Barium titanate particles

Abstract

The disclosed barium titanate particles have voids inside, and the average ratio of the void area to the particle area in the transmission electron microscope image, determined by binarizing the transmission electron microscope image, is in the range of 0.05% to 1.0%, and the ratio of barium atoms to titanium atoms A / B is 0.990 or higher.

Description

[Technical Field]

[0001] This disclosure relates to barium titanate particles. [Background technology]

[0002] Barium titanate particles are used as dielectric materials in various fields. For example, barium titanate particles are used as a material for multilayer ceramic capacitors (MLCCs). Various technologies related to barium titanate particles have been proposed over the years.

[0003] Claim 1 of Patent Document 1 (Japanese Patent Publication No. 2013-209250) discloses "a ceramic powder containing barium titanate having a perovskite structure with an average particle size (median diameter) of 200 nm or less as measured by SEM observation, wherein the proportion of twin defects measured by TEM observation of the barium titanate is 13% or more, and the c / a ratio in the crystal lattice is 1.0080 or more."

[0004] Claim 1 of Patent Document 2 (Japanese Unexamined Patent Publication No. 2006-36603) discloses "a method for producing barium titanate powder, comprising: a solution preparation step of preparing a titanium oxide powder mixed solution by including at least titanium oxide powder, a water-soluble barium salt, and a water-soluble organic solvent, and adjusting the volume ratio of the water-soluble organic solvent to the total volume of water and the water-soluble organic solvent in the titanium oxide powder mixed solution to 50% or more and less than 100%; and a hydrothermal reaction step of hydrothermally reacting the titanium oxide powder mixed solution at 80°C or higher to obtain barium titanate powder."

[0005] Claim 1 of Patent Document 3 (International Publication No. 2007 / 074731) discloses a multilayer ceramic capacitor comprising a plurality of dielectric layers composed of barium titanate-based crystalline particles having pores in the crystalline particles, a plurality of internal electrode layers formed between the dielectric layers, and external electrodes electrically connected to the internal electrode layers, wherein the barium titanate-based crystalline particles have a core-shell structure composed of a core portion and a shell portion formed around the core portion with a lower proportion of tetragonal crystals than the core portion, and the pores are mainly formed in the core portion.

[0006] Non-patent document 1 (Creative, No. 5, 2004, pp. 67-77) discloses that a large number of pores exist within the crystals of barium titanate synthesized by hydrothermal synthesis. Patent document 1 also discloses that barium titanate particles synthesized by hydrothermal synthesis have a high proportion of vacancies. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2013-209250 [Patent Document 2] Japanese Patent Publication No. 2006-36603 [Patent Document 3] International Publication No. 2007 / 074731 [Non-patent literature]

[0008] [Non-Patent Document 1] Creative, No. 5, 2004, pp. 67-77 [Overview of the project] [Problems that the invention aims to solve]

[0009] Currently, with the miniaturization and higher performance of electronic devices, high characteristics are also required for barium titanate, which is the raw material for such devices. In such circumstances, one object of the present disclosure is to provide barium titanate particles suitable for manufacturing highly reliable capacitors. [Means for Solving the Problem]

[0010] One aspect of the present disclosure relates to barium titanate particles, wherein the barium titanate particles have pores inside, the ratio is obtained by binarizing a transmission electron microscope image, the average of the ratio of the area of the pores to the area of the barium titanate particles in the transmission electron microscope image is in the range of 0.05% to 1.0%, and the ratio A / B of the number of barium atoms A to the number of titanium atoms B is 0.990 or more. [Effect of the Invention]

[0011] According to the present disclosure, barium titanate particles suitable for manufacturing highly reliable capacitors can be obtained. The novel features of the present invention are set forth in the appended claims, but the present invention will be better understood from the following detailed description taken in conjunction with the drawings, both with respect to the construction and content thereof, together with other objects and features of the invention. [Brief Description of the Drawings]

[0012] [Figure 1] FIG. 1 shows the result of binarization processing for an example of a transmission electron microscope image of the barium titanate particles according to the present disclosure. [Mode for Carrying Out the Invention]

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values and materials may be exemplified, but other numerical values and other materials may be applied as long as the effects of the present disclosure can be obtained. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "not less than numerical value A and not more than numerical value B". In the following description, when lower limits and upper limits of numerical values for specific physical properties, conditions, etc. are exemplified, any one of the exemplified lower limits and any one of the exemplified upper limits can be arbitrarily combined as long as the lower limit is not greater than or equal to the upper limit. In the following description, when examples of constituent elements and examples of methods are listed, unless otherwise specified, only one of the listed examples may be used, or a plurality of the listed examples may be used in combination. In this specification, the term "particles" may be read as "powder" in some cases.

