Dielectric compositions and electronic components

Abstract

To provide a dielectric composition exhibiting a high relative permittivity and an electronic part including dielectric layers composed of the dielectric composition.SOLUTION: A dielectric composition includes main phases having a tungsten bronze structure and grain boundaries existing between the main phases. When at least one rare earth element selected from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy is defined as RE, the concentration ratio of RE in the central portions of the main phases to RE in the peripheral portions of the main phases is 0.2 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a dielectric composition and an electronic component comprising a dielectric layer composed of the dielectric composition. [Background technology]

[0002] Electronic circuits and power supply circuits incorporated into electronic devices often contain numerous electronic components, such as multilayer ceramic capacitors, that utilize the dielectric properties exhibited by dielectric materials. Barium titanate-based dielectric compositions are widely used as the dielectric material for such electronic components.

[0003] Patent Document 1 discloses a dielectric composition having a tungsten bronze structure as an alternative to barium titanate-based dielectric compositions, and there is a demand for a dielectric composition having a tungsten bronze structure with a higher relative permittivity. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 3-274607 [Overview of the project] [Problems that the invention aims to solve]

[0005] This invention has been made in view of the above circumstances and aims to provide a dielectric composition exhibiting a high relative permittivity and an electronic component comprising a dielectric layer composed of the dielectric composition. [Means for solving the problem]

[0006] To achieve the above objective, a dielectric composition according to a first aspect of the present invention comprises a main phase having a tungsten bronze structure and grain boundaries existing between the main phases, When RE is defined as at least one rare earth element selected from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy, The dielectric composition is such that the ratio of the concentration of RE in the central part of the main phase to the concentration of RE in the peripheral part of the main phase is 0.2 or less.

[0007] Furthermore, a dielectric composition according to a second aspect of the present invention includes a main phase having a tungsten bronze structure and grain boundaries existing between the main phases, When RE is defined as at least one rare earth element selected from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy, The dielectric composition is such that the ratio of the concentration of RE in the central part of the main phase to the concentration of RE at the grain boundaries is 0.18 or less.

[0008] According to dielectric compositions of the first and second aspects of the present invention, a high relative permittivity can be achieved.

[0009] Furthermore, dielectric compositions according to the first and second aspects of the present invention can also exhibit high strength.

[0010] The average particle size of the main phase is preferably 1.5 μm or less.

[0011] This allows for a higher dielectric constant and higher intensity.

[0012] The composition of the main phase is given by general formula A a B b D4O 15+ It is represented by α, A comprises at least Ba and RE, B comprises at least Zr, and D comprises at least Nb. The dielectric composition may be one in which a is 3.05 or greater and b is 1.01 or greater.

[0013] As a result, the dielectric composition according to the present invention can exhibit a higher resistivity.

[0014] When the content of D in the dielectric composition is 4 mole parts, the content of RE in the dielectric composition is preferably 0.05 to 0.4 mole parts.

[0015] Thereby, the dielectric composition according to the present invention can exhibit a higher dielectric constant. Further, when it is included in the above range, it can exhibit higher strength compared to the case where it is below the above range.

[0016] The dielectric composition preferably further includes a segregation phase having Ba and Nb.

[0017] Thereby, the dielectric composition according to the present invention can exhibit an even higher dielectric constant.

[0018] The electronic component according to the present invention includes a dielectric layer composed of the above dielectric composition.

Brief Description of the Drawings

[0019] [Figure 1] FIG. 1 is a schematic cross-sectional view of a multilayer ceramic capacitor according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view of a dielectric composition constituting the dielectric layer shown in FIG. 1. [Figure 3] FIG. 3 is an enlarged view of part III of FIG. 2.

Embodiments for Carrying Out the Invention

[0020] Hereinafter, the present invention will be described based on specific embodiments.

[0021] < First Embodiment > Multilayer ceramic capacitor Figure 1 shows a multilayer ceramic capacitor 1 as an example of an electronic component according to this embodiment. The multilayer ceramic capacitor 1 has an element body 10 in which dielectric layers 2 and internal electrode layers 3 are alternately stacked. A pair of external electrodes 4 are formed at both ends of the element body 10, each of which is electrically connected to the internal electrode layers 3 that are alternately arranged inside the element body 10. There are no particular restrictions on the shape of the element body 10, but it is usually rectangular. There are also no particular restrictions on the dimensions of the element body 10, and it can be set to an appropriate size depending on the application.

[0022] The dielectric layer 2 is composed of the dielectric composition according to this embodiment, which will be described later. The thickness of each layer of the dielectric layer 2 (interlayer thickness) is not particularly limited and can be arbitrarily set according to the desired properties and applications. Typically, the interlayer thickness is preferably 100 μm or less, and more preferably 30 μm or less. In addition, the number of layers of dielectric layer 2 is not particularly limited, but in this embodiment, for example, it is preferably 20 or more.

