JP2018203590A - Barium dititanate-based complex oxide and manufacturing method therefor - Google Patents

Abstract

To provide a barium dititanate-based complex oxide with suppressed current leakage, and a simple manufacturing method therefor.SOLUTION: The barium dititanate-based complex oxide contains a polycrystal consisting of a composition represented by (Ba(A))(Ti(B1)(B2))O, where (A) is at least one element selected from the group consisting of Ca, Rb, Sr, Cs, Fr and Ra, (B1) is at least one element selected from the group consisting of Nb, Ta, V and Mn, (B2) is at least one element selected from the group consisting of Fe, Co, Ni, Fe, Se, Zr, Pd, Sn and Hf, x is 0 or more and less than 0.5, yis 0 or more and less than 0.1, yis more than 0 and less than 0.5, y+yis more than 0 and less than 0.5, and z is 0 or more and yor less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a barium dititanate-based composite oxide and a method for producing the same.

Barium dititanate is a ferroelectric lead-free material represented by the composition formula BaTi ₂ O ₅ and is expected to be put to practical use. For practical use, it is desired to improve various physical properties by substituting a part of Ba or Ti with other elements and to obtain an inexpensive polycrystal.

For example, Patent Document 1 discloses a method for producing a barium dititanate-based composite oxide in which a part of Ba or Ti is substituted with a divalent or tetravalent other element, respectively. Here, the barium dititanate-based composite oxide is BaTi ₂ O ₅ itself, or a polycrystal of an oxide obtained by substituting at least part of Ba or Ti in BaTi ₂ O ₅ with another element. Say. In Patent Document 1, raw material barium carbonate (BaCO ₃ ) powder, titanium dioxide (TiO ₂ ) powder, and divalent other element carbonate or tetravalent other element dioxide powder are mixed. At the same time, a method of producing by solid phase reaction after pulverization is described. A slight distortion of the crystal lattice occurs in the obtained barium dititanate-based composite oxide, so that a change in dielectric properties is expected.

For example, Non-Patent Document 1 reports a barium dititanate composite oxide in which 0.5 to 3% of Ba is substituted with Sr. It is described that the barium dititanate-based composite oxide is obtained as a polycrystal by arc melting after mixing and simultaneously compressing raw material barium carbonate powder, titanium dioxide powder, and strontium carbonate (SrCO ₃ ) powder. Has been. Non-Patent Document 1 describes that the substituted barium dititanate-based composite oxide exhibits a Curie temperature and a maximum dielectric constant different from those in the case of no substitution.

In addition to the production methods described in Patent Document 1 and Non-Patent Document 1, methods for producing a barium dititanate-based composite oxide are known. For example, Patent Document 2 describes a method in which manganese dioxide (MnO ₂ ) powder is added to BaTi ₂ O ₅ powder, followed by firing after mixing and pulverization.

JP2011-219351A JP 2011-006266 A

X. Yue, two others, Materials Transactions, The Japan Institute of Metals, April 25, 2007, Vol. 48, No. 5, p. 984-989.

  A barium dititanate-based composite oxide may generate a large leakage current when a voltage is applied. Current leakage in ferroelectrics can be treated with dielectric loss tangent as an index, and reduction of this value is desired. In particular, the dielectric loss tangent is desired to be reduced to 0.1 or less.

Non-Patent Document 1 discloses a measurement result of dielectric loss tangent of BaTi ₂ O ₅ obtained by an arc melting method and its 0.1% Sr substitution product (Ba _0.99 Sr _0.01 Ti ₂ O ₅ ). It has been reported. The figure of Non-Patent Document 1 shows that the dielectric loss tangent at 0.1 MHz AC voltage at room temperature is about 0.1. However, although values under lower frequency commercial frequency voltages are not described, it is assumed that the dielectric loss tangent will be greater than about 0.1 because the electrical conduction component of the longer relaxation time generally responds at lower frequencies. .

  Moreover, the manufacturing method of the barium dititanate complex oxide described in Patent Literature 1 and Non-Patent Literature 1 cannot satisfy the following two requirements. One is that the element substitution for the purpose of sufficiently suppressing current leakage cannot be performed after the barium dititanate-based composite oxide is manufactured. The other is that the total amount of the added substitution element cannot be substituted into the barium dititanate-based composite oxide.

In the method for producing a barium dititanate-based composite oxide described in Patent Document 1 and Non-Patent Document 1, a divalent or tetravalent substitution element is used simultaneously with BaCO ₃ and TiO ₂ which are raw materials of BaTi ₂ O _5. It is a method of mixing and chemical reaction. That is, element substitution cannot be performed after manufacturing the barium dititanate-based composite oxide. Therefore, if the current leakage of the barium dititanate-based composite oxide already produced is not sufficiently suppressed, it is necessary to recreate it from the beginning. That is, the raw materials and production time required to produce a sample that cannot sufficiently suppress current leakage are wasted.

On the other hand, in the method for producing a barium dititanate composite oxide described in Patent Document 2, manganese dioxide powder is added later to the BaTi ₂ O ₅ powder already produced. However, it is thought that Mn is mainly substituted by Ti ⁴⁺ sites, and the molar ratio of Mn to Ba and Ti becomes non-stoichiometric. That is, the substitution element is not completely substituted in the barium dititanate-based composite oxide, and impurities may be generated.

