JPWO2007007587A1 - Co-oxide polycrystal with controlled orientation - Google Patents

Abstract

The present invention is a Co oxide polycrystal composed of a Co oxide polycrystal having an inconsistent crystal structure, causing slip deformation on the (001) plane of the polycrystal, and rotating in a certain direction. Further, a slip deformation is caused by compressing a Co oxide polycrystal having a mismatch crystal structure at a strain rate of 1.0 × 10 −5 to 1.0 × 10 −3 s −1 at 800 to 930 ° C. Thus, a Co oxide polycrystal having crystal rotation in a certain direction can be obtained. Thereby, the crystal orientation of the ceramics is controlled, and the ceramics with controlled crystal orientation and having anisotropy in electrical resistance can be provided, and can be used as thermoelectric conversion ceramics.

Description

  The present invention relates to a ceramic manufactured by controlling crystal orientation, and more particularly to a Co oxide having a mismatched crystal structure in which slip deformation in the (001) plane is generated and plastically deformed.

Ceramics generally have a high Peierls potential, and the number of independent slip systems necessary for plastic deformation of a polycrystalline body cannot be secured sufficiently. Therefore, even if a large force is applied for the purpose of plastic deformation, it does not cause plastic deformation. Is normal. Therefore, unlike metal materials, ceramics have no orientation control technology by plastic working.
On the other hand, in order to increase the figure of merit of thermoelectric conversion ceramics by orientation control, a method has been proposed in which a part of a raw material is partially melted while being uniaxially pressed and then gradually cooled (Patent Document 1). Also, anisotropically shaped powders such as needles and plates are present in the compact with a relatively high degree of orientation, and this anisotropically shaped powder is used as a template or reactive template to grow and / or synthesize oxides. In addition, the sintering is performed to adjust the orientation. The usefulness of rolling in a slurry state is also presented (Non-Patent Document 2).
The present inventors have formula _{Bi 2-x Pb x Sr 3} -y Y y Co 2 O 9-δ ceramics represented is reported to have a thermoelectric properties (Non-Patent Document 1).

JP2001-19544 (Patent No. 30830301) JP2003-282965 J. Phys. D: Appl. Phys. 34 (2001) 1017-1024

Conventional ceramic crystal orientation control technology is limited to material systems and compositions that can produce desired crystals by recrystallization, and requires complicated processes such as production and slurrying of anisotropically shaped powders. There were difficulties.
For metal materials, various texture control techniques have been established that adjust the crystal orientation by applying large plastic deformation by plastic working techniques such as rolling. However, even in ceramics, crystalline materials are aligned along specific crystal planes. It is considered that the orientation of the crystal can be adjusted if it can be largely plastically deformed by slip, that is, crystal slip deformation.
An object of the present invention is to provide a method for controlling the crystal orientation of a ceramic and a ceramic manufactured by controlling the crystal orientation. The ceramic whose crystal orientation is controlled in this way has anisotropy, and in the case of a thermoelectric conversion ceramic, it can be used as a thermoelectric conversion ceramic with an improved figure of merit by utilizing the direction of low electrical resistance.

The Co oxide (ceramics having a layered crystal structure) having a misfit structure targeted by the present invention has a direction in which the distance between adjacent atoms is short in the (001) plane and is close to the melting point. If the temperature is raised to temperature, it can overcome the Peierls potential and activate complete dislocations. In this case, since there are only two independent slip systems in the (001) plane, it is difficult to greatly deform the polycrystalline body.
In the present invention, it has been found that large strain processing can be achieved by selecting a temperature and strain rate at which deformation between crystal grains due to diffusion can occur, and the present invention has been completed.