[0023] In this embodiment, the internal electrode layers 3 are stacked such that each end face alternately exposes the surfaces of two opposing ends of the element body 10.

[0024] The main component of the conductive material contained in the internal electrode layer 3 is a metal. The metal is not particularly limited; for example, any known conductive material such as Pd, Pd alloys, Pt, Pt alloys, Ni, Ni alloys, Cu, Cu alloys, etc. may be used. Note that the metal may contain various trace components such as P in amounts of approximately 0.1% by mass or less. Furthermore, the internal electrode layer 3 may be formed using commercially available electrode paste. The thickness of the internal electrode layer 3 should be determined appropriately according to the application.

[0025] The conductive material contained in the external electrode 4 is not particularly limited. For example, known conductive materials such as Ni, Cu, Sn, Ag, Pd, Pt, Au, or alloys thereof, or conductive resins may be used. The thickness of the external electrode 4 may be determined appropriately depending on the application.

[0026] As shown in Figure 2, the dielectric composition according to this embodiment has a main phase 14 and grain boundaries 16 existing between the main phases 14. The grain boundaries 16 contain components diffused from the main phases 14. In this embodiment, the main phase 14 is the main phase 14 after sintering.

[0027] The main phase 14 is composed of a composite oxide having a tungsten bronze structure. In this embodiment, the composite oxide is contained in an amount of 80% by mass or more, and preferably 90% by mass or more, in 100% by mass of the dielectric composition.

[0028] The average particle size of the main phase 14 is preferably 1.5 μm or less, and more preferably within the range of 0.3 to 1.0 μm. In this embodiment, the particle size of the main phase 14 can be measured, for example, as the diameter equivalent to the area of ​​a circle. The diameter equivalent to the area of ​​a circle refers to the diameter of a circle having the same area as the area of ​​the shape in question.

[0029] Furthermore, the particle size D90 of the main phase 14 is preferably 3 μm or less. Here, D90 is the particle size of the particle whose cumulative frequency, counting from the smallest particle size, is 90%.

[0030] The elements other than oxygen contained in the tungsten bronze structure are generally divided into three elemental groups ("A", "B", and "D") based on their valence, and the composite oxide has the general formula A a B b D4O 15+ It is represented by α.

[0031] "A" includes Ba and RE, which will be described later. "B" is a tetravalent element and includes Zr. "D" is a pentavalent element and includes Nb. Furthermore, in the above general formula, "a" indicates the atomic ratio of "A" when the element constituting "D" is present in 4 atoms in the general formula, and "b" indicates the atomic ratio of "B" when the element constituting "D" is present in 4 atoms in the general formula.

[0032] In this embodiment, "a" is 3.05 or greater, and preferably 3.10 or greater. The upper limit of "a" is preferably 3.50 or less, and more preferably 3.30 or less.

[0033] Furthermore, in this embodiment, "b" is 1.01 or greater, and preferably 1.05 or greater. The upper limit of "b" is preferably 1.50 or less, and more preferably 1.30 or less.

[0034] Therefore, the above composite oxide has a stoichiometric composition with the general formula A3B1D4O 15 In the composite oxide represented by [formula], "A" and "B" are present in excess in a predetermined proportion relative to "D".

[0035] In this composite oxide, the amount of oxygen (O) may vary depending on the composition ratio of "A", "B", and "D", oxygen vacancies, etc. Therefore, in this embodiment, the general formula is A3B1D4O 15 The deviation of oxygen from the stoichiometric ratio in the composite oxide represented by is denoted by "α". There are no particular restrictions on the range of "α", for example, it is between -1 and 1.

[0036] In this embodiment, "A" includes at least Ba and RE (described later), but may also include a divalent element A1 other than Ba. Preferably, "A1" includes one or more elements selected from the group consisting of Mg, Ca, and Sr.

[0037] Furthermore, from the viewpoint of obtaining a high relative permittivity, when the total number of atoms constituting "A" is set to 1, the proportion of Mg atoms is preferably 0.20 or less, and more preferably 0.10 or less.

[0038] Furthermore, "B" contains at least Zr, but may also contain tetravalent elements other than Zr, namely B1. Preferably, "B1" contains one or more elements selected from the group consisting of Ti and Hf.

[0039] In this embodiment, from the viewpoint of obtaining a high resistivity, when the total number of atoms constituting "B" is set to 1, the atomic ratio of Ti is preferably 0.25 or less, more preferably 0.125 or less, and even more preferably substantially no Ti is contained. Here, "substantially no Ti is contained" means that Ti may be contained as long as it is in an amount attributable to unavoidable impurities.

