JP2017178744A - Ferroelectric ceramic and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide ferroelectric ceramic having a small variation of relative dielectric constants in the range of -55°C to 200°C.SOLUTION: Ferroelectric ceramic comprises a tungsten bronze type oxide having Nb, and an oxide assistant.SELECTED DRAWING: None

Description

  The present invention relates to a ferroelectric ceramic that can be used for a capacitor used in a wide temperature range, for example, for in-vehicle use or aerospace use, and a method for manufacturing the same.

Conventionally, as a candidate for a ferroelectric ceramic that can be used for a capacitor used in a wide temperature range, for example, for in-vehicle use or aerospace use, Non-Patent Document 1 discloses K ₂ Sr ₄ that is a tungsten bronze compound. Nb _9.78 O _29.45 with a small amount of ZrO ₂ or Ta ₂ O ₅ added and fired has a relative dielectric constant below the Curie temperature compared to K ₂ Sr ₄ Nb _9.78 O _29.45. It has been reported that the temperature dependence increases or the temperature dependence decreases.

However, a material obtained by adding and baking a small amount of ZrO ₂ or Ta ₂ O ₅ to K ₂ Sr ₄ Nb _9.78 O _29.45 has a large temperature dependency of a change in relative dielectric constant. The X7R characteristic, that is, the characteristic that the variation of the relative dielectric constant is within 15% of the soil in the temperature range of −55 ° C. to 125 ° C. could not be achieved.
Under such circumstances, the X8R characteristic in which the variation in relative permittivity is within 15% of the soil in the temperature range of −55 ° C. to 150 ° C., and the variation in relative permittivity in the temperature range of −55 ° C. to 200 ° C. is within 15% of the soil. Development of ferroelectric ceramics that achieve the X9R characteristic is desired.

Tribotte, B., et al. Journal of the European Ceramic Society 19 (6-7) (1999): 1105-1109.

  Under such circumstances, a problem to be solved by the present invention is to provide a ferroelectric ceramic having a small variation in relative dielectric constant in a range of −55 ° C. to 200 ° C.

As a result of intensive studies and repeated experiments to solve the above problems, the inventors of the present application have come to solve the problems with the following configuration.
That is, the present invention is as follows.
[1] A ferroelectric ceramic containing a tungsten bronze type oxide having Nb and an oxide auxiliary agent.
[2] The tungsten bronze oxide is KSr ₂ Nb ₅ O ₁₅ (hereinafter also referred to as “KSN”) or NaSr ₂ Nb ₅ O ₁₅ (hereinafter also referred to as “NSN”). ] Ferroelectric ceramics described in the above.
[3] The ferroelectric ceramic according to [1] or [2], wherein the oxide auxiliary agent is ZrO ₂ or Ta ₂ O ₅ or a mixture thereof.
[4] The ferroelectric according to any one of [1] to [3], wherein the tungsten bronze type oxide is KSr ₂ Nb ₅ O ₁₅ having a lattice constant a of more than 12.46 and less than 12.54. Ceramics.
[5] The ferroelectric material according to any one of [1] to [3], wherein the tungsten bronze oxide is NaSr ₂ Nb ₅ O ₁₅ having a lattice constant a of 12.30 or more and less than 12.35. Body ceramics.
[6] Any of [1] to [5] above, having a relative dielectric constant of less than 5000 in the range of −55 ° C. to 200 ° C. and having two or more maximum values of relative dielectric constant. The ferroelectric ceramic described.
[7] The ferroelectric ceramic according to any one of [1] to [6], wherein the Curie temperature is 80 ° C. or higher and 190 ° C. or lower.
[8] The maximum value ε _max and the minimum value ε _min of the relative dielectric constant in the range of −55 ° C. to 200 ° C. satisfy the relationship of (ε _max− ε _min ) / (ε _max + ε _min ) ≦ 0.4. The ferroelectric ceramic according to any one of [1] to [7].
[9] The maximum value ε _max and the minimum value ε _min of the dielectric constant in the range of −55 ° C. to 200 ° C. satisfy the relationship of (ε _max + ε _min ) / 2 ≧ 1000, [1] to [8] The ferroelectric ceramic according to any one of the above.
[10] The strength according to any one of [1] to [9], including a step of sintering the tungsten bronze-type oxide, or the raw material or the precursor thereof, after adding the component of the oxide auxiliary agent. Dielectric ceramic manufacturing method.
[11] The method according to [10], wherein the sintering includes at least one calcination and subsequent sintering at a temperature higher than the temperature of the calcination.

  The ferroelectric ceramic of the present invention contains a tungsten bronze type oxide and an oxide auxiliary, and has a small variation in relative permittivity in the range of −55 ° C. to 200 ° C. It can be used for capacitors used in a wide temperature range. In addition, the effect of the said invention does not describe all the advantages regarding the following embodiment and this invention.

Hereinafter, embodiments of the present invention will be described in detail. The present invention is not limited to these embodiments.
The ferroelectric ceramic of the present embodiment includes a tungsten bronze type oxide having Nb and an oxide auxiliary agent. Hereinafter, each component will be described in detail.
<< Tungsten bronze oxide with Nb >>
The tungsten bronze type oxide has the following composition formula (1):
A _x BO _{3 + α} (1)
{In the formula, A is Li, Na, K, Rb, Cs, Ca, Sr, Ba, Ag, Bi, Y, La, Ce, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Eu. Represents at least one element selected from the group consisting of Tm, Yb, Lu, and Er, and B contains at least Nb, but Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, It may further include an element selected from the group consisting of Ga, Mo, Ru, In, Sn, Sb, Te, Hf, and W, and x represents a ratio of the total of the A element to the total of the B element. , 0 <x ≦ 1, and (3 + α) represents the composition ratio of oxygen atoms to the total of B elements, and −1 ≦ α ≦ 1. }.

