JP2016216272A - Method for producing strontium titanate fine particle having cubic shape, strontium titanate fine particle having cubic shape, metal-doped strontium titanate fine particle having cubic shape, and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide strontium titanate fine particles having a cubic shape at a liquid phase under the atmospheric pressure at high productivity, a method for producing strontium titanate fine particles having a cubic shape and capable of producing rhodium(Rh)-doped strontium titanate fine particles, strontium fine particles having a cubic shape, and rhodium(Rh)-doped strontium titanate fine particles having a cubic shape.SOLUTION: A reaction liquid obtained by adding a strontium raw material, an anatase type titanate raw material and a rhodium salt into an alkaline aqueous solution is prepared, and the reaction liquid is heated at 90°C or more and at the boiling point or less under the atmospheric pressure, and the reaction liquid is made to be reacted.SELECTED DRAWING: Figure 1

Description

One of the electronic components widely used in today's diverse electronic devices is a multilayer ceramic capacitor (commonly known as MLCC (Multi-Chip)) that has been made smaller and larger in capacity by multilayering ceramic dielectrics and metal electrodes. -Layer Ceramic Capacitor)), but the present invention is suitable for forming a layer with improved conductivity of dielectric ceramics in order to improve ohmic characteristics in the vicinity of the electrode layer. The present invention relates to finely shaped strontium titanate fine particles, rhodium-doped strontium titanate fine particles, and a method for producing the same.
At the same time, the present invention has recently developed a shape-controlled titanic acid as a raw material suitable for constituting a photocatalytic material that has been spotlighted as an environmental energy material by decomposing water into hydrogen or oxygen by visible light. The present invention also relates to strontium fine particles and rhodium-doped strontium titanate fine particles and a method for producing the same.

Strontium titanate (SrTiO ₃ ) is a composite oxide material that is expected to be used in various applications as a functional material, such as dielectric properties, thermoelectric properties, photocatalytic properties, high refractive index properties, and photochromic properties. With the recent miniaturization of electronic devices, excellent high-capacitance capacitors with less voltage loss have attracted attention, while high-performance photocatalytic activity has attracted attention from the viewpoint of energy problems and environmental problems. Strontium titanate is expected to be a material for forming electrode interface layers of ceramic capacitors and the like from the viewpoint that the band gap can be controlled by metal doping, and also because of its high stability and light reducing power under light irradiation. As a base material for a photocatalyst material that enables hydrogen production using sunlight, there is an increasing expectation.

Regarding the ohmic formation layer at the electrode interface for the ceramic capacitor, when the work function (φM) of the metal electrode is smaller than the work function (φS) of the semiconductor ceramic, non-rectifying contact, that is, ohmic contact is formed. It is a problem of the relative position of the Fermi surface of the electrode and the semiconductor ceramic, but the semiconductor ceramic is doped with an element that modulates the band structure, and this material is used as an intermediate layer between the electrode layer and the semiconductor ceramic layer. It is expected that sex can be imparted.
Moreover, it is preferable that the host catalyst material for the photocatalyst material has activity with respect to visible light that accounts for a large proportion of sunlight. As a strontium titanate photocatalyst capable of generating highly efficient hydrogen with visible light activity, strontium titanate with a metal such as Pt, Rh, or Cu supported as a co-catalyst, and more effective use of visible light in sunlight For this purpose, strontium titanate having a band structure modulated by doping Rh, Ir or the like is expected.

  Among various functional materials, especially perovskite-type oxide fine particle (nanoparticle) materials can express unique excellent properties and functions, so that it is possible to realize high precision, downsizing, and weight reduction of products. In particular, the particles synthesized via the liquid phase have very high uniformity in terms of particle size, composition, and the like. Particleization technology is being studied.

The perovskite type oxide fine particles are denoted by ABO _{3 in} a general formula, and a +2 valent element such as Ca, Sr, Ba and Pb is present at the A site, and a +4 valent element such as Ti, Zr and Sn is present at the B site. It is known to enter.
Among these, Patent Document 1 is known as a patent relating to a technique capable of directly synthesizing SrTiO ₃ -based perovskite fine particles in an aqueous solution. Although this patent is a liquid phase synthesis under atmospheric pressure, cubic shaped fine particles have not been obtained. In particular, Patent Document 1 describing a production method for directly synthesizing SrTiO ₃ fine particles in an aqueous solution includes, as optimum synthesis conditions,
The pH value of the aqueous solution is 13.5 or higher, and the temperature is near the boiling point at atmospheric pressure of 90 ° C. or higher.
The reaction time is about 2 hours, and the [Sr] / [Ti] molar ratio at the time of charging is preferably 1. On the other hand, regarding the morphology of the obtained fine particles,
“SrTiO ₃ fine particles have a uniform particle size of 100 to 200 mm”, and there is no description regarding the shape.

With the subsequent development of technology, the shape control of strontium titanate fine particles is described in Patent Document 2, Patent Document 3, Patent Document 4, and Non-Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3. ing.
In Patent Document 2, strontium hydroxide and a water-soluble titanium compound such as titanium peroxoammonium lactate are mixed at 200 ° C. in the presence of an amphiphilic compound such as oleic acid and a basic compound not containing a metal element such as hydrazine. It is described that strontium titanate nanoparticles whose crystal shape is controlled can be produced without agglomeration by hydrothermal synthesis under alkaline conditions.

  Patent Document 3 discloses a method for aligning cubic strontium titanate nanocrystals on a substrate and a method for producing a film made of nanocrystals. Paragraph [ [0015] In addition, in the synthesis of strontium titanate nanocrystals, crystal growth proceeds with organic carboxylic acid molecules such as oleic acid adhering to the {100} plane. The study of the particle shape control mechanism such as the fact that all the {111} planes progress without being obstructed by acid molecules and the apexes are formed to form a cube as a whole is also described.

Further, in Patent Document 4, BaTiO ₃ and SrTiO ₃ having the same perovskite type are performed up to 150 ° C. for 120 hours under hydrothermal synthesis conditions. With respect to SrTiO ₃ , cubic-shaped particles are generated by an electron microscope. Reported through observation. However, this is not an example of synthesis under atmospheric pressure, and a system doped with a metal element is not described.

In Non-Patent Document 1 and Non-Patent Document 2, in addition to obtaining cubic SrTiO ₃ fine particles by hydrothermal synthesis at 240 ° C. for 24 hours in a highly alkaline liquid, evaluation by Raman scattering is also performed. Or introducing the technique of attaching Pt to the surface of the dice-like SrTiO ₃ fine particles by atomic layer deposition (ALD) method. Pt clearly has a meaning as a promoter for the photocatalyst. However, neither report mentions metal doping at all.

