Dielectric ceramic composition and ceramic capacitor

Abstract

The purpose of the present invention is to provide a novel dielectric ceramic composition which has a high dielectric constant and low dielectric loss, in which the dielectric constant is increased by DC voltage, and in which the maximum increase rate thereof is large. A dielectric ceramic composition according to the present invention comprises an oxide (I) of B, R, and A, wherein: the oxide (I) has a tetragonal tungsten bronze structure; A includes K and Ba; R is at least one element selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, and Sc; B is at least one element selected from the group consisting of Nb and Ta; the amount of B is 4.75-5.25 moles with respect to 2 moles of A; and the combined molar fraction of A, R, and B in all metallic elements included in the dielectric ceramic composition is not less than 0.975.

Description

[Technical field]

[0001] The present invention relates to a dielectric ceramic composition and a ceramic capacitor. [Background technology]

[0002] Conventionally, barium titanate (BaTiO) has been used as the material for the dielectric part of ceramic capacitors. 3 ) and other ferroelectric ceramics are commonly used.

[0003] In recent years, various characteristics are required as the applications of ceramic capacitors expand. In order to meet such requirements, dielectric ceramic compositions having various compositions have been proposed as materials for the dielectric parts of ceramic capacitors. For example, a new dielectric ceramic composition has been proposed that has a tetragonal tungsten bronze structure that is very similar in crystal structure to the perovskite type but has a different polarization structure (see Patent Documents 1-2, etc.).

[0004] Patent Document 1 describes a compound of the general formula {A 1-x (RE) 2x / 3} y -D 2 O 5+y and a compound having a tungsten bronze structure and an oxide of M, A is at least one selected from the group consisting of Ba, Ca, Sr and Mg, D is at least one selected from the group consisting of Nb and Ta, and RE is at least one selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu; The x and y are 0 <x<1、y> Satisfying the 0 relationship, The dielectric ceramic composition is characterized in that the M is at least one selected from the group consisting of Al, Si, B and Li.

[0005] Patent Document 2 describes a compound of the general formula A 3 (B1)(B2) 4 O15 A dielectric ceramic composition containing a main component having a tetragonal tungsten bronze structure represented by the formula (I) and a subcomponent, A is at least one selected from Ba, Sr, Ca and rare earth elements; B1 and B2 contain Zr and Nb; The auxiliary component is at least one selected from Mn, Cu, V, Fe, Co, and Si, When the sum of B1 and B2 is 100 mol%, the total content of Mn, Cu, V, Fe and Co is 0.5 mol% or more and less than 4 mol%, the Si content is less than 7 mol%, the Ba content is 9.8 mol% or more and 61.8 mol% or less, the Ca content is less than 51.5 mol%, the Sr content is less than 41.2 mol%, and the rare earth element content is less than 30.9 mol%, The ratio of A to B1 and B2 is 0.588 to 0.618, When the whole is taken as 100 mol%, the Zr content is greater than 8 mol% and less than 50 mol%, and the Nb content is 50 mol% or more and 80 mol% or less. A dielectric ceramic composition is described.

[0006] Patent Document 3 describes a dielectric ceramic composition containing oxides of A, R and B and an oxide of Mn, in which A is at least one selected from the group consisting of K and Na, R is at least one selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, and Sc; The B is at least one selected from the group consisting of Nb and Ta; the molar ratio of A:R:N:Mn is 2-x:1+x / 3:5+y:z; wherein x, y, and z satisfy −0.3≦x, 0.6, −0.5≦y≦0.5, and 0.001≦z≦0.5; Dielectric porcelain composition. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2013-180908 A [Patent Document 2] JP 2018-104209 A [Patent Document 3] International Publication No. 2020 / 240986 [Non-patent literature]

[0008] [Non-Patent Document 1] RR Neurgaonkar, et al., "FEROELECTRIC AND STRUCTURAL PROPERTIES OF THE TUNGUSTEN BRONZE SYSTEM K2Ln3+Nb5O15, Ln = La to Lu", Materials Research Bulletin, 1990, Vol. 25, pp. 959-970 Summary of the Invention [Problem to be solved by the invention]

[0009] Barium titanate having a perovskite structure has a drawback that the dielectric constant decreases when a DC voltage is applied due to ferroelectricity (negative bias characteristic). In contrast, the dielectric ceramic compositions having a tetragonal tungsten bronze structure described in Patent Documents 1 and 2 can reduce the decrease in the dielectric constant under a DC voltage by suppressing the ferroelectricity. However, the dielectric ceramic compositions described in Patent Documents 1 and 2 cannot improve the dielectric constant under a DC voltage. In addition, the dielectric ceramic composition having a tetragonal tungsten bronze structure described in Patent Document 3 can improve the dielectric constant under a DC voltage, but in view of the expansion of applications of ceramic capacitors and the improvement of their electrical properties, there is a need to further improve the dielectric constant under a DC voltage.

