JP2003034576A - Crystal-orientated ceramic and its production method, plate-shaped powder for producing crystal-orientated ceramic, and thermoelectric transducer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crystal-oriented ceramic which comprises a cobalt-layered oxide showing thermoelectric properties and has high figure of merit, and to provide its production method, a plate-shaped powder for producing the crystal- orientated ceramic, and a thermoelectric transducer using the same. SOLUTION: The crystal-orientated ceramic comprises a cobalt-layered oxide, preferably a polycrystal of a calcium-cobalt layered oxide expressed by a general formula: (Ca1-x Ax )2 CoO3+α}(CoO2+β )y (wherein A is one or more element selected from among alkali metal, alkaline earth metal and Bi; and 0<=x<=0.3, 0.5<=y<=2.0, 0.85<= 3+α+(2+β)y}/(3+2y)<=1.15), and it is characterized in that each crystal grain composing the polycrystal has a degree of 001} plane orientation of 50% or more. These crystal-oriented ceramics can be obtained by molding mixture of layered oxide-producing raw materials such as Co(OH)2 plate- shaped powders and CaCO3 so as to orient the plate-shaped powders, and by heating at a predetermined temperature.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a crystallographically-oriented ceramic, a method for producing the same, a plate-like powder for producing a crystallographically-oriented ceramic, and a thermoelectric conversion element, and more specifically,
Various thermoelectric generators such as solar thermal power generators, seawater temperature differential thermoelectric power generators, fossil fuel thermoelectric power generators, photodetectors, laser diodes, field effect transistors, photomultiplier tubes, spectrophotometer cells, chromatography columns Crystallographically oriented ceramics suitable as a thermoelectric conversion material constituting a thermoelectric conversion element used in a precision temperature control device such as a thermostatic device, a constant temperature device, a cooling and heating device, a refrigerator, a power source for a watch, etc. And a thermoelectric conversion element using such a crystallographically-oriented ceramic as a thermoelectric conversion material.

[0002]

2. Description of the Related Art Thermoelectric conversion refers to the direct conversion of electric energy into cooling or heating, or conversely, thermal energy into electric energy, utilizing the Sevek effect or the Peltier effect. Thermoelectric conversion (1) does not discharge excess waste during energy conversion, (2) enables effective use of waste heat, (3) can continuously generate power until the material deteriorates (4) It has attracted attention as a technology for highly efficient use of energy because it has features such as no need for moving devices such as motors and turbines, and no need for maintenance.

As an index for evaluating the characteristics of a material capable of converting heat into electricity, that is, a thermoelectric conversion material, in general, a figure of merit Z (= S ² σ / κ, where S: Seebeck coefficient,
σ: electrical conductivity, κ: thermal conductivity), or figure of merit Z
And the dimensionless figure of merit ZT represented as the product of the absolute temperature T indicating that value are used. The Seebeck coefficient represents the magnitude of electromotive force generated by a temperature change of 1K. Thermoelectric conversion materials each have a unique Seebeck coefficient, and are roughly classified into those having a positive Seebeck coefficient (p type) and those having a negative Seebeck coefficient (n type).

Further, the thermoelectric conversion material is usually used in a state where a p-type thermoelectric conversion material and an n-type thermoelectric conversion material are joined. Such a junction pair is generally called a thermoelectric conversion element. The performance index of the thermoelectric conversion element is the performance index Z _p of the p-type thermoelectric conversion material and the performance index Z of the n-type thermoelectric conversion material.
_n and the shape of the p-type and n-type thermoelectric conversion materials, and when the shape is optimized, the larger Z _p and / or Z _n is, the larger the figure of merit of the thermoelectric conversion element is. Is known to be. Therefore, in order to obtain a thermoelectric conversion element having a high figure of merit, the figure of merit Z _p , Z _n
It is important to use a high thermoelectric conversion material.

As such a thermoelectric conversion material, for example, various materials such as Bi-Te series, Pb-Te series, Si-Ge series, and oxide ceramic series are known. Among these, Bi-Te-based and Pb-Te-based compound semiconductors exhibit excellent thermoelectric properties (ZT to 0.8) near room temperature and in the medium temperature range of 300 to 500 ° C, respectively.
However, it is difficult to use these compound semiconductors in a high temperature range. In addition, there is a problem that the material contains expensive rare elements (eg, Te, Sb, Se, etc.) and highly toxic environmental load substances (eg, Te, Sb, Se, Pb, etc.).

On the other hand, the Si-Ge-based compound semiconductor is 1
Excellent thermoelectric properties (ZT-
1.0) and that the material does not contain environmentally hazardous substances. However, the Si-Ge-based compound semiconductor has a problem that it is necessary to protect the material surface in order to use it in a high temperature atmosphere for a long time, and the thermal durability is low.

On the other hand, oxide ceramics thermoelectric conversion materials do not necessarily contain rare elements or environmentally hazardous substances. In addition, the thermoelectric property is less deteriorated even when used in a high temperature atmosphere for a long time, and the thermal durability is excellent. Therefore, oxide ceramics thermoelectric conversion materials are attracting attention as alternatives to compound semiconductors, and new materials with high thermoelectric properties and their manufacturing methods are
Various proposals have been made in the past.

For example, AC Masset et al. Produced polycrystalline and single crystals of Ca ₃ Co ₄ O ₉ which is a kind of layered oxide containing cobalt, and evaluated its crystal structure and thermoelectric properties ( ACMasset et al., Phys. Rev. B, 62
(1), pp.166-175, 2000). In the same document, Ca ₃ C
o ₄ O ₉ is Ca ₂ CoO ₃ having a rock salt type crystal structure.
It is described that the layer and the CoO ₂ layer having a CdI ₂ type crystal structure are lattice-mismatched layered oxides stacked in the c-axis direction at a predetermined cycle.

Further, in the document, the resistivity of Ca ₃ Co ₄ O ₉ has anisotropy, and the resistivity in the {001} plane is {0
It is described that the specific resistance is significantly smaller than the specific resistance in the direction perpendicular to the 0l plane (that is, the c-axis direction). Furthermore, C
It is described that the Seebeck coefficient in the {00l} plane direction of the a ₃ Co ₄ O ₉ single crystal reaches approximately 125 μV / K in the vicinity of 300 K, and the temperature dependence of the Seebeck coefficient is also small.

The "{001} plane" of the layered oxide containing cobalt is a plane having high thermoelectric properties, that is,
The plane parallel to the CoO ₂ layer. In many layered oxides containing cobalt, the crystal structure has not been clarified, and the definition of the crystal axis and the crystal plane is different depending on how the unit cell is taken. In the present invention, the {001} plane is It is defined as above.

Further, for example, Japanese Patent Laid-Open No. 2001-19544.
No._TwoSr_2-xCa _xCo_TwoO_w, Bi
_2-yPb_ySr_TwoCo_TwoO_w, Bi_TwoSr_2-zLa
_zCo_TwoO_w(Where 0 ≦ x ≦ 2, 0 ≦ y ≦
0.5, 0 <z ≦ 0.5) and has a layered structure
And has a crystal structure of 1.0 × 10^FourS / m or more
A composite oxide sintered body having gas conductivity is disclosed.
Further, in the publication, Bi supply source, Sr supply source, Ca supply
Source, Co supply source, etc.
By heating in an oxygen atmosphere while applying axial pressure, the original
After partially melting a part of the material, slowly cooling the composite oxide
A manufacturing method is disclosed.

[0012]

Problems to be Solved by the Invention Ca ₃ Co ₄ O ₉ , B
The layered oxide containing cobalt, such as i ₂ Sr _2-x Ca _x Co ₂ O _w , is a p-type thermoelectric conversion material having a relatively large Seebeck coefficient, and moreover, its thermoelectric property has a crystal orientation. There is anisotropy according to. Therefore, by using a material in which crystal planes ({001} planes) having high thermoelectric properties are oriented in one direction, the anisotropy of thermoelectric properties can be utilized to the maximum extent, and improvement in the figure of merit can be expected. Further, improvement in the figure of merit of the thermoelectric conversion element using this can also be expected.

