Powder for manufacturing sintered bodies and method for manufacturing the same, and ceramic sintered bodies and method for manufacturing the same

Abstract

The object of the present invention is to provide a novel powder for manufacturing a ceramic sintered body with excellent electrical properties, a method for manufacturing the novel powder for manufacturing a ceramic sintered body, a ceramic sintered body with excellent electrical properties, and a method for manufacturing the ceramic sintered body. [Solution] The powder for manufacturing sintered bodies of the present invention contains a metal element M that satisfies the following condition A, and has a crystal structure selected from pyrochlore structure and spinel structure, and is a powder for manufacturing sintered bodies synthesized by a liquid-phase method. (Condition A) The metal element M is a combination of a metal element M1 which is at least one selected from the group consisting of Ca, Sr, Zn, Cd, Hg, Bi, Pb and rare earth elements, and a metal element M2 which is at least one selected from the group consisting of B, Sn, Ti, Zr, V, Mo, Pt, Ru, Ir, Si, Ge, Hf, Nb, Ta and Sb.

Description

Technical Field

[0001] The present invention relates to a powder for manufacturing a sintered body, a method for manufacturing the same, a ceramic sintered body, and a method for manufacturing the same.

Background Art

[0002] Conventionally, in order to improve the performance of ceramic electronic components, the types, blending amounts, particle sizes, etc. of composite oxides used as raw materials have been studied. Patent Document 1 describes a technique related to zinc oxide powder for manufacturing a zinc oxide sintered body.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In electronic components composed of ceramics, the demands for higher performance, reliability, miniaturization, etc. are increasing more and more, and the importance of controlling the structure of ceramic sintered bodies is increasing. Conventionally, regarding the control of the structure of ceramic sintered bodies, it can be said that attention has mainly been paid to the particle size and variation of raw materials used, elements including additives and addition amounts, and crystallinity. However, as a result of long-term research on these technologies, it can be said that there are limitations in significantly improving performance, reliability, accuracy, etc. at the manufacturing level.

[0005] Therefore, an object of the present invention is to provide a novel powder for manufacturing a sintered body for manufacturing a ceramic sintered body having excellent electrical characteristics. Another object of the present invention is to provide a method for manufacturing a novel powder for manufacturing a sintered body, a ceramic sintered body having excellent electrical characteristics, and a method for manufacturing the ceramic sintered body. [Means for solving the problem]

[0006] As a result of diligent research, the inventors have found that the above problems can be solved by adopting the following configuration.

[0007] In other words, the present invention relates to the following [1] to [7]. [1] A powder for manufacturing sintered bodies, which contains a metal element M that satisfies the conditions A described later, and has a crystal structure selected from pyrochlore structure and spinel structure, and is synthesized by a liquid-phase method. [2] The powder for manufacturing a sintered body as described in [1], wherein the crystallite size determined by measurement based on X-ray diffraction is 10 to 500 nm. [3] A method for producing powder for sintered bodies according to [1] or [2], comprising: a precipitate generation step of reacting a salt of metal element M with an alkali in an aqueous buffer solution containing at least one salt selected from the group consisting of carbonates, bicarbonates, sulfates, chlorides, acetates and nitrates (excluding a salt of the metal element M), thereby precipitating a precursor containing the metal element M; and a heat treatment step of heat treating the precursor to obtain powder for sintered bodies. [4] The method for producing powder for sintered bodies according to [3], wherein in the precipitate formation step, an aqueous solution containing the salt of the metal element M and an organic acid, and an aqueous solution containing the alkali are each added dropwise to the buffer aqueous solution to react the salt of the metal element M with the alkali. [5] A ceramic sintered body obtained by sintering the powder for manufacturing a sintered body described in [1] or [2]. [6] A ceramic sintered body obtained by sintering a mixture of a ceramic material and the powder for manufacturing a sintered body described in [1] or [2]. [7] A method for producing a ceramic sintered body, comprising the steps of: preparing a mixture by mixing a ceramic material with the sintered body production powder described in [1] or [2]; molding the mixture to obtain a molded body; and sintering the molded body to obtain a ceramic sintered body. [Effects of the Invention]

[0008] According to the present invention, a novel powder for manufacturing sintered bodies with excellent electrical properties can be provided. Furthermore, according to the present invention, a method for manufacturing a novel powder for manufacturing sintered bodies, a ceramic sintered body with excellent electrical properties, and a method for manufacturing said ceramic sintered body can be provided. [Modes for carrying out the invention]

[0009] In this specification, a numerical range represented by "~" means a range that includes the numbers written before and after "~" as the lower and upper limits, respectively. In this specification, each component may be represented by a single substance or by a combination of two or more substances. When two or more substances are used in combination for each component, the content of that component refers to the total content of the combined substances unless otherwise specified.

