JP2014084267A - Dielectric ceramic and laminated ceramic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dielectric ceramic having crystal grains capable of attaining a high dielectric constant and improving high insulation, and a laminated ceramic capacitor in which the dielectric ceramic is applied to dielectric layers.SOLUTION: The dielectric ceramic is formed of a plurality of crystal grains including barium titanate as a principal component and at least a rare earth element. The rare earth element has a maximum concentration on the crystal grain surface and is 0.2-1.0 at.% in a region to the depth of 15 nm from the surface of the crystal grain, 0.2 or more at.% in a region to the depth of 20-50 nm from the surface and 0.1 or less at.% in a region deeper than 100 nm from the surface.

Description

  The present invention relates to a dielectric ceramic composed of crystal particles mainly composed of barium titanate and a multilayer ceramic capacitor in which the dielectric ceramic is applied to a dielectric layer.

  Conventionally, barium titanate has been used as a dielectric material for multilayer ceramic capacitors because of its high relative dielectric constant, and inexpensive base metals (such as Ni) have been used for internal electrode layers of multilayer ceramic capacitors. ing. When the dielectric layer mainly composed of barium titanate and the internal electrode layer are fired at the same time, it is necessary to reduce the oxygen partial pressure (for example, 0.03 Pa or less at 1300 ° C.) in order not to oxidize Ni. In this case, there is a problem that the dielectric layer is reduced and the insulating property is lowered, so that practical characteristics cannot be obtained.

  Therefore, when obtaining a multilayer ceramic capacitor satisfying the X5R characteristic (or JIS standard B characteristic) of the EIA standard, the dielectric material is, for example, barium titanate as a main component, and a rare earth element oxide or the like. A reduction-resistant dielectric porcelain to which an auxiliary component is added is used (see, for example, Patent Document 1).

  The crystal particles constituting such a dielectric ceramic are composed of a core part with a small amount of auxiliary component such as a rare earth element and a shell part surrounding the core part and having a relatively large amount of auxiliary component in solid solution. It has a so-called core-shell structure.

  The crystal particles having the core-shell structure are the portions where the shell portion mainly contributes to the insulating properties. Therefore, in order to improve the insulating properties of the dielectric ceramic, the amount of the auxiliary component that is usually dissolved in the shell portion is added. In this method, although the insulation is improved, the dielectric constant is decreased because the ratio of the core portion exhibiting ferroelectricity decreases with the increase of the auxiliary component. Therefore, it is difficult to achieve both high insulation and high dielectric constant.

JP 2001-230150 A

  Accordingly, an object of the present invention is to obtain a dielectric ceramic having crystal particles capable of improving the dielectric constant and the insulation, and a multilayer ceramic capacitor in which the dielectric ceramic is applied to a dielectric layer.

  The dielectric ceramic of the present invention is a dielectric ceramic composed of a plurality of crystal particles containing barium titanate as a main component and containing at least a rare earth element, wherein the rare earth element has a concentration on the surface of the crystal particles. In the region where the depth from the surface of the crystal grain is up to 15 nm, 0.2 atomic percent or more in the region where the depth from the surface is 20 to 50 nm, It is characterized by being 0.1 atomic% or less in a region deeper than 100 nm from the surface.

  The multilayer ceramic capacitor of the present invention is characterized in that dielectric layers made of the above dielectric ceramics and internal electrode layers are alternately laminated.

  According to the present invention, a dielectric ceramic having crystal grains capable of improving the dielectric constant and insulation, and applying this to the dielectric layer, a high-capacity and high-insulation multilayer ceramic capacitor can be obtained. Can be obtained.

It is a graph which shows the density | concentration change of the rare earth element contained in a crystal grain, the graph A is the crystal particle which comprises the dielectric material ceramic of this embodiment, and the graph B is the crystal which comprises the dielectric material ceramic obtained by the conventional manufacturing method It corresponds to a particle. It is a schematic sectional drawing which shows an example of the multilayer ceramic capacitor of this invention.

