JP2010030855A - Crystal-oriented structure and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crystal-oriented structure which is manufactured without a complicated and expensive process and to provide a method for manufacturing the same. <P>SOLUTION: The crystal-oriented structure is a polycrystalline crystal-oriented structure obtained by orientation-treating and further heat-treating plate-like particles of layered metallic hydroxide containing bivalent metallic ions or layered metallic hydroxide containing bivalent and trivalent metallic ions. The crystal-oriented structure is utilized as a material exhibiting high thermoelectric conversion function. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a crystal orientation structure and a manufacturing method thereof.

In recent years, in the production of crystalline orientation structures composed of oxides, research has been actively conducted on polycrystalline crystalline orientation structures that can be produced at a relatively low cost instead of high-cost single crystal materials. .
For example, in a thermoelectric conversion element using a metal oxide, attempts have been reported to improve characteristics by using a crystalline orientation polycrystal. In a thermoelectric conversion element usually formed from pellets cut into a bulk shape, the performance is expressed by the figure of merit Z (= S ² σ / κ: S is Seebeck coefficient, σ is electrical conductivity (conductivity), κ is Thermal conductivity), and further evaluated by the value of the dimensionless figure of merit ZT multiplied by the absolute temperature T. The larger these values, the better the thermoelectric properties. Here, the thermal conductivity is composed of lattice thermal conductivity caused by lattice vibration (phonon) and electronic thermal conductivity transmitted by electron conduction.
Here, as described in Non-Patent Document 1, it is known that the crystal anisotropy of the electrical conductivity and thermal conductivity in an oxide is greatly dependent on the carrier characteristics. Whether or not can be controlled even in the bulk shape is a factor that greatly affects the improvement of the characteristics of the oxide thermoelectric conversion element.

  Moreover, since the volume of the element required in order to extract energy efficiently from a heat source becomes very large, the thermoelectric conversion element needs to be able to synthesize a large amount of oxide bulk used for the element. Therefore, in order to replace conventional thermoelectric conversion elements using expensive metal compounds with oxides, it is essential to be able to manufacture oxide bulk bodies that are the heart of thermoelectric conversion devices at low cost and in large quantities. Can be cited as a major issue.

Here, in order to produce a thermoelectric conversion element, it is required that power can be generated with high efficiency by a combination of a p-type semiconductor in which carriers are holes and an n-type semiconductor in which electrons are carriers. However, compared to the p-type in which NaCo ₂ O ₄ polycrystal is reported to have a high ZT of about 0.7, which is comparable to a metal compound, the n-type oxide system has a ZT of only about 0.3. The fact that it has not been obtained is an obstacle to the widespread use of oxide thermoelectric conversion devices. At present, there is an increasing demand for breakthroughs in thermoelectric properties of n-type oxides.

  Oxides doped with trivalent or tetravalent metal ions based on zinc oxide (ZnO) have been reported to exhibit high ZT among n-type thermoelectric materials, and are promising candidate materials for oxide thermoelectric conversion elements. Has been attracting much attention (Non-Patent Document 2).

  In addition, ZnO having a wurtzite crystal structure is known as a highly conductive surface in which the plane perpendicular to the c-axis (c-plane) is lined with Zn. Therefore, if a molded body based on ZnO having c-axis orientation such that current flows in a direction parallel to the c-plane of ZnO can be designed and manufactured, high thermoelectric conversion ability can be expected.

  As a technique for achieving crystal anisotropy with such a ZnO molded body, a perfectly oriented structure can be obtained by producing a bulk single crystal, but an extremely high temperature (˜2000 for growth of a metal oxide having a high melting point). ° C) and a dedicated single crystal growth apparatus are required, and there is a problem that the production is very expensive.