[0014] (Barium titanate particles) Hereinafter, the barium titanate particles according to the present embodiment may be referred to as "barium titanate particles (P)" or "particles (P)". Particles (P) have pores inside. The average value of the ratio of the area of pores to the area of particles (P) in a transmission electron microscope image of particles (P), which is obtained by binarizing the transmission electron microscope image, is in the range of 0.05% to 1.0%. Hereinafter, this average ratio may be referred to as "average ratio R". In particles (P), the ratio (atomic ratio) A / B of the number A of barium atoms to the number B of titanium atoms is 0.990 or more. The composition of particles (P) is typically Ba A Ti B represented by O3.

[0015] It is preferable that the ratio A / B is close to 1. The ratio A / B is 0.990 or more. The ratio A / B may be 0.996 or more, or 0.998 or more, and may be 1.008 or less, or 1.000 or less. By setting the average ratio R within the above range and setting the ratio A / B to 0.990 or more, a highly reliable capacitor can be manufactured as shown in the examples.

[0016] Vacuum formation can occur within barium titanate particles. Barium titanate particles produced by hydrothermal synthesis are known to have a greater amount of vacancies compared to barium titanate particles produced by solid-phase synthesis or oxalic acid synthesis.

[0017] Barium titanate particles are used in the manufacture of ceramic capacitors (for example, multilayer ceramic capacitors (MLCCs)). The following explanation primarily focuses on the case where the capacitor is an MLCC, but the explanation can also be applied when the particles (P) are used in capacitors other than MLCCs. It has been believed that vacancies within barium titanate particles reduce the electrical characteristics and lifespan of MLCCs. Therefore, techniques to reduce vacancies within barium titanate particles have been proposed.

[0018] However, as a result of their investigation, the inventors of the present invention have newly discovered that highly reliable ceramic capacitors (e.g., long-life ceramic capacitors) can be manufactured by using barium titanate particles in which the amount of pores is within a predetermined range and the ratio A / B is 0.990 or higher. This disclosure is based on this new finding.

[0019] The reason why barium titanate particles with a predetermined amount of vacancies are preferable is not currently clear. However, it is possible to consider the following: In MLCCs, locally high voltages can be applied near the vacancies of barium titanate particles. Therefore, if barium titanate particles with a large amount of vacancies are used, the electric field concentrates at the grain boundaries, and dielectric breakdown is induced by an increase in tunnel current, resulting in a reduced lifespan of the MLCC.

[0020] Barium titanate particles may be calcined before being used in the manufacture of MLCCs. Furthermore, barium titanate particles used in the manufacture of MLCCs are sintered during the manufacturing process. Another factor that degrades the properties of MLCCs is cracks within the barium titanate sintered body. If cracks are present within the barium titanate sintered body, moisture and other substances can easily penetrate, degrading the properties of the MLCC (such as its lifespan). Therefore, it is preferable to have as few cracks as possible within the barium titanate sintered body.

[0021] Barium titanate is known to change its crystal structure with temperature. For example, tetragonal barium titanate is known to undergo a phase transition to cubic at around 120°C, and then transition back to tetragonal when cooled to near room temperature. Compared to barium titanate with a tetragonal crystal structure, barium titanate with a cubic crystal structure expands in the a and b axes and contracts in the c axis (Appl. Phys. Lett., 2000, 77, 3547-3549).

[0022] Therefore, barium titanate undergoes a phase transition due to temperature changes during the sintering process when manufacturing MLCCs and when soldering the MLCCs to the substrate. Because this phase transition of barium titanate occurs instantaneously, these temperature changes increase the strain within the barium titanate crystal, causing cracks to form and making them very prone to growth.

[0023] When barium titanate particles with no voids are sintered, there is no area within the sintered barium titanate to relieve the strain within the crystal due to temperature changes, which may lead to crack formation and growth. On the other hand, when barium titanate particles with a small amount of voids are sintered, voids remain within the sintered material, and the strain within the crystal due to temperature changes is relieved by these voids. As a result, the growth of cracks within the sintered barium titanate may be suppressed. For these reasons, maintaining the amount of voids within barium titanate particles within a predetermined range may improve the reliability (lifespan, etc.) of the capacitor.

[0024] Expansion, contraction, and phase transitions of the crystal structure due to temperature changes occur for each crystallite in barium titanate particles. Therefore, strain generated within sintered barium titanate particles due to temperature changes is thought to cause cracks at the crystallite interfaces within the sintered particles. For this reason, it is desirable to have as few crystallites as possible within barium titanate particles. The number of crystallites contained in barium titanate particles can be evaluated by the ratio Ds / Dc, which is the ratio of the specific surface area diameter Ds of the particle (P) to the crystallite diameter Dc. The closer the ratio Ds / Dc is to 1, the fewer crystallites are contained in the barium titanate particles.

