Barium titanate films

Although the above-described examples have all been based on relatively simple nanocrystalline metal oxides, additional phases might have been introduced. The use of more complex metal oxides has also been investigated, with nanocrystalline thick films of both barium titanate [96] and cobalt titanate [97] having been considered as possible sensor materials. When the response of such barium titanate films doped with 10% CuO and 10% CdO was studied with respect to CO, LPG, H2S, and H2 [96], sensor selectivity was improved for LPG over the other gases at 250 °C. However, the addition of 0.3 wt% Pd resulted in an even greater selectivity to LPG at a lower temperature, of 225 °C. 

Barium titanate thin films can be deposited on various substances by treating with an aqueous solution containing barium salts and an alkanolamine-modifted titanate such as TYZOR TE (151). In a similar fashion, reaction of a tetraalkyl titanate with an alkah metal hydroxide, such as potassium hydroxide, gives oxyalkoxide derivatives (KTi O(OR) ), which can be further processed to give alkali metal titanate powders, films, and fibers (152—155). The fibers can be used as adsorbents for radioactive metals such as cesium, strontium, and uranium (156). 

Ihlefeld, J. F. Borland, W. Maria, J. P. 2005. Synthesis and properties of barium titanate thin film on copper substrates. In Ferroelectric Thin Films XIII, edited by Ramesh, R. Maria, J. P. Alexe, M. Joshi, V. Mat. Res. Soc. Symp. Proc. 902 7-14. 

Figure 14.4. XRD (left) and AFM (right) images of a barium strontium titanate film grown by solution processing.17...

Barium titanate is made by sintering a finely powdered mixture of barium carbonate and titanium dioxide in a furnace at 1,350°C. The calcined mass is finely ground and mixed with a binder (plastic). The mixture is subjected to extrusion, pressing or film casting to obtain ceramic bodies of desired shapes. Plastic is burnt off by heating and the shaped body is sintered by firing and then pobshed. 

The bending piezoelectricity in drawn and polarized polymer films was studied in detail by Kawai (1) (1970). Kitayama and Nakayama (1971) reported a very high piezoelectricity in composite films of polymer (PVDF, nylon 11, PVC) and powdered ceramics (barium titanate, PZT) after poling. In the case of PVDF and nylon, the piezoelectric constant increase by a factor of 102 when the ceramics make up 50% of the volume. The pyroelectricity and optical nonlinearity of polarized PVDF films have been studied by Bergmann, McFee, and Crane (1971). 

The effect of k on d is most clearly demonstrated in the experiment by Fukada and Date (1970) on the polyester resin film, filled with powdered barium titanate and polarized under a d.c. field. The strong piezoelectricity, as shown in Fig. 29, is ascribed to the polarization charge of the ceramic filler and heterogeneous strain due to the composite structure. The real part d exhibits a maximum at 90° C and d" has a peak and a succeeding dip at this temperature where the primary relaxation of polyester resin occurs. The behavior of d and d" is quite similar to that of k and k" in Fig. 16, respectively, in which decreasing X = an corresponds to increasing temperature. 

Basantakumar Sharma and Sarma H. N. K., A Mansingh, Ferroelectric and dielectric properties of sol-gel processed barium titanate ceramics and thin film. J. Materials Science. 34(1999) pp. 1385-1388. 

Robins LH, Kaiser DL, Rotter LD, Schenck PK, Stauf GT, Rytz D (1994) Investigation of the structure of barium titanate thin films by Raman spectroscopy. J Appl Phys 76 7487... 

All the aforementioned precursors are pivotal to the development of nonsupercon-ducting metal oxide films such as the barium titanates, barium tantalates, and tantalum... 

M. Nagai, K. Yamashita, T. Umegaki and Y. Takuma, Electrophoretic Deposition of Ferroelectric Barium TiTanate Thick Films and Their Dielectric Properties J. Am. Ceram. Soc. 76 (1993) 253-255. 

K. Yamashha, E. Yonehara and T. Umegaki, Dielectric Properties of Electrophoretically Layered Barium Strontium Titanate Films K. Yamashita, E. Yonehara and T. Umegaki, to be published in the IEEE proc. 

Cho, S. D., Lee, J. Y, and Paik, K. W., Effect of particle size on dielectric constant and leakage current of epoxy/barium titanate (BaTiOs) composite films for embedded capacities, in International Conference on Electronic Materials and Packaging, 2001, pp. 63-68. 

Piezoelectricity links the fields of electricity and acoustics. Piezoelectric materials are key components in acoustic transducers such as microphones, loudspeakers, transmitters, burglar alarms and submarine detectors. The Curie brothers [7] in 1880 first observed the phenomenon in quartz crystals. Langevin [8] in 1916 first reported the application of piezoelectrics to acoustics. He used piezoelectric quartz crystals in an ultrasonic sending and detection system - a forerunner to present day sonar systems. Subsequently, other materials with piezoelectric properties were discovered. These included the crystal Rochelle salt [9], the ceramics lead barium titanate/zirconate (pzt) and barium titanate [10] and the polymer poly(vinylidene fluoride) [11]. Other polymers such as nylon 11 [12], poly(vinyl chloride) [13] and poly (vinyl fluoride) [14] exhibit piezoelectric behavior, but to a much smaller extent. Strain constants characterize the piezoelectric response. These relate a vector quantity, the electrical field, to a tensor quantity, the mechanical stress (or strain). In this convention, the film orientation direction is denoted by 1, the width by 2 and the thickness by 3. Thus, the piezoelectric strain constant dl3 refers to a polymer film held in the orientation direction with the electrical field applied parallel to the thickness or 3 direction. The requirements for observing piezoelectricity in materials are a non-symmetric unit cell and a net dipole movement in the structure. There are 32-point groups, but only 30 of these have non-symmetric unit cells and are therefore capable of exhibiting piezoelectricity. Further, only 10 out of these twenty point groups exhibit both piezoelectricity and pyroelectricity. The piezoelectric strain constant, d, is related to the piezoelectric stress coefficient, g, by... 

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... 

Chien, A.T., Speck, J.S., Lange, F.F., Daykin, A.C., Levi, C.G. Low temperature/low pressure hydrothermal synthesis of barium titanate powder and heteroepitaxial thin films. J. Mater. Res. 10, 1784-1789 (1995)... 

Yong JW, Li J, Tomomi K, Makoto K. Low-temperature synthesis of barium titanate thin film by nanoparticles electrophoretic deposition. J Electroceram 2008 21 189-92. 

The dielectric layer for ceramic capacitors is formed by preparing a barium titanate paste that is rolled into a flexible film. The film is covered by conducting ink to form the electrode layer. Then the film is cut, stacked into layers, and the procedure is completed in a manner similar to that already described. 

Lee and Zhang synthesized barium titanate aqueous sol (Lee and Zhang, 2001). They used barium acetate dissolved in acetic acid. An aqueous solution of an equimolar titanium bis(ammonium lactato) dihydroxide, which was perhaps 50 wt%, was added to the barium acetate solution. After adjusting the concentration by diluting with water/ethanol, the solution was refluxed at 100 C for 8 h, and a viscous barium titanate sol with pH of 10.6 resulted. This solution was used for preparation of thin films by spin-on process. It is very... 

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