JPS6324949B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing barium titanate (BaTiO ₃ ) sintered bodies that are extremely useful as dielectric and piezoelectric materials, and provides sintered bodies with particle orientation that significantly improves their electrical properties. It is. In the field of magnetic materials, acicular or columnar magnetic crystal grain powders that are mainly composed of iron oxide and that are elongated in a specific crystal direction have been produced for quite some time, and are made by mixing them with organic matter. A composite material in the form of a film or sheet in which acicular or columnar magnetic crystal grains are arranged in one direction has been produced. These materials are widely used in magnetic tape and other purposes. In addition, in the field of magnetic materials, at least one of the raw materials is a raw material powder consisting of particles with special shapes such as needles and plates, and the mixture is sintered by the so-called hot press method. , a sintered body in which crystal grains of a magnetic material are oriented in one direction has been produced. This sintered body is widely used as a magnetic head material for video tape recorders and the like as a magnetic material whose magnetic properties differ significantly depending on the direction. In this way, in the field of magnetic materials, materials that utilize the remarkable anisotropy of the magnetic properties of magnetic crystal grains are widely used in practical use. In the field of dielectric and piezoelectric materials that form double walls, very few materials have been created that take advantage of the anisotropy of the dielectric and piezoelectric properties of crystal grains. slightly,
It has been reported that a sintered body with oriented grains can be produced using a Bi layered compound, but the dielectric and piezoelectric properties of the Bi layered compound are compared with those of perovskite compounds, which play a leading role in the fields of dielectric and piezoelectric materials. It looks quite inferior. On the other hand, perovskite compounds, especially BaTiO ₃
Sintered bodies of Ti-containing perovskite compounds such as PbTiO ₃ series and PbTiO ₃ -PbZrO ₃ series have extremely excellent properties as piezoelectrics and dielectrics, and are widely used in various piezoelectric and dielectric applications. It is provided. The dielectric and piezoelectric properties of these materials differ significantly depending on the crystal axis direction, so if a sintered body with grain orientation can be produced, the performance can be improved to a greater degree than before, and even higher performance can be achieved. This means that we can fully expect new fields of application. Therefore, although an oriented sintered body of such a perovskite compound is desired, it has not been realized until now. In the case of Bi layered compounds, the crystal structure has a layered structure, so when hot press sintering is performed,
Since crystal grains whose layered structure is perpendicular to the pressing direction are likely to be formed, an oriented sintered body is formed. However, in perovskite compounds, the crystal structure itself does not have a characteristic structural part such as a layered structure that tends to cause particle orientation. A uniform sintered body cannot be produced. The following method can be considered as a method for producing such an oriented sintered body. That is, (1) using powder of needle-like or plate-like particles with a specific crystal orientation as a raw material, arranging them in a certain direction and molding them, and sintering the molded product to create an oriented sintered body. Manufacturing method, using the raw materials of (2) and (1),
Alternatively, other methods may be used to prepare powder consisting of product particles having a specific particle shape and specific crystal orientation, and then sintering the molded body by arranging and molding the powder to produce an oriented sintered body. Conceivable. In the present invention, a powder consisting essentially of BaTiO ₃ particles elongated in the direction of the crystal axis is produced, then a molded body in which the elongation directions of these particles are arranged in the same direction is produced, and this is sintered. As a result, we succeeded in producing a sintered body with grain orientation in which one of the crystal axes of each BaTiO ₃ crystal grain constituting the sintered body is oriented in a certain direction. Hereinafter, the manufacturing method of the present invention will be explained in detail with reference to Examples. First, potassium tetratitanate (K ₂ O.4TiO ₂ ) fibers were produced using the so-called flux method.
i.e. potassium carbonate K ₂ CO ₃ , titanium dioxide
TiO ₂ and potassium molybdate K ₂ MoO ₄ ,
Mixed into a composition of 6K ₂ CO ₃ + 24TiO ₂ + 7OK ₂ MoO ₄ ,
It was fired in a platinum crucible at 1100°C for 2 hours and cooled to room temperature at a cooling rate of 4°C/hour. This was washed with water to completely remove the _four K ₂ MoO components, and then dried to remove K ₂ O.
_4TiO2 fibers were produced. Next, K ₂ O・4TiO ₂ fibers and barium oxide BaO are combined into K ₂ O・4TiO ₂ +4BaO
The composition was mixed and baked at a temperature of 800 to 1000°C for 5 hours. After firing, the sample was immersed in water to wash and remove free potassium components, and then dried. X-ray diffraction revealed that the obtained powder sample consisted of a single phase of BaTiO ₃ , and electron microscopy and electron beam diffraction revealed that it had needle-like or columnar-like shapes of 0.5 to 2 μm extending in the crystal axis direction. It consisted of ₃ BaTiO particles. 15 parts by weight of butyral resin, 15 parts by weight of n-butyl phthalate, and 25 parts by weight of isopropyl alcohol were added to 100 parts by weight of the prepared BaTiO ₃ powder sample, and after thorough kneading, a thread-like product with a diameter of 0.5 mmφ was added. Extrusion molded. The fabricated thread-like molded body was cut into lengths of 15 mm, and they were lined up in one direction and pressure molded to form a product with a length of 15 mm, a width of 15 mm, and a thickness of 15 mm.
A 10 mm pressure molded body was produced. Heat this at 400℃ for 5
After holding for a time to remove the organic binder, 1350℃,
A square sintered body was produced by firing for 2 hours. After polishing the surface of the produced sintered body perpendicular to the direction in which the filament shaped bodies are arranged and removing the surface layer,
When line diffraction was performed, the diffraction intensities of the (hoo) and (ool) planes were significantly increased. _BaTiO3
For the sum ΣI of the integrated intensities of all the diffraction lines,
The sum of the intensities of the diffraction lines of the (hoo) and (ool) planes Σ(I _hpp +
Let the ratio of I _pp1 ) be P (P=Σ(I _hpp + I _ppl )/ΣI),
If the non-oriented sintered body is expressed as P ₀ , then (hoo)
The degree of orientation of the (ool) plane can be conveniently expressed by P/P ₀ . In the oriented sintered body obtained in the example, P/P ₀ was 2.2 as shown in the following table. Further, the ratio of the diffraction intensities of the (hoo) plane and the (ool) plane was about 2:1. These facts indicate that one of the crystal axes of most of the crystal grains in the BaTiO ₃ sintered body of this example is oriented in the direction in which the filament shaped bodies are arranged, and the degree of a-axis orientation is equal to the degree of c-axis orientation. This shows that it has approximately doubled. Next, this sintered body was sliced to create a thin plate-like sample perpendicular to the direction in which the filamentous molded bodies were arranged, and further processed into a disk-like shape to create a disk-like sample with a thickness of 0.3 mm and a diameter of 6 mm. . Silver electrodes were formed on both surfaces by vapor deposition, and the dielectric constant ε/ε ₀ was measured. on the other hand,
A non-oriented BaTiO ₃ sintered body was produced by a conventional method, and ε/ε ₀ ,
ε ₃₃ /ε ₀ and k _t were measured. These results are shown in the table below.