[0025] The average proportion R and ratio A / B can be determined by the methods described in the examples. Particles (P) whose average proportion R and ratio A / B are within the above range can be manufactured by the method described later.

[0026] The average percentage R is 0.05% or greater (0.0005 or greater), and may be 0.10% or greater, 0.32% or greater, 0.35% or greater, 0.37% or greater, 0.57% or greater, or 0.88% or greater. The average percentage R is 1.0% (0.010) or less, and may be 0.96% or less, 0.88% or less, 0.57% or less, 0.37% or less, 0.35% or less, 0.32% or less, or 0.10% or less. The average percentage R is in the range of 0.05% to 1.0%, and may be in the range of 0.10% to 1.0%, 0.32% to 1.0%, 0.35% to 1.0%, 0.37% to 1.0%, 0.57% to 1.0%, or 0.88% to 1.0%. Within these ranges, the upper limit may be 0.96%, 0.88%, 0.57%, 0.37%, 0.35%, 0.32%, or 0.10%, as long as the lower limit does not exceed the upper limit.

[0027] The specific surface area of ​​particle (P) determined by the BET method is 10 m². 2 / g or less, or 8.4m 2 Less than / g, or 6.8m 2 It may be less than / g. Specific surface area of ​​10 m² 2 By keeping it below / g, a particularly high effect can be obtained. The specific surface area of ​​the particle (P) is 3m². 2 / g or more, or 5m 2 It may be greater than or equal to / g. The specific surface area is measured by the BET method using nitrogen gas.

[0028] The barium titanate particles (P) may have a tetragonal crystal structure. The lattice constant ratio c / a of the particles (P) may be 1.0057 or higher, 1.0080 or higher, or 1.0092 or higher, and may be 1.0104 or lower, or 1.01026 or lower. The lattice constant ratio c / a of the particles (P) may be in the range of 1.0080 to 1.0104. Having the lattice constant ratio c / a in this range results in a sufficiently large relative permittivity of the resulting MLCC, leading to higher capacitance. If the lattice constant ratio c / a is less than 1.0057, the relative permittivity of the MLCC decreases, and sufficient capacitance may not be obtained.

[0029] The lattice constant ratio c / a is the ratio obtained by dividing the length c of the c-axis of the unit cell of a barium titanate crystal by the length a of the a-axis of the unit cell. The lattice constant ratio c / a indicates the degree of tetragonality of the barium titanate particles. A larger value of c / a indicates higher tetragonality. When a barium titanate crystal has a tetragonal crystal structure, the lattice constant ratio c / a is approximately 1.01. The lattice constant ratio c / a can be determined by X-ray diffraction. Specifically, it can be determined by the method described in the examples.

[0030] The specific surface area equivalent diameter Ds of the particles (P) calculated from the specific surface area may be 45.0 nm or more, 121.0 nm or more, 146.6 nm or more, 149.9 nm or more, 150.1 nm or more, or 155.7 nm or more, and may also be 201.2 nm or less, 155.7 nm or less, 150.1 nm or less, 149.9 nm or less, 146.6 nm or less, or 121.0 nm or less. The specific surface area equivalent diameter Ds may also be in the range of 120 nm to 210 nm. By having the diameter Ds within this range, a sufficient amount of barium titanate sintered particles can be present in the dielectric layer of the MLCC, making it possible to obtain a highly reliable MLCC. By setting the diameter Ds to 120 nm or more, it is possible to suppress a decrease in sheet formability, a decrease in productivity due to abnormal grain growth during sintering, and a decrease in the electrical properties and reliability of the MLCC. By setting the diameter Ds to 220 nm or less, it is possible to arrange a sufficient number of barium titanate sintered particles within the dielectric layer, resulting in a highly reliable MLCC. The diameter Ds is determined by the method described in the examples.

[0031] The crystallite size Dc of the particle (P) may be 45.9 nm or greater, 99.3 nm or greater, 101.8 nm or greater, 109.7 nm or greater, 116.8 nm or greater, 118.5 nm or greater, or 131.0 nm or less, 118.5 nm or less, 116.8 nm or less, 109.7 nm or less, 101.8 nm or less, or 99.3 nm or less. The size Dc is determined by the method described in the examples.

[0032] The ratio Ds / Dc of the specific surface area-converted diameter Ds of a particle (P) to its crystallite diameter Dc may be 0.90 or greater, or 0.98 or greater, and may be 1.60 or less, or 1.54 or less. The ratio Ds / Dc increases as the number of crystal grains contained in a single particle increases. A ratio Ds / Dc of 1.60 or less indicates a small number of grain boundaries within the particle. It is believed that setting the ratio Ds / Dc in the range of 0.90 to 1.60 reduces the frequency of crack occurrence.