However, in a general ceramics manufacturing process in which a mixture of simple compounds containing constituent elements such as CaCO ₃ and Co ₃ O ₄ is calcined, and this is molded and sintered,
It is not possible to obtain a sintered body of cobalt layered oxide in which crystal planes having high thermoelectric properties are oriented in one direction.

On the other hand, in Japanese Patent Laid-Open No. 2001-19544, a part of a raw material is partially melted while uniaxially pressing a molded body and then gradually cooled, recrystallization occurs in the cooling process, and parallel to the pressing surface. It is described that a sintered body composed of crystal grains having {001} planes grown along the direction can be obtained. However, in this method, it is limited to only a material system or composition that can obtain a desired crystal by recrystallization, for example,
There is a problem that it cannot be applied to a system that causes a phase separation or a change in crystal structure during crystallization.

Further, in order to orient the crystal planes having high thermoelectric properties, it may be possible to single crystallize the layered oxide containing cobalt. However, the single crystal has a problem of high manufacturing cost. In general, a small single crystal can be obtained, but it is difficult to manufacture a bulk material of millimeter order size used for thermoelectric conversion.

An object of the present invention is to provide a crystallographically-oriented ceramic which is composed of a layered oxide containing cobalt showing excellent thermoelectric properties and has a high figure of merit. Further, another problem to be solved by the present invention is to provide a method for producing a crystallographically-oriented ceramics which can be applied to a wide range of crystallographically-oriented ceramics regardless of a material system and which can be efficiently produced. To do.

Another object of the present invention is to provide a plate-like powder for producing crystal-oriented ceramics, which is suitable for producing such crystal-oriented ceramics. Furthermore, another problem to be solved by the present invention is to provide a thermoelectric conversion element using such a crystallographically-oriented ceramic as a thermoelectric conversion material.

[0018]

In order to solve the above-mentioned problems, the crystallographically-oriented ceramics according to the present invention is composed of a polycrystalline layered oxide containing cobalt. The gist is that the degree of orientation of the {001} plane is 50% or more.

The crystallographically-oriented ceramics according to the present invention is composed of a layered oxide polycrystal containing cobalt exhibiting excellent thermoelectric properties, and the {00l} plane of each crystal grain is oriented with a high degree of orientation. Therefore, the figure of merit in the direction parallel to the direction in which the {001} plane is oriented is higher than the figure of merit of the non-oriented sintered body having the same composition.

Further, in the method for producing a crystallographically-oriented ceramic according to the present invention, a plate-like powder whose developed surface has lattice matching with the CoO ₂ layer of a layered oxide containing cobalt is reacted with the plate-like powder. And a layered oxide forming raw material to be the layered oxide, a mixing step, a molding step of molding the mixture obtained in the mixing step so that the plate-like powder is oriented, and a molding step obtained in the molding step. The gist of the present invention is to include a sintering step of heating the molded body and reacting the plate-like powder with the layered oxide forming raw material.

When a plate-like powder whose developed surface has lattice matching with the CoO ₂ layer ({001} plane) of a layered oxide containing cobalt and a layered oxide forming raw material having a predetermined composition are reacted with each other. , Plate-like crystals of layered oxide containing cobalt which inherits the orientation of the plate-like powder are formed. Therefore, if such a plate-like powder is oriented in a compact and heated at a predetermined temperature, the crystal orientation in which the plate-like crystals of the layered oxide containing cobalt having a developed {001} plane are oriented in one direction. Ceramics are obtained.

Further, the plate-like powder for producing a crystallographically-oriented ceramic according to the present invention comprises Co (OH) ₂ and
A plate powder having a {001} plane as a development plane, Co ₃ O ₄ and a plate powder having a {111} plane as a development plane, and a plate made of CoO and having a {111} plane as a development plane. It is composed of one or more plate-like powders selected from powdery powders. Co (OH) ₂ , Co ₃ O ₄ and CoO are relatively easy to produce a plate-like powder having the {001} plane, {111} plane and {111} plane as the developed planes, respectively. Also,
These crystal planes have extremely good lattice matching with the CoO ₂ layer of the cobalt layered oxide. Therefore, if these plate-like powders are used as the reactive template, the crystal oriented ceramics according to any one of claims 1 to 6 can be easily manufactured.

Further, the gist of the thermoelectric conversion element according to the present invention is that the crystal oriented ceramics according to the present invention is used as a thermoelectric conversion material. Since the crystal-oriented ceramics according to the present invention has a performance index higher than that of a non-oriented sintered body having the same composition, a thermoelectric conversion element using the same has a non-oriented sintered body having the same composition. Shows a higher figure of merit than the thermoelectric conversion element using.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below. The crystallographically-oriented ceramics according to the present invention is composed of a polycrystal of layered oxide containing cobalt (hereinafter, referred to as “cobalt layered oxide”), and {001} of each crystal grain constituting the polycrystal. The orientation of the surface is 5
It is characterized by being 0% or more.

Here, the "cobalt layered oxide" means a structure.
Structure is not clarified, but CoO _TwoFirst sub-layer consisting of layers
Lattice and CoO_TwoA second sub-lattice consisting of a layer different from the layer
Layered compound deposited in a predetermined cycle, that is, CoO
_TwoA layered compound having a layer as a sublattice. Of these, the first
One sublattice (CoO_TwoLayer) is a conductive layer, and the second sublattice is
It is currently considered to be an insulating layer.

The first sublattice is one layer or two or more layers of CoO.
_It consists of _two layers. The “CoO ₂ layer” has one Co atom at the center of the octahedron and has a total of 6 at the apex.
It means that CoO ₆ octahedra having oxygen atoms are two-dimensionally connected so as to share oxygen. In this case, CoO
Part of the Co atoms contained in the _two layers may be replaced with another metal element (for example, Cu).

On the other hand, the second sublattice may be a layer different from the CoO ₂ layer, and its composition and structure are not particularly limited. That is, the second sub-lattice may be composed of one type of layer, or may be a combination of two or more types of layers having different compositions and sub-lattice structures regularly or irregularly. Is also good. However, in order to obtain high thermoelectric properties, it is particularly preferable that the second sublattice has a rock salt structure or a distorted rock salt structure.

Further, the first sub-lattice and the second sub-lattice may be deposited alternately, and the deposition cycle is not particularly limited. That is, in the cobalt layered oxide, one layer or two or more layers of CoO ₂ (first sub-lattice) and one layer or two or more layers of another (second sub-lattice) have a short period or a long period. May be regularly deposited, or these may be irregularly deposited.

Specific examples of the layered cobalt oxide include Ca ₃ Co ₄ O ₉ , Bi ₂ Ca ₂ Co ₂ O ₉ and Bi.
_{As a} preferable example, ₂ Sr ₂ Co ₂ O ₉ , Bi ₂ Ba ₂ Co ₂ O ₉ , and the like, and a layered oxide in which a part of the cation element constituting these layered oxides is replaced with another element are preferable. Can be mentioned. Among these, the cobalt layered oxide containing calcium (hereinafter, referred to as “calcium cobalt layered oxide”), in particular, the calcium cobalt layered oxide represented by the general formula of the following chemical formula 1 has high thermoelectricity. Since it has characteristics, a thermoelectric conversion material having a high figure of merit can be obtained by aligning the crystal orientations in one direction.

