Composite particle, conductive paste and electronic component

Abstract

To provide composite particles capable of suppressing a crack occurrence rate during debinding processing and improving the continuity rate of an internal electrode layer and to provide a conductive paste using the composite particles.SOLUTION: There are provided composite particles having large particles and small particles which are adhered to the surface of the large particles and have a smaller average particle diameter than the large particles, wherein the large particles are metal particles, the main component of the metal particles is nickel or a nickel alloy, the average coverage of the small particles adhered to the surface of the large particles is 3% or more and 60% or less and the average oxidation degree of the outermost surface of the large particles is 30% or more and 90% or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electronic component having an electrode layer, and to composite particles and a conductive paste used to form the electrode layer of the electronic component. [Background technology]

[0002] In ceramic electronic components such as multilayer ceramic capacitors, the ceramic layers and internal electrode layers are becoming thinner in response to demands for smaller size and higher capacitance. However, when the internal electrode layers are made thinner, cracks and discontinuities can occur in the internal electrode layers after sintering due to the difference in sintering start temperatures between the ceramic layers and the internal electrode layers, which can reduce the continuity rate of the internal electrode layers relative to the ceramic layers (the coverage rate of the internal electrode layers).

[0003] As a measure to reduce the difference in sintering start temperature, a method of forming internal electrode layers using a conductive paste to which ceramic common material powder is added has been proposed (for example, Patent Document 1). Adding ceramic common material powder to the conductive paste is expected to have the effect of delaying the sintering of the internal electrode layers (sintering delay effect). However, in such conductive paste, the ceramic common material powder is prone to agglomeration, and the metal components become spherical during the process of sintering the internal electrode layers, which may prevent a sufficient sintering delay effect from being obtained. In addition, the ceramic common material powder may diffuse into the ceramic layer and affect the composition of the ceramic layer.

[0004] In addition to the above measures, a method has also been proposed in which composite particles, in which minute ceramic particles are fixed to the surface of metal particles, are used as raw material powder for conductive paste (for example, Patent Document 2). The thermal shrinkage onset temperature of such composite particles is higher than that of uncomposite metal particles. Furthermore, ceramic particles fixed to the surface are less likely to agglomerate than ceramic core powders added individually to the conductive paste. Therefore, by using such composite particles as raw material powder for conductive paste, an improvement in the continuity rate of the internal electrode layers can be expected.

[0005] However, in recent years, there has been an increasing demand for thinner layers in ceramic electronic components, and there is a need for further improvements in the thermal shrinkage properties of the composite particles used as raw material powder. For example, in Patent Document 2, Ni particles with an average particle size (converted to Feret's diameter) of 0.2 μm or 0.5 μm are used to evaluate the thermal shrinkage properties of the composite particles, but in order to meet the recent demand for thinner layers, metal particles with a smaller particle size than those in Patent Document 2 are sometimes used. However, if the diameter of the metal particles is reduced, the thermal shrinkage onset temperature will decrease, and there is a possibility that the continuity rate of the internal electrode layer will not be sufficiently ensured.

[0006] Furthermore, when Ni particles are used as a raw material for the conductive paste for forming the internal electrode layers, there has been a problem that cracks may occur in the green chip when the green chip is subjected to a binder removal process. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-55314 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-282102 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of an exemplary embodiment of the present invention is to provide composite particles that can suppress the rate of crack occurrence during binder removal treatment and can improve the continuity rate of internal electrode layers, and a conductive paste using the composite particles. [Means for solving the problem]

[0009] In order to achieve the above object, the composite particles according to the present invention are A composite particle having a large particle and a small particle attached to the surface of the large particle and having an average particle size smaller than that of the large particle, the large particles are metal particles; The metal particles are mainly composed of nickel or a nickel alloy, the average coverage of the small particles attached to the surfaces of the large particles is 3% or more and 60% or less; the average oxidation degree of the outermost surface of the large particles is 30% or more and 90% or less; The degree of oxidation is defined by the following formula (2): Oxidation degree (%)=100×M / (L+M+N) ··· Formula (2) When the outermost surface of the large particle is measured by X-ray photoelectron spectroscopy, L is an atomic ratio calculated from the peak area of ​​the metallic nickel peak, M is an atomic ratio calculated from the peak area of ​​the nickel oxide peak, The N is an atomic ratio calculated from the peak area of ​​the satellite peak.

[0010] When the composite particles have the above properties, it is possible to suppress the rate of crack occurrence during binder removal treatment and also to improve the continuity rate of the internal electrode layers.

[0011] Preferably, the average value of the L slope of the large particles is greater than 0%, The L slope is defined by the following equations (3) and (4): L ratio=L / (L+M+N) Equation (3) L slope (%) = 100 × (IL ratio - SL ratio) / 2 ··· Formula (4) the SL ratio is the L ratio at the outermost surface of the large particle, The IL ratio is the L ratio at a depth of 2 nm from the outermost surface of the large particle toward the center of the large particle.

[0012] When the composite particles have the above properties, the continuity ratio of the internal electrode layers can be further improved.

[0013] Preferably, the small particles contain one or more main components selected from barium titanate, silicon oxide, titanium oxide, aluminum oxide, zirconium oxide, zinc oxide, praseodymium oxide, cobalt oxide, chromium oxide, bismuth oxide, boron oxide, calcium oxide, magnesium oxide, strontium oxide, bismuth ferrite, bismuth titanate, potassium sodium niobate, bismuth sodium titanate, potassium bismuth titanate, Ir, Rh, Ru, Pt, Pd, Re, Fe, Au, Ni, Cu, Ag, Co, W, Mn, Cr, Mo, V, Nb, Ta, Ti, Zr, Sn, and Os.

[0014] Preferably, the average value of the coverage is 5% or more and 50% or less.

[0015] The conductive paste according to the present invention contains the composite particles, a binder, and a solvent.

[0016] The electronic component according to the present invention has an electrode layer formed using the conductive paste. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a cross-sectional view showing a multilayer ceramic electronic component according to one embodiment. [Figure 2] FIG. 2 is a schematic diagram showing a cross section of a composite particle according to one embodiment. [Figure 3] FIG. 3 is a schematic diagram for explaining a method for measuring the coverage of a composite particle. [Figure 4] FIG. 4 is a schematic diagram for explaining a method for measuring the coverage of a composite particle. [Figure 5] FIG. 5 is a schematic diagram for explaining a method for measuring the coverage of a composite particle. [Figure 6] FIG. 6 is a graph for explaining the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0019] First embodiment: Composite particles As shown in FIG. 2, each composite particle 12 according to this embodiment has one large particle 14 and a plurality of small particles 16 attached to the surface of the large particle 14.

[0020] The large particles 14 are conductive metal particles. The main component of the metal particles is nickel or a nickel-containing alloy. Here, the main component of the metal particles is a component that preferably accounts for 70 to 100 parts by mass, and more preferably 90 to 100 parts by mass, when the total of the elements constituting the metal particles, excluding oxygen, is taken as 100 parts by mass.

[0021] The large particles 14 are preferably nickel particles or nickel alloy particles containing tin (hereinafter referred to as NiSn-based alloy particles).

