KR101002702B1 - A hydrothermal synthesis method of perovskite nano-powder - Google Patents

Abstract

The present invention is to select a raw material that can prevent the generation of secondary phase to synthesize the powder, and by adding a washing process to improve the molar ratio of the synthetic powder perovskite can effectively produce a multi-component perovskite-type nanopowder The present invention relates to a hydrothermal synthesis method of nano-powders.
According to the hydrothermal synthesis method of the perovskite-type nanopowder according to the present invention, the single-phase multicomponent perovskite-type nanopowder having no secondary phase can be produced more economically.

Description

A hydrothermal synthesis method of perovskite nano-powder

The present invention relates to a hydrothermal synthesis method of a perovskite-type nanopowder, and more particularly, to select a raw material capable of preventing the formation of a secondary phase to synthesize a powder and to improve the molar ratio of the resulting powder. The present invention relates to a hydrothermal synthesis method of perovskite-type nanopowders which can effectively produce multicomponent perovskite-type nanopowders.

Nanopowders can be applied to ion-conducting ceramic separators or electrolyte thin film systems in solid-state fuel cell systems that allow oxygen to pass through, and can be made into dense membranes, such as multi-layer ceramic capacitors (MLCCs). It is also used to make slurry materials for coating dielectric thin films of layers.

In addition, it can be applied as a source material to membranes, catalysts, sensors, environmental detectors for syngas production. For example, in order to coat a thin film layer having a thickness of several micrometers, the particle size of the raw material powder for preparing the thin film should be smaller than micro, and more preferably, the more uniform the fine nanopowder is synthesized.

When synthesizing the nanopowder, the composition of the molar ratio between metals in the synthetic powder particles is very important. For example _{, in} the case of barium titanate (BaTiO ₃₎ , if the atomic ratio of barium (Ba) and titanium (Ti) does not maintain 1, Ba ₂ Secondary phases such as TiO ₄ , BaTi ₂ O ₅ and BaCO ₃ are generated to act as a cause of lowering the dielectric constant. Even if secondary phases are not produced, excess Ba acts as an inhibitor against sintering and excess Ti acts as a sintering accelerator. This causes abnormal particle growth.

Abnormal particle growth is not only unsuitable for dispersing properties and optimal packing during wet dispersion, but also as a barrier to the growth of equiaxed particles during sintering as a final product, which creates large voids and cracks in the thin film layer, which negatively affects thin film production.

When the synthetic powder is used as an ion-conductive membrane material such as oxygen separation or SOFC, if a secondary phase is formed in the powder, the mixture deviates from the perovskite structure and blocks the passage of ions, thereby inhibiting the membrane's performance. If the different phases are generated due to the operating conditions of the separator operating at a high temperature of 600 ℃ or more, the thin film is damaged due to the difference in coefficient of thermal expansion.

Therefore, it is very important to control the metal molar ratio of the resultant powder of the synthesized perovskite material and to suppress the generation of the secondary phase.

The two-component or more perovskite-type powders such as BaTiO ₃ , LaFeO ₃ and La _1-x Sr _x Co _1-y Fe _y O _3-δ , which are the powders to be attempted in the present invention, are applied to a process requiring a thin film. More advantageous when synthesized into a powder.

In order to manufacture the powders, a high temperature firing method has been conventionally used in which an oxide or carbonate of a raw material component is mixed and reacted at a high temperature. However, the powder obtained by this method not only has a large average particle diameter, but also is not good in terms of particle size distribution, and since the powder is obtained in a coarse particle size according to a high temperature reaction, the powder is not uniform in shape, thereby slurrying or pasting the powder. If so, there is a problem that the dispersibility is not good.

In addition, the high temperature firing method has a limitation in thinning because impurities are easily introduced during the mixing of raw materials and the size of the synthesized particles is large. Due to these disadvantages, high purity can be obtained in terms of chemical quality, and the chemical composition can be made homogeneous. In addition, a liquid phase reaction method for controlling the microstructure of the sintered body has been developed and applied.

