Composition using Schiff base copper complex for preparing compound metal oxides

A composition for forming a compound metal oxide of a specific composition and a process for preparing said compound oxide are disclosed. The composition comprises an alkoxide of a rare earth metal, an alkoxide of an alkaline earth metal and an organic acid salt of an organic complex of copper. The process comprises refluxing said composition for reaction and thermally decomposing the reaction product. Also a film-forming composition for forming a thin layer of a compound metal oxide is disclosed. Said film-forming compound comprises the above-mentioned composition plus a film forming resin and an organic solvent.

FIELD OF THE INVENTION 
This invention relates to a composition and a process for preparing 
compound metal oxides. More specifically, this invention relates to 
composition and a process for preparing compound metal oxides which have 
specific compositions and are useful as superconductor materials, oxygen 
sensors, catalysts, etc. Especially, compound metal oxides of a rare earth 
metal, an alkaline earth metal and copper of specific compositions have 
recently drawn attention as superconductor materials which exhibit 
superconductivity at temperatures over 77 K. 
BACKGROUND OF THE INVENTION 
As methods for preparing compound metal oxides, there have been known 
processes in which 
(1) Oxides, carbonates or oxalates of the respective component metals are 
physically mixed in the state of powder, whereafter the mixture is fired 
and pulverized; 
(2) Water-soluble salts such as nitrates of the respective component metals 
are dissolved in water to make a homogeneous solution, the metals are 
coprecipitated as insoluble hydroxide, carbonate, oxalates, etc. by 
addition of hydroxide ions, carbonate ions, oxalate ions, etc. the 
precipitate is collected and fired into a compound metal oxide, etc. 
In process (1), powders are mixed and fired. Therefore, the reaction 
proceeds from the contact boundaries of the powder particles and there 
remain some unreacted portions. Thus the product often deviates in 
composition from the intended exact composition. 
In process (2), the condition of precipitation differs from metal to metal. 
Therefore, a precipitate containing a rare earth metal, an alkaline earth 
metal and copper, for instance, in the content ratio exactly the same as 
the content ratio in the solution is not always formed. Therefore, a 
compound metal oxide of a composition different from that intended is 
inevitably formed. 
The above-mentioned problems can be solved by heating for reaction a 
composition comprising an alkoxide of a rare earth metal, an alkoxide of 
an alkaline earth metal and an organic acid salt, a .beta.-diketone 
complex, a .beta.-ketoester complex or a Schiff base chelate complex of 
copper, optionally containing an organic solvent, and thermally 
decomposing the reaction product. 
SUMMARY OF THE INVENTION 
This invention provides a composition for preparing a compound oxides of a 
rare earth metal, an alkaline earth metal and copper in a specific content 
ratio, which contains: 
(1) an alkoxide of a rare earth metal, 
(2) an alkoxide of an alkaline earth metal, and 
(3) an organic acid salt, a .beta.-diketone complex, a .beta.-ketoester, 
complex or a Schiff base chelate complex of copper 
in such content ratio that the amount of the rare earth metal in said 
alkoxide, the amount of the alkaline earth metal in said alkoxide and the 
amount of copper in said organic acid salt or complex correspond to the 
amounts of these metals in the object compound metal oxide, and further 
optionally containing 
(4) an organic solvent. 
This invention also provides a process for preparing a compound metal oxide 
of a rare earth metal, an alkaline earth metal and copper in a specific 
content ratio, which comprises: 
heating for reaction a composition which contains: 
(1) an alkoxide of a rare earth metal, 
(2) an alkoxide of an alkaline earth metal, and 
(3) an organic acid salt, a .beta.-diketone complex, a .beta.-ketoester, 
complex or a Schiff base chelate complex of copper, 
in such content ratio that the amount of the rare earth metal in said 
alkoxide, the amount of the alkaline earth metal in said alkoxide and the 
amount of copper in said organic acid salt or complex correspond to the 
amounts of these metals in the object compound metal oxide, and optionally 
containing 
(4) an organic solvent; 
thermally decomposing the formed reaction product. 
Further, this invention provides a film-forming composition which is useful 
for forming thin film of the compound metal oxide. Said composition 
comprises the above-described composition to which a film-forming resin 
and an organic solvent are added. 
In the present invention, the term "rare earth metal" means Sc, Y, La, Ce, 
Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. 
In the present invention, the term "alkaline earth metal" means Be, Mg, Ca, 
Sr and Ba. 
In the present invention, alkoxides of rare earth metals are represented by 
the formula R(OR.sup.1) (OR.sup.2) (OR.sup.3), wherein R stands for one 
rare earth metal, R.sup.1 R.sup.2 and R.sup.3 are the same or different 
C.sub.1 -C.sub.6 alkyl groups. 
In the present invention, alkoxides of alkaline earth metals are 
represented by the formula A(OR.sup.1) (OR.sup.2), wherein A stands for an 
alkaline earth metal and R.sup.1 and R.sup.2 are the same or different 
C.sub.1 -C.sub.6 alkyl groups. 
