Chemistry of inorganic compounds – Rare earth compound
Patent
1996-11-14
1998-10-20
Straub, Gary P.
Chemistry of inorganic compounds
Rare earth compound
423608, C01F 1700, C01G 2502
Patent
active
058242783
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a process for producing precipitates of a perovskite type complex oxide, for example, a process for forming a thin film of a perovskite type complex oxide on the surface of a substrate or precipitating said complex oxide in a liquid, more specifically to a process for producing precipitates of said complex oxide from an aqueous solution, for example, a process for forming the precipitates as a thin film on the surface of a substrate.
BACKGROUND ART
Perovskite type complex oxides, particularly rare earth transition metal perovskite, rare earth 3B group metal perovskite and alkaline earth transition metal perovskite type complex oxides are excellent in heat resistance and corrosion resistance and also have high oxide ion conductivities and electronic conductivities, and further, in some of the complex oxides, superconductivity is generated at relatively high temperature so that they have been used as an electrolyte and an electrode of a fuel cell, an oxygen sensor, an oxygen-enrich membrane, a heating element, a dielectric material, a magnetic material, a superconductor, etc. Also, they have oxidation-reduction catalystic ability so that they have been also used as a catalyst. In these uses, in order to make moving distances of electrons and ions smaller to heighten electric conductivity and sensitivity or heighten a gas permeation amount; or in order to obtain a wide surface area or contact area, or in order to save weight, it has been desired to form a thin uniform film or, depending on the use, precipitates existing dispersedly on the surface of a substrate, easily on the surfaces of various substrates.
As a method for forming such an oxide thin film, there may be mentioned methods such as CVD, ion plating, sputtering, etc. However, in these methods, not only a special expensive apparatus is required, but also formation of a thin film having a large area and formation of a thin film on the surface of a substrate having a complicated shape are difficult, in particular, a thin film required for a large fuel cell cannot be obtained easily.
Therefore, it has been attempted that a solution of a compound containing metal elements constituting a perovskite type complex oxide is coated on a substrate, and a thin film of said complex oxide is formed by oxidation. For example, in Japan Ceramics Society, Annual meeting in 1994 (Nagoya), Lecture previous manuscripts 3G04, Oya et al. have formed a perovskite type complex oxide thin film of Ln(Cr,Mn)O.sub.3 by using a solution obtained by dissolving the respective 2-ethylhexanoates of rare earth elements, chromium and manganese in isopropanol, as a coating solution, adding diethanolamine thereto and producing a thin film on the surface of a silica glass substrate by dip coating and carrying out heat treatment at 800.degree. C.
However, in such a method, there are problems that there is a limit in formation of precipitates on the surface of a substrate having a large area or a complicated shape, it is necessary to crystallize an oxide coated on a substrate by heating, there is possibility that heat shrinkage and deformation are caused during heating, and some substrates cannot stand such heating.
On the other hand, in Japanese Provisional Patent Publication No. 58635/1993, there has been disclosed a method in which a substrate is soaked in an aqueous solution containing lead ions, hexafluorotitanic acid ions and boric acid ions to form a complex oxide thin film of titanium and lead on the surface of said substrate. Here, as a lead source, lead chloride, lead acetate or lead nitrate is used. A PbTiO.sub.3 thin film obtained by this method on the surface of the substrate has a pyrochlore type crystal structure. In order to convert this film into perovskite type PbTiO.sub.3, a step of carrying out heat treatment at 300.degree. to 900.degree. C. is further required.
An object of the present invention is to provide a process for producing perovskite type complex oxide precipitates, in which, by using a simple apparatus, precipita
REFERENCES:
patent: 5433531 (1995-07-01), Bosserman
Derwent Publications Ltd, AN 87-046179, Shirasaki Shinichi, "Production of easily sintering perovskite raw material powder by powder dispersing" Abstract of JP 62 003 005 A (1987).
Derwent Publications Ltd., AN 93-012008, Dexi Shigeto, Production of thin oxide film, Abstract of JP 04 338 136 A (1992).
Hoya Corporation
Straub Gary P.
Takeshi Yao
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