JP4086219B2 - High purity bismuth tris (β-diketonate) and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a bismuth compound suitable as a raw material for forming a bismuth-containing ferroelectric thin film or an oxide high-temperature superconductor thin film by a CVD method and a method for producing the same.
[0002]
[Prior art]
Ferroelectric thin films such as SrBi ₂ Ta ₂ O ₉ , Bi ₃ Ti ₄ O ₁₂ , Bi _3.25 La _0.75 Ti ₃ O ₁₂ and Bi ₂ Sr ₂ CaCu ₂ O, which are dielectric materials containing bismuth oxide. Attempts have been made to produce oxide superconductor thin films such as ₈ by the CVD method. In this case, triphenyl bismuth, trimethyl bismuth, and tritertiary myroxy bismuth have been studied as bismuth raw material compounds, and bismuth tris (dipivaloylmethanate) (hereinafter referred to as Bi (dpm) ₃ ) is Few. However, when the other elemental compound is a dpm salt, Bi (dpm) ₃ is preferably employed so that ligand exchange with the bismuth compound does not occur. However, conventional Bi (dpm) ₃ is not preferable because it has low volatility and thermal stability and has many impurities such as Na and Cl. When these impurities are contained in a large amount, there are problems that the leakage current of the ferroelectric increases, the defects increase, and the durability decreases.
[0003]
The production method and physical properties of conventional Bi (dpm) ₃ will be described below.
MC. Massiani et al. Polyhedron Vol. 10,437 (1991) extracted white precipitates formed by reacting BiCl ₃ and Na (dpm) in THF solvent with hexane or dichloromethane, and sublimated and separated unreacted Na (dpm) under high vacuum. Then, sublimation was performed at 110 ° C. and 4 × 10 ⁻⁴ Torr to obtain Bi (dpm) ₃ . The melting point of this was 78 ° C., and an attempt was made to sublime at 110 ° C. in an ampoule in order to obtain a single crystal, but it was thermally decomposed. Therefore, Bi (dpm) ₃ is described as being thermally unstable and difficult to sublimate.
S. Yuhya et al. Mol. Cryst. Liq. Cryst. Vol. 184, 231 (1990) describes that Bi (dpm) ₃ was thermally decomposed to Bi ₂ O ₃ without volatilization.
[0004]
On the other hand, recently US5859274 claims an anhydrous monomer Bi (dpm) ₃ . Its melting point is 139 ° C. The production method of reacting Na (dpm) and BiCl ₃ in a neutral solvent such as octane, THF, toluene in an oxygen-free atmosphere is claimed. For example, a recrystallization method is described as a purification method. However, the yield of Bi (dpm) ₃ thus obtained and the impurity concentration of Na and Cl are not described. In addition, although TGA of [Bi (dpm) ₃ ] ₂ which is a dimer is disclosed, TGA of monomer Bi (dpm) ₃ of the present invention is not disclosed. When Na (dpm) and chloride are used as raw materials, it is usually difficult to make the product Na and Cl impurity concentrations on the order of ppm even after purification by recrystallization or sublimation.
[0005]
The present inventor synthesized Bi (dpm) ₃ by the reaction of Na (dpm) and BiCl ₃ and attempted purification by recrystallization or sublimation. The yield of the final purified product was as low as 0 to 20%, and Na and Cl were contained in an amount of 30 to 100 ppm, and it was difficult to say that the purity was high.
[0006]
[Problems to be solved by the invention]
An object of the present invention is to provide high-purity bismuth tris (β-diketonate) having an impurity concentration of Na, K, Cl, and Br of 5 ppm or less. Furthermore, this invention is providing the manufacturing method of the compound.
[0007]
[Means for Solving the Problems]
The present invention is a high-purity bismuth tris (β-diketonate) characterized in that Na, K, Cl, and Br are each 5 ppm or less as impurity concentration.
The present invention is a method for producing this high-purity bismuth tris (β-diketonate), in which bismuth tritertiary myroxide and β-diketone are reacted in an organic solvent, and then the solvent, by-products and unreacted substances are distilled off. And then purifying by evaporation or sublimation under reduced pressure.