[0030]

## STR1 ## _{{(Ca 1-x A x} ) 2 CoO 3 + α} (Co
O _{2 + β} ) _y (where A is an alkali metal, an alkaline earth metal and B
one or more elements selected from i, 0 ≦ x ≦ 0.
3, 0.5 ≦ y ≦ 2.0, 0.85 ≦ {3 + α + (2+
β) y} / (3 + 2y) ≦ 1.15)

In the formula of Chemical formula 1, "0.85≤
{3 + α + (2 + β) y} / (3 + 2y) ≦ 1.15 ”
Is a basic composition ({(Ca _1-x A _x ) ₂ CoO ₃ } (CoO
₂ ) _y ) with respect to the stoichiometric amount of oxygen (3 + 2y) contained in the calcium-cobalt layered oxide having a maximum of ± 1
Oxygen becomes excessive in the range of 5 atm%, or
Indicates that oxygen deficiency may occur. in this case,
The increasing / decreasing oxygen may be either oxygen (β) contained in the first sublattice or oxygen (α) contained in the second sublattice, or may be both oxygens.

In the calcium-cobalt layered oxide represented by the chemical formula 1, when Ca is partially replaced by the element A, the electrical conductivity of the layered oxide is improved. However, if the amount of substitution of Ca by the element A becomes excessively large, it becomes chemically unstable by reacting with moisture in the atmosphere, so the amount of substitution is preferably 30 atm% or less.

In the calcium-cobalt layered oxide represented by the chemical formula 1, part of Co contained in the first sublattice and / or the second sublattice is Cu, Sn, Mn, Ni, F.
You may substitute by 1 type (s) or 2 or more types of element C selected from e, Zr, and Cr. Substitution of element C for part of Co has the effect of improving the Seebeck coefficient of the layered oxide. In this case, the substitution amount of Co by the element C is 25
Atm% or less is preferable.

As another specific example of the cobalt layered oxide exhibiting high thermoelectric properties, one represented by the general formula of the following chemical formula 2 is given as a preferable example. The cobalt layered oxide represented by the formula (2) also becomes a thermoelectric conversion material having a high figure of merit by aligning the crystal orientations in one direction.

[0035]

Embedded image (Bi _1−x−y B _x Co _y O _{1 + α} ) (Co
O _{2 + β} ) _z (where B is one or more elements selected from alkali metals and alkaline earth metals, 0.2 ≦ x ≦ 0.
8, 0 ≦ y <0.5, 0.2 ≦ x + y ≦ 1, 0.25 ≦
z ≦ 0.5, 0.85 ≦ {1 + α + (2 + β) z} /
(1 + 2z) ≦ 1.15)

In the equation (2), "0.85≤
{1 + α + (2 + β) z} / (1 + 2z) ≦ 1.15 ”
Is the basic composition ((Bi _1−x−y B _x Co _y O) (CoO
₂ ) At most ± 15 atm% with respect to the stoichiometric amount of oxygen (1 + 2z) contained in the cobalt layered oxide having _z ).
It means that oxygen may become excessive or oxygen deficiency may occur in the range. In this case, the increasing / decreasing oxygen may be either oxygen contained in the first sublattice (β) or oxygen contained in the second sublattice (α),
Alternatively, both oxygen may be used.

In the cobalt layered oxide represented by the formula (2), part of Co contained in the first sublattice and / or the second sublattice may be replaced with the element C. When a part of Co is replaced with the element C, the Seebeck coefficient of the layered oxide and /
Alternatively, there is an effect that the electric conductivity is improved. In this case, the substitution amount of Co with the element C is preferably 25 atm% or less.

The "orientation degree" of each crystal grain is the Lotgering (Lotgerin) expressed by the following equation (1).
g) The average degree of orientation Q (HKL) by the method.

[0039]

[Equation 1]

In the equation (1), ΣI (hkl)
Is the sum of the X-ray diffraction intensities of all crystal planes (hkl) measured for the crystallographically-oriented ceramic, and ΣI ₀
(hkl) is the sum of the X-ray diffraction intensities of all the crystal planes (hkl) measured for unoriented ceramics having the same composition as the crystallographically oriented ceramics. Also, Σ'I
(HKL) is the sum of the X-ray diffraction intensities of the crystallographically equivalent specific crystal planes (HKL) measured for the crystallographically-oriented ceramics, and Σ'I ₀ (HKL) is the same composition as the crystallographically-oriented ceramics. 3 is a sum of X-ray diffraction intensities of a crystallographically equivalent specific crystal plane (HKL) measured for a non-oriented ceramics having a crystallinity. In the present invention, the average orientation degree Q (HKL) is calculated by using Cu- as an X-ray source.
Diffraction peaks obtained when 2θ-θ measurement was performed using Kα ray, and those in the range of 2θ = 5 ° to 60 ° were used.

Therefore, when the crystal grains constituting the polycrystalline body are non-oriented, the average orientation degree Q (HKL) is 0%, and the (HKL) planes of all the crystal grains are oriented in one direction. If it is, it becomes 100%.

In the crystal oriented ceramics according to the present invention, in order to obtain a high figure of merit, the higher the degree of orientation of the {001} plane is, the better. Specifically, the degree of orientation of the {001} plane is preferably 50% or more, and more preferably 80%.
That is all.

Next, the function of the crystallographically-oriented ceramic according to the present invention will be described. The cobalt layered oxide is a p-type thermoelectric conversion material having a relatively large Seebeck coefficient. Further, the cobalt layered oxide has a layered structure in which a CoO ₂ layer which is a conductive layer having a high electric conductivity and another layer which is considered to be an insulating layer are laminated at a predetermined cycle. It is known that there is a lattice mismatch at the interface. The thermoelectric properties of cobalt layered oxides have anisotropy depending on the crystallographic orientation, in addition to having a layered crystal structure, due to the lattice mismatch existing at the interface between the conducting layer and the insulating layer, It is thought that this is because the scattering of phonons and phonons is different.

The crystallographically-oriented ceramics according to the present invention comprises a polycrystal of a cobalt layered oxide exhibiting such excellent thermoelectric properties, and the {001} plane having high thermoelectric properties is oriented in one direction. Since the crystal grains constituting the polycrystalline body are oriented with a high degree of orientation, the performance index in the direction parallel to the direction in which the {001} plane is oriented is that of a non-oriented sintered body having the same composition. The value is higher than the figure of merit. In particular, the crystallographically-oriented ceramics composed of the calcium-cobalt layered oxide represented by the chemical formula 1 and the cobalt layered oxide represented by the chemical formula 2 exhibit good thermoelectric properties. Therefore, the thermoelectric conversion element using this shows a higher figure of merit than the thermoelectric conversion element using the non-oriented sintered body having the same composition.

Next, the plate-like powder for producing a crystallographically-oriented ceramic according to the present invention will be described. Ceramics with complex compositions such as cobalt layered oxides are usually prepared by mixing simple compounds containing constituent elements in a stoichiometric ratio, shaping and calcining this mixture, then crushing it, and then crushing it. It is manufactured by a method of re-molding and sintering crushed powder. However, with such a method, it is extremely difficult to obtain an oriented sintered body in which a specific crystal plane of each crystal grain is oriented in a specific direction.

In order to solve this problem, the present invention orients a plate-like powder satisfying a specific condition in a compact, and uses this plate-like powder as a reactive template to synthesize a cobalt layered oxide and its synthesis. It is characterized in that the {001} plane of each crystal grain constituting the polycrystalline body is oriented in one direction by sintering. In the present invention, as the plate-like powder, one satisfying the following conditions is used.

First, as the plate-like powder, one having a shape that can be easily oriented in a fixed direction during molding is used. For that purpose, the average aspect ratio of the plate-like powder (= the average value of the diameter / thickness of the plate-like powder) is preferably 3 or more. If the average aspect ratio is less than 3,
It becomes difficult to orient the plate-like powder in one direction during molding. The average aspect ratio of the plate-like powder is more preferably 5 or more.

Generally, the larger the average aspect ratio of the plate-like powder, the easier the orientation of the plate-like powder tends to be. However, if the average aspect ratio becomes excessively large, the plate-like powder may be crushed in the mixing step described later, and a molded product in which the plate-like powder is oriented may not be obtained. Therefore, the average aspect ratio of the plate-like powder is preferably 100 or less, more preferably 20 or less.

