JP2002012427A - Solid solution type electroconductive niobate containing transition metal and method of producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid solution type electroconductive niobate containing a transition metal, and to provide a method of producing the same. SOLUTION: This is a perovskite type tetragonal niobate material having electroconductivity of 0.01 to 10 Ωm and allowing the switching of electroconductive characteristic between n-type and p-type corresponding with metal species in a solid solution, which comprises a niobate, a transition metal (Mn, Fe, Cu, Ni, Co) and an alkaline earth metal (Ca, Sr, Ba), and if necessary, a rare earth metal (La, Ce, Eu or the like) and is expressed by a formula A0.8-αBαNbO3-δ (α is 0-0.2, A is an alkaline earth metal of Ca, Sr or Ba, or a rare earth metal, and B is a transition metal) or a formula (A, B)xNbO3 (x<=1). The method of producing the tetragonal niobate material in which a transition metal is uniformlydissolved to form a solid solution comprises the steps of mixing under agitation an aqueous alkylamines with a precursor solution in which niobium oxalate, a soluble transition metal and an alkaline earth metal salt, and if necessary, a soluble rare earth metal salt are uniformly solved in water, forming a precipitate, and calcining the obtained precipitate at 900 to 1100 deg.C in air.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a transition showing conductivity.
A of metal solid solution type tetragonal niobate material_0.8-αB_α NbO
_3-δ(Α = 0-0.2, A = Ca, Sr, Ba Alka
Rare earth metal or rare earth metal, B = Cu, Ni, Co, M
n, transition metal of Fe) or (A, B)_x NbO_Three 
(X ≦ 1) and its novel manufacturing process.

[0002]

2. Description of the Related Art Metal oxide ceramics having conductivity and semiconductor properties have been attracting attention as electronic materials such as photoenergy reaction catalysts, high-temperature fuel cell electrodes, and thermoelectric conversion materials. Further, as these materials, demands for materials having high-temperature stability and high chemical stability are increasing. That is, semiconductor and conductive oxide materials, for example,
It can be expected to be used in various fields such as electronic components, photocatalyst materials, electrode materials for high-temperature fuel cells required for next-generation energy development, and thermoelectric conversion materials for effective use of waste heat. Are being considered. Among these materials, tetragonal perovskite-type alkaline earth metal niobate materials are compounds having a layered structure, for example,
Materials exhibiting semiconducting and metallic conductive properties by substituting and solid-dissolving metal ions such as rare earth metals and partially reducing niobium have been reported. Furthermore, since alkaline earth metal niobate materials are excellent in thermal stability and chemical stability, recently, for example, signal conversion elements, dielectrics, memory materials, spectral filters, and light energy reaction catalysts Use as such is being considered.

[0003] In semiconductor and conductive oxide materials, the choice of the synthesis process is important because the synthesis process greatly affects composition control, particle morphology, and the photoelectric properties of the final product. Generally, alkaline earth metal niobate materials are synthesized by a solid phase method. However, in the synthesis by the solid-phase method, a large-scale synthesis is possible, but there is a limit in the process of homogenizing and controlling the composition of the product. Further, alkaline earth metal niobate having a layered structure,
In the solid phase reaction, it is difficult to control the growth of particles, so that it is difficult to prepare a fine raw material by the solid phase method, and it is not easy to sinter a dense polycrystal at normal pressure.

Many alkaline earth metal niobate materials have been reported to exhibit n-type or metallic conductivity because electrons generated by oxygen vacancies accompanying reduction of niobium are used as carriers. Alkaline earth metal niobate materials exhibiting p-type electric conduction characteristics are hardly known. However, if the niobate having the same structure is used as a host material, and the carrier type is controlled by controlling the solid solution composition of a transition metal or the like, the electric conduction characteristics can be arbitrarily controlled to either n-type or p-type. As electronic materials such as photocatalysts and thermoelectric conversion elements, application fields and applications will be expanded. Until now, the addition of conductivity with an alkaline earth metal niobate material required reduction of niobium by annealing treatment in a hydrogen atmosphere or a reduced pressure atmosphere. However, this requires an annealing treatment at a high temperature and for a long time, and therefore there is a demand for improvement in conductivity by controlling the solid solution composition. Furthermore, when used as a powder material, it is necessary to increase the specific surface area of the material. Even when used as a bulk material, it is desirable that the raw material be fine particles having good crystallinity in order to improve the sinterability of the product. Therefore, it is necessary to easily synthesize single-phase crystalline fine particles of nanometer size as a final product.

