JP2000119065A - Manufacturing method of oriented ceramics - Google Patents

Abstract

(57) [Problem] To provide a method for easily producing various ceramics having a tungsten bronze type crystal structure and having a crystal orientation in a uniaxial direction with a high yield. SOLUTION: Needle-like particles having a tungsten bronze type crystal structure as a host material and a guest material to be added to form a guest ceramic having a tungsten bronze type crystal structure and having an arbitrary composition are prepared. By mixing and molding the host material and the guest material to form a molded body, and firing the molded body while using the crystal plane of the host material or the orientation of the crystal axis of the host material as a mold, Orient guest ceramics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing an oriented ceramic made of a material having a tungsten bronze type crystal structure.

[0002]

2. Description of the Related Art As a method for producing oriented ceramics made of a material having a tungsten bronze type crystal structure, for example, the following method is known. (1) JP-A-61-106454 (2) Collection of lectures on powder and powder metallurgy, vol.1986, No. Sprin
g, p102-103,

In the method (1), needle-like particles having a tungsten bronze type crystal structure are synthesized by a flux method, and the needle-like particles are divided into two stages and fired by hot pressing (hot pressing). Thereby, oriented ceramics having uniaxial crystal orientation can be manufactured.

[0004] In the method (2), a needle-like particle similar to the above (1) is prepared, and is extruded to form a uniaxially particle-shaped molded body, and the molded body is fired. .
As a result, oriented ceramics having uniaxial crystal orientation can be manufactured. In the manufacturing method described above, the needle-like particles and the ceramic to be finally obtained have the same composition, and the needle-like particles are grown and densified by hot pressing or sintering, and bulk sintering is performed. The body is made of oriented ceramics.

[0005]

However, the above-mentioned conventional method has the following problems. That is, in the above-mentioned conventional methods (1) and (2), acicular particles corresponding to the composition of the oriented ceramics to be produced must be produced in advance. However, it is difficult to control the composition of the acicular particles by a general method of synthesizing particles through a liquid phase and a gaseous phase, and it is difficult to produce acicular particles having a desired composition. It was difficult. In particular, when the target compound has a complicated composition, it has been necessary to spend a lot of time to conduct trial and error studies for determining the conditions for synthesizing the acicular particles.

Further, in the above-mentioned conventional method, it is necessary to produce needle-like particles one by one according to the composition of the oriented ceramics to be obtained. Therefore, when attempting to produce a plurality of types of oriented ceramics having different compositions, the time and effort required to derive the conditions required for synthesizing the acicular particles increase in proportion to the type of the oriented ceramics. It was a target.

Further, various ceramics having practically useful properties as ferroelectric materials, piezoelectric materials, and optical materials often have complicated compositions. Such ceramics include, for example, (Sr _x Ba _1-x ) ₂ (K _1-y Na
_{y) Nb 5 O 15, (} Sr x Ba 1 -x) 2 (K 1-yz Na y L
_iz ) Nb ₅ O _{15 and the} like. However, since the composition of these ceramics is very complicated, the above-mentioned problem may cause difficulty in production.

Further, as described in (1), firing by hot pressing not only raises the production cost but also often results in a density distribution in the sintered body obtained by this method. For this reason, oriented ceramics having a uniform density distribution that can withstand practical use can be obtained from only a small number of pieces cut out from the obtained sintered body, and there is a problem that the yield is low.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and is a method for easily producing various ceramics having a tungsten bronze type crystal structure in a uniaxial direction with high yield. It is intended to provide.

[0010]

An object of the present invention is to form needle-like particles having a tungsten bronze type crystal structure as a host material and guest ceramics having a tungsten bronze type crystal structure and having an arbitrary composition. The guest material to be added to the host material is prepared, and the host material and the guest material are mixed and formed into a molded body, and the orientation of the crystal plane of the host material or the crystal axis of the host material is used as a template. A method for producing an oriented ceramic having a tungsten bronze type crystal structure, wherein the guest ceramic is oriented by firing the molded body.