On the other hand, in Non-Patent Document 3, strontium hydroxide and titanium dioxide are mixed in ethanol in a nitrogen atmosphere, and then subjected to an annealing treatment in a temperature range of 800 ° C. to 1000 ° C. after hydrothermal synthesis at 170 ° C. for 3 days. It has been reported that cubic-shaped visible light responsive Rh-doped strontium titanate fine particles are produced by implementation. The amount of doping is 1%, and there is no discussion from the viewpoint of how much doping is possible. Furthermore, there is no description of the crystal lattice constant and the like, and it is determined that the material is doped from the optical absorption spectrum. The important point here is an electron micrograph (SEM photograph), which explains the shape of the non-doped SrTiO ₃ fine particles immediately after hydrothermal synthesis as a cubic shape, but only in the text without clearly showing the SEM photograph. "The particle shape of hydrothermally synthesized 1% Rh-doped SrTiO ₃ does not affect the non-doped cubic shape by doping." As described above, in this document, there is almost no description of the form and crystallinity of fine particles immediately after hydrothermal synthesis, and a high-temperature heat treatment at 800 ° C. to 1000 ° C. is performed immediately after hydrothermal synthesis. Since the evaluation of the material is evaluated at that time, it can be said that it is unclear how much the doping state is realized only by hydrothermal synthesis. In addition, in this Non-Patent Document 3, it is added that Ru, Ir, Pt, and Pd are reported in addition to Rh.

The situation so far is shown in Table 1 on the next page.
Rh-doped SrTiO ₃ fine particles, the shape of which is a cubic shape, and the method of synthesis by liquid phase synthesis under atmospheric pressure that does not require high temperature and high pressure exist in conventional published literature. Not.
On the other hand, there have been no reported cases in the published literature so far regarding the production method of liquid phase synthesis under atmospheric pressure of non-doped pure SrTiO ₃ cubic fine particles.

  Now, the reason for the research purpose of Non-Patent Document 3 describing Rh doping is to increase the efficiency of photocatalytic activity by doping metal elements such as Rh and iridium (Ir) into strontium titanate. is there. Specifically, there are Rh-doped or Ir-doped strontium titanate fine particles having a high photocatalytic ability described in Patent Document 5. This Patent Document 5 is an invention of an Rh-doped SrTiO 3 photocatalytic material, and shows that the efficiency is highest when doped with 1% Rh in the range of 3% Rh-doped. Among them, the sample preparation method is a typical ceramic solid phase reaction method, in which calcining is performed at 1150 ° C. for 10 hours after calcining at 1000 ° C. for 1 hour. Patent Document 5 does not mention any liquid phase synthesis such as hydrothermal synthesis.

The doping amount of Rh synthesized as a single phase is less than 7%. (4% is proved to be a single phase by X-ray diffraction.) This single-phase data of less than 7% Rh is based on a solid-phase reaction method and is not a knowledge based on a liquid phase method or a hydrothermal synthesis method. . Looking at these situations, there are no reports in the literature so far that Rh-doped SrTiO ₃ fine particles were obtained in a single phase by liquid phase synthesis or hydrothermal synthesis under atmospheric pressure. .

Further, the background that the inventor attaches importance to the particle shape of the cubic shape is not only the convenience for the particle orientation control and arrangement, but also the idea of effective use of the active surface as a photocatalyst. Here, Non-Patent Document 4 shows that the active surface of the SrTiO ₃ photocatalytic material is the {100} surface, and if such morphological control is performed at the time of fine particle synthesis, great progress will be made in future photocatalytic technology. We believe that is expected.

Japanese Patent Publication No. 3-39016 JP, 2011-68500, A) Patent No. 5618087 Japanese Patent No. 5216186 Japanese Patent No. 4076793

F. A. Rabuffetti et al., Chem. Mater., 20 (2008) 5628-5635. S. T. Christensen et al., Small, 5 (2009) 750-757. S. W. Bae et al, Applied Physics Lett. 2008, 92, 104107. Jennifer L. Giocondi et al., Topics in Catalysis, 44 (2007) 529-533.

From the viewpoint of directly synthesizing crystalline strontium titanate (SrTiO ₃ ) fine particles in a liquid phase in which highly uniform fine particles can be obtained and a specific shape control such as a cubic shape is possible, From the above, Patent Document 2, Patent Document 3, Patent Document 4, Non-Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3 all synthesize fine particles under hydrothermal synthesis conditions that require high temperature and pressure. doing. These patent documents clearly indicate that the obtained fine particles are in a cubic shape, but in any case, it is a chemical reaction under high temperature and high pressure, and has a relatively long time. From the viewpoint of productivity and capital investment in mass synthesis, there are significant barriers to industrialization. In addition, the description of Rh doping is only Non-Patent Document 3 among these patent documents and non-patent documents. However, as described above, since the high-temperature annealing treatment is performed immediately after the hydrothermal treatment, the fine particles after the hydrothermal treatment are used. The nature of is often unclear.

On the other hand, Patent Document 1 has been reported as a liquid phase production method of strontium titanate fine particles under atmospheric pressure, but there is no description or suggestion about a method of controlling the shape of a cubic having a specific crystal plane. Further, there is no description regarding doping of metal elements such as Rh.
In view of such a situation, it is concluded that there is no previous report that cubic strontium titanate (SrTiO ₃ ) fine particles have been synthesized in the liquid phase synthesis process under atmospheric pressure. Needless to say, there are no previous cases in which the metal-doped cubic SrTiO ₃ fine particles were synthesized by a liquid phase process under atmospheric pressure.

  By the way, although the example of the hydrothermal synthesis which performed Rh dope is described only in the nonpatent literature 3, the doped Rh density | concentration is about 1%, As a synthesis process, hydrothermal synthesis is carried out by the first stage process. After this, heat treatment may be performed in the second stage process, and it is not easy to estimate from this paper only how much Rh-doped SrTiO3 fine particles have been synthesized by only hydrothermal treatment. In any case, the hydrothermal reaction under high temperature and high pressure is not suitable for production at low cost rather than synthesis under atmospheric pressure.

  The present invention has been made in view of the above circumstances, and manufactured cubically controlled strontium titanate fine particles or Rh-doped strontium titanate fine particles having a specific crystal plane with high productivity under atmospheric pressure. It is intended to do.

The method for producing strontium titanate fine particles having a cubic shape according to the present invention,
A reaction liquid preparation step of preparing a reaction liquid in which a strontium raw material and a titanium raw material are added in an alkaline aqueous solution;
A reaction step of reacting the reaction solution by heating the reaction solution to 80 ° C. or higher under atmospheric pressure.

  In the present specification, unless otherwise specified, the term “strontium titanate fine particles” includes non-doped strontium titanate fine particles and metal-doped strontium titanate fine particles.

  In the present specification, “reacting the reaction solution” means reacting one or more components contained in the reaction solution.

