conductive paste

Abstract

To provide a conductive paste for an internal electrode of a layered ceramic capacitor, which is capable of maintaining relatively high coverage even if the internal electrode constitutes a thin layer.SOLUTION: Provided is a conductive paste for forming internal electrodes 4 and 5 of a layered ceramic capacitor 1 fabricated through a firing step. The conductive paste includes conductive metal powder, ceramic powder, an organic solvent, and an organic binder. The conductive metal powder contains silver. At least a portion of the ceramic powder comprises an ABO3 type oxide having a specific ion radius in which the ratio of the ion radius in the 6-coordination of an element at the A site in ABO3 with respect to the ion radius in the 6-coordination of silver is 0.89 or more and 1.02 or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a conductive paste, and particularly to a conductive paste for forming an internal electrode of a multilayer ceramic capacitor.

Background Art

[0002] A multilayer ceramic capacitor generally includes a laminate having a plurality of stacked dielectric layers made of ceramic and a plurality of internal electrodes respectively disposed along a plurality of interfaces between the dielectric layers, and a plurality of external electrodes provided on an outer surface of the laminate and electrically connected to the internal electrodes. The internal electrodes include a plurality of first internal electrodes and a plurality of second internal electrodes alternately arranged in the stacking direction of the laminate, and the external electrodes include a first external electrode electrically connected to the first internal electrode and a second external electrode electrically connected to the second internal electrode.

[0003] In order to make such a multilayer ceramic capacitor smaller and have a larger capacitance, it is required to make the dielectric layer and the internal electrode thinner and to increase the coverage (electrode continuity) of the internal electrode. Generally, in the firing process in the manufacture of a multilayer ceramic capacitor, the temperature at which the conductive metal particles contained in the conductive paste film to be the internal electrode sinter is lower than the temperature at which the ceramic constituting the dielectric layer sinters, so the metal particles contained in the internal electrode sinter first. This causes a decrease in the coverage of the internal electrode. Particularly, in the case of an internal electrode thinned to, for example, a thickness of 1 μm or less, the coverage is likely to decrease, and there is a problem that such a decrease in coverage tends to inhibit an increase in capacitance.

[0004] Therefore, in order to form thin internal electrodes with high coverage, it is necessary to raise the sintering temperature of the conductive metal particles contained in the conductive paste film that will become the internal electrodes during the firing process in the manufacturing of multilayer ceramic capacitors. This brings the sintering temperature of the metal particles in the conductive paste film that will become the internal electrodes closer to the temperature at which the ceramic constituting the dielectric layer begins to sinter, and brings the shrinkage timing during sintering closer between the internal electrodes and the dielectric layer. As a result, the coverage of the internal electrodes is increased, enabling higher capacitance.

[0005] In order to increase the coverage of the internal electrodes and achieve high capacity using the method described above, it is known to add a ceramic material, i.e., a co-material, to the conductive paste for forming the internal electrodes, which has a composition similar to that of the ceramic constituting the dielectric layer, as described in paragraph 0004 of Patent Document 1 (Japanese Patent Application Publication No. 2016-31807). By adding a co-material, the sintering timing of the metal particles contained in the conductive paste film that will become the internal electrodes can be shifted to a higher temperature, and the temperature at which the metal particles contained in the conductive paste film sinter can be brought closer to the temperature at which the ceramic constituting the dielectric layer sintersects. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2016-31807 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, even if a co-material is added to the conductive paste for forming internal electrodes, the temperature at which the metal particles in the conductive paste sinter is still lower than the temperature at which the ceramic constituting the dielectric layer sintersects, and further improvements are desired. In particular, for internal electrodes that are thinned to a thickness of 1 μm or less, there is a strong need for an effective solution to the problem of reduced coverage that hinders the increase in capacitance.