[0010] [Powder for sintered body manufacturing] The powder for manufacturing sintered bodies of the present invention (hereinafter also simply referred to as "this powder") contains a metal element M that satisfies the following condition A, and has a crystal structure selected from pyrochlore structure and spinel structure, and is synthesized by a liquid-phase method. (Condition A) Metal element M, A metallic element M1 is at least one selected from the group consisting of Ca, Sr, Zn, Cd, Hg, Bi, Pb, and rare earth elements. It is a combination with a metallic element M2, which is at least one element selected from the group consisting of B, Sn, Ti, Zr, V, Mo, Pt, Ru, Ir, Si, Ge, Hf, Nb, Ta, and Sb.

[0011] This powder is used, for example, in the manufacture of sintered bodies used as ceramic electronic components, to precisely control the performance and reliability of the sintered bodies. More specifically, as described later, by adding this powder to a ceramic material (hereinafter also simply referred to as "ceramic material") used to manufacture a sintered body for use as a ceramic electronic component, and then molding and firing the mixture of this powder and the ceramic material, a ceramic sintered body with excellent electrical properties can be manufactured.

[0012] The detailed reason why adding this powder to ceramic materials can produce ceramic sintered bodies (hereinafter also simply referred to as "sintered bodies") with excellent electrical properties is still unknown, but the inventors of the present invention surmise that it is due to the following mechanism. The pyrochlore and spinel structures contained in ceramic sintered bodies are one of the factors that affect the electrical properties and reliability of the sintered body, and are thought to be generated by the thermal reactions of each oxide contained in the ceramic material during the molding and firing processes of the ceramic material. Since the generation and growth of crystalline phases having pyrochlore or spinel structures differ depending on the composition of the ceramic material, the distribution of oxides in the molded body, the molding method, the sintering method, and the size of the sintered body, the distribution and grain size of the above-mentioned crystalline phases contained in the sintered body become non-uniform, and as a result, it is presumed that the electrical properties and reliability of the sintered body are greatly impaired. In contrast, when this powder, which contains a predetermined metal element M and has a pyrochlore structure, is pre-added to a ceramic material, and a sintered body is manufactured using the resulting mixture, the powder acts as a seed crystal during the manufacturing process, causing a pyrochlore-structured crystalline phase to grow. This allows for control over the grain size, distribution, and content of the pyrochlore-structured crystalline phase, thereby significantly suppressing variations. As a result, it is believed that using a mixture containing this powder and a ceramic material will enable a more stable supply of ceramic sintered bodies with excellent electrical properties and high reliability. The present invention will be described in more detail below.

[0013] This powder contains a metal element M that satisfies condition A. In other words, this powder contains a combination of metal element M1 and metal element M2. Metal element M1 is at least one selected from the group consisting of Ca, Sr, Zn, Cd, Hg, Bi, Pb, and rare earth elements. Examples of the rare earth elements contained in metal element M1 include Sc, Y, and lanthanoids, and Sc or Y is preferred. As metal element M1, at least one selected from the group consisting of Ca, Sr, Zn, Cd, Hg, Bi, Pb, and rare earth elements is preferred, and Zn and either or both of Bi and Pb are more preferred.

[0014] Metal element M1 may be used alone or in combination of two or more. The content of metal element M1 is preferably 30 to 75% by mass, more preferably 40 to 65% by mass, based on the total mass of this powder.

[0015] Metal element M2 is at least one selected from the group consisting of B, Sn, Ti, Zr, V, Mo, Pt, Ru, Ir, Si, Ge, Hf, Nb, Ta, and Sb. As metal element M2, at least one selected from the group consisting of Sn, Ti, Zr, Ru, Si, Ge, and Sb is preferred, and Sb is more preferred.