  In the present specification, the term “fine particles” means those having an average particle size of less than 1 μm, and preferably nanoparticles. Nanoparticles may generally have a mean particle size of 200 nm or less, preferably 200 nm or less. In some cases, the nanoparticles may be those having an average particle size of 100 nm or less, and in other cases, the average particle size may be 50 nm or less. In a preferred case, the nanoparticles have a mean particle size of 20 nm or less, and in another case, the mean particle size is 10 nm or less or 5 nm or less. Good. In a preferred case, the nanoparticles have a uniform particle size, but a mixture of particles having different particle sizes at a certain ratio may be preferable.

The average particle diameter can be measured by a method known in the art. For example, transmission electron microscopy (TEM), adsorption method, light scattering method, X-ray small angle scattering method (SAXS: Small Angle X-ray Scattering). In TEM, observation is performed with an electron microscope. When the particle size distribution is wide, it is necessary to pay attention to whether or not the particles entering the field of view represent all particles. The adsorption method evaluates the BET surface area (the surface area value of the material based on the theory of extending the Langmuir theory, in which three of Brunauer, Emmett, and Teller are monolayer adsorption theory) to multiple molecular layers by N ₂ adsorption and the like. is there.

In the method for producing strontium titanate fine particles of the present invention, the titanium raw material preferably contains titanium oxide, more preferably contains titanium dioxide, and the main component of titanium dioxide is anatase-type titanium dioxide. preferable. Here, the main component means a component having a content of 70% by mass or more.
The strontium raw material preferably contains at least one of strontium acetate, nitrate, chloride, carbonate, sulfide, and hydroxide.

In the present specification, “titanium oxide” means TiO ₂ having a stoichiometric composition, titanium dioxide having a stoichiometric composition represented by TiO _x (1.5 ≦ x ≦ 2), and oxygen. It means a group of oxides in the Magneli phase with defects. In addition, titanium oxide may be a hydroxide or a hydrate such as Ti (OH) ₄ or TiO ₂ · nH ₂ O (0 <n <2) in an aqueous solution.

The temperature at which the reaction solution is reacted in the reaction step is preferably 90 ° C. or higher and the boiling point or lower at atmospheric pressure, and more preferably near the boiling point. The “boiling point” naturally means the boiling point of the reaction solution to be reacted.
In the reaction step, the pH of the reaction solution is preferably 13.5 or more.

  In the reaction solution preparation step, Rh-doped strontium titanate fine particles can be produced by including Rh (rhodium) in addition to strontium (Sr) and titanium (Ti) in the alkaline aqueous solution. Further, a part of the Rh is mixed with V (vanadium), Cr (chromium), Mn (manganese), Fe (iron), Co (cobalt), Ni (nickel), Cu (copper), Zn (zinc), Ga ( Gallium), Nb (niobium), Mo (molybdenum), Ru (ruthenium), Pd (palladium), In (indium), Sb (antimony), Ta (tantalum), W (tungsten), Re (rhenium), Ir ( It is also possible to substitute at least one metal raw material of iridium), Pt (platinum / platinum), Bi (bismuth) or (La (lanthanum)), and strontium titanate fine particles doped with these metals The doped metal preferably has at least Rh, and the metal raw material is a water-soluble raw material. Preferred.

  The total molar ratio of the metal raw material to be doped to the strontium raw material in the reaction solution is preferably 0.15 or less. The total molar ratio of the metal raw material to the strontium raw material means a ratio to the molar concentration of the sum of the respective metal elements. For example, the molar ratio of rhodium chloride to strontium hydroxide is expressed as [Rh] / [Sr], which is the ratio of rhodium molar concentration [Rh] to strontium molar concentration [Sr] in the reaction solution. When a part of rhodium is substituted with a kind of metal element M, it means [Rh] + [M] / [Sr].

The cubic strontium titanate fine particles of the present invention are produced by the method for producing strontium titanate fine particles of the present invention.
The cubic rhodium-doped strontium titanate fine particles of the present invention are
Represented by the general formula Sr (Ti _1-x (Rh _1-y , M _y ) _x ) O ₃ ,
0 <x ≦ 0.07 and 0 ≦ y <1, and M is V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Nb, Mo, Ru, Pd, In, Sb, It is at least one metal element selected from the group consisting of Ta, W, Re, Ir, Pt, Bi, and La.

In the present specification, “cubic-shaped (cubic-shaped) strontium titanate fine particles and rhodium-doped strontium titanate fine particles” are strontium titanate fine particles and rhodium-doped strontium titanate having a chamfered part at the top. Also includes fine particles. The strontium titanate fine particles and rhodium-doped strontium titanate fine particles of the present invention have a substantially cubic shape. In a transmission electron microscope (TEM) image, one isolated particle is circumscribed in a rectangle that minimizes the area. When the rectangular area S ₀ and the particle image area S _cube are used, the particles satisfy 0.8 <S _cube / S ₀ . Since strontium titanate fine particles and rhodium-doped strontium titanate fine particles have a stable cubic structure at room temperature, the ideal fine particle shape is cubic, but cubic strontium titanate fine particles and rhodium-doped titanium. It is assumed that hexahedral fine particles within a range regarded as the shape of strontium acid fine particles are substantially cubic.

  In such strontium titanate fine particles and rhodium-doped strontium titanate fine particles, it is preferable that 85% or more of crystal planes exposed on the particle surface are {100} planes. Further, the length of one side of the cubic particles is preferably 10 nm or more and 500 nm or less.

The cubic rhodium-doped strontium titanate fine particles of the present invention preferably have a lattice constant value in the range from 0.3915 nm to 0.3930 nm. The optical band gap is preferably in the range of 3.21 eV to 3.54 eV.
The cubic rhodium-doped strontium titanate fine particles of the present invention preferably have a cubic shape having an average length of one side of 30 nm to 80 nm.
In this specification, the average value of the length of one side (average particle diameter) is an arbitrary ten fine particles having a cubic shape selected from a TEM photograph with a magnification of 100,000 times, and the length of one side of each fine particle. It is the average value which measured (particle diameter).

  The method for producing strontium titanate fine particles of the present invention comprises a reaction liquid preparation step for preparing a reaction liquid in which a strontium raw material and a titanium raw material are added to an alkaline aqueous solution, and the adjusted reaction liquid at 80 ° C. or higher under atmospheric pressure. And a reaction step of reacting the reaction solution by heating. According to such a configuration, the strontium titanate fine particles or the Rh-doped strontium titanate fine particles whose surface is controlled in a cubic shape having a {100} plane by preferentially growing the <111> crystal orientation of the strontium titanate crystal. Can be produced with high productivity under atmospheric pressure.

