JP2010090021A - Method for producing sintered compact of compound with perovskite structure - Google Patents

Abstract

A method for producing a sintered body of a perovskite structure compound having a high degree of orientation is provided.
A step of preparing a single crystal powder comprising single crystal particles of a perovskite structure compound, a step of producing a ceramic slurry containing the single crystal powder as a dispersed phase, and molding the ceramic slurry in a magnetic field To obtain a ceramic molded body and to sinter the ceramic molded body. More practically, a polycrystalline powder comprising polycrystalline particles of the same perovskite structure compound as the perovskite structure compound constituting the single crystal powder is further prepared, and the ceramic slurry is not only a single crystal powder as a dispersed phase, The polycrystalline powder is also included.
[Selection] Figure 7

Description

  The present invention relates to a method for producing a sintered body made of a compound having a perovskite structure, and particularly relates to an improvement for enhancing the crystal orientation of the sintered body.

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 ceramics having a perovskite structure, it is known that various properties are improved by orienting the crystal.

  In order to obtain high crystal orientation, for example, a TGG (Templated Grain Growth) method is applied in the case of a Bi layered compound, but in the case of a perovskite structure compound, since the crystal shape anisotropy is small, the TGG method In order to orient the film, it is necessary to introduce a costly process such as a TMC method (Topochemical Micro-crystal Conversion Method).

  On the other hand, in the case of a tungsten bronze compound, even if the crystal shape anisotropy is small, the crystal anisotropy is large (the difference in magnetic susceptibility is large depending on the crystal axis). Thus obtained sintered body is obtained. However, in the case of a perovskite structure compound, since the crystal anisotropy is small, it is generally difficult to achieve high orientation by molding in a magnetic field.

  Thus, attention is focused on the technique described in Japanese Patent Application Laid-Open No. 2008-37064 (Patent Document 1) as a molding technique in a magnetic field that can be applied to a perovskite structure compound. Patent Document 1 discloses a technique for orienting ceramic polycrystalline powder in a magnetic field. More specifically, the technique described in Patent Document 1 is intended to form a ceramic slurry in a magnetic field that contains a perovskite structure compound as a main component of a dispersed phase and contains, for example, a 3d element as a subcomponent. .

However, the technique described in Patent Document 1 has a problem that it costs because it includes, for example, a 3d element as a subcomponent. Further, even with the technique described in Patent Document 1, there is still room for improvement with respect to the improvement of the orientation degree, and further improvement of the orientation degree is desired.
JP 2008-37064 A

  Accordingly, an object of the present invention is to provide a method for producing a sintered body of a perovskite structure compound that can solve the above-described problems.

  In order to solve the technical problem described above, a method for producing a sintered body of a perovskite structure compound according to the present invention includes a step of preparing a single crystal powder composed of single crystal particles of a perovskite structure compound, and It comprises a step of producing a ceramic slurry containing crystal powder, a step of obtaining a ceramic molded body by molding the ceramic slurry in a magnetic field, and a step of sintering the ceramic molded body.

  In carrying out the method for producing a sintered body of a perovskite structure compound according to the present invention, in a more practical aspect, a polycrystalline powder comprising polycrystalline particles of the same perovskite structure compound as the perovskite structure compound constituting the single crystal powder. Is prepared, and the ceramic slurry includes not only a single crystal powder but also the polycrystalline powder as a dispersed phase.

  In the embodiment described above, it is preferable that the single crystal powder occupies 5 mol% or more of the dispersed phase in the ceramic slurry.

  The single crystal powder preferably accounts for 90 mol% or less of the dispersed phase in the ceramic slurry.

  In the present invention, the step of preparing the single crystal powder preferably includes the step of crystal-growing the particles of the perovskite structure compound by heat-treating the calcined powder of the perovskite structure compound in a flux. In this case, at least one of KCl and NaCl is advantageously used as the flux.

The perovskite structure compound is preferably composed mainly of PbTiO ₃ .

  According to the present invention, the ceramic slurry containing the single crystal powder composed of the single crystal particles of the perovskite structure compound is molded in a magnetic field and sintered, so that even if the crystal shape anisotropy is small A sintered body having a uniform crystal orientation, that is, a high degree of orientation can be obtained.

  The reason for this can be estimated as follows. In normal calcined powder, since the particles are composed of polycrystals, the moment that the magnetic field rotates the particles cancels out as a whole. Since the rotating moments do not cancel each other, it can be assumed that a high degree of orientation can be obtained even with a perovskite structure compound having a small crystal anisotropy.