As the liquid phase reaction method, an organic acid synthesis method, an alkoxide method, or a sol-gel method is used, and in the case of a oxalate synthesis method using oxalic acid as an organic acid or a sol-gel method, homogenization of chemical composition is possible, but addition is performed to obtain a corresponding powder. Special crystallization heat treatment and grinding may be required. As such, the particles produced through the heat treatment and pulverization process easily retain coarse aggregates even after firing, and coarse aggregated particles are easily formed. Can be generated.

Furthermore, oxalic acid, malic acid, citric acid and the condensation functional groups included in the alkoxide method or the sol-gel method used in the organic acid synthesis method contain a large amount of hydrocarbon and are emitted from the powder in the form of CO ₂ during firing or sintering. BaCO ₃ , SrCO _3, etc. are generated by CO ₂ , and there is a disadvantage in that they exist in the secondary phase. In order to solve this problem, increasing the firing temperature can remove CO ₂ , but at least 1000 ° C. or more is required, so that the particle size may not be increased due to sintering. The particles produced in this way are therefore inadequate for forming ultra-thin ceramic films.

In order to solve the problems of the liquid phase reaction method, a hydrothermal synthesis method was developed, and in the 'method of preparing barium titanate powder' disclosed in Korean Patent No. 0542374, a hydrothermal synthesis method for maintaining a ratio of Ba / Ti to 1 is introduced. have. In this method, solubility was used to remove BaCO ₃ that may be present in the Ba raw material, but the amount of CO ₂ that could be absorbed in the solution or in the air was not taken into account when the Ba solution was added to the reactor. Thus, in trace amounts, Ba (OH) ₂ can be converted to BaCO ₃ .

Perovskite materials can be prepared by precipitation or coprecipitation using potassium hydroxide (KOH), sodium hydroxide (NaOH) or ammonia, but in this case the initial materials consist of chloride or nitrate. In addition, there is a problem that NO ₂ , Cl _2, etc. may occur when firing the precipitate, causing secondary phase contamination.

The present invention has been proposed to solve all the problems of the conventional method as described above, by using a hydrothermal synthesis method, by selecting a raw material that can prevent the formation of the secondary phase to synthesize the powder and the molar ratio of the resulting powder It is an object of the present invention to provide a hydrothermal synthesis method of perovskite-type nanopowders, which can effectively prepare a multi-component perovskite-type nanopowder by adding a washing process to improve the efficiency.

In the hydrothermal synthesis method of the perovskite-type nanopowder according to an embodiment of the present invention for solving the technical problem, the step of quantifying the titanium-containing hydroxide and barium-containing hydroxide so that the ratio of Ba / Ti is fixed to 1.01 to 1.02, Mixing the quantified titanium-containing hydroxide and the barium-containing hydroxide to form a slurry, hydrothermally reacting the slurry to form a primary barium titanate powder, washing the primary barium titanate powder, and washing the primary water Calcining the barium titanate powder to produce a perovskite-type nanopowder, wherein the nanopowder is tetragonal It is characterized by having a structure.

According to another embodiment of the present invention for solving the above technical problem, a method of hydrothermal synthesis of perovskite-type nanopowder includes La (OH) ₃ and Fe (NO ₃ ) ₃ .9H ₂ O, in which the ratio La / Fe is 1; Quantifying each so as to be fixed to, a step of making a slurry by mixing the quantified La (OH) ₃ and the Fe (NO ₃ ) ₃ · 9H ₂ O, making a primary powder by hydrothermally reacting the slurry, water washing Calcining the primary powder to prepare a perovskite-type nanopowder, wherein the nanopowder has a single phase structure free of impurities.

Hydrothermal synthesis method of a perovskite-type nanopowder according to another embodiment of the present invention for solving the technical problem, La (OH) _3, Sr (NO ₃ ) ₂ , Co (NO ₃ ) ₂ · 6H ₂ Quantifying O and Fe (NO ₃ ) ₃ .9H ₂ O to be fixed at La: Sr: Co: Fe = 0.6: 0.4: 0.2: 0.8, respectively, the quantified La (OH) _3, Sr (NO ₃ ) ₂ , Co (NO ₃ ) ₂ · 6H ₂ O and Fe (NO ₃ ) ₃ · 9H ₂ O to make a slurry, the hydrothermal reaction of the slurry to make a primary powder, firing the primary powder Preparing a perovskite-type nanopowder, wherein the nanopowder has a single phase structure free of impurities.