In the present invention, specific examples of the organic acid salts of 
copper are formate, propionate, acetate, citrate, gluconate, tartrate, 
oxalate, etc. 
.beta.-Diketone complexes and .beta.-ketoester complexes of copper are 
represented by the formula Cu(OR).sub.l (X).sub.m, wherein R is a C.sub.1 
-C.sub.6 hydrocarbyl group, l=0 or 1; m=1 or 2 and l+m=2; and X stands for 
a group represented by the formula 
##STR1## 
wherein R.sup.1 and R.sup.2 are respectively a C.sub.1 -C.sub.6 
hydrocarbyl group, and R.sup.3 is a hydrogen atom or a C.sub.1 -C.sub.6 
hydrocarbyl group. 
Schiff base chelate complexes of copper are represented by the formula 
##STR2## 
wherein R.sup.1 and R.sup.3 is --CH.sub.3, --C.sub.2 H.sub.5, C.sub.6 
H.sub.5 or --CF.sub.3 ; R.sup.2 is --H, --CH.sub.3, --C.sub.2 H.sub.5, 
--C.sub.6 H.sub.5 or --CF.sub.3 ; and B is --(CH.sub.2).sub.n --, wherein 
n is 2, 3 or 4, 
##STR3## 
Of these copper complexes, Schiff base chelate complexes are most 
preferable, because the solubility thereof in organic solvents is highest 
and thus compound metal oxides of higher copper content can be prepared. 
In the present invention, almost all organic solvents can be used if they 
dissolve the above-mentioned alkoxides, copper salts, and the 
above-mentioned copper complexes. 
Specific examples of such solvents are esters such as ethyl acetate, ethyl 
propionate, etc.; alcohols such as methyl alcohol, ethyl alcohol, n- and 
iso-propyl alcohol, n-, iso- and tert-butyl alcohol, octyl alcohol; 
aliphatic saturated hydrocarbons such as pentane, cyclohexane, 
methylcyclohexane, etc.; aromatic hydrocarbons such as benzene, toluene, 
xylene, etc.; cycloethers such as tetrahydrofuran, dioxane, etc.; 
cellosolves such as methyl cellosolves, ethyl cellosolve, butyl 
cellosolve, etc.; formamides such as dimethylformamide, diethylformamide, 
etc.; sulfoxides such as dimethyl sulfoxide, diethyl sulfoxide, etc.; 
ketones such as acetone, methylethylketone, etc. The solvents can be used 
singly or in combination. 
The solvent should preferably be well dried and free from carbon dioxide 
gas. 
The composition of the present invention can be prepared by simply mixing 
the component compounds each in an predetermined amount usually together 
with a suitable amount of a suitable solvent. In order to assist 
dissolution of the components, the mixture can be heated, but the 
temperature should not exceed 100.degree. C. to avoid decomposition or 
premature reaction of the components. 
The process of the present invention is carried out as follows. The above 
composition is heated usually with a solvent added usually preferably at 
the reflux temperature. A small amount of water can be added so as to 
promote the reaction. It is not yet well understood what is formed by this 
reaction. However, it is sure that a precursor substance for the compound 
metal oxide is formed. 
The thermal decomposition of this reaction product mixture is preferably 
conducted in the sprayed condition. For instance, the reaction product 
mixture can be sprayed into a heated quartz reaction tube through a 
pressure nozzle or a two-fluid nozzle. The reaction product mixture can be 
dropped onto a rapidly rotating disc and the formed fine drops are 
introduced into a high temperature reaction zone. Or, supersonic wave can 
be applied to the reaction product mixture so as to produce mist of the 
mixture, which is then introduced into a high temperature reaction zone. 
Thus the reaction product is thermally decomposed into the object compound 
oxide in the form of powder. Or, the reaction product mixture can be 
applied on the surface of a substrate and thermally decomposed. Thus a 
film of a compound metal oxide, a superconductive layer for instance, can 
be formed. 
The thermal decomposition of said reaction product mixture requires a 
temperature not lower than 500.degree. C. But on the other hand, it is 
preferred to carry out the decomposition at a temperature not higher than 
1000.degree. C. If the decomposition occurs at a temperature in excess of 
1000.degree. C., thermal decomposition starts from the surface of the 
drops and polymerization of oxide is incomplete and thus hollow particles 
are formed. At temperatures below 500.degree. C., the thermal 
decomposition is insufficient and some reaction product remains although 
polymerization of the oxides proceeds. 
As mentioned above, the reaction product mixture can be applied on the 
surface of a substrate and thermally decomposed to form a compound metal 
oxide. In this case, cellulosic polymers such as methyl cellulose, ethyl 
cellulose, nitro cellulose, ethylhydroxyethyl cellulose, etc. are 
preferred as film-forming resins. One or more of these resins are added to 
the composition of the present invention. Benzene, toluene, methyl 
cellosolve, ethyl cellosolve, etc. are preferred solvents.