A is Li, Na, K, Rb, Cs, Ca, Sr, Ba, Ag, Bi, Y, La, Ce, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Eu, Tm, Yb Two or more elements from the group consisting of, Lu, and Er may be included.
B includes at least Nb, but is selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Mo, Ru, In, Sn, Sb, Te, Hf, and W. It may further contain two or more kinds of elements. The total of B elements is 1 in the composition formula (1).
x is a ratio of the total of the A elements to the total of the B elements, 0 <x ≦ 1, preferably 0.1 ≦ x <1, more preferably 0.2 ≦ x ≦ 0.8. Yes, and more preferably 0.3 ≦ x ≦ 0.7.
α is −1 ≦ α ≦ 1, and from the viewpoint of stability of the crystal structure, preferably −0.5 ≦ α ≦ 0.5, and more preferably −0. 4 ≦ α ≦ 0.4.

The fact that the tungsten bronze type oxide of this embodiment contains Nb can be confirmed by a composition analysis by fluorescent X-ray analysis.
Specifically, the tungsten bronze type oxide of the composition formula (1) includes SBN (strontium barium niobate), Ba ₂ KNb ₅ O ₁₅ , Ba ₂ LiNb ₅ O ₁₅ , Ba ₂ AgNb ₅ O ₁₅ , Ba ₂ RbNb. ₅ O ₁₅ , SrNb ₂ O ₆ , Sr ₂ NaNb ₅ O ₁₅ , Sr ₂ LiNb ₅ O ₁₅ , Sr ₂ KNb ₅ O ₁₅ , Sr ₂ RbNb ₅ O ₁₅ , Ba ₃ Nb ₁₀ O ₂₈ , K ₃ Li ₂ Nb ₅ O ₁₅ , K ₂ RNb ₅ O ₁₅ (R: Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho), K ₂ BiNb ₅ O ₁₅ , Ba ₂ NaNb ₅ O ₁₅ , Ba _{2 KNb 5 O 15 KSr 2 Nb} 5 O 15, NaSr 2 Nb 5 O tungsten bronze-type oxide such as _15, these solid solutions And the like.

The tungsten bronze type oxide of the present embodiment is particularly preferably KSr ₂ Nb ₅ O ₁₅ or NaSr ₂ Nb ₅ O ₁₅ .

The fact that the ferroelectric ceramic of this embodiment has a tungsten bronze type oxide means that the tungsten ceramic bronze is measured by X-ray diffraction (hereinafter also simply referred to as “XRD”) using the ferroelectric ceramic as an X-ray source. This can be confirmed by having a peak attributed to the type oxide. For example, when the ferroelectric ceramic is measured by XRD and has a peak of interplanar spacing described in PDF card number 00-34-0108, it can be confirmed that KSr ₂ Nb ₅ O ₁₅ is included, and PDF card number 00-34. It can be confirmed that NaSr ₂ Nb ₅ O ₁₅ is contained when it has a peak of interplanar spacing described in —0429.
When the dielectric ceramic contains KSr ₂ Nb ₅ O ₁₅ , if the lattice constant a is more than 12.46 and less than 12.54, the variation in relative dielectric constant in the temperature range of −55 ° C. to 200 ° C. is small. Therefore, it is preferable. The lattice constant a of KSr ₂ Nb ₅ O ₁₅ alone is 12.46. However, the lattice constant a prepared by adjusting the type and mass concentration of the oxide auxiliary agent and the molding and firing conditions is more than 12.46. The ferroelectric ceramic containing KSr ₂ Nb ₅ O ₁₅ which is less than 54 surprisingly has a small variation in relative dielectric constant in the temperature range of −55 ° C. to 200 ° C. The inventors have unexpectedly discovered that when the lattice constant a is 12.54 or more, the variation in relative dielectric constant in the temperature range of −55 ° C. to 200 ° C. increases again. The lattice constant a is more preferably 12.47 or more and 12.53 or less, and further preferably 12.48 or more and 12.52 or less. The fact that the lattice constant a is more than 12.46 and less than 12.54 can be confirmed by measuring the XRD, and that the peak of the (400) plane appears at more than 2θ = 28.4474 ° and less than 28.6339 °. it can.
When a ferroelectric ceramic containing KSr ₂ Nb ₅ O ₁₅ is prepared, it is sintered to a relative density of 80% or more while being fired at a relatively low temperature and having a lattice constant a of more than 12.46 and less than 12.54. be able to. In order to fire at a relatively low temperature, it is preferable to increase the molding pressure and raise the oxygen concentration in the firing atmosphere. For example, when ZrO ₂ or Ta ₂ O ₅ or both are selected as the oxide assistant and the mass concentration is in the range of 0.5% to 10%, the firing temperature is less than 1300 ° C. and the molding pressure is 150 MPa. The oxygen concentration is preferably 50% or more. For example, assuming that the molding pressure is 200 MPa and the oxygen concentration during firing is 100% (pure oxygen atmosphere), firing at 1250 ° C. for 8 hours results in a relative density of 80 while maintaining a lattice constant a of more than 12.46 and less than 12.54. It can be sintered to more than%.

