Powder for sintered body production, method for producing same, ceramic sintered body, and method for producing same

Abstract

The present invention addresses the problem of providing: a novel powder for sintered body production for manufacturing a ceramic sintered body having excellent electrical properties; a method for producing the novel powder for sintered body production; a ceramic sintered body having excellent electrical properties; and a method for producing the ceramic sintered body. The powder for sintered body production according to the present invention contains a metal element M satisfying the following condition A, has a crystal structure selected from among the pyrochlore structure and the spinel structure, and is synthesized by a liquid phase method. (Condition A) The metal element M is a combination of a metal element M1 that is at least one element selected from the group consisting of Ca, Sr, Zn, Cd, Hg, Bi, Pb, and rare earth elements, and a metal element M2 that 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.

Description

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

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

[0002] Conventionally, in order to improve the performance of ceramic electronic components, the type, blending amount, and particle size of composite oxides used as raw materials have been investigated. Patent Document 1 describes a technology relating to zinc oxide powder for manufacturing zinc oxide sintered bodies.

[0003] International Publication No. 2021 / 029421

[0004] In electronic components constructed using ceramics, the demand for higher performance, reliability, and miniaturization is increasing, making structural control of ceramic sintered bodies increasingly important. Traditionally, structural control of ceramic sintered bodies has primarily focused on the particle size and variability of the raw materials used, the elements and amounts of additives, and crystallinity. However, despite long-term research, these technologies have limitations in significantly improving performance, reliability, and precision at the manufacturing level.

[0005] Therefore, an object of the present invention is to provide a novel powder for manufacturing sintered bodies that has excellent electrical properties. Another object of the present invention is to provide 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.

[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 a sintered body, which contains a metal element M satisfying the condition A described later, and has a crystal structure selected from a pyrochlore structure and a spinel structure, and is synthesized by a liquid-phase method. [2] The powder for manufacturing a sintered body according to [1], wherein the crystallite size determined by measurement based on X-ray diffraction is 10 to 500 nm. [3] A method for manufacturing the powder for manufacturing a sintered body according to [1] or [2], comprising: a precipitate generation step of reacting a salt of the 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 (except for 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 a powder for manufacturing a sintered body. [4] A 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 producing sintered bodies according to [1] or [2]. [6] A ceramic sintered body obtained by sintering a mixture of a ceramic material and the powder for producing sintered bodies according to [1] or [2]. [7] A method for producing a ceramic sintered body, comprising the steps of: mixing a ceramic material and the powder for producing sintered bodies according to [1] or [2] to prepare a mixture; molding the mixture to obtain a molded body; and sintering the molded body to obtain a ceramic sintered body.

[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.

[0009] In this specification, numerical ranges expressed using "~" mean a range that includes the numbers before and after "~" as the lower and upper limits. In this specification, each component may be made using one substance alone or using two or more substances in combination. Here, when two or more substances are used in combination for each component, the content of that component refers to the total content of the substances used in combination, unless otherwise specified.

[0010] [Powder for Sintered Body Production] The powder for sintered body production 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 a powder 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.

[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 body. More specifically, as described later, by adding this powder to a ceramic material (hereinafter also simply referred to as "ceramic material") for manufacturing sintered bodies used as ceramic electronic components, 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 speculate that it is due to the following mechanism. The pyrochlore structure and spinel structure contained in the ceramic sintered body 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 reaction of each oxide contained in the ceramic material during the molding and firing processes of the ceramic material. 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, etc. Therefore, the distribution and grain size of the above-mentioned crystalline phases contained in the sintered body become non-uniform, and as a result, the electrical properties and reliability of the sintered body are thought to be 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 of the sintered body, causing a crystalline phase with a pyrochlore structure to grow. This allows for control over the grain size, distribution, and content of the crystalline phase with the pyrochlore structure, and is presumed to significantly suppress 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 rare earth elements included in metal element M1 include Sc, Y, and lanthanides, with Sc or Y being 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 more of Bi and Pb are more preferred.

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

[0015] The 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. Preferably, the metal element M2 is at least one selected from the group consisting of Sn, Ti, Zr, Ru, Si, Ge, and Sb, and more preferably Sb.

[0016] Metal element M2 may be used alone or in combination of two or more elements. The content of metal element M2 is preferably 15 to 45% by mass, and more preferably 20 to 40% by mass, based on the total mass of the 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 elements M1 and M2 may be oxygen atoms. The oxygen atom content varies depending on the type of metal element contained in this powder, but may be, for example, 5 to 30% by mass or 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 has composition formula (A ２ B ２ O ７ The crystal structure is represented by the compositional formula (AB ２ O ４ The crystal structure is represented by ). In each compositional formula, A and B are metallic elements that exist in cationic form. Some of the metallic elements constituting a particular crystal structure may be substituted with different types of metallic elements. Pyrochlore structures or spinel structures may be doped.