The acicular particles used as the host material will be described. Any compound having a tungsten bronze type crystal structure can be used as the needle-like particles. However, in order to utilize the effect of the present invention more,
It is preferable to select a relatively simple compound containing two or three metal elements. This is because such a compound can easily produce needle-like particles. Also,
Such compounds include, for example, PbNb ₂ O ₆ , S
rNb ₂ O ₆ , BaNb ₂ O ₆ , Sr ₂ KNb ₅ O _{15 and the} like.

The selection of needle-like particles used as a host material according to the present invention has the following restrictions. For the acicular particles according to the present invention, it is necessary to use a compound containing some or all of the metal elements contained in the oriented ceramics to be obtained. For example, (Pb,
K) When obtaining oriented ceramics composed of Nb ₂ O _6, it is preferable to use PbNb ₂ O ₆ as the acicular particles used as the host material. In addition,
In order to obtain oriented ceramics composed of Sr ₂ KNb ₅ O ₁₅ , it is preferable to use SrNb ₂ O ₆ .
In order to obtain an oriented ceramic of (Sr, Ba) Nb ₂ O ₆ , it is preferable to use SrNb ₂ O ₆ .

The needle-like particles can be synthesized by a liquid phase method or a gas phase method. By synthesizing by these methods, needle-shaped particles reflecting the anisotropy of the crystal structure can be easily synthesized. As the liquid phase method,
A flux method using a low melting point chloride, sulfide, nitrate or the like as a flux component, a precipitation method utilizing a precipitation reaction from an aqueous solution, or a hydrothermal method can be used. Further, as the vapor phase method, a CVD method or the like can be used.

Further, as the guest raw material according to the present invention, for example, oxides, carbonates, nitrates and the like of metal elements contained in the oriented ceramics to be obtained can be used. Further, as a part of the guest raw material, a ceramic powder itself to be produced by utilizing the present invention, which is produced by using a solid phase method, a solution method, a gas phase method or the like, can be used. Further, a composite oxide composed of a metal element contained in ceramics to be manufactured can also be used.

For example, when the oriented ceramic to be obtained is Sr ₂ KNb ₅ O ₁₅ and the acicular particles are SrNb ₂ O ₆ , the guest material is SrCO ₃ , K ₂ CO _3
3 , Nb ₂ O ₅ , or Sr ₂ KNb ₅ O ₁₅ or KNbO ₃ synthesized by a solid phase method, a solution method, a gas phase method or the like can be used.

The method for orienting the guest ceramics using the orientation of the crystal plane of the host material or the crystal axis of the host material as a template includes, for example, the following method. For example, it is preferable to perform a firing step in which the host material and the guest raw material are mixed, subjected to orientation molding, and then fired. By orientation molding, it is possible to obtain an oriented molded body in which needle-like particles of the host material are aligned in one direction, and then by firing, it is possible to obtain guest ceramics that have inherited the orientation state of the host material. .

As the orientation molding, a pressure molding method, a doctor blade method, an extrusion molding method, or the like can be used. In the pressure molding method, an oriented molded article in which needle-like particles are uniaxially oriented can be obtained by biaxially pressing a mixed powder composed of a host material and a guest raw material. In the doctor blade method and the extrusion molding method, a slurry is prepared by adding a solvent, a binder, a plasticizer, etc. to the above mixed powder, and then the needle-like particles are uniaxially oriented by utilizing the shear stress during tape molding and extrusion molding. An oriented molded article can be obtained. In particular, the doctor blade method and the extrusion method are preferable because the needle-like particles can be relatively easily oriented.

Next, the firing step performed after the above-mentioned orientation molding will be described. When the above-mentioned oriented molded article contains an organic component, it is necessary to perform a degreasing treatment before the firing step.
In some cases, after the degreasing, the firing step may be performed after increasing the density of the oriented green body by cold isostatic pressing or the like.

