Hydrothermal synthesis of ferroelectric perovskites from chemically modified titanium isopropoxide and acetate salts
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Hydrothermal synthesis of ferroelectric perovskites from chemically modified titanium isopropoxide and acetate salts Jooho Moon, Jeffrey A. Kerchner, Henrik Krarup, and James H. Adaira) Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611 (Received 30 April 1997; accepted 12 June 1998)
The feasibility of the acetylacetonate-Ti isopropoxide complex as a new precursor for synthesis of Ti-based perovskite particles under hydrothermal conditions has been demonstrated. Perovskite powders including BaTiO3 , PbTiO3 , PZT, PLZT, and SrTiO3 were prepared by reacting the acetylacetonate-modified Ti precursor in metal acetate aqueous salt solution under hydrothermal conditions. Synthesis parameters including reaction time and temperature, feedstock concentration, and reaction medium significantly influence particle characteristics of the hydrothermally derived perovskite powders. It is proposed that use of the acetylacetonate-modified Ti precursor promotes intimate mixing among multicomponent reacting species at the molecular level and promotes particle formation through a dissolution/recrystallization mechanism. I. INTRODUCTION
Perovskite ferroelectrics are a special group of advanced electronic materials which undergo spontaneous electric polarization and possess reversible polarization under an applied electric field.1 The onset of ferroelectric states is closely related to the nature of the crystal structure in which each permanent dipole arranges in the direction of an electric field in a cooperative manner at the temperature where the randomizing effect of thermal energy is overcome.2 As a result, ferroelectric materials possess very large dielectric constants (k . 1000), large piezoelectric coefficients, and large pyroelectric coefficients. These characteristics facilitate applications in many areas including multilayer capacitors, transducers, pyroelectric sensors, and electro-optic devices.3 Recently, the growing demand for ferroelectric ceramics with better functionality and performance had accelerated the development of powder synthesis techniques that produce well-defined particles. The performance of electronic ceramics is often determined by the characteristics of the starting powders and the microstructure of the consolidated green body. Since ceramic products are usually formed by powder processing, typically starting with more than 1012 particles per component, the properties of the sintered body are inherited from the characteristics of the initial powders.4 Even careful forming and precise firing does not lead to the desired performance of the final products if inadequate starting powders are involved. In this regard, both physical and chemical properties of the powders must be well defined and characterized with control of homogeneity, purity, particle size, particle shape, and chemical stoichiometry among the more important properties. To this end, a variety of chemical solution a)
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