[0040] Also, "D" contains at least Nb, and may contain a pentavalent element D1 other than Nb. "D1" preferably contains Ta.

[0041] In addition, when the total number of atoms constituting "A" is set to 1, the atomic ratio of the divalent element A1 other than Mg, Ca, and Sr is preferably 0.10 or less. When the total number of atoms constituting "B" is set to 1, the atomic ratio of the tetravalent element B1 other than Ti and Hf is preferably 0.10 or less. When the total number of atoms constituting "D" is set to 1, the atomic ratio of the pentavalent element D1 other than Ta is preferably 0.10 or less.

[0042] As described above, the dielectric composition according to this embodiment has a main phase 14 and grain boundaries 16 existing between the main phases 14. The main phase 14 contains a predetermined rare earth element represented by "RE", and the grain boundaries 16 also contain RE.

[0043] In this embodiment, RE means a rare earth element having a trivalent valence and a six-coordinate coordination number, and the six-coordinate ionic radius of the trivalent is not less than the six-coordinate ionic radius of Dy. That is, RE is a rare earth element having a relatively large ionic radius, and the six-coordinate ionic radius of the trivalent is close to the six-coordinate ionic radius of Ba (1.35 Å). For this reason, RE easily substitutes for the Ba 2+ site of the tungsten bronze structure that constitutes the main phase 14. RE that satisfies such conditions is La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy. In this embodiment, it is preferable that RE is at least one selected from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy, and more preferably Sm

[0044] The ionic radius of La in a trivalent, six-coordinate state is 1.032 Å. The ionic radius of Ce in a trivalent, six-coordinate state is 1.01 Å. The ionic radius of Pr in a trivalent, six-coordinate state is 0.99 Å. The ionic radius of Nd in a trivalent, six-coordinate state is 0.983 Å. The ionic radius of Sm in a trivalent, six-coordinate state is 0.958 Å. The ionic radius of Eu in a trivalent, six-coordinate state is 0.947 Å. The ionic radius of Gd in a trivalent, six-coordinate state is 0.938 Å. The ionic radius of Tb in a trivalent, six-coordinate state is 0.923 Å. The ionic radius of Dy in a trivalent, six-coordinate state is 0.912 Å.

[0045] In the dielectric composition according to this embodiment, the larger the ionic radius of the contained RE, the smaller the particle size of the main phase 14 tends to be.

[0046] The composition of the main phase 14 is general formula A a B b D4O 15+ In the case represented by α, when the content of D in the dielectric composition is 4 moles, the content of RE in the dielectric composition is preferably 0.05 to 0.4 moles, and more preferably 0.06 to 0.35 moles.

[0047] Figure 3 is an enlarged view of part III of Figure 2. In the dielectric composition according to this embodiment, the concentration of RE in the peripheral portion 14b of the main phase 14 shown in Figure 3 (peripheral RE concentration) is higher than the concentration of RE in the central portion 14a of the main phase 14 (central RE concentration).

[0048] The central part 14a of the main phase 14 is not particularly limited, but is, for example, the position of the centroid G calculated from the particle size of the main phase 14.

[0049] Furthermore, the peripheral portion 14b of the main phase 14 is not particularly limited, but for example, it is located at a distance of thickness T from the boundary between the main phase 14 and the grain boundary 16 (outer circumference of the main phase 14) toward the inside of the main phase 14. Therefore, as shown in Figure 3, the peripheral portion 14b can be said to be any position on the curve shown by the dashed line. Note that T is preferably 100 nm.

[0050] In this embodiment, the ratio of "central RE concentration / peripheral RE concentration" is preferably 0.2 or less, and more preferably 0.04 or less.

[0051] Furthermore, in the dielectric composition according to this embodiment, the concentration of RE at the grain boundaries 16 of the main phase 14 shown in Figure 3 (grain boundary RE concentration) is higher than the concentration of RE in the central part.

[0052] The ratio of "central RE concentration / grain boundary RE concentration" is preferably 0.18 or less, and more preferably 0.03 or less.

[0053] Furthermore, the dielectric composition according to this embodiment may contain other components such as Al, V, alkali metals, and Mn, in addition to the elements constituting the composite oxide described above or Ba, Sr, and Si. The content of other components is preferably 20% by mass or less, and more preferably 10% by mass or less, per 100% by mass of the dielectric composition. In particular, from the viewpoint of improving resistivity, the total content of Fe2O3 is preferably 0.1% by mass or less per 100% by mass of the dielectric composition.