  The present invention has been made in view of the above circumstances, and an object thereof is to obtain a barium dititanate-based composite oxide in which current leakage is suppressed. Also, a method for producing a barium dititanate composite oxide in which even if a substitution element is added after producing the barium dititanate composite oxide, the total amount of the added substitution element can be substituted in the barium dititanate composite oxide The purpose is to provide.

  The present invention provides the following means in order to solve the above problems.

Two barium titanate based composite oxide according to one embodiment of the present invention have the general _formula: in _{(Ba 1-x (A)} x) (Ti 1-y1-y2 (B1) y1 (B2) y2) 2 O 5 + z In the above general formula, (A) is at least one element selected from the group consisting of Ca, Rb, Sr, Cs, Fr and Ra, and (B1) is Nb. , Ta, V, and Mn, and (B2) is at least selected from the group consisting of Fe, Co, Ni, Ge, Se, Zr, Pd, Sn, and Hf. 1 element, x is 0 or more and less than 0.5, y ₁ is 0 or more and less than 0.1, y ₂ is more than 0 and less than 0.5, and y ₁ + y ₂ is more than 0 Largely less than 0.5, z is 0 or more and y ₁ or less It is.

In the barium dititanate-based composite oxide according to the above aspect, (B1) is one or more elements selected from Nb, Ta, V, or Mn. These elements have the same coordination number (coordination number 6) as Ti ⁴⁺ ions, and are close in ion radius. Therefore, Ti ⁴⁺ can be effectively replaced. In addition, since these substituted elements have a pentavalent valence in the oxide, the current leak tendency of the barium dititanate-based composite oxide is reduced.

In the above general formula, (B1) may contain at least Nb or Ta, and y ₁ = 0.001 ± 0.0005 may be satisfied. With this configuration, a necessary and sufficient charge can be effectively compensated for the valence change at the Ti ⁴⁺ site, so that the current leakage of the barium dititanate complex oxide can be reduced more effectively. .

  The barium dititanate-based composite oxide may have a relative density of 95% or more with respect to a true density and an average grain diameter of less than 1 μm. With this configuration, the grain boundary resistance can be secured with sufficient grain boundary density, and the cause of leakage current such as surface current and creeping current can be reduced. It can be effectively reduced.

Another two-barium titanate-based composite oxide according to aspects of the present invention consists of the general formula _{(Ba 1-x (A)} x) (Ti 1-y1 (B1) y1) composition represented by _{2 O 5 + z} In the above general formula, (A) is at least one element selected from the group consisting of Ca, Rb, Sr, Cs, Fr and Ra, and (B1) is Nb, Ta, V and It is at least one element selected from the group consisting of Mn, x is 0 or more and less than 0.5, y ₁ is 0 or more and less than 0.1, and z is 0 or more and y ₁ or less.

  In the barium dititanate-based composite oxide according to the above aspect, (B1) is substituted with a predetermined element, and these substituted elements have a pentavalent valence in the oxide, Current leakage tendency of the barium titanate-based composite oxide is reduced.

Two production method of barium titanate according to one aspect of the present invention is a method of manufacturing according to the above aspect two barium titanate based composite oxide, Ba (B1) and _{2 O 6 (Ba 1-x} (A _X ) (Ti _1-y2 (B2) _y2 ) ₂ O ₅ is _subjected to a solid phase reaction at a molar ratio of y ₁ : 1-y ₁ .

  According to this method, after the production of the barium dititanate-based composite oxide, element substitution can be further performed later. In addition, the method can be designed so that the total amount of the substitution element to be added can be substituted in the barium dititanate-based composite oxide. Further, the obtained barium dititanate-based composite oxide has reduced current leakage.

In the method for producing a barium dititanate-based composite oxide according to the above aspect, the crystal structure of the Ba (B1) ₂ O ₆ may belong to an orthorhombic system. According to this method, Ba (B1) ₂ O ₆ and (Ba _1-x (A) _x ) (Ti _1-y2 (B2) _y2 ) ₂ O ₅ are more likely to react. Therefore, it becomes easy to substitute the entire amount of the substitution element to be added into the barium dititanate-based composite oxide.

Method of manufacturing a secondary barium titanate based composite oxide according to one embodiment of the present invention is a method of manufacturing according to the above aspect dititanate barium oxide, Ba (B1) and ₂ O ₆ (Ba _1-x (A) _x ) (Ti _1-y1 ) ₂ O ₅ is _subjected to a solid phase reaction at a molar ratio of y ₁ : 1-y ₁ .
According to this method, after the production of the barium dititanate-based composite oxide, element substitution can be further performed later. In addition, the method can be designed so that the total amount of the substitution element to be added can be substituted in the barium dititanate-based composite oxide. Further, the obtained barium dititanate-based composite oxide has reduced current leakage.

  The barium dititanate-based composite oxide according to the above aspect can suppress current leakage and can be used for various applications. Moreover, according to the barium dititanate-based composite oxide according to the above aspect, the barium dititanate-based composite oxide in which current leakage is suppressed can be manufactured at a low cost. Moreover, the purity of the barium dititanate-based composite oxide obtained can be increased.