[0010] In addition, although not related to ceramic capacitors, another material with a tetragonal tungsten bronze type structure is K 2 Ln 3+ Nb 5 O 15 (Ln=La to Lu) has been reported (Non-Patent Document 1). Non-Patent Document 1 discloses that a substance having such a composition exhibits a low relative dielectric constant and a low resistivity. Since the substance described in Non-Patent Document 1 has a low resistivity, it is considered difficult to use it as a dielectric under a DC voltage, and furthermore, it is not suitable for use as a material for the dielectric portion of a ceramic capacitor.

[0011] An object of the present invention is to provide a novel dielectric ceramic composition having a high dielectric constant, a small dielectric loss, an increase in dielectric constant under a DC voltage, and a large maximum increase rate of the dielectric constant. A further object of the present invention is to provide a ceramic capacitor comprising such a dielectric ceramic composition. [Means for solving the problem]

[0012] The present invention includes the following inventions. [1] A dielectric ceramic composition comprising oxides of A, R and B (I), The oxide (I) has a tetragonal tungsten bronze structure, The A includes K and Ba. R is at least one selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, and Sc; The B is at least one selected from the group consisting of Nb and Ta, The amount of the substance B is 4.75 moles or more and 5.25 moles or less relative to 2 moles of the substance A, A dielectric ceramic composition, wherein the total molar fraction of A, R and B in all metal elements contained in the dielectric ceramic composition is 0.975 or more. [2] Further comprising an oxide of X (II), The dielectric ceramic composition according to [1], wherein the X is at least one selected from the group consisting of Mn, Cu, Fe, Co, Ni, V and Si. [3] The dielectric ceramic composition according to [2], wherein the amount of the substance X is 0.18 mol or less per 2 mol of the substance A. [4] The dielectric ceramic composition according to any one of [1] to [3], wherein the molar fraction of K in A is 0.1 or more and 0.95 or less. [5] The dielectric ceramic composition according to any one of [1] to [4], wherein the amount of R is 0.4 mol or more and 0.967 mol or less per 2 mol of A. [6] The dielectric ceramic composition according to any one of [1] to [5], wherein the total molar fraction of K and Ba in A is 0.8 or more. [7] The dielectric ceramic composition according to any one of [1] to [6], wherein the molar fraction of Nb in said B is 0.8 or more. [8] The dielectric ceramic composition according to any one of [1] to [7], wherein the molar fraction of K in A is 0.2 or more. [9] The dielectric ceramic composition according to any one of [1] to [8], wherein the amount of R is 0.466 mol or more per 2 mol of A.

[10] The dielectric ceramic composition according to any one of [1] to [9], wherein the total molar fraction of La and Pr in R is 0.333 or more.

[11] The dielectric ceramic composition according to any one of [1] to

[10] , wherein the total molar fraction of K and Ba in A is 1.

[12] The dielectric ceramic composition according to any one of [1] to

[11] , wherein the molar fraction of Nb in said B is 1.

[13] A ceramic capacitor comprising two electrodes and a dielectric portion located between the two electrodes, the dielectric portion being formed from the dielectric ceramic composition according to any one of [1] to

[12] . Effect of the Invention

[0013] According to the present invention, there is provided a novel dielectric ceramic composition having a high dielectric constant, a small dielectric loss, an increase in the dielectric constant under a DC voltage, and a large maximum increase rate thereof. Furthermore, according to the present invention, there is provided a ceramic capacitor comprising such a dielectric ceramic composition. [Brief description of the drawings]

[0014] [Figure 1] 1 shows a schematic cross-sectional view of a ceramic capacitor according to one embodiment of the present invention. [Diagram 2] 1A shows a graph of relative dielectric constant ε' versus electric field strength E for samples Nos. 1 to 3. FIG. 1B shows a graph of dielectric loss tan δ versus electric field strength E for samples Nos. 1 to 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, the embodiments of the present invention will be described in detail, however, the present invention is not limited to these embodiments and various modifications are possible.

[0016] (Dielectric ceramic composition) The dielectric ceramic composition of this embodiment (which may also be simply referred to as a “(ferro)dielectric ceramic”) contains oxides of A, R and B (I). The oxide (I) has a tetragonal tungsten bronze structure, The A includes K and Ba. R is at least one selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, and Sc; The B is at least one selected from the group consisting of Nb and Ta, The amount of the substance B is 4.75 moles or more and 5.25 moles or less relative to 2 moles of the substance A, The total molar fraction of A, R and B in all the metal elements contained in the dielectric ceramic composition is 0.975 or more.

