JP2008037064A - Method for producing orientable ceramics - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing orientable ceramics which can be produced by using polycrystalline ceramic powder having a perovskite type structure and is reduced in restrictive conditions in terms of composition. <P>SOLUTION: The method for producing the orientable ceramics includes a process for obtaining ceramic slurry containing the polycrystalline ceramic powder, a process for obtaining a ceramic molding by molding the ceramic slurry in a magnetic field, and a process for baking the ceramic molding. The polycrystalline ceramic powder contains a main component having the perovskite type structure and a subordinate component which is contained in a ratio of 5 mol or below (>0 mol) to 100 mol of the main component. The subordinate component is at least one selected from 3d transition metal ions the magnetic moments of which are not 0 or rare earth metal ions the magnetic moments of which are not zero. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing an oriented ceramic having a perovskite structure and a method for producing a ceramic electronic component using the oriented ceramic.

Conventionally, ceramics having a perovskite structure such as BaTiO ₃ and Pb (Zr, Ti) O ₃ have been used as dielectric materials and piezoelectric materials. In these perovskite type structural ceramics, it is known that various properties are improved by orienting crystals.

Patent Document 1 discloses a host material having shape anisotropy, and a guest material in which at least one crystal plane has lattice matching with at least one crystal plane of the host material and has a small crystal anisotropy. It is described that a crystal alignment material having the same crystal system as that of the guest material is obtained by preparing, mixing, orienting the host material and then heating. It is described that this method can obtain an alignment material of sodium bismuth titanate (Bi _0.5 Na _0.5 TiO ₃ ) having a perovskite structure.

  On the other hand, in Patent Document 2, a slurry is prepared by adding a solvent to a powder containing a bismuth layered compound as a ceramic raw material, and a magnetic field of 1 T or more is applied to the slurry so that the bismuth layered compound powder is perpendicular to the c-plane. A manufacturing method of a bismuth layered compound sintered body is described in which the slurry is solidified while being oriented on a crystal plane and then fired.

Non-Patent Document 1 describes the relationship between the orientation and magnetic field of bismuth titanate (BiTiO ₃ ), lead zirconate (PbZrO ₃ ) and barium titanate (BaTiO ₃ ) powders having a perovskite structure. .
Japanese Patent Laid-Open No. 10-330184 JP 2002-121069 A Hiroshi Masumoto, Satoshi Awaji, Takashi Goto “Effect of Magnetic Field on Orientation of Ferroelectrics” Tohoku University Institute for Materials Research, Magnetic Field Superconducting Materials Research Center Annual 2002, pages 210-211

  According to the method described in Patent Document 1, a highly oriented perovskite structure ceramic can be obtained, but it is necessary to prepare a host material having shape anisotropy in advance. For this reason, there exists a problem that a process becomes complicated and manufacturing cost rises.

  In the first place, there is a problem that a shape anisotropic host material suitable for the composition of the desired oriented ceramics must exist. That is, it is necessary to prepare in advance a shape anisotropic host material composed of an element selected from the constituent elements of the desired final product. This is because the constituent elements of the host material are incorporated into the final product, so that when a material containing an element other than the constituent elements of the desired final product is used as the host material, a final product having a desired composition is obtained. It is because it becomes impossible. And there is not always a shape anisotropic host material that satisfies such conditions.

  On the other hand, as long as it is a method of orienting a crystal by applying a magnetic field as described in Patent Document 2, in principle, any substance can be used as long as it is a nonmagnetic substance having anisotropy in magnetic susceptibility. Is considered to be applicable, and there should be no compositional constraints as in the technique described in Patent Document 1.

  However, in practice, it was difficult to orient ceramics having a perovskite structure by a magnetic field. Non-Patent Document 1 describes that an oriented material could not be obtained when an 8 T magnetic field was applied using polycrystalline bismuth titanate powder. Non-Patent Document 1 describes that the orientation degree has a magnetic field dependency when single crystal barium titanate powder is used, but single crystal powder is higher in cost than polycrystalline powder. It is not an industrially practical method.

  Therefore, an object of the present invention is to provide a method for producing oriented ceramics that can be produced using a polycrystalline ceramic powder having a perovskite structure and has few compositional constraints.