The flowchart of the manufacturing method of the strontium titanate microparticles | fine-particles of this invention. The figure which shows the relationship between the titanium dioxide phase as a starting material, the shape (transmission electron micrograph, TEM photograph) of an obtained strontium titanate fine particle, and an X-ray diffraction pattern. The figure which showed the X-ray-diffraction pattern of the microparticles | fine-particles obtained in each step of a manufacture process with time (Example 3). 9 is a TEM photograph showing changes in the shape of fine particles depending on the synthesis reaction time (Example 3). The figure which showed the relationship between Rh doping amount and an X-ray-diffraction pattern (Example 4). The figure which showed the relationship between Rh doping amount and a lattice constant in Example 4. FIG. TEM photograph (low magnification) showing the relationship between the amount of Rh doping and the form of fine particles (Example 4). TEM photograph (high magnification) showing the relationship between the amount of Rh doping and the form of fine particles (Example 4). The figure which shows a nano beam limited visual field electron diffraction pattern (Example 4). The figure which shows the result of having measured the diffuse reflection spectrum of each sample of Example 4. FIG. The figure which shows the relationship between Rh doping amount and an optical band gap. The figure which shows the electron spin resonance signal (ESR signal) derived from Rh4 valence (Example 4). The figure which shows the ESR signal derived from Rh4 value (solid phase method). The figure (Example 3) which shows the thermogravimetric-mass-analysis result of Rh dope strontium titanate microparticles | fine-particles. The figure which shows the synthetic | combination possible area | region of cube-shaped Rh dope strontium titanate microparticles | fine-particles.

"Production method of strontium titanate fine particles"
With reference to drawings, the manufacturing method of the strontium titanate microparticles | fine-particles of one Embodiment concerning this invention is demonstrated. FIG. 1 shows a flow chart of the method for producing strontium titanate fine particles of the present embodiment.

  As already mentioned, there are several reports on the production of strontium titanate fine particles whose shape is controlled to a cubic shape with a specific crystal plane, but all are based on hydrothermal synthesis under high pressure, Production under atmospheric pressure has not been studied at all.

This means that even in simple oxides such as cerium dioxide (CeO ₂ ) and titanium dioxide (TiO ₂ ), the shape controllability tends to increase by setting the reaction field to a supercritical condition, that is, a high temperature and high pressure condition. This is because it is considered that conditions for controlling the shape of strontium titanate fine particles having a complicated crystal structure are required to be stricter than simple oxides.

  The present inventors diligently studied the mechanism of shape control of strontium titanate fine particles. The case of simple oxide particles whose shape is controlled under supercritical conditions can be seen when the water in the reaction solution exceeds the critical point, the solubility of the substance rapidly decreases, and the formation and growth of crystal nuclei rapidly. This is because the number of particles to be generated is increased, that is, another device or device is necessary to achieve shape control by low-temperature synthesis under atmospheric pressure. In fact, in the production of strontium titanate fine particles, it was confirmed that the shape controllability deteriorated by simply changing the reaction field from hydrothermal conditions to supercritical conditions.

Therefore, the present inventors have studied by focusing on the state of the titanium source and the strontium source in the reaction solution as an important condition for shape control.
The present inventors focused on the potential -pH view of Ti in the aqueous solution, the titanium raw material used in the conventional hydrothermal synthesis, in an aqueous solution, titanium dioxide hydrate by pH conditions (TiO _{2 ·} H 2 O) and, Ti hydroxide (Ti _{(OH) 4)} or HTiO ₃ ^- ion state, it is that the binding state changes were considered to affect the shape control of the strontium titanate particles.
In the conventional method, when the hydrogen ion concentration conditions are comparable to pH 13.5 or higher, the shape controllability is good. Therefore, the Ti hydroxide (Ti (OH) ₄₎ or HTiO ₃ ^- ions, stable be formed in the reaction solution, i.e., in the preparation of the reaction solution, as a titanium raw material to be added to the water, by using a titanium oxide, under atmospheric pressure Even so, it was found that the shape-controlled strontium titanate fine particles can be produced.

That is, the manufacturing method of the strontium titanate fine particles of the present invention,
A reaction liquid preparation step of preparing a reaction liquid in which a strontium raw material and a titanium raw material, particularly a titanium oxide raw material are added in an alkaline aqueous solution;
A reaction step of reacting the reaction liquid by heating the adjusted reaction liquid to 80 ° C. or higher under atmospheric pressure.

  In the reaction liquid preparation step, a reaction liquid is prepared by adding a strontium (Sr) raw material and a titanium (Ti) raw material to an alkaline aqueous solution. If such a reaction solution can be prepared, the order of mixing the Sr raw material, the Ti raw material, and a compound for making the aqueous solution alkaline (hereinafter referred to as a basic compound) is not particularly limited, but the Sr-containing aqueous solution and the Ti-containing aqueous solution are not limited. After preparing each, it is preferable to add an aqueous solution of a basic compound after mixing them. In the reaction liquid preparation step, the aqueous solution prepared after completion of the process is the reaction liquid. In the present specification, in the description of the reaction liquid preparation step, the mixed liquid in the middle of preparation is described as the reaction liquid for convenience. Sometimes.

  The method of mixing these aqueous solutions is not particularly limited, but it is preferable to stir well during the preparation of the reaction solution from the viewpoint of suppressing the formation of precipitates as much as possible in the mixing process. Moreover, it is more preferable to implement stirring until just before performing the reaction process of the following process.

  The Ti raw material is not particularly limited as long as it is a Ti oxide, but titanium dioxide is preferable. Titanium dioxide mainly has anatase type and rutile type, but since it has a skeleton relatively close to the perovskite skeleton, the anatase type is preferable. Therefore, it is most preferable that the Ti raw material contains anatase type titanium dioxide as a main component. As the Ti raw material, it is preferable to use a Ti-containing aqueous solution in which titanium oxide is dissolved in water.

  The concentration of the Ti oxide can be arbitrarily selected depending on the concentration to be obtained, but from the viewpoint of obtaining strontium titanate fine particles with good uniformity and good productivity and having a shape controlled, 1 mmol / L or more and 500 mmol / L L or less is preferable.

  Although it does not restrict | limit especially as a Sr raw material, A water-soluble Sr compound is preferable. Specifically, Sr hydroxides, oxides, chlorides, fluorides, iodides and other halides, nitrates, carbonates, sulfates and other inorganic acid salts, acetates, oxalates, lactates, etc. The organic acid salt of, and the like are preferable, and preferably contains at least one of acetate, nitrate, chloride, sulfide, and hydroxide. As the Sr raw material, it is preferable to use an Sr-containing aqueous solution in which the Sr compound is dissolved in water.