[0022] When the large particles 14 are nickel particles, the purity of the nickel is preferably, for example, 98% by mass or more, and in addition to nickel, trace elements such as iron, cobalt, chromium, manganese, copper, palladium, magnesium, silicon, calcium, sodium, potassium, chlorine, oxygen, carbon, and nitrogen may be contained. When the large particles 14 are NiSn-based alloy particles, the above trace elements may also be contained. The ratio of nickel to tin in the NiSn-based alloy large particles 14 is not particularly limited, and the tin content may be, for example, 1% by mass or more and 50% by mass or less.

[0023] In the composite particle 12, each large particle 14 may have the same material, or the large particle 14 may contain two or more types of particles made of different materials (i.e., two or more types of large particles 14 made of different materials may be mixed together). In this embodiment, "different materials" refers to cases where the elements constituting the particles are different, or cases where the elements constituting the particles are the same but have different composition ratios.

[0024] The average particle diameter (DL) of the large particles 14 may be 200 nm or more, and from the viewpoint of reducing the thickness of the electrode layer formed using the composite particles 12, it is preferably 20 nm or more and 200 nm or less, more preferably 20 nm or more and 150 nm or less, and even more preferably 30 nm or more and 100 nm or less. Furthermore, the coefficient of variation (standard deviation / average particle diameter) in the particle size distribution of the large particles 14 is not particularly limited, but may be, for example, 30% or less. When the large particles 14 include two or more particle groups made of different materials, each particle group may have a different particle size distribution, but it is preferable that the average particle diameter of each particle group be within the above range.

[0025] In this embodiment, the "average particle size" means the arithmetic mean value of the equivalent circle diameter, and the "particle size distribution" means the distribution of the equivalent circle diameter.

[0026] In the composite particle 12 of this embodiment, the crystallite diameter (D C ) is 20 nm or more and 80 nm or less, preferably more than 20 nm and 80 nm or less, more preferably more than 20 nm and 50 nm or less, and even more preferably 30 nm or more and 50 nm or less. Here, the crystallite size refers to the size of the crystals present inside each large particle 14.

[0027] Crystallite diameter (D C ) may be measured by X-ray diffraction (XRD). Specifically, an X-ray diffraction chart of the composite particles 12 is obtained by 2θ / θ measurement, and a diffraction peak attributable to the large particles 14 is identified in the X-ray diffraction chart. Then, from the identified diffraction peak, the crystallite diameter (D C ) can be calculated.

number

[0028] The surfaces of the large particles 14 according to this embodiment are oxidized. In other words, the surfaces of the large particles 14 according to this embodiment are covered with an extremely thin oxide layer. Specifically, the average oxidation degree of the outermost surfaces 14a of the large particles 14 is 30% or more and 90% or less, preferably 50% or more and 90% or less, and more preferably 70% or more and 90% or less.

[0029] The degree of oxidation is defined by the following formula (2): Oxidation degree (%)=100×M / (L+M+M) ··· Formula (2)

[0030] Here, L, M, and N are the values ​​obtained by X-ray photoelectron spectroscopy of the outermost surface 14a of the large particle 14 shown in FIG. It is obtained by measuring by spectroscopy (XPS), where L is the atomic ratio calculated by multiplying the peak area of ​​the metallic nickel peak by the "conversion factor for the metallic nickel peak," M is the atomic ratio calculated by multiplying the peak area of ​​the nickel oxide peak by the "conversion factor for the nickel oxide peak," and N is the atomic ratio calculated by multiplying the peak areas of the satellite peaks derived from metallic nickel and nickel oxide by the "conversion factor for the satellite peak."

[0031] The L slope of the large particles 14 is preferably greater than 0%, more preferably 0.1% or more and 40% or less, and even more preferably 2% or more and 15% or less.

[0032] The L slope is defined by the following equations (3) and (4). L ratio=L / (L+M+N) Equation (3) L slope (%) = 100 × (IL ratio - SL ratio) / 2 ··· Formula (4)

[0033] Here, the SL ratio is the L ratio at the outermost surface 14a of the large particle 14 shown in Figure 2, and the IL ratio is the L ratio at a depth 14b of 2 nm from the outermost surface 14a of the large particle 14 toward the center G of the large particle 14 shown in Figure 2.

[0034] The small particles 16 are particles having a smaller particle size than the large particles 14. The main component of the small particles 16 is preferably at least one selected from barium titanate, silicon oxide, titanium oxide, aluminum oxide, zirconium oxide, zinc oxide, praseodymium oxide, cobalt oxide, and chromium oxide, more preferably barium titanate or silicon oxide, and even more preferably barium titanate. The small particles 16 may contain one or more main components selected from Ir, Rh, Ru, Pt, Pd, Re, Fe, Au, Ni, Cu, Ag, Co, W, Mn, Cr, Mo, V, Nb, Ta, Ti, Zr, Sn, and Os. The sintering suppression effect is improved by including one or more elements selected from Ir, Rh, Ru, Pt, Pd, Re, Fe, Au, Ni, Cu, Ag, Co, W, Mn, Cr, Mo, V, Nb, Ta, Ti, Zr, Sn, and Os as the main component of the small particles 16. Note that "when the small particles 16 include one or more elements selected from Ir, Rh, Ru, Pt, Pd, Re, Fe, Au, Ni, Cu, Ag, Co, W, Mn, Cr, Mo, V, Nb, Ta, Ti, Zr, Sn, and Os as the main component" also includes cases where the small particles 16 include any one or more elements selected from the above element group as the main component. For example, the term "small particles 16 containing one or more elements selected from Ir, Rh, Ru, Pt, Pd, Re, Fe, Au, Ni, Cu, Ag, Co, W, Mn, Cr, Mo, V, Nb, Ta, Ti, Zr, Sn, and Os as the main component" applies to small particles 16 containing Ir as the main component, Rh as the main component, Ir and Rh as the main component, Ir, Ag, and V as the main component, or Cu, Co, and Zr as the main component. The main component of small particles 16 refers to a component that accounts for 20 or more moles when the total number of elements constituting small particles 16 is 100 moles. In composite particles 12, each small particle 16 may be made of the same material, or the small particles 16 may contain two or more particle groups made of different materials (i.e., two or more small particles 16 made of different materials may be mixed).

[0035] It is preferable that the thermal shrinkage initiation temperature of the small particles 16 when mixed with the large particles 14 and fired is 500°C or higher, and it is also preferable that the thermal shrinkage initiation temperature when mixed with the large particles 14 and fired is equivalent to the thermal shrinkage initiation temperature of the ceramic particles that make up the ceramic layer 20 described below.

[0036] The average particle size (DS) of the small particles 16 is preferably, for example, 3 nm or more and 30 nm or less, and more preferably 3 nm or more and 20 nm or less. When the small particles 16 include two or more particle groups made of different materials, each particle group may have a different particle size distribution, but the average particle size of each particle group is preferably within the above range. Furthermore, the ratio of the average particle size of the small particles 16 to the average particle size of the large particles 14 (average DS / average DL) is preferably 0.01 to 0.30, more preferably 0.01 to 0.20, and even more preferably 0.03 to 0.17. By setting the average DS / average DL value within the above range, the steric hindrance described below can be more effectively exerted.