[0016] Metal element M2 may be used alone or in combination of two or more. The content of metal element M2 is preferably 15 to 45% by mass, more preferably 20 to 40% by mass, based on the total mass of this powder.

[0017] This powder is, for example, a composite oxide of metal element M1 and metal element M2. That is, in this powder, the remainder excluding metal element M1 and metal element M2 may be oxygen atoms. The content of oxygen atoms varies depending on the types of metal elements contained in this powder, but may be, for example, 5 to 30% by mass, or may be 10 to 25% by mass.

[0018] This powder has a crystal structure selected from pyrochlore structure and spinel structure (hereinafter also referred to as "specific crystal structure"). The pyrochlore structure is a crystalline structure represented by the chemical formula (A2B2O7), and the spinel structure is a crystalline structure represented by the chemical formula (AB2O4). In each chemical formula, A and B are metallic elements that exist in cation form. Some of the metal elements constituting a particular crystal structure may be substituted with different types of metal elements. The pyrochlore structure or spinel structure may be doped.

[0019] This powder was synthesized using a liquid-phase method. The powder synthesized by the liquid-phase method has a uniform, specific crystal structure. Here, having a uniform, specific crystal structure means that in the diffraction pattern obtained by powder X-ray diffraction analysis, the peak originating from the specific crystal structure is detected as the main peak, and peaks originating from crystal structures other than the specific crystal structure (hereinafter also referred to as "other crystal structures") are not detected or are very small compared to the peak originating from the specific crystal structure. On the other hand, in the case of composite oxide powders synthesized by synthesis methods other than the liquid-phase method, such as the solid-phase method, relatively large peaks originating from crystal structures other than the specific crystal structure are often detected in the diffraction pattern obtained by powder X-ray diffraction analysis, making it difficult to identify the crystal structure to which the powder belongs. This is thought to be because, in the solid-phase synthesis method, during the heat treatment process of the mixture of each oxide particle, the material volatilizes due to heating at high temperatures, and the difference in reaction rates becomes large due to the temperature difference between the exposed surface and the interior, resulting in the formation of unintended crystal structures other than the specific crystal structure.

[0020] The average crystallite size (hereinafter also simply referred to as "crystallite size") of this powder, as determined by measurement based on X-ray diffraction (XRD), is, for example, 10 to 500 nm, preferably 20 to 350 nm, and more preferably 30 to 200 nm.

[0021] <Method for producing this powder> The powder for manufacturing sintered bodies of the present invention is manufactured by a liquid-phase method. A liquid-phase method is a method for manufacturing the powder from raw materials containing a metal element M in the presence or in a liquid, and the powder can be manufactured by a known liquid-phase method. A preferred example of the liquid-phase method for producing this powder is a method (hereinafter also referred to as "production method A") which includes a precipitate formation step in which a salt of metal element M is reacted with an alkali in an aqueous buffer solution containing a salt (excluding a salt of metal element M) to precipitate a precursor containing metal element M, and a heat treatment step in which the precursor is heat-treated to obtain the powder.

[0022] In manufacturing method A, the salt used in the buffer aqueous solution is not particularly limited as long as it does not contain the metal element M, and examples include carbonates, bicarbonates, sulfates, chlorides, acetates, and nitrates. Specific examples of the above salts include ammonium bicarbonate, sodium carbonate, sodium bicarbonate (baking soda), ammonium nitrate, sodium chloride, ammonium chloride, sodium sulfate, ammonium sulfate, sodium acetate, and ammonium acetate, with ammonium bicarbonate, sodium bicarbonate, or ammonium acetate being preferred. In the precipitate formation process and the stirring curing process described later, the temperature of the buffer aqueous solution is preferably kept below 45°C, and more preferably below 25°C.

[0023] The salt of metal element M used in manufacturing method A is not particularly limited, but salts with good water solubility are preferred, and at least one selected from the group consisting of nitrate of metal element M, chloride of metal element M, sulfate of metal element M, acetate of metal element M, and hydrates thereof is preferred. In the precipitation process, the salt of metal element M is preferably used in the form of an aqueous solution, and it is more preferable to add an aqueous solution containing the salt of metal element M and an organic acid dropwise to the buffer aqueous solution. Examples of organic acids include tartaric acid, lactic acid, citric acid, malic acid, fumaric acid, and acetic acid, with tartaric acid, lactic acid, or citric acid being preferred.