  FIG. 1 is a graph showing changes in the concentration of rare earth elements contained in crystal grains. Graph A is a crystal particle constituting the dielectric ceramic according to the present embodiment. Graph B is a dielectric ceramic obtained by a conventional manufacturing method. Corresponds to the crystal grains constituting the.

  The dielectric ceramic of the present embodiment is composed of a plurality of crystal particles containing barium titanate as a main component and containing at least a rare earth element.

  The concentration of the rare earth element contained in the crystal particles constituting the dielectric ceramic according to the present embodiment is such that the surface of the crystal particles is maximized and the depth from the surface of the crystal particles is 15 nm, as shown as graph A in FIG. In the region of 0.2 to 1.0 atomic%, and in the region of 20 to 50 nm in depth from the surface of the crystal grain, it is 0.2 atomic% or more, and further from 100 nm from the surface of the crystal grain. Also shows a change of 0.1 atomic% or less in a deep region.

  On the other hand, in the case of the crystal particle shown as graph B, the concentration of the rare earth element in both the region where the depth from the surface of the crystal particle is 15 nm and the region deeper than 100 nm from the surface of the crystal particle is Although there is not much difference from the case of the crystal particles constituting the dielectric ceramic according to the present embodiment, the rare earth element concentration in the region where the depth from the surface of the crystal particles is 20 to 50 nm is lower than 0.15%. There is a big difference in the concentration change of rare earth elements in this region.

  In the crystal particles constituting the dielectric ceramic according to the present embodiment, since the inner region deeper than 100 nm from the surface is a region containing almost no rare earth element, there are many crystal phases exhibiting ferroelectricity in this region. This makes it possible to increase the dielectric constant. On the other hand, since the region having a depth from the surface of 20 to 50 nm has a high-concentration region of rare earth elements, it is higher than a dielectric ceramic composed of conventional crystal particles as shown in graph B. Insulation can be obtained. In this case, in the region where the depth from the surface is 20 to 50 nm, when the rare earth element concentration is measured at intervals of 10 nm or more, there is no difference of 0.01 atomic% or less, or more than the surface side. The inner side should be higher.

  On the other hand, in the case of a dielectric ceramic composed of crystal particles showing a change in the concentration of rare earth elements as shown in graph B in FIG. 1, although a high dielectric constant can be achieved, it is inferior in insulation. In particular, it is difficult to maintain high insulation at a temperature higher than room temperature.

  Hereinafter, a region where the depth from the surface of the crystal grain is up to 50 nm is referred to as a shell portion, and an inner region deeper than 100 nm from the surface may be referred to as a core portion.

As described above, the dielectric ceramic of this embodiment contains a rare earth element as an additive component. However, the content of the rare earth element (RE) contained in the dielectric ceramic is barium titanate (BaTiO _3). ) Is preferably 0.1 to 1.0 mol in terms of RE ₂ O _{3 with} respect to 100 mol of titanium. When the content of the rare earth element is in the above range, the concentration of the rare earth element in the region where the depth from the surface of the crystal grain is 50 to 90 nm can be 0.1 atomic% or more, and the insulation is more excellent. A dielectric porcelain having crystal grains can be obtained.

  In this case, the rare earth element is at least one selected from the group consisting of yttrium (Y), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), and ytterbium (Yb). In particular, yttrium (Y) is desirable from the viewpoint that a highly insulating dielectric ceramic can be obtained as compared with other elements and the raw material cost is low.

In addition, the dielectric ceramic contains magnesium (Mg) and manganese (Mn) in addition to rare earth elements in order to stabilize the temperature change rate of the dielectric constant and to improve the reduction resistance. It is desirable. In this case, the content of magnesium (Mg) is 0.1 to 1.2 mol in terms of MgO and the content of manganese (Mn) is titanic acid with respect to 100 mol of titanium constituting barium titanate (BaTiO ₃ ). It is desirable that it is 0.03-0.30 mol in terms of MnO with respect to 100 mol of titanium constituting barium (BaTiO ₃ ).