The calcination step may be performed at the same temperature as in the ordinary solid phase synthesis. In this firing step, a reaction occurs between the host material and the guest raw material, and guest ceramics are generated. At the same time, grain growth and densification occur, and dense guest ceramics are produced. In this firing step, the acicular particles of the host material are converted into guest ceramics while maintaining the directional relationship, so that at least a part of the guest ceramics can inherit the orientation of the oriented formed body made of the host material. For this reason, the ceramics produced from the present invention are oriented ceramics oriented in one axis direction.

Next, the operation of the present invention will be described. The most remarkable point in the present invention is to bake a formed body composed of the host material and the guest raw material under the influence of the orientation of the crystal plane or crystal axis of the host material. In the manufacturing method according to the present invention, the acicular particles as the host material and the oriented ceramics as the final composition are also substances having a tungsten bronze type crystal structure. Also,
The guest raw material is a ceramic raw material that needs to be added in addition to the host material in order to produce the oriented ceramics (ie, guest ceramics) to be obtained.

The guest material reacts with the host material under the influence of the orientation of the crystal planes or crystal axes of the host material. The crystal planes and crystal axes are transferred.

[0022] For this reason, by the reaction between the host material and the guest raw material, guest ceramics which maintain the orientation of the crystal plane or crystal axis in the host material are generated.
Since this guest ceramic is a final product in the production method of the present invention, according to the present invention, oriented ceramics can be easily obtained.

In addition, non-oriented ceramics may be synthesized from the guest material itself at a location away from the acicular particles of the host material. Non-oriented ones are absorbed by the oriented ceramics. For this reason,
According to this production method, oriented ceramics having a high degree of uniaxial orientation can be easily produced.

Further, in the manufacturing method according to the present invention, since there is no need for a pressure sintering step involving plastic deformation such as hot pressing or hot forging, oriented ceramics having a uniform density can be easily obtained. it can. When the density varies, various characteristics such as piezoelectricity and dielectricity vary depending on the cut portion. On the other hand, a material having a uniform density does not cause the above-mentioned problem, and therefore has a high practical value in terms of improving the yield of the device and increasing the size of the device.

The needle crystal used in the production method of the present invention may have a composition different from that of the oriented ceramic to be finally obtained, and is a substance capable of producing the ceramic to be obtained by the reaction of the guest raw material. Anything can be used. For this reason, since it is sufficient to use a suitable needle-like crystal which is easy to obtain and manufacture, it is possible to greatly reduce the time and labor required for preparing the needle-like crystal.

As described above, according to the present invention, various ceramics having a tungsten bronze type crystal structure,
It is possible to provide a method for easily and uniaxially orienting a crystal with high yield.

As described above, according to the manufacturing method of the present invention,
Although it is possible to obtain oriented ceramics composed of any composition having a tungsten bronze type crystal structure, in particular, according to the present invention, oriented ceramics composed of a compound containing three or more metal elements can be easily produced. .
Such compounds include, for example, (Pb, K) Nb
₂ O ₆ , Sr ₂ NaNb ₅ O ₁₅ , Sr ₂ KNb ₅ O ₁₅ , (S
r, Ba) Nb ₂ O ₆ , (Sr, Ba) ₂ (Na, K, L
_{i) Nb 5 O 15, K} 3 Li 2 Nb 5 O 15 and the like.

In addition, many ceramics having a tungsten bronze type crystal structure belong to ferroelectrics, and can be used for various devices utilizing piezoelectricity, dielectric properties, and electro-optic effects.

According to the manufacturing method of the present invention, the crystal orientation is 1
Ceramics having a tungsten bronze type crystal structure aligned in the axial direction can be produced. As described above, oriented ceramics having a uniform crystal orientation have high piezoelectricity, dielectric properties, electro-optical properties, etc., as high as single crystals, even though they are polycrystalline, and thus greatly enhance the performance of various devices utilizing these properties. be able to. Further, according to the production method of the present invention, a material having the above characteristics can be obtained at a lower cost than the single crystal production method.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment A method for manufacturing an oriented ceramic according to an embodiment of the present invention will be described with reference to FIGS. To explain the outline of the manufacturing method according to this example, first, acicular particles having a tungsten bronze type crystal structure as a host material,
A guest raw material to be added to form a guest ceramic having a tungsten bronze type crystal structure and an arbitrary composition is prepared.

