JP2002121069A - Sintered compact of bismuth layered compound and method of producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sintered compact of a bismuth layered compound, which has large piezoelectric characteristics and low dispersion in the piezoelectric characteristics. SOLUTION: The sintered compact 1 of the bismuth layered compound, containing, as main crystal 2, flat grains 2 of the bismuth layered compound, expressed by general formula: (Bi2O2)2+(Am-1BmO3m+1)2- (where, A is at least one selected from the group of alkali metals, alkaline earth metals and lead and B is at least one selected from the group of metals of groups 4a and 5a) and having a face A perpendicular to the orientation direction oriented to crystal face perpendicular to face c, is produced. In the sintered compact 1 of the bismuth layered compound, the ratio of grains of the crystal 2, present at the face A perpendicular to the orientation direction and each having a major diameter d satisfying formula: 0.5d<=d<=2d (d is an average major diameter of the main crystal 2), is >=80%, based on the grains of the main crystal 2 present at the face A perpendicular to the orientation direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention has a high Curie temperature, excellent piezoelectric characteristics, and good temperature characteristics.
Bismuth layered compound sintered body suitable for oscillators, ultrasonic transducers, ultrasonic motors, or piezoelectric sensors such as acceleration sensors, knocking sensors, and AE sensors, and particularly suitable for use as a piezoelectric material for resonators of high-frequency resonators And its manufacturing method.

[0002]

2. Description of the Related Art Conventionally, as piezoelectric ceramic compositions used for filters, resonators, oscillators, ultrasonic oscillators, ultrasonic motors, piezoelectric sensors and the like, PbTiO ₃ and Pb (Z
r, Ti) O ₃ , Pb (Mn _1/3 Nb _2/3 ) O ₃ or Pb (N
Piezoelectric ceramic materials containing a large amount of lead such as i _1/3 Nb _2/3 ) O ₃ are widely used.

[0003] Since piezoelectric ceramic materials containing a large amount of lead are harmful to ecosystems, there is a strong demand for the development of piezoelectric ceramic materials having a low lead content from the viewpoint of environmental protection.

[0004] As such a piezoelectric ceramic material having a low lead content, a bismuth layered compound having a high Curie temperature, a large electromechanical coupling coefficient k ₃₃ and a large mechanical quality coefficient Q _m can be mentioned. Although application is expected, at present, the piezoelectric characteristics are lower than those of the lead-based piezoelectric ceramic materials, and improvement of the piezoelectric characteristics is desired.

On the other hand, such a bismuth layered compound easily polarizes in the direction perpendicular to the c-axis (there is an easy polarization axis), so that the anisotropy of the piezoelectric characteristics is large and the crystal is oriented with respect to a specific plane. By doing so, it is known that a large k value comparable to the above-mentioned lead-based piezoelectric ceramic material can be obtained in a direction perpendicular to the c-axis.

For example, Japanese Patent Application Laid-Open No. 52-86198 describes that the piezoelectric characteristics can be improved by hot-press firing to orient a main crystal in a bismuth layered compound sintered body along the c-axis. Also, Japanese Patent Application Laid-Open No. 6-107448 discloses that a bismuth layered compound calcined powder is supplied into a mold and uniaxially molded (press molded) at a high molding pressure of 200 MPa or more, so that the powder is oriented in the pressing axial direction. It describes that the sensitivity of piezoelectricity can be increased by preparing a molded body and a sintered body in which main crystals are oriented so that c-axes are aligned in parallel, that is, the main plane is c-plane oriented.
Further, in Japanese Patent Application Laid-Open No. 2000-34192, a plate-like seed crystal powder such as Bi ₄ Ti ₃ O ₁₂ and a ceramic raw material powder such as CaCO ₃ and TiO ₂ are mixed, formed into a plate, and then fired. CaBi ₄ T with increased relative density and degree of orientation in the c-axis direction without using hot pressing or the like
It describes that a bismuth layered compound sintered body such as i ₄ O ₁₅ can be produced.

[0007]

However, in the method using a hot press disclosed in Japanese Patent Application Laid-Open No. 52-86198, although the degree of orientation is increased, the productivity is poor and the relative density is high due to the reaction with a die or the like. It is difficult to obtain a sintered body, and a large residual stress remains in the sintered body, resulting in cracking or chipping, resulting in poor production yield. There has been a problem that the grain size of the main crystal in the body cannot be made uniform and the piezoelectric characteristics vary.