The present invention is high-purity bismuth tris (dipivaloylmethanate) having an impurity concentration of Na, K, Cl, and Br of 5 ppm or less.
The present invention is a method for producing this high-purity bismuth tris (dipivaloylmethanate), in which bismuth tritertiary myroxide and dipivaloylmethane are reacted in an organic solvent, and then the solvent, by-product, The reaction product is distilled off and then purified by evaporation or sublimation under reduced pressure.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
As the Bi source of the present invention, bismuth tritertiary myroxide Bi (OC (CH ₃ ) ₂ C ₂ H ₅ ) ₃ (hereinafter referred to as Bi (OtAm) ₃ ) is used. Bi (OtAm) ₃ is a monomer, and has a melting point of 90 ° C., a vapor pressure of 0.1 Torr at 87 ° C., and is almost the only bismuth alkoxide capable of being purified by distillation. By performing distillation purification, Na, K, Cl, and Br can be easily set to the ppm order as impurity concentrations.
[0009]
Bi (OtAm) ₃ is produced by the following two methods.
M.M. A. Matchett, M.M. Y. Chiang, W. E. Buhro, Inorg. Chem. Vol. 29, (1990) 360 is reacted with dimethylaminobismuth Bi (N (CH ₃ ) ₂ ) ₃ and tertiary-amyl alcohol HOC (CH ₃ ) ₂ C ₂ H ₅ and then sublimated to yield 90 Bi (OtAm) ₃ is obtained at% or more.
The present inventors react with bismuth bromide BiBr ₃ and sodium (tertiary miloxide) Na (OtAm), and then distill to obtain Bi (OtAm) ₃ having a yield of 70% or more and high purity. Developing a method.
[0010]
Bismaster chaributoxide [Bi (OC (CH ₃ ) ₃ ) ₃ ] is a monomer and has a high vapor pressure, but is not suitable as a raw material of the present invention because it has a melting point of 150 ° C. and is difficult to purify by distillation.
Since bismuth isopropoxide [Bi (OCH (CH ₃ ) ₂ ) ₃ ] and bismuth ethoxide [Bi (OC ₂ H ₅ ) ₃ ] are multimers, they have low vapor pressure, are difficult to purify by distillation, and have high purity. Is hard to get. Even if bismuth isopropoxide or bismuth ethoxide is reacted with dipivaloylmethane C ₁₁ H ₂₀ O ₂ (hereinafter referred to as dpmH), it is thermally decomposed in the evaporation purification step of Bi (dpm) ₃ , and almost Bi. (Dpm) ₃ could not be obtained. This is because bismuth isopropoxide or bismuth ethoxide is not a monomer, so it is difficult to completely replace the alkoxide group with dpmH, or because impurities Na and Cl promote thermal decomposition, It is unknown. In any case, bismuth isopropoxide and bismuth ethoxide cannot be used as the raw material of the present invention.
[0011]
As the β-diketonate of the high-purity bismuth tris (β-diketonate) of the present invention, dipivaloylmethanate (= 2,2,6,6-tetramethyl-3,5-heptanedionate), 2,6 -Dimethyl-3,5-heptanedionate, 2,2,6,6-tetramethyl-3,5-octanedionate, 2,2,6-trimethyl-3,5-heptanedionate, 6-ethyl- 2,2-dimethyl-3,5-octanedionate and the like.
[0012]
As the reaction solvent, inert organic solvents such as toluene and octane can be used.
The reaction conditions are about 100 to 120 ° C. and 2 to 10 hours. Most preferably, the by-produced tersialia alcohol can be distilled by reactive distillation. However, if the charge molar ratio of dpmH / Bi (OtAm) ₃ is set to 3.3 to 5 higher than 3, Bi-OtAm will not remain unreacted.
After the reaction, the solvent and by-produced tersialia alcohol are distilled off at normal pressure, and unreacted dpmH and the like are distilled off under reduced pressure. When the remaining product is charged into an evaporation tube and the heating bath is brought to about 140 ° C. under 0.1 Torr, the product melts and evaporates at 150 to 170 ° C. and precipitates as crystals on the air-cooled tube wall. It is a colorless (white) crystal and the yield is as high as 70% or more. The phenomenon that the thermal decomposition proceeds during the evaporation and the yield is greatly reduced does not occur. Sublimation purification can be carried out under higher vacuum.