Next, the host material and the guest material are mixed and molded to form a molded body. The molded body is fired while using the orientation of the crystal plane of the host material or the crystal axis of the host material as a template, thereby orienting the guest ceramics. Thereby, oriented ceramics can be obtained.

The details will be described below. In the manufacturing method according to this example, needle-like particles of SrNb ₂ O ₆ having a crystal structure of tungsten bronze type are used as needle-like particles serving as a host material, and K ₂ CO ₃ , SrCO ₃ ,
Using a mixed powder of Nb ₂ O ₅ , oriented ceramics of KSr ₂ Nb ₅ O ₁₅ having a tungsten bronze type crystal structure were produced.

First, SrNb ₂ O ₆ needle-like particles were synthesized by a flux method. The powders of SrCO ₃ and Nb ₂ O ₅ were mixed at a stoichiometric ratio of 1: 1 and SrCl ₂ .6H ₂ O was added at a weight ratio of 150 wt% to the mixed raw material and mixed.
The reaction was performed by heat treatment at 1100 ° C. for 1 hour. After the heat treatment, the mixture is repeatedly washed with ion-exchanged water at 80 ° C.
Chloride was removed until the amount of Cl ^- ions could not be detected by the AgNO ₃ solution method. The phase of the obtained powder was identified by an X-ray diffraction method, and it was found that the powder was a single phase of SrNb ₂ O ₆ .

When the powder obtained by a scanning electron microscope was observed, the shaft diameter was 5 to 10 μm and the shaft length was 20 μm.
It was found that acicular particles having an aspect ratio (axial length / axial diameter) of 5 to 10 were obtained. The major axis direction of the acicular particles has an orthorhombic tungsten bronze type structure of <1.
It was found from X-ray diffraction measurement that it corresponded to the <00> axis (<001> axis in pseudo-tetragonal system).

Next, the needle-like particles and the guest material are mixed.
It was fired after orientation molding. Thereby, Sr_TwoK
Nb_FiveO_FifteenA sintered body was produced. The above SrNb_TwoO₆Needle-like
Particles and K as raw material powder_TwoCO_Three, SrCO_Three, Nb_TwoO _Five
Are weighed to give a molar ratio of 2: 1: 2: 3, and wet-mixed.
After mixing, add binder and plasticizer, knead and mix
Was adjusted.

This slurry was extruded into a fiber shape using an extrusion die 2 shown in FIG. Here, in the extrusion die 2, a cylinder 22 into which a piston 21 is vertically movably inserted is disposed above a main body 23 having a tapered molded portion 230. After injecting the slurry into the forming part 230 of the main body 23, by applying a load to the upper part of the piston 21, the extrusion port 231 at the lower end of the forming part 230
The fibrous material 11 according to FIG. 3 was produced.

Further, as shown in FIG. 3, the fibrous material 11 is cut into a length of 20 mm.
Was prepared as a bundle 12 in which 100 pieces were bundled. The bundle 12 was placed in a mold (not shown), and was subjected to thermocompression bonding in the mold. By this, 20mm × 10mm × 5mm
Was obtained.

Subsequently, the molded body 13 was degreased at 600 ° C., and then subjected to a heat treatment at 1400 ° C. × 5 hours in the air to obtain a sintered body. When the X-ray diffraction pattern of the obtained sintered body was measured, it was confirmed that the obtained sintered body was a single phase of Sr ₂ KNb ₅ O ₁₅ having a tetragonal tungsten bronze structure.