[0033] Barium titanate is known to expand and contract anisotropically in response to temperature changes. Furthermore, the lattice constant change during phase transitions is also anisotropic. Therefore, temperature changes during MLCC manufacturing and substrate mounting make it prone to crack formation at the grain interfaces within the barium titanate sintered body. Consequently, when barium titanate particles containing many grains are used as raw materials, crack formation within the barium titanate sintered body is more likely. Barium titanate particles with a ratio Ds / Dc less than 1.60 (P) have fewer grains within the barium titanate, and therefore, crack formation within the barium titanate sintered body can be particularly suppressed.

[0034] The specific surface area equivalent diameter Ds (diameter Ds) is calculated from the specific surface area of ​​the particle (P). Diameter Ds is the diameter of a sphere that has the same specific surface area as the particle (P).

[0035] The crystallite size Dc of a particle (P) is calculated based on the X-ray diffraction spectrum measured using a Cu Kα source. Specifically, it is calculated using Scherrer's formula from the peaks in the region where 2θ is in the range of 38.0 to 40.0° (peaks originating from the (111) plane of tetragonal BaTiO3).

[0036] The barium titanate particles (P) may contain a dispersant placed on their surface. The dispersant content in the barium titanate particles (P) may be 0.5% by mass or more, or 1.0% by mass or more, or 1.5% by mass or less, or 1.25% by mass or less. The dispersant content may be in the range of 0.5 to 1.5% by mass. By setting the dispersant content to 0.5% by mass or more, the barium titanate particles can be given appropriate dispersibility. As a result, a dense dielectric layer can be formed during MLCC fabrication. By setting the dispersant content to 1.5% by mass or less, the sintering of the green sheet can be easily controlled. As a result, the formation of carbides due to incomplete combustion of the dispersant can be suppressed. Note that the dispersant content is the ratio of the mass of the dispersant to the total mass of the barium titanate particles and the mass of the dispersant.

[0037] By adding a dispersant, the dispersibility of barium titanate particles can be improved, making it easier to produce smooth green sheets. As a result, the reliability of the manufactured MLCCs can be increased. Examples of dispersants include polycarboxylic acid-based dispersants (such as high molecular weight polycarboxylic acids and high molecular weight polycarboxylic acid salts). Known dispersants used for barium titanate particles may also be used as the dispersant.

[0038] (Method for producing barium titanate particles (P) (M)) A manufacturing method (M), which is an example of a method for producing barium titanate particles (P), is described below. According to manufacturing method (M), particles (P) can be produced. However, particles (P) may also be produced by methods other than manufacturing method (M). Since the matters described regarding particles (P) can be applied to manufacturing method (M), redundant explanations may be omitted. The matters described regarding manufacturing method (M) may also be applied to particles (P).

[0039] Manufacturing method (M) includes a step of synthesizing barium titanate particles by hydrothermal synthesis. Manufacturing method (M) includes steps (i), (ii), and (iii) in that order. Each step is described below.

[0040] (Step (i)) Step (i) is a step of preparing a raw material slurry used in hydrothermal synthesis. The raw material slurry contains barium titanate seeds. Step (i) can be carried out under the same conditions as step (i) in the method for producing particles (P) (particle A1, etc.) described in the examples. The ratio A / B of particles (P) can be adjusted by the mixing ratio of the materials in step (i).

[0041] (Step (ii)) Step (ii) is a process in which hydrothermal synthesis is performed using the seeds obtained in step (i) to adjust the size and particle size distribution of the barium titanate particles and to improve the lattice constant ratio c / a and crystallinity of the barium titanate particles. Step (ii) can be carried out under the same conditions as step (ii) in the method for producing particles (P) described in the examples.

[0042] In step (ii), a slurry containing barium titanate particles (solids) is obtained by hydrothermal synthesis. It is known that if the solids contain a large amount of chloride ions, the sintering of the barium titanate particles is excessively promoted when the particles are calcined. Excessive promotion of particle sintering reduces the uniformity of the particle size distribution. Therefore, it is desirable to thoroughly wash the barium titanate particles (solids) in the slurry with water or the like. In one example of a washing method, the solids are placed on a filter medium and washed with water. At this time, it is preferable to wash until the conductivity of the filtrate is 200 μS / cm or less. By performing such washing, the chloride ions contained in the solids can be sufficiently reduced. As a result, excessive promotion of sintering in the calcination process can be suppressed, and it becomes easier to obtain barium titanate particles with high particle size distribution uniformity.

[0043] (Step (iii)) Step (iii) is a process of calcining the barium titanate particles obtained in step (ii), followed by crushing and surface treatment with a dispersant. Step (iii) can be carried out under the same conditions as step (iii) in the method for producing particles (P) described in the examples.