The average diameter (average particle diameter) of the plate-like powder is preferably 0.05 μm or more and 20 μm or less. If the average particle size of the plate-like powder is less than 0.05 μm, it becomes difficult to orient the plate-like powder in a certain direction due to the shearing stress acting during molding. On the other hand, if the average particle size of the plate-shaped powder exceeds 20 μm, the sinterability will be reduced. The average particle size of the plate-like powder is more preferably 0.1 μm or more and 5 μm or less.

Secondly, in the plate-like powder, the developed surface (the surface occupying the widest area) is CoO ₂ which is a cobalt layered oxide.
A material having lattice matching with the layer is used. Even in the case of a plate-like powder having a predetermined shape, when the developed surface thereof does not have lattice matching with the CoO ₂ layer of the cobalt layered oxide, the crystal-oriented ceramics according to the present invention can be produced. It is not preferable because it may not function as a reactive template.

Whether or not the lattice matching is good is the absolute value of the difference between the lattice dimension of the developing surface of the plate-like powder and the corresponding lattice dimension of the CoO ₂ layer of the cobalt layered oxide. It can be expressed by a value divided by (hereinafter, this value is referred to as "lattice matching rate"). The smaller the lattice matching rate, the more the plate-like powder functions as a good reactive template. In order to manufacture a crystallographically-oriented ceramic with a high degree of orientation, the lattice matching rate of the plate-like powder is 20%.
The following is preferable, and 10% or less is more preferable.

Thirdly, as the plate-like powder, one which reacts with a layered oxide forming raw material described later to form a cobalt layered oxide is used. Therefore, the plate-like powder itself does not necessarily have to be the cobalt layered oxide. Further, the plate-like powder is selected from compounds or individual solutions containing any one or more of the cationic elements contained in the cobalt layered oxide.

Any plate-like powder satisfying the above conditions functions as a reactive template for producing the crystallographically-oriented ceramic according to the present invention. As a material satisfying such a condition, specifically, Co (O
Cobalt compounds such as (H) ₂ , CoO, CoO (OH), and Co ₃ O ₄ are mentioned as suitable examples.

Co (OH) ₂ has a CdI ₂ type crystal structure. The {00l} plane of Co (OH) ₂ has a smaller surface energy than the other crystal planes, and therefore the plate-like powder having the {001} plane as a developed plane is relatively easy to manufacture. Further, the {00l} plane of Co (OH) ₂ has extremely good lattice matching with the CoO ₂ layer of the cobalt layered oxide. Therefore, Co with the {001} plane as the development plane
(OH) ₂ plate-like powder is particularly suitable as a plate-like powder for producing the crystallographically-oriented ceramic according to the present invention.

Co (OH) ₂ with the {001} plane as the development plane
The plate-like powder can be synthesized by a precipitation method. Specifically, in an aqueous solution containing a cobalt salt such as CoCl ₂ or Co (NO ₃ ) ₂ , an alkaline aqueous solution (NaOH, KOH,
Ammonia water, etc.) may be added dropwise. Alternatively, a method of adding urea to an aqueous solution containing a cobalt salt and heating it may be used. As a result, a plate-like powder of Co (OH) ₂ having a developed {001} plane can be precipitated in the aqueous solution. At this time, if the synthesis conditions are appropriately controlled, the shape of the plate-like powder can be controlled relatively easily.

CoO has a rock-salt type crystal structure, and its {111} plane is CoO of a layered cobalt oxide.
_It has a very good lattice matching with the _two layers. Therefore, the CoO plate-like powder having the {111} plane as the developed plane is suitable as a plate-like powder for producing the crystallographically-oriented ceramic according to the present invention.

After synthesizing Co (OH) ₂ powder by the precipitation method,
When this aqueous solution is stirred in the atmosphere for a long time, Co (OH) ₂
The plate-like powder is gradually oxidized. At this time, if the oxidation conditions are optimized, the {001} plane of Co (OH) ₂ is {1
The CoO plate-like powder having the {111} plane as the developed plane is obtained.

Further, Co ₃ O ₄ has a spinel type crystal structure, and its {111} plane has extremely good lattice matching with the CoO ₂ layer of the cobalt layered oxide. . Therefore, Co ₃ O ₄ with the {111} plane as the developed plane
The plate-like powder is suitable as a plate-like powder for producing the crystallographically-oriented ceramics according to the present invention.

The {00l} plane of CoO (OH) has extremely good lattice matching with the CoO ₂ layer of the cobalt layered oxide. Therefore, the CoO (OH) plate-like powder having the {001} plane as the developed plane is suitable as a reactive template for producing the crystallographically-oriented ceramics according to the present invention.

Next, a method for producing a crystallographically-oriented ceramic according to the present invention will be described. The method for producing a crystallographically-oriented ceramic according to the present invention includes a mixing step, a forming step, and a sintering step.

First, the mixing step will be described. The mixing step is a step of mixing the plate-like powder and the layered oxide forming raw material described above. In this case, the plate-like powder may be a plate-like powder composed of one kind of compound, or a mixture of plate-like powders composed of two or more kinds of compounds.

Further, the "layered oxide forming raw material" means a compound which reacts with the plate-like powder to form a cobalt layered oxide. The composition and blending ratio of the layered oxide forming raw material are determined depending on the composition of the cobalt layered oxide to be synthesized and the composition of the plate-like powder used as the reactive template. The form of the layered oxide-forming raw material is not particularly limited, and hydroxides, oxide powders, complex oxide powders, salts such as carbonates, nitrates, oxalates and acetates, alkoxides, etc. Can be used.

For example, the cobalt layered oxide is a calcium cobalt layered oxide represented by the general formula of Chemical Formula 1 (for example, Ca ₃ Co ₄ O ₉ etc.), and as the plate-like powder, C
o (OH) ₂ , CoO, CoO (OH) and / or Co ₃ O
_{When 4} is used, one or more alkaline earth metal elements (in this case, C
a) containing a second compound and, if necessary, a third element other than the alkaline earth metal element and Co (in this case, one or more elements of alkali metal and Bi) The third compound that does

The second compound may be any compound as long as it can form an oxide of an alkaline earth metal element by firing, and various oxides, hydroxides, salts, alkoxides and the like containing an alkaline earth metal element can be used. Compounds can be used.

Specific examples of the second compound containing Ca include calcium oxide (CaO), calcium hydroxide (Ca (OH) ₂ ), calcium chloride (CaCl ₂ ), calcium carbonate (CaCO ₃ ), and nitric acid. Calcium (Ca
(NO _{3) 2),} calcium dimethoxide (Ca (OCH
₃ ) ₂ ), calcium diethoxide (Ca (OC ₂ H ₅ ).
₂ ), calcium diisopropoxide (Ca (OC ₃ H
₇ ) ₂ ) etc. are mentioned as a suitable example. Also, the second
As the compound, only one of the above compounds may be used, or two or more compounds may be used in combination.

When the second compound is a solid or is mixed in the solid state, the average particle size of the second compound is 10
μm or less is preferable. If the average particle size exceeds 10 μm,
This is not preferable because the reaction becomes non-uniform and the sinterability decreases. The average particle size of the second compound is more preferably 5
μm or less. The smaller the average particle diameter of the second compound is, the better as long as the moldability and handleability are not deteriorated.

The third compound may be any compound as long as it can form an oxide containing the third element by firing, and various compounds such as oxides, hydroxides, salts and alkoxides containing the third element are used. be able to.

As the third compound containing only Na,
Specifically, sodium carbonate (Na _TwoCO_Three), Na nitrate
Thorium (NaNO_Three), Sodium isopropoxide
(Na (OC_ThreeH₇)) Etc. are mentioned as a suitable example.
It

The third compound containing only K is
Physically, potassium carbonate (K_TwoCO _Three), Potassium acetate
(CH_ThreeCOOK), potassium nitrate (KNO_Three), Cali
Umisopropoxide (K (OC_ThreeH₇)) Etc. are suitable
As an example.