The perpendicular direction to the extrusion direction of the obtained sintered body
X-ray diffraction pattern between plane and horizontal plane (by CuKα)
Was measured and described in FIG. In the figure, the parallel plane and the vertical
The pattern with the face is remarkably different. _TwoK
Nb_FiveO_FifteenOnly peaks related to (00l) plane are observed
And the {001} face of the sintered body
Was preferentially oriented. In addition, this grill
The density of the compact was 90% in relative density.

As described above, according to the manufacturing method of the present embodiment, a tungsten bronze type structure is provided.
It was found that oriented ceramics in which the 1｝ plane was preferentially oriented in the uniaxial direction was obtained.

It should be noted that the method of forming the molded body is described above.
It is not limited to the method of crimping the fibrous material 11
To make a large molded body at once by extrusion molding
Can also. Further, using the above acicular particles, (Ba, S
r) Nb_TwoO₆, (Ba, Sr) _Two(Na, K) Nb_FiveO_Fifteen
Etc. can be manufactured in the same way.
Wear.

Next, the operation and effect according to this embodiment will be described. In the manufacturing method according to this example, the acicular particles as the host material and the oriented ceramics as the final composition are also substances classified into a tungsten bronze type crystal structure. The guest material is a ceramic material that needs to be added in addition to the host material in order to produce the oriented ceramics (ie, guest ceramics) to be obtained.

The guest material reacts with the host material under the influence of the orientation of the crystal plane or crystal axis of the host material. The crystal planes and crystal axes are transferred.

For this reason, by the reaction between the host material and the guest raw material, guest ceramics which maintain the orientation of the crystal plane and the crystal axis in the host material are generated. Since this guest ceramic is the final product in this example, according to this example, oriented ceramics can be easily obtained.

Further, in this embodiment, since a pressure sintering step involving plastic deformation such as hot pressing or hot forging is not required, oriented ceramics having a uniform density can be easily obtained. When the density varies, various characteristics such as piezoelectricity and dielectricity vary depending on the cut portion. On the other hand, a material having a uniform density does not cause the above-described problem, so that the device yield can be improved,
Practical value is high in terms of increasing the size of the element.

The composition of the needle-shaped crystal used in the production method of this embodiment may be different from that of the oriented ceramic to be finally obtained. If a simple composition is selected, the production is very easy. The labor and time required for preparing the needle-shaped crystal can be largely saved.

As described above, according to the present embodiment, it is possible to provide a method for easily producing various ceramics having a tungsten bronze type crystal structure in which the crystal is uniaxially oriented at a high yield.

As described above, according to the present invention, it is possible to provide a method for easily producing various ceramics having a tungsten bronze type crystal structure which is uniaxially oriented with a high yield.

[Brief description of the drawings]

FIG. 1 is a diagram showing (a) an X-ray diffraction pattern of a surface parallel to an extrusion direction in a sintered body (oriented ceramic) obtained by firing a molded product in an embodiment, and (b) extrusion. FIG. 4 is a diagram showing an X-ray diffraction pattern of a plane perpendicular to the direction.

FIG. 2 is an explanatory view of an extrusion die for producing a fibrous material from a slurry in the embodiment.

FIG. 3 is an explanatory view of a process for producing a molded product from a fibrous material in the embodiment.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Toshio Kimura 2-1-20 Shimoda-cho, Kohoku-ku, Yokohama-shi, Kanagawa F-term (reference) 4G030 AA04 AA09 AA20 AA66 BA09 BA10 BA16 CA01 CA02 GA19 GA21

Claims (1)

[Claims] 1. A needle material having a tungsten bronze type crystal structure as a host material and a guest material to be added to form a guest ceramic having a tungsten bronze type crystal structure and having an arbitrary composition are prepared. Then, the host material and the guest material are mixed and molded to form a molded body, and the molded body is baked while using the crystal plane of the host material or the orientation of the crystal axis of the host material as a mold, A method for producing an oriented ceramic having a tungsten bronze-type crystal structure, characterized in that the guest ceramic is oriented.