According to the hydrothermal synthesis method of the perovskite-type nanopowder according to the present invention, a single-phase multicomponent perovskite-type nanopowder without secondary phase is avoided by not using a hydrocarbon-containing raw material or a metal mineralizer (KOH, NaOH, etc.). There is an advantage that can be manufactured economically.

In addition, by optimizing the water washing process for controlling the molar ratio of the powder produced, there is an effect that can be prepared more simply and inexpensive nano powder of the desired composition or molar ratio.

FIG. 1 is a diagram showing Ba / Ti molar ratio and K-factor according to the number of times of washing of barium titanate hydrothermally synthesized at 150 ° C. with Ba 1% and Ba 2% excess.
2 is an electron micrograph showing the growth of particles when the powders hydrothermally synthesized at 150 ° C. in excess of Ba 1% and Ba 2% were washed with water and then calcined at 1000 ° C. FIG.
3 is a diagram showing K-factor change and particle size according to water washing of powders synthesized by excessively supplying Ba 1% and 2% at 180 ° C.
Figure 4 is a diagram showing the XRD results before and after firing according to the number of washing times of the powder synthesized at 150 ℃ by supplying an excess of 1%, 2% Ba.
5 is a view showing the XRD results of the powder produced by firing the LaFeO ₃ primary powder prepared by hydrothermal synthesis according to the firing temperature and time changes and the XRD results of the powder prepared by the high temperature baking method.
6 is an electron micrograph of a powder synthesized by a high temperature baking method and a LaFeO ₃ powder fired at 1000 ° C. for 5 hours after synthesis by a hydrothermal synthesis method.
7 shows La (OH) ₃ (99.9%, Aldrich Co.), Sr (NO ₃ ) ₂ (99 +%, Aldrich Co.), Co (NO ₃ ) ₂ · 6H ₂ O (98 +%, Aldrich Co. .), Fe (NO ₃ ) ₃ .9H ₂ O (98 +%, Aldrich Co.) was weighed in a composition ratio (La: Sr: Co: Fe = 0.6: 0.4: 0.2: 0.8) to a mixture of 1M concentration In the case of no addition of ammonia water and the addition of 8 M ammonia water after the preparation, the powders (primary powder) synthesized at 250 ° C. for 12 hours and the powder prepared by the addition of ammonia water were respectively added at 600 ° C. and 1000 ° C., respectively. It is a figure which shows the XRD result of the powder which baked by time.
8 shows La (OH) ₃ (99.9%, Aldrich Co.), Sr (NO ₃ ) ₂ (99 +%, Aldrich Co.), Co (NO ₃ ) ₂ .6H ₂ O (98 +%, Aldrich Co. .), Fe (NO ₃ ) ₃ .9H ₂ O (98 +%, Aldrich Co.) was weighed in a composition ratio (La: Sr: Co: Fe = 0.6: 0.4: 0.2: 0.8) to a mixture of 1M concentration It is an electron micrograph of the perovskite-type powder calcined at 1000 ° C. after the primary powder and primary powder which were hydrothermally synthesized without adding ammonia water.
FIG. 9 shows the XRD results of the primary powders hydrothermally synthesized at 450 ° C. with and without the addition of ammonia water (3 M), and the XRDs of the primary powders hydrothermally synthesized by adding 3 M ammonia at 400 ° C., respectively. It is a figure which shows a result.

Through the hydrothermal synthesis method of the perovskite-type nanopowder according to the present invention, it is possible to synthesize A _1-x A ' _x B _1-y B' _y O _3-δ type powder.

Where A and A 'are lanthanide or rare earth elements (elements between atomic number 57 (lanthanum) and atomic number 71 (ruthenium) in the Periodic Table of Elements, as specified by IUPAC), and B and B' are transition metals (elements) Group II or III metals belonging to the fourth cycle of the periodic table), including titanium, vanadium, chromium, manganese, iron, cobalt, nigel, copper and zinc.

Hereinafter, a method for preparing a multicomponent perovskite-type nanopowder using hydrothermal synthesis will be described in detail.

