Microstructural development of BaTiO 3 powders synthesized by aqueous methods
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Microstructural development of BaTiO3 powders synthesized by aqueous methods L. Zhao, A. T. Chien, F. F. Lange, and J. S. Speck Materials Research Laboratory and Materials Department, University of California, Santa Barbara, Santa Barbara, California 93106 (Received 24 May 1995; accepted 6 March 1996)
The hydrothermal growth of perovskite BaTiO3 powders has been studied by transmission electron microscopy. The growth is carried out under high alkaline conditions (pH , 14) achieved with Ba(OH)2 . Anatase (TiO2 ) is used as a titanium source. The perovskite BaTiO3 nucleates heterogeneously on anatase TiO2 particles with an epitaxial relationship of (001)TiO2 jj (001)BaTiO3 and [010]TiO2 jj [010]BaTiO3 . This epitaxial relationship preserves the parallel alignment of the oxygen octahedra between the structures. A mosaic misorientation between (001)TiO2 and (001)BaTiO3 along k110l is seen in this relationship due to the lattice mismatch between TiO2 and BaTiO3 . After complete conversion of the anatase to BaTiO3 , the BaTiO3 particles develop into h111j octahedrons with ,10 nm h001j and h110j microfacets on the h111j faces. This evolution suggests that h111j becomes the stable crystallographic facet for BaTiO3 under highly alkaline conditions.
Barium titanate is an important material in the electronics industry, particularly because of its high dielectric constant and ferroelectric properties for applications as capacitors and piezoelectric transducers.1 There is current interest in using solution routes to synthesize BaTiO3 films at low temperatures rather than by conventional high temperature methods.2 Hydrothermal synthesis is a technique that involves the growth of oxides from aqueous solutions at elevated temperatures (,100 –400 ±C) and pressures (,0.1–15 MPa). Hydrothermal methods have been studied to understand the synthesis conditions of minerals formed in the earth’s crust3 ; however, the technique is currently being pursued as a route for crystal growth for electronically important oxides such as BaTiO3 and (Pb, Zr)TiO3 .2 Barium titanate has been synthesized as powders and polycrystalline thin films under a wide range of conditions by the hydrothermal method. Lilley and Wusirika4 patented the production of submicron BaTiO3 powder by reacting anatase TiO2 powder in aqueous solutions of barium hydroxide for ,48 h. Chien et al. examined the development of BaTiO3 powders by transmission electron microscopy (TEM) and x-ray diffraction (XRD) for phase, crystallinity, and evolution of the powder morphology; however, a detailed orientational relationship between the two structures was not discussed.5 Hydrothermal dissolution studies of perovskite to anatase and brookite (both TiO2 ) reveal J. Mater. Res., Vol. 11, No. 6, Jun 1996
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that orthorhombic perovskite (CaTiO3 ) and anatase have an epitaxial relationship of h001janatase jj h101jCaTiO3 and [010]anatase jj [010]CaTiO3 .6,7 The focus of the present work is to s
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