  In order to solve the above problems, a method for producing oriented ceramics according to the present invention includes a step of obtaining a ceramic slurry containing polycrystalline ceramic powder, and a step of forming the ceramic slurry in a magnetic field to obtain a ceramic compact. And firing the ceramic molded body, wherein the polycrystalline ceramic powder has a main component having a perovskite structure and 5 mol or less (provided that 0 mol is less than 100 mol). The subcomponent is at least one selected from the group consisting of 3d transition metal ions whose magnetic moment is not 0 or rare earth transition metal ions whose magnetic moment is not 0 It is characterized by being.

In the method for producing an oriented ceramic according to the present invention, the subcomponent is at least selected from the group consisting of Mn ²⁺ , Fe ³⁺ , Ce ³⁺ , Nd ³⁺ , Sm ³⁺ and Dy ^3+. One type is preferable. This is because they are relatively inexpensive and readily available.

  According to the method for producing an oriented ceramic of the present invention, the main component having a perovskite structure is selected from the group consisting of 3d transition metal ions whose magnetic moment is not zero or rare earth transition metal ions whose magnetic moment is not zero. By using a polycrystalline ceramic powder containing a predetermined amount of at least one subcomponent, the polycrystalline ceramic powder can be oriented in a magnetic field even when the polycrystalline ceramic powder is used, and the cost is relatively low. It becomes possible to obtain oriented ceramics using powder. In addition, since it is not necessary to prepare a shape anisotropic host material, there are few restrictions on the composition in applying the present invention.

The oriented ceramic according to the present invention is mainly composed of a composite metal oxide having a perovskite structure represented by the general formula ABO ₃ . Specifically, BaTiO ₃ (barium titanate), SrTiO ₃ (strontium titanate), PbTiO ₃ (lead titanate), Pb (Zr, Ti) O ₃ (lead zirconate titanate), (K, Na, Li) (Nb, Ta) O ₃ , (Na _1/2 Bi _1/2 ) TiO ₃ and their solid solutions can be used.

Then, 5 mol or less (excluding 0 mol) of at least one selected from the group consisting of transition metal ions whose magnetic moment is not 0 and rare earth transition metal ions whose magnetic moment is not 0 is contained with respect to 100 mol of the main component. . Transition metal ions whose magnetic moment is not zero include Ti ³⁺ , V ³⁺ , V ⁴⁺ , Cr ²⁺ , Cr ³⁺ , Mn ²⁺ , Mn ³⁺ , Fe ²⁺ , Fe ³⁺ , Co ^{2. +} , Ni ²⁺ , Cu ²⁺ and the like. The rare earth transition metal ions whose magnetic moment is not 0 are Ce ³⁺ , Pr ³⁺ , Pr ⁴⁺ , Nd ³⁺ , Sm ²⁺ , Sm ³⁺ , Eu ²⁺ , Eu ³⁺ , Gd ^3+. , Tb ³⁺ , Tb ⁴⁺ , Dy ³⁺ , Ho ³⁺ , Er ³⁺ , Tm ²⁺ , Tm ³⁺ and Yb ³⁺ . Hereinafter, in the present specification, these are collectively referred to as magnetic metal ions for convenience.

  Although it is presumed that the magnetic susceptibility of crystal grains is improved by incorporating at least a part of these magnetic metal ions into the crystal lattice having a perovskite structure, and the magnetic particles are oriented by applying a magnetic field, but the detailed mechanism is not clear. In addition, it is considered that the magnetic metal ions taken into the crystal lattice are coordinated to either the A site or the B site depending on the valence and the ion radius, and coordinate to both the A site and the B site. Magnetic metal ions are also thought to exist. However, it is difficult to actually confirm the position in the crystal lattice.

  The reason why the content of magnetic metal ions is limited to 5 mol or less with respect to 100 mol of the main component is as follows. That is, when the magnetic metal ion as a subcomponent exceeds 10 mol with respect to 100 mol of the main component, the degree of orientation decreases. This is because it is difficult to obtain a single phase having a perovskite structure as the main component if there are too many subcomponents.