  The dielectric ceramic according to the present embodiment is suitable for a crystal grain having an average grain size of 0.05 to 0.4 μm, particularly 0.10 to 0.35 μm.

  In the dielectric ceramic of the present embodiment, when the molar ratio of Ba and Ti, which are elements constituting barium titanate, is expressed as a Ba / Ti ratio, Ba in the region where the depth from the surface of the crystal grain is up to 50 nm. The / Ti ratio is desirably smaller than the Ba / Ti ratio in a region where the depth from the surface of the crystal grain is deeper than 100 nm. The Ba / Ti ratio in the region (shell part) where the depth from the surface of the crystal grain is 50 nm is made smaller than the Ba / Ti ratio in the region (core part) where the depth from the surface of the crystal grain is deeper than 100 nm. In this case, the insulation of the dielectric ceramic can be further improved. In this case, the Ba / Ti ratio in the region where the depth from the surface of the crystal grain is up to 50 nm is smaller than the Ba / Ti ratio in the region where the depth from the surface of the crystal grain is deeper than 100 nm. The ratio difference is 0.05 or more.

  Here, the density | concentration of the rare earth element contained in a crystal grain is calculated | required using the transmission electron microscope which attached the element analyzer (EDS). In this case, the sample to be analyzed is polished dielectric ceramic, and crystal particles are extracted on the polished ceramic surface. For each crystal particle to be extracted, the area of each particle is obtained by image processing from the contour, the diameter when replaced with a circle having the same area is calculated, and each crystal particle has an average particle diameter determined by a measurement method described later. The crystal particles are in the range of ± 30%, and about 10 crystal particles in this range are extracted. The spot size of the electron beam when performing elemental analysis is set to 1 to 3 nm. Further, as shown in FIG. 1, the analysis is performed at an interval of about 5 to 40 nm from the grain boundary (corresponding to the surface of the crystal grain) to the center part. In this case, the gap is narrowed near the grain boundary (surface) of the crystal grains because the concentration gradient of rare earth elements is large, and the gap is widened near the center because the concentration gradient of rare earth elements is small. Good. Here, the center part of the crystal grain is a range surrounded by a circle having a length of 1/3 of the radius of the inscribed circle from the center of the inscribed circle of the cross section of the crystal grain. The inscribed circle draws an inscribed circle on the computer screen from the image projected by the transmission electron microscope, and determines the center of the crystal grain from the image on the screen.

In addition, an element analyzer (EDS) attached to the transmission electron microscope is also used when determining the Ba / Ti ratio in each region near the surface (shell portion) and inside (core portion) of the crystal particles. In this case, it calculates | requires from the average value of 2-3 analysis values about each area | region of the surface vicinity (shell part) and the inside (core part), respectively.

  The average particle size of the crystal particles is measured by the following procedure. First, the fracture surface of the dielectric ceramic after firing is polished. Thereafter, a photograph of the internal structure is taken of the polished sample using a scanning electron microscope, a circle containing 20 to 50 crystal particles is drawn on the photograph, and crystal particles that fall within and around the circle are selected. . Next, image processing is performed on the outline of each crystal particle to determine the area of each crystal particle, and the diameter when the crystal particle is replaced with a circle having the same area is calculated and obtained from the average value.

    The composition of the dielectric ceramic is determined using ICP (Inductively Coupled Plasma) analysis and atomic absorption analysis of a solution in which the dielectric ceramic is dissolved in an acid. In this case, the amount of oxygen is determined using the valence of each element as the valence shown in the periodic table.

  Next, a method for manufacturing the dielectric ceramic according to the present embodiment will be described.

  First, barium titanate powder and rare earth oxide powder are prepared as raw powders. As the barium titanate powder, for example, it is preferable to use a powder which is dipped in water and selectively dissolves barium (Ba) on the surface of the powder so that Ba is deficient. If barium titanate powder with Ba deficient on the surface is used, rare earth element oxide powder is likely to react with the Ba deficient part, and rare earth elements are likely to be unevenly distributed near the surface of the crystal grains after firing. Become. In this case, it is desirable that the Ba / Ti ratio on the surface of the barium titanate powder is lower than 1, and particularly 0.80 to 0.99. Note that the overall Ba / Ti ratio of the barium titanate powder obtained from ICP analysis or the like is desirably larger than 1 for the reason that the grain growth at the time of firing can be suppressed, and is particularly preferably from 1.005 to 1.210. It is better to use something.