[0005] It is known that the solid-phase method makes it difficult to equalize and control the composition of the material. On the other hand, in a liquid phase synthesis method such as coprecipitation, the composition of a product is easily controlled by controlling the composition of a mixed solution, and furthermore, the particle morphology of the product can be controlled, so that it is used as a method for synthesizing inorganic materials. However, in the liquid phase synthesis of an alkaline earth metal niobate material, it is difficult to prepare a homogeneous mixed solution serving as a precursor and control the precipitation, and synthesis by a liquid phase synthesis method has not been attempted much.
For niobate materials other than alkaline earth metal niobates,
Fine particles have been synthesized using metal alkoxide complexes. However, the starting metal alkoxide complex is expensive and difficult to handle. Furthermore, since it can be controlled in a reaction at a low concentration, it is useful for synthesizing thin films and the like, but is low in cost performance when used for synthesizing ceramic raw material powders. In addition, a method of preparing a homogeneous solution as a niobium peroxide complex or a chelate complex using a strong acid-soluble reagent such as niobium pentachloride has been used.However, since these are highly water-absorbing reagents, a solution preparation step is performed. Is difficult to handle. Therefore, as a method for synthesizing an alkaline earth metal niobate-based material using a liquid phase reaction process, a simple process that uses a reagent that is easy to handle, prepares a stable mixed solution of niobate, and uses it is necessary. It has been.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a transition metal solid solution type tetragonal niobate material having electrical conductivity of A _0.8-α B _α Nb.
O _3-δ (α = 0 to 0.2, A = Ca, Sr, Ba or rare earth metal, B = transition metal) or (A, B) _x Nb
An object is to provide O ₃ (X ≦ 1, A = alkaline earth metal or rare earth metal, B = transition metal) and a method for producing the same.

[0007]

The present invention for solving the above-mentioned problems comprises the following technical means. (1) Niobate, transition metal (Mn, Fe, Cu, N
i, Co) and alkaline earth metals (Ca, Sr, B)
a) having a conductivity of 0.01 to 10 Ohm, m, containing a rare earth metal (La, Ce, Eu, etc.) as required, and n-type and p-type electric conduction characteristics can be controlled by the solid solution metal species A _0.8-α B _α NbO _3-δ (α = 0-0.2, A = C
a, Sr, Ba alkaline earth metal or rare earth metal, B
= Transition metal) or (A, B) _x NbO ₃ (X ≦ 1)
A perovskite-type tetragonal niobate material represented by the formula: a precursor of a homogeneous mixed aqueous solution in which niobium oxalate, a soluble transition metal, and an alkaline earth metal salt, and if necessary, a soluble rare earth metal salt are dissolved in water A solution and a water-soluble alkylamine are mixed with stirring to form a precipitate, and the obtained precipitate is calcined at 900 to 1100 ° C in the air to obtain a tetragonal niobium in which transition metals are uniformly dissolved. Acid salt material. (2) A method for producing a tetragonal niobate material in which the transition metal according to (1) is uniformly dissolved, wherein niobium oxalate, a soluble transition metal, and an alkaline earth metal are used as starting materials. Using a salt and, if necessary, a soluble rare earth metal salt, dissolving them, preparing a precursor solution as a mixed homogeneous solution, adding a water-soluble strong alkylamine as a precipitant thereto, A hydroxide and an oxide precipitate are efficiently formed while suppressing the dissolution of transition metal ions due to the formation of a soluble transition metal complex, and the resulting precipitate is calcined at 900 to 1100 ° C. in air, so that the transition metal is homogeneous. Transition metal solid solution type niobate characterized by obtaining low-aggregation fine particles of nanoparticle size (10 to 100 nm) consisting of a single phase of tetragonal niobate solid-dissolved in water Method of manufacturing the material.