Therefore, as a technique for producing a crystalline orientation polycrystalline ZnO thermoelectric material, a polycrystalline orientation structure using a reactive templated grain growth (RTGG) method described in Patent Document 1 is described. Body manufacturing methods are known. The polycrystalline ZnO oriented structure using this RTGG method is a doctor blade which is one of tape molding methods using a dispersion slurry obtained by wet mixing basic zinc sulfate plate crystals and Al ₂ O ₃ particles. It is disclosed that the green sheet produced by the method can be cut, stacked several tens of layers, laminated and pressure-bonded, degreased and fired by heating, further subjected to isostatic pressing (CIP) treatment, and then sintered. However, in this manufacturing method, although a c-axis oriented ZnO sintered body doped with Al ³⁺ can be obtained, sulfuric acid remains as an impurity even after firing at a high temperature because a sulfate that does not volatilize at a high temperature is used as a raw material. In addition, since a structure in which large flaky crystals are integrated and the sinterability is lowered, there is a concern that the conductivity and further the thermoelectric properties may be adversely affected. In addition, since Al ₂ O ₃ particles are used as a raw material, there is a possibility that the solid solution of Al ^{3+ in} the crystal of ZnO occurs unevenly. Actually, the output factor (= S ² σ) at 800 ° C. disclosed as an index of thermoelectric conversion performance is 3.0 × 10 ⁻⁴ (W / m · K), which is disclosed in Non-Patent Document 2. Compared to the value [1.5 × 10 ⁻³ (W / m · K)] of an isotropic ZnO molded body doped with Al ³⁺ , the value is considerably low. Furthermore, since a very complicated process is performed as a production method, it is considered difficult to produce a ZnO crystal oriented molded body at a low cost expected for producing a polycrystal.

Also the slurry containing ZnO and Al ₂ O ₃ particles, high while applying a rotating magnetic field (~10T) solidifies and thermoelectric properties of sintered ZnO c-axis oriented fabricated is disclosed by sintering (Patent Document 2). However, even in this method, Al ₂ O ₃ particles are used as a raw material, as in the above-described method of manufacturing a molded body by the RTGG method, so that the solid solution of Al in the ZnO crystal is not uniform. There is a concern that the size of a bulk molded body that can be produced in order to use a rotating magnetic field device is limited, and that a large facility is required, resulting in high costs.

"Monthly Ceramics", 161-165 pages, March 1998, published by the Ceramic Society of Japan “Journal of Materials Chemistry”, p. 85-90, 1996. JP 2003-095741 A JP 2007-243070 A

  In view of the above problems, the present invention intends to provide a crystal orientation structure that can be produced without requiring a complicated and expensive process, and a method for producing the same.

As a result of intensive studies, the present inventors have studied a layered metal hydroxide containing a divalent metal ion or a layered metal hydroxide containing a trivalent metal ion at a predetermined molar ratio with respect to the divalent metal ion. The present inventors have found that a polycrystalline oxide structure obtained by subjecting a plate-like particle of a product to orientation treatment and further heat treatment has crystal orientation, and have reached the present invention.
That is, the crystalline orientation structure of the present invention is obtained by subjecting plate-like particles of layered metal hydroxide containing divalent metal ions to orientation treatment and further heating.

  The crystal-oriented oxide structure of the present invention can be produced without the need for complicated and expensive processes, so that it is excellent in productivity and has crystal anisotropy. Application to elements and magnetic films becomes possible.

Hereinafter, the present invention will be described in detail.
The crystal-oriented oxide structure of the present invention includes a layered metal hydroxide containing a divalent metal ion, or a trivalent metal ion in a molar ratio of greater than 0 to 1 or less with respect to the divalent metal ion. The layered metal hydroxide is used as a raw material. Here, the molar ratio of the trivalent metal ion is represented by the ratio of the molar amount of the trivalent metal ion to the molar amount of the divalent metal ion contained in the layered metal hydroxide.

The layered metal hydroxide used in the present invention is a metal hydroxide salt having a layered structure in which the basic layer has a brucite or CdI ₂ type crystal structure and an anion is included between layers. Such layered metal hydroxide salts having a brucite or CdI ₂ type structure as a basic structure generally tend to have different names depending on the type and number of metal ions contained in the crystal layer. In the present invention, the classification is not particularly limited. For example, a layered metal hydroxide (Layered Metal Hydroxide: hereinafter referred to as LMH) is broadly defined for a layered metal hydroxide salt composed of metal ions. ). Furthermore, in a narrow sense, it contains a layered metal hydroxide salt composed of one or more divalent metal ions and a small amount of trivalent metal ions (molar ratio of trivalent metal ions to divalent metal ions). Is a layered basic metal salt (hereinafter LBMS) or a hydroxy double salt (hereinafter HDS), and a divalent metal ion is a layered basic metal salt (layered basic metal salt (LBMS) or hydroxy double salt (hereinafter HDS)). On the other hand, a layered metal hydroxide salt containing a high concentration of trivalent metal ions (the molar ratio of trivalent metal ions to divalent metal ions is about 0.1 or more and 1 or less) is layered double hydroxide (Layered) Double Hydroxide (hereinafter referred to as LDH). The general formula of the layered metal hydroxide used in the present ^invention, represented by ^{_{M 2+ x M 3+ 1-x}} (OH) 3 (1-y) + x A n- (1 + 3y) / n · zH 2 O. ^{Here, M 2+} is a divalent metal ^{ion, M 3+} is a trivalent metal ^{ion, A n-is} the anion contained in the interlayer, x, y, z, n is any number .