That is, the present invention relates to a Co oxide polycrystal having an inconsistent crystal structure, wherein the crystal is oriented in a certain direction by slip deformation in the (001) plane of the polycrystal. It is. The polycrystal is compressed at a strain rate of 1.0 × 10 ^{−5 to} 1.0 × 10 ⁻³ s ⁻¹ in a temperature range from 800 ° C. or higher to a temperature of 30 ° C. below the melting point of the crystal. This can cause this slip deformation.
This compression process may use a plastic processing method such as uniaxial compression process, plane strain compression process, rolling, or extrusion process.
In the present invention, a polycrystal composed of a Co oxide having an inconsistent crystal structure is 1.0 × 10 ⁻⁵ to 1.0 in a temperature range from 800 ° C. to 30 ° C. below the melting point of the crystal. This is a method for producing a Co oxide having a mismatch crystal structure in which slip deformation in the (001) plane occurs, which is performed by compressing at a strain rate of × 10 ⁻³ s ⁻¹ .
The Co oxide having this inconsistent crystal structure may be further subjected to annealing for 12 to 50 hours in a temperature range from 800 ° C. or higher to a temperature of 30 ° C. below the melting point of the crystal.

The present invention has made it possible to provide a ceramic in which the orientation is aligned in a certain direction by plastically deforming a polycrystalline ceramic composed of crystal grains having random orientation directions.
The Co oxide having an incommensurate crystal structure of the present invention undergoes plastic deformation by high-temperature processing, realizing densification and texture formation, and as a result, improved thermoelectric properties.
The material of the present invention is a high-temperature thermoelectric conversion material that can be used up to around 700 ° C. In addition to fossil fuel thermoelectric conversion generators, the heat generated by combustion in factories and garbage incinerators, etc., has been directly discarded. It can be used for energy supply devices that convert to

The highly oriented polycrystalline ceramic of the present invention is a Co oxide having a mismatch crystal structure.
The “mismatched crystal structure” is a Co oxide composed of a plurality of layers including a CoO ₂ electron conducting layer, in which layers are stacked in the c-axis direction, and there are a and b axes in the perpendicular direction, and b axis It means a structure in which the ratio of the lattice constant of the CoO ₂ layer in the direction and the lattice constant of the other layer in contact with this layer above and below is irrational. However, the lattice constants in the a-axis direction of all layers are equal.
This ceramic has a layered crystal structure, and the maximum value of the pole density in the positive dot diagram measured by the Schulz reflection method is 10 times or more the average pole density. And this layered crystal structure, referred to for example a first sub-grid of Co 2 _O layer as shown in FIG. 1, a structure in which the second sublattice consisting of different layers are deposited in a predetermined cycle and Co 2 _O.
The inconsistent crystal structure can be confirmed by an X-ray diffraction method, but can be confirmed more accurately by neutron beam analysis.
Further, the composition can be confirmed by an EDX measurement method, and more accurately can be confirmed by a wet analysis, but it is generally difficult to determine the amount of oxygen by any method.

As the Co oxide having this inconsistent crystal structure, Bi _2−x Pb _x Sr _3−y Y _y Co ₂ O _9−δ (where, x = 0.4 to 0.8, y = 0.4 to 0.8, δ = 0.2 to 0.6), [Ca ₂ CoO _3−x ] _1−y CoO _2−z (where, x = 0.2 to 0, y = 0.4 to 0, z = 0.2 to 0), [(Ca _1−x Sr _x ) ₂ CoO _3−y ] _1−z CoO _2−w (where, x = 0.2 to 0, y = 0.2 to 0, z = 0.4 to 0, w = 0.2 ˜0), [(Ca ₂ (Co, Cu) _2−x O _4−y ) _0.63−z CoO _2−w (where x = −0.1 to 0.1, y = 0.3 to 0, z = − 0.1~0.1, w = 0.2~0) or _{[Bi 1.74-x Sr 2-} y O 4-z] 0.25-w CoO 2-v ( wherein, x = -0.05~0.05, y = - 0.05-0.05, z = 0.2-0, w = 0.05-0, V = 0.2-0), etc., but [(Ca _1−x Sr _x ) ₂ CoO _3−y ] _{1 -z} CoO _{2 -w} (wherein x = 0.2-0, y = 0.2-0, z = 0.4-0, w = 0.2-0) and [C a ₂ CoO _3−x ] _1−y CoO _2−z (wherein x = 0.2 to 0, y = 0.4 to 0, z = 0.2 to 0) is important.