It is a flowchart which shows an example of the manufacturing method of the barium dititanate complex oxide which concerns on 1 aspect of this invention. It is a figure which shows an example of the polarization (P) -electric field (E) curve of the barium dititanate which concerns on the comparative example 1 of this invention. It is a figure which shows an example of the polarization (P) -electric field (E) curve of the barium dititanate type complex oxide which concerns on Example 3 of this invention.

  Hereinafter, the configuration of the present embodiment will be described with reference to the drawings. The materials, methods, and the like exemplified in the following description are examples, and the present invention is not limited to them.

“First Embodiment”
(Barium dititanate complex oxide)
Two barium titanate based composite oxide according to the first embodiment, the general _{formula: (Ba 1-x (A} ) x) (Ti 1-y1-y2 (B1) y1 (B2) y2) represented by _{2 O 5 + z} Including polycrystals.

  (A) is at least one element selected from the group consisting of Ca, Rb, Sr, Cs, Fr and Ra. (B1) is at least one element selected from the group consisting of Nb, Ta, V and Mn, and more preferably at least one element of Nb or Ta. Furthermore, (B2) is at least one element selected from the group consisting of Fe, Co, Ni, Ge, Se, Zr, Pd, Sn, and Hf.

The coordination number of the elements listed in (B1) is 6, which is the same as Ti ⁴⁺ ions, and the ion radius is also close. For this reason, the elements listed in (B1) can be effectively replaced with Ti ⁴⁺ . The elements listed in (B1) have a pentavalent valence in the barium dititanate composite oxide. By replacing the Ti ⁴⁺ ion with an element that selects the pentavalent valence, current leakage is suppressed. This is thought to be because oxygen deficiency, which is considered to be the main cause of current leakage, and the accompanying valence change of Ti ⁴⁺ ions are compensated by the valence change of the substituted pentavalent element (valence compensation). . In the case of Nb or Ta as the element substituted as (B1), it was confirmed that current leakage was most suppressed.

The valence of the elements listed in (A) is 2 and the coordination number is 12. This valence and coordination number are the same as Ba ²⁺ ions. The elements listed in (A) have an ionic radius close to Ba ²⁺ ions. For this reason, the elements listed in (A) effectively replace Ba ²⁺ . When Ba ions are substituted with the elements listed in (A), the dielectric properties such as the dielectric constant and Curie temperature of the barium dititanate-based composite oxide change.

The valence of the elements listed in (B2) is 4 and the coordination number is 6. This valence and coordination number are the same as Ti ⁴⁺ ions. Further, the elements listed in (B2) have an ionic radius close to that of Ti ⁴⁺ ions. Therefore, Ti ⁴⁺ can be effectively replaced, and dielectric characteristics such as dielectric constant and Curie temperature can be effectively changed.

The subscript y ₁ in the above composition formula represents the substitution rate of the (B1) element at the Ti ⁴⁺ site. The substitution rate of (B1) element is preferably 0 or more and less than 0.1 (ie, 10%), and is in the range of 0.001 ± 0.0005 (ie, 0.1 ± 0.05%). More preferred. y ₂ represents the degree of substitution (B2) elements. (B2) The element substitution rate is in the range of greater than 0 and less than 0.5. However, y ₁ + y ₂ is greater than 0 and less than 0.5 (ie, 50%). x represents the substitution rate of the element (A) at the Ba ²⁺ site, and is 0 or more and less than 0.5. z is 0 or more and y ₁ or less.

(B1) When the element substitution rate y ₁ is 0 or more and less than 0.1, current leakage is suppressed. In particular, when the substitution rate y ₁ is in the range of 0.001 ± 0.0005, the highest current leakage suppression effect can be obtained. This is ^presumably because a necessary and sufficient charge can be effectively compensated for the valence change at the Ti ⁴⁺ site.
On the other hand, when y ₁ is 0.1 or more, the substitution amount of the pentavalent substitution element exceeds the generation rate of oxygen deficiency. As a result, the substitution element (B1) may contribute to current leakage.

(B2) When the element substitution rate y ₂ is greater than 0 and less than 0.5 and y ₁ + y ₂ is greater than 0 and less than 0.5, the main element of the element present in the Ti ⁴⁺ site is Ti It becomes. However, the upper limit of the substitution rate can vary depending on the type of element. Further, y ₂ may be set to 0 when no change in dielectric characteristics is required.

  The barium dititanate-based composite oxide according to the first embodiment preferably has a relative density of 95% or more with respect to the true density determined according to the above composition formula, and an average grain diameter of less than 1 μm. When the relative density with respect to the true density and the average grain diameter are within the above ranges, current leakage is more reliably suppressed. This is presumably because the grain boundary resistance can be secured by a sufficient grain boundary density and the factors of leakage current such as surface current and creeping current can be reduced.

  Here, “true density” means a density in which only the volume occupied by the substance itself is a volume for density calculation. Therefore, the “relative density with respect to the true density” means a relative value with respect to the true density of the particle density having the volume of the outer periphery of the particle having irregularities on the surface. The “average grain diameter” means the average diameter of grains when an arbitrary cross section of a barium dititanate-based composite oxide is measured with a scanning electron microscope (SEM). The “average grain diameter” is obtained from an average value obtained by measuring five grain sizes of arbitrary grains in a cross section taken with an image of 25000 times.