[0037] In this embodiment, each large particle 14 is a core particle in the composite particle 12. On the other hand, each small particle 16 has a smaller particle size than the large particles 14 and acts to create steric hindrance in the composite particle 12. Steric hindrance means the function of preventing the surfaces of adjacent large particles 14 from coming into direct contact with each other. In the composite particle 12, the small particles 16 attached to the surface of each large particle 14 are interposed between adjacent large particles 14, creating steric hindrance. Such steric hindrance can make the thermal shrinkage onset temperature of the composite particle 12 higher than the thermal shrinkage onset temperature of a powder consisting only of large particles 14.

[0038] In addition, in the particle structure in which the above-mentioned steric hindrance occurs, the crystallite diameter (D C) in the range of 20 nm or more and 80 nm or less, the thermal shrinkage starting temperature can be shifted to a higher temperature than that of conventional composite particles. In particular, in the composite particle 12 of this embodiment, the thermal shrinkage starting temperature can be made sufficiently high not only when the average particle size of the large particles 14 is 200 nm or more, but also when the average particle size of the large particles 14 is reduced to less than 200 nm.

[0039] The reason why the heat shrinkage starting temperature increases by controlling the crystallite size is considered to be, for example, as follows.

[0040] In conventional composite particles, even if steric hindrance is exerted, it is thought that the shape of the core metal particle is easily distorted at high temperatures of 400°C or higher. When the shape of the metal particle is distorted, it is thought that adjacent metal particles will bond together in the gaps between microparticles made of inorganic compounds, etc. In particular, when the average particle size of the metal particles is small, less than 200 nm, the particle shape is easily distorted at high temperatures, and bonding between the metal particles between the microparticles becomes significant, which is thought to prevent sufficient improvement in thermal shrinkage properties.

[0041] In contrast, in the composite particle 12 of this embodiment, the large particle 14 has a diameter of 20 nm or less. C By satisfying the average value of DL≦80 nm, the ratio of the average particle size of the large particles 14 to the average crystallite size of the large particles 14 (average value of DL / D C The average value of the volume fraction of the crystallites in each large particle 14 is lower than that of conventional composite particles. In other words, the volume fraction of each crystallite in each large particle 14 is higher than that of conventional composite particles. In this way, by increasing the volume fraction of each crystallite in the interior of the large particle 14, it is thought that the shape of the large particle 14 is less likely to collapse even at high temperatures. As a result, it is thought that it is possible to prevent the large particles 14 from joining together in the gaps between the small particles 16, and to increase the thermal shrinkage initiation temperature.

[0042] When the average diameter (DL) of large particles 14 is in the range of 20 nm to 100 nm, the average value of DL / D CThe average value of is 5.0 or less, and preferably 3.0 or less. When the average particle diameter (DL) of the large particles 14 is in the range of more than 100 nm and 200 nm or less, the average value of DL / D C The average value of DL / D is 10.0 or less, preferably 8.0 or less, and more preferably 4.0 or less. C The lower limit of the average value of DL is 1.0. C By controlling the average value within the above range, the heat shrinkage properties can be further improved.

[0043] The sulfur content of the composite particles 12 is preferably 3000 ppm by mass or less, and more preferably 10 ppm by mass or less. If the sulfur content is less than 10 ppm by mass, the composite particles 12 can be considered to be substantially free of sulfur. The sulfur contained in the composite particles 12 is considered to be mainly derived from the large particles 14. The sulfur component may be mixed as an impurity during the production of the large particles 14, or may be intentionally added as an additive. By controlling the sulfur content of the composite particles 12 to 3000 ppm by mass or less (preferably 10 ppm or less), it is possible to suppress a decrease in the melting point of the large particles 14 due to sulfurization. The sulfur content may be measured using inductively coupled plasma atomic emission spectroscopy (ICP), a carbon / sulfur analyzer, or the like.

[0044] In the composite particle 12, the average coverage of the small particles 16 to the large particles 14 is 3% or more and 60% or less, preferably 5% or more and 50% or less, and more preferably 20% or more and 40% or less. By setting the average coverage of the small particles 16 to the large particles 14 to 3% or more and 60% or less, the steric hindrance by the small particles 16 can be more effectively exerted.

[0045] Furthermore, the standard deviation of the coverage of the small particles 16 with respect to the large particles 14 is preferably 0% or more and 20% or less, and more preferably 0% or more and 5% or less.

[0046] Furthermore, the CV of the coverage of the small particles 16 with respect to the large particles 14 is preferably 0% or more and 60% or less, and more preferably 10% or more and 60% or less.

[0047] By reducing the variation in the coverage, the steric hindrance can be exerted more effectively. The above-mentioned standard deviation of the coverage (particularly, 5% or less) can be achieved by producing the composite particles 12 by, for example, an electrostatic adsorption method.

[0048] The "particle size of the large particles 14 and the small particles 16" and the "coverage ratio of the small particles 16 to the large particles 14" are not necessarily limited, but it is preferable to employ, for example, an image analysis method such as that shown below.

[0049] A liquid containing the composite particles 12 is dropped onto a sample stage and air-dried. Next, the composite particles 12 on the sample stage are observed using a scanning electron microscope (SEM) (a scanning transmission electron microscope (STEM) may also be used) to obtain an SEM image of the composite particles 12. The observation magnification when obtaining the SEM image is not particularly limited and may be determined appropriately depending on the average particle diameter (DL) of the large particles 14. For example, the observation magnification may be set so that the area per field of view is approximately (average DL × 8) × (average DL × 6). Figure 3 shows a schematic diagram of an SEM image.

[0050] Next, "large particles 14 with a visible outline" are selected from the large particles 14 included in the SEM image. In FIG. 4, "large particles 14 with a visible outline" are selected from the large particles 14 included in FIG. 3, and the outlines of the selected large particles 14 are shown in bold. In FIG. 4, the outlines of "small particles 16 with a visible outline" attached to the "large particles 14 with a visible outline" are also shown in bold. Note that "large particles 14 with a visible outline" refers to large particles 14 whose entire outline is included in the SEM image and which are present in the foreground in the SEM image. Therefore, if even a portion of the outline is missing, that large particle 14 does not qualify as a "large particle 14 with a visible outline." Furthermore, if even a portion of a large particle 14 is present behind (behind) another large particle 14, that large particle 14 does not qualify as a "large particle 14 with a visible outline."

[0051] The equivalent circle diameters of the "large particles 14 with visible outlines" identified by the above method are measured, and the particle size distribution and average particle size (DL) of the large particles 14 are calculated. Furthermore, the equivalent circle diameters of the "small particles 16 with visible outlines" attached to the "large particles 14 with visible outlines" are measured, and the particle size distribution and average particle size (DS) of the small particles 16 are calculated. The equivalent circle diameters can be measured using image analysis software, and the average particle sizes (DL and DS) are preferably calculated by measuring the equivalent circle diameters of at least 1,000 particles.