[0044] By calcining barium titanate particles, the particles can be grown to any desired particle size. Furthermore, calcining the barium titanate particles can further improve the lattice constant ratio c / a and crystallinity of the barium titanate particles, thereby reducing the average ratio R mentioned above. Subsequently, by crushing the barium titanate particles, the excessive fusion between particles caused by calcination can be eliminated, and the uniformity of the particle size distribution can be improved.

[0045] The average proportion R and ratio A / B of the barium titanate particles obtained by step (iii) may be within the above range. That is, the barium titanate particles obtained by step (iii) can be used as particles (P). A dispersant is present on the surface of the barium titanate particles obtained by step (iii). That is, the particles (P) obtained by step (iii) contain a dispersant arranged on the surface. The dispersant content may be within the above range. The dispersant content can be controlled by the amount of dispersant added to the barium titanate particles.

[0046] In this manner, barium titanate particles (P) can be produced. In the production method (M), it is particularly important to mix the titanate slurry and the barium hydroxide aqueous solution at a constant temperature in step (i). This allows for the production of fine and highly uniform barium titanate particles in step (ii). By calcining the particles obtained in step (ii) in step (iii), the voids inside the particles are easily diffused to the outside of the particles. As a result, it becomes possible to produce particles (P) in which the average ratio R and ratio A / B are within the above range. In addition, some of the above steps may be modified, or steps other than those described above may be added, as long as barium titanate particles (P) can be produced. [Examples]

[0047] The present disclosure will be described in more detail below with reference to examples. In these examples, barium titanate particles were prepared and evaluated under different conditions. Furthermore, ceramic capacitors were prepared and evaluated using the barium titanate particles. The details of these are described below.

[0048] (Preparation of particle A1) Particle A1, which is a barium titanate particle, was prepared using the following procedure.

[0049] (1) Process (i) 5460g of barium hydroxide octahydrate was added to pure water to obtain a slurry with a concentration of 1.8 kg / L. The slurry was heated to 70°C over 90 minutes to dissolve the barium hydroxide octahydrate and prepare an aqueous barium hydroxide solution (70°C). In addition, 6.672 liters of a titanium hydroxide slurry (a mixture of metatitanic acid and orthotitanic acid) heated to 70°C was prepared. The solid content concentration of this slurry was 120 g / L, and this slurry contained 800 g of titanium hydroxide in terms of TiO2. The titanium hydroxide slurry (approximately 65-75°C) was added to the aqueous barium hydroxide solution (approximately 65-75°C) using a pump to obtain a slurry for hydrothermal synthesis, with a Ba / Ti ratio of 1.65 and a Ti concentration of 0.84 mol / L. The obtained slurry was then maintained at 70°C and stirred with a stirrer for 1 hour.

[0050] (2) Process (ii) The slurry obtained in step (i) was heated to 160°C and held at 160°C for 1.5 hours to perform hydrothermal synthesis. In this way, a slurry containing barium titanate particles was obtained. Subsequently, the solid components were filtered off the slurry. A slurry was obtained by adding pure water to the filtered solid components and dispersing them. Next, the slurry was placed on a filter medium and the solid components were washed by passing water through it until the conductivity of the filtrate was 200 μS / cm or less.

[0051] Next, pure water was added to the washed solid content to disperse it, thereby obtaining a slurry. Next, the solid content concentration in the slurry was adjusted to 210 g / L, and spray drying was performed using a spray dryer to obtain barium titanate particles.

[0052] (3) Step (iii) The barium titanate particles obtained in step (ii) were fired at 975°C for 4 hours in an air atmosphere using a firing furnace. The temperature increase rate was set to 200°C / h up to 850°C, and 25°C / h from 850°C to 975°C.

[0053] To the fired barium titanate particles, pure water was added so that the slurry concentration became 600 g / L. Thereafter, a dispersant corresponding to 1.0% by mass relative to the powder (Marialim AKM-0531, NOF Corporation) was added to the slurry, and the mixture was stirred for 30 minutes. The amount of the added dispersant was 10% by mass of the barium titanate particles. The slurry was fed to a bead mill (MAX Nano-Getter HFM-06, manufactured by Ashizawa Finetech Co., Ltd.) at a flow rate of 6 L / min using a feed pump. In the bead mill, the peripheral speed of the separator and the peripheral speed of the agitator were set to 13 m / s and 8.0 m / s, respectively, to disintegrate the particles in the slurry. Zirconia beads (diameter: 0.1 mm) were used for the disintegration. The filling rate of the zirconia beads was set to 60%. Thereafter, pure water was added so that the slurry concentration became 500 g / L. Then, the particles in the slurry were disintegrated under the same conditions as described above. A portion of the slurry was appropriately collected, dried, and then degreased at 500°C for 1 hour to remove the dispersant. The specific surface area of the particles after degreasing was measured. The specific surface area of the particles after degreasing was 6.70 m 2 / g, and the disintegration was terminated at this point.