In the method of Japanese Patent Application Laid-Open No. 6-107448, in which the calcined powder is oriented by uniaxial pressing, 200
A special device for generating a very high pressure of MPa or higher is required, and the surface of the molded product (contact surface with the mold)
Only in the vicinity, the degree of orientation can be sufficiently increased, and since the density and the degree of orientation between the surface and the inside of the molded body are not uniform, the piezoelectric properties of the sintered body cannot be said to be sufficient, The variation was large.

Further, in the method using a plate-like seed crystal disclosed in Japanese Patent Application Laid-Open No. 2000-34192,
Due to the presence of other raw material powders such as CO ₃ and TiO ₂ , it is difficult to uniformly disperse the plate-like seed crystal in the slurry, so that the degree of orientation of the seed crystal partially varies, Further, since it is necessary to fire at a high temperature so that the seed crystal and the sintering aid component react sufficiently, B
Since there is a possibility that the composition may partially deviate due to volatilization of i, there is a problem that the piezoelectric characteristics of the sintered body also vary.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a bismuth layered compound sintered body having large piezoelectric characteristics and small variations in piezoelectric characteristics.

[0011]

Means for Solving the Problems As a result of studying the above problem, the present inventor has found that a high magnetic field is applied in a specific direction to a slurry obtained by adding a solvent to a powder containing at least 90% by weight of a bismuth layered compound. By applying the bismuth, the bismuth layered compound crystal belonging to the nonmagnetic material can be oriented in a specific direction so that the c-axis is perpendicular to the direction of the application of the magnetic field. As a result, the present inventors have found that a bismuth layered compound sintered body in which flat main crystals having a uniform particle size are oriented in a specific direction can be produced, and high and low-variation piezoelectric characteristics can be achieved.

That is, the bismuth layered compound sintered body of the present invention has a general formula of (Bi ₂ O ₂ ) ²⁺ (A _m-1 B _m O _{3m + 1} ) ^2-
(However, A: at least one selected from the group consisting of alkali metals, alkaline earth metals and lead, B: at least one selected from the group consisting of 4a metals or 5a metals, m> 1) Is a sintered body having a plane perpendicular to the orientation direction oriented in a crystal plane direction perpendicular to the c-plane as a main crystal composed of flat particles consisting of: 0.5d _a ≦ d ≦ 2d
_a (d _a mean major diameter of the main crystal) is characterized in that the percentage of crystals satisfying is not less than 80% of the total primary crystals.

Here, in the X-ray diffraction intensity of the plane perpendicular to the orientation direction, (I ₍₀₂₀₎ + I _{(220 )} ) / (I ₍₀₂₀₎ +
I ₍₂₂₀₎ + I ₍₀₀₆₎ + I ₍₀₀₈₎ + I ₍₀₀₁₀₎ ) is not less than 0.75, the orientation f _{1 on} the surface perpendicular to the orientation direction, The degree of orientation f ₂ on the polished surface obtained by polishing the surface perpendicular to the orientation direction by 0.1 mm.
The ratio of (f ₂ / f ₁₎ is 0.8 or more, it is desirable that the relative density is 95% or more.

It is preferable that the ratio of the major crystal having a major axis of 20 μm or less be 80% or more, and the average aspect ratio of the main crystal be 3 to 10.

Further, in the method for producing a bismuth layered compound sintered body of the present invention, a slurry is prepared by adding a solvent to a powder containing at least 90% by weight of a bismuth layered compound as a ceramic raw material powder, and the slurry is unidirectionally mixed with the slurry. And applying a magnetic field of 1T or more to the slurry to solidify the slurry while orienting the bismuth layered compound powder in a crystal plane perpendicular to the c-plane, and then firing.

Here, it is desirable that the bismuth layered compound powder has an average particle size of 0.5 to 2.0 μm.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Sintered bismuth layer compound of the present invention
The body has the general formula (Bi_TwoO_Two)²⁺(A_m-1B_mO _{3m + 1})
^2-(However, A: alkali metal, alkaline earth metal and
At least one selected from the group consisting of lead, B: 4a metal or
Is at least one selected from the group of 5a metals)
Flat particles composed of a bismuth layered compound
Things.