[0008] Therefore, this invention has been made in view of the above problems, and aims to provide a conductive paste for forming internal electrodes that can maintain relatively high coverage even when the internal electrodes are made into a thin layer. [Means for solving the problem]

[0009] This invention relates to a conductive paste for forming internal electrodes in a multilayer ceramic capacitor, comprising a conductive metal powder, a ceramic powder, an organic solvent, and an organic binder. In order to solve the above-mentioned technical problems, the conductive metal powder contains silver, and at least a portion of the ceramic powder is a powder made of an ABO3 type oxide with a specific ionic radius such that the ratio of the ionic radius of the element at the A site in ABO3 in a 6-coordinate state to the ionic radius of silver in a 6-coordinate state is 0.89 or more and 1.02 or less. [Effects of the Invention]

[0010] By forming the internal electrodes of a multilayer ceramic capacitor using the conductive paste according to this invention, the coverage of the internal electrodes can be increased. Therefore, even if the internal electrodes are made thinner, the coverage of the internal electrodes can be maintained at a high level, and the ability to increase the capacitance of the multilayer ceramic capacitor can not be hindered. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic cross-sectional view showing a multilayer ceramic capacitor 1 to which the conductive paste according to this invention is applied. [Modes for carrying out the invention]

[0012] Referring to Figure 1, the structure of the multilayer ceramic capacitor 1 to which the conductive paste according to this invention is applied will be described.

[0013] The multilayer ceramic capacitor 1 comprises a laminate 2. The laminate 2 comprises a plurality of stacked dielectric layers 3 made of ceramic, and a plurality of internal electrodes 4 and 5 arranged along the interfaces between the plurality of dielectric layers 3. The internal electrodes 4 and 5 are classified into a plurality of first internal electrodes 4 and a plurality of second internal electrodes 5, which are alternately arranged in the stacking direction of the laminate 3. The outer surface of the laminate 2, more specifically, each opposing end face, is provided with a first external electrode 6 and a second external electrode 7, respectively. The first external electrode 6 is electrically connected to the first internal electrode 4, and the second external electrode 7 is electrically connected to the second internal electrode 5.

[0014] The dielectric layer 3 is made of a ceramic mainly composed of ABO3 (where A is at least one of Ba, Ca, and Sr, and B is at least one of Ti and Zr). Alternatively, the ceramic may be mainly composed of the above ABO3 and may also contain at least one of Mn, Mg, Si, Y, Dy, and Gd as a minor component.

[0015] Internal electrodes 4 and 5 contain silver as a conductive component. Furthermore, as a characteristic composition, internal electrodes 4 and 5 include at least one selected from, for example, AgTiO3, EuTiO3, and NaTiO3. AgTiO3, EuTiO3, and NaTiO3 have an ilmenite crystal structure.

[0016] As can be seen from the experimental examples described later, in a preferred embodiment, the dielectric layer 3 is made of a ceramic mainly composed of at least one selected from BaTiO3, SrTiO3, and CaZrO3, and the internal electrodes 4 and 5 contain silver as a conductive component and include at least one selected from AgTiO3, EuTiO3, and NaTiO3 as a ceramic material, and optionally further include at least one selected from BaTiO3, SrTiO3, and CaZrO3 contained in the dielectric layer 3.

[0017] External electrodes 6 and 7 are formed, for example, by applying a conductive paste, mainly composed of Ag or Cu, to the end face of the laminate 2 and baking it. If necessary, a Ni plating and then a Sn plating may be applied to the thick film formed by baking.

[0018] A multilayer ceramic capacitor 1 is manufactured, for example, through the following process. First, a ceramic slurry containing ceramic raw material powder having the above composition is prepared. Next, a suitable sheet molding method is applied to the ceramic slurry to form a ceramic green sheet. Next, conductive pastes that will become the internal electrodes 4 and 5 are applied to a predetermined ceramic green sheet from among several ceramic green sheets by printing or other means. Next, the multiple ceramic green sheets are laminated and then pressed together to obtain a raw laminate. Next, the raw laminate is fired. In this firing process, the ceramic green sheets become the dielectric layer 3. After that, external electrodes 6 and 7 are formed on the end faces of the laminate 3.

[0019] The conductive paste that will form the internal electrodes 4 and 5 used in the manufacture of the multilayer ceramic capacitor 1 described above is preferably prepared as follows.

[0020] In the production of the conductive paste, a first step of preparing a ceramic powder slurry containing a ceramic powder, an organic solvent, and a dispersant, a second step of preparing a metal powder slurry containing a conductive metal powder, an organic solvent, and a dispersant, a third step of preparing an organic vehicle containing an organic resin component and an organic solvent, and a fourth step of mixing the ceramic powder slurry, the metal powder slurry, and the organic vehicle are carried out.