[0008]

Next, the present invention will be described in more detail. In order to add conductivity to the alkaline earth metal niobate material at low temperature and in a short time without requiring atmosphere control, an alkaline earth metal niobate precursor containing a transition metal is coprecipitated from a liquid phase. The conductivity of the tetragonal alkaline earth metal niobate material was controlled by the transition metal solid solution in the calcination reaction. In the present invention, niobium oxalate as an essential material, soluble transition metals (Mn, Fe, Cu, Ni, Co), and alkaline earth metal (Ca, Sr, Ba) salts (nitrate, chloride) are used as starting materials. Solution of a substance, acetate or metal oxide in a strong acid such as nitric acid or hydrochloric acid)
If necessary, use a soluble rare earth metal salt of any material (a solution of nitrate, chloride, acetate or metal oxide in a strong acid such as nitric acid, hydrochloric acid, etc.), and dissolve them in water as a synthesis process Then, a precursor solution is prepared as a homogeneously mixed aqueous solution, and a water-soluble strong alkylamine as a precipitant is mixed with the resulting mixture under stirring to form a precipitate. Filtering,
After washing with water, in a non-reducing atmosphere (that is, in air) 900 to 11
A step of calcining at 00 ° C is employed. After the obtained calcined powder is pulverized, it is molded by an appropriate means.
By sintering at 0 ° C., a conductive sintered body material is manufactured. 2. Description of the Related Art Conventionally, in order to control the composition of a ceramic material raw material and improve the reactivity of synthetic particles, raw material synthesis by coprecipitation from a homogeneous metal mixed solution capable of easily synthesizing fine particles has been frequently performed. However, niobic acid has a high hydrolysis rate, and it is not easy to synthesize a highly concentrated homogeneous solution.
Therefore, it is difficult to control the particle morphology during the precipitation process by the solution method. Therefore, it is important to consider a synthesis process in which preparation and composition control are easy and particle morphology can be controlled by controlling precipitation reaction. In the present invention, the following technical means are employed to solve the above-mentioned problems.

(1) Use of a homogeneous precursor solution of niobate oxalate mixed with a transition metal and a rare earth metal. In the quantitative analysis of metals, niobate and titanate are
It is known to produce soluble niobate peroxide complexes by mixing with hydrogen peroxide under strongly acidic conditions. When dissolving the niobate in the acidic solution, a metal alkoxide complex, niobium pentachloride or the like can be used. However, these reagents are difficult to handle because they easily react with moisture in the air. Therefore, a method of preparing a precursor solution that is easier to operate is needed. Niobium oxalate (Nb (HC ₂ O
₄ ) ₅ ) is gradually dissolved in a nitric acid solution, and further mixed with hydrogen peroxide to form a hydrogen peroxide complex, and pH <
Dissolves stably in acidic solution of 2. They are stable in the air as compared with metal alkoxides and niobium chloride as reagents, and do not precipitate even after several days of standing at room temperature after dissolution, so that a stable solution of niobate can be prepared. In addition, oxalic acid released during precipitation acts as a pH buffer.
Therefore, it contributes to the control of the precipitation reaction in the neutralization precipitation, and can be expected to have an effect on the control of the particle growth rate in the control of the particle morphology. The cost is lower than that of the alkoxide compound. Furthermore, it is possible to simultaneously dissolve other transition metals and rare earth metal salts in a solution of niobium oxalate dissolved in an acid, and it can be used as a mixed metal salt uniform solution in coprecipitation or uniform precipitation. .

(2) Use of water-soluble alkylamines as a precipitant. Next, when the mixed metal salt solution is used to neutralize and co-precipitate a niobate precursor for forming a solid solution of a transition metal or a rare earth, as a generally used strong alkali precipitant, it does not remain as an impurity after firing. However, co-precipitation with a transition metal or the like forms a soluble complex with ammonia, so that metal ions remain in the solution and cannot be used. Therefore, a precipitant which can be controlled to a strong alkali condition in which a precipitate is formed as a hydroxide or an oxide by hydrolysis, has a low ability to form a complex with a transition metal, and does not leave impurities such as alkali metals in the final product. Needed. Alkylamines are water-soluble and can be adjusted to a strongly alkaline solution by mixing with water. In addition, since the rate of complex formation varies depending on the number of alkyl groups bonded, the ability to form a metal complex may be controlled by the length. This makes it possible to coprecipitate transition metal ions, such as nickel and cobalt, which hardly precipitate with ammonia or the like, with niobate. In addition, alkylamines are adsorbed between layers of ion-exchangeable layered clay compounds.
It is used to control the structure between layers by ion exchange and alignment.Similarly, it is incorporated into the precipitate by adsorption during precipitation and acts as a template to control the microstructure in the precursor. We can expect to do it.
Oxalic acid and alkylamines used in these processes are calcined and decomposed at 600 to 900 ° C., so that they can be easily removed from the sample.