  In addition, the sintered body obtained by the present invention has a shape anisotropy of crystals in the sintered body as compared with a sintered body produced by a TGG method that uses crystal shape anisotropy for orientation. Since it is small, it can be made difficult to generate and develop cracks.

  In this invention, if the ceramic slurry contains not only single crystal powder but also polycrystalline powder as the dispersed phase, the polycrystalline powder can be obtained at a lower cost than the single crystal powder. The cost for implementing the manufacturing method of the sintered compact which concerns on this can be reduced, and it can be excellent in practicality.

  In the above-described embodiment, when the single crystal powder occupies 5 mol% or more of the dispersed phase, the effect of improving the orientation by the single crystal powder can be reliably achieved.

The present invention is directed to a method for producing a sintered body of a perovskite structure compound such as a sintered body mainly composed of PbTiO ₃ .

  In order to manufacture a sintered body of a perovskite structure compound according to the present invention, first, a single crystal powder composed of single crystal particles of a perovskite structure compound is produced. Therefore, a calcined powder of the perovskite structure compound is prepared, and this calcined powder is heat-treated in the flux. As a result, the perovskite structure compound particles grow and a single crystal powder composed of the single crystal particles of the perovskite structure compound is obtained. Here, at least one of KCl and NaCl is advantageously used as the flux.

  On the other hand, a polycrystalline powder composed of polycrystalline particles of the same perovskite structure compound as the perovskite structure compound constituting the single crystal powder is further prepared.

  Next, a ceramic slurry containing both the single crystal powder and the polycrystalline powder as a dispersed phase is produced. Here, in order to more reliably achieve the effect of improving the degree of orientation by the single crystal powder, the single crystal powder preferably occupies 5 mol% or more of the dispersed phase in the ceramic slurry.

  In addition, you may use only a single crystal powder as a dispersed phase in a ceramic slurry, without using a polycrystalline powder. The orientation degree can be further improved by using only the single crystal powder. However, since the cost for obtaining a single crystal powder is higher than the cost for obtaining a polycrystalline powder, in practice, the dispersed phase includes both single crystal powder and polycrystalline powder. From the viewpoint of cost, the single crystal powder preferably accounts for 90 mol% or less of the dispersed phase, and more preferably accounts for 50 mol% or less.

  Next, the ceramic slurry is molded in a magnetic field, whereby a ceramic molded body is obtained. In this step, the crystal axes of the single crystal particles constituting the single crystal powder are oriented so as to face a predetermined direction in accordance with the applied magnetic field.

  Next, the ceramic molded body is fired. As a result, a sintered body having a high degree of orientation can be obtained.

  Next, experimental examples carried out to confirm the effects of the present invention will be described.

1. Sample preparation [Sample 1]
Sample 1 is within the scope of the present invention, and in producing a ceramic slurry, only a single crystal powder is used as a dispersed phase.

Each powder of PbO and TiO ₂ was weighed so that the molar ratio of Pb: Ti was 1: 1, and these were wet mixed in a ball mill for 15 hours, then calcined and dried at 1100 ° C., and PbTiO ₃ calcined product Got. FIG. 1 shows an SEM image of the PbTiO ₃ calcined product.

Next, the calcined product was dry pulverized and mixed with KCl so as to have a weight ratio of 1: 1. This at an alumina crucible, and 12 hours heat treatment at 1000 ° C., after cooling to room temperature, dissolved and removed KCl with water, dried, crystallized grown PbTiO ₃ PbTiO ₃ single constituted by a single crystal grain Crystal powder was obtained. Figure 2 shows the SEM images of PbTiO ₃ single crystal particles constituting the PbTiO ₃ single crystal powder, Figure 3 shows a TEM image of the PbTiO ₃ single crystal grains, FIG. 4, the same PbTiO ₃ single crystal grains An electron diffraction image is shown.

As shown in FIG. 2, in the PbTiO ₃ single crystal particles, cubic crystals are grown and the crystal shapes are uniform. It can be seen from FIG. 3 that desirable rectangular parallelepiped particles are obtained. As shown in FIG. 4, when the electron diffraction pattern was measured at several points in the PbTiO ₃ single crystal particle, the spot was formed along a straight line. You can see that the axes are aligned.