Examples of the bismuth layer compound include, for example, P
bBi_FourTi_FourO_Fifteen(PBT), SrBi_FourTi_FourO_Fifteen(S
BT), BaBiTi_FourO_Fifteen(BBT), Na_0.5Bi
_4.5Ti_FourO_Fifteen(NBT), Na_0.475Ca_0.05Bi_4.475
Ti_FourO_Fifteen(NCBT), Bi _TwoSr₁Ca₁Cu_TwoO_y,
(Bi, Pb)_TwoSr_TwoCa_TwoCu_ThreeO_yEtc.
SrBi containing no lead and having large piezoelectric properties_Four
Ti_FourO_Fifteen(SBT), BaBiTi_FourO_Fifteen(BBT),
Na_0.5Bi_4.5Ti_FourO_Fifteen(NBT), Na_0.475Ca
_0.05Bi_4.475Ti_FourO_Fifteen(NCBT) as the main component
Or a composite compound thereof is desirable. In addition,
Some of these compounds are rare earth elements, Mn, and alkali metal elements.
Replacement with element enhances temperature characteristics, etc.
Preferred above.

According to the present invention, as shown in the schematic diagram of the bismuth layered compound sintered body of the present invention in FIG. 1, the bismuth layered compound sintered body 1 has a crystal plane perpendicular to the c-plane (A in FIG. 1).
Alignment direction perpendicular to a plane oriented in the plane) (hereinafter, merely having abbreviated.) And the alignment perpendicular plane of the main crystal 2 in the alignment direction perpendicular to the plane A, the average long diameter d _a On the other hand, a major feature is that the proportion of crystals whose major axis d satisfies 0.5d _a ≦ d ≦ 2d _a is at least 80%, particularly at least 90%, of all main crystals. In addition, a sintered body having small variations in characteristics is obtained. In addition,
The plane perpendicular to the orientation direction in the present invention, the peak intensity ratio of the specific crystal plane is the maximum when X-ray diffraction measurement is performed on the sintered body from a specific direction and the peak intensity ratio of each peak is compared. This is what it means.

[0020] That is, the distribution of the major diameter d is outside the above range, in particular, the piezoelectric property is lowered when the diameter d is the ratio of the small main crystal 2 is increased than 0.5d _a, diameter d is greater than 2d _a When the proportion of the main crystal 2 increases, the variation in piezoelectricity increases and the strength of the sintered body decreases.

Further, in order to enhance the piezoelectricity, the X-ray diffraction intensity of the plane A perpendicular to the orientation direction is, for example, specifically, the degree of orientation f of the (020) plane and the (220) plane is 0.1 mm.
It is desirably 75 or more, especially 0.80 or more, and more preferably 0.90 or more. The degree of orientation f of the present invention is X
A plane A (crystal plane perpendicular to the c-plane) perpendicular to the orientation direction of the bismuth layered compound obtained by line diffraction (020);
(220) plane diffraction intensity and c-plane (006), (0)
08), diffraction intensity ratio on the (0010) plane (I ₍₀₂₀₎
+ I ₍₂₂₀₎ ) / (I ₍₀₂₀₎ + I ₍₂₂₀₎ + I ₍₀₀₆₎ + I ₍₀₀₈₎
+ I ₍₀₀₁₀₎ ).

That is, according to the present invention, the degree of orientation f ′ (f ′ = 1−f) of the c-plane on the plane A perpendicular to the orientation direction is 0.25 or less, particularly 0.20 or less, and more preferably 0.10 or less. It is as follows. Conversely, the degree of c-plane orientation is relatively high in the plane perpendicular to the plane A perpendicular to the orientation direction, and the piezoelectric characteristics in the plane perpendicular to the plane A perpendicular to the orientation direction are improved. The plane A perpendicular to the orientation direction is a plane perpendicular to the direction in which a magnetic field described later is applied.

Further, in order to enhance the piezoelectricity and reduce the variation, the degree of orientation f ₁ of the surface of the surface A perpendicular to the orientation direction and the surface of the surface A perpendicular to the orientation direction are set to 0.1 mm.
Ratio (f ₂ / f ₁ ) to the degree of orientation f ₂ on the polished surface
Is preferably 0.8 or more, particularly 0.9 or more, and more preferably 0.95 or more.

