JPH02225360A - Aggregate powder of orientated ceramic crystal particle and production thereof - Google Patents

Abstract

PURPOSE:To make characteristics of various functional ceramics exhibit like those of single crystal by orientating the crystal axis of crystal particles comprising isometric system of ceramics having pyroelectric properties. CONSTITUTION:In aggregate powder of ceramic crystal particle comprising isometric system having pyroelectric properties but not ferroelectric properties, the crystal axis of crystal particle is orientated to form aggregate powder of orientated ceramic crystal particle. The aggregate powder of orientated ceramics can be obtained by the following method (a) or (b). Namely, (a) crystal particle powder having pyroelectric properties is subjected to temperature change and placed in an electric field so that the crystal axis of crystal particle is orientated. (b) Crystal particle powder having pyroelectric properties is subjected to temperature change in an electric field so that the crystal axis of the crystal particle is orientated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an oriented ceramic crystal particle aggregate powder in which the crystal axes of the crystal particles of a ceramic crystal particle powder having pyroelectric properties are oriented, and a method for producing the same. It is related to.

[Conventional techniques and their problems] When using functional ceramics, by orienting the crystal grains, it is possible to exhibit the properties similar to those of a single crystal, so various methods have been used to realize oriented ceramics. is being attempted.

One example is to use crystal grain powder with a unique crystal grain shape such as needle or plate shape as a raw material, and apply mechanical stress using powder extrusion molding, press molding, doctor blade molding, etc. This is a method of giving a white account.

Another method is to use a magnetic field to orient the crystal grains of ceramic crystal grain powder, and this method is used for powders made of uniquely shaped crystal grains of magnetic materials such as ferrite. Recently, attempts have been made to orient the crystal grains of raw material powder for superconductors. Furthermore, a method of obtaining oriented ceramics using an electric field has been attempted in the case of needle-shaped ferroelectric crystal grains.

Furthermore, in the case of ferroelectric materials, the direction of polarization (that is, the direction of the crystal axis) can be reversed by an external electric field, so ceramics made of oriented crystals are produced using this method.

In other words, in conventionally prototyped oriented ceramics, other than ferroelectric ceramics, it is necessary to first prepare crystal grains with a specific shape such as needle-like or plate-like shapes, and powder raw materials made of crystal grains with a specific shape must be prepared. Special treatment is required to obtain them, and crystal particles with a unique shape are often difficult to obtain, and the types of ceramic powders that can be used are extremely limited.

E. Problems to be Solved by the Present Invention] The present invention aims to improve the properties of functional ceramics by orienting crystal grains, since there are severe restrictions in realizing oriented ceramics using these conventional techniques. Since we know that this can be achieved, we are developing a technology that can be applied to a wider variety of ceramics, and are aiming to realize oriented ceramics that exhibit properties close to single crystals for ceramics with a wide variety of functions. be.

[Structure of the Invention] The present invention has been made to solve the above-mentioned problems, and the oriented ceramic crystal grain aggregate powder of the present invention has pyroelectricity and no ferroelectricity, etc. This is a ceramic crystal particle aggregate powder having an axial shape, and is characterized by the crystal axes of the crystal particles being oriented.

In addition, the other oriented ceramic crystal particle aggregate powder of the present invention is an aggregate powder of ceramic crystal particles having pyroelectricity and having an equiaxed shape, and utilizes the polarization phenomenon caused by temperature change to create an electric field. It is characterized by the fact that the crystal axes of the crystal grains are oriented and sewn.

The method for producing an oriented ceramic crystal particle aggregate powder of the present invention is characterized in that the crystal axes of the crystal particles are oriented by applying a temperature change to the pyroelectric crystal particle powder and then introducing it into an electric field. There is.

Another method for producing an oriented ceramic crystal grain aggregate of the present invention is characterized in that the crystal axes of the crystal grains are oriented by applying a temperature change to a pyroelectric crystal grain powder in an electric field. .

