Dielectric composition, dielectric element, and laminated electronic component

Abstract

The dielectric composition according to the present invention has a crystal phase containing a Sr2NaNb5O15-based oxide having a tungsten bronze-type structure, and has a crystal structure in which the Sr2NaNb5O15-based oxide has a peak top of a synchrotron radiation XRD pattern measured at a measurement wavelength of 0.85 in a range of a diffraction angle 2 [theta] of 10.7-11.0 DEG, and has a peak top of the synchrotron radiation XRD pattern in a range of a diffraction angle 2 [theta] of 10.7-11.0 DEG. The ratio of the intensity of the peak having the peak top to the intensity of the maximum peak having the maximum intensity of the Sr2NaNb5O15-based oxide in the synchrotron radiation XRD pattern is 0.0043 or more.

Description

Technical Field

[0001] The present invention relates to a dielectric composition, a dielectric element, and a laminated electronic component. Background Art

[0002] Dielectric capacitors (e.g., multilayer ceramic capacitors) are capacitors with a dielectric layer formed from a dielectric composition and are used as key components in various electronic devices such as household appliances and automotive control equipment. Among such dielectric capacitors, for example, those used in the powertrain of electric vehicles are subjected to high voltages (e.g., 400V to 800V) as the voltage of the battery increases. Therefore, they are required to have a high withstand voltage (not to break down under the applied high voltage) and to maintain a high relative dielectric constant under high electric fields. Furthermore, such dielectric capacitors are required not only to have a high withstand voltage and a high relative dielectric constant under high electric fields, but also to have a large electrostatic capacitance (i.e., a large capacity).

[0003] Furthermore, as disclosed in Patent Document 1, in order to obtain a large electrostatic capacitance in an environment where a high voltage is applied, a small change (amount of reduction) in the relative dielectric constant when a DC voltage is applied is required.

[0004] Conventionally, dielectric compositions containing BaTiO3, which has a high dielectric constant, have been used for dielectric capacitors. However, the relative dielectric constant of dielectric compositions containing BaTiO3 significantly decreases under high electric fields. Therefore, for example, the use of dielectric compositions with tungsten bronze structures, such as those described in Patent Document 1, for dielectric capacitors has been proposed.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: International Publication No. 2017 / 163845 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] Although the change (decrease) in the relative permittivity of conventional tungsten bronze-type dielectric compositions is small, the relative permittivity under high electric fields is not sufficiently high, which is a problem.

[0010] An object of the present invention is to provide a dielectric composition and the like having a small decrease in relative dielectric constant before and after application of a high DC voltage and a high relative dielectric constant under a high electric field.

[0011] Methods used to solve problems

[0012] The method for solving the above problem is as follows.

[0013] <1> A dielectric composition comprising Sr2NaNb5O having a tungsten bronze structure 15 The crystal phase of the oxide has the following crystal structure: 15 The oxide has a peak top of the synchrotron radiation XRD pattern in the range of a diffraction angle 2θ of 10.7° to 11.0° in the synchrotron radiation XRD pattern measured at a measurement wavelength of 0.85Å, and the Sr2NaNb5O 15 The ratio of the intensity of the peak having the peak top of the oxide to the intensity of the maximum peak having the maximum intensity is 0.0043 or more.

[0014] <2> According to the above <1> The dielectric composition, wherein the above-mentioned Sr2NaNb5O 15 The oxides contain Ca, Y, and Zr.

[0015] <3> A dielectric element comprising the above <1> or <2> A dielectric ceramic formed from the dielectric composition and an electrode mounted on the dielectric ceramic.

[0016] <4> A laminated electronic component having the <1> or <2> A laminated body formed by alternately laminating dielectric layers composed of the dielectric composition and internal electrode layers.

[0017] Effects of the Invention

[0018] According to the present invention, it is possible to provide a dielectric composition or the like which has a small decrease in relative dielectric constant before and after application of a high DC voltage and a high relative dielectric constant under a high electric field. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A perspective view of a dielectric component.

[0020] Figure 2 A cross-sectional view of stacked electronic components.