  The pH of the reaction solution is not particularly limited as long as it is alkaline, but it is preferably a strong alkaline condition of pH 13 or higher. The pH can be adjusted by adding a basic compound having an ionization degree of 0.8 or more such as potassium hydroxide or sodium hydroxide to the reaction solution. When such a basic compound is used, the concentration of the basic compound in the reaction solution is preferably 1 mol / L or more. The basic compound is preferably made into an aqueous solution (alkaline aqueous solution) and dropped into the reaction solution being prepared.

  In the reaction solution preparation step, Rh (rhodium) or a part of Rh in the reaction solution, alkaline solution, V (vanadium), Cr (chromium), Mn (manganese), Fe (iron), Co (cobalt), Ni (nickel), Cu (copper), Zn (zinc), Ga (gallium), Nb (niobium), Mo (molybdenum), Ru (ruthenium), Pd (palladium), In (indium), At least one metal material selected from Sb (antimony), Ta (tantalum), W (tungsten), Re (rhenium), Ir (iridium), Pt (platinum / platinum), Bi (bismuth) or La (lanthanum) By including the metal raw material substituted with strontium titanate fine particles doped with these metals can be produced. From the viewpoint of mixing in an alkaline aqueous solution, the metal raw material is preferably a water-soluble raw material. Examples of the water-soluble metal raw material include chlorides, oxides and nitrates of the above metals.

  Among the metal elements exemplified above, the visible light responsiveness of the obtained oxide particles can be greatly increased by adding Rh element or one obtained by substituting a part of Rh element with another element. In addition, since the band gap can be adjusted and controlled, the capacitor characteristics can be improved by changing the potential barrier with the electrode. Preferred rhodium raw materials include rhodium (III) chloride, rhodium (III) oxide, rhodium (IV) oxide, rhodium (III) nitrate and the like.

  From the viewpoint of obtaining a high photocatalytic ability, it is preferable that the amount of the metal raw material added be large within a range where a perovskite structure can be obtained. From this viewpoint, the total molar ratio of the metal raw material to the Sr raw material in the reaction solution is preferably 0.001 or more and 0.15 or less. The total molar ratio of the metal raw material to the Sr raw material means a ratio of ([Rh] + [M]) / [Sr]. Since the metal raw material is a small amount with respect to the strontium raw material, it is preferable to prepare an aqueous solution of the metal raw material in advance.

  In addition, when adding a metal raw material, addition of alkaline aqueous solution may be after addition of a metal raw material.

<Reaction process>
In the reaction step, the reaction solution prepared in the reaction solution preparation step is reacted at 80 ° C. or higher under atmospheric pressure. The temperature at which the reaction solution is reacted may be 80 ° C. or higher and the boiling point or lower, and preferably 90 ° C. or higher.
The synthesis reaction tank used in the reaction step is not particularly limited as long as it can maintain atmospheric pressure, and a round bottom flask is preferable.

  The method for heating the reaction solution is not particularly limited, and can be selected from aluminum block heating, hot plate heating, electric furnace heating, infrared heating, microwave heating, and the like. The temperature of the heating device is preferably higher than the boiling point of 100 ° C. at normal pressure of water from the viewpoint of heat conduction. The rate of temperature increase is preferably 1 ° C./min to 100 ° C./min from the viewpoint of productivity, but is not a main factor of the synthesis reaction, and thus the rate of temperature increase is not limited.

  During the reaction step, the reaction solution is preferably stirred. The stirring speed should just be a solute disperse | distributing uniformly and about 100 rpm-1000 rpm are preferable.

  The reaction time is preferably shorter as long as the reaction proceeds sufficiently, but it is preferably 2 hours or longer and 12 hours or shorter. Here, 12 hours or less is a cost-conscious view.

After completion of the reaction, the reaction solution is preferably subjected to a desalting step in order to remove alkali components and the like in the solvent. The desalting step is not particularly limited, but a method of separating the solvent and synthesized fine particles by centrifugation or the like is preferable. Preferable centrifugation conditions include 5000 to 20000 rpm, 5 to 15 minutes, and 3 ° C to 30 ° C. The centrifugation operation is preferably repeated twice or more, and between the centrifugation operations, after discarding the supernatant, it may include a step of adding 20 mL to 100 mL of pure water to obtain a synthesized fine particle suspension again. preferable.
On the other hand, after the reaction, the reaction solution is decanted several times, the pH of the whole solution is neutralized, and then simply filtered to sufficiently collect the fine particles.

  The strontium titanate fine particles obtained after desalting are preferably subjected to the following drying step. Although a drying process will not be restrict | limited especially if the water | moisture content of the isolate | separated microparticles | fine-particles can be evaporated completely, it is preferable to dry at 100 to 120 degreeC for 1 to 3 hours. In the drying step, the heat treatment method is not particularly limited, and can be selected from hot plate heating, electric furnace heating, infrared heating, microwave heating, and the like. Moreover, although there is no restriction | limiting in particular in the atmosphere in drying, it is preferable to carry out in air | atmosphere under atmospheric pressure from viewpoints of manufacturing cost etc.

  As will be described later in Examples, the strontium titanate fine particles obtained by the above method are controlled in shape so that the surface has {100} planes, and have a cubic shape. Since the strontium titanate fine particles have a crystal structure in which cubic crystals are stable at normal temperature, the surface of the cubic strontium titanate fine particles has a {100} plane.

  FIG. 13 of the examples described later is a graph in which the vertical axis represents the reaction temperature and the horizontal axis represents the [Rh] / [Sr] values in the reaction liquid, regarding whether or not the shape-controlled rhodium-containing strontium titanate can be produced. FIG. 13 shows a method for producing strontium titanate fine particles according to the present invention, and strontium titanate fine particles having a cubic or cuboid shape and rhodium-doped at a temperature that is markedly lower than 100 ° C. as compared with the conventional method. It has been shown that strontium titanate microparticles can be produced.

  The method for producing strontium titanate fine particles of the present invention comprises a reaction liquid preparation step for preparing a reaction liquid in which an Sr raw material and a Ti raw material are added in an alkaline aqueous solution, and the adjusted reaction liquid at 80 ° C. or higher under atmospheric pressure. And a reaction step of reacting the reaction solution by heating. According to such a configuration, the <111> crystal orientation of the strontium titanate crystal is preferentially grown, and the strontium titanate fine particles whose shape is controlled so that the surface has a {100} plane are obtained under atmospheric pressure. It can be manufactured with high productivity. Since the method for producing strontium titanate fine particles of the present invention can be synthesized under atmospheric pressure, it can be easily synthesized in a large amount by a flow method.