“Polycrystalline” is a collection of the above-mentioned single crystals of about 1 to 10 μm in various directions. This polycrystal can be obtained by assembling and sintering powders of this composition.

“Compression processing” is a plastic processing method in which a shape is changed by applying a compression force to a target object.
When compression processing is performed on the “polyoxide of Co oxide having an inconsistent crystal structure” of the present invention, the Co oxide polycrystal is formed on the (001) plane of crystal grains facing various directions. Slip deformation occurs. Slip deformation causes plastic deformation in which the length of the polycrystalline body in the compression direction is reduced. As a result of this slip deformation, each crystal rotates to a position where the (001) plane is parallel to the compression plane. That is, the crystal rotates so that the normal direction of the (001) plane of the crystal grains constituting the polycrystal coincides with the direction to which compression processing is applied.

“Uniaxial compression processing” is a plastic processing method in which a uniaxial compression force is applied.
“Plane strain compression processing” means that when uniaxial compressive force is applied, deformation in one direction out of deformations in the direction perpendicular to the compressive force in the target object is prevented, and deformation in only one direction remains. This is a compression processing method that allows
The temperature of this compression processing is a temperature range from 800 ° C. or more to a temperature 30 ° C. below the melting point of the crystal. The temperature 30 ° C. below the melting point of the crystal is close to the melting point of the crystal and indicates a temperature at which the crystal is in a solid state. The melting point of the crystal is measured by thermal analysis.
The strain rate of the compression processing is obtained by dividing the compression rate by the height of the object to be compressed, and is 1.0 × 10 ^{−5 to} 1.0 × 10 ⁻³ s ⁻¹ , preferably 2.0 × 10. ^{−5 to} 8.0 × 10 ⁻⁵ s ⁻¹ . When the strain rate is 1.0 × 10 ⁻⁵ s ⁻¹ or less, not only does it take a long time to give sufficient strain, but the main deformation mechanism changes from crystal slip deformation to diffusion creep, and crystal orientation is sufficient. When the polycrystalline body is not ordered and the strain rate is 1.0 × 10 ⁻⁴ s ⁻¹ or more, the contribution of diffusion for alleviating the shortage of the slip system is insufficient.

  Annealing is performed to remove lattice defects such as dislocations grown during crystal slip deformation, and heating is performed in a temperature range from 800 ° C. or higher to a temperature of 30 ° C. below the melting point of the crystal. By annealing after the processing, recovery such as dislocation occurs, and the electrical resistance can be further reduced.

The following examples illustrate the invention but are not intended to limit the invention.
In the following examples, X-ray diffraction was measured using a semi-automatic diffractometer (manufactured by Mac Science) in the range of α = 0 degrees (in the normal direction of the plate surface) to 75 degrees, and the obtained diffraction intensity A positive dot diagram was obtained. The measurement method was a Schulz reflection method, which was performed using CuKα rays, a tube voltage of 40 kV, and a tube current of 30 mA.
Moreover, the structure | tissue photograph was performed using the scanning electron microscope (SEM). The unsintered sintered body sample was thinly cut with a diamond cutter and the surface thereof was observed, and the processed sample was observed on a surface perpendicular to the compression surface of the test piece.
The electrical resistance was measured by a four-terminal method after attaching an electrode to the sample and then connecting a copper wire to the sample with a silver paste. The measurement procedure is as follows: When the prepared sample is set in a Dewar bottle (manufactured by OXFORD), a vacuum is drawn with an oil rotary pump, and in this state, liquid nitrogen is used as a medium, and when the current is increased from about 80K to 340K, a current of 10 mA is applied. The voltage value (working material is 100 mA) was measured at a temperature interval of 1K under GP-IB control. The temperature was measured using a copper-constantan thermocouple.