The basic layer having a brucite or CdI type ₂ structure is a cationic metal hydroxide layer, and an anion is contained between the layers in order to maintain the electrical neutrality of the crystal. As the type of this anion, one that hardly decomposes or volatilizes by heat treatment and hardly remains as an impurity in the molded body is preferable. That is, hardly volatile anions such as sulfate ions and halide ions are difficult to decompose or volatilize by heat treatment, and thus may remain in the crystal. Here, the hardly volatile anion refers to 0 per 1 mol of oxide by being adsorbed or dissolved in the surface of the oxide after firing without being dissipated in the atmosphere by firing at about 1000 ° C. in the atmosphere. .01 mol or more of remaining anion species. Therefore, the anion that can be used in the present invention is not particularly limited as long as it is rapidly decomposed or volatilized by heat treatment at a high temperature. For example, acetate ion, lactate ion, butyrate ion, amino acid ion, etc. Of these, an organic anion and an inorganic anion such as nitrate ion are preferred.

Divalent metal ions contained in the layered metal hydroxide used in the present invention are Mg ²⁺ , Ca ²⁺ , Mn ²⁺ , Fe ²⁺ , Co ²⁺ , Ni ²⁺ , Cu ²⁺ , Zn ²⁺ , Sr ²⁺ , and Cd ^2+. At least one selected, and may include two or more. The layered metal hydroxide used in the present invention may contain a trivalent metal ion at the crystal site of the divalent metal ion. Here, the trivalent metal ion is at least one selected from Al ³⁺ , Ga ³⁺ , Fe ³⁺ , Mn ³⁺ , In ³⁺ , Co ³⁺ , Y ³⁺ , Ce ³⁺ , La ³⁺ , and two or more types. May be included. In the present invention, an oxide structure having a crystal orientation capable of arbitrarily selecting the above-described divalent metal ion and trivalent metal ion is possible. In addition, the presence state of the trivalent metal ion contained in the layered metal hydroxide may be a lattice solution even if it is in a substitutional solid solution state at the divalent metal ion site of the basic layer of the brucite or CdI ₂ type structure. It may be in a state of being intruded and dissolved between them.

In the present invention, the molar ratio of the trivalent metal ion to the divalent metal ion contained in the layered metal hydroxide is preferably 0 to 1. By containing trivalent metal ions at such a molar ratio, oxides having various composition ratios can be produced. The trivalent metal ion in the layered metal hydroxide in the present invention is dissolved in the crystal site of the divalent metal ion by heat treatment. Therefore, in the case of LBMS or HDS which is a metal hydroxide salt containing a trivalent metal ion at a low concentration, the effect as a dopant for improving the conductivity can be exhibited, and the trivalent metal ion is contained at a high concentration. In the case of using LDH, a complex oxide with a divalent metal ion can be formed. For example, a plate-like layered zinc hydroxide salt which is LBMS containing trivalent metal ions such as B ³⁺ , Al ³⁺ , Ga ³⁺ and In ^{3+ in} a molar ratio of 0 to 0.2 with respect to Zn ²⁺ By performing orientation treatment and heat treatment on the particles, a crystal orientation ZnO structure having high thermoelectric conversion performance using a trivalent metal ion as a dopant can be produced. In the case of LDH containing trivalent metal ions at a high concentration of 0.2 to 1 with respect to divalent metal ions, for example, a crystal orientation oxide having a spinel crystal structure is formed. can do. This is considered to be due to the similarity of the lattice between the (001) plane of LDH and the (111) plane of the spinel structure. For example, a plate-like particle of a layered cobalt hydroxide salt containing Fe ³⁺ having a molar ratio of 0.1 to 1 with respect to Co ²⁺ is subjected to an orientation treatment so as to be c-axis oriented, followed by a heat treatment, whereby Co ²⁺ and Co ^A structure in which spinel structure ferrite in which ³⁺ and Fe ³⁺ are mixed can be produced in a crystal orientation on the (111) plane.