[0021] More specifically, in the first step, a ceramic powder slurry is produced by mixing a ceramic powder and a dispersant in an organic solvent.

[0022] As the above-mentioned ceramic powder, for example, one composed of at least one selected from AgTiO3, EuTiO3, and NaTiO3 as ABO3 oxides is used. Further, in addition to this, one composed of at least one selected from BaTiO3, SrTiO3, and CaZrO3 as co-materials may be used.

[0023] Since the conductive metal powder contained in the metal powder slurry produced in the second step described later contains silver, AgTiO3, EuTiO3, and NaTiO3 as the above-mentioned ABO3 oxides are ABO3-type oxides with a specific ionic radius such that the ratio of the ionic radius of the element at the A site in ABO3 to the ionic radius of silver in the 6-fold coordination is 0.89 or more and 1.02 or less.

[0024] According to a ceramic powder composed of at least one selected from AgTiO3, EuTiO3, and NaTiO3 as ABO3 oxides, the reaction that may occur between the ceramic powder and the silver powder contained in the metal powder slurry produced in the second step during firing can be suppressed. The ceramic powder may contain, as a main component, the above-mentioned ABO3 oxide, and further, at least one of Mn, Mg, Si, Y, Dy, and Gd as a sub-component. When such a sub-component is contained, the grain growth of the ceramic particles may be more suppressed, and the sintering of the metal particles may be more effectively suppressed.

[0025] As the dispersant mixed with the ceramic powder in the first step, for example, an anionic polymer dispersant can be used, and as the organic solvent, for example, dihydroterpineol can be used.

[0026] In the second step, a metal powder slurry is prepared by mixing conductive metal powder and a dispersant with an organic solvent. Silver powder is used as the conductive metal powder. The dispersant and organic solvent used in the second step can be the same as those used in the first step.

[0027] In the third step, an organic vehicle is prepared by mixing an organic resin component with an organic solvent. For example, ethyl cellulose resin can be used as the organic resin component. The organic solvent used in the third step can be the same as the one used in the first step.

[0028] In the fourth step, the ceramic powder slurry, metal powder slurry, and organic vehicle described above are mixed. This yields a conductive paste that will become the internal electrodes 4 and 5. This conductive paste contains the ceramic powder slurry, and as mentioned above, the ceramic powder slurry contains ceramic powder consisting of at least one selected from AgTiO3, EuTiO3, and NaTiO3 as ABO3 oxides with specific ionic radii. Therefore, the internal electrodes 4 and 5 provided in the multilayer ceramic capacitor 1 manufactured through the firing process will contain at least one selected from AgTiO3, EuTiO3, and NaTiO3.

[0029] [Example of experiment] Next, we will describe experimental examples conducted to confirm the effects of this invention.

[0030] In this experimental example, silver powder was prepared as the conductive metal powder included in the conductive paste for forming internal electrodes.

[0031] On the other hand, in addition to AgTiO3, EuTiO3, and NaTiO3, CuTiO3, SrTiO3, BaTiO3, and CaZrO3 were prepared as ABO3 oxides with specific ionic radii that constitute the ceramic powder included in the conductive paste for forming internal electrodes. Table 1 shows the "crystal structure," "coordination number," "A-site element," and "ionic radius" for these ABO3 oxides. Note that while Sr, Ba, and Ca are 12-coordinate in their original perovskite structure, they also become 6-coordinate when dissolved in the sites of 6-coordinate elements (Ag, Eu, Na) in the ilmenite structure. Therefore, the "ionic radius" in Table 1 shows the value for 6-coordination.

[0032] [Table 1]

[0033] Below, we describe Experimental Examples 1, 2, and 3, which were conducted by changing the ceramic raw materials that make up the dielectric layer.

[0034] (Experimental Example 1) Main component of the ceramic constituting the dielectric layer: BaTiO3 1. Fabrication of BaTiO3-based ceramic raw materials for the dielectric layer As starting materials, the main components BaCO3 and TiO2 powders were weighed and mixed in a ball mill for 72 hours, then heat-treated at a top temperature of 1000°C for 2 hours to obtain heat-treated powder. On the other hand, as minor components, powders of MnO, Dy2O3, MgO, SiO2, and BaCO3 were prepared. The minor component powders were weighed to the heat-treated powder so that the composition ratio was 100BaTiO3 + 0.5Mn + 1.0Dy + 1.0Mg + 1.0Si + 2.0Ba. These minor component powders were added to the heat-treated powder and mixed in a ball mill for 24 hours, then dried to obtain BaTiO3-based ceramic raw material powder.