Production Example 1
Bi ₂ O ₃ (Purity 99.9%, Wako Pure Chemical Industries, Ltd.), PbO ₂ (Purity 97%, Nakarai Desk Co., Ltd.), Sr ₂ O ₃ (Purity 99.9%, Soekawa Riken Co., Ltd.), Y ₂ O ₃ (purity 99.9%, Wako Pure Chemical Industries, Ltd.) and Co ₃ O ₄ (purity 99.9%, Soekawa Riken Co., Ltd.) with a molar ratio of 45: 30: 51: 15: 40 and a total weight of about 15g The mixture was weighed and wet-mixed with methanol using an agate mortar. The mixing time was 1 hour 30 minutes.
Next, this mixture was dry-mixed for 60 minutes using an agate ball mill and a milling machine (SPEX Corp. CertiPrep).
Next, the sample was placed in an alumina boat and calcined at 790 ° C. for 12 hours in a muffle furnace.
Since the sample after calcination had grown, the powder was refined by drying and crushing using an agate mortar.
The obtained powder was molded into a cylinder having a diameter of about 11 mm and a height of about 4 mm, placed in an alumina boat, and baked in air in a muffle furnace at 840 ° C. for 24 hours.
The obtained crystal is a Co oxide having a mismatched crystal structure with a composition of Bi _1.5 Pb _0.5 Sr _1.7 Y _0.5 Co ₂ O _9-δ , and is a polycrystal in which crystal grains of about 1 to 10 μm are aggregated. It was. The X-ray diffraction pattern is shown in FIG. 2, and a cross-sectional photograph (SEM) of the crystal is shown in FIG. The melting point of this crystal was 930 ° C.

Using the 2t autograph (manufactured by Shimadzu Corporation), the sample produced in Production Example 1 was sandwiched between magnesia plates at right angles to the axial direction of the cylinder and heated in an infrared image furnace. While the temperature rose to 840 ° C., the temperature of the sample was measured using a thermocouple. Even after reaching the target temperature, the thermal expansion of the jig continued, so the temperature was maintained for about 70 minutes until it settled.
After maintaining the temperature, compress with a 2t autograph at a constant crosshead speed (corresponding to 5.0 × 10 ⁻³ mm / min, strain rate of 2.0 × 10 ⁻⁵ s ⁻¹ ) along the axial direction of the sample cylinder. Thus, high temperature uniaxial compression processing was performed. The results are shown in Table 1.
4 and 5 show the diffraction pattern of the plane perpendicular to the axis of the cylinder of the obtained test piece and its positive electrode dot diagram. In the diffraction pattern, a large peak was confirmed by jumping to around 30 degrees, and a positive point map of this peak was taken to measure Imax. From this positive pole figure, it can be seen that the (001) plane is oriented parallel to the compression plane and rotated by various angles around the normal of the (001) plane.
A cross-sectional photograph (SEM) in a direction parallel to the axis of the cylinder of the obtained test piece is shown in FIG. From this photograph, it can be seen that the dimensions of the crystal grains differ between the direction perpendicular to the compression direction (longitudinal direction in the figure) and the direction parallel to the direction, and plastic deformation occurred in the compression direction.

The same operation as in Example 1 was performed so that the final strains were 0.47, 0.9, 1.27, and 1.87. The density is shown in FIG. 7, the positive dot diagram is shown in FIG. 8, and the resistivity is shown in FIG.
From the density change in FIG. 7, it can be seen that the density increases monotonously until the strain is close to 0.9, and the sintered body is densified. Up to this stage is the hot pressing process employed in the prior art. In this technology, by setting the processing conditions as described above, the compression was further continued and plastic processing up to a maximum true strain of 1.87 was achieved. At this time, no cracks were observed in the product, and it was confirmed that the product was a healthy material.
The maximum value of the pole density in the (001) pole figure (FIG. 8) determined by the Schulz reflection method was 1.0 before processing, but increased to 11.7 as the amount of strain increased, and high orientation was realized.
As shown in FIG. 9, the electrical resistance monotonously decreases with increasing strain (ε) due to processing up to true strain 1.87. In addition, the material manufactured by plane strain compression shows a lower specific resistance than the processed material up to the true strain of 1.87. Furthermore, the electrical resistance of the material produced by this method maintains a low value even in a high temperature range.