[0017] Thus, in the dielectric ceramic composition containing oxides (I) of A, R and B, by limiting A, R and B, and further limiting the relationship between the amounts of substance of A and B and the ratio of oxide (I) in the dielectric ceramic composition so as to satisfy the above conditions, the inventors have clarified through their research that the dielectric constant is high, the dielectric loss is small, the dielectric constant increases under DC voltage, and further the maximum increase rate is large.

[0018] Here, the "tetragonal tungsten bronze type structure" described in this specification refers to a compound represented by the general formula A 6 B 10 O 30 (Therefore, A 3 B 5 O 15 It is characterized by having a tetragonal crystal structure in a certain temperature range, but is not limited to tetragonal in other temperature ranges, and may have other crystal structures including orthorhombic, orthorhombic, and monoclinic with displacement of each atomic position. In addition, it is possible to introduce various site defects, including A-site and B-site, interstitial sites, and site-substitution solid solutions into the tetragonal tungsten bronze type structure, and structures into which these have been introduced are all referred to as tetragonal tungsten bronze type. In particular, tungsten bronze having the basic general formula A 6 B 10 O 30 With respect to this A site 6, those with no deficiency in the A site are called filled type, those with only 1 deficiency in the A site are called unfilled type, and those with only 1.33 deficiency in the A site are called empty type, and these are also included in the tetragonal tungsten bronze type structure.

[0019] The dielectric porcelain composition contains the oxides (I) of A, R, and B. The amounts of substances of A, R, and B, as well as the total amount of substance of the metal elements contained in the dielectric porcelain composition, can be confirmed and determined by any appropriate elemental analysis. Based on the confirmed and determined amounts of substances of A, R, B, and other metal elements, the amount of substance of B relative to 2 moles of A, and the mole fractions of A, R, and B in all the metal elements contained in the dielectric porcelain composition can be confirmed and determined. That the oxide (I) has a tetragonal tungsten bronze structure can be confirmed by X-ray diffraction (XRD) analysis or the like.

[0020] In this specification, metal elements usually include, in addition to elements classified as metals, metalloid elements such as B, Si, Ge, As, Sb, Te, etc.

[0021] The oxides of A, R, and B (or the tetragonal tungsten bronze structure) are typically represented by the general formula K 2-2x Ba 2x (A1) y R σ(1-2x / 3) B 5+z O 15+δ (wherein R and B are as described above, A1 is an element other than K and Ba among the elements corresponding to A, and x, y, and z can satisfy 0 < x < 1, 0 ≤ y ≤ 0.5, -0.25 ≤ z ≤ 0.25.) It can be expressed as follows. Although not limiting the present embodiment, in this case, B can be located at the B site of the tetragonal tungsten bronze type structure, K, Ba and A1 can be located at the A site of the tetragonal tungsten bronze type structure, and R can be located at the A site of the tetragonal tungsten bronze type structure (A is replaced by R, and R is in a solid solution state). The molar ratio in the dielectric ceramic composition can be determined based on the amount of A (the sum of K, Ba and A1, which corresponds to "2+y"). Here, the amount (molar) of oxygen O, "15+δ", is difficult to identify by analysis, and δ can take any value depending on the oxidation state or defect state of the substance, but the value of δ does not affect the effect of the present invention. Although not limiting the present invention, for example, δ can satisfy -5≦δ≦7.5. Also, σ can take any value depending on the type of A1 and the ratio of K, Ba and A1. Although not intended to limit the present invention, σ may satisfy 0.8≦σ≦1.2, and may further satisfy 0.9≦σ≦1.1.

[0022] A contains K and Ba. This makes it possible to reduce the dielectric loss while maintaining the relative dielectric constant, and also to increase the relative dielectric constant under direct current and to increase the maximum increase rate. Although the present invention is not bound by any theory, it is believed that by containing both K and Ba, which have similar ionic radii and different valences, the polarization structure of the tetragonal tungsten bronze structure is modulated (the polarization network is modulated) while the ferroelectricity is appropriately suppressed, thereby obtaining a great effect.

[0023] The mole fraction (or atomic proportion) of K in A may be, for example, 0.1 or more, even 0.2 or more, and may be, for example, 0.95 or less.

[0024] The molar fraction (or atomic proportion) of Ba in A may be, for example, 0.05 or more, and may be, for example, 0.9 or less, or even 0.8 or less.