[0054] The method for observing the structure of a dielectric composition is not particularly limited, but for example, a cross-section of the dielectric composition can be observed using backscattered electron images from a scanning electron microscope (SEM) or HAADF images from a scanning transmission electron microscope (STEM). In this case, the main phase 14 is often recognized as a bright area of ​​contrast. This is because the main phase 14 is often denser than the grain boundaries 16 or the Ba-Nb segregation phase described later. Therefore, the grain boundaries 16 or the Ba-Nb segregation phase described later, which are often denser than the main phase 14, are often recognized as dark areas of contrast. The width of the field of view to be photographed, i.e., the "predetermined field of view," is not particularly limited, but for example, it is about 1 to 50 μm square.

[0055] Manufacturing method for multilayer ceramic capacitors Next, an example of a manufacturing method for the multilayer ceramic capacitor 1 shown in Figure 1 will be described below.

[0056] The multilayer ceramic capacitor 1 according to this embodiment can be manufactured in a manner generally similar to that of conventional multilayer ceramic capacitors. A conventional method, for example, involves creating a green chip using a paste containing the raw materials for a dielectric composition, and then firing this chip to manufacture a multilayer ceramic capacitor. The manufacturing method will be described in detail below.

[0057] First, the starting materials for the dielectric composition are prepared. As the starting materials, the composite oxide that constitutes the main phase 14 of the dielectric composition described above can be used. Alternatively, oxides of each metal contained in the composite oxide can be used. Furthermore, various compounds that become components of the composite oxide through calcination can be used. Examples of such compounds include carbonates, oxalates, nitrates, hydroxides, and metal-organic compounds.

[0058] Furthermore, various compounds containing RE, or compounds that become RE oxides upon calcination, are prepared as starting materials for RE. In this embodiment, the starting materials for the main phase 14 and RE are preferably in powder form.

[0059] From the prepared starting materials, the raw materials for the main phase 14 are weighed in a predetermined proportion and then wet-mixed for a predetermined time using a ball mill or the like. After drying the mixed powder, it is heat-treated in the air at a temperature of 700 to 1300°C to obtain calcined powder of the complex oxides that constitute the main phase 14.

[0060] Furthermore, the starting material for RE is finely pulverized to obtain pulverized RE. The calcined powder of the composite oxide constituting the main phase 14 and the pulverized RE are dispersed under high pressure together with a dispersion medium and dried to uniformly disperse the pulverized RE around the composite oxide constituting the main phase 14, thereby obtaining a mixture of the composite oxide constituting the main phase 14 and RE. The dispersion medium is not particularly limited and can be, for example, water.

[0061] In this way, by uniformly dispersing the pulverized RE around the composite oxide constituting the main phase 14, it becomes easier to make the peripheral RE concentration and grain boundary RE concentration sufficiently high relative to the central RE concentration.

[0062] Next, a paste for producing green chips is prepared. The mixture of the composite oxide and RE constituting the obtained main phase 14, a binder, and a solvent are kneaded together to form a paint-like paste for the dielectric layer. Known binders and solvents may be used. The dielectric layer paste may also contain additives such as plasticizers and dispersants as needed.

[0063] The paste for the internal electrode layer is obtained by kneading the conductive material raw materials, a binder, and a solvent as described above. Known binders and solvents may be used. The paste for the internal electrode layer may also contain additives such as co-materials or plasticizers, as needed.

[0064] The paste for the external electrode can be prepared in the same manner as the paste for the internal electrode layer.

[0065] Using the obtained pastes, green sheets and internal electrode patterns are formed, and these are stacked to obtain green chips.

[0066] The obtained green chips are subjected to a binder removal treatment as needed. The binder removal treatment conditions can be known conditions, for example, the holding temperature is preferably set to 200 to 350°C.

[0067] After the binder removal process, the green chips are fired to obtain the element body. In this embodiment, firing can be performed in air. Firing can also be performed under a reducing atmosphere (reduction firing). Other firing conditions can be known conditions; for example, the holding temperature is preferably set to 1200-1450°C.

[0068] After firing, the obtained element body is subjected to a re-oxidation treatment (annealing) as needed. The annealing conditions can be known conditions; for example, it is preferable to set the oxygen partial pressure during annealing to be higher than the oxygen partial pressure during firing, and the holding temperature to 1150°C or lower.

[0069] The dielectric composition constituting the dielectric layer 2 of the element body 10 obtained as described above is the dielectric composition described above. The element body 10 is subjected to end face polishing, and an external electrode paste is applied and baked to form the external electrode 4. Then, if necessary, a coating layer is formed on the surface of the external electrode 4 by plating or the like.

[0070] In this way, the multilayer ceramic capacitor 1 according to this embodiment is manufactured.

[0071] The dielectric composition according to this embodiment can exhibit a high relative permittivity. In the main phase 14 having a tungsten bronze structure, when the average particle size of the main phase 14 is about 1.5 μm or less, the relative permittivity tends to improve as the average particle size of the main phase 14 increases. However, when the average particle size of the main phase 14 is larger than about 1.5 μm, the relative permittivity tends to decrease as the average particle size of the main phase 14 increases.