(3) Low-temperature synthesis of a transition metal solid solution type tetragonal niobate conductive material using the precursor prepared in the above (1) and (2). The transition metal solid solution type tetragonal niobate material changes the electric conduction structure in the crystal by controlling the composition, and furthermore, the electron conductivity can be controlled by controlling the metal species to be dissolved and the concentration, so that the high temperature fuel It is attracting attention as an electrode material for batteries and a thermoelectric conversion material. However, its synthesis temperature is 1200
° C or higher, and furthermore, there is a limit to the composition control and uniformity of the composition by the solid phase method, and further to the characteristic control by the control of the particle morphology. Therefore, after various investigations, it was possible to synthesize the desired transition metal solid solution type tetragonal niobate conductive material at low temperature by using the above methods (1) and (2). It has been found that the electrical conduction characteristics (n-type / p-type) of the material can also be controlled by the transition metal species.

According to the present invention, there is provided a transition metal solid solution type square having a fine particle diameter which is expected to be used for various optoelectronic materials as an electrically conductive oxide ceramic material and having a controlled electric conduction property by a solid solution metal species. It is possible to provide a process for synthesizing a crystalline niobate conductive material at a low temperature by using a reagent which is easier to handle and a simple process. In the synthesis process, water-soluble niobium oxalate, soluble transition metals (Mn, Fe, Cu, Ni, Co) and alkaline earth metals (Ca, Sr, Ba) and, if necessary, soluble rare earth metals (La, Ce) , Eu etc.) are dissolved and mixed with a water-soluble salt (nitrate, chloride, acetate or oxide dissolved in a strong acid such as nitric acid) to prepare a precursor solution as a homogeneous mixed solution. Alkylamine solution (methylamine, ethylamine, tetramethylamine,
Propylamine, butylamine, etc.) to prevent the transition metal from dissolving due to the formation of a stable soluble complex, and to efficiently form hydroxides and oxide precipitates. 90 in the air
By calcining at 0 to 1100 ° C., a tetragonal niobate material in which the transition metal is uniformly dissolved can be synthesized as a single phase at a low temperature. Furthermore, the material synthesized in this synthesis process is finer than the powder synthesized by solid-phase reaction and pulverization, and has a relative density of 95% or more as a raw material powder for synthesizing a polycrystalline sintered body. Material can be synthesized. Further, by changing the transition metal species to be dissolved, the electric conduction characteristics can be improved by p.
Type and n-type.

[0013]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples. Example 1 FIG. 1 shows a flow chart of a method for synthesizing a transition metal solid solution type tetragonal niobate conductive oxide material of the present invention using an oxalic acid complex precursor solution and an amine-based precipitant. As shown in FIG. 1, commercially available niobium oxalate Nb (HC ₂ O ₄ ) ₅
(Soekawa Chemical Co., Ltd.) was dissolved in a nitric acid solution containing aqueous hydrogen peroxide, and then the transition metal nitrate Fe (NO ₃ )
₂ , Ni (NO ₃ ) ₂ or Co (NO ₃ ) ₂ and a strontium nitrate solution (Sr (NO ₃ ) ₂ ) at a predetermined ratio, for example, a molar ratio of niobium: transition metal: strontium = 1
0:20:60 to prepare a yellow-green clear homogeneous mixed solution. If necessary, a predetermined amount of a rare earth nitrate solution was mixed. In addition, a 10-fold molar amount of 50
A predetermined amount of a 50% aqueous solution of ammonia or a 50% aqueous solution of butylamine was added with stirring to adjust the pH to 11 to 12, and the mixture was stirred at room temperature for 4 hours to obtain a precipitate. The obtained precipitate is subjected to 1000 rpm
m, separated by a centrifuge for 5 minutes, and washed three times with three times the volume of distilled water. The precipitate was dried at 90 ° C. overnight and calcined at 900 to 1100 ° C. for 10 hours. The obtained precipitates and products were subjected to thermogravimetric analysis, powder X-ray analysis, scanning electron microscope observation, and the like. Also, regarding the electrical characteristics and the heat conduction characteristics, after the calcined powder was pulverized, 200 MPa
, And examined using a molded body sintered at 1200 to 1350 ° C. for 6 hours.