The sample compressed in Example 2 (with a strain of 1.87) was annealed in air at 840 ° C. for 24 hours in a muffle furnace. The resistivity is shown in FIG. The electrical resistance was further reduced by annealing, and was reduced to a maximum of 1/20. That is, by realizing high orientation by the orientation control technique of the present invention, the figure of merit of thermoelectric characteristics was dramatically improved by 20 times.

A magnesia plate used for uniaxial compression was cut into a strip shape having a width of 5 mm, and was pressed perpendicularly from the axial direction of the cylinder of the sample produced in Production Example 1 to perform high-temperature plane strain compression.
As in Example 1, the crosshead speed is constant (5.0 × 10 ⁻³ mm / min, the strain rate is 2.0 × 10 ⁻⁵ s ⁻¹⁾ along the axial direction of the cylinder of the sample at 840 ° C. and 2t autograph. )) To perform high-temperature plane strain compression processing. The results are shown in Table 2.

  Moreover, the diffraction pattern of a surface perpendicular | vertical to the axis | shaft of the cylinder of the obtained test piece and its positive electrode dot diagram are shown in FIG.10 and FIG.11. In the positive pole figure (FIG. 5) of Example 1 (high-temperature uniaxial compression process), the (001) plane was aligned, but the direction was not aligned, but this example (high-temperature plane strain compression process). In the positive pole figure, the (001) plane is not concentrically distributed with respect to the surface normal, and this plane is not only oriented parallel to the compression plane but also aligned in a specific direction. It is considered that the plane and direction could be aligned by plane strain compression. In other words, it is considered that a material having a structure orientation close to that of a single crystal was produced, and it is considered that the material has excellent thermoelectric properties.

Production Example 2
CaCO ₃ (Wako Pure Chemical Industries, purity 99.9%), Co ₃ O ₄ (Rare Metallic, purity 99.9%), SrCO ₃ (Wako Pure Chemical Industries, purity, purity) 99.9%) of raw material powder was weighed so as to be [(Ca _0.9 Sr _0.1 ) ₂ CoO ₃ ] _0.62 CoO _2, and calcined at 920 ° C. for 12 hours after wet mixing. After calcining and pulverization, the powder was press-molded into a 6 mm cube shape and sintered at 920 ° C. for 24 hours. Further, final annealing was performed at 700 ° C. for 12 hours in an oxygen atmosphere. The melting point of this crystal was 1350-1400 ° C.

Using the 2t autograph (manufactured by Shimadzu Corporation), the sample produced in Production Example 2 was sandwiched between magnesia plates at right angles to the axial direction of the prism and heated in an infrared image furnace. While the temperature rose to 880 ° C., the temperature of the sample was measured using a thermocouple. Even after reaching the target temperature, the thermal expansion of the jig continued, so the temperature was maintained for about 70 minutes until it settled.
After holding the temperature, true strain with a crosshead speed constant (corresponding to 2.0 × 10 ⁻² mm / min, strain rate 5.5 × 10 ⁻⁵ s ⁻¹ ) along the axial direction of the prism of the sample in 2t autograph − By compressing to 1.14, high-temperature uniaxial compression was performed. FIG. 12 shows a (001) positive electrode dot diagram measured for this sample. The projection surface is a compression surface, and the average pole density is 1. Accumulation of high pole density exceeding the maximum pole density of 12 is confirmed at the center of the figure, that is, the normal position of the compression surface. Also, the accumulation of extreme density is spreading concentrically. This result is the same as in Example 2.