In the case of the metal nitrate, it can react with CO ₂ in the air to form carbonate as shown in Equation (1) below.

_{M (OH) 2 · xH 2} O + CO 2 → MCO 3 + (x + 1) H 2 O (1)

Here, it is a periodic table group 2 element containing M = Ba, Sr, etc.

In order to prevent this, it is possible to separate and quantify using solubility according to temperature, such as BaCO _3, and prepare a solution by weighing in a glove box filled with nitrogen without CO ₂ to prevent the formation of carbonate. In the case of small-capacity powder synthesis, absorption of CO ₂ can be neglected between the glove box and the solution injected into the reactor, but if the amount is large, the absorption can not be ignored. Possible dissolved CO ₂ should be considered.

In addition, since a small amount of water may be included when the raw material is deliquescent, the amount of M may be excessively supplied to 2% or less, more preferably 1% or less.

After the mixture is injected into the reactor according to the quantification, hydrothermal synthesis proceeds according to temperature, concentration, and pH change of the solution as follows.In the case of unreacted or excess material, the amount can be calculated through ICP analysis of the filtered supernatant. . For example, in the case of slurry reaction of a material such as BaTiO ₃ , hydrothermal reaction proceeds as shown in Equation (2) below.

Ba (OH) _{2 8} H ₂ O + TiO ₂ x (H ₂ O) → BaTiO ₃ + (x + 9) H ₂ O (2)

In the case of LaFeO ₃ to form a perovskite-type powder by the reaction as shown in the formula (3) below.

La (OH) ₂ + Fe (NO ₃ ) ₃ 9H ₂ O → LaFeO ₃ + xH ₂ O + 3 (NO ₃ ) ^- + yH ⁺ (3)

In the case of a two-component system, the reaction temperature may be reacted at 80 ° C. to 250 ° C. or lower, but an unreacted substance is present at 120 ° C. or lower, and preferably 150 ° C. to 250 ° C.

Finally, when the reaction is completed, the powder is washed with deionized water to remove excess unreacted ions and ions generated in the ammonia water remaining after the reaction. At this time, since a part of the metal may be eluted according to the washing method, the washing frequency is preferably set to 10 times or less when the molar ratio is initially adjusted.

In the case of BaTiO ₃ synthesis, when cooled to room temperature when unreacted, CO ₂ in the air may be absorbed to form BaCO ₃ , so that the reaction product is slowly cooled to remove the supernatant when it is about 50 ° C. to 60 ° C., followed by filtration to prepare a cake. do. At this time, it is washed with distilled water corresponding to the weight of the cake to remove the hydroxyl groups present in the cake. At the first washing, not only the hydroxyl group but also about 0.00384 mol of Ba ²⁺ ions per ₃ mol of BaTiO are eluted, and a smaller amount of Ba ² is increased as the number of washings increases. ⁺ Ions are eluted, but the continuous elution proceeds, so if the water washing more than 5 times, the molar ratio cannot be matched.

Also, in the case of perovskite powder containing Sr, Sr elutes with washing with water, and in order to control this, it is appropriate to wash with 10 times or less, preferably 5 times or less, to remove unreacted ions.

The primary powder obtained by washing with water can be calcined at an appropriate temperature to increase the crystallinity or change to a desired crystal system. In the case of BaTiO ₃ , the crystal system can be changed from a cubic to a tetragonal system by firing at 900 ° C to 1300 ° C. In 1100 ° C to 1250 ° C is preferable because the transition to tetragonal occurs small and sintering occurs at 1200 ° C or more resulting in excessive grain growth.

In case of LaFeO ₃ or La _1-x Sr _x Co _1-y Fe _y O _3-δ powder, Fe ₂ O ₃ crystal structure is shown in the case of primary powder, but when firing at 900 ℃ to 1300 ℃, It is changed to a skye crystal system, and the powder of 500 nm or less can be prepared through such a washing and firing process.

Hereinafter, the present invention will be described in more detail based on examples. The following examples are only one of the most preferred embodiments of the present invention, it is obvious that the protection scope of the present invention is not limited thereto.