Further, in order to increase the piezoelectricity and the strength of the sintered body, the relative density of the sintered body must be 95%.
% Or more, particularly 97% or more, and the proportion of the main crystal having a major axis of 20 μm or less is 80% or more, particularly 90% or more, and the average major axis of the main crystal is 3 to 10 μm, particularly It is preferable that the average aspect ratio of the main crystal is 3 to 10 μm.
The major axis is the maximum diameter (major axis) d of each main crystal in a photograph obtained by mirror-processing the surface A perpendicular to the orientation direction and observing the structure with a SEM or a metallographic microscope. The aspect ratio (d / t), which is the ratio, can be obtained from d and the length in the vertical direction) t.

Further, the sintered body of the above embodiment, the alignment direction perpendicular to the plane A, i.e. 30% or more as k ₃₃ value of c plane perpendicular alignment direction perpendicular to the plane of the main crystal, in particular more than 40% ,
A further 50% or higher, the k ₃₃ value of the variation 5% or less, preferably 3% or less, more preferably having an excellent piezoelectric characteristic of less than 1%.

Furthermore, when this sintered body is used as an electronic component such as a resonator, for example, it is made into a plate-like body having a thickness of 3 mm or less, especially 1 mm or less, and a crystal whose main crystal is perpendicular to the c-plane in the main plane. oriented in the plane, i.e. that the main plane is formed so as to form the alignment direction perpendicular to the plane a desirable, whereby, in particular, thickness longitudinal vibration k ₃₃ for exciting electrodes are formed on both surfaces becomes large.

(Production Method) Next, a method for producing the bismuth layered compound sintered body of the present invention will be described. First, for example, a ceramic raw material for forming a bismuth layered compound powder is prepared. As the ceramic raw material, powders such as oxides, nitrates, acetates, and carbonates of the respective metals can be used, and other solutions such as metal alkoxides may be used.

Mixing and mixing these ceramic raw materials,
800 to 1300 ° C, especially 850 to 1200 ° C, further 900 to 1000 ° C for 1 to 8 hours, especially 1 to 5 hours,
90% by weight by further heat treatment for 1-2 hours
As described above, a calcined powder of a bismuth layered compound in which 95% by weight or more, particularly 99% by weight or more forms a bismuth layered compound is prepared. In addition, as a method for producing the calcined powder, a known coprecipitation method, a sol-gel method, a hydrothermal synthesis method, or the like can be employed in addition to the above.

Here, if the content of the bismuth layered compound in the calcined powder is less than 90% by weight, the grain size (major axis) of the main crystal in the sintered body cannot be uniformed, and As the piezoelectric characteristics decrease, the dispersion of the characteristics increases. The content of the bismuth layered compound in the calcined powder is determined from the X-ray diffraction chart of the calcined powder by the Rietveld method. In the calcined powder, a small amount of unreacted substances or intermediate products is 10% by weight or less, particularly 5% by weight.
Hereinafter, 1% by weight or less remains, but these function as sintering aids during sintering, which will be described later, and serve to lower the sintering temperature or shorten the sintering time.

After the obtained calcined body is crushed to obtain a calcined powder, a predetermined amount of a solvent is added, and the mixture is mixed with, for example, a ball mill to prepare a slurry. As the solvent, water, alcohols such as isopropyl alcohol (IPA), acetone, and the like can be used, and water is particularly desirable in terms of safety and environment. In addition, an organic binder such as polyvinyl alcohol (PVA), a plasticizer, and a dispersant may be added together with the solvent. PVA also has a function as a dispersant, and functions to enhance the orientation of a calcined powder described later. .

Further, in order to suppress the aggregation of the calcined powder, enhance the dispersibility of the calcined powder in the slurry, and easily displace the calcined powder in a magnetic field described later, the average particle size of the calcined powder is adjusted. Diameter 0.5-2μm, especially 0.5-1.5μ
m, more preferably 0.5 to 1.0 μm.
Note that the average particle diameter of the calcined powder which is the meaning of the d ₅₀ value obtained by the micro track method.

Next, the slurry is molded while applying a specific parallel magnetic field H from one direction. Here, it is important that the strength of the applied magnetic field H is 1 T or more, particularly 9 T or more, and further 11 T or more in order to orient the calcined powder in a desired direction. As a device for generating such a magnetic field, for example, it is desirable to use a magnetic field generator provided with a superconducting magnet capable of generating a high magnetic field. If the applied magnetic field is smaller than 1T, the calcined powder will not be oriented in a predetermined direction.
In addition, as a molding method, a tape molding method such as a cast molding method, an injection molding method, an extrusion molding method, a doctor blade method, and a calendar roll method can be adopted.