[0025] The total mole fraction (or total atomic proportion) of K and Ba in A may be, for example, 0.8 or more, further 0.9 or more, particularly 0.94 or more, and may be 1 or less.

[0026] A may further contain an alkali metal element such as Na, or an alkaline earth metal element such as Sr.

[0027] The molar fraction (or atomic ratio) of A in all metal elements contained in the oxide (I) may be, for example, 0.2 or more, further 0.23 or more, particularly 0.25 or more, and may be, for example, 0.3 or less, further 0.28 or less.

[0028] R is a rare earth element, and is at least one selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, and Sc. Preferably, R contains La and Pr. This increases the relative dielectric constant under a DC voltage, and further increases the maximum increase rate. Although the present invention is not bound by any theory, it is believed that by combining La and Pr, which have large ionic radii, the polarization structure is appropriately adjusted (the polarization network is modulated), and a greater effect is obtained.

[0029] In this case, the total molar fraction (or total atomic ratio) of La and Pr in R can be appropriately selected, and can be, for example, 0.25 or more, or even 0.333 or more, and can be, for example, 1 or less.

[0030] R may consist of only La and Pr, or may contain at least one other element in addition to La and Pr.

[0031] The amount of R per 2 moles of A may be, for example, 0.4 moles or more, or even 0.466 moles or more, and may be, for example, 0.967 moles or less.

[0032] B is at least one selected from the group consisting of Nb and Ta, and preferably contains Nb.

[0033] The mole fraction (or atomic ratio) of Nb in B may be, for example, 0.8 or more, or even more than 0.9, and may be 1 or less.

[0034] The amount of substance B is 4.75 moles or more and 5.25 moles or less relative to 2 moles of A. This makes it possible to reduce the dielectric loss while maintaining the relative dielectric constant, and also to increase the relative dielectric constant under direct current and to increase the maximum increase rate. Although the present invention is not bound by any theory, it is believed that by having the ratio of A to B in a certain range, heterogeneous phase segregation is suppressed to maintain the tetragonal tungsten bronze type structure, and the polarization structure of the tetragonal tungsten bronze type structure is modulated (the polarization network is modulated), resulting in a significant effect.

[0035] The total molar fraction (or total atomic ratio) of A, R and B in all metal elements contained in the ceramic composition is 0.975 or more, for example, 0.980 or more, and may be 0.985 or more, and may be 1 or less, and may be 0.997 or less. It is considered that the high molar fractions of A, R and B contained in the ceramic composition and the presence of oxide (I) as a main component make it easier to appropriately adjust the polarization structure (makes it easier to modulate the polarization network), and a great effect can be obtained.

[0036] The dielectric ceramic composition may further contain an oxide (II) of X. The form of existence of the oxide (II) of X in the dielectric ceramic composition is not particularly limited, and at least a part of the oxide may exist as the oxide (II) of X, or the oxide (II) of X may be solid-dissolved in the oxide (I) of X. That is, at least a part of the elements (constituent elements) contained in the oxide (II) of X may replace at least a part of the elements (constituent elements) contained in the oxide (I), or the elements (constituent elements) contained in the oxide (II) of X may penetrate between the elements (constituent elements) contained in the oxide (I).

[0037] X is preferably at least one selected from the group consisting of Mn, Cu, Fe, Co, Ni, V and Si, and more preferably at least one selected from the group consisting of Mn, Si, Fe and Cu.

[0038] The amount of X may be, for example, 0.18 mol or less, further 0.15 mol or less, particularly 0.1 mol or less, and may be, for example, 0 mol or more, further 0.025 mol or more, relative to 2 mol of A.

[0039] The total mole fraction (or total atomic ratio) of A, R, B and X in all metal elements contained in the dielectric ceramic composition may be, for example, 0.8 or more, further 0.9 or more, particularly 0.95 or more, and may be 1 or less.

[0040] The dielectric ceramic composition of this embodiment contains oxides (I) of A, R, and B, and may further contain oxide (II) of X, and may typically consist essentially of oxide (I) or oxides (I) and (II). However, the dielectric ceramic composition of this embodiment may contain other trace substances, such as trace elements that may be unavoidably mixed in. In addition, as long as the dielectric composition of this embodiment contains oxides of A, R, and B as essential components, it may contain any other appropriate third component (in a relatively small amount relative to the essential components) depending on the desired application of the dielectric magnetic composition, etc.

[0041] The dielectric ceramic composition of the present embodiment can be produced by any appropriate method, but for example, it can be produced as follows.