[0072] Furthermore, there is a correlation between the diffusion coefficient of the atom with the slowest diffusion rate among the atoms constituting a compound and the grain growth rate. Here, if the compound is an oxide, "oxygen" is the atom with the slowest diffusion rate. It has been found that the diffusion coefficient of oxygen tends to decrease with the addition of a donor element, and increases with the addition of an acceptor element.

[0073] Based on these findings, among the donor elements, some of the elements that make up the tungsten bronze structure, particularly Ba, are considered to be the key elements. 2+ The site is easy to replace, i.e., Ba 2+ RE was selected as a donor with a similar ionic radius, and an attempt was made to distribute it in a dielectric composition under predetermined conditions ("central RE concentration / peripheral RE concentration" being 0.2 or less, or "central RE concentration / grain boundary RE concentration" being 0.18 or less), and it was found that the dielectric composition exhibited a high relative permittivity.

[0074] Thus, according to this embodiment, the presence of RE in the dielectric composition in a predetermined distribution makes it possible to reduce the diffusion coefficient of oxygen, and as a result, it is thought that grain growth of the main phase 14 during firing can be suppressed. Furthermore, according to this embodiment, since grain growth of the main phase 14 during firing can be suppressed, the particle size of the main phase 14 can be adjusted to a desired range, and as a result, it is thought that a high relative permittivity can be achieved. In addition, according to this embodiment, high strength can also be achieved.

[0075] As mentioned above, the addition of acceptor elements increases the oxygen diffusion coefficient, which can cause abnormal growth of the main phase 14 and a decrease in the dielectric constant. Therefore, in conventional techniques, the addition of acceptor elements such as Mn or Fe can decrease the dielectric constant.

[0076] < Second Embodiment > This embodiment is the same as the first embodiment, except as described below. In the dielectric composition according to this embodiment, a segregation phase having Ba and Nb at the grain boundaries between the main phases is included. Hereinafter, the segregation phase having Ba and Nb will be referred to as the "Ba-Nb segregation phase".

[0077] The Ba-Nb segregation phase according to this embodiment has a high Ba content relative to Nb. The composition of the Ba-Nb segregation phase is, for example, Ba5Nb4O 15 That is the case.

[0078] In this embodiment, there is no particular limit to the method for determining whether the dielectric composition constituting the dielectric layer has a Ba-Nb segregation phase, but one example is to compare the mapping image of Ba with the mapping image of Nb. The main phase in this embodiment also contains Ba and Nb, but the main phase has a higher Nb content than Ba. Therefore, even if a stronger signal is detected in the Ba mapping image than in the surrounding area, a region where a weaker signal is detected in the Nb mapping image can be determined to be a Ba-Nb segregation phase.

[0079] The method for manufacturing the multilayer ceramic capacitor according to this embodiment is not particularly limited. For example, in the step of preparing the paste for making the green chip in the first embodiment, in addition to the mixture of the composite oxide constituting the main phase and RE, the binder and solvent, an "oxide containing Ba and Nb" is added and kneaded to form a paint to prepare a paste for the dielectric layer, and the method is the same as the method for manufacturing the multilayer ceramic capacitor described in the first embodiment except for this step, thereby obtaining the multilayer ceramic capacitor according to this embodiment.

[0080] In the above-described embodiment, the case in which the electronic component according to the present invention is a multilayer ceramic capacitor was explained, but the electronic component according to the present invention is not limited to a multilayer ceramic capacitor, and any electronic component having the dielectric composition described above may be used.

[0081] Although embodiments of the present invention have been described above, the present invention is not limited in any way to the embodiments described above, and may be modified in various ways within the scope of the present invention.

[0082] For example, in the first embodiment, only the calcined powder of the composite oxide constituting the main phase 14 was obtained, but some of the RE oxides may also be calcined together with the raw materials of the main phase 14. That is, some of the RE oxides may be wet-mixed together with the raw materials of the main phase 14 for a predetermined time using a ball mill or the like, the mixed powder may be dried, and then heat-treated in the air at a temperature of 700 to 1300°C to obtain calcined powder of the composite oxide constituting the main phase 14 and some of the RE oxides.

[0083] However, as described above, by uniformly dispersing the pulverized RE around the composite oxide constituting the main phase 14, it becomes easier to make the peripheral RE concentration and grain boundary RE concentration sufficiently high relative to the central RE concentration. Therefore, it is preferable that the RE oxides that are calcined together with the composite oxide constituting the main phase 14 are only a portion of the RE oxides. Specifically, 0 to 50% by mass of the RE oxides may be calcined together with the composite oxide constituting the main phase 14.