Next, 30 g of the crystal-grown PbTiO ₃ single crystal particles obtained as described above were taken out, and 0.5 parts by weight of polyvinyl alcohol and 40 parts by weight of pure water were added to 100 parts by weight of the PbTiO ₃ single crystal particles. Was added and mixed with a ball mill for 12 hours to obtain a ceramic slurry.

  Next, the ceramic slurry was cast and molded in a magnetic field of 12 T to obtain a ceramic molded body. And the sintered compact which concerns on the sample 1 was obtained by baking this ceramic molded object at the temperature of 1200 degreeC.

[Sample 2]
Sample 2 is within the scope of the present invention, and uses both single crystal powder and polycrystalline powder as a dispersed phase when producing a ceramic slurry.

In the same manner as in the case of Sample 1, a PbTiO ₃ single crystal powder composed of crystal-grown PbTiO ₃ single crystal particles was obtained.

On the other hand, each powder of PbO and TiO ₂ was weighed so that the molar ratio of Pb: Ti was 1: 1, and these were wet mixed in a ball mill for 15 hours, then calcined and dried at 900 ° C., and PbTiO ₃ A calcined product was obtained. FIG. 5 shows an SEM image of the PbTiO ₃ calcined product. In comparison Figure 5 with the FIG. 1 described above, PbTiO ₃ calcined product shown in Figure 5, since the calcination temperature is lower than the PbTiO ₃ calcined product shown in FIG. 1, folded crystals sufficiently grown It can be seen that the PbTiO ₃ polycrystalline powder is composed of PbTiO ₃ polycrystalline particles.

Next, the PbTiO ₃ single crystal powder 5g, and the PbTiO ₃ polycrystalline powder extraction 45g respectively, per 100 parts by weight of PbTiO ₃ single crystal powder and PbTiO ₃ polycrystalline powder, 0.5 part by weight Of polyvinyl alcohol and 40 parts by weight of pure water were added and mixed in a ball mill for 12 hours to obtain a ceramic slurry.

In addition, as a result of evaluating the disperse phase contained in the ceramic slurry produced as described above by TEM, it was found that 5 mol% of PbTiO ₃ single crystal powder was contained in the disperse phase. Thus, although the PbTiO ₃ single crystal powder was 10 mol% before mixing, the reason why the PbTiO ₃ single crystal powder was reduced to 5 mol% after mixing was thought to be because the crystals were broken during the mixing process. It is done.

  Next, the ceramic slurry was cast and molded in a magnetic field of 12 T to obtain a ceramic molded body. And the sintered compact which concerns on the sample 2 was obtained by baking this ceramic molded object at the temperature of 1200 degreeC.

[Sample 3]
Sample 3 is outside the scope of the present invention and uses only polycrystalline powder as a dispersed phase when preparing a ceramic slurry.

30 g of PbTiO ₃ polycrystalline powder composed of the PbTiO ₃ polycrystalline particles used for the preparation of Sample 2 was taken out, and 0.5 parts by weight of polyvinyl alcohol and 40 parts by weight of 100 parts by weight of the PbTiO ₃ polycrystalline particles. Pure water was added and mixed with a ball mill for 12 hours to obtain a ceramic slurry.

  Next, the ceramic slurry was cast and molded in a magnetic field of 12 T to obtain a ceramic molded body. And the sintered compact which concerns on the sample 3 was obtained by baking this ceramic molded object at the temperature of 1200 degreeC.

2. Evaluation XRD charts of the sintered bodies according to each of Samples 1, 2, and 3 obtained as described above are shown in the upper stages of FIGS. 6 (a), (b), and (c), respectively. In each lower stage of FIGS. 6A, 6B and 6C, a ceramic molded body formed without applying a magnetic field is fired while using the ceramic slurry according to each of Samples 1, 2, and 3. An XRD chart of each sintered body obtained in this manner is shown.

  According to the sample 1, as shown in the upper part of FIG. 6A, only the peak in the <100> direction is observed, and it can be seen that the degree of orientation is almost 100%.

  Next, according to Sample 2, as shown in the upper part of FIG. 6B, it can be seen that the peak in the <100> direction is high and the orientation is in the <100> direction.

  On the other hand, in the sample 3, it can be seen that the upper pattern in FIG. 6C is almost the same as the lower pattern and is not oriented.

  Next, the degree of orientation of the sintered body according to each sample obtained was calculated based on the following formula (1) by the Lotgering method. In the calculation of the degree of orientation, a sintered body having the same composition obtained by firing a ceramic molded body molded without applying a magnetic field was used as a comparative sample.