[0042] First, a main component composition consisting of oxides of A, R, and B may be obtained, and an oxide of X may be introduced therein as a subcomponent to obtain the dielectric ceramic composition of this embodiment. Such a main component composition may be prepared by any suitable method, which may be a solid-phase method, a wet method, or a gas-phase method. The solid-phase method is a method in which at least one selected from the group consisting of oxides, hydroxides, carbonates, and other compounds of each element is used as the element source of A, R, and B, a mixture of powders of such element sources is calcined, and oxides of A, R, and B are obtained by a solid-phase reaction, and the main component composition may be in the form of a calcined raw material powder. Examples of the wet method include a coprecipitation method, a hydrothermal method, and an oxalic acid method. Examples of the gas-phase method include a method using high-frequency plasma.

[0043] The main component composition may have a tetragonal tungsten bronze type structure consisting of oxides of A, R and B, but this is not essential to this embodiment as long as a tetragonal tungsten bronze type structure consisting of oxides of A, R and B is obtained in the finally obtained dielectric ceramic composition.

[0044] The introduction of the oxide of X into the main component composition can be carried out by any suitable method. For example, at least one selected from the group consisting of oxides, hydroxides, carbonates and other compounds of X may be used as the element source of X, and the powder of the element source of X may be added to the main component composition, and the X mixed raw material composition obtained thereby may be subjected to heat treatment to obtain a dielectric ceramic composition into which the oxide of X has been introduced. The element sources of A, R, B and X used may be weighed according to the molar ratio desired for the finally obtained dielectric ceramic composition. The amount of X (auxiliary component) contained in the dielectric ceramic composition is small compared to the amounts of A, R and B (main components), and therefore is considered to have no substantial effect on the tetragonal tungsten bronze type structure consisting of the oxides of A, R and B.

[0045] The dielectric ceramic composition of this embodiment has a high relative dielectric constant. Although this embodiment is not limited thereto, at room temperature (10 to 30°C, typically 25°C) and in a state where no DC voltage is applied, the relative dielectric constant ε(-) may be, for example, 280 or more, further 330 or more, particularly 380 or more, and may be, for example, 1,200 or less, further 800 or less, particularly 700 or less. The dielectric loss may be, for example, less than 1%, further 0.8% or less, particularly 0.7% or less. Such a dielectric ceramic composition of this embodiment may be suitably used as a material for the dielectric portion of a ceramic capacitor.

[0046] Furthermore, the dielectric constant of the dielectric ceramic composition of this embodiment increases under DC voltage (positive bias characteristics), and the maximum rate of increase is large. To explain the behavior of the dielectric constant under DC voltage in more detail, when the DC voltage value is increased from 0 V, the dielectric constant initially increases, reaches a peak (maximum value) at a certain voltage value, and then decreases at voltage values ​​above that value. The electric field strength at which the dielectric constant changes from increasing to decreasing (electric field strength at the voltage value showing the peak) is called the peak electric field strength E DC and the peak electric field strength E DC The relative dielectric constant at the peak relative dielectric constant ε DC (-), the dielectric ceramic composition of the present embodiment has a peak dielectric constant ε DC Increase rate Δε up to (-) DC is large.

[0047] The relative dielectric constant ε(-) when no voltage is applied to the peak relative dielectric constant ε DC Increase rate Δε up to (-) DC (%) is given by the following formula: Δε DC (%)(=(ε DC -ε) / ε×100) The positive bias peak value Δε DC (%) may be, for example, greater than 23%, even greater than 25%, and especially greater than 30%. DCcan be, for example, 4 MV / m or more, or even 5 MV / m or more, and can be, for example, 20 MV / m or less, or even 15 MV / m or less.

[0048] The dielectric ceramic composition of the present embodiment can be suitably used as a material for the dielectric portion of a ceramic capacitor intended for applications in which a high DC voltage is applied, and can effectively reduce, for example, power loss during charging and discharging of the ceramic capacitor.

[0049] (Ceramic capacitor) The ceramic capacitor of the present embodiment includes two electrodes and a dielectric portion located between the two electrodes, and the dielectric portion is formed from the above-mentioned dielectric ceramic composition.

[0050] In a ceramic capacitor, there are at least two electrodes, and two or more electrodes are provided with the dielectric portion located between them. The electrodes may include an internal electrode present inside the dielectric portion and an external electrode present outside the dielectric portion and connected (at least electrically) to a specific internal electrode. The material of the electrodes is not particularly limited, and any suitable conductive material may be used.

