Size-controlled synthesis of nanocrystalline BaTiO 3 by a sol-gel type hydrolysis in microemulsion-provided nanoreactors
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Size-controlled synthesis of nanocrystalline BaTiO3 by a sol-gel type hydrolysis in microemulsion-provided nanoreactors Ch. Beck, W. H¨artl, and R. Hempelmanna) Physikalische Chemie, Universit¨at Saarbr¨ucken, D-66123 Saarbr¨ucken, Germany (Received 4 June 1997; accepted 7 October 1997)
Using the hydrolysis of appropriate alkoxide mixtures in water-in-oil microemulsions, nanocrystalline BaTiO3 has been prepared in the form of nonaggregated, cube-shaped crystals at room temperature without any sintering process as is demonstrated by means of x-ray diffractograms and transmission electron micrographs. By variation of the length of the hydrophilic part of the surfactant molecules, the diameter of the water droplets in the microemulsions could be tuned to values between 8 and 55 nm as determined by dynamic light scattering. The size of the resulting nano-BaTiO3 (6 nm < kdlvol < 17 nm) was evaluated from the line broadening of x-ray reflections and correlates to the droplet size. The particle size distribution is very narrow, and in some cases nearly monodisperse.
I. INTRODUCTION
Nanostructured materials are of interest both for fundamental and applied research.1 They consist of small crystallites with sizes below 50 nm joined together by disordered regions such that many physical properties of nanoscaled materials differ drastically from those of single crystals or coarse grained polycrystals with the same chemical composition. It is expected that these novel properties will give rise to many applications; actually, nanoscaled WCyCo alloys exhibit an enhanced hardness and toughness,2 nanostructured AlyAl2 O3 composites combine low weight with high strength up to the melting point,3 and nano-TiO2 ceramics have the advantage of high ductility and toughness.4 In these applications mostly interface-dominated properties are utilized based on the large volume fraction of the grain boundary region. The other feature of nanoscaled materials is the reduced grain size. We mention quantum-size effects in semiconductors,5 the size dependence of the diffusion coefficient of positive muons in metals,6 and the effect of phonon confinement.7 In order to systematically study these effects in fundamental research, techniques for the preparation of comparatively large quantities of nanocrystalline materials with high purity, definite and intentionally chosen grain size, and narrow grain size distribution are an important prerequisite. For nanocrystalline metals like Pd8 and Cu,9 Natter and Hempelmann have developed the technique of pulsed electrodeposition. A similar preparation technique has been described by Erb10 for nanocrystalline Ni. For nanocrystalline ceramics different wet chemical synthesis techniques in microemulsions are possible.11–17 a)
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http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 11, Nov 1998
Downloaded: 12 Feb 2015
Herrig and Hempelmann have recently briefly reported about a colloidal approach to nanometer-sized
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