Moreover, when using the crystal orientation structure in this invention for a thermoelectric element as a thermoelectric conversion material, the trivalent metal ion contained in a layered metal hydroxide substitutes for the Zn element which exists in the crystal lattice of zinc oxide. by a metal element such as improved conductivity, ^{preferably, B 3+, Al 3+, Ga} 3+, in 3+, Fe 3+, Co 3+, Y 3+, Sc 3+, is at least one selected from ^{Eu 3+.} Since these metal ions have more valence electrons than zinc, they are dissolved in the zinc site in zinc oxide to generate free electrons as carriers. Therefore, the conductivity of zinc oxide doped with these metal elements can be expected to improve dramatically. Since these metal elements have an ionic radius relatively close to that of zinc ions, they can be dissolved in zinc oxide crystals stably without causing distortion in the crystal structure. A more preferable metal element has a small distortion when dissolved in ZnO, and can be doped into a ZnO crystal at a molar ratio of up to about 0.1. As a result, high conductivity and thermoelectric conversion characteristics can be expected. Al. ("New development of transparent conductive film II", 31-40 pages, October 2002, CMC Publishing)

In the present invention, the structure formed by orienting the layered metal hydroxide plate-like particles containing divalent metal ions is derived from the plate-like shape of the layered metal hydroxide, resulting in brucite or CdI. _It has crystal orientation preferentially oriented in an orientation (c-axis) perpendicular to the base layer sheet of type ₂ structure. Further, by heating the c-axis oriented layered metal hydroxide structure, it is possible to produce a polycrystalline oxide structure having crystal orientation.

In the present invention, this layered metal hydroxide orientation treatment and heat treatment can topographically convert the crystal structure into an oxide structure while maintaining the crystal anisotropy of the layered metal hydroxide structure. Is important. In addition, the crystalline structure of the present invention has a different crystal structure depending on the type of metal ions contained in the layered metal hydroxide. For example, when plate-like particles of layered zinc hydroxide salt containing Al ³⁺ in a molar ratio of about 0 to 0.2 are subjected to an orientation treatment and further subjected to a heat treatment, the crystal orientation of the wurtzite ZnO oriented to the c-axis A conductive oxide structure can be manufactured. In this ZnO crystal orientation structure, Al ³⁺ is highly dispersed in advance in the layered zinc hydroxide salt as a raw material, so that Al ³⁺ is uniformly solid-solved and parallel to the highly conductive c-plane. Because of the oriented structure, high thermoelectric conversion performance can be expected. Also, the alignment process plate-like particles of the layered cobalt hydroxide salt containing Fe ^3+, by further heat treatment, produce the crystal orientation structure comprising a spinel structure ferrite oriented in (111) direction. Since this (111) -oriented spinel ferrite structure has magnetic anisotropy, application to a magnetic material, a magnetic film, etc. can be expected.

The presence state of trivalent metal ions contained in the layered metal hydroxide is a state in which the trivalent metal ions are substituted and dissolved in the divalent metal ion site of the brucite or CdI ₂ base layer sheet constituting the layered metal hydroxide. Even if it exists, it may be in the state of entering and dissolving between the lattices.

  In the present invention, the layered metal hydroxide plate-like particles can be produced, for example, by a wet process using a hydrolysis reaction of a raw material metal salt in an aqueous solution, and among others, a coprecipitation method, a hydrothermal synthesis method, and the like. A method such as a uniform precipitation method can be suitably used.

The layered metal hydroxide used in the present invention has a brucite or CdI ₂ structure as a basic structure as described above. Since the basic layer of the brucite or CdI ₂ structure is cationic, an anion is contained between the layers in order to maintain the electrical neutrality of the crystal.