[0024] The alkali used in manufacturing method A is not particularly limited, but suitable examples include sodium hydroxide and potassium hydroxide. When the alkali is used in aqueous solution form, ammonium hydroxide may also be used. In the precipitate formation process, it is preferable that the alkali is also used in the form of an aqueous solution.

[0025] In the precipitate formation process, while adding an aqueous solution containing a salt of metal element M (more preferably an aqueous solution containing a salt of metal element M and an organic acid) dropwise, it is preferable to add an alkaline aqueous solution to the buffer aqueous solution to maintain a constant pH of the buffer aqueous solution. The pH of the buffer aqueous solution, which is maintained at a constant value, is preferably 6.0 or higher, more preferably 7.0 or higher, preferably 10.0 or lower, more preferably 9.0 or lower, and even more preferably 8.0 or lower.

[0026] In manufacturing method A, it is preferable to further include a step of stirring and curing the precursor containing the metal element M produced as a precipitate between the precipitate generation step and the heat treatment step. The stirring and curing time is preferably 1 hour or more, more preferably 5 hours or more, even more preferably 10 hours or more, and particularly preferably 15 hours or more. When the stirring and curing time is longer than the lower limit above, the density of the molded body and sintered body will be higher and more stable compared to when the stirring and curing time is shorter, provided that the content of metal element M is the same. Furthermore, when the stirring and curing time is longer than the lower limit above, it is thought that the flake shape, which is the characteristic shape of layered hydroxide, will disappear due to repeated collisions caused by stirring, and it will tend to become granular. The upper limit of the stirring and curing time is not particularly limited and depends on the concentration of the reaction solution and the stirring force, but is, for example, 32 hours or less, and preferably 24 hours or less.

[0027] This powder is obtained by a heat treatment process in which the precursor obtained by the precipitate formation reaction is heat-treated. The heat treatment temperature is preferably 250°C or higher, and more preferably 320°C or higher. When the heat treatment temperature is higher than the lower limit mentioned above, decarboxylation and dehydration during firing are suppressed, and sintering can be further promoted. In addition, the higher the heat treatment temperature, the more dense secondary particles are formed by necking of the primary particles. On the other hand, the heat treatment temperature is preferably 1200°C or lower, and more preferably 1000°C or lower. When the heat treatment temperature is lower than the above upper limit, the formation of linked grains, in which primary particles are bonded together, can be suppressed. Linked grains grow quickly, and the formation of linked grains leads to the formation of larger sintered particles, a phenomenon well known as Ostwald growth. When the heat treatment temperature is below the above upper limit, the formation of linked grains is suppressed, and it is thought that the particle size of the sintered body becomes more uniform. The heat treatment time in the heat treatment process is not particularly limited, but is preferably 2 to 12 hours, and more preferably 4 to 10 hours.

[0028] [Ceramic sintered body] This powder is used in the manufacture of ceramic sintered bodies. A method for producing a ceramic sintered body (hereinafter also simply referred to as "sintered body") using this powder includes, for example, a molding step of molding a raw material powder containing this powder to obtain a molded body, and a sintering step of sintering the molded body to obtain a sintered body.

[0029] The raw material powder may be the powder alone or a mixture containing the powder and a ceramic material, with the mixture containing the powder and a ceramic material being preferred. As the ceramic material, known materials used in the manufacture of ceramic sintered bodies can be used, such as metal oxides containing one or more metals such as zinc (Zn), bismuth (Bi), cobalt (Co), manganese (Mn), and nickel (Ni). The metal oxide may also be a composite oxide containing two or more of the above metals. The content of this powder in the above mixture is, for example, 0.5 to 10% by mass, and preferably 1.5 to 6.0% by mass, relative to the total content of the ceramic material and this powder.

[0030] The method for manufacturing a sintered body, including the molding and sintering steps, is not particularly limited, and known manufacturing methods using ceramic materials can be applied. The raw material powder used for molding may be crushed using a bead mill as needed. Alternatively, the raw material powder may be manufactured by granulation using a spray dryer.