  Further, from the viewpoint of obtaining a higher altitude, the content of the subcomponent is preferably 0.1 mol or more and 1.0 mol or less with respect to 100 mol of the main component.

  In the present invention, oriented ceramics are obtained by applying a magnetic field when forming a ceramic slurry containing the main component and the magnetic metal ions. The applied magnetic field is preferably 1 T (tesla) or more.

  The method for producing an oriented ceramic according to the present invention is performed, for example, by the following procedure.

  First, oxides, hydroxides, carbonates or the like containing constituent elements of the main component and magnetic metal ions are prepared as raw materials, and these are weighed and mixed at a predetermined ratio. The obtained mixture is calcined under suitable conditions of a peak temperature of about 1200 to 1400 ° C. to obtain a calcined ceramic powder (polycrystalline ceramic powder).

  After pulverizing the ceramic calcined powder, an appropriate amount of water and a dispersing agent are added and dispersed to obtain a ceramic slurry. The obtained ceramic slurry is poured into a porous mold, and the mold is formed by absorbing moisture. During molding, a magnetic field is applied to the ceramic slurry. Thereby, a ceramic molded body is obtained.

  After sufficiently drying the obtained ceramic molded body, it is heated to about 500 ° C. to remove organic components, and then fired under appropriate conditions of about 1200 ° C. to 1400 ° C. Oriented ceramics can be obtained.

  According to the present invention, since at least one selected from the group consisting of 3d transition metal ions whose magnetic moment is not 0 or rare earth transition metal ions whose magnetic moment is not 0 is contained as a subcomponent, Crystals are oriented by applying a magnetic field, and oriented ceramics can be obtained. Such oriented ceramics are expected to have high electrical characteristics.

A first embodiment of the present invention will be described. The first embodiment relates to a method for producing an oriented ceramic mainly composed of barium titanate (BaTiO ₃ ).

BaCO ₃ and TiO ₂ are prepared as starting materials for main components, and MnCO ₃ , Fe ₂ O ₃ , Nd ₂ O ₃ , Ce ₂ (CO ₃ ) ₃ , Sm ₂ O ₃ and Dy ₂ O ₃ are prepared as subcomponents. These were weighed at a ratio satisfying the following general formula (A).

100BaTiO ₃ + aM (A)
(In the formula, M represents at least one of the subcomponents Mn ²⁺ , Fe ³⁺ , Nd ³⁺ , Ce ³⁺ , Sm ³⁺ and Dy ³⁺ .)
The weighed product was put into a ball mill, water was added, and wet mixing was performed for 16 hours to obtain a mixture. The obtained mixture was dried and calcined at 1250 ° C. to 1350 ° C. for 2 hours to obtain a calcined ceramic powder (polycrystalline ceramic powder). This ceramic calcined powder was put into a rotary pulverizer using a cutter blade and pulverized for 60 seconds, and further wet pulverized for 100 hours using a ball mill.

  A ceramic slurry was obtained by adding and mixing 25 parts by weight of water and 1 part by weight of a dispersant with respect to 100 parts by weight of the calcined ceramic calcined powder. The viscosity of the ceramic slurry was measured and found to be 100 mPa · s. In order to further improve dispersibility, ultrasonic stirring was performed for 5 minutes while dispersing with a stirrer.

  The ceramic slurry was poured into a porous mold, and the mold was formed by absorbing moisture. During molding, a predetermined magnetic field was applied to the ceramic slurry. Thereby, a ceramic molded body of 30 mm × 30 mm × 5 mm was obtained.

  After sufficiently drying this ceramic molded body, heat treatment was performed at 500 ° C. for 2 hours to remove organic components. Subsequently, the sintered body (oriented ceramic) was obtained by performing baking for 2 hours at 1300-1400 degreeC in air | atmosphere.

  The surface of this sintered body was analyzed by an X-ray diffraction method (ray source CuKα, 40 kV, 200 mA), and the peak intensity of each crystal plane was measured. Further, for comparison, each sample was pulverized to prepare a powder sample, and the peak intensity of each crystal plane was also measured for the powder sample by the X-ray diffraction method. Then, the degree of orientation was measured by the Lotgering method using a comparative powder sample as a reference.