Example 1

All experiments of Example 1 were performed using a 500 ml autoclave autoclave, and the titanium-containing hydroxide had a specific surface area of 335 m ² / g and a weight loss of 16 kWh 2% due to loss of ignition.

Barium hydroxide was quantified by removing BaCO ₃ at a solubility difference at 80 ° C. using an industrial 98% purity raw material. Ba / Ti was weighed to fix 1.01 or 1.02 to correct for BaCO ₃ that could be generated during the reaction. That is, the reaction was performed by adding 0.01 mol and 0.02 mol of Ba, and the effect of excess Ba of the powder produced and the effect of washing with the produced powder were examined.

After dissolving Ba (OH) ₂ · 8H ₂ O at 80 ° C. for 30 minutes, the Ti sample was introduced into a high pressure reactor (or at the same time after injection), and barium titanate was prepared by changing the reaction temperature to 150 and 180 ° C. Analyzed as well.

1) crystal structure

In order to investigate the crystal phase and the secondary phase of the hydrothermally synthesized sample under each condition, X-ray diffraction analysis was performed by powder method. The X-ray diffractometer used Rigaku powder diffractometer model D / Max 2200-Ultima ^plus system, and XRD in 2θ 20 ~ 70 ㅀ at 0.02 step using CuK _α1 light source (λ = 1.54041Å) of 30kV, 40mA The analysis was performed.

2) tetragonal transition

In the present invention, the transition of the tetragonal system according to the firing temperature was quantified using a k-factor, and the k-factor representing the degree of transition between the tetragonal system and the cubic system can be expressed by the following equation (4).

3) particle shape

The morphology change and particle size of the hydrothermally synthesized sample powder under each reaction condition were observed by scanning electron microscopy (SEM). After applying a small amount of sample to the carbon tape, the Au coating with an Ion Coater was observed at 20,000 times magnification.

4) Ba / Ti molar ratio

The molar ratios of metals are largely wet and X-ray Fluorescence Spectrometer (XRF), and barium titanate powder is dissolved by adding sulfuric acid, and then formed by barium sulfate and titanium-cuperon precipitation. There is an error due to contamination in the recent years and has been replaced by the XRF method which can be analyzed simply.

In the present invention, a glass bead was made by using five standard materials of Ba / Ti = 0.994, 0.996, 0.998, 1.000, and 1.002 purchased from Japan High Purity Chemistry, and the correction lines were obtained and analyzed. The analysis was performed using Philips PW2404 (manufactured by Philips Analytical BV) of the Scientific Research Institute.

FIG. 1 shows a case of Ba / Ti = 1.01, in which a Ti raw material is mixed with 2.0 mol and a Ba raw material with 2.02 mol (an excess of Ba 1%, Ba 1% on the chart) and 2.0 mol of a Ba raw material and a Ba raw material. In the case of Ba / Ti = 1.02 mixed with 2.04 mol (Ba 2% excess, Ba 2% on the chart), the hydrothermally synthesized powder was filtered at 150 ° C. to prepare a cake, and washed with distilled water corresponding to the cake weight. It shows Ba / Ti ratio and K-factor according to the number of times.

As shown in FIG. 1, the Ba / Ti ratio gradually decreases as the number of washes increases in both 1% and 2% Ba excess synthetic powders, and in the case of 1% excess Ba between 2 and 3 times, Ba 2% In case of excess, the Ba / Ti ratio is 1 between 6 and 7, respectively. However, it can be seen that the K-factor has the highest value when the water is washed one or two times more than the number of times the water washes Ba / Ti = 1, not the number of water washes Ba / Ti is one. This is because the BaCO ₃ contained in the Ba raw material was not removed when barium was supplied.

Therefore, the amount of BaCO ₃ which is not included in the calculation of Ba concentration by ICP is present in the powder, so it is considered that the removal of this portion increases the K-factor. The value of K-factor is about 6.94 at 4 times of water at 1%, and 6.35 at 9% at 2%. This K-factor value is more than the value suggested by Korean Patent No. 0542374 (Ba = Ti = 2.5 M, 6 hour reaction, K-factor 6.94) because it is obtained by reacting for 2 hours at a lower concentration of Ti = 2.0 M. It can be seen that the excellent performance.