“Second Embodiment”
The barium dititanate _- based composite oxide according to the second embodiment is composed of a composition represented by the general formula: (Ba _1-x (A) _x ) (Ti _1-y1 (B1) _y1 ) ₂ O _{5 + z} Contains crystals. The barium dititanate composite oxide according to the second embodiment corresponds to the case of y ₂ = 0 of the barium dititanate composite oxide according to the first embodiment.

In the above general formula, (B1) is at least one element selected from the group consisting of Nb, Ta, V and Mn. Therefore, similarly to the barium dititanate-based composite oxide according to the first embodiment, the oxygen vacancies considered to be the main cause of current leakage and the valence change of Ti ⁴⁺ ions associated therewith are substituted pentavalent valences. It can be compensated by valence change of elements (valence compensation). Therefore, the barium dititanate complex oxide according to the second embodiment can suppress current leakage. Further, when Nb or Ta is used as the element substituted as (B1), current leakage is most suppressed.

In the above general formula, (A) is at least one element selected from the group consisting of Ca, Rb, Sr, Cs, Fr and Ra. Similar to the barium dititanate-based composite oxide according to the first embodiment, the elements listed in (A) can be effectively replaced with Ba ²⁺ . The range of y _1, the relative density for new density of the composition, for the average grain diameter, it is preferable to adopt the same range and secondary barium titanate based composite oxide according to the first embodiment.

(Method for producing barium dititanate-based composite oxide)
A method for producing a barium dititanate-based composite oxide according to this embodiment will be described with reference to FIG. FIG. 1 is a process flow diagram showing an example of a method for producing a barium dititanate-based composite oxide according to this embodiment. This manufacturing method includes a first weighing step S1, a first mixing step S2, a first heat treatment step S3, a second weighing step S4, a second mixing step S5, a second heat treatment step S6, a pulverizing step S7, a compacting step S8, It has a sintering step S9 and an annealing step S10. In addition, when the Ba (B1) ₂ O ₆ obtained in the first weighing step S1 to the first heat treatment step S3 is obtained from the outside and substituted, the first weighing step S1 to the first heat treatment step S3 can be omitted. Further, when the barium dititanate-based composite oxide obtained in the second heat treatment step has a relative density of 95% or more, the pulverization step S7 to the annealing step S10 can be omitted.

In the first weighing step S1, the compound containing Ba element and the oxide containing (B1) are weighed so that the atomic ratio (B1) / Ba of (B1) to Ba is in the range of 2 ± 0.2. To do. It is more preferable to weigh the atomic ratio (B1) / Ba to be 2. The compound containing Ba element may contain O, H, and / or C in addition to Ba. For example, BaCO ₃ , Ba (OH), and BaO are listed as compounds containing the Ba element. In the compound containing Ba element, it is preferable that elements other than Ba are only O, H, and / or C. When these elements are only these elements, no impurities are generated in the product. The oxide containing (B1) is a simple substance or a mixture of oxides containing at least one element (B1) selected from the group consisting of Nb, Ta, V and Mn. For example, when either Nb or Ta is adopted as (B1), Nb ₂ O ₅ , Ta ₂ O ₅ , or a composite oxide or mixture thereof can be used. In the first mixing step S2 described later, the amount of these raw materials is such that (B1) / Ba satisfies 2 ± 0.2 in the range where (B1) / Ba satisfies 2 ± 0.2. The amount of Ba can be adjusted as appropriate. In addition, a solid or liquid additive may be mixed with the raw material as necessary within a range that does not affect the composition of the product.

  In the first mixing step S2, the weighed product obtained in the first weighing step S1 is uniformly mixed. The mixing operation may be dry or wet, and may be manual or mechanical. For example, mixing operations such as container rotation type, container swing type, ribbon type, screw type, paddle type, high speed flow type, rotating disk type, wheel type, air flow type, liquid flow type, weight type, stir bar type, etc. Can be used.

  The first mixing step S2 also involves pulverization of particles when the raw material is powder. The average particle diameter of the mixed powder finally obtained in this step is preferably 10 to 700 nm. By setting the average particle size to 700 nm or less, the processing efficiency in the first heat treatment step S3 described later is improved. As a result, a very standard electric furnace can be used. Further, by setting the average particle size to 10 nm or more, the particles can be sufficiently larger than the lattice constant, and the crystal structure of the raw material can be maintained.

  Examples of the mixing method involving particle pulverization include a mill type, a blade type, a raid type, a stone mortar type, a mortar type, and a crusher type. In the case of wet processing, it is preferable to use a liquid medium that prevents adhesion between particles as a dispersion medium or a solvent, and it is more preferable to use a medium having a low viscosity. For example, as a liquid medium, water, alkanes, alcohols, ketones, aromatic or other organic solvents, or a mixture or mutual solution thereof can be preferably used.