Bi (dpm) ₃ obtained by evaporation or sublimation as described above is vaporized once and does not contain any non-volatile content, so it is optimal as a raw material for CVD. It is essential for the solution flash method that everything is evaporated.
[0013]
The impurity of Bi (dpm) ₃ obtained in Example 1 is
Na 2ppm
K <1ppm
Cl 1ppm
Br 1ppm
The purity was small and high.
The TG-DTA is shown in FIG.
The measurement conditions are as follows.
Sample weight 26.5mg under Ar1 atmospheric pressure
Temperature increase rate 10.0 deg / min
[0014]
[Figure 1]
[0015]
From this figure, the melting point is about 140 ° C. Weight loss started at around 200 ° C, 50% at 330 ° C, 93.5% at 340 ° C and constant. In TGA under 1 atm, the evaporation temperature has to be high, and as a result, a little thermal decomposition occurs, but under a reduced pressure of about 10 Torr, the evaporation is completed at a temperature lower than the temperature at which the thermal decomposition occurs. Therefore, the weight loss should be 100%. As can be seen, the phenomenon of low thermal stability as described in conventional literature does not occur. This is presumed to be because Bi (dpm) ₃ of the present invention has high purity both in terms of molecular structure and chemical purity.
[0016]
[Example 1]
Production of high-purity Bi (dpm) ₃ A 300 ml four-necked flask equipped with a reflux condenser, a thermometer, and a stirrer was evacuated to an argon atmosphere, charged with 180 ml of toluene, and then 20.2 g (43 mmol) of Bi (OtAm) ₃ ) And dipivaloylmethane dpmH (32 g, 174 mmol) were charged. Next, the temperature was raised with stirring, and the reaction was carried out for 6 hours while heating under reflux. Next, under 1 atm, the solvent, by-product tert-amyl alcohol and the like were distilled off, and finally, volatile components such as unreacted dpmH were distilled off at 1 Torr and 120 ° C. The pale yellow solid in the flask was collected, pulverized, and charged into an evaporation tube. When the pressure is reduced to 0.3 Torr and the temperature is raised, this powder melts at a heating bath temperature of around 140 ° C. When the temperature is further raised, the powder evaporates from around 165 ° C and white crystals appear on the air-cooled tube wall. As a result, most of them were evaporated up to 175 ° C. The white crystals were 23.5 g (31 mmol) and the yield was 72%.
The crystals were wet-decomposed and quantified by ICP emission analysis. As a result, the Bi content was 26.8% (calculated value 27.5%).
Furthermore, as a result of impurity analysis,
Na 2ppm
Cl 1ppm
K <1ppm
Br 1ppm
Fe 1ppm
Si 4ppm
And high purity.
[0017]
【The invention's effect】
As a bismuth raw material for producing a ferroelectric thin film such as SrBi ₂ Ta ₂ O ₉ or an oxide superconductor thin film such as Bi ₂ Sr ₂ CaCu ₂ O ₈ by the CVD method, it has high thermal stability when supplied. Bi (dpm) ₃ of high purity that sublimates can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing measurement results of Bi (dpm) ₃ by TG-DTA.

Claims (4)

High-purity bismuth tris (β-diketonate) characterized in that Na, K, Cl, and Br each have an impurity concentration of 5 ppm or less. The reaction is characterized in that bismuth tritertiary myroxide and β-diketone are reacted in an organic solvent, then the solvent, by-products and unreacted substances are distilled off, and then purified by evaporation or sublimation under reduced pressure. 1. A method for producing high-purity bismuth tris (β-diketonate). The high purity bismuth tris (dipivaloylmethanate) according to claim 1, wherein the β-diketonate is dipivaloylmethanate. It is characterized by reacting bismuth tritercia triamyloxide and dipivaloylmethane in an organic solvent, then distilling off the solvent, by-products and unreacted substances, and then purifying by evaporation or sublimation under reduced pressure. The manufacturing method of the high purity bismuth tris (dipivaloylmethanate) of Claim 3.

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