[0054] Next, the slurry was dried using a spray dryer. In this way, Particle A1 was obtained.

[0055] (Fabrication of Ceramic Capacitor) A mixed powder was obtained by mixing particle A1 (BaTiO3 particles) with other ceramic particles. The other ceramic particles used were Y2O3 particles, MgO particles, Cr2O3 particles, V2O5 particles, MnCO3 particles, and BCS particles (Ba-Ca-Si oxide particles). The mass of each ceramic particle was kept to 0.5% or less of the mass of particle A1. For example, the mass of the Y2O3 particles and the mass of the MgO particles were each approximately 0.4% of the mass of particle A1. Specifically, the composition was based on the X5R system.

[0056] Next, a green sheet for a ceramic capacitor was prepared using the above mixed powder. A laminate was prepared by laminating the green sheet with an electrode layer. Next, the laminate was fired. The laminate was fired by heating it at 1250°C in a nitrogen gas atmosphere containing hydrogen gas (hydrogen gas concentration: 2 vol%). After firing, the laminate was heat-treated (re-oxidized) at 950°C in a nitrogen gas atmosphere. In this way, a ceramic capacitor (capacitor MA1) was prepared. Specifically, a ceramic capacitor having one dielectric layer (layer thickness: 3.3 μm) and two Ni internal electrode layers was prepared.

[0057] (evaluation) The fabricated particles A1 and capacitor MA1 were evaluated using the following method.

[0058] (1) Calculation of diameter Ds converted to specific surface area First, the specific surface area of ​​particle A1 was measured. The specific surface area of ​​particle A1 was determined by the BET method using nitrogen gas. Specifically, the specific surface area was measured using a continuous flow type surface area analyzer (Macsorb HM-1201) manufactured by Mountec Co., Ltd. Degassing treatment for measuring the specific surface area was performed at 205°C for 30 minutes.

[0059] Next, the specific surface area equivalent diameter Ds was calculated from the measured specific surface area using the following calculation. Specific surface area conversion diameter Ds (nm)=6×1000 / (r S)

[0060] In the above formula, r is the density of the particles (g / cm³). 3 ) and S is the specific surface area (m 2 The density r is 5.93 g / cm³, which is the theoretical density of tetragonal BaTiO3. 3 The following was used. Furthermore, in calculating the diameter Ds for particles other than particle A1, the density r was 5.93 g / cm³. 3 That's what I decided.

[0061] (2) X-ray diffraction measurement (XRD measurement) Samples for XRD measurement were prepared by press-molding particle A1. Next, the X-ray diffraction spectrum of the sample was obtained by performing X-ray diffraction measurements of the sample under the following conditions using an X-ray diffractometer (D8 ADVANCE, Bruker Japan). Optical system: Concentration method X-ray source: Cu Kα ray 2θ angle: 20.0°~120.0° Tube voltage, tube current: 40kV, 40mA Step width: 0.01° Step time: 0.2s

[0062] By analyzing the obtained XRD spectrum using analysis software (DIFFRAC.EVA), the primary crystalline phase of barium titanate was identified as tetragonal. The crystallite size Dc was calculated using Scherrer's equation from the peaks in the XRD spectrum where 2θ is in the range of 38.0 to 40.0° (peaks originating from the (111) plane of tetragonal BaTiO3). The lattice constant ratio c / a was determined by peak fitting and Rietveld analysis of the measurement data using analysis software (TOPAS BBQ).

[0063] (3) Particle ratio A / B (Ba / Ti ratio) Samples were prepared by press-molding particle A1. These samples were analyzed using a wavelength-dispersive X-ray fluorescence spectrometer (Simultix14, Rigaku Corporation). The Ba / Ti ratio (atomic ratio) of particle A1 was then obtained using a calibration curve method.

[0064] (4) Measurement of the average ratio R First, a sample for measurement was prepared by coating a copper grid for measurement with an ethanol dispersion of particle A1 and drying it. The resulting particle A1 sample was then photographed at a magnification of 500,000 times using a field emission transmission electron microscope (JEM-2100F, manufactured by JEOL Ltd.) to obtain a STEM image.

[0065] Next, the STEM image was binarized to separate the region containing vacancies from the region without vacancies within particle A1. The internal vacancy region within the barium titanate particle shows a brighter contrast compared to the barium titanate particle itself, allowing for binarization using this as an indicator. An example of the binarized STEM image is shown in Figure 1. In Figure 1, the regions identified as vacancies are numbered.