  As the kind of anion, an anion that is hardly decomposed or volatilized by heat treatment at a high temperature of the molded body, and hardly remains as an impurity in the molded body is preferable. That is, since hardly volatile anions such as sulfate ions and halide ions are difficult to decompose or volatilize by heat treatment, there is a concern that they may remain in the zinc oxide crystal, resulting in adverse effects on the performance as a thermoelectric conversion element. This is because there is a risk of effect. Here, the hardly volatile anion means that it is adsorbed or dissolved in the surface of the oxide after firing without being dissipated in the atmosphere by firing at about 1000 ° C. in the atmosphere. Anion species remaining at 0.01 mol or more are shown. The remaining anionic species is indicated. Therefore, the interlayer anion in the present invention is not particularly limited as long as it is rapidly decomposed or volatilized by heat treatment at a high temperature. For example, acetate ions, lactate ions, butyrate ions, amino acid ions, etc. Organic anions and inorganic anions such as nitrate ions are preferred.

  The layered metal hydroxide used in the present invention has an average plate surface diameter of 50 nm to 30000 nm and an average plate thickness of 5 nm to 1000 nm. The average aspect ratio represented by (average plate surface diameter / average plate thickness) of the plate-like particles of the layered metal hydroxide used in the present invention is 10 or more and 1000 or less.

  When the average plate surface diameter, average plate thickness, and average aspect ratio of the layered metal hydroxide are out of the above ranges, the plate-like particles are not sufficiently oriented by the molding process, and the compact is in a random crystal orientation state. There is a risk of becoming. Here, the average plate surface diameter and the average plate thickness in the present invention are each a plate of 50 particles observed in a field of view of a magnification of 10,000 times of a scanning electron microscope (for example, “S-800” manufactured by Hitachi, Ltd.). It can be measured by averaging the surface diameter and the plate thickness.

  In another aspect of the present invention, the method includes a step of molding layered hydroxide plate-like particles. The molded body is derived from the plate-like shape of the layered metal hydroxide and has crystal orientation preferentially oriented in an orientation (c-axis) perpendicular to the basic layer sheet constituting the layered hydroxide. . Further, in the crystal orientation structure of the present invention, the c-axis oriented layered metal hydroxide molded body is heated to maintain the crystal anisotropy of the layered metal hydroxide structure in a topotropic manner. By converting the crystal structure into a structure, a polycrystalline crystal orientation structure can be obtained. In the present invention, it is also possible to obtain a crystallographically oriented structure by calcining a raw material powder of a layered metal hydroxide and making a phase transition to an oxide, and then producing a molded body and heat-treating it. It is.

  Moreover, as another aspect in this invention, it is a crystal orientation structure which has the form of a self-supporting molded object. This self-supporting molded body can be obtained, for example, by subjecting plate-like particles of layered metal hydroxide to orientation treatment and further heat treatment. As a method for producing a layered metal hydroxide used in the present invention or a molded body of the calcined body, any of a dry molding method and a wet molding method can be suitably used. Examples of the dry molding method include a uniaxial press molding method, a hot press method, and a hot forge method. In addition, when a coating agent such as a slurry or sol in which plate-like particles of layered metal hydroxide are dispersed is used, examples of wet molding methods include injection molding, casting molding, extrusion molding, and pressure molding. Method, centrifugal molding method, and the like. In the present invention, the uniaxial press molding method which is the simplest method and can be mass-produced can be used more suitably for producing a crystal orientation structure at low cost. Moreover, in order to improve the filling density of the molded object shape | molded by the said shaping | molding method, you may perform a hydrostatic pressure press (CIP) process.

  In the present invention, the heating temperature for producing the crystal orientation structure may be any temperature at which a crystal phase transition from a layered metal hydroxide to an oxide occurs, and varies depending on the type of metal ion, for example 50 ˜1500 ° C. is preferred. In order to improve the sinterability, a spark plasma sintering (SPS) method or the like may be used.

  Since the zinc oxide sintered body is preliminarily contained in the layered zinc hydroxide salt as a raw material alone as a dopant, the dopant is uniformly doped in the crystal lattice of ZnO after firing. Conductivity and thermoelectric conversion characteristics can be realized. Therefore, it can be used as a thermoelectric material.