[0031] Examples of sintered bodies produced using this powder include sintered bodies made by sintering this powder, and sintered bodies made by sintering a mixture of this powder and a ceramic material. The sintered body is preferably a solid solution containing the metal element M. In sintered bodies, depending on its content and / or firing temperature, the metal element M may form compounds such as oxides and exist as a secondary phase at grain boundaries.

[0032] Sintered bodies are used as various components made of ceramics. Sintered bodies can be suitably used as components requiring uniform composition, such as sputter targets and varistors; gas sensors such as thick-film gas sensors that undergo repeated thermal history; filters such as antibacterial filters that prevent the growth of E. coli and other bacteria; and ceramic structures for high-temperature furnaces that are repeatedly heated. [Examples]

[0033] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the following examples.

[0034] [Example of Invention 1] <Production of powder for sintered body manufacturing by liquid phase method> As salts of metal element M, zinc nitrate hexahydrate, bismuth(III) nitrate pentahydrate, and antimony(III) chloride (all manufactured by Kishida Chemical Co., Ltd.) were prepared; as a carbonate, ammonium bicarbonate (manufactured by Kishida Chemical Co., Ltd.); and as an alkali, 7.4 mol / L aqueous ammonia (manufactured by Kishida Chemical Co., Ltd.).

[0035] A mixed aqueous solution containing zinc nitrate, bismuth nitrate, and antimony chloride was prepared by dissolving 15 g of tartaric acid in 200 mL of 2 mol / L aqueous nitric acid solution, and then dissolving 7.44 g of zinc nitrate hexahydrate, 18.19 g of bismuth nitrate pentahydrate, and 8.73 g of antimony chloride in this mixed solvent.

[0036] 200 mL of 0.8 M ammonium bicarbonate solution was placed in a 2 L beaker. A pH electrode for pH control was inserted into the ammonium bicarbonate aqueous solution. The mixed aqueous solution was added dropwise at a rate of 1 L / h to the ammonium bicarbonate aqueous solution, which was being stirred by a rotor set to a rotation speed of 500 rpm.

[0037] To prevent the pH of the ammonium bicarbonate solution from decreasing due to the addition of the acidic mixed aqueous solution, 7.4 mol / L ammonia water was added to the ammonium bicarbonate solution dropwise using a liquid delivery pump controlled by a pH controller (TDP-51, manufactured by Toko Chemical Research Institute). This maintained the pH of the reaction solution in the beaker at a constant value of 8 during the addition of the mixed aqueous solution. In this way, a precipitate was formed through the precipitate formation reaction. All the mixed aqueous solutions were added dropwise, and after the precipitate formation reaction was completed, the formed precipitate was stirred and cured for 20 hours using a rotor set to the same rotation speed of 500 rpm as during the precipitate formation reaction, to obtain a slurry of precursor A containing zinc, bismuth, and antimony.

[0038] The slurry, after stirring and curing, was separated into solid and liquid components by suction filtration to obtain the solid component. The obtained solid component was washed with water to remove ammonia, chlorine, nitric acid, and other substances. The washing of the solid component with water was continued until the electrical conductivity of the filtrate was 5 ms / m or less. The solid components after washing were vacuum-dried at 40°C for 20 hours using a vacuum dryer. In this way, a dried powder of precursor A containing zinc, bismuth, and antimony was obtained.

[0039] By measuring the loss on heat using a TG-DTA instrument (STA 2500 Regulus, manufactured by Netch Japan), we confirmed the heating temperature at which carbonate groups, hydroxyl groups, and adsorbed water are completely detached from precursor A upon heating, and oxides are formed. Furthermore, measurements using an X-ray fluorescence analyzer (Rigaku ZSX Prius 4) confirmed that the composition ratio of zinc, bismuth, and antimony contained in precursor A was as specified in the initial calculations. Furthermore, analysis of the filtrate revealed that the yield of precipitate was over 90% by mass.

[0040] The dried powder of the obtained precursor A was placed in an alumina crucible and heat-treated at 500°C in an air atmosphere to decarbonate and dehydrate it. During the heat treatment, the temperature was increased at a rate of 5°C / min, held at 500°C for 6 hours, and then cooled by natural cooling. In this way, powder A for sintering body production was obtained.