[0021] Figure 3 It is a graph showing the synchrotron radiation XRD patterns of the measurement samples of Examples 1 to 4 and Comparative Examples 1 to 4 in the range of the diffraction angle 2θ of 10° to 20°.

[0022] Figure 4 It is a graph showing the synchrotron radiation XRD patterns of the measurement samples of Examples 1 to 4 and Comparative Examples 1 to 4, in which the diffraction angle 2θ is in the range of 9° to 12°. DETAILED DESCRIPTION

[0023] Hereinafter, the dielectric composition, dielectric element, and laminated electronic component according to the embodiments will be described.

[0024] The dielectric composition comprises Sr2NaNb5O having a tungsten bronze structure. 15 In this specification, "Sr2NaNb5O with tungsten bronze structure" 15 "Oxide" refers to Sr2NaNb5O in tungsten bronze structure 15 The oxide has a trace amount of a specific element introduced into the A site and the B site. The specific element is not particularly limited as long as it does not impair the purpose of the present invention, and examples thereof include Ca, Y, and Zr.

[0025] The dielectric composition may contain the above-mentioned Sr2NaNb5O as long as the purpose of the present invention is not impaired. 15 The main phase may include the crystal phase of the oxide of the above-mentioned Sr2NaNb5O 15 The crystalline phase of the oxide is used as a secondary phase. It should be noted that the main crystalline phase refers to the crystalline phase corresponding to the peak pattern that occupies the largest proportion in the synchrotron radiation XRD pattern described later. Furthermore, the secondary crystalline phase refers to the crystalline phase corresponding to the peak pattern other than the main phase in the synchrotron radiation XRD pattern described above. The method for measuring the synchrotron radiation XRD pattern will be described later.

[0026] The above Sr2NaNb5O 15 The oxide has a peak top of the synchrotron XRD pattern described above within a diffraction angle 2θ range of 10.7° to 11.0° in a synchrotron XRD pattern measured at a measurement wavelength of 0.85Å. The diffraction peak corresponding to the peak top consists of a peak having a maximum value within the range of 10.7≤2θ(°)≤11.0 and a half-value width greater than 0.02°. It should be noted that the diffraction peak within the range of 10.7≤2θ(°)≤11.0 at a measurement wavelength of 0.85Å corresponds to a lattice spacing of 4.43Å to 4.56Å.

[0027] Generally, it is known that Sr2NaNb5O has a tetragonal tungsten bronze structure. 15 It has a structure in which NbO6 octahedrons are connected in a straight line along the c-axis direction. In contrast, the dielectric composition of this embodiment is presumed to have a crystal structure in which the octahedron structure is tilted relative to the c-axis direction.

[0028] It is speculated that the Sr2NaNb5O 15 The introduction of trace amounts of specific elements (such as Ca, Y, and Zr) into the A and B sites causes the octahedral structure to tilt, and as described later, a diffraction peak (peak top) is confirmed within the range of a diffraction angle 2θ of 10.7° to 11.0°.

[0029] In addition, the dielectric composition has the above-mentioned Sr2NaNb5O15 The ratio of the intensity of the peak having the peak top to the intensity of the maximum peak having the maximum intensity (peak intensity ratio) of the oxide is 0.0043 or greater. The maximum peak is selected from the diffraction peaks derived from the tungsten bronze type structure in the synchrotron XRD pattern.

[0030] It should be noted that the dielectric composition of the present embodiment may include a crystal phase of a perovskite crystal structure or other crystal phases as long as the purpose of the present invention is not impaired.

[0031] Furthermore, the dielectric composition of this embodiment may contain inevitable impurities at a ratio of 1000 ppm or less.

[0032] Examples of raw materials used in the production of the dielectric composition include Sr-containing compounds containing strontium, Na-containing compounds containing sodium, Nb-containing compounds containing niobium, Ca-containing compounds containing calcium, Y-containing compounds containing yttrium, and Zr-containing compounds containing zirconium.

[0033] Examples of the Sr-containing compound include various inorganic powders such as Sr oxides, Sr composite oxides, Sr hydroxides, Sr carbonates, Sr chlorides, Sr sulfates, Sr nitrates, and Sr phosphates. Specifically, strontium carbonate powder is mentioned.