[0052] When measuring the coverage, first, a particle to be measured is selected from among the "large particles 14 whose outlines can be confirmed." The particle diameter (DL) of the particle to be measured is then measured, and the center of gravity G of the particle to be measured is identified. Next, as shown in Figure 5, a circle with a radius 0.25 times the DL is drawn from the center of gravity G, and this circle is designated as a virtual circle 18. Next, the area A0 of the virtual circle 18 and the total area A1 of the small particles 16 contained in the virtual circle 18 are measured, and the coverage of the small particles 16 on the particle to be measured is calculated as the ratio of A1 to A0 (A1 / A0). Using the method described above, the coverage of at least 100 large particles 14 is determined, and the average value is designated as the average coverage.

[0053] The standard deviation of the coverage may be calculated based on the following formula (5).

number

[0054] The CV of the coverage may be calculated based on the following formula (6). CV of coverage = (standard deviation of coverage) / (average coverage) Equation (6)

[0055] In the image analysis described above, the composite particles 12 may contain particles with a coverage of 0%, but the number ratio (number density) of particles with a coverage of 0% in the composite particles 12 is preferably 10% or less.

[0056] Furthermore, in the image analysis described above, it is preferable that the number of agglomerates of small particles 16 in an area of ​​(average DL value × 80) × (average DL value × 60) is 3 or less, more preferably 1 or less, and even more preferably 0.

[0057] The degree of oxidation and L slope of the outermost surface 14a of the large particles 14 are measured by XPS. Specifically, the composite particles 12 are formed into pellets using a press, and the resulting pellets are measured for the outermost surface 14a of the large particles 14 and a 2 nm depth 14b from the outermost surface 14a of the large particles 14 toward the center G of the large particles 14 by sputtering, as shown in FIG. 2. Even if measurement at the 2 nm depth 14 from the outermost surface 14a of the large particles 14 toward the center G of the large particles 14 is not possible due to the influence of measurement resolution in the depth direction, the measurement result of the "2 nm depth 14" may be estimated by interpolation from the measurement results of two points sandwiching the "2 nm depth 14" in the depth direction.

[0058] Next, the obtained XPS data is analyzed. Specifically, an XPS spectrum of the Ni2p orbital is obtained, and the Ni2p peak is separated into a metallic nickel peak, a nickel oxide peak, and a satellite peak.

[0059] As a separation method, it is preferable to perform peak separation analysis by the least squares method or to make a comprehensive judgment in light of literature and databases.

[0060] Among the metallic nickel peak, nickel oxide peak, and satellite peak, the peak located on the lowest energy side can be determined to be the metallic nickel peak. The peak range of the metallic nickel peak is affected by correction of the charging state and the influence of the substrate, but is often in the range of 851.5 to 852.9 eV.

[0061] Satellite peaks and nickel oxide peaks can be close in energy, making it difficult to distinguish them strictly. However, peaks higher in energy than the lowest-energy peak can be considered to be derived from nickel oxide peaks or satellite peaks. Nickel oxide peaks include NiO, Ni2O3, and Ni(OH)2, but it is preferable to make a comprehensive judgment based on literature and databases when separating these peaks and their satellite peaks. Nickel oxide peaks often fall within the range of 853.5-854.4 eV and 855.8-857.3 eV.

[0062] As mentioned above, there are cases where a plurality of nickel oxide peaks are detected, and in such cases, the peak area of ​​the nickel oxide peak is defined as the sum of the peak areas of the nickel oxide peaks.

[0063] Similarly, multiple satellite peaks may be detected, and in such cases, the peak area of ​​the satellite peak is determined as the sum of the peak areas of the individual satellite peaks.

[0064] The areas of the metallic nickel peak, nickel oxide peak, and satellite peak obtained by peak separation analysis are used as detection intensities (signal intensities).

[0065] The atomic ratio (L) derived from the metallic nickel peak is calculated by multiplying the peak area of ​​the metallic nickel peak by the conversion factor of the metallic nickel peak.

[0066] The atomic ratio (M) derived from the nickel oxide peak is calculated by multiplying the peak area of ​​the nickel oxide peak by the conversion factor of the nickel oxide peak.

[0067] The atomic ratio (N) derived from the satellite peak is calculated by multiplying the peak area of ​​the satellite peak by the conversion factor of the satellite peak.

[0068] The degree of oxidation can be calculated using the above formula (2).

[0069] Furthermore, the L slope can be calculated using the above formulas (3) and (4).

[0070] An example of a method for producing the composite particle 12 according to this embodiment will be described below.

[0071] First, large particles 14 and small particles 16 are prepared. The method for producing the large particles 14 may be a liquid phase synthesis method or a gas phase synthesis method, and the method for producing the large particles 14 is not necessarily limited. The crystallite diameter (D C ) can be controlled based on various conditions, such as the type of precursor, the temperature, and the cooling rate, during synthesis of the large particles 14.

[0072] In terms of producing metal particles with small particle sizes, the liquid phase method is more suitable than the gas phase method, and the liquid phase method is generally used to produce metal particles with a particle size of 200 nm or less. In addition, since the current liquid phase method tends to result in small crystallite diameters, the crystallite diameter may be increased by heat treating the large particles 14 at a low temperature that does not destroy the shape of the large particles 14.

[0073] From the viewpoint of producing metal particles with a small particle size to crystallite size ratio, gas phase methods such as PVD and CVD are more suitable than liquid phase methods, and it is preferable to use a gas phase method in producing composite particles 12. However, current gas phase methods tend to produce large particle sizes. For this reason, the base powder is produced under conditions that result in a wide particle size distribution with a predetermined crystallite size. The base powder may then be classified until the desired average particle size (for example, preferably 200 nm or less, more preferably 100 nm or less) is obtained, thereby obtaining large particles 14.

[0074] The sulfur content in the composite particles 12 may be controlled, for example, by carrying out a desulfurization treatment when the large particles 14 are produced.

[0075] The method for producing the small particles 16 is not particularly limited, and they may be produced by, for example, a liquid phase synthesis method or a solid phase synthesis method.

[0076] Next, the composite particles 12 are produced by attaching the small particles 16 to the surfaces of the large particles 14. The method of attaching the small particles 16 is preferably electrostatic adsorption. The electrostatic adsorption method involves giving the large particles 14 and the small particles 16 opposite electric charges, mixing them, and then combining the large particles 14 and the small particles 16 by electrical attraction.

[0077] The nanometer-order oxide particles used as the small particles 16 have hydroxyl groups on their outermost surfaces, making them generally highly hydrophilic and dispersible in water or highly polar solvents, such as alcohols and glycols. While this depends on the manufacturing method and dispersion method, oxide particles often have a negative surface charge. Small particles 16 with such a negative surface charge are dispersed in an organic solvent, such as alcohols, glycols, or ketones, to obtain a dispersion containing the small particles 16. To stabilize the dispersion of the small particles 16, a small amount of additive may be added to the dispersion.

[0078] On the other hand, the metal particles used as the large particles 14 have a very weak positive or negative charge, depending on the element and manufacturing method. It is preferable to change the surface potential of the large particles 14 to a strong positive potential using a charge adjuster such as a polymer electrolyte and / or a specific acid.

[0079] As the polymer electrolyte, for example, polydiallyldimethylammonium chloride (PDDA), polyethyleneimine (PEI), etc. can be used.