When the ferroelectric ceramic of the present embodiment contains NaSr ₂ Nb ₅ O ₁₅ , the dielectric constant in the temperature range of −55 ° C. to 200 ° C. when the lattice constant a is 12.30 or more and less than 12.35. This is preferable because the variation of the rate becomes small. The lattice constant a of NaSr ₂ Nb ₅ O ₁₅ alone is 12.35, but the lattice constant a is 12.30 or more and 12.12 which is prepared by adjusting the type and amount of the oxide auxiliary and the molding firing conditions. Ferroelectric ceramics containing NaSr ₂ Nb ₅ O ₁₅ of less than 35 surprisingly have a small variation in relative dielectric constant in the temperature range of −55 ° C. to 200 ° C. The inventors have unexpectedly discovered that when the lattice constant a is less than 12.30, the variation in the dielectric constant again in the temperature range of −55 ° C. to 200 ° C. becomes large again. The lattice constant a is more preferably 12.31 or more and 12.34 or less, and further preferably 12.32 or more and 12.34 or less. It can be confirmed that the lattice constant a is 12.30 or more and less than 12.35 because XRD is measured and the peak of the (400) plane appears at 2θ = 28.8945 ° to 29.0145 ° or less. it can.
When a ferroelectric ceramic containing NaSr ₂ Nb ₅ O ₁₅ is prepared, it is sintered to a relative density of 80% or more by firing at a relatively low temperature while setting the lattice constant a to 12.30 or more and less than 12.35. be able to. In order to fire at a relatively low temperature, it is preferable to increase the molding pressure and raise the oxygen concentration in the firing atmosphere. For example, when ZrO _{2 and} / or Ta ₂ O ₅ or both are selected as the oxide assistant and the mass concentration is in the range of 0.5% to 10%, the firing temperature is less than 1400 ° C. and the molding pressure is 150 MPa. The oxygen concentration is preferably 50% or more. For example, when the molding pressure is 200 MPa and the oxygen concentration during firing is 100% (pure oxygen atmosphere), when firing at 1300 ° C. for 8 hours, the relative density of 80 is maintained while the lattice constant a is 12.30 or more and less than 12.35. It can be sintered to more than%.

<< Oxide aid >>
Examples of the oxide auxiliary agent in this embodiment include oxides of B, Mg, Al, Si, P, Ge, Zr, and Ta. As representative oxides of each element, B ₂ O ₃ , MgO, Al ₂ O ₃ , SiO ₂ , P ₂ O ₅ , GeO ₂ , ZrO ₂ , and Ta ₂ O ₅ are known. As the material aid, for example, a partial oxide such as SiO may be used. Further, it may be crystalline or amorphous.
The oxide auxiliary agent of this embodiment is preferably B ₂ O ₃ , MgO, Al ₂ O ₃ , SiO ₂ , ZrO ₂ , Ta ₂ O ₅ , more preferably ZrO ₂ , Ta ₂ O ₅ . Two or more types of ferroelectric ceramics may be included as oxide assistants.
The content of the oxide auxiliary is preferably 0.01% or more and less than 50% as a mass concentration (%), more preferably 0.1% or more and 40% or less, and further preferably 0.3% or more and 30%. % Or less, and most preferably 0.5% or more and 20% or less.
The content (mass concentration) of the oxide auxiliary agent can be measured as a bulk oxide by X-ray fluorescence analysis, as shown in the composition analysis method described later. In the present embodiment, the oxide auxiliary agent may be present alone as an oxide, may replace a constituent element of the tungsten bronze type oxide, or is in solid solution with the tungsten bronze type oxide. Alternatively, a new composite oxide may be formed with a constituent element of the tungsten bronze oxide.

<< Ferroelectric Ceramics >>
In this specification, a ferroelectric ceramic means a ceramic having ferroelectricity. Ferroelectricity means that electric dipoles are aligned even if there is no external electric field, and A property whose direction can be changed by an electric field.

In this specification, ceramics refers to ceramics obtained by sintering an inorganic substance.
The ferroelectric ceramic in the present embodiment is obtained by mixing the tungsten bronze type oxide or its raw material or its precursor and the component of the oxide auxiliary agent, followed by molding and firing. As disclosed in Non-Patent Document 1, it is known that a ceramic containing a tungsten bronze type oxide having Nb becomes a ferroelectric ceramic.

<< Relative permittivity >>
In this specification, the “relative permittivity” is a real part of a relative permittivity obtained as a complex number by forming electrodes on both sides of a measurement sample to form a capacitor, and measuring at a frequency of 1 kHz using an LCR meter. Refers to that.
It is preferable that the maximum value ε _max and the minimum value ε _min of the relative dielectric constant in the range of −55 ° C. to 200 ° C. satisfy the relationship of (ε _max− ε _min ) / (ε _max + ε _min ) ≦ 0.4. More preferably, the relationship of (ε _max− ε _min ) / (ε _max + ε _min ) ≦ 0.3, more preferably (ε _max− ε _min ) / (ε _max + ε _min ) ≦ 0.2 is satisfied.

The ferroelectric ceramic of the present embodiment has a maximum relative dielectric constant ε in the range of −55 ° C. to 200 ° C. from the viewpoint of reducing variation in the relative dielectric constant within the temperature range of −55 ° C. to 200 ° C. It is preferable that _max is less than 5000. More preferably, ε _max is 4000 or less, and further preferably ε _max is 3000 or less.

  In the ferroelectric ceramic of the present embodiment, from the viewpoint of reducing the relative permittivity distribution over a wide temperature range, the X in the graph with the X axis as the temperature and the Y axis as the relative permittivity is in the range of −55 ° C. to 200 ° C. In the above, it is preferable that the relative dielectric constant has two or more maximum values.

  The ferroelectric ceramic of the present embodiment preferably has a Curie temperature of 80 ° C. or higher and 190 ° C. or lower from the viewpoint of reducing the relative permittivity distribution over a wide temperature range. Curie temperature is the temperature at which the peak of relative permittivity in the range of 30 ° C. to 200 ° C. shows a maximum value, or when the relative permittivity has a shoulder peak that does not have a maximum value, the shoulder peak is separated. It refers to the temperature at the peak peak.