  The transmission electron microscope provided with an element analyzer (EDS) is used also in the case of obtaining the Ba / Ti ratio in each region of the surface and inside of the barium titanate powder as in the case of the crystal particles. In this case, elemental analysis is performed by placing the barium titanate powder on the sample stage as it is.

  Next, barium titanate powder and rare earth element oxide powder are mixed together with an organic vehicle to prepare granules or slurry. In this case, the addition amount of the rare earth element oxide powder is preferably 0.1 to 1.0 mol per 100 mol of the barium titanate powder.

  Thereafter, the granule or slurry is molded into a predetermined shape using a dry press molding method, an injection molding method, a doctor blade method, or the like. Next, the compact is fired at a temperature of 1000 to 1300 ° C. to produce a sintered body.

In order to further stabilize the temperature change rate of the dielectric constant of the dielectric porcelain or to further improve the reduction resistance, a magnesium oxide (MgO) powder or manganese oxide (manganese carbonate is added to the rare earth element oxide). May be used). In this case, the added amount of MgO powder is 0.1 to 1.2 mol per 100 mol of barium titanate (BaTiO ₃ ), and the added amount of MnCO ₃ is MnO per 100 mol of barium titanate (BaTiO ₃ ). It is desirable that it is 0.03 to 0.30 mol in terms of conversion. Further, a sintering aid such as glass powder may be added as long as the dielectric properties are not impaired.

Next, the multilayer ceramic capacitor of this embodiment will be described in detail based on the schematic cross-sectional view of FIG. FIG. 2 is a schematic cross-sectional view showing an example of the multilayer ceramic capacitor of the present invention. In the multilayer ceramic capacitor of this embodiment, external electrodes 3 are formed at both ends of the capacitor body 1. The external electrode 3 is formed, for example, by baking Cu or an alloy paste of Cu and Ni.

  The capacitor body 1 is configured by alternately laminating dielectric layers 5 and internal electrode layers 7. In this case, the dielectric layer 5 constituting the capacitor body 1 is constituted by the dielectric ceramic according to the above-described embodiment. In FIG. 2, the laminated state of the dielectric layer 5 and the internal electrode layer 7 is shown in a simplified manner, but the multilayer ceramic capacitor of this embodiment has several hundreds of dielectric layers 5 and internal electrode layers 7. It is a laminate.

  According to the multilayer ceramic capacitor of this embodiment, by applying the above dielectric ceramic as the dielectric layer 5, high insulation can be ensured even if the dielectric layer 5 is thinned. A multilayer ceramic capacitor having a high dielectric constant and excellent lifetime characteristics in a high temperature load test can be obtained. In this case, the thickness of the dielectric layer 5 is preferably 3 μm or less, and particularly preferably 2 μm or less. This makes it possible to reduce the size and capacity of the multilayer ceramic capacitor. If the thickness of the dielectric layer 5 is 0.5 μm or more, it becomes possible to stabilize the temperature characteristics of the capacitance.

  The internal electrode layer 7 is preferably made of nickel (Ni) in that the manufacturing cost can be suppressed even when the internal electrode layer 7 is made highly laminated, and simultaneous firing with the dielectric layer 5 can be achieved.

  Next, a method for manufacturing the multilayer ceramic capacitor of this embodiment will be described.

  First, a ceramic green sheet is formed by the method described above. Next, a rectangular internal electrode pattern is printed and formed on the main surface of the obtained ceramic green sheet. The conductor paste used as the internal electrode pattern is prepared by mixing Ni or an alloy powder thereof as a main component metal, mixing barium titanate powder as a co-material, and adding an organic binder, a solvent and a dispersant.