[0019] This powder is synthesized by a liquid-phase method. Powders synthesized by a liquid-phase method have 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, for example, by a solid-phase method, relatively large peaks originating from crystal structures other than the specific crystal structure are detected in the diffraction pattern obtained by powder X-ray diffraction analysis, and it is often difficult to identify the crystal structure to which the powder belongs. This is thought to be because, in solid-phase synthesis methods, during the process of heat-treating 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 the Powder> The powder for producing sintered bodies of the present invention is produced by a liquid-phase method. A liquid-phase method is a method for producing the powder from raw materials containing a metal element M in the presence or in liquid, and the powder can be produced by a known liquid-phase method. A preferred specific example of the method for producing the powder by a liquid-phase method is a method (hereinafter also referred to as "production method A") which includes a precipitate generation step in which a salt of a metal element M is reacted with an alkali in an aqueous buffer solution containing a salt (excluding a salt of a metal element M) to precipitate a precursor containing a 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 metal element M, and examples include carbonates, bicarbonates, sulfates, chlorides, acetates, and nitrates. Specific examples of the above salts include ammonium bicarbonate (bisulfite), 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 step and the stirring curing 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 step, the salt of metal element M is preferably used in aqueous solution form, and it is more preferable to dropwise add an aqueous solution containing the salt of metal element M and an organic acid to an aqueous buffer 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 step, it is preferable that the alkali is also used in aqueous solution form.

[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 that 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 formation 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 the metal element M is the same. Also, 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 easily 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 for example it is 32 hours or less, and 24 hours or less is preferable.

[0027] The powder is obtained by a heat treatment step 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. If the heat treatment temperature is higher than the lower limit, decarboxylation and dehydration during firing can be suppressed, and sintering can be further promoted. Also, the higher the heat treatment temperature, the more dense secondary particles are formed by necking of primary particles. On the other hand, the heat treatment temperature is preferably 1200°C or lower, and more preferably 1000°C or lower. If the heat treatment temperature is lower than the 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. If the heat treatment temperature is below the 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 step 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 manufacturing a ceramic sintered body using this powder (hereinafter also simply referred to as "sintered body") 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, for example, 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 the 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 the 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 a metal element M. In the sintered body, 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 the grain boundaries.

[0032] Sintered bodies are used as various components made of ceramics. They are suitable for use 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.

[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> Zinc nitrate hexahydrate, bismuth(III) nitrate pentahydrate, and antimony(III) chloride (all manufactured by Kishida Chemical Co., Ltd.) were prepared as salts of metal element M, ammonium bicarbonate (manufactured by Kishida Chemical Co., Ltd.) as a carbonate, and 7.4 mol / L aqueous ammonia (manufactured by Kishida Chemical Co., Ltd.) as an alkali.

[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 a 0.8 M aqueous ammonium bicarbonate solution was placed in a 2 L beaker. A pH electrode for pH control was inserted into the aqueous ammonium bicarbonate solution. The above mixed aqueous solution was dropped into the aqueous ammonium bicarbonate solution being stirred by a rotor with a set rotational speed of 500 rpm at a rate of 1 L / h.

[0037] In order to prevent the pH of the aqueous ammonium bicarbonate solution from decreasing due to the dropping of the acidic mixed aqueous solution, 7.4 mol / L aqueous ammonia was dropped into the aqueous ammonium carbonate solution by a liquid delivery pump that was on / off controlled by a pH controller (manufactured by Dongxing Chemical Research Institute, TDP - 51). As a result, the pH of the reaction solution in the beaker was maintained at a constant value of 8 during the dropping of the mixed aqueous solution. Thus, a precipitate was generated by the precipitation reaction. After all of the mixed aqueous solution was dropped and the generation of the precipitate by the precipitation reaction was completed, the generated precipitate was subjected to stirring and aging for 20 hours using a rotor with a set rotational speed of 500 rpm, the same as during the precipitation reaction, to obtain a slurry of precursor A containing zinc, bismuth, and antimony.