[0080] The predetermined acid may be a carboxylic acid, hydrochloric acid, nitric acid, or the like.

[0081] The degree of oxidation and L slope of the outermost surface 14a of the large particles 14 can be controlled by subjecting the large particles 14 to an acid treatment using the charge adjusting agent. That is, in this embodiment, the large particles 14 are subjected to charge adjustment and acid treatment.

[0082] The degree of oxidation of the outermost surface 14a of the large particle 14 and the L gradient can be controlled by changing the temperature during the acid treatment, the acid concentration, the treatment time, and the amount of acid added.

[0083] The large particles 14, which have a positive surface potential as a result of charge adjustment and have also been treated with acid, are then dispersed in an organic solvent such as an alcohol, glycol, or ketone, similar to the small particles 16, to obtain a dispersion containing the large particles 14. To stabilize the dispersion of the large particles 14, a small amount of additive may be added to the dispersion.

[0084] Next, a dispersion containing small particles 16 and a dispersion containing large particles 14 are mixed in a desired ratio, and the small particles 16 are electrostatically adsorbed onto the surfaces of the large particles 14. The organic solvent is then removed to obtain composite particles 12.

[0085] The electrostatic adsorption method allows the small particles 16 to adhere to the surfaces of the large particles 14 in a nearly monodisperse state, thereby suppressing aggregation of the small particles 16. Furthermore, the electrostatic adsorption method makes it easy to control the amount of small particles 16 to adhere to the large particles 14, and the coverage of the small particles 16 with respect to the large particles 14 can be controlled within an optimum range for effectively exerting steric hindrance.

[0086] The composite particles 12 according to this embodiment can be used as a raw material powder for forming electrode layers in various electronic components, and are preferably used as a raw material powder for forming internal electrode layers of multilayer ceramic electronic components. The electrode layers (internal electrode layers) described above are formed by sintering a conductive paste containing the composite particles 12. The conductive paste may be produced by mixing the composite particles 12 with a known binder and a known solvent.

[0087] Second embodiment: Multilayer ceramic electronic component In the second embodiment, a multilayer ceramic capacitor 2 shown in FIG. 1 will be described as an example of a multilayer ceramic electronic component that uses the composite particles 12 of the first embodiment.

[0088] The multilayer ceramic capacitor 2 has an element body 4 and a pair of external electrodes 6 formed on the outer surface of the element body 4. The element body 4 has ceramic layers 20 and internal electrode layers 10 that are substantially parallel to a plane including the X-axis and Y-axis, and inside the element body 4, the ceramic layers 20 and internal electrode layers 10 are alternately stacked along the Z-axis direction. Here, "substantially parallel" means that most of the portions are parallel, but there may be some portions that are not parallel, and the ceramic layers 20 and internal electrode layers 10 may have some irregularities or be tilted.

[0089] The ceramic layer 20 includes a dielectric composition. The composition of the dielectric composition is not particularly limited. For example, the ceramic layer 20 may include BaTiO3, CaTiO3, SrTiO3, CaZrO3, (K 1-x Na x )Sr2Nb5O 15 , Ba3TiNb4O15 , and (Ba 1-x Ca x )(Ti 1-y Zr y )O3, etc. as a main component. In addition to the main component, the ceramic layer 20 may also contain one or more accessory components. Examples of accessory components of the ceramic layer 20 include manganese compounds, magnesium compounds, chromium compounds, cobalt compounds, nickel compounds, compounds containing rare earth elements, silicon compounds, and lithium compounds.

[0090] The average thickness of each ceramic layer 20 is not particularly limited, and is preferably 2 μm or less, more preferably 1.5 μm or less, and even more preferably 0.8 μm or less. The lower limit of the average thickness of the ceramic layer 20 is not particularly limited, and may be, for example, about 0.3 μm. The number of layers of the ceramic layer 20 may be determined appropriately depending on the desired properties, and is not particularly limited. For example, the number of layers of the ceramic layer 20 is preferably 20 or more, and more preferably 50 or more.

[0091] The internal electrode layers 10 are formed by sintering the composite particles 12 of the first embodiment, and the large particles 14 in the composite particles 12 become the conductive components of the internal electrode layers 10 after sintering. The internal electrode layers 10 are preferably formed from composite particles 12 containing large particles 14 made of nickel or a nickel alloy (for example, a NiSn-based alloy). In other words, the conductive component of the internal electrode layers 10 is preferably nickel or a nickel alloy.

[0092] On the other hand, the small particles 16 of the composite particles 12 may remain as insulating material inside the internal electrode layer 10 after sintering. When the total of the conductor component and insulating material in the internal electrode layer 10 is taken as 100 mass%, the content of the insulating material in the internal electrode layer 10 may be, for example, 0.4 mass% or more and 20 mass% or less, and preferably 3 mass% or more and 15 mass% or less. Some of the small particles 16 may be diffused into the ceramic layer 20 after sintering. By using barium titanate particles as the small particles 16, even if the small particles 16 diffuse into the ceramic layer 20, fluctuations in the composition of the ceramic layer 20 can be suppressed.

[0093] The internal electrode layers 10 are laminated between the ceramic layers 20, and the number of layers is determined according to the number of ceramic layers 20. The average thickness of each internal electrode layer 10 is not necessarily limited, and is preferably 2.0 μm or less, more preferably 1.5 μm or less, and even more preferably 0.8 μm or less. By using the composite particles 12 of the first embodiment as raw material powder, the internal electrode layers 10 can be made thin (for example, 0.8 μm or less) while suppressing the occurrence of cracks and discontinuities. The lower limit of the average thickness of the internal electrode layers 10 is not particularly limited, and may be, for example, about 0.3 μm. The average thickness t E In order to form the internal electrode layer 10, E It is preferable to use large particles 14 having an average particle size of 0.2 times or less.

[0094] The internal electrode layers 10 are stacked such that one end is alternately exposed on two end faces of the element body 4. A pair of external electrodes 6 are formed on both end faces of the element body 4 and electrically connected to the exposed ends of the alternately arranged internal electrode layers 10. By connecting the internal electrode layers 10 and the external electrodes 6 in the manner shown in FIG. 1, a capacitor circuit is formed by the external electrodes 6 and the internal electrode layers 10. In other words, the ceramic layers 20 present in the capacitance region are sandwiched between internal electrode layers 10 of opposite polarity, and a voltage can be applied to the ceramic layers 20.

[0095] The pair of external electrodes 6 can include a baked electrode layer, a resin electrode layer, a plated electrode layer, etc., and can be composed of a single electrode layer or a laminate of multiple electrode layers. For example, the external electrodes 6 can have a three-layer structure of a baked electrode layer containing copper, a nickel-plated layer, and a tin-plated layer (laminated in the order listed). When the external electrodes 6 are formed with this three-layer structure, the tin-plated layer is located on the outermost surface of the external electrodes 6, which improves the solder wettability of the external electrodes 6.

[0096] Next, an example of a method for manufacturing the multilayer ceramic capacitor 2 shown in FIG. 1 will be described.

[0097] First, a conductive paste used to form the internal electrode layers 10 and a ceramic layer paste used to form the ceramic layers 20 are prepared.