  Next, a desired number of ceramic green sheets with internal electrode patterns are stacked, and a plurality of ceramic green sheets without internal electrode patterns are stacked on top and bottom of the ceramic green sheets so that the upper and lower layers have the same number. Form the body. The internal electrode patterns in the temporary laminate are shifted by half patterns in the longitudinal direction. By such a laminating method, the internal electrode pattern can be formed so as to be alternately exposed on the end face of the cut laminate.

  Next, the temporary laminate is pressed under conditions of higher temperature and higher pressure than the temperature and pressure at the time of temporary lamination to form a laminate in which the ceramic green sheet and the internal electrode pattern are firmly adhered.

  Next, the capacitor body molded body in which the end portions of the internal electrode patterns are exposed is formed by cutting the laminate into a lattice shape.

  Next, the capacitor body 1 is formed by firing the capacitor body molded body in a predetermined atmosphere under temperature conditions. In some cases, the ridge line portion of the capacitor body 1 may be chamfered, and barrel polishing may be performed to expose the internal electrode layer 7 exposed from the opposite end surface of the capacitor body 1.

  Next, the obtained capacitor body molded body is degreased and fired. The firing is desirably performed in a hydrogen-nitrogen atmosphere at a maximum temperature of 1000 to 1300 ° C. and a holding time of 0.1 to 4 hours. Then, the capacitor body 1 is obtained by performing reoxidation treatment in the temperature range of 900 to 1100 ° C.

In this way, the concentration of the rare earth element maximizes the surface of the crystal grains, and the depth from the surface of the crystal grains is 0.2 to 1.0 atomic% in the region up to 15 nm from the surface of the crystal grains. Capacitor body 1 having dielectric layer 5 as a dielectric ceramic exhibiting a change of 0.2 atomic% or more in a region of ˜50 nm and 0.1 atomic% or less in a region deeper than 100 nm from the surface of crystal grains. Can be obtained.

  Next, an external electrode paste is applied to the opposing ends of the capacitor body 1 and baked to form the external electrodes 3. In some cases, a plating film is formed on the surface of the external electrode 3 in order to improve mountability. Thus, the multilayer ceramic capacitor of the present invention is obtained.

First, barium titanate powder having a Ba / Ti ratio shown in Table 1 and having an average particle size of 0.3 μm was prepared as a raw material powder. In Table 1, the Ba / Ti ratio indicated in the inner column was equivalent to the Ba / Ti ratio of the entire barium titanate as a result of ICP analysis. The powders of Sample Nos. 3 to 6 having a Ba / Ti ratio on the surface lower than the inside were prepared by immersing them in water to dissolve the surface Ba.

  The Ba / Ti ratio in the surface and internal regions of the barium titanate powder is obtained by performing elemental analysis by placing the barium titanate powder directly on the sample stage using a transmission electron microscope equipped with an element analyzer (EDS). It was. At this time, the surface of the barium titanate powder was positioned at a position of 30 nm from the surface, while the inside was positioned at substantially the center of the powder. In this measurement, five powders of each sample were measured to obtain an average value.

Next, Y ₂ O ₃ powder, MgO powder, MnCO ₃ powder and SiO ₂ —BaO—CaO—Li ₂ O glass powder are added to the barium titanate powder shown in Table 1 to prepare a dielectric powder. did.

The amount of each auxiliary component added was 0.5 mol of Y ₂ O ₃ powder, 0.5 mol of MgO powder, and 0.1 mol of MnCO ₃ powder with respect to 100 mol of barium titanate powder, respectively. . The glass powder was ₂ parts by mass with respect to 100 parts by mass of barium titanate powder containing Y ₂ O ₃ powder, MgO powder and MnCO ₃ powder.

  Next, the obtained mixed powder was put into a mixed solvent of polyvinyl butyral resin and toluene and alcohol, and wet-mixed using a zirconia ball having a diameter of 1 mm to prepare a ceramic slurry. A 5 μm ceramic green sheet was produced.

