Barium titanate preparation

Table 5.10 Properties of nanocrystalline powders of barium titanate prepared in modes with different heating rates...

The most significant commercial product is barium titanate, BaTiO, used to produce the ceramic capacitors found in almost all electronic products. As electronic circuitry has been rniniaturized, demand has increased for capacitors that can store a high amount of charge in a relatively small volume. This demand led to the development of highly efficient multilayer ceramic capacitors. In these devices, several layers of ceramic, from 25—50 ]lni in thickness, are separated by even thinner layers of electrode metal. Each layer must be dense, free of pin-holes and flaws, and ideally consist of several uniform grains of fired ceramic. Manufacturers are trying to reduce the layer thickness to 10—12 ]lni. Conventionally prepared ceramic powders cannot meet the rigorous demands of these appHcations, therefore an emphasis has been placed on production of advanced powders by hydrothermal synthesis and other methods. 

Other. Insoluble alkaline-earth metal and heavy metal stannates are prepared by the metathetic reaction of a soluble salt of the metal with a soluble alkah—metal stannate. They are used as additives to ceramic dielectric bodies (32). The use of bismuth stannate [12777-45-6] Bi2(Sn02)3 5H20, with barium titanate produces a ceramic capacitor body of uniform dielectric constant over a substantial temperature range (33). Ceramic and dielectric properties of individual stannates are given in Reference 34. Other typical commercially available stannates are barium stannate [12009-18-6] BaSnO calcium stannate [12013 6-6] CaSnO magnesium stannate [12032-29-0], MgSnO and strontium stannate [12143-34-9], SrSnO. ... 

Composite Oxyalkoxides. Composite oxyalkoxides can be prepared by reaction of tetraalkyl titanates and alkaline-earth metal hydroxides. These oxyalkoxides and their derivatives can be hydroly2ed and thermally decomposed to give alkaline-earth metal titanates such as barium titanate (150). 

Titanium forms a series of oxoanions called titanates, which are prepared by heating Ti02 with a stoichiometric amount of the oxide or carbonate of a second metal. One of these compounds, barium titanate, BaTi03, is piezoelectric, which means that it becomes electrically charged when it is mechanically distorted. The ability to convert mechanical vibration into an electrical signal makes barium titanate useful for underwater sound detection. 

Hennings, D. Rosenstein, G. Schreinemacher, H. 1991. Hydrothermal preparation of barium titanate from barium-titanium acetate gel precursors. J. Euro. Ceram. Soc. 8 107-115. 

Barium titanate, BaTiOs, is a ferroelectric material (see Chapter 9) widely used in capacitors because of its high dielectric constant. It was initially prepared by heating barium carbonate and titanium dioxide at high temperature. 

What are the advantages and disadvantages of using the sol-gel method to prepare barium titanate for use in a capacitor ... 

Electroceramics. Titanates like barium, strontium, calcium and lead titanate prepared from finely divided, high-purity TiOz hydrolysates are used in capacitors, PTC-resistors and piezoelectric materials. The specifications of the Ti02 starting materials with respect to purity, reactivity, and sintering properties are expected to become more stringent. The market is estimated to be several thousand of tonnes a year as TiOz. A strong annual growth is expected. 

The PTC effect is distinguished from the majority of other critical temperature effects in the ease with which the critical temperature can be shifted by altering the composition. The replacement of barium in BaTiC>3 by strontium lowers the critical temperature by 4°C per percentage atomic replacement, whilst replacement by lead raises the critical temperature by 4.3 °C per percentage atomic replacement (see Fig. 2.47). Since the critical temperature for BaTiC>3 is 120-130 °C, it is a simple matter to prepare ceramics with PTC regions anywhere between -100 °C and +250 °C, although the highest temperature coefficients are found in barium titanate compositions without major quantities of substituents. 

Amorphous barium titanate gel is obtained in couples of minutes. The gel is then dried in vacuum at temperature of 333K for 24 h, and nanometer BaTiOj is prepared by calcining the dry gel at 973-1073K for 2h. 

The inverse-micelle approach may also offer a generalized scheme for the preparation of monodisperse metal-oxide nanoparticles. The reported materials are ferroelectric oxides and, thus, stray from our emphasis on optically active semiconductor NQDs. Nevertheless, the method demonstrates an intriguing and useful approach the combination of sol-gel techniques with inverse-micelle nanoparticle synthesis (with OTO erafe-temperature nucleation and growth). Monodisperse barium titanate, BaTiOs, nanocrystals, with diameters controlled in the range from 6-12nm, were prepared. In addition, proof-of-principle preparations were successfully conducted for Ti02 and PbTiOs. Single-source alkoxide precmsors are used to ensure proper stoichiometry in the preparation of complex oxides (e.g. bimetallic oxides) and are commercially available for a variety of systems. The... 

Nakamura, T., Kamiya, M., Watanabe, H., and Nakanishi, Y, Preparation and characterization of zinc sulfide phosphors coated with barium titanate using sol-gel method, J. Electrochem. Soc., 142, 949, 1995. 

In an extension of the spray-drying technique called spray roasting , evaporative decomposition of solutions (EDS) , spray pyrolysis , or aerosol pyrolysis , the temperature of the heated chamber is high enough to decompose the dried salts after the solvent has evaporated. Nitrate salts are used because of their low decomposition temperatures. The technique eliminates the problems of handling dried nitrate powders, which can be hydroscopic. These methods are used to prepare chalcogenide powders" and barium titanate . 

Many different preparations of colloidal barium sulfate for roentgenography are available commercially. The so-called barium meals are not limited to liquid suspensions they also appear as tablets (73). Barium sulfate suspensions containing an effervescent agent have been introduced for use in doublecontrast studies (74,75). Barium sulfate may also be coated with Fe203, MgO, and Al Oa (63,761. The coated material has good dispersibility and very low viscosity in acidic media. Other barium preparations are also useful. A barium titanate suspension was compared with barium sulfate (72). An emulsified mixture containing castor oil and barium sulfate can visualize colon fistula more economically than can iodinated contrast media (77). 

Chen. J.E at al.. Preparation and properties of barium titanate nanopowder by conventional and high gravity reactive precipitation methods, Scripta Mater., 49, 509, 2003. 

A strange method of preparation of optically active compounds without any chiral inductors was described using an electrochemical cell with electrodes of special asymmetric configuration made of barium titanate Reduction of fumaric acid resulted in (R)-(+)-malic acid with an ee of 17%, or... 

Y.-S. Her, E. Matijevic, and M.C. Chon Preparation of Well Defined Colloidal Barium Titanate Crystals by the Controlled Double Jet Precipitation. J. Mater. Res., 10, 3106-3114 (1995). Controlled Double-Jet Precipitation of Uniform Colloidal CiystalUne Sr-and Zr-Doped Barium Titanates. J. Mater. Res., 11, 3121-3127 (1996). 

Li J, Wu YJ, Tanaka H, Yamamoto T, Kuwabara M (2004) Preparation of a monodispersed suspension of barium titanate nanoparticles and electrophoretic deposition of thin films. J Am Ceram Soc 87 1578-1581... 

Wei, J.H., J.G. Guan, W.Y. Chen, and R.Z. Yuan. 2002. Preparation and characteristics of polyaniline-barium titanate nanocomposite particles. Acta Phys Chim Sin 18 (7) 653-656. 

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