[0051] Typically, the ceramic capacitor of this embodiment may be, for example, a multilayer ceramic capacitor 10 shown in Fig. 1. The multilayer ceramic capacitor 10 includes a dielectric portion 1 formed from a dielectric ceramic composition, internal electrodes 3 and 5 embedded in the dielectric portion 1 and arranged alternately, and external electrodes 7 and 9 connected to the internal electrodes 3 and 5, respectively. In the illustrated example, three each of the internal electrodes 3 and 5 are shown typically, but the number of internal electrodes can be appropriately selected depending on the specifications of the capacitor, etc.

[0052] The ceramic capacitor of the present embodiment can be manufactured by any suitable method. For example, the ceramic capacitor of the present embodiment may be manufactured by using the X mixed raw material composition described above in relation to the manufacturing method of the dielectric ceramic composition as a ceramic raw material in a known manufacturing method of a ceramic capacitor, but is not limited thereto.

[0053] The ceramic capacitor of this embodiment can achieve the same effects as the dielectric ceramic composition of this embodiment described above, and has a high relative dielectric constant, which is improved under a DC voltage. EXAMPLES

[0054] (Sample No. 1-37) The following procedure was used to obtain a dielectric ceramic composition containing oxides of A, R, and B, and optionally an oxide of X (a dielectric ceramic composition having a tetragonal tungsten bronze structure consisting of oxides of A, R, and B, and optionally further containing an oxide of X), in which the molar ratios of A, R, B, and X are variously different as shown in sample numbers 1 to 37 in Tables 1 to 2. More specifically, a ceramic capacitor was produced that includes two electrodes and a dielectric portion located between the two electrodes, and the dielectric portion is formed from a dielectric ceramic composition having variously different molar ratios of A, R, B, and X as described above. Among sample numbers 1 to 37 in Tables 1 to 2, those that correspond to comparative examples of the present invention are indicated with a symbol "*", and the rest correspond to examples of the present invention.

[0055] First, as the source of the elements A, R and B, K 2 CO 3 , Na 2 CO 3 , BaCO 3 , SrCO 3 , La(OH) 3 ,Pr 6 O 11 , Nd(OH) 3 , Sm 2 O 3 , Gd 2 O 3 , Dy 2 O 3, Nb 2 O 5 , Ta 2 O 5 These element sources were weighed out so as to correspond to the molar ratios of the elements A, R, and B shown in Tables 1 and 2. These element sources were wet-mixed in a ball mill together with PSZ (partially stabilized zirconia) balls with a nominal diameter of 2 mm, pure water, a dispersant, and an antifoaming agent. The resulting slurry was dried and sized, and then calcined at 1,000 to 1,200°C in air to synthesize a calcined raw powder having a tetragonal tungsten bronze structure composed of oxides of A, R, and B as the main component composition.

[0056] The calcined raw material powder was mixed with MnCO as an element source of X. 3 , SiO 2 , Fe 2 O 3 , CuO, and the element sources were weighed and added so as to correspond to the molar ratio of X to each of the elements A, R, and B shown in Tables 1 and 2, to obtain an X mixed raw material composition.

[0057] To this X mixed raw material composition, polyvinyl butyral binder, plasticizer, ethanol and toluene were added, and the mixture was wet mixed with PSZ balls in a ball mill to prepare a ceramic slurry for sheet molding. This ceramic slurry for sheet molding was formed into a sheet shape by a doctor blade method so that the sheet thickness was 20 μm, and a rectangular ceramic green sheet was obtained. Furthermore, a conductive paste containing Pt powder as a conductive component was screen printed on this ceramic green sheet in a predetermined pattern to form a precursor layer of an internal electrode.

[0058] A laminate was obtained by stacking a predetermined number of ceramic green sheets printed with a conductive paste (internal electrode precursor layer) containing Pt powder as a conductive component, so that the sides where the conductive paste reaches the sheet end (pulled out to the outside) were alternated. A conductive paste containing Pt powder as a conductive component was applied to both end faces of the laminate where the conductive paste (internal electrode precursor layer) was exposed, forming a precursor of an external electrode, and the laminate was degreased by heating at 500°C in air. After this degreasing, the laminate was held in air at 1,300 to 1,450°C for 120 minutes to densify the ceramic containing the oxides of the elements shown in Tables 1 and 2, and to form internal and external electrodes from the conductive paste.

[0059] As a result, a multilayer ceramic capacitor 10 was produced, including a dielectric portion 1 formed from a dielectric ceramic composition, internal electrodes 3 and 5 embedded in the dielectric portion 1 and arranged alternately, and external electrodes 7 and 9 connected to the internal electrodes 3 and 5, respectively, as shown typically in Fig. 1. The external dimensions of the resulting multilayer ceramic capacitor were width 2.7 mm, length 3.6 mm, and thickness 0.56 mm, the total number of internal electrodes was two, the thickness of the dielectric layer interposed between adjacent internal electrodes was 48 μm, the thickness of each internal electrode was 1 μm, and the opposing electrode area of ​​adjacent internal electrodes was 3.2 mm 2 It was.