"Cubic-shaped strontium titanate fine particles, cubic-shaped rhodium-doped strontium titanate fine particles"
The cubic strontium titanate fine particles of the present invention are produced by the above-described method for producing strontium titanate fine particles having the cubic shape of the present invention, and have a cubic shape.
The cubic rhodium-doped strontium titanate fine particles of the present invention are
Represented by the general formula Sr (Ti _1-x (Rh _1-y , M _y ) _x ) O ₃ ,
0 <x ≦ 0.07 and 0 ≦ y <1, and M is V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Nb, Mo, Ru, Pd, In, Sb, It is at least one metal element selected from the group consisting of Ta, W, Re, Ir, Pt, Bi, and La.
In the above general formula, Rh-only doped strontium titanate fine particles in which y is 0 are preferable.

  In such strontium titanate fine particles and rhodium-doped strontium titanate fine particles, it is preferable that 85% or more of crystal planes exposed on the surface of the cube or rectangular parallelepiped are {100} planes. The average value of the length of one side of the cube is preferably 10 nm or more and 500 nm or less, and more preferably 30 nm or more and 80 nm or less.

  There is no particular limitation on the use of the fine particles obtained by the method for producing the cubic strontium titanate fine particles of the present invention, but the Rh element or a part of the Rh element is selected from V, Cr, Mn, Fe, Co. , Ni, Cu, Zn, Ga, Nb, Mo, Ru, Pd, In, Sb, Ta, W, Re, Ir, Pt, Bi, or other metal element substituted with at least one metal raw material Doping the substance substituted with can greatly increase the visible light response capability of the resulting oxide particles, and the band gap can be adjusted and controlled, so that the potential barrier with the electrode can be changed. Thus, the capacitor characteristics can be improved. Fine particles whose shape is controlled in a cubic shape are suitable as a catalyst having a large contribution of surface area and plane orientation, and are therefore suitable as a raw material for photocatalysts and capacitors as a material having a very high catalytic performance suitable for a hydrogen / oxygen generation photocatalyst system. It can be preferably used.

A hydrogen generation photocatalyst system and an oxygen generation photocatalyst system (hereinafter sometimes abbreviated as a hydrogen / oxygen photocatalyst system) are photocatalysts that generate hydrogen and oxygen by irradiation with sunlight. It is known that the contribution is large. According to the method for producing cubic rhodium-doped strontium titanate fine particles of the present invention, for example, as shown in FIG. 9, the band gap can be clearly controlled by Rh doping. It is shown for the first time that can be used effectively. At the same time, it is very likely that the controllability of the contact resistance near the electrode can be improved.
On the other hand, since the {100} plane, which is considered to be the active surface of the photocatalyst from Non-Patent Document 4, can be produced, it is possible to produce fine particles having a uniform cubic shape of about 50 nm.

  Although it does not restrict | limit especially as an aspect at the time of using for a hydrogen and oxygen production | generation photocatalyst system, For example, the aspect of the thin film for hydrogen manufacture formed by apply | coating a metal dope strontium titanate microparticles | fine-particles to a board | substrate is mentioned.

  For use as a photocatalyst, the metal-doped strontium titanate fine particles are preferably provided with a promoter on the surface of the fine particles. Strontium titanate microparticles carrying a metal cocatalyst suppress the recombination with holes because electrons excited in the strontium titanate by light irradiation move to the surface quickly due to the presence of the metal cocatalyst on the surface. Therefore, hydrogen can be efficiently generated.

  When adding a cocatalyst, the addition method is not particularly limited, and examples thereof include a method using a photo-deposition method, an impregnation method, electroless plating and the like. From the viewpoint of obtaining a higher photocatalyst and from the viewpoint of performing photocatalytic activity evaluation simultaneously with the addition of a cocatalyst, a method using a photo-deposition method is preferred.

  Examples of the light source for photo-deposition include xenon lamps, mercury lamps or sunlight, which have a distribution with energy higher than the absorption wavelength of oxide particles, but from the viewpoint of irradiating uniformly and inexpensively over a large area. A xenon lamp is preferred. In the photodeposition process, it is preferable to irradiate the surface of the reaction vessel with visible light having a wavelength of 420 nm or more with illuminance.

There is no restriction | limiting in the atmosphere in a photodeposition process, Although it may be under atmospheric pressure or in arbitrary gas, When evaluating photocatalytic ability simultaneously, it is preferable to carry out in argon atmosphere.
In order to suppress the evaporation of the solvent, the highest reaction temperature of the reaction solution in the photodeposition step is preferably 40 ° C. or less, more preferably 10 ° C. to 25 ° C.

  As the metal promoter, any one of platinum, silver, gold, rhodium, chromium and the like is preferable, and any one of platinum and rhodium exhibiting high photocatalytic activity is more preferable. For example, as a platinum raw material, it is preferable to use either hexachloroplatinic acid hexahydrate or tetrachloroplatinic acid hexahydrate from the viewpoint of adhering to strontium titanate fine particles by a reduction reaction in a solvent. The concentration of platinum is preferably 0.1% by weight to 20.0% by weight with respect to the weight of strontium titanate.

When an electron trap is generated between the supported metal promoter and the strontium titanate as the mother catalyst (interface), it is difficult for the promoter to fully exert its effect. In order to make it difficult for electron traps to occur, it is preferable that the strontium titanate fine particles have a crystal plane that has as much lattice matching as possible with the supported metal. The lattice constant of cubic strontium titanate whose shape is controlled as described above is about 0.392 nm. The lattice constant of the lattice constant of Pt, Ir, Pd, Rh, Ru, Cu, Ni, and Co, which are the supported metals, is 12% or less, Ir, Pd is 5% or less, and Pt is 0. Therefore, a highly efficient photocatalyst with few electron traps at the interface with the supported metal can be realized by using cubic strontium titanate fine particles with a high {100} surface ratio on the surface.
Accordingly, the cubic rhodium-doped strontium titanate fine particles of the present invention preferably have a lattice constant value in the range of 0.3915 nm to 0.3930 nm.

  The rhodium-doped strontium titanate fine particles obtained by the present invention can be used for applications other than the hydrogen / oxygen generating photocatalytic system. For example, by using an organic substance such as a ruthenium complex as a cocatalyst, it can be incorporated into an artificial photosynthesis apparatus that generates an organic substance from carbon dioxide. Furthermore, by combining with an oxygen-generating photocatalyst, water can be completely decomposed, which is suitable for a photocatalytic device that simultaneously produces hydrogen and oxygen. As an oxygen generation photocatalyst, it can be suitably combined with tungsten oxide, bismuth vanadate, or the like.

  Furthermore, the cubic strontium titanate fine particles have various advantages such as the fact that the cubic shape is the original shape of the cubic crystal particles, easy to arrange, and easy to form a dense film, other than for photocatalytic applications. Have.

"Design changes"
The present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the gist of the present invention.