FIG. 2 is a SEM photograph showing the growth of particles when the powders hydrothermally synthesized at 150 ° C. in excess of Ba 1% and Ba 2% were washed with water and then calcined at 1000 ° C. FIG.

Referring to FIG. 2, in the case of the 1% Ba excess reaction, when firing without washing with water, 200 nm primary powder and calcined powder are present together, resulting in abnormal grain growth. As this eluted more, it was confirmed that the grain shape was unevenly grown.

On the other hand, in the case of powder washed four times, it can be seen that the particles grow evenly and the size is about 400 nm. This even grain growth is thought to result in higher K-factor. Similarly, 2% of synthetic powder shows abnormal grain growth without washing with water, and SEM photographs with 9 times of washing with the best K-factor show the most even particle size distribution.

Figure 3 shows the K-factor change and particle size according to the water washing of the synthesized powder by supplying an excess of 1% Ba, 2% at 180 ℃. What is unique is that at 180 ° C, the K-factor value does not increase or decreases with washing frequency.

This shows that the powder synthesized at 180 ° C has a high crystallinity and is not easy to remove Ba by washing with water, and even when the particle size is 2% and 1%, evenly grown particles do not show uniform particle growth and are measured by SEM. It can be seen that one particle size does not increase to the 400 nm level.

Therefore, when synthesize | combining at 180 degreeC, since elution of Ba by water washing is small, it is advantageous to synthesize | combine Ba / Ti ratio exactly to 1 as much as possible.

Figure 4 shows the XRD results before and after firing according to the number of times of washing the powder synthesized at 150 ℃ by supplying an excess of 1%, 2% Ba. The barium titanate powder before firing exhibits a typical perovskite simple cubic lattice, and all the powders calcined at 1000 ° C are tetragonal. In addition, the K-factor of the powder washed four times and five times is increased compared to the powder not washed with water after synthesis, but the 14-washed powder has a Ba / Ti molar ratio of deviated from 1, indicating that the K-factor decreases again. .

Example 2

The experiment of Example 2 was also performed using a 500 ml autoclave autoclave and the raw materials used were reagent grade La (OH) ₃ (99.9%, Aldrich Co.), Fe (NO ₃ ) ₃ .9H ₂ O. (98 +%, Aldrich Co.) was weighed in a ratio of composition (1: 1) to prepare a mixture of 1M concentration, and then hydrothermally synthesized at 250 to 450 ° C. for 2 hours to prepare a bicomponent perovskite powder.

In order to investigate the crystal phase and the secondary phase of the hydrothermally synthesized LaFeO ₃ sample under each condition, X-ray diffraction analysis was performed by powder method. The X-ray diffractometer used Rigaku powder diffractometer model D / Max 2200-Ultima ^plus system, and XRD in 2θ 20 ~ 70 ㅀ at 0.02 step using CuK _α1 light source (λ = 1.54041Å) of 30kV, 40mA The analysis was performed.

In addition, the morphology change and particle diameter of the hydrothermally synthesized sample powder were observed by scanning electron microscope (SEM). After applying a small amount of sample to the carbon tape, the Au coating with an Ion Coater was observed at 20,000 times magnification. At all reaction temperatures, XRD of the powder obtained after synthesis and the powder after washing show only peaks of Fe ₂ O ₃ powder (JCPDS No. 33-0664).

LaFeO ₃ powder is not formed even when 1 M to ₃ M of ammonia water is added at 250 to 450 ° C., and the firing temperature is also fired at 600 ° C. for 10 hours or 1000 ° C. for 2 hours. LaFeO ₃ powder was not formed. However, it was found that when the primary powder showing Fe ₂ O ₃ was calcined at 1000 ° C. for 5 hours, LaFeO ₃ powder (JCPDS 37-1493) was formed.

Therefore, the optimal condition for LaFeO ₃ powder synthesis is to hydrothermally synthesize at 250 ° C. without adding ammonia water and then to bake at 1000 ° C. for at least 5 hours. At this time, the effect of washing with water after synthesis of primary powder and calcined powder or without washing with water was hardly found.

5 shows the XRD results of the powders and the XRD results of the powders prepared by the high temperature firing method according to the firing temperature and the time change of the primary powders.