  Another embodiment of the present invention is a crystal orientation structure having a film shape formed on a substrate. The crystal orientation structure having this film shape is obtained by applying, for example, a coating agent containing plate-like particles of layered hydroxide containing divalent and trivalent metal ions, spin coating method, dip coating method, tape molding method, By orientation on the substrate in film formation using a doctor blade method or the like, the plate surface of the plate-like particles is oriented parallel to the substrate, and further heat-treated. These methods may be selected to obtain a desired film thickness. When a thin film shape (film thickness of 5 nm to 1 μm) is obtained, a spin coating method or a dip coating method is preferably used, and a thick film shape (film When a thickness of 1 μm or more and 1 mm or less is obtained, a tape molding method, a doctor blade method, or the like can be preferably used. In this case, the heat treatment temperature may be equal to or lower than the heat resistant temperature of the material used as the substrate. As a coating agent containing plate-like particles of layered metal hydroxide containing divalent and trivalent metal ions, as a solvent, if the plate-like particles can be dispersed well, an aqueous system, a solvent system, and a mixture thereof are mixed. Any of these can be applied. In order to improve the dispersibility of the plate-like particles in the coating agent, a dispersant may be added to the coating agent. This dispersant may be either ionic (cationic or anionic) or nonionic. And the density | concentration in the coating agent of the plate-like particle | grains of a layered metal hydroxide can be adjusted to a desired density | concentration, and when considering the dispersibility and film forming efficiency of a plate-like particle, it is 0.001 in conversion of weight concentration. It can be used at 50 wt%.

  Then, by heating the crystal orientation film of the layered metal hydroxide produced by the method as described above, the film of the present invention is promoted by promoting the crystal phase transition to the oxide while maintaining the crystal anisotropy. A crystal orientation structure having a shape can be manufactured. At this time, the temperature at which the heat treatment is performed varies depending on the type of metal ion, but may be any temperature that is not higher than the heat resistance temperature of the material used as the substrate in which a crystal phase transition from the layered metal hydroxide to the oxide occurs. For example, when using a resin substrate, 50 to 300 ° C., when using a glass substrate, 50 to 700 ° C., and when using a metal and ceramic substrate having high heat resistance, 50 to 1500 ° C. are preferable.

The crystal orientation in the crystal orientation structure can be examined by, for example, an X-ray diffraction measurement apparatus (Panalytic “Xpert Pro”, X-ray source: CuKα, wavelength: 1.54 Å, applied voltage: 45 kV). Further, it is possible to quantitatively calculate the degree of orientation by analyzing the peak intensity obtained by the X-ray diffraction measurement by the Lottgering method. Assuming that the crystal orientation plane of the crystal orientation structure in the present invention is an (xyz) plane, the degree of axial orientation by the Lottgering method is to obtain I (h k l) peak intensities obtained by X-ray diffraction, and these peak intensities The ratio of I (x yz) to the sum of, and is calculated by f 1 given by the following equation.
_{f = (P - P 0)} / (1 - P 0)
Here, P is a peak intensity expressed by P = ΣI (xyz) / ΣI (hkl) and obtained from an oriented sample. P ₀ is represented by P ₀ = ΣI ₀ (x yz) / ΣI ₀ (h k l), and is a peak intensity obtained from an unoriented sample. The axial orientation degree f of the crystal orientation structure of the present invention is 0.5 or more and less than 1.0, and exhibits high crystal orientation.

When the crystal orientation structure in the present invention described above is used as a thermoelectric material for a thermoelectric conversion element, it has excellent characteristics because a plane parallel to the highly conductive c-plane of zinc oxide is arranged. Thermoelectric conversion characteristics can be exhibited. The thermoelectric conversion characteristics of the thermoelectric material in the present invention can be measured with a thermoelectric characteristic measuring device (for example, “RZ2001i” manufactured by Ozawa Science). Thus, using a measurement sample cut into a prismatic shape of about 5 mm × about 5 mm × about 15 mm, the conductivity (σ) when a temperature difference is given to both ends of the sample in each temperature range (for example, 0 to 1000 ° C.). ) And Seebeck coefficient (S) can be measured, whereby the output factor (σS ² ) can be obtained. Further, the thermal conductivity κ can be obtained by a laser flash thermophysical property measuring apparatus (for example, “LFA-502” manufactured by Kyoto Electronics Industry Co., Ltd.). Specifically, when the surface of a measurement sample cut into a plate of about 5 mm x about 5 mm x about 1 mm is irradiated with a laser beam with a uniform energy density in a pulse shape and heated uniformly, the heat is applied to the back of the sample. The thermal diffusivity can be determined by detecting the time and temperature change to diffuse, and the thermal conductivity can be obtained from this and the sample density. By the above measurements, the conductivity at various temperatures range, Seebeck coefficient, the thermal conductivity can be obtained ^{ZT (= σS 2 / κ)} .