[0034] Examples of Na-containing compounds include various inorganic powders such as Na oxides, Na composite oxides, Na hydroxides, Na carbonates, Na chlorides, Na sulfates, Na nitrates, and Na phosphates. Specifically, sodium carbonate powder can be used. Specifically, sodium carbonate powder can be used.

[0035] Examples of the Nb-containing compound include various inorganic powders such as Nb oxides, Nb composite oxides, Nb hydroxides, Nb carbonates, Nb chlorides, Nb sulfates, Nb nitrates, and Nb phosphates. Specifically, niobium oxide powder is mentioned.

[0036] Examples of the Ca-containing compound include various inorganic powders such as Ca oxides, Ca composite oxides, Ca hydroxides, Ca carbonates, Ca chlorides, Ca sulfates, Ca nitrates, and Ca phosphates. Specifically, calcium carbonate powder is mentioned.

[0037] Examples of the Y-containing compound include various inorganic powders such as Y oxides, Y composite oxides, Y hydroxides, Y carbonates, Y chlorides, Y sulfates, Y nitrates, and Y phosphates. Specifically, yttrium oxide powder is included.

[0038] Examples of the Zr-containing compound include various inorganic powders such as Zr oxides, Zr composite oxides, Zr hydroxides, Zr carbonates, Zr chlorides, Zr sulfates, Zr nitrates, and Zr phosphates. Specifically, zirconium oxide powder is included.

[0039] The method for producing the dielectric composition of the present embodiment will be appropriately described in the description of each method for producing the dielectric element and the laminated electronic component to be described later.

[0040] The dielectric composition of this embodiment has a relative dielectric constant of 1000 or greater under a high electric field (8 kV / mm), and the rate of decrease (rate of change) in the relative dielectric constant before and after application of a high DC voltage is -35% or greater, minimizing the decrease in the relative dielectric constant.

[0041] Note that, for the dielectric composition of this embodiment, the relative dielectric constant in a state where no electric field is applied (0 kV / mm) is not particularly limited unless the purpose of the present invention is impaired, but is preferably 1300 or greater.

[0042] Next, refer to Figure 1 A dielectric element 200 including a dielectric ceramic 100 composed of a dielectric composition will be described. Figure 1 is a perspective view of the dielectric element 200. Figure 1 As shown, dielectric element 200 has a disc-shaped appearance and includes a disc-shaped dielectric ceramic (dielectric layer) 100 and electrodes 301 and 302 mounted on the upper and lower surfaces of dielectric ceramic 100. Dielectric ceramic 100 is formed from the dielectric composition described above. Electrodes 301 and 302 are made of, for example, Au.

[0043] Here, an example of a method for manufacturing the dielectric element 200 is described. First, powders of strontium carbonate, sodium carbonate, niobium oxide, calcium carbonate, yttrium oxide, and zirconium oxide are prepared as raw material powders, and these powders are weighed to obtain a target composition.

[0044] Ethanol was added to the weighed raw material powders and wet-mixed using a ball mill for at least 15 hours to obtain a slurry. The resulting slurry was then dried to obtain a mixed powder. The resulting mixed powder was pre-calcined at 1100°C to 1300°C in an atmosphere for 5 to 7 hours to obtain a calcined powder.

[0045] A dispersant, a binder, and ethanol were added to the calcined powder, and the mixture was pulverized and mixed to obtain a slurry. The slurry was dried and granulated, and the resulting granules were uniaxially pressed at a pressure of 20 MPa to obtain a disc-shaped preform. The disc-shaped preform was then subjected to a CIP (cold isostatic pressing) treatment at a pressure of 150 MPa to obtain a compact.

[0046] The resulting compact was held at 650°C for 4 hours to remove the binder. The debindered compact was then sintered in air at 1300-1350°C for 4 hours to obtain a dielectric ceramic (dielectric layer) composed of the dielectric composition. Both main surfaces (upper and lower surfaces) of the resulting dielectric ceramic were polished, and then external electrodes made of Au were formed on both main surfaces by sputtering, thereby obtaining dielectric element 200.

