiO3 were obtained by epitaxial growth on tabular tetragonal Sr3Ti2O7. Transmission electron microscopy revealed that both the shape and the size of the single-crystal particles was regulated by selecting a precursor material that can act as a reaction site in molten KCl and has an epitaxial relation with SrTiO3. The [001] and [110] directions of tabular SrTiO3 are parallel to the [001] and [110] directions of the Sr3Ti2O7 host particle, respectively. Tabular SrTiO3 particles with rectangular faces having an edge length of 10–20 m and a thickness of ∼2 m were obtained by reacting TiO2 and tabular Sr3Ti2O7 particles of the same edge length in molten KCl.
The formation of anisotropically shaped single-crystal particles of materials with a cubic crystal structure is of considerable interest due to the favorable properties of such materials. However, by virtue of their crystal symmetry, cubic materials typically grow as equiaxed crystals.1,2 In this study we describe the formation of anisotropically shaped particles of SrTiO3, a cubic perovskite material. The use of platelike or tabular particles offers several potential advantages over the use of particles with equiaxed shapes. For example, platelike or tabular particles yield thinner coatings for a given areal coverage. Applications such as multilayer capacitors require thinner layers of ceramic powders for improved properties. Platelike or tabular single-crystal particles can be used to modify readily available substrates to control the orientation in deposited thin films. For example, Moon and colleagues3 showed that substrates seeded with oriented, tabular PbTiO3 particles can be used to grow fibertextured PbTiO3 thin films. Another application for tabular or acicular particles is in templated grain growth (TGG) of textured polycrystalline ceramics.4–9 The development of texture by TGG is based on the preferential growth of large, oriented single-crystal particles distributed in a fine-grained matrix. The initial orientation of templates in the matrix is
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Permanent address: National Industrial Research Institute of Nagoya, Nagoya 462-8510, Japan.
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J. Mater. Res., Vol. 15, No. 4, Apr 2000 Downloaded: 18 Mar 2015
achieved by subjecting a slurry of anisotropic singlecrystal particles and fine powder to a shear field during tape casting or extrusion. Therefore, the ability to synthesize and orient anisotropically shaped templates is crucial to texture formation by TGG. Another area of potential application for anisotropically shaped particles of a cubic material is in high-strain actuator materials. Park et al.10 reported very high strains in relaxor lead zinc niobate–lead titanate (PZN
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