  Next, a plurality of conductive pastes containing Ni as a main component were formed on the upper surface of the ceramic green sheet so as to form a rectangular internal electrode pattern. The conductor paste for forming the internal electrode pattern was obtained by adding barium titanate powder to 100 parts by mass of Ni powder having an average particle size of 0.3 μm.

Next, 200 ceramic green sheets on which internal electrode patterns were printed were laminated, and 20 ceramic green sheets on which the internal electrode patterns were not printed were laminated on the upper and lower surfaces, respectively, using a press machine at a temperature of 60 ° C. and pressure A laminated body was prepared by closely adhering under conditions of 10 ⁷ Pa and time 10 minutes, and then the laminated body was cut into a predetermined size to form a capacitor body molded body.

Next, the capacitor body molded body was treated to remove the binder in the atmosphere, and then fired at a temperature of 1150 ° C. at a temperature rise rate of 2000 ° C./h in hydrogen-nitrogen to produce a capacitor body. This firing was performed using a roller hearth kiln.

Subsequently, the manufactured capacitor body was re-oxidized at 1000 ° C. for 4 hours in a nitrogen atmosphere. The size of the capacitor body was 2.05 × 1.28 × 1.28 mm ³ , the thickness of the dielectric layer was 1.0 μm, and the effective area of one internal electrode layer was 1.78 mm ² . Here, the effective area is an area of overlapping portions of the internal electrode layers formed alternately in the stacking direction so as to be exposed at different end faces of the capacitor body.

  Next, after barrel-polishing the capacitor body, an external electrode paste containing Cu powder and glass was applied to both ends of the capacitor body and baked at 850 ° C. to form external electrodes. Thereafter, using an electrolytic barrel machine, Ni plating and Sn plating were sequentially performed on the surface of the external electrode to produce a multilayer ceramic capacitor.

  The obtained multilayer ceramic capacitor was evaluated as follows.

  The relative dielectric constant is measured under the measurement conditions of a capacitance of 25 ° C., a frequency of 1.0 kHz, and a measurement voltage of 1 Vrms. From the obtained capacitance, the thickness of the dielectric layer, the effective area of all the internal electrode layers And converted based on the dielectric constant of vacuum. The number of samples was 20, and the average value was obtained.

  The insulation properties of dielectric ceramics were evaluated by the high temperature load life. The high temperature load life was performed under the condition of an applied voltage of 20 V at a temperature of 170 ° C. The number of samples in the high-temperature load test was 30 samples, and the average failure time, which was the time when the failure probability reached 50%, was examined.

  The change in the concentration of rare earth elements (RE) in the crystal grains, the Ba / Ti ratio, and the average grain size of the crystal grains were determined as follows.

  The concentration of the rare earth element contained in the crystal particles was determined using a transmission electron microscope equipped with an element analyzer (EDS). In this case, the sample to be analyzed was polished dielectric ceramic, and crystal particles were extracted on the polished ceramic surface. For each extracted crystal particle, the area of each particle is obtained by image processing from its contour, the diameter when replaced with a circle having the same area is calculated, and each crystal particle has an average particle size determined by a measurement method described later. The crystal grains were in the range of ± 30%, and the crystal grains were in this range. The spot size of the electron beam at the time of elemental analysis was about 2 nm. The analysis was performed at intervals of about 5 to 40 nm from the grain boundaries of the crystal grains (corresponding to the surface of the crystal grains) toward the center. In this case, the gap was narrowed near the grain boundary (surface) of the crystal grains because the rare earth element concentration gradient was large, and the gap was widened near the center because the rare earth element concentration gradient was small. Here, the center part of the crystal particle is a range surrounded by a circle having a length of 1/3 of the radius of the inscribed circle from the center of the inscribed circle of the cross section of the crystal particle, and the inscribed circle of the crystal particle is An inscribed circle was drawn on the computer screen for the image projected by the transmission electron microscope, and the center of the crystal grain was determined from the image on the screen. This operation was performed on three crystal grains, and the average value was obtained.