Examples will be described below, but the present invention is not limited to these examples.
Example 1
As shown in the flow in FIG. 1, 1 mol of sodium hydroxide (NaOH) was dissolved in 160 mL of pure water placed in a Teflon (registered trademark) three-necked flask to prepare an aqueous sodium hydroxide solution, and strontium (II) nitrate anhydride ( Sr, Ti obtained by adding 2.04 mmol of Wako Pure Chemical Industries, 98%) and 2.04 mmol of titanium oxide (TiO ₂ (P25)) (Degussa, 99.5%) to 40 mL of pure water. The aqueous solution was mixed with an aqueous sodium hydroxide solution to obtain a mixed solution. To this mixed solution, rhodium chloride trihydrate (RhCl ₂ .3H ₂ O) (manufactured by Wako Pure Chemicals, 95%) was added, and the Rh molar concentration in the reaction solution was 1.0% of the Sr molar concentration ([Rh] /[Sr]=0.01), followed by irradiation with ultrasonic waves for several minutes to obtain a suspended reaction solution. The pH of the reaction solution was 14.3.

  The three-necked flask was placed in an aluminum block thermostatic bath with a stirrer (Synflex, BBS-108RB), heated and stirred while stirring at a stirring speed of 500 rpm, and refluxed for 6 hours to react the reaction solution. . The set temperature of the thermostatic bath during heating was set to 150 ° C. The temperature of the reaction liquid at the time of boiling was 100 ° C.

In the desalting step, first, the reaction product was divided into 5 centrifuge tubes of 40 mL each, and each was subjected to a washing step by centrifugation. Then, the supernatant of the centrifuge tube was discarded, and then 20 mL of pure water was added. The suspension was sonicated and the cleaning process was performed again. Centrifugation conditions in the washing step were 10 minutes at 10,000 rpm.
After desalting, 30 mL of pure water is added to each centrifuge tube containing the precipitate to obtain a suspension in which the precipitate is dispersed. The resulting suspension is transferred to a petri dish, and the petri dish is placed on a hot plate. And dried at 100 ° C. for 1 hour to obtain a desalted precipitate.

(Example 2)
Rhodium-doped strontium titanate fine particles were produced in the same manner as in Example 1 except that the titanium raw material was made into a rutile type.

  The result of having measured the TEM photograph and XRD pattern of the rhodium dope strontium titanate fine particles obtained in Example 1 and Example 2 is shown in FIG. In FIG. 2, the results of Example 1 are shown as anatase type, and the results of Example 2 are shown as rutile type. When the titanium raw material was made into a rutile type, the number of cubic particles was small, and many different phases other than the perovskite phase were observed.

Example 3
In this example, under the same production conditions as in Example 1, 4 mL each of the reaction solution in the flask was sampled before heating, immediately after boiling, and every hour after boiling in order to confirm the time-series change of the product. Then, a desalting step and a drying step for removing alkali components and the like in the solvent are performed on each reaction solution to collect precipitates in each sample, and XRD measurement of each precipitate (FIG. 3). ) And TEM photographs were taken (FIG. 4). 3 and 4, it was confirmed that the rhodium-doped strontium titanate fine particles having a cubic perovskite structure can be obtained in at least one hour after boiling.

About the rhodium dope strontium titanate fine particle by Example 3, the result of having performed the thermogravimetric-mass simultaneous analysis (Thermogravimetric-mass simultaneous analyzer (made by Rigaku Corporation, using TG8121)) is shown in FIG. It was estimated that the rhodium-doped strontium titanate fine particles contained water because the substance corresponding to the molecular weight 18 was eliminated along with the decrease. It is estimated that this is slightly increased from the known lattice constant value of SrTiO ₃ (0.3905 nm).

Example 4
The amount of rhodium chloride (RhCl ₂ ) added in the reaction solution was [Rh] / [Sr] = 0 (Example 4-1), 0.02 (Example 4-2), 0.03 (Example 4-3), 0.05 (Example 4-4), 0.10 (Example 4-5), and 0.15 (Example 4-6). Thus, rhodium-doped strontium titanate fine particles were prepared. The results of photographing these XRD spectra and TEM images are shown in FIG. 5 and FIGS. 7A and 7B. First, from the X-ray diffraction pattern of FIG. 5, it was confirmed that a single-phase perovskite structure was obtained up to a rhodium doping concentration of 5%, and a heterogeneous phase was generated at a rhodium doping concentration of 10% or more. 7A and 7B, it was confirmed that rhodium-doped strontium titanate fine particles having a cubic shape can be obtained at any doping concentration. Furthermore, the result of calculating the lattice constant from the peak position of the XRD pattern is shown in FIG. The lattice constant gradually increased in proportion to the rhodium doping concentration, showed a maximum at about 7%, and then gradually decreased. Judging from these matters, it can be determined that rhodium has entered the lattice properly and is in solid solution up to a rhodium doping concentration of about 7%.

  Furthermore, the result of measuring the limited-field electron diffraction pattern is shown in FIG. 7C. From these results, it was confirmed that the exposed surface of the rhodium-doped strontium titanate fine particles by this synthesis method was a (100) surface.

  It was confirmed that the color tone of the synthesized product changed to yellow as the rhodium doping amount was increased. Then, when the diffuse reflection spectrum was measured, the absorption of 350 nm-500 nm increased with the increase in rhodium dope amount (FIG. 8). When the optical band gap is calculated from these diffuse reflection spectra, it is 3.54 eV in the case of non-doping, and the band gap becomes narrower as the rhodium doping amount increases, and it becomes 3.21 eV at the rhodium doping amount of 15%. Was confirmed (FIG. 9). These results are experimental evidence to support that Rh properly substitutes and dissolves Ti sites as the rhodium doping amount increases. It also shows that the wavelength of the visible part of sunlight can be efficiently absorbed by the narrow bandwidth.

(Composition analysis)
Inductively coupled plasma (ICP) for Rh-doped strontium titanate fine particles having a Rh concentration of 3 mol% in Example 4 and Rh-doped strontium titanate fine particles having a Rh concentration of 1 mol% produced by a solid phase method The results are shown in Table 2. In the solid phase method, strontium carbonate (SrCO ₃ ), titanium dioxide (TiO ₂ ), and rhodium oxide (Rh ₂ O ₃ ) are mixed, pre-fired at 900 ° C. for 1 hour, pulverized, and 1000 ° C. Rh-doped strontium titanate fine particles were obtained by performing main firing in 10 hours and grinding.
As shown in Table 2, it was confirmed that the rhodium concentration in the fine particles obtained by synthesis was substantially the same as the charged composition.