[0047] Next, refer to Figure 2 The laminated electronic component 1 including the dielectric layer 11 composed of the dielectric composition will be described. Figure 2 is a cross-sectional view of a laminated electronic component 1. The laminated electronic component 1 is a so-called laminated ceramic capacitor, such as Figure 2 As shown, the laminated electronic component 1 includes: a laminate 10 having a plurality of dielectric layers 11 formed from a dielectric composition; first internal electrode layers (an example of an internal electrode layer) 12 and second internal electrode layers (an example of an internal electrode layer) 13 alternately stacked with the dielectric layers 11 interposed therebetween; and first external electrodes 14 and second external electrodes 15 formed on the outer surfaces of the laminate 10 and electrically connected to the first and second internal electrode layers 12, 13. The first internal electrode layers 12 and 14 are connected on one side of the laminated electronic component 1, and the second internal electrode layers 13 and the second external electrode 15 are connected on the opposite side.

[0048] Examples of materials constituting the first internal electrode layer 12 and the second internal electrode layer 13 include Cu, Ag, and Ni. Examples of materials constituting the first external electrode 14 and the second external electrode 15 include Au.

[0049] Here, an example of a method for producing the laminated electronic component 1 is described. First, powders of strontium carbonate, sodium carbonate, niobium oxide, calcium carbonate, yttrium oxide, and zirconium oxide are prepared as raw material powders, and these powders are weighed to obtain a target composition.

[0050] Ethanol was added to the weighed raw material powders and wet-mixed using a ball mill for at least 15 hours to obtain a slurry. The resulting slurry was then dried to obtain a mixed powder. The resulting mixed powder was pre-calcined at 1100°C to 1300°C in an atmosphere for 5 to 7 hours to obtain a calcined powder.

[0051] A dispersant, a binder, and ethanol are added to the calcined powder, pulverized, and mixed to obtain a slurry, which is then processed into sheets using a doctor blade method to produce a plurality of ceramic green sheets.

[0052] Next, a conductive paste for internal electrodes is applied to one side of the ceramic green sheet, for example, by screen printing, to form internal electrode layers (first internal electrode layer and second internal electrode layer). The electrode layers are primarily composed of a base metal, such as nickel (Ni).

[0053] Next, multiple ceramic green sheets with electrode layers are stacked so that the electrode layers are exposed alternately from both sides. Ceramic green sheets without electrode layers are further stacked on both the front and back sides of the resulting stack. The resulting stack is then press-bonded to produce a laminate consisting of alternating ceramic green sheets and electrode layers. This laminate is cut into the desired shape and then held at a temperature of, for example, 200 to 400°C for 2 to 10 hours to remove the binder.

[0054] The binder-removed laminate is fired in air at 1300-1350° C. for 4 hours. After firing, the ceramic green sheets become the dielectric layers 11, and the electrode layers become the internal electrode layers (first and second internal electrode layers).

[0055] After the fired laminate 10 has its side surfaces appropriately polished (by barrel polishing, sandblasting, etc.), a pair of external electrodes (first external electrode 14 and second external electrode 15) made of Au are formed on the side surfaces of the laminate 10, for example, by sputtering. Thus, the laminated electronic component 1 is obtained.

[0056] The dielectric composition disclosed in this specification exhibits a small decrease in relative permittivity before and after application of a high DC voltage, a high relative permittivity under high electric fields, and a high withstand voltage.

[0057] Dielectric elements and laminated electronic components comprising a dielectric layer formed from the dielectric composition are used, for example, in powertrains for electric vehicles that are subject to high voltages (e.g., 400V to 800V). Examples of such laminated electronic components include dielectric capacitors and laminated ceramic capacitors. Furthermore, the dielectric composition can be used in various electronic devices, including home appliances and automotive control devices.

[0058] Example

[0059] Hereinafter, the present invention will be described in more detail based on examples. However, it should be noted that the present invention is not limited to these examples.