[0060] [Table 1]

[0061] [Table 2]

[0062] The multilayer ceramic capacitors of sample numbers 1 to 37 thus fabricated were dissolved and subjected to ICP analysis, and the molar ratios, except for Pt, which is the main component of the internal and external electrodes, were as shown in Tables 1 to 2. Furthermore, when XRD analysis (structural analysis) was performed on the multilayer ceramic capacitors of sample numbers 1 to 37, it was found that all of the samples except for sample number 32 only had diffraction peaks identified as the tetragonal tungsten bronze structure and its modulated structure, and thus it was found that the samples had a tetragonal tungsten bronze structure without any heterophase. In sample number 32, in addition to the diffraction peaks derived from the tetragonal tungsten bronze structure, slight diffraction peaks derived from another crystal phase (heterophase) that could not be identified as the tetragonal tungsten bronze structure were observed, and it was found that heterophase segregation was present.

[0063] The capacitance and dielectric loss tan δ of the multilayer ceramic capacitors of sample numbers 1 to 37 were measured using an LCR meter at room temperature under conditions of a measurement frequency of 1 kHz and a measurement voltage of 1 Vrms, without applying a DC voltage. The relative dielectric constant ε(-) was calculated from the capacitance. Those with a dielectric loss tan δ of less than 10% were judged to have good insulation and were rated as G, and those with a dielectric loss tan δ of 10% or more were rated as poor insulation and NG.

[0064] Generally, the dielectric loss is a value indicating the dielectric properties of a material, but when leakage current occurs due to insufficient insulation of the sample, the value of the dielectric loss tan δ increases in accordance with the current value of the leakage current. Since the value of the dielectric loss tan δ derived from the dielectric properties of the dielectric magnetic composition of this embodiment is generally less than 10%, when the value of the dielectric loss tan δ is 10% or more, this is considered to be due to leakage current, and it is judged as poor insulation. In the case of poor insulation, it was not possible to measure the capacitance under DC voltage as described below.

[0065] Combining an LCR meter with an external power supply, a DC voltage was applied at room temperature with a measurement frequency of 1 kHz and a measurement voltage of 1 Vrms while varying the voltage value from 0 V to 770 V, and the capacitance at each voltage was measured and the dielectric constant was calculated. For some samples, the dielectric constant decreased monotonically under DC voltage (negative bias characteristics), while for some samples, the dielectric constant increased as the voltage was increased (positive bias characteristics). All samples that showed positive bias characteristics had a peak (maximum value) in dielectric constant at a certain voltage value, and at voltage values ​​above that, the dielectric constant began to decrease.

[0066] For example, as shown in Fig. 2(a), when the change in the dielectric constant ε' is plotted against the electric field strength E (MV / m) for the samples 1 to 3, where the dielectric constant ε' is calculated under the above conditions, it is found that the dielectric constant ε' increases, then decreases, and has a peak (maximum value) in all cases. The same is true for the dielectric loss tan δ, which increases, then decreases, and has a peak (maximum value) as shown in Fig. 2(b).

[0067] Therefore, in a sample that exhibits positive bias characteristics, the electric field strength at which the relative dielectric constant changes from increasing to decreasing is called the peak electric field strength E DC Furthermore, the peak electric field strength E DC The relative dielectric constant at the peak relative dielectric constant ε DC The rate of increase from the relative dielectric constant ε(-) to the peak relative dielectric constant when no voltage is applied (peak value of positive bias) Δε DC was calculated based on the following formula: Δε DC (%)(=(ε DC -ε) / ε(-)×100)

[0068] Those with a calculated positive bias peak value of 25% or more were rated as G, and those with a calculated positive bias peak value of 30% or more were judged to be more suitable for practical use and rated as G+. The results are shown in Table 3. Among sample numbers 1 to 37 in Table 3, those that correspond to comparative examples of the present invention are marked with a symbol "*", and the rest correspond to examples of the present invention.