[0066] Next, ten particles (particle A1) were arbitrarily selected from the binarized STEM image. For each particle, the area of ​​the particle in the STEM image, Sax, and the area of ​​the void within the particle, Spx, were calculated. Then, the average proportion Rx (Rx = Spx / Sax) was calculated for each particle. The average of the 10 obtained average proportions Rx (average proportion R) was calculated by taking the arithmetic mean of the average proportions Rx.

[0067] (5) Relative permittivity of ceramic capacitors The relative permittivity of the fabricated ceramic capacitors was measured using an LCR meter (Agilent, 4363B).

[0068] (6) Lifespan of MLCCs in HALT The lifespan of capacitor MA1 was measured using Highly Accelerated Life Testing (HALT). The HALT test was performed under the conditions of 140°C (ambient temperature) and 25V / μm (applied voltage) (condition N). The lifespan was determined when the ceramic capacitor broke down. The lifespan of each of the 10 MA1 capacitors was measured, and the Mean Time to Failure (MTTF) was calculated by arithmetic mean of the 10 lifespans.

[0069] Note that when calculating the MTTF of other MLCCs described later, the condition N was sometimes changed to 160°C and 50V / μm (condition A), or 160°C and 20V / μm (condition B). The MTTF calculated under conditions A and B is calculated using the following empirical formula, which is the acceleration coefficient A. L The MTTF under condition N was converted using the following method. Specifically, the MTTF calculated under condition A or B was converted to A. L By multiplying by [a certain factor], the MTTF under condition N was obtained.

[0070]

number

[0071] In the above formula, each letter represents the following. Note that the voltage acceleration constant n=3 and the temperature acceleration constant θ=10. Note that the standard condition is condition N, and the acceleration condition is either condition A or condition B. A L : Acceleration coefficient L N Life under standard conditions (condition N) L A Life under acceleration conditions (condition A or condition B) V A : Voltage (V) under acceleration conditions V N : Voltage under standard conditions (V) n: Voltage acceleration constant T A : Temperature under acceleration conditions (K) T N : Temperature under standard conditions (K) θ: Temperature acceleration constant

[0072] (Preparation of particle A2) Barium titanate particles (particle A2) were prepared using the same method and conditions as particle A1, except that the firing temperature in process (iii) was changed to 1000°C.

[0073] (Preparation of particle A3) The calcination temperature in process (iii) was changed to 930°C, and the specific surface area of ​​the degreased particles during crushing was 5.1 m². 2 Barium titanate particles (particle A3) were prepared using the same method and conditions as particle A1, except that the point at which the crushing process ended was defined as the point at which the weight reached / g.

[0074] (Preparation of particle A4) Barium titanate particles (particle A4) were prepared using the same method and conditions as particle A1, except that the temperature of the hydrothermal reaction was set to 120°C.

[0075] (Preparation of particle A5) The hydrothermal reaction temperature was set to 120°C, the calcination temperature in step (iii) was changed to 950°C, and the specific surface area of ​​the degreased particles during crushing was 8.4 m². 2 Barium titanate particles (particle A5) were prepared using the same method and conditions as particle A1, except that the point at which the crushing process ended was defined as the point at which the weight reached / g.

[0076] (Preparation of particle C1) Barium titanate particles (particle C1) were prepared using the same method and under the same conditions as particle A1, except that the method for preparing the slurry for hydrothermal synthesis in step (i) was changed, the hydrothermal synthesis temperature was set to 200°C, and no dispersant was added during crushing in step (iii). In preparing the slurry for hydrothermal synthesis, first, solid barium hydroxide octahydrate was directly added to the titanium hydroxide slurry to prepare a mixture. Then, water was added to the mixture and further heating was performed to dissolve the barium hydroxide octahydrate. In this way, the slurry for hydrothermal synthesis was prepared.

[0077] (Preparation of particle C2) The amounts of barium and titanium sources were adjusted so that the ratio A / B was the value shown in Table 1, and the raw materials containing them were mixed. Next, the resulting mixture was calcined to obtain a powder. The powder was crushed, and the surface of the powder was treated with a dispersant (Marialim AKM-0531, manufactured by NOF Corporation) equivalent to 1.0% by mass of the powder. In this way, barium titanate particles (particle C2) were obtained.

[0078] (Preparation of particle C3) The amounts of barium and titanium sources were adjusted so that the ratio A / B was the value shown in Table 1, and the raw materials containing them were mixed. Next, the resulting mixture was calcined to obtain a powder. The powder was crushed. The powder was not subjected to surface treatment with a dispersant. In this way, barium titanate particles (particle C3) were obtained.

[0079] (Preparation of particle C4) Barium titanate powder was prepared by the oxalic acid method, while adjusting the amounts of barium and titanium sources so that the ratio A / B was the value shown in Table 1. The obtained powder was crushed, and the surface of the powder was treated with a dispersant (Marialim AKM-0531, manufactured by NOF Corporation) equivalent to 1.0 mass% of the powder. In this way, particle C4 was obtained.