[0060] [Examples 1 to 4, Comparative Examples 1 to 4]

[0061] As raw material powders, powders of strontium carbonate, calcium carbonate, sodium carbonate, potassium carbonate, niobium oxide, yttrium oxide, and zirconium oxide were prepared. The desired powders were selected and weighed to give the compositions shown in Table 1. Ethanol was added to the weighed raw material powders, and wet mixing was performed using a ball mill for at least 15 hours to obtain a slurry. The obtained slurry was suitably dried to obtain a mixed powder. The obtained mixed powder was pre-calcined at 1200°C in an atmosphere for 6 hours to obtain a calcined powder.

[0062] A dispersant, a binder, and ethanol were added to the calcined powder, and the mixture was pulverized and mixed to obtain a slurry. The slurry was dried and granulated, and the resulting granules were uniaxially pressed at a pressure of 20 MPa to obtain a disc-shaped preform. The disc-shaped preform was then subjected to a CIP (cold isostatic pressing) treatment at a pressure of 150 MPa to obtain a compact.

[0063] The resulting compact was held at 650°C for 4 hours to remove the binder. The debindered compact was then sintered in air at 1300-1350°C for 4 hours to obtain a dielectric ceramic composed of the dielectric composition. Both main surfaces (upper and lower surfaces) of the resulting dielectric ceramic were polished to obtain a measurement sample having both mirror-finished main surfaces.

[0064] Then, in order to evaluate the electrical characteristics, external electrodes made of Au were formed on both main surfaces of the dielectric ceramic by sputtering, thereby obtaining a dielectric element (measurement sample for evaluating the electrical characteristics).

[0065] 〔evaluate〕

[0066] The following tests were performed on the respective measurement samples of Examples 1 to 4 and Comparative Examples 1 to 4.

[0067] (Relative dielectric constant)

[0068] The relative dielectric constants (0 kV / mm and 8 kV / mm) of the samples used for electrical property evaluation were calculated from the capacitance values ​​at 1 kHz measured using an impedance analyzer at room temperature with no DC voltage applied (i.e., 0 kV / mm) and the capacitance values ​​at 1 kHz measured using an impedance analyzer at room temperature with a DC voltage of 8 kV / mm applied. The results are shown in Table 1.

[0069] (Reduction rate of relative dielectric constant)

[0070] From the relative dielectric constant at an applied voltage of 0 kV / mm, the rate of decrease (rate of change) [%] of the relative dielectric constant at an applied voltage of 8 kV / mm was calculated as [(relative dielectric constant at 8 kV / mm) - (relative dielectric constant at 0 kV / mm)] / (relative dielectric constant at 0 kV / mm) × 100. The results are shown in Table 1.

[0071] (Synchronous XRD)

[0072] The polished surface of the measurement sample without the external electrode was subjected to structural analysis based on synchrotron radiation XRD (X-ray diffraction). The wavelength of the synchrotron radiation was 0.85 Å. The synchrotron radiation XRD pattern obtained for each measurement sample is shown in FIG. Figure 3 . Figure 3 The synchrotron XRD patterns with a diffraction angle 2θ in the range of 10° to 20° are shown in FIG. Figure 3 The horizontal axis represents the diffraction angle 2θ (°), and the vertical axis represents the intensity (arbitrary unit).

[0073] It should be noted that, in the obtained synchrotron radiation XRD pattern, background subtraction was performed by setting the peak width threshold to 0.1 and the intensity threshold to 1 using the Sonneveld-Visser method. Then, the peak intensity value of the peak with the highest intensity (maximum peak) was set to 1 to normalize the synchrotron radiation XRD pattern. Figure 3 As shown in the figure, in all cases of the measured samples, the peak with the highest intensity (maximum peak) is observed in the range of diffraction angle 2θ of 17° to 18°. It should be noted that the maximum peak here is selected from Sr2NaNb5O with a tungsten bronze structure in the synchrotron radiation XRD pattern. 15 It is the peak of oxide.

[0074] In addition, the synchrotron radiation XRD patterns of the samples measured with a diffraction angle 2θ in the range of 9° to 12° are shown in FIG. Figure 4 . Figure 4 The horizontal axis represents the diffraction angle 2θ (°), and the vertical axis represents the intensity (arbitrary unit).