[0035] 2. Preparation of conductive paste for internal electrode formation The "ABO3 oxide" powder shown in Table 2 below, along with the BaTiO3-based ceramic raw material powder for the dielectric layer, were used as ceramic powders included in the conductive paste for forming the internal electrodes.

[0036] These "ABO3 oxide" powders and BaTiO3-based ceramic raw material powders were weighed to the "addition ratios" shown in Table 2. These powders, along with dihydroterpineol as an organic solvent and an anionic polymer dispersant as a dispersant, were pre-mixed in a medium-free stirring mill, and then dispersed in a medium-stirring mill to produce a ceramic powder slurry (Step 1).

[0037] On the other hand, silver powder as a conductive metal powder, dihydroterpineol as an organic solvent, and an anionic polymer dispersant as a dispersant were dispersed in a three-roll mill to prepare a metal powder slurry (second step).

[0038] Furthermore, an organic vehicle was obtained by mixing ethylcellulose resin, which is an organic resin component, with dihydroterpineol, which is an organic solvent (third step).

[0039] Subsequently, the above-mentioned metal powder slurry and ceramic powder slurry were added to the above-mentioned organic vehicle and mixed and dispersed to prepare a conductive paste for forming internal electrodes (Step 4).

[0040] Table 2 shows the ratio of the ionic radius of the A-site element in a 6-coordinate state to the ionic radius of the silver that should be included in the internal electrode, i.e., the "ionic radius ratio (A-site element / metallic silver)". For sample 8, the ratio of the ionic radius of the Ba element in a 6-coordinate state (1.35 Å) shown in Table 1 to the ionic radius of the silver in a 6-coordinate state (1.15 Å) is shown.

[0041] 3. Fabrication of multilayer ceramic capacitors A ceramic slurry containing the BaTiO3-based ceramic raw material powder prepared in step 1 above was prepared, and then a doctor blade method was applied to the ceramic slurry to form a ceramic green sheet. Next, the conductive paste for forming internal electrodes, prepared in step 2 above, was applied to a predetermined ceramic green sheet from among several ceramic green sheets by screen printing. Then, the multiple ceramic green sheets were stacked and pressed together to obtain a raw laminate. Next, the raw laminate was fired. After that, external electrodes were formed on the end faces of the sintered laminate to produce a multilayer ceramic capacitor sample.

[0042] 4. Evaluation

[0043] [Table 2]

[0044] The internal electrode and dielectric layer located in the central part of the laminate in the height direction of the multilayer ceramic capacitor sample were separated from each other by field delamination.

[0045] Next, the central part of the exposed internal electrode (at the 1 / 2 point in both the width and length directions) was observed using a microscope at a magnification of 100x. By analyzing the obtained images, the percentage of the area occupied by the conductive film as the internal electrode in the exposed portion was determined as "coverage," as shown in Table 2. Samples with a "coverage" of 80% or more were judged as good and marked with "○" in the "Evaluation" column, while samples with a "coverage" lower than 80% were judged as poor and marked with "×" in the "Evaluation" column.

[0046] 5. Discussion Samples 1-3 and 5-7 in Table 2 are marked with "○" for "Evaluation". These samples 1-3 and 5-7 contain one of the following ABO3 oxides in their internal electrodes: AgTiO3, EuTiO3, or NaTiO3. Additionally, the internal electrodes contain silver as a conductive component.

[0047] Focusing on the ionic radius, first, as shown in the "AgTiO3" section of Table 1, the ionic radius of silver in 6-coordinate state is 1.15 Å. On the other hand, the ionic radii of the elements at the A site of AgTiO3, EuTiO3, and NaTiO3, respectively, as ABO3 oxides contained in the internal electrodes of samples 1-3 and 5-7, in 6-coordinate state are 1.15 Å, 1.17 Å, and 1.02 Å, respectively, as shown in Table 1.