  The Curie temperature of the ferroelectric ceramic of the present embodiment is more preferably 100 ° C. or higher and 180 ° C. or lower, and further preferably 120 ° C. or higher and 170 ° C. or lower.

The ferroelectric ceramic of this embodiment preferably has a high relative dielectric constant. Specifically, (ε _max + ε _min ) / 2 ≧ 1000 is preferable, (ε _max + ε _min ) / 2 ≧ 1400 is more preferable, and (ε _max + ε _min ) / 2 ≧ 1800 is more preferable.

<< Production method of tungsten bronze type oxide >>
The tungsten bronze type oxide can be produced by a solid phase reaction. As a raw material of tungsten bronze type oxide in solid phase reaction, element A (Li, Na, K, Rb, Cs, Ca, Sr, Ba, Ag, Bi, Y, La, Ce, Pr, Nd, Pm, Sm , Gd, Tb, Dy, Ho, Eu, Tm, Yb, Lu, and Er, and at least one element selected from the group consisting of Er, and element B (including at least Nb, Ti, V , Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Mo, Ru, In, Sn, Sb, Te, Hf, and one or more further selected from the group consisting of W May be used), hydroxides, chlorides, carbonates, acetates, nitrates, sulfates, ammonium salts, alkoxides, and the like.

  A tungsten bronze-type oxide can be obtained by pulverizing and mixing the above raw materials with, for example, a ball mill, a planetary ball mill or the like and then firing. From the viewpoint of mixing efficiency, a method in which various raw materials are dissolved in a solvent and then mixed, the mixed solution is evaporated to dryness, and then fired is preferable. As the solvent, an organic solvent such as alcohol can be used, but water may be used. When various raw materials are mixed, precipitation may occur by reaction. Further, when various raw materials are mixed, an acid or a base may be added to perform a hydrolysis reaction or a polymerization reaction, and as a result, precipitation may occur. The acid or base is preferably an organic acid, an organic amine, hydrochloric acid, nitric acid, aqueous ammonia, or the like from the viewpoint that it can be removed by calcination. Evaporation to dryness may be performed under reduced pressure, for example, using an evaporator. Alternatively, a tungsten bronze-type oxide may be prepared by evaporating to dryness by a spray drying method using a uniform solution without precipitation after mixing, and firing the obtained evaporated dry solid. The evaporation to dryness temperature by the spray drying method is preferably 100 ° C to 300 ° C. Spray drying can be simply performed by spraying the raw material preparation liquid on a plate such as an iron plate heated to 100 ° C to 300 ° C.

For the element having low solubility in an aqueous solvent, a complex solution in which an organic ligand such as oxalic acid, citric acid, tartaric acid, malic acid or the like is coordinated may be used as a raw material solution. For example, Nb preferably uses an oxalic acid complex aqueous solution as a raw material solution. The molar ratio of oxalic acid / niobium is 1 or more and 10 or less, preferably 2 or more and 4 or less.
In order to improve the solubility and dispersibility of the raw material in the aqueous solvent, hydrogen peroxide water may be added. For example, the molar ratio of hydrogen peroxide solution / niobium is preferably 0.5 or more and 10 or less, more preferably 2 or more and 6 or less.

When mixing raw materials using an aqueous solvent, the raw materials used are preferably organic metal complexes such as oxalic acid solution and acetate, organic salts, nitrates, and chlorides from the viewpoint of solubility and thermal decomposability.
The tungsten bronze type oxide is temporarily calcined at a temperature of 600 ° C. or higher and 1150 ° C. or lower after mixing the raw materials to obtain a tungsten bronze type oxide precursor, and the precursor is pulverized and mixed. When it is manufactured by firing at a high temperature, it is preferable because sub-crystals are hardly formed. Calcination may be performed twice or more at different temperatures. In particular, when producing a tungsten bronze type oxide from a plurality of components having different decomposition temperatures, it is preferable to perform calcination at each temperature at which each raw material decomposes. The tungsten bronze type oxide precursor may be a tungsten bronze type oxide having low crystallinity, or an intermediate that transitions to a tungsten bronze type oxide by firing.

  The firing time is appropriately selected according to the progress of the decomposition of the raw materials and the reaction of producing the tungsten bronze type oxide, but the firing time under one firing temperature condition is preferably 30 minutes or more and within 20 hours, more preferably. Is between 1 hour and 10 hours.

  The atmosphere at the time of firing may be air, but may be fired in an atmosphere of pure oxygen, nitrogen, argon or the like in order to set α to a desired value. Further, by adding an organic substance such as oxalic acid and baking, reductive baking can be performed to satisfy α <0.

<< Method of adding oxide auxiliary agent >>
The oxide assistant may be present in the form of oxides of B, Mg, Al, Si, P, Ge, Zr, and Ta in the ferroelectric ceramic of the present embodiment, or a tungsten bronze type oxide. These constituent elements may be substituted, or may be solid-solved with the tungsten bronze type oxide, or a new composite oxide may be formed with the constituent element of the tungsten bronze type oxide. Ferroelectric ceramics are manufactured by adding a component of an oxide aid to a tungsten bronze type oxide or its raw material or its precursor, followed by molding and firing.
For this reason, as a component (raw material) of the oxide auxiliary agent added to the tungsten bronze type oxide or its raw material or its precursor, any form may be used as long as the oxide is formed by firing. . That is, B, Mg, Al, Si, P, Ge, Zr, Ta oxides, hydroxides, chlorides, carbonates, acetates, nitrates, sulfates, ammonium salts, alkoxides, and the like can be used.