[0075] (peak intensity ratio)

[0076] In the synchrotron radiation XRD pattern of each measured sample, when there is a peak top (maximum value) in the range of diffraction angle 2θ of 10.7° to 11.0°, the ratio of the intensity of the peak with the peak top to the intensity of the maximum peak (peak intensity ratio) is calculated. The results are shown in Table 1. It should be noted that the peak intensity ratio here is determined by the Sr2NaNb5O having a tungsten bronze structure in the synchrotron radiation XRD pattern. 15 The peak intensity ratio of the oxide was determined.

[0077]

[0078] According to the results of synchrotron radiation XRD (ref. Figure 3 and Figure 4 ), it was confirmed that the dielectric compositions of Examples 1 to 4 have Sr2NaNb5O having a tungsten bronze structure. 15 It is a crystalline phase of oxide.

[0079] In addition, the dielectric compositions of Examples 1 to 4 all have a peak top of the synchrotron radiation XRD pattern within the range of a diffraction angle 2θ of 10.7° to 11.0°, and the Sr2NaNb5O 15 The ratio of the intensity of the peak having the peak top to the intensity of the maximum peak having the maximum intensity (peak intensity ratio) of the oxide is 0.0043 or more. Figure 3 As shown, in the case of any of the measured samples, the 15 In the synchrotron XRD patterns of the oxides, the peaks with the highest intensity (maximum peak) were all observed within the diffraction angle 2θ range of 17° to 18°. For the dielectric compositions of Examples 1 to 4, the relative permittivity reached over 1000 under a high electric field (8 kV / mm), and the rate of decrease (rate of change) in the relative permittivity before and after application of a high DC voltage was over -35%, indicating that the decrease in the relative permittivity was minimal.

[0080] In addition, according to the results of synchrotron XRD (refer to Figure 3 and Figure 4 ), it was confirmed that the dielectric compositions of Examples 1 to 4 also contained a crystal phase of a perovskite-type crystal structure.

[0081] In the case of the dielectric compositions of Comparative Examples 1 to 4, Figure 4 As shown, no peak is observed within the diffraction angle 2θ range of 10.7° to 11.0°. In the case of Comparative Examples 1 to 4, the results show that the reduction rate (change rate) of the relative dielectric constant is -54.1 to -50.5%, and the reduction range of the relative dielectric constant is large.

[0082] The dielectric composition of Comparative Example 1 has a tungsten bronze type crystal phase with no tilted octahedral structure. It should be noted that the dielectric composition of Comparative Example 1 also contains a perovskite type crystal phase. In addition, regarding the dielectric compositions of Comparative Examples 2 to 4, Figure 3 and Figure 4 As shown, it was confirmed that the main phase (tungsten bronze type crystal phase) was the only component, without any secondary phase. It is speculated that in the case of Comparative Examples 2 to 4, the octahedral structure was not tilted during K substitution, resulting in the absence of a peak in the range of 10.7° to 11.0°.

[0083] Explanation of symbols

[0084] 100…Dielectric ceramic (dielectric layer), 200…Dielectric element, 301, 302…Electrodes, 1…Laminated electronic component, 10…Laminated body, 11…Dielectric layer, 12…First internal electrode layer (internal electrode layer), 13…Second internal electrode layer (internal electrode layer), 14…First external electrode, 15…Second external electrode

Claims

1. A dielectric composition comprising Sr2NaNb5O having a tungsten bronze structure 15 The crystal phase of the oxide has the following crystal structure: 15 The oxide has a peak top of the synchrotron radiation XRD pattern in the range of a diffraction angle 2θ of 10.7° to 11.0° in the synchrotron radiation XRD pattern measured at a measurement wavelength of 0.85Å, and the Sr2NaNb5O 15 The ratio of the intensity of the peak having the peak top to the intensity of the maximum peak having the maximum intensity of the oxide is 0.0043 or more.

2. The dielectric composition according to claim 1, wherein The Sr2NaNb5O 15 The oxides include Ca, Y, and Zr. 3 . A dielectric element comprising a dielectric ceramic formed from the dielectric composition according to claim 1 , and an electrode mounted on the dielectric ceramic. A laminated electronic component comprising a laminate in which dielectric layers composed of the dielectric composition according to claim 1 and internal electrode layers are alternately laminated.

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