[0048] In samples 1-3 and 5-7, which were evaluated as "○", the ratio of the ionic radius of the element at the A site in ABO3 in a 6-coordinate state to the ionic radius of silver in a 6-coordinate state, i.e., the "ionic radius ratio", is 0.89 or greater and 1.02 or less.

[0049] Thus, in samples 1-3 and 5-7, AgTiO3, EuTiO3, and NaTiO3, as ABO3 oxides, have ionic radii at the A site of ABO3 in a 6-coordinate state that are equal to or close to the ionic radius of silver in a 6-coordinate state, which is the conductive metal that should be included in the internal electrode. As a result, the energy difference with the silver in the internal electrode becomes zero or small, and the materials remain without being discharged from the internal electrode, thus improving the heat resistance of the internal electrode. Consequently, it is presumed that the coverage in samples 1-3 and 5-7 was high, exceeding 82%.

[0050] Furthermore, as seen in samples 5-7, the addition ratio of AgTiO3, EuTiO3, and NaTiO3 was not necessarily 100%. When the ratio was 10% or higher, an improvement in coverage was observed compared to the case where none of AgTiO3, EuTiO3, or NaTiO3 were included.

[0051] In contrast to these, sample 4, which was evaluated as "×", used SrTiO3 as the ABO3 oxide, and the ionic radius of Sr, the element at the A site in ABO3, in a 6-coordinate state is 1.18 Å, as shown in Table 1. Therefore, the ratio of the ionic radius of Sr in a 6-coordinate state to the ionic radius of silver in a 6-coordinate state, i.e., the "ionic radius ratio", is 1.03. In other words, the "ionic radius ratio" falls outside the range of 0.89 or higher and 1.02 or lower, resulting in a low coverage of 76%.

[0052] Furthermore, in sample 8, which was also evaluated as "×", only BaTiO3 as a co-material was added to the internal electrode. In this case, although Ba, the element at the A site in the perovskite structure ABO3, is 12-coordinate, when solid-solubilating into the A site of the ilmenite structure, it is necessary to compare the ionic radius at 6-coordinate, which is the coordination number of the A site in the ilmenite structure. As shown in Table 1, the ionic radius of Ba at 6-coordinate is 1.35 Å. Therefore, the ratio of the ionic radius of Ba at 6-coordinate to the ionic radius of silver at 6-coordinate, i.e., the "ionic radius ratio," is 1.17. Thus, the "ionic radius ratio" falls outside the range of 0.89 or higher and 1.02 or lower, resulting in a low coverage of 75%.

[0053] In samples 4 and 8, the "ionic radius ratio" fell outside the range of 0.89 or higher and 1.02 or lower. It is presumed that BaTiO3 was discharged from the internal electrode portion, preventing improvement in the heat resistance of the internal electrode and resulting in low coverage.

[0054] (Experimental Example 2) Main component of the ceramic constituting the dielectric layer: CaZrO3 1. Fabrication of CaZrO3-based ceramic raw materials for the dielectric layer As starting materials, the main components CaCO3 and ZrO2 powders, along with the minor components MnO, SiO2, and MgO powders, were weighed, mixed in a ball mill for 72 hours, and then heat-treated at a top temperature of 1000°C for 2 hours to obtain CaZrO3-based ceramic raw material powder.

[0055] 2. Preparation of conductive paste for internal electrode formation The "ABO3 oxide" powder shown in Table 3 below and the CaZrO3-based ceramic raw material powder for the dielectric layer were used as ceramic powders included in the conductive paste for forming the internal electrodes.

[0056] These "ABO3 oxide" powders and CaZrO3-based ceramic raw material powders were weighed to the "addition ratios" shown in Table 3, and a conductive paste for forming internal electrodes was prepared by following the same process as in Experimental Example 1 above.

[0057] Table 3 shows the "ionic radius ratio (A-site element / metallic silver)," similar to Table 2. For sample 18, the ratio of the ionic radius of Ca element in the 6-coordinate state (1.00 Å) shown in Table 1 to the ionic radius of silver in the 6-coordinate state (1.15 Å) is shown.

