One-step Solvothermal Synthesis and Characterization of BaTiO 3 Nanoparticles
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One-step Solvothermal Synthesis and Characterization of BaTiO3 Nanoparticles Helen Reveron, Cyril Aymonier, Anne Loppinet-Serani, Mario Maglione, Catherine Elissalde and Francois Cansell Institut de Chimie de la Matière Condensée de Bordeaux (ICMCB), 87 Av. du Dr. Schweitzer, 33608 Pessac, FRANCE. ABSTRACT Using a continuous-flow reactor, barium titanate (BaTiO3) nanoparticles have been successfully synthesized at temperatures ranging from 150 to 380°C and 16 MPa. Ba-Ti alkoxide solutions were used as precursors and water as reagent. The influence of synthesis parameters on the powder characteristics was investigated. Results showed that the purity, crystallinity and stoichiometry of the as-synthesized BaTiO3 powder depend mainly on the reactor temperature, quantity of water injected into the reactor and the Ba:Ti molar ratio of alkoxide solutions.
INTRODUCTION In recent years, solvothermal method has attracted considerable interest to prepare different kinds of materials (ceramics, metals and organic polymers) in several forms (powders, single crystals, fibers, or coatings), due to the relatively low temperatures involved and the possibility to control precisely the stoichiometry, morphology and particle-size [1, 2]. Barium titanate (BaTiO3) is an important material used in the electronic industry (mainly in multilayer ceramic capacitors and thermistors/thermal switches) due to its high dielectric constant and good ferroelectric properties. Depending on the temperature, micrometric BaTiO3 crystallizes in five distinct polymorphic-forms [3]. However, among these structures, only the tetragonal phase (0 to 120°C) and the cubic phase (120 to 1460°C) are interesting from a technological point of view. Conventionally, barium titanate is synthesized through a solid-state reaction between BaCO3 and TiO2 powders at high temperature (T>1200°C) [4]. Nevertheless, the overall reaction involves successive steps of grinding and calcination and usually leads to large particles with inhomogeneous compositions. Some alternative methods for synthesizing barium titanate powders employing lower temperatures have been developed. Table I summarizes different BaTiO3 synthesis methods described recently in the literature [5-28]. The investigations are mainly focused on the preparation of barium titanate nanoparticles with high purity, particularly without barium carbonate pollution, in order to prepare well-sintered ceramics with outstanding ferroelectric properties. The study of the controversial particle-size effect over BaTiO3 ferroelectric properties has also interested many researchers. There are some limitations associated with some of these BaTiO3 synthesis methods: (a) long reaction times, (b) preparation of large particles, (c) powder pollution with BaCO3 or nonstoichiometric phases, (d) post-treatments for powder washing, drying and crystallization and (e) tedious synthesis in batch mode or semi-continuous mode. We report in this paper a one-step solvothermal route to obtain pure and well-crystallized BaTiO3 nanopartic
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