Chemical perovskite thin film

Schwartz, R. W. 1997. Chemical solution deposition of perovskite thin films. Chem. Mat. 9 2325-2340. 

Post, M.L., and B.W. Sanders, 1993, Oxygen sensing irsing the bulk properties of perovskite thin-films, in Proc. Symp. on Chemical Sensors II, 1993, eds M. Butler, A. Ricco and N. Yamazoe (Electrochemical Society, Pertrrington) pp. 358-362. 

It may thus be concluded that application of metal alkoxides for preparation of PZT-based thin films in many aspects may be nowadays considered to be a routine technique widely used in many laboratories. The research work is presently mostly focused on electrical and microstructural aspects of these films rather than on chemical routes of their preparation. Irrespective of the technique for the precursor preparation, when 10% excess of Pb is introduced (to prevent loss of lead due to the PbO volatility) the ferroelectric perovskite PZT films are obtained after annealing at about 700°C, demonstrating nonlinear properties of the level acceptable for most of the desired applications. Their typical microstructure is presented in Fig. 10.3. 

Thin films, to attain enough sensitivity and response time, of oxide materials normally deposited on a substrate are typically used as gas sensors, owing to their surface conductivity variation following surface chemisorption [183,184], Surface adsorption on a Sn02 film deposited on alumina produces a sensitive and selective H2S gas sensor [185]. In addition, a number of perovskite-type compounds are being used as gas sensor materials because of their thermal and chemical stabilities. BaTi03, for example, is used as sensor for C02 [183],... 

Numerous ceramics are deposited via chemical vapor deposition. Oxide, carbide, nitride, and boride films can all be produced from gas phase precursors. This section gives details on the production-scale reactions for materials that are widely produced. In addition, a survey of the latest research including novel precursors and chemical reactions is provided. The discussion begins with the mature technologies of silicon dioxide, aluminum oxide, and silicon nitride CVD. Then the focus turns to the deposition of thin films having characteristics that are attractive for future applications in microelectronics, micromachinery, and hard coatings for tools and parts. These materials include aluminum nitride, boron nitride, titanium nitride, titanium dioxide, silicon carbide, and mixed-metal oxides such as those of the perovskite structure and those used as high To superconductors. 

Perovskite-structured membranes, in the form of thin films supported on porous ceramic or metal substrates, have been studied extensively in the past decade. Thin films offer several advantages including reduced material cost, improved mechanical strength and possibly higher H2 flux. Chemical vapor deposition (CVD) [99], electrochemical vapor deposition (EVD) [100] and sputtering [101] represent typical methods. However, dense films have been difficult to obtain by these methods. It was found that the continuity and gas-tightness of the deposited films were very sensitive to the morphologies and pore size of substrates. 

These tilts and rotations are extremely sensitive to external conditions, including temperature, pressure and strain. This latter aspect is particularly important in the case of thin films which are epitaxially grown onto a suitable substrate. Considerable tensile or compressive strain in the film often arises because of mismatch between the lattice parameter of the substrate and the lattice parameter of the film. Such effects can cause considerable (and sometimes surprising) changes in the physical properties of the film itself or of the interface region. In addition, chemical substitution at A- and B-sites in a perovskite may significantly alter the tilt and rotation of... 

Johnson J.A., Lisoni J.G., Wonters D.J. Iridium based electrodes for ferroelectric capacitor fabrication. Mater. Res. Soc. Symp. Proc. 2002 688 59-64 Kang J., Yoko T., Kozuka H., Sakka S. Preparation of Pb-based complex perovskite coating films by sol-gel method. In Sol-Gel Optics, vol. II, J.D. Mackenzie, ed. Pfoc. SPIE 1992 1758 249-259 Kim Dong-Joo, Maria Jon-Paul, Kingon A.I. Compositional effect on the piezoelectric and ferroelectric properties of chemical deposited PZT thin films. Mater. Res. Soc. Symp. Proc. 2002 688 351-356... 

It has been reported that the dielectric constant of thin BST films decreases with decreasing film thickness when metal electrodes are adopted even without any interfacial non-perovskite material. This is due to the intrinsic interfacial low dielectric layer that originates from the termination of the chemical bonding of the perovskite structure at the interfaced. The large dielectric, polarizability of the perovskite can not penetrate into the metal layer due to the extremely high carrier concentration of the metal. 

In the catalytic partial oxidation of methane to produce syngas the use of permselective dense perovskite membranes avoids (or minimizes) the need of air separation, the most costly step in the process. Although both these O2- and H2-permeoselective membranes (based on perovskites or thin supported Pd-based dense films, respectively) have still to be further developed for commercial applications the outlook appears quite interesting for intensifying various large chemical processes. 

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