[0098] The conductive paste is produced by kneading the composite particles 12 of the first embodiment, a binder, and a solvent. In addition to the above, the conductive paste may contain additives such as a dispersant, an antioxidant, a ceramic powder, and an organometallic solution. The conductive paste may be an organic paint or a water-based paint, and the binder and solvent used in the conductive paste are not particularly limited.

[0099] For example, when the conductive paste is an organic paint, polyvinyl butyral, acrylic, ethyl cellulose, etc. may be used as the binder, and methyl ethyl ketone, methanol, ethanol, acetone, toluene, terpineol, butyl carbitol, acetate, etc. may be used as the solvent. When the conductive paste is a water-based paint, water may be used as the solvent, and polyvinyl alcohol, water-soluble acrylic resin, water-soluble polyvinyl butyral resin, etc. may be used as the binder.

[0100] The ceramic layer paste may be produced by kneading the main component powder of the dielectric composition, a binder, and a solvent. In addition to the above, additives such as subcomponent powder, a dispersant, and an antioxidant may be added to the ceramic layer paste. The ceramic layer paste may be an organic paint or a water-based paint, and the binder and solvent used in the conductive paste are not particularly limited. The ceramic layer paste may also use the same binder and solvent as the conductive paste.

[0101] Next, the ceramic layer paste is formed into a sheet by a method such as a doctor blade to obtain a ceramic green sheet. Then, a conductive paste is applied in a predetermined pattern onto this ceramic green sheet by various printing methods such as screen printing or a transfer method to obtain a green sheet on which an internal electrode pattern is formed. As a method for applying the conductive paste, screen printing or gravure printing is preferably used from the viewpoint of easily maintaining the structure of the composite particles 12.

[0102] A mother laminate is obtained by laminating multiple green sheets on which internal electrode patterns have been formed and then pressing them in the lamination direction. At this time, one or more green sheets on which no internal electrode patterns have been formed are laminated on the top and bottom surfaces of the mother laminate in the lamination direction.

[0103] The mother laminate obtained by the above steps is cut into a predetermined size by dicing or cutting to obtain a plurality of green chips. If necessary, the green chips may be solidified and dried to remove plasticizers, and after solidification and drying, they may be barrel polished using a horizontal centrifugal barrel machine or the like.

[0104] Next, the green chip obtained above is subjected to a binder removal process and a firing process to obtain the element body 4.

[0105] The conditions for the binder removal treatment are not particularly limited and may be determined appropriately depending on the types of binders added to the ceramic layer paste and the conductive paste. For example, the temperature rise rate may be preferably 5°C / hour to 300°C / hour, the holding temperature may be preferably 180°C to 800°C, and the temperature holding time may be preferably 0.5 hours to 24 hours. The atmosphere for the binder removal treatment may be an ambient atmosphere (i.e., air) or a reducing atmosphere.

[0106] The firing conditions are not particularly limited as long as they are set to conditions under which the internal electrode layers 10 and the ceramic layers 20 are sintered. For example, in the firing process, the temperature rise rate may be 50°C / hour to 500°C / hour, and preferably 200°C / hour to 300°C / hour. The holding temperature in the firing process is preferably 1200°C to 1350°C, and more preferably 1220°C to 1300°C. The temperature holding time is preferably 0.5 hours to 8 hours, and more preferably 2 hours to 3 hours. The firing process is preferably performed in a reducing atmosphere, and the atmospheric gas is preferably, for example, a humidified mixed gas of N2 and H2.

[0107] The oxygen partial pressure in the firing atmosphere may be appropriately determined depending on the type of conductive component in the conductive paste. When the conductive component is a base metal such as nickel or a nickel alloy, the oxygen partial pressure in the firing atmosphere is 1.0×10 -14 MPa~1.0×10 -10 The temperature drop rate in the firing treatment is preferably 50°C / hour to 500°C / hour.

[0108] After firing in a reducing atmosphere, the element body 4 may be subjected to an annealing treatment. The conditions for the annealing treatment are not particularly limited. For example, the oxygen partial pressure in the atmosphere is 1.0×10 -9 MPa~1.0×10 -5 The annealing temperature may be 950°C to 1150°C, and the temperature holding time may be 0 to 20 hours. As the atmospheric gas for annealing, for example, humidified N2 gas or the like may be used.

[0109] In the above-mentioned binder removal treatment, firing treatment, and annealing treatment, a wetter or the like may be used to humidify the N2 gas or mixed gas, and in this case, the water temperature is preferably about 5° C. to 75° C. Furthermore, the binder removal treatment, firing treatment, and annealing treatment may be performed consecutively or independently.

[0110] Next, a pair of external electrodes 6 are formed on the outer surfaces of the element body 4 obtained above. The method for forming the external electrodes 6 is not particularly limited. For example, when forming baked electrodes as the external electrodes 6, a conductive paste containing glass frit may be applied to the end surfaces of the element body 4 by a dipping method, and then the element body 4 may be heated at a predetermined temperature. When forming resin electrodes as the external electrodes 6, a conductive paste containing a thermosetting resin may be applied to the end surfaces of the element body 4, and then the element body 4 may be heated at a temperature at which the thermosetting resin hardens. Furthermore, after forming baked electrodes or resin electrodes by the above method, sputtering, vapor deposition, electrolytic plating, electroless plating, or the like may be performed to form the external electrodes 6 having a multilayer structure.

[0111] Through the above steps, a multilayer ceramic capacitor 2 having a cross section as shown in FIG. 1 can be manufactured.

[0112] In the multilayer ceramic capacitor 2, composite particles 12 with a high thermal shrinkage start temperature are used to form the internal electrode layers 10, thereby reducing the difference between the sintering start temperature of the internal electrode layers 10 and the sintering start temperature of the ceramic layers 20. Furthermore, because the small particles 16 are uniformly attached to the large particles 14, the amount of the small particles 16 is adjusted to an appropriate amount, and aggregation of the small particles 16 is prevented. This prevents cracks and discontinuities from occurring in the internal electrode layers 10, and improves the continuity ratio of the internal electrode layers 10 to the ceramic layers 20 compared to conventional methods. Specifically, in the multilayer ceramic capacitor 2 using the composite particles 12, the continuity ratio of the internal electrode layers 10 to the ceramic layers 20 can be 80% or more (preferably 90% or more). By improving the continuity ratio of the internal electrode layers 10, various properties of the multilayer ceramic capacitor 2, such as capacitance, can be improved.

[0113] The inventors also discovered that the catalytic activity of the metallic nickel contained in the conductive paste causes the binder to rapidly decompose during the binder removal process, which results in cracks occurring in the green chip during the binder removal process. In contrast, in this embodiment, the average oxidation degree of the outermost surfaces 14a of the large particles 14 is 30% or more, which inhibits the catalytic activity of the metallic nickel and allows the binder to decompose slowly during the binder removal process, thereby preventing cracks from occurring in the green chip.

[0114] Furthermore, in this embodiment, since the average oxidation degree of the outermost surface 14a of the large particles 14 is 90% or less, the composite particles 12 can be well dispersed in the conductive paste for forming the internal electrode layer 10, and as a result, the occurrence of cracks in the green chip during the binder removal process can be suppressed.