The compact obtained at this time is oriented so that the c-axis is perpendicular to the direction in which the magnetic field is applied, that is, the crystal plane perpendicular to the c-plane in the direction in which the magnetic field is applied. In addition, although the particle orientation mechanism by the magnetic field is not clearly understood,
This is considered to be because the c-axis susceptibility of the bismuth layered compound crystal is smaller than that of the c-axis in the a and b-axis directions.

Therefore, when forming a plate-like body for a piezoelectric component such as a resonator, the direction in which the magnetic field is applied may be either the thickness direction or the plane direction of the plate-like body, but is particularly preferably in the thickness direction. It is desirable to apply.

In the above-mentioned magnetic field, for example, by-products other than the bismuth layered compound may be formed at a predetermined ratio in the calcined powder, or Bi ₄ Ti ₃ O ₁₂ or the like may be added to the calcined powder. On the other hand, they can be added separately, but these sub-components serve to promote the sinterability of the crystal.

The orientation of the particles in the magnetic field is completed in a very short time, but in order to maintain the orientation of the bismuth layered compound powder in the compact, the solvent in the slurry volatilizes and the slurry solidifies. In the case of molding by cast molding or the like, the solvent in the slurry is removed through the pores of the molding die using a molding die made of a porous body such as gypsum, and the powder is flown. It is desirable to apply a magnetic field to a fixed hardness without being fixed. For this reason, in order to accelerate the solidification of the slurry that forms the molded body, the solidification of the slurry is accelerated by applying ultraviolet rays after applying a magnetic field by including an ultraviolet curable resin in the slurry, The solidification of the slurry can be accelerated by changing the temperature after adding a magnetic field by adding a magnetic field or a thermoplastic resin.

Further, in the above-mentioned crystal orientation method, the degree of orientation of the main crystal can be easily increased not only on the surface but also inside the compact, and the c-axis of the main crystal is perpendicular to the direction of application of the magnetic field. It is possible to produce a formed body oriented on a specific surface so as to be aligned.

Thereafter, the obtained molded body is processed into a predetermined shape as required and subjected to a binder removal treatment, and then, in an oxidizing atmosphere such as the air, at 1000 to 1300 ° C., particularly 110 ° C.
By firing at a temperature of 0 to 1250 ° C., particularly for 1 to 6 hours, a bismuth layered compound sintered body can be produced.

According to the present invention, since the calcined powder is oriented on a specific surface by the above-described crystal orientation method, the c-plane, which has a high crystal grain growth rate even by firing, preferentially grows, The degree of orientation of the main crystal on a specific plane can be further increased. Further, according to the method of the present invention, it is possible to produce a molded body and a sintered body having an arbitrary shape as compared with a hot press or the like, and the sizes and directions of the main crystals in the sintered body are aligned. It is possible to obtain high piezoelectric characteristics with little variation.

Further, according to the present invention, in order to further increase the density of the sintered body and to increase the mechanical strength, H
Heat treatment under high temperature and high pressure such as IP (hot isostatic press) can also be performed.

[0041]

(Examples) SrCO ₃ powder, BaCO ₃ powder, Bi ₂ O ₃ powder, TiO ₂ powder, Na powder having a purity of 99.9%
_{The 2} CO ₃ powder and the CaCO ₃ powder were each used as a bismuth layered compound shown in Table 1 as SrBi ₄ Ti ₄ O ₁₅ (SBT),
BaBiTi ₄ O ₁₅ (BBT), Na _0.5 Bi _4.5 Ti ₄ O
₁₅ (NBT), Na _0.475 Ca _0.05 Bi _4.475 Ti ₄ O ₁₅
(NCBT), and MnO ₂ powder was added thereto at 0.2% by weight based on 100 parts by weight of the total amount of the powder. These mixed powders were mixed in a rotary mill for 16 hours, calcined in the air at the temperature shown in Table 1 for 3 hours, and pulverized so as to have the average particle size shown in Table 1. X-ray diffraction measurement is performed on the calcined powder obtained, and the ratio of the bismuth layered compound (crystallinity, described in the table as ratio) by the Rietveld method.
Was calculated.

Next, 1.5% by weight of an acrylic resin and water as a solvent were added to the obtained calcined powder so that the solid (calcined powder) content was 40% by volume. A slurry was prepared by mixing with a ball mill. The viscosity of the slurry was 0.4 to 0.6 Pa · s at 100 sec ⁻¹ .