When the component of the oxide auxiliary agent is mixed with the tungsten bronze type oxide or its raw material or its precursor, it can be pulverized and mixed, for example, with a ball mill, a planetary ball mill or the like.
From the viewpoint of mixing efficiency, after dissolving the oxide auxiliary component in a solvent to form a solution, the tungsten bronze type oxide or its raw material or its precursor is mixed with the solution, and the mixed solution is evaporated to dryness. You may bake. As the solvent, an organic solvent such as alcohol can be used, but water may be used. During mixing, precipitation may occur due to the reaction. Further, when the raw materials are mixed, hydrolysis reaction or polymerization reaction may be performed by adding an acid or a base, and as a result, precipitation may occur. The acid or base is preferably an organic acid, an organic amine, hydrochloric acid, nitric acid, aqueous ammonia, or the like from the viewpoint that it can be removed by calcination. Evaporation to dryness may be performed under reduced pressure, for example, using an evaporator. In addition, when the oxide raw material is precipitated in the insoluble tungsten bronze type oxide or its raw material or its precursor at the time of mixing, the solvent may be removed by filtration instead of evaporation to dryness, and then fired.

Further, if a tungsten bronze type oxide or its raw material or its precursor and the component of the oxide auxiliary agent are mixed and a uniform dispersion without precipitation is obtained, the uniform dispersion can be used for spray drying. The ferroelectric ceramic may be formed by evaporating to dryness, and preliminarily firing and baking the obtained evaporated dry solid. The evaporation to dryness temperature by the spray drying method is preferably 100 ° C to 300 ° C. Spray drying can be simply performed by spraying the raw material preparation liquid on a plate such as an iron plate heated to 100 ° C to 300 ° C.
For the element having low solubility in an aqueous solvent, a complex solution in which an organic ligand such as oxalic acid, citric acid, tartaric acid, malic acid or the like is coordinated may be used as a raw material solution. For example, for Ta, an oxalic acid complex aqueous solution is preferably used as a raw material solution. The molar ratio of oxalic acid / tantalum is 1 or more and 10 or less, preferably 2 or more and 4 or less.
In order to improve the solubility and dispersibility of the raw material in the aqueous solvent, hydrogen peroxide water may be added. For example, the molar ratio of hydrogen peroxide solution / tantalum is preferably 0.5 or more and 10 or less, more preferably 2 or more and 6 or less.

When mixing materials using an aqueous solvent, the raw materials used are preferably organic metal complexes such as oxalic acid solutions and acetates, organic salts, nitrates, and chlorides from the viewpoints of solubility and thermal decomposability.
After adding the oxide auxiliary component to the tungsten bronze type oxide or its raw material or its precursor, it is temporarily calcined at a temperature of 600 ° C. or higher and 1150 ° C. or lower, and the calcined powder is pulverized and mixed to form. It is preferable to produce a ferroelectric ceramic by firing because it is difficult to form a sub-crystal.
The calcining time of the calcining after the addition of the oxide auxiliary component is appropriately selected according to the decomposition of the oxide auxiliary component and the progress of the reaction, but the calcining time is 30 under one baking temperature condition. It is preferably within the range of minutes to 20 hours, more preferably 1 hour to 10 hours.
The atmosphere during the calcination firing after the addition of the oxide auxiliary component may be air, but in order to reduce the oxide auxiliary, it may be fired in an atmosphere of pure oxygen, nitrogen, argon or the like. Moreover, an oxide adjuvant can be reduced by adding and baking organic substances, such as an oxalic acid.

  From the viewpoint of obtaining dense ferroelectric ceramics, the component of the oxide auxiliary is not added to the tungsten bronze type oxide raw material, but the tungsten bronze type oxide powder or its precursor (calcined powder). It is preferable to add to. It is more preferable to add an oxide auxiliary component to the tungsten bronze type oxide precursor (calcined powder).

<< Manufacturing method of ferroelectric ceramics >>
The ferroelectric ceramic of the present embodiment is formed by performing die press molding, CIP molding, etc. on a powder obtained by adding a component of an oxide auxiliary agent to a tungsten bronze type oxide or a precursor thereof or a raw material thereof. After being made into a body, it is manufactured by firing. When molding, molding methods such as mold press molding, CIP molding, cast molding, injection molding, extrusion molding, and green sheet molding can be used. In molding, various organic molding aids such as polyvinyl alcohol may be added.

  The molding pressure is preferably 10 MPa or more and 400 MPa or less. If the molding pressure is less than 10 MPa, the strength of the molded body is insufficient, and if it exceeds 400 MPa, the time required for the pressurizing step is increased, which is not preferable from the viewpoint of productivity. The molding pressure is more preferably 100 MPa or more and 350 MPa or less, and further preferably 150 MPa or more and 300 MPa or less.

  The relative density of the molded body is preferably 30% or more and 70% or less. If it is less than 30%, the strength of the molded product is insufficient, and in order to achieve more than 70%, a high molding pressure is required, and the time required for the pressurizing step becomes long, which is not preferable from the viewpoint of productivity. The relative density of the ferroelectric ceramic obtained by firing the formed body is preferably 80% or more, more preferably 85% or more, and further preferably 90% or more. If the relative density is 80% or less, the relative dielectric constant of the ferroelectric ceramic is lowered, which is not preferable. The relative density of the formed body of the ferroelectric ceramic of the present embodiment was determined from the relative magnitude of the measured density value when the bulk density of the single compound serving as the tungsten bronze type oxide was 100%.