6 shows the powder form of the powder synthesized by the high temperature baking method and the powder synthesized by the hydrothermal synthesis method. The powder form of the powder synthesized by the high temperature firing method of FIG. 6 is the same as that of the powder of the XRD result of FIG. 5.

In the case of high-temperature firing, the powder is calcined at 1000 ° C. for 5 hours after mixing with each oxide using a ball mill. In the case of hydrothermal synthesis, the primary powder is calcined at 1000 ° C. for 5 hours. Although calcined at the same temperature for the same time, the size of the hydrothermal powder is twice smaller than that of the high-temperature firing method, and the size of the hydrothermal powder is about 200 nm.

Example 3

The experiment of Example 3 was carried out using reagent grade La (OH) ₃ (99.9%, Aldrich Co.), Sr (NO ₃ ) ₂ (99 +%, Aldrich Co.), Co (R) using an autoclave autoclave. NO ₃ ) ₂ · 6H ₂ O (98 +%, Aldrich Co.), Fe (NO ₃ ) ₃ · 9H ₂ O (98 +%, Aldrich Co.) samples according to the molar ratio (La: Sr: Co: Fe = 0.6: 0.4: 0.2: 0.8) to prepare a mixture of 1M concentration and then hydrothermally synthesized at 250 ° C. for 2 to 12 hours when ammonia water was added and ammonia water was not added. Skyt powder was prepared. Since the LaFeO ₃ powder synthesis was possible at 250 ° C., the temperature was fixed at 250 ° C. The analysis was performed XRD and SEM analysis as in Example 2.

7 shows powders (primary powders) synthesized at 250 ° C. for 12 hours and no powders calcined at 600 ° C. and 1000 ° C. for 5 hours, respectively, when no ammonia water was added and 8 M ammonia water was added. Show XRD results.

In the case of hydrothermally synthesized powder without ammonia water, Fe ₂ O ₃ crystallized without perovskite structure, but when 8 M ammonia water was added, La (OH) ₃ was formed instead of Fe ₂ O _3. . On the other hand, firing the synthesized primary powder regardless of the ammonia water at 600 ℃ gradually produced a perovskite structure, and firing at 1000 ℃ produced a perovskite structure without secondary phase.

This means that the primary synthetic powder changes according to the pH of the reaction solution. Crystals of Fe ₂ O ₃ are formed under low pH (pH = 1.5) and OH ⁻ under high pH (pH = 9.5). It can be seen that La (OH) ₃ is dominantly produced due to the relatively large number of groups.

In the case where the reaction was carried out after adding 1 M ammonia in the middle pH, two crystals, Fe ₂ O ₃ and La (OH) ₃ , were present at the same time. In these two crystals, however, other unreacted metals coexist, and when fired without washing, they react with other crystals to form perovskite powder.

At this time, when the powder synthesized under low pH conditions is washed several times, the metal component present in the crystal is eluted, and Fe ₂ O ₃ is formed even after firing. And La (OH) ₃ is produced after firing. In this case, therefore, firing without washing with water is advantageous for producing perovskite powder.

_{La 0.6 Sr 0.4 Co 0.2 Fe 0.8} O 3-δ composition actual La, Sr, the atomic ratio of Co and Fe metal powder synthesized by the initial weighing the La: Sr: Co: Fe = 0.6: 0.4: 0.2: 0.8 Powders were analyzed after firing by inductively coupled plasma luminescence spectroscopy (ICP-OES, Inkinly Coupled Plasma-Optical Emission Spectrometer, Perkin-Elmer Co.).

ICP analysis detected La 1050ppm, Sr 600ppm, Co 101.5ppm, Fe 760ppm, and did not exactly match La: Sr: Co: Fe = 0.6: 0.4: 0.2: 0.8, but did not exactly match (La, Sr) The ratio of (Co, Fe) to La: Sr = 0.64: 0.36 and Co: Fe = 0.12: 0.88 shows that the ratio approaches the initially weighed atomic ratio.

Therefore, when the hydrothermally synthesized powder is washed with water at a minimum of 250 ° C and calcined at 1000 ° C, a four-component perovskite powder can be synthesized.