[0115] Specifically, in the multilayer ceramic capacitor 2 using the composite particles 12, the crack occurrence rate of the green chip during the binder removal process can be suppressed to 2% or less.

[0116] Furthermore, when the internal electrode layer 10 is formed using the composite particles 12, it is possible to suppress the diffusion of the small particles 16 into the ceramic layer 20. As a result, it is possible to suppress deviation of the composition of the ceramic layer 20 from the target composition.

[0117] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit of the present invention.

[0118] The electronic components to which the composite particles 12 are applied are not limited to multilayer ceramic capacitors, and the composite particles 12 can be applied to other electronic components as well. The other electronic components include all electronic components in which ceramic layers are laminated via internal electrode layers, such as bandpass filters, inductors, multilayer three-terminal filters, piezoelectric elements, PTC thermistors, NTC thermistors, and varistors.

[0119] The internal electrode layer 10 may also be formed using a conductive paste containing the composite particles 12 together with conductive particles other than the composite particles 12. The conductive particles other than the composite particles 12 are not particularly limited, and may be, for example, nickel particles, nickel-based alloy particles, copper particles, or copper-based alloy particles that are not composited with the small particles 16. The conductive paste used in this case preferably contains 20% by mass or more and 60% by mass or less, and more preferably 25% by mass or more and 45% by mass or less, of the composite particles 12, with the total content of the composite particles 12 and the conductive particles being 100% by mass.

[0120] The internal electrode layer 10 may also contain a co-material not derived from the small particles 16. The co-material not derived from the small particles 16 is added to the conductive paste as a single co-material, not as part of the composite particles 12. The average particle size of the co-material not derived from the small particles 16 is not particularly limited, and may be larger than the average particle size of the small particles 16, and may be 0.003 μm or more and 0.100 μm or less. The material of the co-material not derived from the small particles 16 is not particularly limited, but it is preferable to use an oxide contained in the ceramic layer 20 in order to reduce the effect on the composition of the ceramic layer 20.

[0121] Furthermore, the composite particles 12 may be used to form the external electrodes 6. For example, the external electrodes 6 may be formed using a conductive paste containing the composite particles 12 and a thermosetting resin. [Example]

[0122] The present disclosure will be described below in more detail based on examples, but the present disclosure is not limited to these examples.

[0123] (Experiment 1) In experiment 1, the composite particles shown in Table 1 were produced by changing the "average value of the coverage," "average value of the oxidation degree of the outermost surface of the large particles," and "average value of the L slope."

[0124] The mother powder was produced by the CVD method (vapor phase method) using nickel as the raw material. Note that the mother powder was subjected to desulfurization treatment during the production by the CVD method.

[0125] Next, the mother powder was classified to obtain large particles (hereinafter sometimes referred to as Ni particles).

[0126] Small particles of barium titanate (hereinafter referred to as BT particles) were attached to the surface of the Ni particles using electrostatic adsorption. Specifically, the Ni particles were mixed with an aqueous solution containing a charge control agent (PDDA and carboxylic acid), and the surface of the Ni particles was positively charged and treated with acid. Next, the BT particles, which originally had a negative surface potential, were introduced into an aqueous solution containing positively charged Ni particles, and the Ni particles and BT particles were composited by electrostatic adsorption. The resulting powder was then recovered from the aqueous solution and dried to obtain composite particles for each sample.

[0127] The amount of charge control agent added was changed for each sample to change the degree of oxidation of the outermost surface of the large particles and the L slope.

[0128] In addition, the coverage was changed by changing the blending ratio of BT particles during electrostatic adsorption for each sample.

[0129] The composite particles of each sample were evaluated as follows.

[0130] Average particle size of large particles (Ni particles), average particle size of small particles (BT particles) and average coverage rate The composite particles were added to ethanol at a ratio of 0.5% by mass and mixed using a vortex mixer for 1 minute. The ethanol solution containing the composite particles was left to stand for 1 to 2 hours to allow the composite particles to settle. The supernatant of the ethanol solution was then removed by decantation, and the remaining liquid was added to ethanol again and mixed. The resulting composite particle-containing liquid was dropped onto an SEM stage and air-dried. The composite particles remaining on the SEM stage were then observed using an SEM, and SEM images of the composite particles were obtained.

[0131] The above SEM images were analyzed using image analysis software, the particle sizes of 100 or more Ni particles were measured and the average value was calculated, the particle sizes of 100 or more BT particles were measured and the average value was calculated, and the coverage rate of BT particles relative to Ni particles was measured and the average value was calculated.

[0132] Table 1 shows the average coverage of BT particles with respect to Ni particles.

[0133] The average size of Ni particles was between 80 nm and 250 nm in all samples.

[0134] In the samples containing BT particles, the average particle size of the BT particles was 5 nm to 40 nm in all samples, which confirmed that the average particle size of the BT particles was smaller than the average particle size of the Ni particles in all samples.

[0135] Average oxidation degree of the outermost surface of large particles (Ni particles) The degree of oxidation of the outermost surfaces of 100 or more Ni particles was measured by the method described in the first embodiment above, and the average value was calculated. The results are shown in Table 1. A Quantera II (ULVAC-PHI, Inc.) was used for the XPS measurement.

[0136] L average slope The L slopes of 100 or more Ni particles were measured by the method described in the first embodiment, and the average value was calculated. The results are shown in Table 1.

[0137] (Experiment 2) In Experiment 2, each composite particle produced in Experiment 1 was used to produce a multilayer ceramic capacitor according to the following procedure.

[0138] First, a conductive paste for forming the internal electrode layers was prepared. The conductive paste was manufactured by kneading the composite particles of each sample with ethyl cellulose (binder) and terpineol (solvent). The compounding ratio of the composite particles in the conductive paste was set to 45 mass %, the compounding ratio of the binder to 3 mass %, and the compounding ratio of the solvent to 52 mass %.

[0139] Next, green sheets for the ceramic layers containing BaTiO3 as the main component were prepared, and a conductive paste was applied to these green sheets to form internal electrode patterns. Then, multiple green sheets with the internal electrode patterns formed on them were stacked and pressed in the stacking direction to obtain a mother laminate. At this time, protective green sheets without internal electrode patterns were stacked on the top and bottom surfaces of the mother laminate. The mother laminate was then cut to a predetermined size by dicing to obtain multiple green chips.

[0140] Next, the green chip was subjected to binder removal, firing, and annealing to obtain an element body (fired body). Next, a pair of external electrodes was formed by applying and firing an external electrode paste to two end faces of the element body, resulting in a multilayer ceramic capacitor (hereinafter referred to as a capacitor sample) having the structure shown in Figure 1. The dimensions of the element body in the capacitor sample were 12 mm wide x 20 mm deep x 12 mm high. In addition, the average thickness of each ceramic layer in the capacitor sample was 0.80 μm, the average thickness of each internal electrode layer was 0.50 μm, and the number of ceramic layers sandwiched between the internal electrode layers was four.

[0141] Crack occurrence rate during binder removal (debinding process) The 1,000 green chips after the binder removal treatment were examined under a microscope to see if cracks had occurred, and the crack occurrence rate was calculated. The results are shown in Table 1.