[0084] Furthermore, in the first embodiment, a mixture of the composite oxide constituting the main phase 14 and RE was obtained by dispersing the calcined powder of the composite oxide constituting the main phase 14 and pulverized RE in a dispersion medium under high pressure, uniformly dispersing the pulverized RE around the composite oxide constituting the main phase 14, and then drying it. However, a mixture of the composite oxide constituting the main phase 14 and RE can also be obtained by mixing the calcined powder of the composite oxide constituting the main phase 14 with a dispersion medium in which the RE compound is dissolved and then drying it, thereby uniformly dispersing RE around the composite oxide constituting the main phase 14. The "RE compound" dissolved in the dispersion medium can be, for example, a metal-organic compound of RE.

[0085] Furthermore, when preparing the paste for producing the green chips, the dielectric layer paste may be prepared by kneading a mixture of calcined powder of the composite oxide constituting the main phase 14 (which has not been high-pressure dispersed) and pulverized RE, along with a binder and a solvent, to form a paint-like mixture, which is then high-pressure dispersed. This method also allows for the uniform dispersion of RE around the composite oxide constituting the main phase 14.

[0086] Furthermore, when preparing the paste for producing the green chips, the dielectric layer paste may be prepared by kneading a mixture of calcined powder of the composite oxide constituting the main phase 14, which has been dispersed under high pressure, and pulverized RE, along with a binder and a solvent, to form a paint-like mixture, which is then dispersed under high pressure. This method also allows for the uniform dispersion of RE around the composite oxide constituting the main phase 14. [Examples]

[0087] The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to the following examples.

[0088] Experiment 1 Powders of barium carbonate (BaCO3), zirconium oxide (ZrO2), and niobium oxide (Nb2O5) were prepared as starting materials for the main phase 14 of the dielectric composition. The prepared starting materials were weighed so that the molar ratio of BaCO3, ZrO2, and Nb2O5 was BaCO3:ZrO2:Nb2O5 = 3.1:1.1:2.

[0089] Next, each weighed powder was wet-mixed for 16 hours using deionized water as a dispersion medium in a ball mill, and the mixture was dried to obtain a mixed raw material powder. Subsequently, the obtained mixed raw material powder was heat-treated in air at a holding temperature of 900°C for a holding time of 2 hours to obtain calcined powder of the composite oxide constituting the main phase 14.

[0090] Furthermore, the RE oxides listed in Table 1 were weighed out in amounts corresponding to 4 moles of Nb in the composite oxide constituting the main phase 14. The amounts of RE added in Table 1 are those added when the Nb content in the composite oxide constituting the main phase 14 is 4 moles.

[0091] The oxide of RE was finely ground using a bead mill to obtain a finely ground product of RE oxide.

[0092] The calcined powder of the obtained composite oxide and the finely ground oxide of RE were wet-ground for 16 hours using a ball mill with deionized water as the dispersion medium, then dispersed under high pressure using a high-pressure homogenizer, and dried to obtain a dried powder.

[0093] To 100% by mass of the dried pulverized material, 10% by mass of an aqueous solution containing 6% by mass of polyvinyl alcohol resin as a binder was added, and granulation was performed to obtain granulated powder.

[0094] The resulting granulated powder is placed into a φ12mm mold at a rate of 0.6 ton / cm³. 2 Pre-press forming is performed with a pressure of 1.2 tons / cm², and then further, 1.2 tons / cm² is applied. 2 A disc-shaped green molded body was obtained by press molding under this pressure.

[0095] The obtained green molded body was fired in air to obtain a sintered body. The firing conditions were a heating rate of 200°C / h, a holding temperature of 1375°C, and a holding time of 2 hours.

[0096] A disc-shaped ceramic capacitor sample was obtained by coating both main surfaces of the resulting sintered body with an In-Ga alloy to form a pair of electrodes.

[0097] (Average particle size of the main phase) The obtained sintered body was thinned using a focused ion beam (FIB) system to prepare samples. The thinned samples were observed using a STEM to identify the main phase 14. The observation field was 2 μm × 2 μm. The main phase 14 was similarly identified in two other observation fields, for a total of three observation fields. The average value of the particle size (equivalent diameter of circular area) of the main phase 14 in the above three observation fields was defined as the "average particle size of the main phase." The results are shown in Table 1. Note that the average particle size was calculated using the main phase 14 where the entire outer circumference of the main phase 14 was included in the observation field. That is, for the main phase 14 that had even a part extending beyond the observation field, the area was not calculated and was not included in the area used to calculate the average particle size of the main phase.

[0098] (Center RE concentration / Peripheral RE concentration, Center RE concentration / Grain boundary RE concentration) In the three observation fields described above, the central RE concentration was measured at three points in each observation field, for a total of nine points, and the average value was calculated from these measurements.