[0041] The obtained powder A was analyzed using a powder X-ray diffractometer (Brooker, D8 ADVANCE), and the resulting X-ray diffraction pattern showed a pyrochlore structure (Zn2Bi3Sb3O 14 While a main peak originating from ) was detected, it was confirmed that no peaks originating from other crystal structures were detected. Furthermore, the crystallite size of the obtained powder A was evaluated from the X-ray diffraction pattern and found to be 40 nm.

[0042] [Comparative Example 1] <Production of powder for sintered body manufacturing by solid-phase method> As Comparative Example 1, a powder for sintered body production was manufactured by a solid-phase method. Specifically, an oxide consisting of Sb2O3 (particle size 0.7 μm), Bi2O3 (particle size 1.2 μm), and ZnO (particle size 0.5 μm) was used as the metal element M, and mixed pulverization was carried out for 24 hours under ion-exchanged water. The resulting pulverized material was heat-treated by heating at 750°C for 5 hours to obtain powder C1. The obtained pulverized material was also heat-treated by heating at 900°C for 5 hours to obtain powder C2.

[0043] More specifically, the above oxides were mixed and ground using a bead mill in a wet environment with deionized water. Zirconia media with a particle size of 0.05 to 0.15 mm was used as the grinding media, and the resulting composite oxide pulverized material was sized so that the particle size was within the range of 0.2 to 0.9 μm. In addition, to ensure dispersibility in the wet environment, a polyacrylic acid-based dispersion solvent in an amount of 5% by mass relative to the above oxides was added.

[0044] The mixture of the pulverized composite oxide obtained by mixed pulverization and the solvent was filtered by suction, the filtrate was dried at a temperature below 100°C, and then processed into a powder using an ultrasonic sieve. The obtained powdered composite oxide was heat-treated using a rotary kiln. To obtain a uniform and stable powder, the heat treatment was performed at a temperature lower than the crystallization temperature for an extended period. The heat treatment temperature was set to 750°C for the production of powder C1 and to 900°C for the production of powder C2, and each temperature was maintained for 5 hours. The powders obtained by the heat treatment were then crushed and dried using a bead mill to obtain powders C1 and C2, respectively. The particle sizes of powders C1 and C2 were in the range of 0.2 to 0.8 μm.

[0045] Similar to Invention Example 1, powder X-ray diffraction analysis was performed on the obtained powders C1 and C2. As a result, in each powder produced by the solid-phase method of Comparative Example 1, a stable crystalline phase could not be obtained, and in addition to the peak originating from the pyrochlore structure, many peaks with high peak intensity originating from other crystalline structures were detected. Therefore, the powder X-ray diffractometer could not identify the crystalline structure to which each powder belonged, and the crystalline structure of each powder was determined to be "Unknown".

[0046] <Manufacturing of molded products> Powder X and powder Y, mainly containing zinc oxide, were prepared as ceramic materials for the manufacture of molded and sintered bodies. Table 1 shows the compositions of powder X and powder Y. Powder X was used as is, as powder X for sintered body manufacturing in the reference example. Mixed powder YA for sintered body production was prepared by adding powder A to powder Y. Similarly, mixed powder YC1 for sintered body production was prepared by adding powder C1 to powder Y. The amount of powder A added to mixed powder YA relative to the total mass, and the amount of powder C1 added to mixed powder YC1 relative to the total mass, were both 4.98% by mass. The compositions of powder X, mixed powder YA, and mixed powder YC1 (the content of each metal oxide shown in the table below) were all identical. In other words, the composition and mixing ratio of each powder were adjusted so that the compositions of powder X, mixed powder YA, and mixed powder YC1 were identical.

[0047] [Table 1]

[0048] Polyvinyl alcohol was added to each of the mixed powders YA, YC1, and X for sintering body production in an amount equivalent to 0.5% by mass of each powder. The resulting mixtures were then press-molded at a pressure of 100 MPa to produce disc-shaped molded bodies with dimensions of φ20 mm × 2 mm.