Example 2 The results of thermogravimetric analysis of the niobium-nickel strontium mixed precipitate prepared in Example 1 using ammonia and butylamine as the precipitating agent are shown in FIGS. 2 and 3. The mixed precipitate formed by mixing ammonia is about 2
An endothermic peak due to the elimination of water contained in the precipitate by 00 ° C. and an exothermic peak due to the decomposition and elimination of oxalic acid coprecipitated around 450 ° C. were observed. Further, in the case of the precursor precipitated using butylamine, an exothermic peak due to the decomposition and desorption of butylamine incorporated in the precipitate is observed at around 350 ° C., and butylamine is incorporated in the precipitate. Further, it was found that when the mixed precipitate was heated, no change in weight was observed at 900 ° C. or higher, and the complex and the precipitant were completely eliminated by firing at 900 ° C. or higher. FIG. 4 shows the powder X-ray diffraction patterns of the niobium-nickel strontium mixed precipitate prepared in Example 1 using ammonia and butylamine as the precipitant, and the product calcined at 1100 ° C. for 10 hours. In addition, FIG. 5 shows electron micrographs thereof.

The niobium-nickel strontium mixed precipitate prepared using ammonia as a precipitant is mainly a mixture of strontium hydroxide and niobium oxide hydrate. When butylamine is mixed, the powder X-ray diffraction is low. Peaks were observed at the corners, indicating that niobate having a layered structure was partially contaminated by the incorporation of butylamine during the precipitation process, together with the results of thermal analysis. When those mixed precipitates are calcined at 1100 ° C., the powder X-ray diffraction peak caused by the hydroxide and the layered compound disappears, and the peak of the tetragonal Sr _X NbO ₃ structure (X = 0.5 to 1.0) disappears. Was seen. When the precipitate synthesized with ammonia is calcined, tetragonal Sr having a lattice constant of a = 4.1256 °
An X-ray diffraction peak of the _X NbO ₃ structure (X = 1.0) was generated as a main product, but an X-ray diffraction peak of a pyrochlore phase was also confirmed as a by-product. On the other hand, when the mixed precipitate co-precipitated with butylamine is calcined, a tetragonal crystal having a lattice constant of a = 4.1256 ° and a = 3.955 ° (N
Only the X-ray diffraction peak of the (i, Sr) _X NbO ₃ structure (x = 1.0 and 0.7) was confirmed, and a tetragonal single phase product was obtained. As a result, the desired product could be synthesized at a lower temperature and in a shorter time than the conventional solid phase synthesis of the tetragonal Sr _X NbO ₃ structure (X = 0.5 to 1.0).

The sample coprecipitated with ammonia was a white powder even after firing, but when the sample coprecipitated with butylamine was fired at 1100 ° C. for 10 hours, the color of the resulting powder changed from white to white. It turned black. From this, it is considered that Ni was dissolved in the sample coprecipitated with butylamine. Also, when co-precipitated with ammonia,
It is considered that the color of the solution remained bluish due to the formation of the nickel-ammonium complex, and almost no co-precipitation of nickel into the mixed precipitate occurred. Therefore, no change in the lattice constant and no change in the sample color due to the solid solution of nickel was observed. The mixed precipitate prepared by using butylamine as a precipitant, and a sample obtained by calcining the mixed precipitate were fine particles of 1 μm or less and had low cohesion. Also,
FIG. 6 shows the particle size distribution of a sample obtained by calcining the mixed precipitate prepared by using the solid phase method (1350 ° C., 36 hours), ammonia and butylamine as the precipitant. Powder co-precipitated using solid phase method and ammonia and calcined is 3 μm
When the mixed precipitate prepared with butylamine was calcined, ultra-fine particles of the order of nanometers having a radian diameter of 0.8 μm were obtained.