[0099] In the three observation fields described above, peripheral RE concentrations were measured at three points per observation field, for a total of nine points, and the average value was calculated.

[0100] In the three observation fields described above, the grain boundary RE concentration was measured at three points in each observation field, for a total of nine points, and the average value was calculated.

[0101] The ratios "central RE concentration / peripheral RE concentration" and "central RE concentration / grain boundary RE concentration" were calculated from the average values ​​of the obtained central RE concentration, peripheral RE concentration, and grain boundary RE concentration.

[0102] (Presence or absence of Ba-Nb segregation phase) The presence or absence of the Ba-Nb segregation phase was determined in the three observation fields described above.

[0103] (Relative permittivity) Capacitance and tanδ were measured on the sample at room temperature (20°C) using a digital LCR meter (YHP 4284A) with a frequency of 1 kHz and an input signal level (measurement voltage) of 1 Vrms. The relative permittivity (unitless) was then calculated based on the dielectric layer thickness, the effective electrode area, and the measured capacitance. A higher relative permittivity is preferable. The results are shown in Table 1.

[0104] (Probability of breakage during polishing) First, a metal plate heated on a hot plate was prepared. Paraffin wax was applied to the metal plate, and a sintered body fired in air was placed on top of it. The sintered body was fixed to the metal plate by cooling to room temperature. With the sintered body fixed, the metal plate was moved, and the natural surface on the opposite side of the sintered body from the side in contact with the metal plate was polished and removed using #800 waterproof sandpaper. After that, the metal plate with the fixed sintered body was immersed in acetone to remove the paraffin wax. The number of cracks in the polished sintered bodies was observed and counted using a stereomicroscope. The probability of failure during polishing was calculated by dividing the number of cracked sintered bodies by the number of polished sintered bodies. A lower probability of failure during polishing indicates higher strength.

[0105] Experiment 2 Experiment 2 concerns sample number 21. In Experiment 2, a ceramic capacitor sample was obtained in the same manner as in Sample No. 6, except that the entire amount of RE was calcined together with the starting material of the main phase 14.

[0106] For the obtained sintered body or ceramic capacitor samples, the "average particle size of the main phase," "center RE concentration / peripheral RE concentration," "center RE concentration / grain boundary RE concentration," "relative permittivity," and "probability of breakage during polishing" were measured using the same method as described above, and the "presence or absence of Ba-Nb segregated phases" was determined. The results are shown in Table 2.

[0107] Experiment 3 Experiment 3 concerns sample number 22. In Experiment 3, half of the RE was calcined together with the starting material for the main phase 14, and the other half of the RE was processed as a fine pulverized material in the same manner as in Experiment 1. This pulverized material was then mixed with the calcined composite oxide powder, dispersed under high pressure, and dried to obtain a dried pulverized material. A ceramic capacitor sample was obtained in the same manner as sample number 6.

[0108] For the obtained sintered body or ceramic capacitor samples, the "average particle size of the main phase," "center RE concentration / peripheral RE concentration," "center RE concentration / grain boundary RE concentration," "relative permittivity," and "probability of breakage during polishing" were measured using the same method as described above, and the "presence or absence of Ba-Nb segregated phases" was determined. The results are shown in Table 2.

[0109] Experiment 4 Experiment 4 concerns samples number 31-34. In Experiment 4, a ceramic capacitor sample was obtained in the same manner as sample number 6, except that the amount of additive added was changed.

[0110] For the obtained sintered body or ceramic capacitor samples, the "average particle size of the main phase," "center RE concentration / peripheral RE concentration," "center RE concentration / grain boundary RE concentration," "relative permittivity," and "probability of breakage during polishing" were measured using the same method as described above, and the "presence or absence of Ba-Nb segregation phase" was determined. The results are shown in Table 3.

[0111] Experiment 5 Experiment 5 concerns sample number 41. In Experiment 5, Ba5Nb4O was used for 100% by mass of the dried pulverized material. 15A ceramic capacitor sample was obtained in the same manner as sample number 6, except that granulation was performed by adding 10% by mass of an aqueous solution containing 2% by mass of the powder and 6% by mass of polyvinyl alcohol resin as a binder, and granulating the solution to obtain granulated powder.

[0112] For the obtained sintered body or ceramic capacitor samples, the following parameters were measured using the same method as described above: "average particle size of the main phase," "center RE concentration / peripheral RE concentration," "center RE concentration / grain boundary RE concentration," "relative permittivity," "probability of breakage during polishing," and "resistivity." The presence or absence of a Ba-Nb segregated phase was then determined. The results are shown in Table 4.