[0058] 3. Fabrication of multilayer ceramic capacitors A ceramic slurry containing the CaZrO3-based ceramic raw material powder prepared in step 1 above was prepared, and then a doctor blade method was applied to the ceramic slurry to form a ceramic green sheet. Subsequently, a multilayer ceramic capacitor to be used as a sample was fabricated through the same process as in Experimental Example 1.

[0059] 4. Evaluation

[0060] [Table 3]

[0061] Following the same procedure as in Experimental Example 1, "coverage" was calculated and evaluated in the same manner, as shown in Table 3.

[0062] 5. Discussion Samples 11-13 and 15-17 in Table 3 are marked with "○" for "Evaluation". These samples (11-13 and 15-17) contain one of the following ABO3 oxides in their internal electrodes: AgTiO3, EuTiO3, or NaTiO3. Additionally, the internal electrodes contain silver as a conductive component.

[0063] Focusing on the ionic radius, first, as shown in the "AgTiO3" section of Table 1, the ionic radius of silver in 6-coordinate state is 1.15 Å. On the other hand, the ionic radii of the elements at the A site of AgTiO3, EuTiO3, and NaTiO3, respectively, as ABO3 oxides contained in the internal electrodes of samples 11-13 and 15-17, in 6-coordinate state are 1.15 Å, 1.17 Å, and 1.02 Å, respectively, as shown in Table 1.

[0064] In samples 11-13 and 15-17, which were evaluated as "○", the ratio of the ionic radius of the element at the A site in ABO3 in a 6-coordinate state to the ionic radius of silver in a 6-coordinate state, i.e., the "ionic radius ratio", is 0.89 or greater and 1.02 or less.

[0065] Thus, in samples 11-13 and 15-17, AgTiO3, EuTiO3, and NaTiO3, as ABO3 oxides, have ionic radii at the A site in ABO3 in a 6-coordinate state that are equal to or close to the ionic radius of silver in a 6-coordinate state, which is the conductive metal that should be included in the internal electrode. As a result, the energy difference with the silver in the internal electrode becomes zero or small, and the materials remain without being discharged from the internal electrode, thus improving the heat resistance of the internal electrode. Consequently, it is presumed that the coverage in samples 11-13 and 15-17 was high, exceeding 81%.

[0066] Furthermore, as seen in samples 15-17, the addition ratio of AgTiO3, EuTiO3, and NaTiO3 was not necessarily 100%. When the ratio was 10% or higher, an improvement in coverage was observed compared to the case where none of AgTiO3, EuTiO3, or NaTiO3 were included.

[0067] In contrast to these, sample 14, which was evaluated as "×", used CuTiO3 as the ABO3 oxide, and the ionic radius of Cu, the element at the A site in ABO3, in a 6-coordinate state is 0.73 Å, as shown in Table 1. Therefore, the ratio of the ionic radius of Cu in a 6-coordinate state to the ionic radius of silver in a 6-coordinate state, i.e., the "ionic radius ratio", is 0.63. In other words, the "ionic radius ratio" falls outside the range of 0.89 or higher and 1.02 or lower, resulting in a low coverage of 75%.

[0068] Furthermore, in sample 18, which was also evaluated as "×", only CaZrO3 as a co-material was added to the internal electrode. In this case, Ca, the element at the A site in the perovskite structure ABO3, is 12-coordinate, but when solid-solubilating into the A site of the ilmenite structure, it is necessary to compare the ionic radius at 6-coordinate, which is the coordination number of the A site in the ilmenite structure. As shown in Table 1, the ionic radius of Ca at 6-coordinate is 1.00 Å. Therefore, the ratio of the ionic radius of Ca at 6-coordinate to the ionic radius of silver at 6-coordinate, i.e., the "ionic radius ratio," is 0.87. Thus, the "ionic radius ratio" falls outside the range of 0.89 or higher and 1.02 or lower, resulting in a low coverage of 72%.

[0069] In samples 14 and 18, the "ionic radius ratio" fell outside the range of 0.89 or higher and 1.02 or lower. It is presumed that CaZrO3 was discharged from the internal electrode portion, preventing improvement in the heat resistance of the internal electrode and resulting in low coverage.