Example 1
Preparation of layered zinc hydroxide salt containing Al ³⁺ A layered zinc hydroxide salt containing a dopant was synthesized by the following procedure.
Zinc acetate (manufactured by Wako Pure Chemical Industries) 0.098 mol and Al 2 ⁺ ion source aluminum acetate n hydrate (manufactured by Wako Pure Chemical Industries) 0.002 mol as a dopant are dissolved in 1000 ml of distilled water, and about 1 hour at room temperature. Stir. To the prepared aqueous metal salt solution, 1000 ml of a 0.1 M aqueous sodium hydroxide solution was added dropwise over 1 hour while stirring at room temperature, and then stirred for about 20 hours. After the stirring, the white gel was recovered by centrifuging, and the white gel was obtained by repeating washing with distilled water and centrifuging until the pH of the supernatant reached about 7. The obtained white gel was subjected to suction filtration, washed with 100 ml of ethanol, and dried at 60 ° C. for 2 hours to obtain a white thin plate.

  X-ray diffraction (XRD) measurement and crystal structure identification of this thin plate-like body using an X-ray diffraction measurement apparatus (Panalytic “Xpert Pro”, X-ray source: CuKα, wavelength: 1.54 Å, applied voltage: 45 kV) Was assigned to a single phase of layered zinc hydroxide acetate having a brucite structure. The c-axis of the layered zinc hydroxide acetate was strongly oriented perpendicular to the surface of the thin plate, and the degree of c-axis orientation by the Lottgering method was about 0.8. FIG. 1 shows the result of observation of this thin plate-like body with a scanning electron microscope (SEM, manufactured by Hitachi, Ltd., “S-800”). As can be seen from FIG. 1, the plate surface diameter is 100 to 10,000 nm, the plate thickness is 20 to 100 nm, and the thin plate-like particles having an aspect ratio of 10 to 200 are stacked in parallel to the plate surface. I understood. The average plate surface diameter, average plate thickness, and average aspect ratio determined by SEM observation were 5000 nm, 30 nm, and 100, respectively.

Preparation of crystal-oriented ZnO sintered body by calcining and sintering of layered zinc hydroxide acetate Next, the thin plate-like body obtained above is fired at 700 ° C. for 5 hours and crushed in a mortar. As a result of measuring the XRD pattern of the white powder obtained in Step 1, it was found to be wurtzite type ZnO oriented in the c-axis. The c-axis oriented ZnO white powder was pressed with a uniaxial press molding machine, and further subjected to isostatic pressing (CIP) to produce a disk-shaped pellet having a diameter of about 25 mm and a thickness of about 7 mm.

  This disk-shaped pellet was sintered by firing at 1000 ° C. for 10 hours and further at 1400 ° C. for 10 hours (ZnO—Al 2% sintered body). After polishing the surface of the sintered body with sandpaper and measuring the XRD pattern, the c-axis of ZnO is strongly oriented perpendicular to the circular surface of the sintered body, and the degree of c-axis orientation by the Lottgering method is It was 0.89. Moreover, when the energy dispersive X-ray analysis (EDX) of the powder which grind | pulverized this sintered compact was measured, and the substance amount ratio of metal conversion was calculated | required, Al contained about 2% with respect to Zn, and It was confirmed that elements other than Zn, Al and O were not contained as impurities.

Measurement of Thermoelectric Properties of Crystalline Oriented ZnO Sintered Body The c-axis oriented ZnO-Al2% sintered body produced as described above is 5 mm × 5 mm with a diamond cutter so that the longitudinal direction is in the direction perpendicular to the c-axis. A thermoelectric property measurement sample was prepared by cutting out to a size of 15 mm and polishing all surfaces with sandpaper.