  The firing temperature of the molded body is preferably 900 ° C. or higher and 1400 ° C. or lower. When the temperature is less than 900 ° C., sintering of the molded body does not proceed, the relative density of the ferroelectric ceramic is lowered, and the relative dielectric constant is lowered, which is not preferable. If it exceeds 1400 ° C., a tungsten bronze-type oxide cannot be obtained, or only a ferroelectric ceramic having a shape remarkably different from that of the formed body can be obtained due to a decrease in viscosity during firing.

The calcining time of the calcining after the addition of the oxide auxiliary component is appropriately selected depending on the degree of progress of the sintering of the molded body, but it is preferably 30 minutes or more and 20 hours or less in the calcining time under one firing temperature condition, More preferably, it is 1 hour or more and 10 hours or less. The atmosphere at the time of firing may be air, but may be fired in an atmosphere of pure oxygen, nitrogen, argon or the like in order to set _α in the composition formula (1): A _x BO _{3 +} α to a desired value. In particular, firing in a pure oxygen atmosphere is preferable because a ferroelectric ceramic with a high relative density can be obtained.

The present invention will be specifically described by the following examples, but the scope of the present invention is not limited thereby.
[Preparation method of pellet]
Using a tablet molding machine having a diameter of 10 mm, 0.5 g of the molding powder was molded at a molding pressure of 200 MPa to prepare pellets having a diameter of 10 mm and a thickness of about 2 mm.

[Measurement of relative density]
The thickness of the pellet is determined by measuring the center with a micrometer, and the diameter of the pellet is the average value of the measured values measured with two calipers in the orthogonal direction, (pellet diameter (cm)) ² × 3.14 / The volume (cm ³ ) of the pellet was determined from 4 × (the thickness of the pellet (cm)).
The weight (g) of the pellet was determined by an electronic balance, and the density of the pellet (g / cm ³ ) was determined by dividing the weight of the pellet by the volume of the pellet.
In the case of a ferroelectric ceramic containing KSr ₂ Nb ₅ O ₁₅ , the relative density was determined as relative density (%) = (pellet density) /4.98×100.
In the case of a ferroelectric ceramic containing NaSr ₂ Nb ₅ O ₁₅ , the relative density was determined as relative density (%) = (pellet density) /5.04×100.

[Measurement method of relative permittivity]
Electrodes with a diameter of 8 mm were prepared on both sides of the ferroelectric ceramic pellets using silver paste, platinum wires were connected, and an LCR meter (Part No. 4284A) manufactured by Hewlett-Packard Company was used, and the dielectric constant was determined by the two-terminal method. The rate was measured. The measurement frequency was 1 kHz.
The sample was placed in a cell with a heater, cooled to −195.8 ° C. with liquid nitrogen, gradually heated to 200 ° C., and the relative dielectric constant at each temperature was measured.
The temperature of the ferroelectric ceramic pellet at the time of measuring the relative dielectric constant was measured with a thermometer (product number TR2114) manufactured by Advantest Corporation using a platinum resistor UNR-141-100S manufactured by Nethshin.
In the range of −55 ° C. to 200 ° C., the maximum value ε _max and the minimum value ε _min of the dielectric constant were determined, and (ε _max −ε _min ) / (ε _max + ε _min ) was determined.
In addition, when the relative dielectric constant peak seen in the range of 30 ° C. to 200 ° C. has a maximum value, or when the relative dielectric constant has a shoulder peak that does not have a maximum value, the peak obtained by separating the shoulder peak The temperature at the top of the curve was obtained and used as the Curie temperature.
When the relative permittivity has two or more maximum values in the range of −55 ° C. to 200 ° C., “○” in the row of “Relative permittivity two peaks” in Table 1 below, If there was only one, “x” was entered.

[Composition analysis method]
The powder obtained by pulverizing the ferroelectric ceramics of Examples and Comparative Examples was filled into a ring made of vinyl chloride having an inner diameter of 25 mm, a thickness of 5 mm, and a width of 3 mm, and pressure-molded by a press to obtain a thickness. A pellet of about 3 mm was used as a measurement sample for fluorescent X-ray analysis. After total qualitative analysis of the measurement sample using a scanning X-ray fluorescence analyzer ZSX Primus II (trade name, manufactured by Rigaku Corporation), the sample model is selected as bulk, the component form is selected as oxide, and the SQX calculation is performed. The mass concentrations of K ₂ O, Na ₂ O, SrO, Nb ₂ O ₅ , ZrO ₂ , and Ta ₂ O ₅ were measured.

[X-ray diffraction (XRD) measurement method, lattice constant a calculation method]
X-ray diffraction (XRD) was measured using a D8 ADVANCE type X-ray diffractometer manufactured by Bruker AXS. Ferroelectric ceramics were pulverized in an agate mortar and then placed on an XRD measurement cell, and the surface was flattened for measurement. X-ray source is CuKα1 + CuKα2, tube voltage is 40 kV, tube current is 40 mA, divergence slit (DS): 0.3 °, step width: 0.02 ° / step, counting time: 0.5 sec, measurement range: 2θ = 5 It was set to -90 degree.
The lattice constant a of the tungsten bronze type oxide was obtained as 2θ of the peak corresponding to the (400) plane, and from that θ, a = 1.54059 / 2 / sin θ × 4. The peak corresponding to the (400) plane refers to the 2θ value and strength described in PDF card number 00-34-0108 when the ferroelectric ceramic contains KSr ₂ Nb ₅ O ₁₅ , and the ferroelectric ceramic is NaSr _2. When Nb ₅ O ₁₅ was included, the identification was made with reference to the 2θ value and intensity described in PDF card number 00-34-0429.