Example 3 Tetragonal (Ni, Sr) _X NbO ₃ (x = 0.7) prepared in Example 2 using butylamine as a precipitant.
After pulverizing the calcined powder, a compact formed by uniaxial pressure molding to 3 × 3 × 20 mm and CIP molding at 200 MPa was sintered at 1200 ° C. for 6 hours. (Sr _3/4 Ni _1/4 ) _X NbO ₃ (x
= 0.7) and the relative density of the sintered body calculated as about 95%
And a powder obtained by the solid-phase method (1350 ° C., 36 hours) was similarly compacted and sintered (relative density: 83%), and was denser. The surface of the sintered body sample was
The mirror surface was polished with C polishing paper, and the electric resistance value and the thermoelectromotive force (Seebeck coefficient) at a predetermined temperature difference were measured by a DC four-terminal method. Temperature dependence of the electric resistance value of the synthesized tetragonal (Ni, Sr) _x NbO ₃ sintered body and the thermoelectromotive force (Seebeck coefficient) at a predetermined temperature difference, and synthesized in the same manner as in Examples 1 and 2. FIG. 7 shows the electrical resistivity and the thermoelectromotive force of the obtained tetragonal (Sr, Fe) _x NbO ₃ .

The prepared tetragonal (Ni, Sr) _x NbO ₃
The sintered body exhibits a resistance value of about 10 Ohm, m at room temperature, and its resistance value increases from 1.5 × 10 ^-1 to 4.0 × 10 ^-2 Ohm, m (450 to 750 ° C.) as the temperature increases. And decreased. The thermoelectromotive force at 450 to 750 ° C. is 0.1
It showed a positive electromotive force with respect to the temperature difference of about 1.0 mV / K, and its value increased as the temperature increased. Thus, the prepared tetragonal (Ni, Sr) _x NbO
₃ was confirmed to be a p-type conductive oxide material.
On the other hand, tetragonal (Sr, Fe) _x N synthesized by the same method
Although bO ₃ was one order of magnitude lower than tetragonal (Ni, Sr) _x NbO ₃ , conductivity was also confirmed. However, tetragonal (Sr, Fe) _x NbO ₃ was 450 to 7
It exhibited a negative thermoelectromotive force of -0.43 to -0.47 mV / K at 50 ° C, and was an n-type conductive oxide material. From this, tetragonal Sr _x NbO _{3 is formed} by the transition metal to be dissolved.
It was possible to control the electric conduction characteristics (n-type / p-type) of the mold material.

In general, it is known that nickel oxide exhibits p-type conduction characteristics due to hole formation due to oxidation and hopping conduction. Therefore, it is considered that Ni ²⁺ dissolved in the Sr _x NbO ₃ host reduces Nb ⁵⁺ to Nb ⁴⁺ to generate Ni ³⁺ , whereby electron conduction carriers are generated by holes, and conductivity is observed. Further, it is considered that the higher the temperature, the faster the carrier generation and its movement speed, and thus the higher the temperature, the lower the resistance value and the higher the thermoelectromotive force. Further, the control of the electric conduction characteristics (n-type / p-type) by the transition metal dissolved in the tetragonal Sr _x NbO ₃ type material is carried out by using a thermoelectric conversion material or an electronic device material requiring a pn junction such as a vise for rectification. It is important to use this material for easy control of electrical conduction characteristics, and it is expected to prevent problems such as crack destruction due to high temperature strain due to differences in the coefficient of thermal expansion at the time of joining because the same host material is used. it can.

Next, FIG. 8 shows the temperature change of the thermal conductivity of the tetragonal (Sr, Ni) _x NbO ₃ sintered body measured by the laser flash method. Synthesized tetragonal (Sr, Ni) _X N
The heat capacity of bO ₃ at room temperature (23 ° C.) is 0.4922 J /
gK, the thermal diffusivity was 0.004 cm ² / s, and the thermal conductivity was 0.906 W / mK, which was lower than the other conductive oxide materials. In addition, the thermal conductivity increases with an increase in temperature.
The value was 1.45 W / mK. The increase in conductivity at high temperatures is presumably due to the increase in carrier concentration with increasing temperature. In general, it is considered that since the lattice is composed of a heavy element such as niobium, the lattice vibration due to heat is small and the thermal conductivity is low.

According to the above examples, the easily prepared sho
Mixed metal homogeneous solution precursor and butyrate using niobium acid reagent
Coprecipitation of alkaline amines such as
The transition metal that is conductive at low temperature and short time
Solid solution type tetragonal Sr_X NbO_Three Particles can be easily prepared
I found out. In addition, control of the solid solution transition metal composition
It was also found that the electric conduction characteristics could be controlled.