The slurry was poured into a porous gypsum mold having an inner diameter of 50 mm and 10 cc (5 mm in thickness), and the bore diameter was 100 m.
m in a refrigerator type magnetic field device capable of generating a magnetic field of 10T, and the solvent in the slurry is applied in a state where the magnetic field shown in Table 1 is applied so that the thickness direction of the slurry is parallel to the application direction of the magnetic field. Was removed and casting was performed. The magnitude of the magnetic field was changed by changing the value of the current supplied to the superconducting magnet. The obtained molded body was demolded from the gypsum, debindered at 500 ° C. in the air, and fired in the air under the conditions shown in Table 1 (described as PLS in the table).

The relative density of the obtained sintered body was measured by the Archimedes method. Further, X-ray diffraction measurement was performed at any five points on the surface (main plane) of the sintered body, and (020), (220), (006),
From the (008) and (0010) peak intensities, the degree of orientation f ₁ =
(I ₍₀₂₀₎ + I ₍₂₂₀₎ ) / (I ₍₀₂₀₎ + I ₍₂₂₀₎ + I ₍₀₀₆₎
+ I ₍₀₀₈₎ + I ₍₀₀₁₀₎ ), and the average value was taken as the degree of orientation.

Further, the obtained sample was measured to be 2 mm × 3 mm × thickness 1 such that the surface on which the X-ray diffraction was measured was the main plane.
2 mm x 3 mm x 1 m in thickness so that the surface on which the X-ray diffraction was measured is a side surface.
m, silver electrodes are formed on both main surfaces thereof, and
Polarization was performed by applying 3 to 5 kV / mm for 1 hour in an oil bath at 0 ° C. Then, determined by the sample 5 by one of the k ₃₃ value resonant-antiresonance method using an impedance analyzer was calculated as the variation of the difference between maximum and minimum for a plane perpendicular to the magnetic field.

The sintered body was mirror-finished on the X-ray diffraction measurement surface, subjected to thermal etching, and then subjected to SEM observation to determine the length of the major axis d of each crystal with respect to a plate-like crystal of 300 particles. measuring the thickness t by the image analyzer, and obtain the average long diameter _{d a, (0.5d a ≦ d} ≦ 2d / number 300 of _a that satisfies crystals) × 100 the value of (%) (in Table, K ₁ ), the ratio of the main crystal having a long diameter of 20 μm or less (in the table,
K ₂ and described) was calculated. Furthermore, JISR-1601
The three-point bending strength was measured in such a manner that the X-ray diffraction measurement surface became a tensile surface in accordance with the above. The results are shown in Table 1.

(Comparative Example 1) Using the calcined powder of 1 to 7, 40MPa without applying a magnetic field
The sample was subjected to hot press firing at 1150 ° C. for 2 hours while applying a load to produce a sintered body, which was similarly evaluated (sample N
o. 19). The results are shown in Table 1.

(Comparative Example 2) 200MPa without applying a magnetic field
After performing uniaxial press molding under the pressure of a, a sintered body was prepared in the same manner as in the example except that the sintered body was fired in the atmosphere under the conditions shown in Table 1.
Evaluation was performed in the same manner (Sample No. 20). The results are shown in Table 1.

(Comparative Example 3) Bi_FourTi_ThreeO₁₂Powder, SrC
O_ThreePowder and TiO_TwoPowder and SrBi_FourTi_FourO _FifteenTona
A slurry is prepared using the powder mixed in
Forming tape of 300μm thickness by tar blade method
Then, the tape is laminated and baked at 1225 ° C for 10 hours.
A sintered body was prepared and evaluated in the same manner as in the example except that
(Sample No. 21). The results are shown in Table 1.

[0050]

[Table 1]

As is clear from Table 1, Sample No. 1 to which no magnetic field of 1 T or more was applied during molding. In 1,2, the main crystals are not oriented in the sintered body were those k ₃₃ value is small. In addition, as the ceramic raw material powder in the slurry, the sample No. having a bismuth layered compound content of less than 90% by weight was used. 1
In 3, large diameter variations in the primary crystals in the sintered body, variations in the k ₃₃ value between samples is increased.

Further, Sample No. 2 was subjected to hot press firing without applying a magnetic field. No. 19 and Sample No. 19 tape-formed using powders other than the bismuth layered compound. 21
In Example 2, the variation in the major diameter of the main crystal was large, and the variation in the piezoelectric characteristics was large. Further, the sample No. which was press-formed at a high forming pressure was used. In 20, it is a heterogeneous tissue,
k ₃₃ value is small, the variation was large.