Thermoelectric properties at room temperature (20 ° C.) to 1000 ° C. of the measurement sample of the ZnO sintered body were evaluated using a thermoelectric property measuring apparatus (“RZ2001i” manufactured by Ozawa Kagaku). Conductivity at each temperature sigma, the data of the Seebeck coefficient S and the power factor .sigma.s ² shown in FIG.
The conductivity is 100 S / cm or more in the entire temperature range, and the conductivity tends to decrease slightly as the temperature rises. Since the ZnO—Al 2% sintered body shows metallic electronic conduction, Al ³⁺ Is dissolved in the ZnO crystal as a dopant. Both Seebeck coefficient and output factor were high.

  Furthermore, from a room temperature to a 5 mm × 5 mm × 1 mm thick plate sample cut out with a laser flash thermophysical property measuring device (“LFA-502” manufactured by Kyoto Electronics Industry Co., Ltd.) so that the plate thickness direction is perpendicular to the c-axis direction. The thermal conductivity κ up to 1000 ° C. was measured. The graph which calculated | required the dimensionless figure of merit ZT from these results is shown in FIG. ZT at 1000 ° C. was about 0.35, and showed high thermoelectric properties.

(Example 2)
Example 1 except that layered zinc hydroxide nitrate containing Al ³⁺ produced using 0.095 mol of zinc nitrate hexahydrate (manufactured by Wako Pure Chemical Industries) and 0.005 mol of aluminum nitrate nonahydrate was used as a raw material. A ZnO—Al 5% sintered body was produced in the same procedure as described above. Both the lamellar zinc hydroxide nitrate sheet and the ZnO—Al 5% sintered body had a c-axis orientation of 0.87 by the Lottgering method.

  The thermoelectric properties (conductivity, Seebeck coefficient, output factor) of this ZnO—Al 5% sintered body are shown in FIG. 4, and the temperature dependence of ZT is shown in FIG. It can be seen that the ZnO—Al 5% sintered body has high thermoelectric conversion characteristics.

2 is a diagram showing an SEM image of a layered zinc hydroxide acetate containing Al ³⁺ in Example 1. FIG. 2 is a diagram showing thermoelectric properties of a ZnO—Al 2% sintered body in Example 1. FIG. It is a figure which shows the temperature dependence of ZT of the ZnO-Al2% sintered compact in Example 1. FIG. 6 is a diagram showing thermoelectric properties of a ZnO—Al 5% sintered body in Example 2. FIG. It is a figure which shows the temperature dependence of ZT of the ZnO-Al5% sintered compact in Example 2. FIG.

Claims (10)

A crystal-oriented structure obtained by subjecting plate-like particles of layered metal hydroxide containing divalent metal ions to orientation treatment and further heating. It is obtained by subjecting plate-like particles of layered metal hydroxide containing trivalent metal ions in a molar ratio of greater than 0 to 1 or less to divalent metal ions, and further heating. 2. The crystal orientation structure according to 1. The divalent metal ion is at least one selected from Mg ²⁺ , Ca ²⁺ , Mn ²⁺ , Fe ²⁺ , Co ²⁺ , Ni ²⁺ , Cu ²⁺ , Zn ²⁺ , Sr ²⁺ , and Cd ^2+. 3. The crystal orientation structure according to 2. The trivalent metal ^{ions, Al 3+, Ga 3+, Fe} 3+, Mn 3+, In 3+, Co 3+, Y 3+, Ce 3+, is at least one selected from ^{La 3+,} according to claim 2 or 3 Crystal orientation structure. The crystal orientation structure according to any one of claims 1 to 4, wherein the crystal orientation structure is a self-supporting molded body. The crystal orientation structure according to any one of claims 1 to 4, wherein the crystal orientation structure is a film formed on a substrate. A method for producing a crystallographic orientation structure, comprising subjecting plate-like particles of layered metal hydroxide containing divalent metal ions to orientation treatment and further heating. The thermoelectric element which uses the crystal orientation structure as described in any one of Claims 1-6 as a thermoelectric conversion material. The dielectric element which uses the crystal orientation structure as described in any one of Claims 1-6 as a dielectric material. The magnetic element which uses the crystal orientation structure as described in any one of Claims 1-6 as a magnetic body.

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