[Example 1]
Filling a 500 mL plastic polyamide ball mill container with 6.91 g of K ₂ CO ₃ powder, 29.5 g of SrCO ₃ powder and 66.5 g of Nb ₂ O ₅ powder together with a plastic polyamide ball having a diameter of 10 mm and an isopropanol solvent. Then, using a planetary ball mill device P-5 manufactured by Fritsch, mixing was performed at 200 rpm for 20 hours.
After mixing, the isopropanol solvent was distilled off with an evaporator to obtain a mixed powder.
200 mL of isopropanol solvent was added to 92.6 g of this mixed powder, and then zirconium tetrapropoxide (Zr (C ₃ H ₇ O) ₄ ) 70% 1-propanol solution was used while stirring. 2.95 g was added as propoxide, and further 10 mL of 1 mol / L acetic acid aqueous solution diluted with 40 mL of isopropanol solvent was added, and the mixture was stirred at 25 ° C. for 24 hours and allowed to stand.
Thereafter, the solvent was removed by an evaporator, and the obtained powder was baked at 600 ° C. for 8 hours to obtain a calcined powder.
Pellets are prepared using the calcined powder as a molding powder, fired at 1250 ° C. for 8 hours in a pure oxygen atmosphere, and contain KSr ₂ Nb ₅ O ₁₅ as a tungsten bronze type oxide and ZrO ₂ as an oxide auxiliary. The ferroelectric ceramic of Example 1 was obtained.
The relative density measurement results, composition analysis results, dielectric constant measurement results, and XRD measurement results of the ferroelectric ceramic of Example 1 are shown in Table 1 below.

[Example 2]
6. ₂ g of K ₂ CO ₃ powder, 29.5 g of SrCO ₃ powder and 66.5 g of Nb ₂ O ₅ powder were mixed in the same manner as in Example 1 to obtain a mixed powder.
200 mL of isopropanol solvent was added to 92.6 g of this mixed powder, and then 10 mL diluted with 11.0 g of tantalum pentaethoxide (Ta (C ₂ H ₅ O) ₅ ) and 40 mL of isopropanol solvent while stirring. Of 1 mol / L acetic acid aqueous solution was added, and the mixture was stirred at 25 ° C. for 24 hours and then allowed to stand.
Thereafter, the solvent was removed by an evaporator, and the obtained powder was baked at 600 ° C. for 8 hours to obtain a calcined powder.
Pellets were prepared using the calcined powder as a molding powder, fired at 1250 ° C. for 8 hours in a pure oxygen atmosphere, KSr ₂ Nb ₅ O ₁₅ as a tungsten bronze type oxide, and Ta ₂ O ₅ as an oxide auxiliary. A ferroelectric ceramic of Example 2 containing was obtained.
The relative density measurement results, composition analysis results, dielectric constant measurement results, and XRD measurement results of the ferroelectric ceramics of Example 2 are shown in Table 1 below.

[Example 3]
Na ₂ CO ₃ powder 5.30 g, SrCO ₃ powder 29.5 g, a _Nb 2 _{O 5} powder 66.5 g, was mixed in the same manner as in Example 1 to obtain a mixed powder.
The mixed powder was fired at 1150 ° C. for 8 hours to obtain a calcined powder.
1.11 g of ZrO ₂ powder was added to 81.3 g of the calcined powder, filled in a 500 mL zirconia ball mill container together with an isopropanol solvent and a zirconia ball having a diameter of 3 mm, and a planetary ball mill device P- 5 and mixed at 200 rpm for 1 hour.
Thereafter, the solvent was distilled off by an evaporator to obtain a molding powder.
Pellets were produced from the powder for molding, fired at 1300 ° C. for 8 hours in a pure oxygen atmosphere, and strong in Example 3 containing NaSr ₂ Nb ₅ O ₁₅ as a tungsten bronze type oxide and ZrO ₂ as an oxide auxiliary. A dielectric ceramic was obtained.
The relative density measurement results, composition analysis results, dielectric constant measurement results, and XRD measurement results of the ferroelectric ceramic of Example 3 are shown in Table 1 below.

[Example 4]
Na ₂ CO ₃ powder 5.30 g, SrCO ₃ powder 29.5 g, a _Nb 2 _{O 5} powder 66.5 g, was mixed in the same manner as in Example 1 to obtain a mixed powder.
200 mL of isopropanol solvent was added to 91.2 g of the mixed powder, and then, with stirring, 3.66 g of tantalum pentaethoxide (Ta (C ₂ H ₅ O) ₅ ) and 10 mL diluted with 40 mL of isopropanol solvent. Of 1 mol / L acetic acid aqueous solution was added, and the mixture was stirred at 25 ° C. for 24 hours and then allowed to stand.
Thereafter, the solvent was removed by an evaporator, and the obtained powder was baked at 600 ° C. for 8 hours to obtain a calcined powder.
Pellets were prepared using the calcined powder as a molding powder, fired at 1300 ° C. for 8 hours in a pure oxygen atmosphere, NaSr ₂ Nb ₅ O ₁₅ as a tungsten bronze type oxide, and Ta ₂ O ₅ as an oxide auxiliary. Thus, a ferroelectric ceramic of Example 4 was obtained.
The relative density measurement results, composition analysis results, dielectric constant measurement results, and XRD measurement results of the ferroelectric ceramics of Example 4 are shown in Table 1 below.