[0113] [Table 1]

[0114] [Table 2]

[0115] [Table 3]

[0116] [Table 4]

[0117] Table 1 shows that when the rare earth element is RE (at least one selected from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy) and the "center RE concentration / peripheral RE concentration" is 0.2 or less (sample numbers 2-10), the dielectric constant is higher and the probability of breakage during polishing is lower compared to when the rare earth element is Ho, Er, Tm, or Yb and the "center RE concentration / peripheral RE concentration" is 0.2 or less (sample numbers 11-14). The D90 particle size of the main phase 14 in samples 2-10 was 3 μm or less.

[0118] Table 1 shows that when the rare earth element is RE (at least one selected from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy) and the "center RE concentration / grain boundary RE concentration" is 0.18 or less (sample numbers 2-10), the dielectric constant is higher and the probability of breakage during polishing is lower compared to when the rare earth element is Ho, Er, Tm, or Yb and the "center RE concentration / peripheral RE concentration" is 0.2 or less (sample numbers 11-14).

[0119] Table 2 shows that when the ratio of "center RE concentration / peripheral RE concentration" is 0.2 or less (samples 22 and 6), the dielectric constant is higher and the probability of breakage during polishing is lower compared to when the ratio is 0.870 (sample 21).

[0120] Table 2 shows that when the "center RE concentration / grain boundary RE concentration" is 0.18 or less (samples 22 and 6), the dielectric constant is higher and the probability of breakage during polishing is lower compared to when the "center RE concentration / peripheral RE concentration" is 0.641 (sample 21).

[0121] Table 3 shows that when the D(Nb) content in the dielectric composition is 4 moles, the relative permittivity is higher when the RE content in the dielectric composition is 0.05 to 0.4 moles (samples 32, 6, and 33) compared to when the RE content in the dielectric composition is 0.03 moles (sample 31) or 0.5 moles (sample 34).

[0122] Table 3 shows that when the D(Nb) content in the dielectric composition is 4 moles, the probability of breakage during polishing is lower when the RE content in the dielectric composition is 0.05 to 0.4 moles (samples 32, 6, and 33) compared to when the RE content in the dielectric composition is 0.03 moles (sample 31).

[0123] Table 4 shows that the dielectric constant was higher in the case of the sample containing a Ba-Nb segregation phase (sample number 41) compared to the case of the sample not containing a Ba-Nb segregation phase (sample number 6).

[0124] For sample number 41, the obtained dielectric composition was pulverized and subjected to powder X-ray irradiation. When measured at different times, Ba5Nb4O 15 Since it was detected, the composition of the Ba-Nb segregation phase is Ba5Nb4O 15 It is thought that this is the case. [Explanation of symbols]

[0125] 1… Multilayer ceramic capacitor 10… Element body 2… Dielectric layer 14… Main phase 14a… Center 14b… Peripheral area 16… Grain boundary 3… Internal electrode layer 4… External electrode

Claims

1. It comprises a main phase having a tungsten bronze structure and grain boundaries existing between the main phases, The composition of the main phase is represented by the general formula A a B b D 4 O 15+α, A comprises at least Ba and RE, B comprises at least Zr, and D comprises at least Nb. If a is 3.05 or higher, and b is 1.01 or higher, When RE is defined as at least one rare earth element selected from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy, A dielectric composition in which the ratio of the concentration of RE in the central part of the main phase to the concentration of RE in the peripheral part of the main phase is 0.2 or less.

2. It comprises a main phase having a tungsten bronze structure and grain boundaries existing between the main phases, The composition of the main phase is represented by the general formula A a B b D 4 O 15+α, A comprises at least Ba and RE, B comprises at least Zr, and D comprises at least Nb. If a is 3.05 or higher, and b is 1.01 or higher, When RE is defined as at least one rare earth element selected from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy, A dielectric composition in which the ratio of the concentration of RE in the central part of the main phase to the concentration of RE in the grain boundaries is 0.18 or less.

3. The dielectric composition according to claim 1, wherein the average particle size of the main phase is 1.5 μm or less.

4. The dielectric composition according to claim 2, wherein the average particle size of the main phase is 1.5 μm or less.

5. When the content of D in the dielectric composition is 4 moles, The dielectric composition according to claim 1, wherein the content of RE in the dielectric composition is 0.05 to 0.4 molar parts.

6. When the content of D in the dielectric composition is 4 moles, The dielectric composition according to claim 2, wherein the content of RE in the dielectric composition is 0.05 to 0.4 molar parts.

7. The dielectric composition according to claim 1, further comprising a segregation phase having Ba and Nb.

8. The dielectric composition according to claim 2, further comprising a segregation phase having Ba and Nb.

9. An electronic component comprising the dielectric composition according to any one of claims 1 to 8.

Images