[0070] (Experimental Example 3) Main component of the ceramic constituting the dielectric layer: SrTiO3 1. Fabrication of SrTiO3-based ceramic raw materials for the dielectric layer As starting materials, the main components SrCO3 and TiO2 powders, along with the minor components MnO, SiO2, and MgO powders, were weighed, mixed in a ball mill for 72 hours, and then heat-treated at a top temperature of 1000°C for 2 hours to obtain SrTiO3-based ceramic raw material powder.

[0071] 2. Preparation of conductive paste for internal electrode formation The "ABO3 oxide" powder shown in Table 4 below, along with the SrTiO3-based ceramic raw material powder for the dielectric layer, were used as ceramic powders included in the conductive paste for forming the internal electrodes.

[0072] These "ABO3 oxide" powders and SrTiO3-based ceramic raw material powders were weighed to the "addition ratios" shown in Table 4, and a conductive paste for forming internal electrodes was prepared by following the same process as in Experimental Example 1 above.

[0073] Table 4 shows the "ionic radius ratio (A-site element / metallic silver)," similar to Table 2. For sample 28, the ratio of the ionic radius of Sr element in a 6-coordinate state (1.18 Å) to the ionic radius of silver in a 6-coordinate state (1.15 Å) shown in Table 1 is also shown.

[0074] 3. Fabrication of multilayer ceramic capacitors A ceramic slurry containing the SrTiO3-based ceramic raw material powder prepared in step 1 above was prepared, and then a ceramic green sheet was formed by applying the doctor blade method to the ceramic slurry. Subsequently, a multilayer ceramic capacitor to be used as a sample was fabricated through the same process as in Experimental Example 1.

[0075] 4. Evaluation

[0076] [Table 4]

[0077] Following the same procedure as in Experimental Example 1, "coverage" was calculated and evaluated in the same manner, as shown in Table 4.

[0078] 5. Discussion Samples 21-23 and 25-27 in Table 4 are marked with "○" for "Evaluation". In these samples, the internal electrodes contain one of the following ABO3 oxides: AgTiO3, EuTiO3, or NaTiO3. Additionally, the internal electrodes contain silver as a conductive component.

[0079] Focusing on the ionic radius, first, as shown in the "AgTiO3" section of Table 1, the ionic radius of silver in 6-coordinate state is 1.15 Å. On the other hand, the ionic radii of the elements at the A site of AgTiO3, EuTiO3, and NaTiO3, respectively, as ABO3 oxides contained in the internal electrodes of samples 21-23 and 25-27, in 6-coordinate state, are 1.15 Å, 1.17 Å, and 1.02 Å, respectively, as shown in Table 1.

[0080] In samples 21-23 and 25-27, which were evaluated as "○", the ratio of the ionic radius of the element at the A site in ABO3 in a 6-coordinate state to the ionic radius of silver in a 6-coordinate state, i.e., the "ionic radius ratio", is 0.89 or greater and 1.02 or less.

[0081] Thus, in samples 21-23 and 25-27, AgTiO3, EuTiO3, and NaTiO3, as ABO3 oxides, have ionic radii in the A-site of ABO3 in a 6-coordinate state that are equal to or close to the ionic radius of silver in a 6-coordinate state, which is the conductive metal that should be included in the internal electrode. As a result, the energy difference with the silver in the internal electrode becomes zero or small, and the materials remain without being discharged from the internal electrode, thus improving the heat resistance of the internal electrode. Consequently, it is presumed that the coverage in samples 21-23 and 25-27 was high, exceeding 80%.

[0082] Furthermore, as seen in samples 25-27, the addition ratio of AgTiO3, EuTiO3, and NaTiO3 was not necessarily 100%. When the ratio was 10% or higher, an improvement in coverage was observed compared to the case where none of AgTiO3, EuTiO3, or NaTiO3 were included.

[0083] In contrast to these, sample 24, which was evaluated as "×", used CuTiO3 as the ABO3 oxide, and the ionic radius of Cu, the element at the A site in ABO3, in a 6-coordinate state is 0.73 Å, as shown in Table 1. Therefore, the ratio of the ionic radius of Cu in a 6-coordinate state to the ionic radius of silver in a 6-coordinate state, i.e., the "ionic radius ratio", is 0.63. In other words, the "ionic radius ratio" falls outside the range of 0.89 or higher and 1.02 or lower, resulting in a low coverage of 72%.