[Example 5]
6. ₂ g of K ₂ CO ₃ powder, 29.5 g of SrCO ₃ powder and 66.5 g of Nb ₂ O ₅ powder were mixed in the same manner as in Example 1 to obtain a mixed powder.
The mixed powder was fired at 1150 ° C. for 8 hours to obtain a calcined powder.
To 112.7 g of the calcined powder, 0.111 g of ZrO ₂ powder and 3.98 g of Ta ₂ O ₅ powder are added, and together with an isopropanol solvent and a zirconia ball having a diameter of 3 mm, filled into a 500 mL zirconia ball mill container, Using a planetary ball mill device P-5 manufactured by Frichtu, mixing was performed at 200 rpm for 1 hour.
Thereafter, the solvent was distilled off by an evaporator to obtain a molding powder.
Pellets are prepared from the powder for molding, fired at 1250 ° C. for 8 hours in a pure oxygen atmosphere, and contain KSr ₂ Nb ₅ O ₁₅ as a tungsten bronze type oxide and ZrO ₂ and Ta ₂ O ₅ as oxide assistants. A ferroelectric ceramic of Example 5 was obtained.
The relative density measurement results, composition analysis results, dielectric constant measurement results, and XRD measurement results of the ferroelectric ceramics of Example 5 are shown in Table 1 below.

[Example 6]
Na ₂ CO ₃ powder 5.30 g, SrCO ₃ powder 29.5 g, a _Nb 2 _{O 5} powder 66.5 g, was mixed in the same manner as in Example 1 to obtain a mixed powder.
The mixed powder was fired at 1150 ° C. for 8 hours to obtain a calcined powder.
To 81.3 g of the calcined powder, 0.111 g of ZrO ₂ powder and 1.99 g of Ta ₂ O ₅ powder are added, and together with an isopropanol solvent and a zirconia ball having a diameter of 3 mm, filled into a 500 mL zirconia ball mill container, Using a planetary ball mill device P-5 manufactured by Frichtu, mixing was performed at 200 rpm for 1 hour.
Thereafter, the solvent was distilled off by an evaporator to obtain a molding powder.
Pellet is produced from powder for molding, fired at 1300 ° C. for 8 hours in a pure oxygen atmosphere, and contains NaSr ₂ Nb ₅ O ₁₅ as tungsten bronze type oxide and ZrO ₂ and Ta ₂ O ₅ as oxide assistants The ferroelectric ceramic of Example 6 was obtained.
The relative density measurement results, composition analysis results, dielectric constant measurement results, and XRD measurement results of the ferroelectric ceramic of Example 6 are shown in Table 1 below.

[Comparative Example 1]
6. ₂ g of K ₂ CO ₃ powder, 29.5 g of SrCO ₃ powder and 66.5 g of Nb ₂ O ₅ powder were mixed in the same manner as in Example 1 to obtain a mixed powder.
The mixed powder was fired at 1200 ° C. for 4 hours to obtain a calcined powder.
1.26 g (1.52% by weight of the calcined powder) of ZrO ₂ powder is added to 82.7 g of the calcined powder, together with an isopropanol solvent and a zirconia ball having a diameter of 3 mm, in a 500 mL zirconia ball mill container. The mixture was filled and mixed at 200 rpm for 1 hour using a planetary ball mill device P-5 manufactured by Fritsch.
Thereafter, the solvent was distilled off by an evaporator to obtain a molding powder.
The molding powder was molded at 100 MPa using a tablet molding machine, and the obtained pellets were fired in air at 1300 ° C. for 2 hours to obtain a ferroelectric ceramic of Comparative Example 1.
The relative density measurement results, composition analysis results, dielectric constant measurement results, and XRD measurement results of the ferroelectric ceramic of Comparative Example 1 are shown in Table 1 below.

  The ferroelectric ceramic of the present invention contains a tungsten bronze type oxide and an oxide auxiliary, and has a small variation in relative permittivity in the range of −55 ° C. to 200 ° C. It can be used for capacitors used in a wide temperature range.

Claims (11)

  A ferroelectric ceramic comprising a tungsten bronze oxide having Nb and an oxide auxiliary. _{2. The} ferroelectric ceramic according to claim 1, wherein the tungsten bronze oxide is KSr ₂ Nb ₅ O ₁₅ or NaSr ₂ Nb ₅ O ₁₅ . The ferroelectric ceramic according to claim 1, wherein the oxide auxiliary agent is ZrO ₂ or Ta ₂ O ₅ or a mixture thereof. 4. The ferroelectric ceramic according to claim 1, wherein the tungsten bronze type oxide is KSr ₂ Nb ₅ O ₁₅ having a lattice constant a of more than 12.46 and less than 12.54. ₅ . 4. The ferroelectric ceramic according to claim 1, wherein the tungsten bronze oxide is NaSr ₂ Nb ₅ O ₁₅ having a lattice constant a of 12.30 or more and less than 12.35.   The ferroelectric according to any one of claims 1 to 5, having a relative dielectric constant of less than 5000 in a range of -55 ° C to 200 ° C and having two or more maximum values of dielectric constant. Ceramics.   The ferroelectric ceramic according to any one of claims 1 to 6, wherein the Curie temperature is 80 ° C or higher and 190 ° C or lower. The maximum value ε _max and the minimum value ε _min of the relative dielectric constant in the range of −55 ° C. to 200 ° C. satisfy a relationship of (ε _max− ε _min ) / (ε _max + ε _min ) ≦ 0.4. The ferroelectric ceramic according to any one of? 7. The maximum value ε _max and the minimum value ε _min of the relative dielectric constant in the range of −55 ° C. to 200 ° C. satisfy a relationship of (ε _max + ε _min ) / 2 ≧ 1000, according to claim 1. The ferroelectric ceramic described.   The production of a ferroelectric ceramic according to any one of claims 1 to 9, comprising a step of sintering after adding a component of an oxide auxiliary agent to a tungsten bronze type oxide or a raw material or a precursor thereof. Method.   The method according to claim 10, wherein the sintering includes at least one calcination followed by sintering at a temperature higher than the temperature of the calcination.