On the other hand, according to the present invention, sample No. 1 was formed by applying a magnetic field of 1 T or more to a slurry containing a powder containing 90% by weight or more of a bismuth layered compound. 3 ~
In 12,14～18, any high major axis orientation degree in uniform even main crystal sample, k ₃₃ value of the main surface of the plate is 30%
It had excellent piezoelectric characteristics, which was larger than that and had a small variation of 5% or less.

[0054] Further, for the sample, measuring the same degree of orientation f ₂ and f ₁ the surface which is polished by 0.1mm respectively from the surface of the measurement of the degree of orientation f _1, the ratio (f ₂ / f ₁₎
Was calculated, the sample No. Sample Nos. 1, 2 and 3 to 18 all had values of 0.95 to 1.05. 19, 0.9, sample no. 0.7 for 20
0, sample no. 21 was 0.75.

[0055]

As described above in detail, according to the bismuth layered compound sintered body of the present invention, a bismuth layered compound powder is prepared by applying a high magnetic field in a specific direction to a slurry obtained by adding a solvent to the bismuth layered compound powder. The compound crystal can be oriented so that the c-axis is perpendicular to the direction in which the magnetic field is applied. By firing this, a flat main crystal having a uniform grain size is formed due to the anisotropy of crystal growth. Bismuth layered compound sintered body oriented in a specific direction can be manufactured,
It is possible to obtain a sintered body having high piezoelectric characteristics with small variations.

[Brief description of the drawings]

FIG. 1 is a schematic view of a bismuth layered compound sintered body of the present invention.

[Explanation of symbols]

 Reference Signs List 1 sintered bismuth layered compound 2 main crystal A plane perpendicular to orientation direction H direction of application of magnetic field

Claims (8)

[Claims] (1) The general formula is (Bi ₂ O ₂ ) ²⁺ (A _m-1 B
_m O _{3m + 1} ) ^2- (where A: at least one selected from the group consisting of alkali metals, alkaline earth metals and lead, B: 4
at least one selected from the group of a metal or 5a metal
Seed, a sintered body having flat particles of a bismuth layered compound represented by m> 1) as a main crystal and oriented in a crystal plane direction perpendicular to the c-plane, and a main crystal in a plane perpendicular to the orientation direction. of major axis d is _{0.5d a ≦ d ≦ 2d a (} d a mean major diameter of the main crystal) bismuth layered compound sintered body, wherein the proportion of the crystals that satisfies is not less than 80% of the total primary crystals . 2. An X-ray diffraction intensity of a plane perpendicular to the orientation direction, wherein (I ₍₀₂₀₎ + I ₍₂₂₀₎ ) / (I ₍₀₂₀₎ + I ₍₂₂₀₎ +
I ₍₀₀₆₎ + I ₍₀₀₈₎ + I ₍₀₀₁₀₎ ) (where I _{( hkl)} is the peak intensity of each crystal plane) and the degree of orientation f is 0.75.
The bismuth layered compound sintered body according to claim 1, wherein: 3. A degree of orientation on a surface perpendicular to the orientation direction.
f₁And the surface perpendicular to the orientation direction is polished by 0.1 mm.
Degree of orientation f on the polished surface_TwoAnd the ratio (f_Two/ F ₁)But
3. The screw according to claim 2, wherein the ratio is 0.8 or more.
Mass layered compound sintered body. 4. The bismuth layered compound sintered body according to claim 1, wherein the relative density is 95% or more. 5. The method according to claim 1, wherein the ratio of the major crystal having a major axis of 20 μm or less is 80% or more.
The bismuth layered compound sintered body according to any one of the above. 6. The main crystal has an average aspect ratio of 3 to 10.
The bismuth layered compound sintered body according to claim 1, wherein: 7. A slurry in which a solvent is added to a powder containing at least 90% by weight of a bismuth layered compound as a ceramic raw material powder, and a magnetic field of 1 T or more is applied to the slurry in one direction to produce the bismuth layered compound powder. Solidifying the slurry while orienting the slurry to a crystal plane perpendicular to the c-plane, and then firing the slurry to produce a bismuth layered compound sintered body. 8. The method for producing a bismuth layered compound sintered body according to claim 6, wherein the average particle diameter of the bismuth layered compound powder is 0.5 to 2.0 μm.