[Brief description of the drawings]

FIG. 1 shows a flow chart of a method for synthesizing a transition metal solid solution type tetragonal niobate conductive oxide material using an oxalic acid complex precursor solution and an amine-based precipitant.

FIG. 2 shows the results of thermogravimetric analysis of a niobium-nickel strontium mixed precipitate prepared using ammonia as a precipitant.

FIG. 3 shows the results of thermogravimetric analysis of a niobium-nickel strontium mixed precipitate prepared using butylamine as a precipitant.

FIG. 4. Niobium-nickel strontium mixed precipitate prepared using ammonia and butylamine as precipitants, and powder of product fired at 1100 ° C. for 10 hours
3 shows an X-ray diffraction pattern.

FIG. 5 shows electron micrographs of a niobium-nickel strontium mixed precipitate prepared using ammonia and butylamine as precipitants, and a product calcined at 1100 ° C. for 10 hours.

FIG. 6 shows a particle size distribution of a sample obtained by calcining a mixed precipitate prepared by a solid phase method (1350 ° C., 36 hours) using ammonia and butylamine as a precipitant.

FIG. 7 shows the electric resistance values of the synthesized tetragonal (Ni, Sr) _x NbO ₃ and tetragonal (Sr, Fe) _x NbO ₃ sintered bodies,
And the temperature dependence of the thermoelectromotive force (Seebeck coefficient) at a predetermined temperature difference.

FIG. 8 shows a tetragonal crystal (S) measured by a laser flash method.
The temperature change of the thermal conductivity of the (r, Ni) _x NbO ₃ sintered body is shown.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masanobu Aano 1-70 Heiwagaoka, Meito-ku, Nagoya-shi, Aichi Prefecture Inogishi House 9 Building 306 (72) Inventor Hiroyoshi Takagi 1 Kamijo-cho, Kasugai-shi, Aichi Prefecture −5-2, Towa City Corp. Kasugai Station (72) Inventor Kunihiro Maeda 2-14-16, Taiharacho, Hitachi City, Ibaraki Prefecture (72) Inventor Motoyuki Miyata 3-26 Higashi-Osugicho Kita-ku, Nagoya City, Aichi Prefecture F-term (Reference) 4G048 AA05 AB02 AB05 AB08 AC04 AD04 AD06 AD08 AE05 AE08 5G301 CA02 CA18 CD04 CE02 5H018 AA01 AS01 BB01 BB12 BB16 EE12 HH08

Claims (2)

[Claims] 1. Niobate, transition metal (Mn, Fe, C)
u, Ni, Co) and alkaline earth metals (Ca, S)
r, Ba) and, if necessary, rare earth metals (La, Ce, Eu)
Including equal), 0.01~10Ohm, has conductivity of m, n-type through solution metallic metal species, p-type electric conduction characteristic is _{controllable, A 0.8-α B α NbO} 3-δ ( α = 0 to 0.
2, A = alkaline earth metal or rare earth metal of Ca, Sr, Ba, B = transition metal) or (A, B) _x NbO ₃
A perovskite-type tetragonal niobate material represented by (X ≦ 1), wherein niobium oxalate, a soluble transition metal,
And a precursor solution of a homogeneously mixed aqueous solution in which an alkaline earth metal salt and, if necessary, a soluble rare earth metal salt are dissolved in water, and a water-soluble alkylamine are mixed with stirring to form a precipitate. A tetragonal niobate material in which transition metals are uniformly dissolved, obtained by calcining at 900 to 1100 ° C in air. 2. A method for producing a tetragonal niobate material in which a transition metal is uniformly dissolved as claimed in claim 1, wherein niobium oxalate, a soluble transition metal, and an alkaline earth are used as starting materials. Using a metal salt and, if necessary, a soluble rare earth metal salt, dissolving them, preparing a precursor solution as a homogeneous mixed solution, and adding a water-soluble strong alkylamine as a precipitant thereto; , Forming hydroxide and oxide precipitates efficiently while suppressing the dissolution of transition metal ions due to the formation of soluble transition metal complexes,
The obtained precipitate is calcined at 900 to 1100 ° C. in the air to obtain a nanoparticle size (10 to 100 n) consisting of a single phase of tetragonal niobate in which a transition metal is uniformly dissolved.
m) A method for producing a transition metal solid solution type conductive niobate material, wherein fine particles having low cohesion are obtained.