[0038] The slurry after stirring and aging was subjected to solid-liquid separation by the suction filtration method to obtain a solid content. The solid content was washed with water to remove ammonia, chlorine, nitric acid, etc. from the obtained solid content. The washing of the solid content was continued until the electrical conductivity of the filtrate became 5 ms / m or less. The washed solid content was subjected to vacuum drying at 40 °C for 20 hours using a vacuum dryer. Thus, a dry powder of precursor A containing zinc, bismuth, and antimony was obtained.

[0039] From the measurement of the thermal weight loss by a TG - DTA device (STA 2500 Regulus manufactured by Netzsch Japan), the heating temperature at which carbonate groups, hydroxyl groups, and adsorbed water were completely desorbed from precursor A and oxides were formed by heating precursor A was confirmed. Also, by measurement using a fluorescent X-ray analyzer (ZSX Primus 4 manufactured by Rigaku), it was confirmed that the composition ratios of zinc, bismuth, and antimony contained in precursor A were as per the charged values. Further, when the filtrate was analyzed, the yield of the precipitate was 90 mass% or more.

[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 perform decarburization and dehydration. In the heat treatment, the temperature was raised at a rate of 5 °C / min, held at 500 °C for 6 hours, and then cooled by natural cooling. Thus, powder A for producing a sintered body was obtained.

[0041] As a result of analyzing the obtained powder A using a powder X-ray diffractometer (D8 ADVANCE manufactured by Bruker), in the obtained X-ray diffraction pattern, while the main peaks derived from the pyrochlore structure (Zn ２ Bi ３ Sb ３ O １４ ) were detected, it was confirmed that no peaks derived from other crystal structures were detected. Also, as a result of evaluating the crystallite size from the X-ray diffraction pattern, the crystallite size of the obtained powder A was 40 nm.

[0042] [Comparative Example 1] <Production of Powder for Producing Sintered Body by Solid Phase Method> As Comparative Example 1, a powder for producing a sintered body was produced by the solid phase method. Specifically, as the metal element M, Sb ２ O ３ (particle size 0.7 μm), Bi ２ O ３ (particle size 1.2 μm), and oxides composed of ZnO (particle size 0.5 μm) were used, and wet grinding was carried out for 24 hours under ion-exchanged water. The obtained grindings were heat-treated by heating at 750 °C for 5 hours to obtain powder C1. Also, the obtained grindings were 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 using ion-exchanged water. Zirconia media with a particle size of 0.05 to 0.15 mm were used as the grinding media, and the particle size of the obtained composite oxide grindings was adjusted to be in the range of 0.2 to 0.9 μm. Also, in order to ensure dispersibility by wet method, a polyacrylic acid-based dispersion solvent in an amount of 5% by mass was added to the above oxides.

[0044] The mixture of the pulverized composite oxide obtained by mixing and grinding, and the solvent, was filtered by suction, dried at a temperature below 100°C, and then processed into a powder using an ultrasonic sieve. The resulting 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 again ground 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 Bodies> Powder X and powder Y, mainly containing zinc oxide, were prepared as ceramic materials to be used in the manufacture of molded bodies and sintered bodies. Table 1 shows the compositions of powder X and powder Y. Powder X was used as is as the reference example powder X for manufacturing sintered bodies. Powder A was added to powder Y to produce mixed powder YA for manufacturing sintered bodies. Powder C1 was added to powder Y to produce mixed powder YC1 for manufacturing sintered bodies. The amount of powder A added to the total mass of mixed powder YA, and the amount of powder C1 added to the total mass of mixed powder YC1 were both 4.98% by mass. The compositions of powder X, mixed powder YA, and mixed powder YC1 (content of each metal oxide shown in the table below) were all the same. 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 the same.

[0047]

[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 atmospheric environment. 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, the sintered bodies manufactured using the mixed powder YA, mixed powder YC1, and powder X for sintered body manufacturing 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 the bodies were baked at 600°C to fabricate elements on disks. The main electrical characteristics of the nonlinear resistors of the fabricated elements were then evaluated. Table 2 shows the electrical characteristics 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 the elements on disks, measured after each sintered body was stored in an 85°C 85RH bath for 2000 hours.

[0051]

[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 characteristics, 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 characteristics 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. The reason for this is thought to be that in powder C1 manufactured by the solid-phase method, a large amount of undetermined substances precipitated as 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 synthesized by a liquid-phase method, containing a metal element M that satisfies the following condition A, and having a crystal structure selected from pyrochlore structure and spinel structure. (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.

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 sintered bodies according to claim 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 claim 3, wherein in the precipitate formation 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 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 claim 1 or 2; molding the mixture to obtain a molded body; and sintering the molded body to obtain a ceramic sintered body.

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