As the third compound containing only Bi,
Specifically, bismuth oxide (Bi_TwoO_Three), Bismuth nitrate
Su (Bi (NO_Three)_Three), Bismuth chloride (BiCl_Three),
Bismuth hydroxide (Bi (OH)_Three), Bismuth triisop
Ropoxide (Bi (OC_ThreeH ₇)_Three), Bi metal alone, etc.
It is mentioned as a suitable example.

Further, the third compound may be a composite compound containing two or more kinds of third elements. As the layered oxide-forming raw material, only one of the above-mentioned third compounds may be used, or two or more types of third compounds may be used in combination.

When the third compound is solid or is mixed in the solid state, the average particle size of the third compound is preferably 10 μm or less, more preferably 5 μm.
The following points are the same as the second compound.

Further, for example, the cobalt layered oxide is a calcium cobalt layered oxide represented by the general formula of Chemical Formula 1, and a part of Co is replaced by the element C. OH) ₂ , CoO, CoO (OH) and / or Co ₃ O ₄ is used, as a layered oxide-forming raw material, one kind containing an element C in addition to the above-mentioned second compound and third compound Alternatively, two or more kinds of fourth compounds may be used.

The fourth compound may be any compound as long as it can form an oxide containing the element C by firing, and various compounds such as oxides, hydroxides, salts and alkoxides containing the element C can be used. it can. Specific examples of the fourth compound containing Cu include copper oxide (CuO, Cu ₂ O), copper carbonate (CuCO ₃ ), copper chloride (CuCl, CuC).
l ₂ ), Cu metal simple substance, etc. are mentioned as suitable examples. Further, as the fourth compound, any one of the above compounds may be used, or two or more compounds may be used in combination.

When the fourth compound is solid or is mixed in the solid state, the average particle size of the fourth compound is preferably 10 μm or less, more preferably 5 μm.
The following points are the same as the second compound and the third compound.

In addition to the calcium cobalt layered oxide, the manufacturing method according to the present invention can be applied to a cobalt layered oxide which is considered to have a CoO ₂ layer as a sublattice layer. For example, a cobalt layered oxide represented by the general formula of Chemical formula 2 (for example, Bi ₂ Sr ₂ Co ₂ O ₉ , B
i ₂ Ba ₂ Co ₂ O _{9 and the} like), and as a plate-like powder, C
o (OH) ₂ , CoO, CoO (OH) and / or Co ₃ O
_{When 4} is used, one or more alkaline earth metal elements (in this case, S
r, Ba, etc.) containing one or more second compounds, and optionally containing an alkali metal and Bi.
One kind or two or more kinds of third compounds may be used.

Further, the cobalt layered oxide is represented by the general formula of Chemical Formula 2, and a part of Co is replaced by the element C, and as a plate-like powder, Co (OH) ₂ , CoO,
When CoO (OH) and / or Co ₃ O ₄ is used,
As the layered oxide forming raw material, in addition to the second compound and the third compound described above, one or more fourth compounds containing the element C may be used. The same applies to the case of producing a crystallographically-oriented ceramic made of a cobalt layered oxide having another composition.

In the mixing step, with respect to the plate-like powder and the layered oxide forming raw material mixed in a predetermined ratio,
Further, non-plate-like fine powder (hereinafter referred to as "layered oxide fine powder") made of a compound having the same composition as the cobalt layered oxide obtained by these reactions may be added. The addition of the layered oxide fine powder to the raw material has the effect of increasing the density of the sintered body.

In this case, if the compounding ratio of the layered oxide fine powder becomes excessively large, the compounding ratio of the plate-like powder in the whole raw material will inevitably become small, and the crystallographically oriented ceramics {001}
The degree of orientation of the surface may decrease. Therefore, it is preferable to select an optimum value for the mixing ratio of the layered oxide fine powder so that the required degree of orientation of the {001} plane can be obtained.

Mixing of the plate-like powder and the layered oxide-forming raw material and the layered oxide fine powder which is added as necessary,
It may be performed by a dry method, or may be performed by a wet method by adding an appropriate dispersion medium such as water or alcohol. Further, at this time, a binder and / or a plasticizer may be added if necessary.

Next, the molding process will be described. The molding step is a step of molding the mixture obtained in the mixing step so that the plate-like powder is oriented. Here, "the plate-like powder is oriented" means that the development planes of the plate-like powders are arranged in parallel to each other (hereinafter, such a state is referred to as "plane orientation"), or the plate-like powders. The developed surface of is aligned parallel to one axis penetrating the molded body (hereinafter, such a state is referred to as "axial orientation").

In the case of axial orientation, the degree of orientation cannot be defined by the same degree of orientation (equation 1) as that of plane orientation. However, Lotgeri regarding {001} diffraction when X-ray diffraction is performed on a plane perpendicular to the orientation axis.
The degree of axial orientation can be expressed by using the average orientation degree by the ng method (hereinafter, referred to as “axial orientation degree”).
In the case of a molded body in which the plate-like powder is axially oriented, the degree of axial orientation has a negative value. In addition, the degree of axial orientation of the molded body in which the plate-like powder is almost completely axially oriented is similar to the degree of axial orientation measured for the molded body in which the plate-like powder is substantially completely plane-oriented.

The molding method is not particularly limited as long as it can orient the plate-like powder. As a molding method for orienting the plate-like powder in a plane,
Specifically, a doctor blade method, a press molding method, a rolling method, an extrusion method (tape shape) and the like can be mentioned as suitable examples. Further, as a method for axially orienting the plate-like powder, specifically, an extrusion molding method (non-tape shape) is mentioned as a preferable example.

Further, in order to increase the thickness of the molded product in which the plate-like powder is surface-oriented (hereinafter referred to as "plane-oriented molded product") and to increase the degree of orientation, Processing such as stacking pressure bonding, pressing, and rolling (hereinafter, referred to as “plane orientation processing”) may be performed. in this case,
Any one type of surface orientation treatment may be performed on the surface orientation molded body, or two or more types of surface orientation treatment may be performed. In addition, one kind of surface orientation treatment may be repeated a plurality of times for the surface orientation molded body, or 2
You may repeat the surface orientation process of 1 or more types multiple times, respectively.

Next, the sintering process will be described. The sintering step is a step of heating the molded body obtained in the molding step to react the plate-like powder with the layered oxide forming raw material. When a molded body containing the plate-like powder and the layered oxide-forming raw material is heated to a predetermined temperature, a cobalt layered oxide is produced by these reactions, and at the same time, the produced cobalt layered oxide is also sintered.

The heating temperature is such that the plate-like powder to be used, the layered oxide forming raw material,
The optimum temperature may be selected according to the composition of the crystallographically-oriented ceramic to be produced, but the temperature is 800 ° C or higher and 120
It is preferably 0 ° C or lower. For example, when a crystallographically-oriented ceramic having a Ca ₃ Co ₄ O ₉ composition is produced from Co (OH) ₂ plate-like powder and CaCO ₃ , the heating temperature is preferably 930 ° C. or lower at which no different phase occurs. Further, the heating time may be selected as an optimum value depending on the heating temperature so that a predetermined sintered body density can be obtained.

Further, as a heating method, a method of gradually raising the temperature from room temperature to a predetermined temperature, a method of introducing the oriented compact into a furnace preheated to a predetermined temperature and heating the crystal at once, etc. The optimum method may be selected according to the composition of the oriented ceramics.

Further, the sintering step is preferably performed in an atmosphere in which oxygen is present (that is, in the air or in oxygen). It is not preferable to heat the molded body in an oxygen-free atmosphere because the amount of oxygen in the obtained crystallographically-oriented ceramic may decrease and the thermoelectric properties may deteriorate. In particular, when the molded body is heated in oxygen, a crystallographically-oriented ceramic having high thermoelectric properties can be obtained.