[0069] [Table 3]

[0070] Referring to Table 3, among sample numbers 1 to 37, those corresponding to the examples of the present invention (those not marked with the symbol "*") were all judged to be "G" or "G+", had a high relative dielectric constant ε and a small dielectric loss tan δ, and had a positive bias peak value Δε DC was high (i.e., the dielectric constant increased under DC voltage, and the maximum increase rate was large). From this, it can be said that good insulating properties and positive bias characteristics are compatible. Also, as shown in sample numbers 1 to 6, 8 to 17, 30, 31, and 33 to 36, when A is made of K and Ba, the total molar fraction of La and Pr in R is 0.333 or more, B is made of Nb, the molar fraction of K in A is 0.2 or more, and the amount of substance of R per 2 moles of A is 0.466 or more, a larger rate of change in dielectric constant Δε was obtained under DC voltage. DC Without being bound by any theory, this is believed to be due to the moderate suppression of ferroelectricity and the appropriate modulation of the polarization network in this crystal system.

[0071] In contrast, among sample numbers 1 to 37, those corresponding to the comparative examples of the present invention (those marked with the symbol "*") were all given an overall judgment of "NG." When A did not contain K, as in sample numbers 20 to 22, ferroelectricity was strongly exhibited, so that the relative dielectric constant monotonically decreased under DC voltage and no positive bias characteristics were exhibited. When A did not contain Ba, as in sample numbers 23 to 25, the polarization structure was not sufficiently modulated, and although positive bias characteristics were exhibited, the positive bias peak value Δε DCHowever, it was not fully satisfactory. As shown in sample number 29, when the amount of substance B was less than 4.75 moles relative to 2 moles of A, the ferroelectricity was strongly exhibited, so that the relative dielectric constant monotonically decreased under DC voltage and no positive bias characteristics were shown. As shown in sample number 32, when the amount of substance B exceeded 5.5 moles relative to 2 moles of A, heterophase segregation (segregation of a crystal phase not having a tetragonal tungsten type structure) occurred, and the insulation property deteriorated. As shown in sample number 37, when the total molar fraction of A, R, and B in all metal elements contained in the dielectric ceramic composition was less than 0.975, slight impurity segregation occurred, and the insulation property deteriorated. [Industrial Applicability]

[0072] The dielectric ceramic composition of the present invention can be suitably used as a material for the dielectric portion of a ceramic capacitor, but is not limited thereto. The ceramic capacitor of the present invention can be used in a wide variety of applications in which a DC voltage is applied, but is not limited thereto. [Explanation of symbols]

[0073] 1 Dielectric part (dielectric layer) 3, 5 Internal electrode 7, 9 External electrode 10 Ceramic capacitors (multilayer ceramic capacitors)

Claims

1. A dielectric ceramic composition comprising oxides (I) of A, R and B, The oxide (I) has a tetragonal tungsten bronze structure, The A includes K and Ba, and may further include at least one selected from the group consisting of Na and Sr, R is at least one selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, and Sc; The B is at least one selected from the group consisting of Nb and Ta, The amount of the substance B is 4.75 moles or more and 5.25 moles or less relative to 2 moles of the substance A, A dielectric ceramic composition, wherein the total molar fraction of A, R and B in all metal elements contained in said dielectric ceramic composition is 0.975 or more.

2. Further comprising an oxide of X (II), 2. The dielectric ceramic composition according to claim 1, wherein said X is at least one selected from the group consisting of Mn, Cu, Fe, Co, Ni, V and Si.

3. 3. The dielectric ceramic composition according to claim 2, wherein the amount of said X is 0.18 moles or less per 2 moles of said A.

4. 2. The dielectric ceramic composition according to claim 1, wherein a mole fraction of K in A is 0.1 or more and 0.95 or less.

5. 2. The dielectric ceramic composition according to claim 1, wherein the amount of said R is 0.4 moles or more and 0.967 moles or less per 2 moles of said A.

6. 2. The dielectric ceramic composition according to claim 1, wherein a total molar fraction of K and Ba in said A is 0.8 or more.

7. 2. The dielectric ceramic composition according to claim 1, wherein a mole fraction of Nb in said B is 0.8 or more.

8. 2. The dielectric ceramic composition according to claim 1, wherein a mole fraction of K in said A is 0.2 or more.

9. 2. The dielectric ceramic composition according to claim 1, wherein the amount of said R is 0.466 moles or more per 2 moles of said A.

10. 2. The dielectric ceramic composition according to claim 1, wherein a total molar fraction of La and Pr in said R is 0.333 or more.

11. 2. The dielectric ceramic composition according to claim 1, wherein the total mole fraction of K and Ba in A is 1.

12. 2. The dielectric ceramic composition according to claim 1, wherein a mole fraction of Nb in said B is 1.

13. A ceramic capacitor comprising two electrodes and a dielectric portion located between the two electrodes, the dielectric portion being formed from the dielectric ceramic composition according to any one of claims 1 to 12.

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