In the first heat treatment step S3, the mixture obtained in the first mixing step S2 is heated and reacted to obtain a compound represented by a composition formula Ba (B1) ₂ O ₆ containing one or more types of (B1). As an example of Ba (B1) ₂ O ₆ , barium diniobate (composition formula BaNb ₂ O ₆ ) when Nb is adopted for (B1), and barium ditantalate when Ta is adopted for (B1) (composition) Formula BaTa ₂ O ₆ ) or a composite oxide thereof. The crystal structure of Ba (B1) ₂ O ₆ obtained in the first heat treatment step S3 is preferably orthorhombic or monoclinic, and more preferably orthorhombic. Since the crystal structure of Ba (B1) ₂ O ₆ is orthorhombic or monoclinic, particularly orthorhombic, it becomes easy to obtain a barium dititanate-based composite oxide in the second heat treatment step S6 described later. When the crystal structure of Ba (B1) ₂ O _{6 is} a monoclinic crystal, it is easily incorporated into the same monoclinic barium dititanate-based complex oxide in the second heat treatment step S6 described later. Further, when the crystal structure of Ba (B1) ₂ O ₆ is orthorhombic, it becomes easy to activate at a high temperature, and is more easily incorporated into the barium dititanate complex oxide than other crystal structures.

As heat treatment conditions, the atmosphere is preferably an oxygen-containing atmosphere such as air or oxygen. The heat treatment temperature is preferably 800 to 1150 ° C, and more preferably 800 to 1050 ° C. By setting the heat treatment temperature to 800 to 1050 ° C., a compound represented by the composition formula Ba (B1) ₂ O ₆ mainly composed of orthorhombic crystals can be obtained, and by setting the heat treatment temperature to 1050 ° C. to 1150 ° C. A compound represented by the composition formula Ba (B1) ₂ O ₆ mainly composed of oblique crystals can be obtained. When the reaction accompanying the heat treatment is generally a solid phase reaction that is extremely slow, the yield can vary depending on the type or particle size of the raw material. In order to maximize the yield, it is preferable to adjust the treatment temperature or treatment time within the above range. On the other hand, the elements selected for (B1) are limited, and if the average particle size is adjusted in the range of 10 to 700 nm in the first mixing step S2, a sufficient yield can be obtained even in the above temperature range. Can do. In particular, when (B1) is Nb or Ta, there is no significant difference in processing temperature and processing time. The processing time is approximately several hours and within a few days at the most, and it is a very standard range in the industry.

In the second weighing step S4, the compound represented by the composition formula Ba (B1) ₂ O ₆ obtained in the first heat treatment step S3 and the barium dititanate complex oxide are weighed. The two barium titanate based composite oxide are weighed in step S4 is a composition formula _{(Ba 1-x (A)} x) (Ti 1-y2 (B2) y2) represented by 2 _{O 5.} (A) is at least one element selected from the group consisting of Ca, Rb, Sr, Cs, Fr and Ra. x is 0 or more and less than 0.5. (B2) is at least one element selected from the group consisting of Fe, Co, Ni, Ge, Se, Zr, Pd, Sn, and Hf. y ₂ is 0 to less than 0.5. y ₂ is set in consideration of the sum of the _{y 1,} y 1 + _{y 2} is in the range of greater than 0 and less than 0.5. However, the upper limit of the substitution rate y ₁ varies depending on the type of (B2). For example, in the case of Zr, empirically y ₁ is about 0.08. Examples of (Ba _1-x (A) _x ) (Ti _1-y2 (B2) _y2 ) ₂ O ₅ include BaTi ₂ O ₅ , (Ba _0.99 Sr _0.01 ) Ti ₂ O ₅ , Ba (Ti _0.94 Zr _0.06 ) ₂ O _{5 and the} like. These can be obtained by a conventional method for producing a barium dititanate composite oxide.

The molar fraction of the compound represented by the composition formula Ba (B1) ₂ O ₆ with respect to the sum of the two kinds of compounds to be weighed is expressed as (B1) at the Ti ⁴⁺ site in the barium dititanate-based composite oxide which is the production purpose. to correspond to the substitution rate y ₁ and weighed. For example, the case of obtaining the final _{Ba (Ti 1-y1 Nb y1} ) 2 O 5 + z, the BaNb ₂ O ₆ and BaTi ₂ O ₅ as raw materials in the second weighing step _{S4, BaNb 2 O 6: BaTi} 2 O 5 = Y ₁ : Weigh as 1-y ₁ However, _{y 1} is less than 0.1 0 or more, preferably a value in the range of 0.001 ± 0.0005 (i.e. 0.1 ± 0.05%). By y ₁ is less than 0.1, (B1) becomes possible substitution charged amount of (B2) to the ^{Ti 4+} sites. Furthermore, by setting y ₁ in the range of 0.001 ± 0.0005, the effect of suppressing current leakage of the barium dititanate-based composite oxide obtained in the second heat treatment step S6 described later is maximized.

  In the second mixing step S5, the weighed product obtained in the second weighing step S4 is uniformly mixed. As the mixing method, the method mentioned in the first mixing step S2 can be adopted. The same applies to the case where the raw material is powder, and the average particle size of the mixed powder finally obtained in this step is preferably 10 to 500 nm. By setting the average particle size to 500 nm or less, the processing efficiency in the second heat treatment step S6 described later is improved. Moreover, the density of the obtained product can be set to a desired density. On the other hand, the average particle size is preferably 10 nm or more, which is sufficiently larger than the lattice constant.