The present invention relates to a ceramic crystal grain aggregate powder in which the crystal grains of a ceramic crystal grain powder having an equiaxed shape of ceramics having pyroelectric properties are oriented, including various types of functional ceramics, and a method for producing the same. Although there is a restriction that materials have pyroelectricity, the range of target materials is much wider than that of the conventional technology. Although the oriented ceramics referred to here are polycrystalline ceramics, by aligning the crystal orientation of the crystal grains, it is possible to realize a model that is almost equivalent to a single crystal.

In the present invention, the orientation of crystal grains is aligned using an electric field, but unlike conventional techniques, it is not necessary to have ferroelectricity or magnetism in the raw material crystal grain powder. It can be applied to powders that do not have a particle shape and are made of equiaxed particles that are easily available.

Ceramic crystals are classified into 32 groups based on the combination of elements of their crystal structure, and constitute 32 crystal groups. Among these, crystals that exhibit pyroelectricity are the IO point group IO crystal group, in which the fish school to which they belong has a center of symmetry, and which also exhibits polarity (Shioya Shigeo et al., Handbook of Optical Physics, p.
321 Asakura Shoten 1984). That is, the oriented ceramic crystal grain aggregate powder of the present invention has 10 of these 32 crystal groups.
Shinzoku (fish school: 1, 2.rs, 2i+m, 4.4m
It can be applied to crystals classified as 3.3m, 6.6mm). In addition to ZnO, examples of specific ceramics having pyroelectricity include LiNb0. .

LfTa03. BaTiOs, NaNO2, BaT
iO+z, 5bSI, Yλ1nOi.

BaNaNb5Ola, PbTiOs, KIO3, Pb
Zr0i, ZnS, CdS, LiKSO4゜CaJba
Examples include Ot, CdSe, KNbOs, and the like. That is,
In the manufacturing method of the oriented ceramic crystal grain aggregate powder of the present invention, by heat-treating the crystal grain powder, a surface charge (polarization) is generated on the crystal grains due to pyroelectricity, and this surface charge is caused to interact with coulombs in an electric field. It acts to orient it. Therefore, crystal particles that have been polarized by heat treatment may be fed into an electric field to be oriented, or they may be oriented in the same way by being placed in an electric field and then heat treated in the electric field. Which method should be selected depends on the properties of the powder, the configuration of the electrodes for creating the electric field, and the final shape of the aggregated powder desired to be created. In order to orient the ceramic shaped particles by Coulomb interaction, it is preferable that the crystal particles are not aggregated.

In aggregated particles, the charges on the particle surface cancel each other out, making it difficult for orientation to occur due to an external electric field, so even if orientation is obtained, it tends to be incomplete.
It is preferable to conduct the reaction by heating to 00°C because it is easy to operate. Further, since the electric charge generated on the surface discharges and dissipates over time, it is preferable to perform the heat treatment immediately before orienting in an electric field.

Coulomb force interaction with surface charges makes it easier to orient the larger crystal particles because they have a larger charge and are less likely to aggregate, but equiaxed particles can change their orientation relatively easily. With appropriate formulation, even fine particle powders can be applied.

In the present invention, the term "equiaxed particles" means a particle shape with a small ratio (aspect ratio) between the major axis and the minor axis, such as the particle shape when a crystal without interfolds is crushed, and is not necessarily a spherical particle shape. It does not have to be a shape close to a cube.

The oriented ceramic crystal grain aggregate powder according to the present invention is formed into a formed shape using a uniaxial press, an isostatic press, etc. so as not to disturb the orientation of the crystal grains, and then sintered. can do. Hot pressing is effective in suppressing crystal growth and recrystallization during sintering. As for the shape, it is possible to use not only a sheet-like shape that can be easily oriented, but also a thick-walled crystal grain-aggregated powder by stacking oriented sheet-like crystal particle-aggregated powders.

[Example] Zinc oxide (ZnO) powder having an equiaxed shape with a particle diameter of 200 μm and not agglomerated was used as a ceramic crystal particle powder having pyroelectricity. This crystal is a school of fish 6m111
It is classified into the crystal group (hexagonal system). A ZnO crystal particle powder was dropped through an electric furnace preheated to 120° C., and dropped between electrodes placed below with a gap of 4II111 to which a voltage was applied, and deposited on a substrate placed below.