[0142] Continuity rate of internal electrode layers The cross sections of the 10 capacitor samples manufactured as described above were mirror-polished and observed with an SEM. The continuity ratio of the internal electrode layers was calculated based on the SEM observation. The results are shown in Table 1.

[0143] [Table 1]

[0144] From sample numbers 1 to 6, it was confirmed that when the average value of the coverage was 3% or more and 60% or less (sample numbers 2 to 6), the crack occurrence rate when removing the binder was lower and the continuity rate of the internal electrode layer was higher than when the average value of the coverage was 2% (sample number 1). In sample numbers 2 to 6, the effect of increasing the thermal shrinkage starting temperature due to the small particles can be fully exerted, so it is possible to suppress the occurrence of cracks and discontinuity of the internal electrode layer when removing the binder, and as a result, it is thought that the continuity rate of the internal electrode layer was higher.

[0145] From sample numbers 2 to 7, it was confirmed that when the average value of the coverage was 3% or more and 60% or less (sample numbers 2 to 6), the continuity rate of the internal electrode layer was higher than when the average value of the coverage was 65% (sample number 7). If small particles are present in excess, the internal electrode layer may be interrupted by the presence of the small particles. In contrast, in sample numbers 2 to 6, the small particles were not excessive relative to the large particles and were attached moderately and uniformly, so it is thought that the interruption of the internal electrode layer could be suppressed and the continuity rate of the internal electrode layer was increased.

[0146] From samples 8 to 11, it was confirmed that when the average oxidation degree of the outermost surface of the large particles was 30% or more and 90% or less (samples 9 to 11), the crack occurrence rate during the binder removal process was lower than when the average oxidation degree of the outermost surface of the large particles was 25% (sample 8). The inventors discovered that the catalytic activity of metallic nickel causes the binder to rapidly decompose during the binder removal process, which leads to cracks occurring in the green chip during the binder removal process. In contrast, in samples 9 to 11, the average oxidation degree of the outermost surface of the large particles was 30% or more, which inhibited the catalytic activity of metallic nickel and caused the binder to slowly decompose during the binder removal process, which is thought to have suppressed the occurrence of cracks in the green chip.

[0147] From samples 9 to 12, it was confirmed that when the average oxidation degree of the outermost surface of the large particles was 30% or more and 90% or less (samples 9 to 11), the crack occurrence rate during binder removal was lower than when the average oxidation degree of the outermost surface of the large particles was 95% (sample 12). In samples 9 to 11, the average oxidation degree of the outermost surface of the large particles was 90% or less, so the amount of oxidant reduced during binder removal was small. Therefore, in samples 9 to 11, less gas was generated during binder removal and the shrinkage stress was also small. As a result, it is believed that in samples 9 to 11, the occurrence of cracks in the green chip during binder removal was suppressed.

[0148] From samples 13 to 17, it was confirmed that when the average value of the L slope was greater than 0% (samples 14 to 17), the continuity rate of the internal electrode layer was higher than when the average value of the L slope was -0.5% (sample 13). An L slope greater than 0% indicates that the degree of oxidation gradually decreases from the surface to the interior of the large particles. This structure is thought to have made it possible to moderate the reduction behavior of nickel oxide during the binder removal process and to prevent significant disruption of the structure around the electrode. Therefore, it is thought that the final structure after firing also reflected the good condition during the binder removal process, resulting in a high continuity rate of the internal electrode layer.

[0149] Samples 20 and 21 are large particles that have been charge-adjusted and acid-treated. The small and large particles are not composited in Samples 20 and 21. Figure 6 relates to Sample 20.

[0150] In sample number 20, 1.5 parts by mass of the charge control agent was added to 100 parts by mass of Ni particles, and in sample number 21, 5.0 parts by mass of the charge control agent was added to 100 parts by mass of Ni particles.

[0151] In Figure 6, the X axis represents the depth from the outermost surface of the large particle toward the center of the large particle, and the Y axis represents the ratio of each peak area to the total peak area (L+M+N). In Figure 6, ◆ represents the ratio of the peak area (L) of the metallic nickel peak to (L+M+N), ▲ represents the ratio of the peak area (M) of the nickel oxide peak to (L+M+N), and ■ represents the ratio of the peak area (N) of the satellite peak to (L+M+N).

[0152] It was confirmed from sample No. 20 and sample No. 21 that increasing the concentration of the charge control agent tends to increase the L slope. This is thought to be because the higher the concentration of the charge control agent, the thinner the oxide layer becomes, causing the L ratio to increase sharply in the depth direction of the large particles, resulting in a higher L slope. [Explanation of symbols]

[0153] 12 … Composite particles 14...Large particles 14a … outermost surface of large particles 14b: Imaginary circle showing a depth of 2 nm from the outermost surface of a large particle to the center of the large particle 16 … small particles 18... Virtual circle 2... Multilayer ceramic capacitors 4... Element body 10 … Internal electrode layer 20...ceramic layer 6 … External electrode

Claims

1. A composite particle having a large particle and a small particle attached to the surface of the large particle and having an average particle size smaller than that of the large particle, the large particles are metal particles; The metal particles are mainly composed of nickel or a nickel alloy, the average coverage of the small particles attached to the surfaces of the large particles is 3% or more and 60% or less; the average oxidation degree of the outermost surface of the large particles is 30% or more and 90% or less; The degree of oxidation is defined by the following formula (2): Oxidation degree (%) = 100 × M / (L + M + N) ... Formula (2) When the outermost surface of the large particle is measured by X-ray photoelectron spectroscopy, L is the peak area of ​​the metallic nickel peak, M is the peak area of ​​the nickel oxide peak, The N is the peak area of ​​the satellite peak of the composite particle.

2. the average L slope of the large particles is greater than 0%, The L slope is defined by the following equations (3) and (4): L ratio = L / (L+M+N)... Formula (3) L slope (%) = 100 × (IL ratio - SL ratio) / 2 ... Formula (4) the SL ratio is the L ratio at the outermost surface of the large particle, The composite particle according to claim 1 , wherein the IL ratio is the L ratio at a depth of 2 nm from the outermost surface of the large particle toward the center of the large particle.

3. 2. The composite particle according to claim 1, wherein the small particles contain one or more elements selected from barium titanate, silicon oxide, titanium oxide, aluminum oxide, zirconium oxide, zinc oxide, praseodymium oxide, cobalt oxide, chromium oxide, bismuth oxide, boron oxide, calcium oxide, magnesium oxide, strontium oxide, bismuth ferrite, bismuth titanate, potassium sodium niobate, bismuth sodium titanate, potassium bismuth titanate, Ir, Rh, Ru, Pt, Pd, Re, Fe, Au, Ni, Cu, Ag, Co, W, Mn, Cr, Mo, V, Nb, Ta, Ti, Zr, Sn, and Os as a main component.

4. 2. The composite particle according to claim 1, wherein the average coverage is 5% or more and 50% or less.

5. A conductive paste comprising the composite particles according to any one of claims 1 to 4, a binder, and a solvent.

6. An electronic component having an electrode layer formed using the conductive paste according to claim 5.

Images