In the second heat treatment step S6, the mixture obtained in the second mixing step S5 is heated to obtain a barium dititanate-based composite oxide. In the second heat treatment step S6, composition formula _{(Ba 1-x (A)} x) (Ti 1-y1-y2 (B1) y1 (B2) y2) 2 O 5 + two barium titanate based composite oxide represented by _z Is obtained as the main component. y ₁ and _{y 2} is a value determined by the second weighing step S4. z is approximately equal to _{y 1.}

  Any heat treatment apparatus may be used as long as it can be heated to several hundred degrees Celsius or higher and can cause a reaction between raw materials, and an electric furnace or kettle can be suitably used. In addition to obtaining the same effect, an effect accompanied by high density of the sample such as sintering may occur, and a spark / plasma sintering apparatus, a hot press apparatus, or the like may be employed. The treatment atmosphere may be atmospheric air, vacuum, an inert gas such as nitrogen or argon, or a water vapor atmosphere, but an oxygen-containing atmosphere such as air or oxygen is more preferable. When an atmosphere lacking oxygen such as a vacuum or an inert gas is employed and heat treatment accompanied by sintering is performed, it is necessary to add an annealing step S10 described later after the treatment in order to sufficiently suppress current leakage.

The heat treatment temperature is preferably 750 to 1100 ° C. By selecting the temperature range, a barium dititanate composite oxide can be obtained as a main component. The yield can vary depending on the raw material particle size and element substitution rate. Therefore, in maximizing the yield, the processing temperature and processing time may be adjusted within the above ranges. Especially if _{y 1} is 0.001 ± 0.0005, the large difference without treatment temperature and treatment time easily adjusted within the above range. The processing time is a very standard range in the industry, such as approximately several hours, at most within a few days.

  When the second heat treatment step S6 is performed without sintering, it is preferable to add a later-described sintering step S9. Along with the sintering step S9, a pulverizing step S7, a compacting step S8, and an annealing step S10 may be added as necessary. The relative density after sintering is preferably 95% or more of the true density, and the average diameter of the grains is preferably less than 1 μm at most. As a result, the effect of suppressing current leakage is easily ensured.

  In the pulverization step S7 added as necessary, the barium dititanate-based composite oxide obtained in the second heat treatment step S6 can be pulverized. The pulverizing apparatus and conditions are the same as in the second mixing step S5. The same applies to the average particle diameter obtained after pulverization, and it is preferably 10 to 500 nm. Thereby, it becomes easy to obtain a relative density of 95% or more with respect to the true density in the sintering step S9 described later.

In the compacting step S8 added as necessary, the barium dititanate-based composite oxide obtained as a powder in the second heat treatment step S6 to the pulverization step S7 is compacted. Thereby, the processing efficiency in sintering process S9 mentioned later improves. As the compacting method, an isotropic compression method or a binder method can be used, and the isotropic compression method is particularly preferable. Further, a sintering aid may be added in the compacting step S8. In the case of the isotropic compression method, a pressure of several hundred MPa can be applied, regardless of whether it is cold or hot, wet or dry. When the pressure in the compacting step S8 is several tens of MPa or less, the processing efficiency decreases in the sintering step S9 described later. Further, in the case of the binder method, a binder having a high surface tension or viscosity is mixed at several volume% or less. When the mixing ratio exceeds several volume%, it becomes difficult to increase the density in the sintering step S9 described later, or impurities are likely to be generated. When adding a sintering aid, the amount of the sintering aid to be mixed is preferably several mass% or less. Examples of the sintering aid include zirconium dioxide (ZrO ₂ ) or boron oxide (B ₂ O ₃ ). When the amount of the sintering aid is more than several mass%, it becomes difficult to increase the density in the sintering step S9 described later, and impurities are easily generated. Moreover, you may combine the above-mentioned compacting method.

  In the sintering step S9 added as necessary, the barium dititanate-based composite oxide obtained in any of the previous steps (S6 to S8) is sintered, and the relative density with respect to the true density is set to 95% or more. . As the heat treatment apparatus, an electric furnace, a kettle, a spark / plasma sintering apparatus, a hot press apparatus, or the like can be suitably used. The treatment atmosphere may be air, vacuum, an inert gas such as nitrogen or argon, or a water vapor atmosphere. When an atmosphere lacking oxygen such as a vacuum or an inert gas is employed, an annealing step S10 described later is added after the processing in order to ensure a current leakage suppressing effect.

The sintering temperature is preferably 950 to 1300 ° C, and more preferably 1000 to 1250 ° C. By setting the sintering treatment temperature to 950 to 1230 ° C., the barium dititanate-based composite oxide is the main component, and the relative density to the true density can be 95% or more. If the temperature is lower than 950 ° C., it is difficult to increase the density, and if it is 1300 ° C. or higher, it is difficult to keep the barium dititanate-based composite oxide as a main component. Further, the processing efficiency may be improved by applying pressure. When the sintering temperature is 950 to 1150 ° C., it is preferable to apply a pressure of several tens to several hundreds of MPa. It has also been reported that BaTi ₂ O ₅ can be destabilized at 1150 ° C. to 1200 ° C. and 1230 ° C. or higher. When processing near this temperature, it is preferable to process within several tens of hours under normal pressure, or within several tens of minutes under pressure that improves processing efficiency. Since the sintering treatment temperature at which the treatment efficiency can be optimized can vary depending on the element substitution rate and additives, the treatment temperature and treatment time may be adjusted within the above ranges.