[Table] As is clear from the table, when the BaTiO ₃ sintered body is oriented, the dielectric constant ε/ε ₀ before polarization increases significantly, and after polarization the dielectric constant ε ₃₃ /ε ₀ decreases significantly, and the thickness The electromechanical coupling coefficient k _t in the direction becomes significantly large. BaTiO ₃ is a material whose dielectric and piezoelectric properties differ significantly depending on the direction of the crystal axis. For example, the dielectric constant in the a-axis direction is 10 to 20 times larger than that in the c-axis direction. Therefore, in the oriented sintered body according to the present invention, the a-axis direction, which has a high dielectric constant, is oriented more effectively than the c-axis direction, so that the dielectric constant becomes significantly large. In addition, in the oriented sintered body according to the present invention, one of the crystal axes of each crystal grain is oriented in substantially the same direction, and the other crystal axes exist in a direction perpendicular to it, so that the direction of the oriented axis is When polarized, the C-axis is effectively aligned in the polarization direction. Therefore, in the polarization direction, the dielectric constant ε ₃₃ /ε ₀ becomes significantly smaller, and the electromechanical coupling coefficient k _t becomes significantly larger. BaTiO ₃ is widely used as a dielectric material, a piezoelectric material, and as a PTC thermistor material in the form of a pure sintered body or a sintered body with other components added thereto. thus important
With regard to BaTiO ₃ sintered bodies, the particle orientation technology of the present invention can impart significantly better properties than non-oriented sintered bodies, which will only serve to further improve performance in conventional application fields. Not,
New application fields can also be expected. for example,
Since the dielectric constant is significantly increased, it can be applied to increase the capacitance of capacitors, and the polarized material is extremely useful as a piezoelectric material having a low dielectric constant and a large electromechanical coupling coefficient. In addition, although the examples refer to pure BaTiO ₃ porcelain, it is possible to add binders and trace ingredients that are commonly used in the past to control properties, or to add BaTiO ₃ porcelain.
SrTiO ₃ , CaTiO ₃ , which can form solid solutions with
Of course, PbTiO ₃ , PbZrO ₃ and other substances may be added. In short, in relation to the well-known sintered body whose main component is BaTiO ₃ , in its manufacture, powder consisting of needle-like or columnar-shaped particles of BaTiO ₃ elongated in the crystal axis direction is used. It is important to use these particles to create a molded body in which the elongation direction of the particles is aligned in a certain direction, and then sinter this body.

Claims (1)

[Claims] 1. In a method for producing a barium titanate sintered body in which one of the crystal axes of the barium titanate crystal particles constituting the sintered body is oriented in substantially the same direction, barium titanate particles extending in the crystal axis direction are used. A method for producing a barium titanate sintered body, the method comprising: producing a molded body in which the elongation directions of the particles are aligned in the same direction using a powder substantially composed of powder, and sintering the molded body. .