[0049] <Manufacturing of sintered bodies> Each manufactured disc-shaped molded body was fired in an air atmosphere. The firing temperature (maximum temperature) was set to 1100°C. The holding time at the firing temperature was 3 hours, the heating rate was 200°C / h, and cooling was performed by furnace cooling. In this way, disc-shaped sintered bodies (ceramic nonlinear resistors) were manufactured. Hereinafter, sintered bodies produced using mixed powder YA, mixed powder YC1, and powder X for sintered body production will also be referred to as sintered body A (Inventive Example 1), sintered body C (Comparative Example 1), and sintered body X (Reference Example).

[0050] <evaluation> Ag electrodes were printed on both sides of the three types of sintered bodies A, C, and X obtained, and then baked at 600°C to fabricate elements on disks. After that, the main electrical properties of the nonlinear resistors of the fabricated elements were evaluated. Table 2 shows the electrical properties and evaluation results of the evaluated elements. The values ​​shown in the "Continuous Load Characteristics [%]" column of Table 2 represent the percentage change in the varistor voltage measured before storage of each sintered body, measured after 2000 hours in an 85°C 85RH bath.

[0051] [Table 2]

[0052] Compared to the reference example sintered body X manufactured using conventional ceramic materials, the sintered body A of Invention Example 1, manufactured using mixed powder YA, which has a pyrochlore structure according to the present invention and is produced by adding powder A synthesized by a liquid-phase method to a ceramic material, showed significant improvements in electrical properties, which are important for achieving high performance, high reliability, and miniaturization, particularly the nonlinearity coefficient α value (a large value is desirable), surge current withstand capability (a large value is desirable), and the reliability characteristic, continuous load characteristics (a small rate of change is desirable). This indicates that by using mixed powder YA, to which powder A of the present invention has been pre-added as a raw material for manufacturing the sintered body by sintering oxide powder, grain growth during firing was stabilized, and the current applied when the electrical properties were tested was distributed more uniformly.

[0053] Furthermore, in the case of sintered body C manufactured using mixed powder YC1, which was produced by adding powder C1 manufactured by the solid-phase method to a ceramic material, the results were actually inferior to the reference example in many of the major electrical properties of the nonlinear resistor. This is thought to be because powder C1 manufactured by the solid-phase method precipitated a large amount of undetermined by-products during manufacturing, and many crystal structures other than the specific crystal structure were present, thus reducing the effect of adding powder with the specific crystal structure.

Claims

1. A powder for manufacturing sintered bodies, containing a metal element M that satisfies the following condition A, and having a crystal structure selected from pyrochlore structure and spinel structure, synthesized by a liquid-phase method. (Condition A) The aforementioned metal element M is A metallic element M1 is at least one selected from the group consisting of Ca, Sr, Zn, Cd, Hg, Bi, Pb, and rare earth elements, This is a combination with a metal element M2, which is at least one selected from the group consisting of B, Sn, Ti, Zr, V, Mo, Pt, Ru, Ir, Si, Ge, Hf, Nb, Ta, and Sb.

2. The powder for manufacturing a sintered body according to claim 1, wherein the crystallite size determined by measurement based on X-ray diffraction is 10 to 500 nm.

3. A method for producing powder for manufacturing a sintered body according to claim 1 or 2, A precipitate formation step in which a salt of metal element M is reacted with an alkali in an aqueous buffer solution containing at least one salt selected from the group consisting of carbonates, bicarbonates, sulfates, chlorides, acetates, and nitrates (excluding salts of the metal element M), thereby precipitating a precursor containing the metal element M. A method for producing powder for sintered bodies, comprising a heat treatment step of heat-treating the precursor to obtain powder for producing sintered bodies.

4. The method for producing powder for sintered bodies according to claim 3, wherein in the precipitate generation step, an aqueous solution containing a salt of the metal element M and an organic acid, and an aqueous solution containing the alkali are each added dropwise to the buffer aqueous solution to react the salt of the metal element M with the alkali.

5. A ceramic sintered body obtained by sintering the powder for manufacturing a sintered body according to claim 1 or 2.

6. A ceramic sintered body obtained by sintering a mixture of a ceramic material and the powder for manufacturing a sintered body described in claim 1 or 2.

7. A step of preparing a mixture by mixing a ceramic material with the powder for manufacturing a sintered body according to claim 1 or 2, A step of molding the mixture to obtain a molded body, The process includes the step of sintering the molded body to obtain a ceramic sintered body. A method for manufacturing ceramic sintered bodies.

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