  In the annealing step S10 added as necessary, deficient oxygen can be compensated by annealing the barium dititanate-based composite oxide obtained in the previous steps (S6 to S9). For example, an electric furnace or a kettle can be suitably used as the annealing apparatus. About processing atmosphere, the gas containing oxygen should just be used, air can be used conveniently, and the gas whose oxygen partial pressure is higher than air can be used more suitably. In order to further improve the processing efficiency, an oxygen inflow atmosphere is preferable. The annealing treatment temperature is preferably 800 to 1150 ° C, and more preferably 1000 ° C ± 50 ° C. By setting the processing temperature to 1000 ° C. ± 50 ° C., the risk of composition change can be minimized and sufficient oxygen can be supplied. The processing time is a very standard range in the industry, such as approximately several hours or less, and at most several days.

Example 1
As the first weighing step S1, barium carbonate (BaCO ₃ ) powder and niobium oxide (Nb ₂ O ₅ ) powder were weighed. Weighing was performed after drying at 300 ° C. or lower and 700 ° C. or lower, respectively. 74.00 g of barium carbonate (BaCO ₃ ) powder and 78.12 g of niobium oxide (Nb ₂ O ₅ ) powder were weighed.

  The two kinds of raw material powders weighed in the first weighing step S1 were put in a hard ceramic pot together with hard ceramic beads and water, and mixed and pulverized by a planetary ball mill (first mixing step S2). The mixed sample was sieved to remove the beads and then dried. The particle size of the obtained sample was 10 nm to 700 mm.

Next, the mixed powder obtained in the first mixing step S2 was heated in air at 800 to 1150 ° C. to obtain barium niobate (BaNb ₂ O ₆ ) as a main component (first heat treatment step S3). When the temperature condition in the first heat treatment step S3 was changed, it was found that the diniobic acid at 800 to 1050 ° C. from the powder X-ray diffraction (XRD) pattern of the sample obtained by heat treatment at a constant temperature in the range of 450 to 1250 ° C. It was confirmed that barium was obtained as the main component. Further, it was confirmed that orthorhombic crystals were obtained at 800 to 1050 ° C. and monoclinic crystals were obtained at 1050 to 1150 ° C.

Next, in the second weighing step S4, the produced barium diniobate and barium dititanate (BaTi ₂ O ₅ ) were dried at 700 ° C. or lower and then weighed. 8.80 g of barium diniobate was weighed and 125.0 g of barium dititanate (BaTi ₂ O ₅ ) was weighed.

  The powder weighed in the second weighing step S4 was put in a hard ceramic pot together with hard ceramic beads and water, and mixed and pulverized by a planetary ball mill (second mixing step S5). The sample after mixing was sieved to remove the beads and dried. The particle size of the obtained sample was 10 nm to 500 mm.

Next, the mixed powder obtained in the second mixing step S5 was heated in air at 750 to 1100 ° C. using an electric furnace, and the barium dititanate complex oxide (Ba (Ti _0.95 Nb _0.05 ) ₂ O _{5 + z} ) as a main component was obtained (second heat treatment step S6). When the temperature condition in the second heat treatment step S6 was changed, a barium dititanate-based composite oxide was obtained as a main component from the powder XRD pattern of the sample obtained by heat treatment at a constant temperature in the range of 750 to 1100 ° C. The sample obtained by heat treatment at 900 to 925 ° C. was particularly high purity.

  Thereafter, in the sintering treatment step S9, the barium dititanate composite oxide powder is treated at 1050 ° C. and 30 MPa in a vacuum using a spark plasma sintering furnace, and the relative density to the true density is 95% without thermal decomposition. The above samples were obtained.

  Finally, in the annealing step S10, the barium dititanate-based composite oxide sintered body is annealed in the air at 800 to 1000 ° C. using an electric furnace, and a white sample having a relative density of 95% or more with respect to the true density without thermal decomposition. Got.

The dielectric loss tangent of the sintered body of the barium dititanate-based composite oxide represented by the composition Ba (Ti _0.95 Nb _0.05 ) ₂ O _{5 + z} prepared in Example 1 was determined. The dielectric loss tangent was obtained from the measurement of impedance. The results are shown in Table 1.

(Example 2)
In Example 2, dititanic acid was used under the same conditions as in Example 1 except that in the second weighing step S4, the weighing ratio of barium diniobate and barium dititanate (BaTi ₂ O ₅ ) was changed. A barium-based composite oxide was prepared. The composition formula of the obtained barium dititanate-based composite oxide was Ba (Ti _0.999 Nb _0.001 ) ₂ O _{5 + z} . The dielectric loss tangent of the obtained barium dititanate-based composite oxide sintered body was determined. The results are shown in Table 1.

Example 3
In Example 3, dititanate was used under the same conditions as in Example 1 except that the weighing ratio of barium diniobate and barium dititanate (BaTi ₂ O ₅ ) was changed in the second weighing step S4. A barium-based composite oxide was prepared. The composition formula of the obtained barium _dititanate- based composite oxide was Ba (Ti _0.9995 Nb _0.0005 ) ₂ O _{5 + z} . The dielectric loss tangent of the obtained barium dititanate-based composite oxide sintered body was determined. The results are shown in Table 1.