In the case of a compact containing a binder, a heat treatment mainly for degreasing may be performed before the sintering step. In this case, the degreasing temperature is not particularly limited as long as it is at least a temperature sufficient to thermally decompose the binder. However, when a compound containing a low melting point metal such as Na is used as a starting material, it is preferable to perform degreasing at 500 ° C. or lower in order to prevent evaporation of Na or the like. Degreasing is preferably performed in an atmosphere in which oxygen exists.

When the oriented compact is degreased, the degree of orientation of the plate-like powder in the oriented compact may be lowered, or the reaction may proceed to expand the oriented compact. In such a case, after degreasing and before sintering, it is preferable to further subject the oriented compact to a hydrostatic pressure (CIP) treatment. When the hydrostatic pressure treatment is further performed on the degreased oriented molded body, the degree of orientation is decreased due to degreasing, or
There is an advantage that it is possible to suppress the decrease in the density of the sintered body due to the decrease in the density of the oriented compact.

Next, the operation of the method for producing a crystallographically-oriented ceramic according to the present invention will be described. When the plate-like powder and the layered oxide forming raw material are mixed and formed by a forming method in which shear stress acts on the plate-like powder, the plate-like powder is oriented in the formed body. When such an oriented compact is heated at a predetermined temperature, the plate-like powder reacts with the layered oxide forming raw material to form a cobalt layered oxide.

At this time, since there is lattice matching between the developed surface of the plate-like powder and the CoO ₂ layer of the cobalt layered oxide,
The developed surface of the plate-like powder is succeeded as the {001} surface of the produced cobalt layered oxide. As a result, in the sintered body, a plate-like crystal of a cobalt layered oxide was grown with the {001} plane oriented in one direction, and {001} of each crystal grain was formed.
It is possible to obtain a crystallographically-oriented ceramic whose planes are oriented with a high degree of orientation.

The manufacturing method according to the present invention is low in cost because the ordinary ceramics process can be used as it is. Further, it is possible to obtain a crystallographically-oriented ceramic having not only a high degree of orientation on the {001} plane but also a uniform degree of orientation and composition. Furthermore, since the crystallographically-oriented ceramics obtained by the manufacturing method according to the present invention is a polycrystalline body, it has a higher fracture toughness than a single crystal, and since phonons are scattered at grain boundaries and vacancies, it is more heat The conductivity is low. On the other hand, in the crystallographically-oriented ceramic obtained by the production method according to the present invention, the plane having high electrical conductivity is oriented,
It has higher electrical conductivity than non-oriented ceramics. Therefore, when the crystallographically-oriented ceramic obtained by the manufacturing method according to the present invention is used as a thermoelectric conversion material, a thermoelectric conversion element having excellent durability and thermoelectric characteristics can be manufactured.

[0094]

Example (Example 1) Co (OH)
_Two plate-like powders were synthesized. First, a CoCl ₂ aqueous solution with a concentration of 0.1 mol / l and Na with a concentration of 0.4 mol / l
An aqueous OH solution was prepared. Then 600 ml CoCl
_{For 2} aqueous solutions, add 300 ml of NaOH aqueous solution to 100
It was added dropwise at a rate of ml / h. As a result, in the solution,
A blue precipitate (Co (OH) ₂ ) formed.

After the dropping of the aqueous NaOH solution was completed, N ₂
The solution was stirred while bubbling, and aged at room temperature for 24 hours to obtain pink crystals (Co (OH) ₂ ). The crystals were suction filtered and dried at room temperature with N ₂ gas for 24 hours. FIG. 1 shows an SEM photograph of the obtained powder. The Co (OH) ₂ powder obtained in this example was a hexagonal plate-like powder. The average particle size of the plate-like powder was 0.5 μm, and the average aspect ratio was about 5.

Example 2 According to the procedure shown in FIG. 2, Ca
A crystallographically-oriented ceramic having a ₃ Co ₄ O ₉ composition was produced. First, in step 1 (hereinafter, simply referred to as “S1”), CaCO ₃ powder (average particle size 0.2 μm) is used.
m), Co (OH) ₂ plate-like powder synthesized in Example 1, toluene and absolute ethanol were weighed in predetermined amounts in respective containers. Then, put these raw materials in a ball mill,
It was wet-mixed for an hour (S2). After the mixing was completed, a predetermined amount of binder and plasticizer were added to the slurry (S3), and further wet-mixed for 3 hours with a ball mill (S4). Table 1 shows the charged amount of each raw material.

[0097]

[Table 1]

Next, the slurry was taken out of the pot and formed into a sheet having a thickness of about 100 μm by tape casting (S5). Furthermore, stack the obtained sheets,
Pressure bonding was performed under the conditions of temperature: 80 ° C. and pressure: 10 MPa (S
6).

Next, the obtained molded body was degreased in the atmosphere under the conditions of temperature: 700 ° C. and heating time: 2 hours (S7). Next, the molded body after degreasing is subjected to pressure: 300
Pressure molding (hydrostatic pressure treatment) under the condition of MPa (S
8). Further, the molded body was subjected to a temperature:
Sintered under the conditions of 920 ° C. and heating time: 48 hr (S
9).

(Embodiment 3) First, the same procedure as in Embodiment 2
According to (from S1 to S7 in FIG. 2), Co (OH) _TwoPlate
A molded body in which the powder was plane-oriented was prepared and degreased.
Next, do not subject the obtained degreased body to hydrostatic pressure treatment.
Then, put it in the sintering furnace as it is, and perform pressure sintering in oxygen.
went. The pressure sintering is performed under pressure: 2 MPa and heating temperature.
The temperature was 920 ° C. and the heating time was 48 hours.
The pressure is applied from the direction perpendicular to the tape surface.
It was

Example 4 As a layered oxide forming raw material,
CaCO_ThreePowder and Na_TwoCO_ThreePowder (average particle size 0.2
μm), 5 atm% of Ca is replaced by Na
The same procedure as in Example 3 except that these ingredients were blended.
Therefore, (Ca_0.95Na_0.05}_ThreeCo _FourO₉Composition
A crystal oriented ceramic having the above was prepared.

Example 5 As a layered oxide forming raw material,
CaCO ₃ powder and Na ₂ CO ₃ powder (average particle size 0.2
.mu.m) and were blended so that 10 atm% of Ca was replaced by Na, and following the same procedure as in Example 3, {Ca _0.9 Na _0.1 } ₃ Co ₄ O ₉ composition was obtained. A crystal oriented ceramic having the above was prepared.

Comparative Example 1 First, the same procedure as in Example 2
According to (from S1 to S7 in FIG. 2), Co (OH) _TwoPlate
A molded body in which the powder was plane-oriented was prepared and degreased.
Next, the obtained degreased body is crushed in a mortar and the crushed powder is crushed in a mold.
After preforming, CIP molding is performed at a pressure of 300 MPa.
It was. Further, the obtained molded body is treated in oxygen.
Sintered under conditions of heat temperature: 920 ° C., heating time: 48 hr
did.

Sintering obtained in Examples 2 and 3 and Comparative Example 1
Perform X-ray diffraction on the surface of the body parallel to the tape surface.
It was. The X-ray diffraction pattern is shown in FIG. Note that Ca_Three
Co _FourO₉Although the details of the crystal structure of is not clear,
In the report by A.C.Masset et al.
sset et al., Phys. Rev. B, 62 (1), pp.166-175, 200
The surface index is displayed according to (0). From FIG. 3, Example 2,
The sintered body obtained in No. 3 is {001} compared with Comparative Example 1.
It can be seen that the faces are oriented with a high degree of orientation.

Further, using the result of FIG. 3 and the expression of Equation 1,
The average orientation degree of the {001} plane by the Lotgering method was obtained. As a result, the average orientation degree of Comparative Example 1 was 2%, the average orientation degree of Example 2 was 73%, and the average orientation degree of Example 3 was 92%.