  Here, ΣI (HKL) is the sum of X-ray peak intensities of specific crystal planes (HKL) in the ceramic sintered body to be evaluated, and ΣI (hkl) is the total crystal plane of the ceramic sintered body to be evaluated ( hkl) is the sum of the X-ray peak intensities.

  ΣIo (HKL) is the sum of X-ray peak intensities of specific crystal planes (HKL) of the comparative sample, and ΣIo (hkl) is the X-ray peak intensities of all crystal planes (hkl) of the comparative sample. Is the sum of

  The measurement conditions were 2θ = 20-60 deg. Moreover, each intensity | strength of <001>, <011>, <111>, <002>, <102>, and <112> was used as a X-ray peak intensity of all the crystal planes (hkl). As specific crystal planes (HKL), strengths of <001> and <002> were used.

  Table 1 shows the degree of orientation of the sintered bodies according to Samples 1 to 3 thus obtained.

  As can be seen from Table 1, according to samples 1 and 2, a high degree of orientation was obtained, and in particular, in sample 1, an extremely high degree of orientation such as 99% was obtained. On the other hand, in sample 3, the degree of orientation is 0%, indicating that the sample is not oriented.

  FIG. 7 shows an SEM image of the surface of the sintered body according to Sample 1. From FIG. 7, it can be seen that in the sintered body according to Sample 1, crystal grains are isotropically grown and the shape anisotropy is small. In general, in order to increase the degree of orientation of the sintered body, it is necessary to apply a TGG method or the like, but in that case, the shape anisotropy is large, cracks are likely to progress, and the strength cannot be obtained. Although there is a problem, according to the sintered body according to sample 1, as described above, since the shape anisotropy is small, cracks are hardly generated or propagated, and a sintered body having high strength can be obtained.

In experimental examples, it is a view showing an SEM image of PbTiO ₃ calcined product was used to prepare a sample 1. In Experimental Examples, to prepare a sample 1, is a view showing an SEM image of the obtained PbTiO ₃ single crystal particles by crystal growth PbTiO ₃ calcined product shown in FIG. PbTiO shown in FIG. 2 ₃ is a view showing a TEM image of single-crystal particles. FIG. ₃ is a diagram showing an electron beam diffraction image of the PbTiO ₃ single crystal particle shown in FIG. 2. In experimental examples, it is a view showing an SEM image of PbTiO ₃ calcined product used to make Samples 2 and 3. The XRD charts of the sintered bodies according to each of Samples 1, 2, and 3 prepared in the experimental example are shown in the upper sections of (a), (b), and (c), respectively, and (a), (b) And in each lower stage of (c), there is an XRD chart of each sintered body obtained by firing a ceramic molded body molded without applying a magnetic field while using the ceramic slurry according to each of Samples 1, 2, and 3. FIG. It is a figure which shows the SEM image of the surface of the sintered compact concerning the sample 1 produced in the experiment example.

Claims (7)

Preparing a single crystal powder comprising single crystal particles of a perovskite structure compound;
Producing a ceramic slurry containing the single crystal powder as a dispersed phase;
Forming a ceramic molded body by molding the ceramic slurry in a magnetic field;
A method for producing a sintered body of a perovskite structure compound, comprising the step of sintering the ceramic molded body.   A step of preparing a polycrystalline powder composed of polycrystalline particles of the same perovskite structure compound as the perovskite structure compound constituting the single crystal powder, and the ceramic slurry includes the single crystal powder and the polycrystalline as the dispersed phase. The manufacturing method of the sintered compact of the perovskite structure compound of Claim 1 containing both powder.   The method for producing a sintered body of a perovskite structure compound according to claim 2, wherein the single crystal powder occupies 5 mol% or more of the dispersed phase in the ceramic slurry.   The method for producing a sintered body of a perovskite structure compound according to claim 2 or 3, wherein the single crystal powder occupies 90 mol% or less of the dispersed phase in the ceramic slurry.   The step of preparing the single crystal powder includes a step of crystal-growing the particles of the perovskite structure compound by heat-treating the calcined powder of the perovskite structure compound in a flux. A method for producing a sintered body of a perovskite structure compound.   The method for producing a sintered body of a perovskite structure compound according to claim 5, wherein at least one of KCl and NaCl is used as the flux. The method for producing a sintered body of a perovskite structure compound according to any one of claims 1 to 6, wherein the perovskite structure compound contains PbTiO ₃ as a main component.