(Rhodium electronic state evaluation)
In order to investigate the electronic state of rhodium contained in the rhodium-doped strontium titanate prepared by this synthesis method, Rh valence measurement by electron spin resonance (ESR) (EMX type ESR device manufactured by Bruker Biospin) FIG. 10 shows the result of the above. Moreover, the result of having measured the RSR tetravalent ESR signal about the sample manufactured by the solid-phase method is shown in FIG. For rhodium-doped strontium titanate synthesized by this synthesis method, no rhodium tetravalent peak signal was detected. Rhodium is known to be trivalent or tetravalent, and rhodium trivalent is inactive against ESR. These results suggested that rhodium was trivalent. It is believed that trivalent rhodium contributes to the improvement of the photocatalytic ability, and rhodium-doped strontium titanate produced by this synthesis method is expected to be a suitable raw material for the photocatalyst.

(Example 5)
Next, in order to verify the influence of pH, pH 14.3 (Example 5-1), pH 13.5 (Example 5-2), pH 12 (Example 5-3) were set, and the Rh concentration was [Rh]. Strontium titanate fine particles were prepared in the same manner as in Example 1 except that / [Sr] = 0.
(Example 6)
In order to verify the influence of pH and reaction temperature, the pH is set to 12, the reaction temperature is 90 ° C. (Example 6-1) or 80 ° C. (Example 6-2), and the Rh concentration is [Rh] / [Sr] = 0. Except that, strontium titanate fine particles were produced in the same manner as in Example 1.
(Example 7)
In order to verify whether or not the shape-controlled rhodium-containing strontium titanate could be produced, it was produced in the same manner as in Example 1 except that the reaction temperature was 90 ° C.

(Comparative Example 1)
In order to verify whether or not the shape-controlled rhodium-containing strontium titanate can be produced, it was produced in the same manner as in Example 1 except that the reaction temperature was 77 ° C.

(Evaluation of reaction conditions and cube shape)
Table 3 shows the reaction temperature and pH conditions, the [Rh] / [Sr] values, and the evaluation results of the cubic shape of the strontium titanate fine particles or rhodium-doped strontium titanate fine particles obtained in the above Examples and Comparative Examples. It is. In Table 3, the evaluation of the cube shape is described in four stages of Excellent, Good, Passable, and Bad. The evaluation is performed by circumscribing an isolated single particle image in a rectangle that minimizes the area in an electron microscope (TEM) photograph, and from the rectangular area S ₀ , the particle image area S _cube to S _cube / S ₀ . 0.9 <S _cube / S ₀ is excellent, 0.85 <S _cube / S ₀ ≦ 0.9 is good, and 0.8 <S _cube / S ₀ ≦ 0.85 is passable. , S _cube / S ₀ ≦ 0.8 was defined as Bad.

  Whether or not the shape-controlled rhodium-containing strontium titanate can be produced is mapped to FIG. 13 with the vertical axis representing the reaction temperature and the horizontal axis representing the [Rh] / [Sr] value in the reaction solution. In FIG. 13, the symbols of each plot correspond to the evaluation of the particle shape in the examples described later, the ◎ plot is the excellent evaluation fine particle, the ◯ plot is the Good evaluation fine particle, the Δ plot is the Passable evaluation fine particle, X plots indicate fine particles of Bad evaluation.

  The method for producing oxide fine particles of the present invention can provide cubic oxide fine particles having a uniform particle system distribution at a low temperature under atmospheric pressure, and thus can be used for devices using various metal oxide particles. is there. For example, it can be preferably used as a raw material for a photocatalyst of a hydrogen generation photocatalyst system and an oxygen generation photocatalyst system. At the same time, it can be preferably used as a raw material for electrode constituent materials (such as ohmic forming layers) for electronic components such as ceramic multilayer capacitors.

Claims (17)

A reaction liquid preparation step of preparing a reaction liquid in which a strontium raw material and a titanium raw material are added in an alkaline aqueous solution;
A method for producing strontium titanate fine particles having a cubic shape, comprising a reaction step of reacting the reaction solution by heating the reaction solution to 80 ° C. or higher under atmospheric pressure.   The method for producing strontium titanate fine particles having a cubic shape according to claim 1, wherein the titanium raw material contains a titanium oxide.   The method for producing strontium titanate fine particles having a cubic shape according to claim 2, wherein the titanium oxide is titanium dioxide.   The method for producing strontium titanate fine particles having a cubic shape according to claim 3, wherein the main component of the titanium dioxide is anatase type titanium dioxide.   5. The strontium titanate having a cubic shape according to claim 1, wherein the strontium raw material contains at least one of strontium acetate, nitrate, carbonate, chloride, sulfide, and hydroxide. A method for producing fine particles.   The method for producing strontium titanate fine particles having a cubic shape according to any one of claims 1 to 5, wherein a temperature at which the reaction solution is reacted in the reaction step is 90 ° C or higher and a boiling point or lower.   The method for producing strontium titanate fine particles having a cubic shape according to any one of claims 1 to 6, wherein the pH of the reaction solution is 13.5 or more in the reaction step.   In the reaction liquid preparation step, an Rh raw material is added to the alkaline aqueous solution, or the Rh raw material is mixed with V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Nb, Mo, Ru. 8. The reaction solution is prepared by adding at least one metal raw material of Pd, In, Sb, Ta, W, Re, Ir, Pt, Bi, or La. The manufacturing method of the strontium titanate microparticles | fine-particles which have the cube shape of description.   The method for producing strontium titanate fine particles having a cubic shape according to claim 8, wherein the Rh raw material and the metal raw material in the reaction liquid are water-soluble raw materials.   The method for producing strontium titanate fine particles having a cubic shape according to claim 8 or 9, wherein a total molar ratio of the Rh raw material and the metal raw material to a molar amount of the strontium raw material in the reaction solution is 0.15 or less.   The method for producing strontium titanate fine particles having a cubic shape according to any one of claims 8 to 10, wherein an Rh raw material is added to the alkaline aqueous solution in the reaction solution preparation step.   Cubic strontium titanate fine particles produced by the method for producing strontium titanate fine particles according to claim 1. Represented by the general formula Sr (Ti _1-x (Rh _1-y , M _y ) _x ) O ₃ ,
0 <x ≦ 0.07 and 0 ≦ y <1, and M is V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Nb, Mo, Ru, Pd, In, Sb, Cubic rhodium-doped strontium titanate fine particles that are at least one metal element selected from the group consisting of Ta, W, Re, Ir, Pt, Bi, and La.   The cubic rhodium-doped strontium titanate fine particles according to claim 13, wherein y is 0.   The cubic rhodium-doped strontium titanate fine particles according to claim 13 or 14, wherein a lattice constant value is in a range of 0.3915 nm or more and 0.3930 nm or less.   The cubic rhodium-doped strontium titanate fine particles according to claim 13 or 14, wherein the optical band gap is in the range of 3.21 eV to 3.54 eV.   The average value of the length of one side is 30 nm-80 nm, The cubic rhodium dope strontium titanate fine particles according to any one of claims 13-16.