Next, rod-shaped samples were cut out from the sintered bodies obtained in Examples 3 to 5 and Comparative Example 1 along a direction parallel to the tape surface. Then, using this rod-shaped sample, 180
The Seebeck coefficient, the thermal conductivity, and the electrical conductivity were measured in the temperature range of ℃ to 700 ℃ in the direction parallel to the tape surface. In the examples of the present invention, Seebeck coefficient and electric conductivity are thermoelectric property evaluation devices (RZ2001 manufactured by Ozawa Scientific Co., Ltd.), and thermal conductivity is laser flash method thermal constant measurement device (Vacuum Riko Co., Ltd.). Made, TC-
7000). Further, the dimensionless figure of merit ZT was calculated using the obtained Seebeck coefficient, electric conductivity and thermal conductivity. The result is shown in FIG.

From FIG. 4, the dimensionless figure of merit ZT of the oriented sintered body obtained in Example 3 is shown in Comparative Example 1 in the entire temperature range.
It is understood that it is larger than the non-oriented sintered body of No. This is because the {001} plane having high electric conductivity is oriented in one direction to improve the electric conductivity in the direction parallel to the tape surface,
This is because the performance index Z is improved by this.

Also, from FIG. 4, when a part of Ca contained in Ca ₃ Co ₄ O ₉ is replaced with Na, the dimensionless figure of merit ZT
It can be seen that the dimensionless figure of merit ZT increases as the amount of Na substitution increases. Na substitution amount is 1
In the case of Example 4 with 0 atm%, the dimensionless figure of merit ZT at 700 ° C. reached 0.27. This is because the electric conductivity of the conductive layer, that is, the electric conductivity in the direction parallel to the tape surface was improved by replacing a part of Ca contained in the insulating layer with Na.

Example 6 Co (O) obtained in Example 1
H)_TwoPlate powder, CaCO_ThreePowder (average particle size 0.2μ
m) and Bi_TwoO_ThreeUse powder (average particle size 0.3μm)
Yes, except that these were blended in a stoichiometric ratio,
Following the same procedure as in Example 2, (Ca_0.9Bi _0.1}
_ThreeCo_FourO₉Preparation of crystal-oriented ceramics with composition
did.

With respect to the obtained crystallographically-oriented ceramics,
Under the same conditions as in Example 3, the average orientation degree of the {001} plane and the dimensionless figure of merit were measured. As a result, the average degree of orientation of the {001} plane was 82%, and the dimensionless figure of merit ZT at 600K was 0.158.

Comparative Example 2 Co (OH)_TwoInstead of plate powder
And amorphous Co (OH)_TwoPowder (average particle size 0.1 μm)
Following the same procedure as in Example 6, except that
_0.9Bi_0.1} _ThreeCo_FourO₉Unoriented cell with composition
Ramix was made.

With respect to the obtained non-oriented ceramics, the average orientation degree of the {001} plane and the dimensionless figure of merit were measured under the same conditions as in Example 2. As a result, the average degree of orientation of the {001} plane was 10%, and the dimensionless figure of merit ZT at 600K was 0.091.

Example 7 The Co (O) obtained in Example 1 was used.
H)_TwoPlate powder, Bi_TwoO_ThreePowder (average particle size 0.3μ
m) and SrCO_ThreeUse powder (average particle size 0.3μm)
Yes, except that these were blended in a stoichiometric ratio,
Following the same procedure as in Example 2, Bi_TwoSr_TwoCo _TwoO₉
A crystallographically-oriented ceramic having a composition was produced.

Regarding the obtained crystallographically-oriented ceramics,
Under the same conditions as in Example 3, the average orientation degree of the {001} plane and the dimensionless figure of merit were measured. As a result, the average degree of orientation of the {001} plane was 71%, and the dimensionless figure of merit ZT at 600K was 0.097.

Comparative Example 2 Amorphous Co (OH) ₂ powder (average particle size 0.1 μm) was used instead of Co (OH) ₂ plate-like powder.
According to the same procedure, as in Example 7 except for using, Bi ₂
A non-oriented ceramic having a Sr ₂ Co ₂ O ₉ composition was produced.

With respect to the obtained non-oriented ceramics, the average orientation degree of the {001} plane and the dimensionless figure of merit were measured under the same conditions as in Example 2. As a result, the average degree of orientation of the {001} plane is 8%, and the dimensionless figure of merit Z at 600K is
T was 0.035.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments and various modifications can be made without departing from the gist of the present invention. .

For example, in Example 2 above, the atmospheric pressure sintering method is used as the sintering method, but after the atmospheric pressure sintering, HIP processing or hot press processing may be further performed.
In particular, when hot pressing is performed, in addition to obtaining a dense crystallographically-oriented ceramic, the degree of {001} plane orientation can be further improved by uniaxial pressing during hot pressing.

Further, for example, although the plate-like powder is surface-oriented by tape casting by the doctor blade method in the above embodiment, the plate-like powder may be axially oriented by an extrusion molding method. Even when the plate-like powder is axially oriented in this way, a crystal-oriented ceramic having a higher figure of merit than an unoriented sintered body can be obtained. Further, the extrusion molding method has an advantage that a sintered body having a certain thickness can be manufactured at low cost.

In the above embodiment, a cobalt compound is used as the plate-like powder, and a layered oxide producing material is
Although the example using the second compound, the third compound, and the fourth compound has been mainly described, an amorphous cobalt compound powder may be used as the layered oxide forming raw material. In this case, if the plate-like powder of the cobalt compound, and the amorphous powder of the cobalt compound, the second compound, the third compound and the fourth compound are blended in a predetermined ratio so that the intended crystallographically-oriented ceramic is obtained. good.

Further, since the crystallographically-oriented ceramics according to the present invention has a high figure of merit, it constitutes a thermoelectric power generating element used in a thermoelectric generator, a precision temperature control device, a constant temperature device, a cooling and heating device, a refrigerator, a power supply for a watch and the like. However, the application of the present invention is not limited to this, and can be applied to various electronic elements (for example, magnetic heads) utilizing the giant magnetoresistive effect.

[0122]

The crystal-oriented ceramics according to the present invention are
An effect of exhibiting a higher figure of merit than non-oriented ceramics having the same composition, since it is composed of a polycrystal of cobalt layered oxide and the {001} planes of each crystal grain are oriented with a high degree of orientation. There is.

Further, the method for producing a crystallographically-oriented ceramics according to the present invention, the plate-like powder is produced when the oriented plate-like powder and the layered oxide forming raw material react with each other to form the cobalt layered oxide. The development surface of cobalt is layered oxide {0
Since it is succeeded as the 0l} plane, there is an effect that the crystal oriented ceramics in which the plate crystals of the cobalt layered oxide with the developed {001} plane are oriented with a high degree of orientation can be easily produced.

In addition, Co (OH) ₂ , Co ₃ O ₄ , CoO
Since the plate-like powder composed of (OH) or CoO and having a predetermined crystal plane as a development plane has extremely good lattice matching between the development plane and the CoO ₂ layer of the cobalt layered oxide, When synthesizing the cobalt layered oxide, there is an effect that it functions as an extremely excellent reactive template and the crystal oriented ceramics according to the present invention can be easily produced.

Further, the crystal-oriented ceramics according to the present invention has a higher figure of merit than non-oriented ceramics having the same composition. Therefore, if a thermoelectric conversion element is constructed using this, a thermoelectric material having a high figure of merit is obtained. There is an effect that a conversion element can be obtained.

[Brief description of drawings]

FIG. 1 is a scanning electron microscope (SEM) photograph of a Co (OH) ₂ plate-like powder synthesized by a precipitation method.

FIG. 2 is a process drawing showing a method for producing a crystallographically-oriented ceramic according to an embodiment of the present invention.

3 is an X-ray diffraction pattern of the crystallographically-oriented ceramics obtained in Examples 2 and 3 and the non-oriented ceramics obtained in Comparative Example 1. FIG.