[0080] (Preparation of particle C5) Barium titanate particles (particle C5) were prepared using the same method and under the same conditions as particle A1, except that the method for preparing the slurry for hydrothermal synthesis in step (i) was changed, and a dispersant was not added during crushing in step (iii). In preparing the slurry for hydrothermal synthesis, first, solid barium hydroxide octahydrate was directly added to the titanium hydroxide slurry to prepare a mixture. Then, water was added to the mixture, and the mixture was further heated to dissolve the barium hydroxide octahydrate. In this way, the slurry for hydrothermal synthesis was prepared.

[0081] (Preparation of particle C6) 5460g of barium hydroxide octahydrate was added to pure water to obtain a slurry with a concentration of 1.8 kg / L. The slurry was heated to 70°C over 90 minutes to dissolve the barium hydroxide octahydrate, preparing an aqueous barium hydroxide solution (70°C). Additionally, 6.672 liters of titanium hydroxide slurry (a mixture of metatitanic acid and orthotitanic acid) heated to 70°C were prepared. The solid content concentration of this slurry was 120 g / L, and it contained 800 g of titanium hydroxide in terms of TiO2 equivalent.

[0082] Next, a slurry for hydrothermal synthesis was obtained by adding a titanium hydroxide slurry (approximately 65-75°C) to an aqueous barium hydroxide solution (approximately 65-75°C) using a pump, so that the Ba / Ti ratio (molar ratio) was 1.65 and the Ti concentration was 0.84 mol / L. The obtained slurry was then maintained at 70°C and stirred with a stirrer for 1 hour.

[0083] The obtained slurry was kept at 60°C in a storage tank. Next, the slurry was heated to 150°C and held at 150°C for 18 hours to perform hydrothermal synthesis. In this way, a slurry containing barium titanate particles was obtained. Subsequently, the slurry was filtered to separate the solid components. A slurry was obtained by adding pure water to the filtered solid components and dispersing them. Next, concentrated hydrochloric acid (concentration: 35 mass%) was added to the slurry so that its pH became 7.0. Then, the slurry was placed on a filter medium and water was passed through it until the conductivity of the filtrate was 1455 μS / cm. Next, pure water was added to the solid components on the filter medium and dispersed them to obtain a slurry. The slurry was placed on a filter medium and the solid components were washed by passing water through it until the conductivity of the filtrate was 200 μS / cm or less.

[0084] Next, pure water was added to the solids and dispersed. Barium hydroxide aqueous solution was then added to the slurry so that the ratio A / B was a predetermined value, and the slurry was thoroughly stirred. Then, the slurry was dried using a spray dryer. In this way, particles C6 were obtained.

[0085] Capacitors MA2-MA5 and MC1-MC6 were fabricated using the same methods and conditions as those used for capacitor MA1, except that particles A2-A5 and C1-C6 were used instead of particle A1. However, in the fabrication of some capacitors, the number of dielectric layers included in the capacitor was changed as shown in Table 1. In addition, the number of internal electrode layers was changed to match the number of dielectric layers.

[0086] Particles A2-A5 and C1-C6 were evaluated in the same way as particle A1. Furthermore, capacitors MA2-MA5 and MC1-MC6 were evaluated in the same way as capacitor MA1.

[0087] Table 1 shows some of the manufacturing conditions and evaluation results for each particle and MLCC. In Table 1, diameter Ds represents the diameter converted to specific surface area. Specific surface area is the specific surface area determined by the BET method. The ratio Ds / Dc is the ratio of the particle's diameter converted to specific surface area Ds to the particle's crystallite diameter Dc. The number of layers in Table 1 indicates the number of dielectric layers. In Table 1, the ratio A / B represents the ratio of the number of Ba atoms A to the number of Ti atoms B.

[0088] [Table 1]

[0089] Particles A1 to A5 are barium titanate particles (P) according to this disclosure. Particles C1 to C6 are comparative example particles. As shown in Table 1, by using particles (P), it was possible to manufacture highly reliable capacitors (capacitors with a long lifespan). [Industrial applicability]

[0090] This invention can be used for barium titanate particles. Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

Claims

1. Barium titanate particles, It has a void inside, A ratio obtained by binarizing a transmission electron microscope image, wherein the average ratio of the area of ​​the vacancies to the area of ​​the barium titanate particles in the transmission electron microscope image is in the range of 0.05% to 1.0%. Barium titanate particles in which the ratio A / B of the number of barium atoms to the number of titanium atoms B is 0.990 or greater.

2. The specific surface area calculated by the BET method is 10 m². ２ Barium titanate particles according to claim 1, wherein the amount is less than or equal to / g.

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