(Example 4)
In Example 4, in a second weighing step S4, was produced by the manufacturing method of the conventional two barium titanate based composite oxide in place of the two barium titanate _{(BaTi 2 O 5) (Ba} 1-10 / 999 Ca 10 _{/ 999} ) (Ti _{1-59 / 999} Zr _59/999 ) ₂ O ₅ and _dititanic acid under the same conditions as in Example 1 except that the weighing ratio of the substance to barium _diniobate was changed. A barium-based composite oxide was prepared. The composition formula of the obtained barium dititanate-based composite oxide was (Ba _0.99 Ca _0.01 ) (Ti _0.94 Zr _0.059 Nb _0.001 ) ₂ O _{5 + z} . The dielectric loss tangent of the obtained barium dititanate-based composite oxide sintered body was determined. The results are shown in Table 1.

(Comparative Example 1)
In Comparative Example 1, only the first weighing step S1 and the first mixing step S2 were performed to produce barium dititanate. The composition formula of the obtained barium dititanate-based composite oxide was BaTi ₂ O ₅ . The dielectric loss tangent of the obtained sintered body of barium dititanate-based composite oxide was determined. The results are shown in Table 1.

  From these results, all of the barium dititanate composite oxides according to Examples 1 to 4 exhibited a lower dielectric loss tangent than the barium dititanate composite oxide according to Comparative Example 1. That is, in the barium dititanate-based composite oxide shown in Examples 1 to 4, current leakage is suppressed. In addition, the barium dititanate-based composite oxides according to Examples 1 to 4 all have a volume resistivity at a 100 Hz AC voltage at room temperature of the order of several tens of MΩ · cm, and current leakage is sufficiently suppressed. It had been.

  Moreover, about the sintered compact of the barium dititanate-type complex oxide which concerns on Examples 1-4 and the comparative example 1, change of polarization (P) with respect to an electric field (E) (henceforth, PE) for ferroelectric characteristic evaluation Curve). The PE curves measured by the double wave method for the samples according to Comparative Example 1 and Example 3 are shown in FIGS. 2 and 3, respectively. Compared to the sample according to Comparative Example 1, the circular curve was greatly reduced, and a hysteresis curve characterized by ferroelectricity was obtained. Also from this result, it is shown that the current leakage of the barium dititanate composite oxide according to Examples 1 to 4 is suppressed as compared with the barium dititanate composite oxide of Comparative Example 1. .

S1 ... first weighing step, S2 ... first mixing step, S3 ... first heat treatment step, S4 ... second weighing step, S5 ... second mixing step, S6 ... second heat treatment step, S7 ... grinding step, S8 ... pressure Powder process, S9 ... Sintering process, S10 ... Annealing process

Claims (7)

Including a polycrystal composed of a composition represented by the general formula: (Ba _1-x (A) _x ) (Ti _1-y1-y2 (B1) _y1 (B2) _y2 ) ₂ O _{5 + z} ,
In the general formula, (A) is at least one element selected from the group consisting of Ca, Rb, Sr, Cs, Fr and Ra,
(B1) is at least one element selected from the group consisting of Nb, Ta, V and Mn;
(B2) is at least one element selected from the group consisting of Fe, Co, Ni, Ge, Se, Zr, Pd, Sn and Hf,
x is 0 or more and less than 0.5, y ₁ is 0 or more and less than 0.1, y ₂ is greater than 0 and less than 0.5, and y ₁ + y ₂ is greater than 0 and less than 0.5. , z is two barium titanate based composite oxide, wherein is 0 or more y ₁ below. 2. The barium dititanate-based composite oxide according to claim 1, wherein (B1) in the general formula includes at least Nb or Ta, and y ₁ = 0.001 ± 0.0005.   3. The barium dititanate-based composite oxide according to claim 1, wherein the composition has a relative density of 95% or more with respect to a true density and an average grain diameter of less than 1 μm. Including a polycrystal composed of a composition represented by the general formula (Ba _1-x (A) _x ) (Ti _1-y1 (B1) _y1 ) ₂ O _{5 + z} ,
In the general formula, (A) is at least one element selected from the group consisting of Ca, Rb, Sr, Cs, Fr and Ra,
(B1) is at least one element selected from the group consisting of Nb, Ta, V and Mn;
x is 0 or more and less than 0.5, y ₁ is 0 or more and less than 0.1, and z is 0 or more and y ₁ or less. A method for producing a barium dititanate-based composite oxide according to any one of claims 1 to 3,
Ba (B1) ₂ O ₆ and (Ba _1-x (A) _x ) (Ti _1-y2 (B2) _y2 ) ₂ O ₅ are _subjected to a solid phase reaction at a molar ratio of y ₁ : 1-y _1. The manufacturing method of the barium dititanate type complex oxide characterized by including this. 6. The method for producing a barium dititanate-based composite oxide according to claim 5, wherein the crystal structure of Ba (B1) ₂ O ₆ belongs to an orthorhombic system. A method for producing a barium dititanate-based composite oxide according to claim 4,
Ba (B1) ₂ O ₆ and (Ba _1−x (A) _x ) (Ti _1−y1 ) ₂ O ₅ are included in a solid phase reaction at a molar ratio of y ₁ : 1−y _1. A method for producing a barium dititanate composite oxide, which is characterized.

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