FIG. 4 is a diagram showing the relationship between the temperature and the dimensionless figure of merit of the crystal-oriented ceramics obtained in Examples 3 to 5 and the non-oriented ceramics obtained in Comparative Example 1.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toshihiko Tani             Aichi Prefecture Nagachite Town Aichi District             Ground 1 Toyota Central Research Institute Co., Ltd. (72) Inventor Kunihito Kawamoto             9-401 Meijo 3-chome, Kita-ku, Nagoya-shi F-term (reference) 4G030 AA03 AA04 AA08 AA17 AA22                       AA25 AA27 AA28 AA29 AA31                       AA39 AA43 BA01 BA21 CA01                       CA02 CA04 CA08 GA01 GA11                       GA14 GA17 GA20 GA22 GA25                       GA27                 4G048 AA02 AB02 AC08 AD04 AD06                       AE05 AE06

Claims (29)

[Claims] 1. A layered oxide polycrystal containing cobalt, wherein {00} of each crystal grain constituting the polycrystal is formed.
A crystallographically-oriented ceramic having a degree of orientation of 1} plane of 50% or more. Wherein said layered oxide is claim 1 are those having a first sub-grid of CoO ₂ layers, a structure in which a second sublattice of different layers are deposited alternately and CoO ₂ layers The crystallographically-oriented ceramic according to 1. 3. The crystallographically-oriented ceramic according to claim 2, wherein the second sublattice has a rock salt structure or a distorted rock salt structure. Wherein said layered oxide has the general _{formula: {(Ca 1-x A} x) 2 CoO 3 + α} (Co
O _{2 + β} ) _y (where A is an alkali metal, an alkaline earth metal and B
one or more elements selected from i, 0 ≦ x ≦ 0.
3, 0.5 ≦ y ≦ 2.0, 0.85 ≦ {3 + α + (2+
The crystallographically-oriented ceramic according to claim 1, which is represented by β) y} / (3 + 2y) ≦ 1.15). 5. The layered oxide has the general formula: (Bi _{1−x−y Bx} Co _y O _{1 + α} ) (Co
O _{2 + β} ) _z (where B is one or more elements selected from alkali metals and alkaline earth metals, 0.2 ≦ x ≦ 0.
8, 0 ≦ y <0.5, 0.2 ≦ x + y ≦ 1, 0.25 ≦
z ≦ 0.5, 0.85 ≦ {1 + α + (2 + β) z} /
The crystallographically-oriented ceramic according to claim 1, which is represented by (1 + 2z) ≦ 1.15). 6. In the layered oxide, a part of Co is 0 to
Cu, Sn, Mn, Ni, Fe, in the range of 25 atm%
The crystallographically-oriented ceramic according to claim 4 or 5, which is substituted with one or more elements C selected from Zr and Cr. 7. A plate-like powder whose developed surface has lattice matching with a CoO ₂ layer of a layered oxide containing cobalt, and a layered oxide producing raw material which reacts with the plate-like powder to form the layered oxide. And a molding step of molding the mixture obtained in the mixing step so that the plate-like powder is oriented, and the molded body obtained in the molding step is heated to obtain the plate-like powder. A method for producing a crystallographically-oriented ceramic, comprising a sintering step of reacting the layered oxide-forming raw material. Wherein said layered oxide claim a first sublattice consisting of CoO ₂ layers, and a second sublattice consisting of different layers and CoO ₂ layer has the structure deposited alternately 7 The method for producing a crystallographically-oriented ceramic according to 1. 9. The method for producing a crystallographically-oriented ceramic according to claim 8, wherein the second sublattice has a rock salt structure or a distorted rock salt structure. Wherein said layered oxide has the general _{formula: {(Ca 1-x A} x) 2 CoO 3 + α} (Co
O _{2 + β} ) _y (where A is an alkali metal, an alkaline earth metal and B
one or more elements selected from i, 0 ≦ x ≦ 0.
3, 0.5 ≦ y ≦ 2.0, 0.85 ≦ {3 + α + (2+
The method for producing a crystallographically-oriented ceramic according to claim 7, wherein β) y} / (3 + 2y) ≦ 1.15). 11. The layered oxide has the general formula: (Bi _{1−x−y Bx} Co _y O _{1 + α} ) (Co
O _{2 + β} ) _z (where B is one or more elements selected from alkali metals and alkaline earth metals, 0.2 ≦ x ≦ 0.
8, 0 ≦ y <0.5, 0.2 ≦ x + y ≦ 1, 0.25 ≦
z ≦ 0.5, 0.85 ≦ {1 + α + (2 + β) z} /
The method for producing a crystallographically-oriented ceramic according to claim 7, which is represented by (1 + 2z) ≦ 1.15). 12. In the layered oxide, part of Co is 0.
Cu, Sn, Mn, Ni, F in the range of up to 25 atm%
The method for producing a crystallographically-oriented ceramic according to claim 10 or 11, which is substituted with one or more elements C selected from e, Zr and Cr. 13. The plate-like powder is Co (OH) ₂ , Co.
The method for producing a crystallographically-oriented ceramic according to claim 7, which comprises one or more cobalt compounds selected from O, CoO (OH), and Co ₃ O ₄ . 14. The method for producing a crystallographically-oriented ceramic according to claim 7, wherein the plate-like powder has an average aspect ratio of 3 or more. 15. The plate-like powder has an average particle size of 0.05.
The method for producing a crystallographically-oriented ceramic according to claim 7, which has a size of not less than μm and not more than 20 μm. 16. The layered oxide-forming raw material is one or two containing one or more alkaline earth metal elements.
The method for producing a crystallographically-oriented ceramic according to claim 13, which comprises at least one second compound. 17. The second compound is an oxide or hydroxide containing one or more alkaline earth metal elements,
The method for producing a crystallographically-oriented ceramic according to claim 16, which is a salt or an alkoxide. 18. The average particle size of the second compound is 1
The method for producing a crystallographically-oriented ceramic according to claim 17, which has a thickness of 0 μm or less. 19. The layered oxide-forming raw material further comprises:
The method for producing a crystallographically-oriented ceramic according to claim 16, which comprises one or more third compounds containing one or more third elements selected from alkali metals and Bi. 20. The method for producing a crystallographically-oriented ceramic according to claim 19, wherein the third compound is an oxide, a hydroxide, a salt or an alkoxide containing one kind or two or more kinds of the third element. 21. The average particle size of the third compound is 1
The method for producing a crystallographically-oriented ceramic according to claim 20, which has a thickness of 0 μm or less. 22. The layered oxide-forming raw material further comprises:
The crystallographically-oriented ceramic according to claim 16, which contains one or more fourth compounds containing one or more elements C selected from Cu, Sn, Mn, Ni, Fe, Zr and Cr. Manufacturing method. 23. The method for producing a crystallographically-oriented ceramic according to claim 22, wherein the fourth compound is an oxide, hydroxide, salt or alkoxide containing the element C. 24. The fourth compound has an average particle size of 1
The method for producing a crystallographically-oriented ceramic according to claim 23, which has a thickness of 0 μm or less. 25. The method for producing a crystallographically-oriented ceramic according to claim 7, wherein in the sintering step, the compact is heated in an atmosphere containing oxygen. 26. A composition comprising Co (OH) ₂ and {00
a plate-like powder having a 1} plane as a development plane, Co ₃ O ₄ ,
And plate-like powder having a {111} plane as a developed plane and CoO
7. The crystallographically-oriented ceramics according to claim 1, which is one or two or more kinds of plate-like powders selected from the plate-like powders consisting of and having a {111} plane as a development plane. A plate-like powder for producing crystal-oriented ceramics used for. 27. The plate-like powder for producing a crystallographically-oriented ceramic according to claim 26, which has an average aspect ratio of 3 or more. 28. An average particle size of 0.05 μm or more and 20 μm
The plate-like powder for producing a crystallographically-oriented ceramic according to claim 26, which is as follows. 29. A thermoelectric conversion element using the crystallographically-oriented ceramic according to any one of claims 1 to 6.