[0084] Furthermore, in sample 28, which was also evaluated as "×", only SrTiO3 as a co-material was added to the internal electrode. In this case, Sr, the element at the A site in the perovskite structure ABO3, is 12-coordinate, but when solid-solubilating into the A site of the ilmenite structure, it is necessary to compare the ionic radius at 6-coordinate, which is the coordination number of the A site in the ilmenite structure. As shown in Table 1, the ionic radius of Sr at 6-coordinate is 1.18 Å. Therefore, the ratio of the ionic radius of Sr at 6-coordinate to the ionic radius of silver at 6-coordinate, i.e., the "ionic radius ratio," is 1.03. Thus, the "ionic radius ratio" falls outside the range of 0.89 or higher and 1.02 or lower, resulting in a low coverage of 70%.

[0085] In samples 24 and 28, the "ionic radius ratio" fell outside the range of 0.89 or higher and 1.02 or lower. It is presumed that SrTiO3 was discharged from the internal electrode portion, preventing improvement in the heat resistance of the internal electrode and resulting in low coverage.

[0086] In the experimental examples 1 to 3 described above, the powder consisting of an ABO3 type oxide with a specific ionic radius, which was at least a part of the ceramic powder contained in the conductive paste, was at least one selected from AgTiO3, EuTiO3, and NaTiO3, but other types may also be used. In other words, any ABO3 type oxide with a specific ionic radius may be used as long as the ratio of the ionic radius of the element at the A site in ABO3 with a 6-coordinate configuration to the ionic radius of the silver contained in the conductive paste with a 6-coordinate configuration is 0.89 or more and 1.02 or less.

[0087] Embodiments of this invention include the following:

[0088] <1> A conductive paste for forming internal electrodes of a multilayer ceramic capacitor, comprising conductive metal powder, ceramic powder, an organic solvent, and an organic binder, The conductive metal powder contains silver, A conductive paste comprising, at least a portion of the ceramic powder, a powder of an ABO3 type oxide with a specific ionic radius, wherein the ratio of the ionic radius of the element at the A site in ABO3 in a 6-coordinate configuration to the ionic radius of silver in a 6-coordinate configuration is 0.89 or more and 1.02 or less.

[0089] <2> The aforementioned ABO3 type oxide with a specific ionic radius has an ilmenite crystal structure. <1> The conductive paste described above.

[0090] <3> The ABO3 type oxide with the specified ionic radius is at least one selected from AgTiO3, EuTiO3, and NaTiO3. <2> The conductive paste described above.

[0091] <4> The ceramic powder comprises at least 10% by volume of an ABO3 type oxide with the specified ionic radius, and the remainder of the ceramic powder is a powder mainly composed of at least one selected from BaTiO3, SrTiO3, and CaZrO3. <1> or <3> A conductive paste as described in any of the following. [Explanation of symbols]

[0092] 1. Multilayer ceramic capacitor 2 Laminate 3. Dielectric layer 4,5 Internal electrode 6,7 External electrode

Claims

1. A conductive paste for forming internal electrodes of a multilayer ceramic capacitor, comprising conductive metal powder, ceramic powder, an organic solvent, and an organic binder, The conductive metal powder contains silver, At least a portion of the aforementioned ceramic powder is ABO relative to the ionic radius of silver in 6-coordinate state. ３ ABO of a specific ionic radius such that the ratio of ionic radii of the element at site A in 6-coordinate is 0.89 or greater and 1.02 or less. ３ A conductive paste, which is a powder made of a specific type of oxide.

2. The ABO of the specified ionic radius ３ The conductive paste according to claim 1, wherein the oxide of the type has an ilmenite crystal structure.

3. The ABO of the specified ionic radius ３ The oxide of this type is AgTiO ３ , EuTiO ３ and NaTiO ３ The conductive paste according to claim 2, which is at least one selected from the following.

4. At least 10% by volume of the ceramic powder is a powder composed of an ABO type oxide having the specific ionic radius, and the remainder of the ceramic powder is BaTiO, SrTiO, and CaZrO. ３ type oxide powder, and the remainder of the ceramic powder is BaTiO ３ , SrTiO ３ and CaZrO ３ The conductive paste according to any one of claims 1 to 3, which is a powder having at least one selected therefrom as a main component.

Images