8 shows La (OH) ₃ (99.9%, Aldrich Co.), Sr (NO ₃ ) ₂ (99 +%, Aldrich Co.), Co (NO ₃ ) ₂ .6H ₂ O (98 +%, Aldrich Co. .), Fe (NO ₃ ) ₃ .9H ₂ O (98 +%, Aldrich Co.) was weighed in a composition ratio (La: Sr: Co: Fe = 0.6: 0.4: 0.2: 0.8) to a mixture of 1M concentration After the preparation, shows the SEM shape of the primary powder synthesized by hydrothermal synthesis without the addition of ammonia water and the perovskite-type powder calcined at 1000 ° C without washing with water after hydrothermal synthesis.

After hydrothermal synthesis, the primary powder shows a particle size of about 100 to 120 nm and has a round shape, whereas the powder calcined at 1000 ° C. shows an irregular shape of about 500 nm. It can be seen that the crystal structure of the primary powder is different from that of the small powder due to the completely different shape, and other amorphous metals in the primary powder particles react upon firing to newly form a perovskite lattice structure. I think that.

Example 4

Four-component composite oxides were synthesized with the same sample in the same reactor as in Example 3, and the reaction temperature was changed to 300 to 450 ° C., and the experiment was performed by dividing the case with or without the addition of ammonia water. The analysis was analyzed by the same analyzer as in Example 3.

Fig. 9 shows the XRD results of the primary powders hydrothermally synthesized with and without the addition of ammonia water (3 M) at 450 ° C, and the XRD of the primary powders hydrothermally synthesized by adding 3M ammonia water at 400 ° C. The results are shown by comparison.

When ammonia water is not added, the perovskite crystals are partially formed and other impurities are abundant, whereas when ammonia water is added, the perovskite structure is formed from the primary powder to the main product. It can be seen that the content decreases. Increasing the concentration of ammonia water, Fe ₂ O ₃ gradually decreased, and when the hydrothermal synthesis at 450 ℃ by adding ammonia water of 5 M ~ 8 M Fe ₂ O ₃ almost disappeared to form a single-phase perovskite structure. At this time, the particle size of the powder is about 10 to 20 nm and the particle size is about 1000 times smaller than the particle size of 5 to 10 μm when synthesizing the same composition by citric acid method.

Therefore, the optimum conditions for producing perovskite single-phase powder when hydrothermal synthesis of the four-component metal complex oxide is injected from a water of 3 M to 8 M, more preferably 5 M to 8 M to 250 ℃ to 450 ℃ More preferably in the range is synthesized from 400 ℃ to 450 ℃.

The technical spirit of the present invention has been described above with reference to the accompanying drawings, but this is only illustrative of the most preferred embodiments of the present invention, and the present invention is not limited thereto. In addition, any person skilled in the art to which the present invention pertains may make various modifications and imitations by the description of the present specification, but it will be apparent that the present invention is not outside the scope of the present invention.

Claims (8)

delete delete delete In the hydrothermal synthesis method of the perovskite type nanopowder,
(a) La (OH) _3, Sr (NO ₃ ) ₂ , Co (NO ₃ ) ₂ .6H ₂ O and Fe (NO ₃ ) ₃ .9H ₂ O without using potassium hydroxide and sodium hydroxide were converted into La: Quantifying each to fix Sr: Co: Fe = 0.6: 0.4: 0.2: 0.8;
(b) mixing the quantified La (OH) _3, Sr (NO ₃ ) ₂ , Co (NO ₃ ) ₂ .6H ₂ O and Fe (NO ₃ ) ₃ .9H ₂ O to form a slurry;
(c) adding 5M to 8M of ammonia water to the slurry and making a primary powder by hydrothermal reaction at 250 ° C to 450 ° C; And
(d) calcining the primary powder at 900 ° C. to 1000 ° C. to produce a perovskite-type nanopowder,
The nanopowder has a single phase structure free of impurities, hydrothermal synthesis method of a perovskite-type nanopowder, characterized in that. delete delete The method of claim 4, wherein after step (c)
(c1) A hydrothermal synthesis method of perovskite-type nanopowder, further comprising the step of washing the primary powder. delete

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