  Also, an element analyzer (EDS) attached to the transmission electron microscope was used to determine the Ba / Ti (molar) ratio in the vicinity of the surface (shell portion) and inside (core portion) of the crystal particles. In this case, it calculated | required from the analysis value of three places, respectively about each area | region of the surface vicinity (shell part) and the inside (core part).

The average grain size of the crystal grains is determined by first polishing the fracture surface of the dielectric ceramic, taking a picture of the internal structure using a scanning electron microscope, and drawing a circle containing about 30 crystal grains on the photograph. Crystal grains were selected that were in and around the circumference. Next, the outline of each crystal particle was image-processed, the area of each crystal particle was calculated | required, the diameter when it replaced with the circle | round | yen which has the same area was calculated, and it calculated | required from the average value. The average particle size of the measured crystal grains of the sample is the sample No. 1 is 0.30 μm, sample no. 2 is 0.34 μm, sample no. 3-6 was 0.32 micrometer.

    Further, the composition of the dielectric ceramic was determined by using a solution in which the dielectric ceramic was dissolved in an acid, using ICP (Inductively Coupled Plasma) analysis and atomic absorption analysis. In this case, the amount of oxygen was determined using the valence of each element as the valence shown in the periodic table. The composition obtained was consistent with the formulation composition. The results are shown in Table 1.

  As is clear from the results in Table 1, sample No. 3 to 6, the high temperature load life was 13 hours or more while the relative dielectric constant at room temperature (25 ° C.) was 3520 or more. In these samples (Nos. 3 to 6), the concentration of the rare earth element is 0.2 to 1.0 atomic% in the region where the surface of the crystal particle is the maximum and the depth from the surface is up to 15 nm. The depth was 0.2 atomic% or more in a region of 20 to 50 nm and 0.1 atomic% or less in a region deeper than 100 nm from the surface. In addition, these samples have a Ba / Ti ratio in the region where the depth from the surface of the crystal particles is up to 50 nm, which is 0.05 than the Ba / Ti ratio in a region where the depth from the surface of the crystal particles is deeper than 100 nm. It was lower than that. Moreover, in these samples, when the concentration of yttrium was measured at intervals of 20 nm in a region having a depth of 20 to 50 nm from the surface, the concentration difference was 0.01 atomic% or less.

  On the other hand, Sample No. 1 and 2 are samples prepared without immersing barium titanate powder in water. The crystal grains constituting the dielectric ceramic of these samples are rare earth elements in a region having a depth of up to 15 nm from the surface. The concentration of the rare earth element in the region where the concentration is 0.2 to 1.0 atomic%, the depth from the surface is 20 to 50 nm is 0.15 atomic% or less, and the rare earth element in the region deeper than 100 nm from the surface of the crystal grain. The concentration was 0.05 atomic%, and as shown in graph B of FIG. 1, the concentration of rare earth elements gradually decreased from the surface to the inside of the crystal particles. These samples had a relative dielectric constant of 3540 or more at room temperature (25 ° C.), but had a high temperature load life of 8 hours or less.

1 Capacitor body 3 External electrode 5 Dielectric layer 7 Internal electrode layer

Claims (3)

  A dielectric ceramic composed of a plurality of crystal particles containing barium titanate as a main component and containing at least a rare earth element, wherein the rare earth element has a maximum concentration on the surface of the crystal particle, In a region having a depth of up to 15 nm from the surface, 0.2 to 1.0 atomic%, in a region having a depth of 20 to 50 nm from the surface, 0.2 atomic% or more, and in a region deeper than 100 nm from the surface Dielectric porcelain characterized by being 0.1 atomic% or less.   When the molar ratio of the elements Ba and Ti constituting the barium titanate is expressed as a Ba / Ti ratio, the Ba / Ti ratio in the region up to 50 nm in depth from the surface of the crystal particles is The dielectric ceramic according to claim 1, wherein a depth from the surface is smaller than a Ba / Ti ratio in a region deeper than 100 nm.   3. A multilayer ceramic capacitor, wherein dielectric layers comprising the dielectric ceramic according to claim 1 and internal electrode layers are alternately stacked.

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