  Here, the oriented ceramic satisfying the general formula (A) exhibits a tetragonal crystal at room temperature, but the orientation degree of {100} plane, that is, {100} plane and {001} plane in the tetragonal crystal when viewed as a pseudo-cubic crystal. Asked. Pseudocubic refers to a crystal lattice that is slightly distorted than cubic.

  Table 1 shows the composition, applied magnetic field, and orientation of each sample. In Table 1, the sample numbers marked with * are comparative examples outside the scope of the present invention.

  Since sample numbers 1 and 2 do not contain M, which is a subcomponent, the degree of orientation is low and substantially non-oriented. It should be noted that although the degree of orientation of Sample No. 2 is 4.1%, it seems to be slightly oriented, but it is known that the accuracy is lowered when the degree of orientation is particularly low in the Lotgering method. The degree may be regarded as substantially non-oriented.

In sample numbers 3, 5, 6, 7, and 8 containing Mn ²⁺ as the subcomponent M, the degree of orientation is in the range of 10.4 to 60.1%, respectively. It turns out that is now possible. In particular, a high degree of orientation of 49.6% or more was obtained with sample numbers 3, 5, and 6 in which the molar ratio a of the subcomponent M to 100 mol of the main component was in the range of 0.1 to 1.0.

Sample No. 9 contains Mn ²⁺ as an accessory component M, but its content ratio a is 15.0, which exceeds the range of the present invention, so the degree of orientation is 1.8%, which is substantially non-oriented. It was. This is presumably because it became difficult to obtain a single phase having a perovskite structure as a main component by containing the subcomponent M excessively.

Even in sample numbers 10 to 16 containing Fe ³⁺ , Nd ³⁺ , Ce ³⁺ , Sm ³⁺ or Dy ³⁺ as subcomponent M, an orientation degree of 10.8 to 85.4% could be obtained. . In particular, Sample No. 16 containing 1.0 mol of Dy ³⁺ as the subcomponent M with respect to 100 mol of the main component was able to obtain a high degree of orientation of 85.4%.

Next, a method for producing an oriented ceramic according to the second embodiment of the present invention will be described. The oriented ceramic according to the present example is composed mainly of lead zirconate titanate (Pb (Zr, Ti) O ₃ .

Pb ₃ O ₄ , ZrO ₂ and TiO ₂ were prepared as starting materials for the main component, and MnCO ₃ was prepared as a raw material for the accessory component, and these were weighed at a ratio satisfying the following general formula (B).

100Pb (Zr _0.5 Ti _0.5 ) O ₃ + aM (B)
(In the formula, M represents an auxiliary component Mn ²⁺ .)
Using this weighed product, a sintered body (oriented ceramic) was produced by the same production method as in Example 1. The degree of orientation was determined by the same method as in Example 1. Table 1 shows the composition, applied magnetic field, and orientation of each sample. In Table 2, the sample numbers marked with * are comparative examples outside the scope of the present invention.

  Sample No. 17 containing no subcomponent M was substantially non-oriented even when a 12T magnetic field was applied. However, sample numbers containing 0.5 mol and 1.0 mol of subcomponent M with respect to 100 mol of main component, respectively. In 18 and 19, an orientation degree of 15.4 to 32.0% could be obtained.

Claims (2)

Obtaining a ceramic slurry comprising polycrystalline ceramic powder;
Forming the ceramic slurry in a magnetic field to obtain a ceramic molded body;
Firing the ceramic molded body, and a method for producing an oriented ceramics comprising:
The polycrystalline ceramic powder includes a main component having a perovskite structure and subcomponents contained at a ratio of 5 mol or less (excluding 0 mol) with respect to 100 mol of the main component,
The method for producing oriented ceramics characterized in that the subcomponent is at least one selected from the group consisting of 3d transition metal ions whose magnetic moment is not 0 or rare earth transition metal ions whose magnetic moment is not 0. The subcomponent ^{Mn 2+, Fe 3+, Ce 3+} , Nd 3+, according to claim 1, characterized in that at least one member selected from the group consisting of Sm ³⁺ and Dy ³⁺ A method for producing oriented ceramics.