By this method, the voltage can be set to OKV, 1.0KV, 1.
5KV, 2. OKV, 2.5KV, 3. OK
The orientation of the (002) plane, that is, the direction perpendicular to the C-axis deposition plane, of the crystal grain aggregate powder deposited to a thickness of about 0.5 mm on a substrate with a change in V was investigated by powder X-ray diffraction. Ta. Figure 1 shows a powder X-ray diffraction diagram of a crystal grain aggregate powder oriented with an applied voltage of 3.0 and ■, and Figure 2 shows an unoriented powder obtained in the same manner without applying a voltage between the electrodes. The powder X-ray diffraction pattern of the crystal grain aggregate powder is shown. In the non-oriented aggregated powder shown in Figure 2, (100),
Three sharp diffraction lines due to (002) and (101) crystal plane spacings are observed.

On the other hand, in the case of oriented aggregate powder, the (002) diffraction line is strong and sharp, but the (1001 diffraction line is weak and the (101)
1 diffraction line is hardly recognized. Diffraction angle (20) 45~
In the non-oriented aggregated powder, several diffraction lines with moderate intensity are observed near 70°, whereas in the oriented aggregated powder, the diffraction lines between this period are weak and hardly observed. On the other hand, the (004) diffraction line, which was not observed in the non-oriented aggregated powder, was clearly observed in the oriented aggregated powder.

This result shows that the zinc oxide particles are oriented with the C-axis direction of the crystal perpendicular to the deposition surface of the substrate. This is consistent with the fact that surface charges due to pyroelectricity are generated on the zero surface of the crystal.

When the relationship between the orientation of the ceramic crystal particle aggregate powder and the applied electric field strength was investigated using the Lotgering method, there was a nearly linear proportional relationship between the two, and the applied voltage was 3. In OKV, approximately 80% orientation was obtained in relative comparison with a single crystal.

Note that if the electric field strength is too strong, a discharge will occur between the electrodes, so it is not possible to increase the electric field any further in air, but in a vacuum or in an insulating fluid such as SF or gas, an even stronger electric field can be used. It is possible.

[Effects of the Invention] The present invention makes it possible to arrange equiaxed crystal grain powder, which could not be oriented using conventional techniques. This makes it possible to orient a wide variety of ceramic crystal grain powders that have pyroelectric properties, creating oriented ceramics, which are polycrystalline ceramics and are precursors of functional ceramics that have properties close to single crystals. Crystal grain aggregate powders have become possible for many types of ceramics.

[Brief explanation of the drawing]

FIG. 1 is an X-ray diffraction diagram of an oriented ceramic crystal grain aggregate powder showing an example of the present invention, in which zinc oxide crystal grain powder having an equiaxed shape with a particle diameter of 200 μm is oriented. FIG. 2 is an X-ray diffraction diagram of a ceramic crystal particle aggregate powder which is the same as that shown in FIG. 1 and shown as a comparative example, in which the zinc oxide crystal particle powder is not subjected to the orientation treatment. Agent (bu ``buried earth'') Heishichi + Rigo

Claims (4)

[Claims] (1) Oriented ceramic, which is a ceramic crystal grain aggregate powder having an equiaxed shape that has pyroelectricity and no ferroelectricity, and is characterized in that the crystal axes of the crystal grains are oriented. Crystal particle aggregate powder. (2) An aggregate powder of ceramic crystal particles having pyroelectric properties and an equiaxed shape, in which the crystal axes of the crystal particles are oriented in an electric field by utilizing the polarization phenomenon caused by temperature changes. An oriented ceramic crystal particle aggregate powder characterized by: (3) A method for producing an oriented ceramic crystal particle aggregate powder, characterized in that the crystal axes of the crystal particles are oriented by subjecting a pyroelectric crystal particle powder to a temperature change and then introducing it into an electric field. . (4) A method for producing an oriented ceramic crystal grain aggregate powder, which comprises orienting the crystal axes of the crystal grains by applying a temperature change to the pyroelectric crystal grain powder in an electric field.