Production Example 3
[Ca ₂ CoO ₃ ] _0.62 CoO ₂ powder (manufactured by Seimi Chemical Co., Ltd.) was used to form a cylindrical base material having a diameter of 11 mm and a height of 5 mm by press molding, followed by sintering at 920 ° C. for 24 hours.

Using the 2t autograph (manufactured by Shimadzu Corporation), the sample produced in Production Example 3 was sandwiched between magnesia plates at right angles to the axial direction of the cylinder and heated in an infrared image furnace. While the temperature rose to 920 ° C., the temperature of the sample was measured using a thermocouple. Even after reaching the target temperature, the jig continued to expand, so the temperature was held for about 70 minutes until it reached the target temperature.
After holding the temperature, the true strain at a constant crosshead speed (corresponding to 2.0 × 10 ⁻² mm / min, strain rate 6.7 × 10 ⁻⁵ s ⁻¹ ) along the axial direction of the cylinder of the sample in the 2t autograph − By compressing to 1.01, high temperature uniaxial compression was performed. FIG. 13 shows the (001) positive electrode dot diagram measured for this sample. The projection surface is a compression surface, and the average pole density is 1. Accumulation of high pole density exceeding the maximum pole density of 17 is confirmed at the center of the figure, that is, at the normal position of the compression surface. Also, the accumulation of extreme density is spreading concentrically. This result is the same as in Examples 2 and 5, and shows that the conductive surface is frequently oriented parallel to the compression surface.
The electrical resistance of Example 6 was measured by a four-terminal method after attaching an electrode to the sample and then connecting a copper wire to the sample with a silver paste. The results are shown in FIGS.
FIG. 14 shows the measurement result of the specific resistance of [Ca ₂ CoO ₃ ] _0.62 CoO ₂ and, for comparison, the specific resistance among the results of Bi _1.5 Pb _0.5 Sr _1.7 Y _0.5 Co ₂ O _9-δ shown in FIG. Both the results for the low value, 1.87 processed material and flat strain compression material are shown. [Ca ₂ CoO ₃ ] _0.62 CoO ₂ shows the results of heating and cooling. [Ca ₂ CoO ₃ ] _0.62 CoO ₂ with controlled orientation shows a low electrical resistivity value up to 1000K, which is a fraction of Bi _1.5 Pb _0.5 Sr _1.7 Y _0.5 Co ₂ O _9-δ . FIG. 15 is an enlarged view of the result of [Ca ₂ CoO ₃ ] _0.62 CoO ₂ . The electrical resistivity reaches a minimum of 2 mΩcm.

FIG. 16 shows the crystal structures of Example 2 (Bi—Sr—Co—O) and Examples 5 and 6 (Ca—Co—O), both of which are layered oxides having a misfit structure.
FIG. 17 shows the result of confirming the crystal structure of [Ca ₂ CoO ₃ ] _0.62 CoO ₂ by X-ray diffraction. _{[(Ca 0.9 Sr 0.1) 2} CoO 3] 0.62 CoO 2 because the _{[Ca 2 CoO 3] 0.62 CoO} 2 of Ca is partially substituted material with Sr, the crystal structure _{[Ca 2 CoO 3] 0.62 CoO} 2 Is the same. In Example 2, there are 4 insulator layers between CoO ₂ layers, and in Examples 5 and 6, there are 3 insulator layers between CoO ₂ layers. Is possible.

It is a diagram showing the crystal structure of _{Bi 1.5 Pb 0.5 Sr 1.7 Y 0.5} Co 2 O 9-δ. In the figure, the atomic plane whose normal is the vertical direction (the c-axis direction of the crystal) is the (001) plane. 6 is a diagram showing a diffraction pattern of a polycrystal prepared in Production Example 1. FIG. 2 is a cross-sectional photograph (SEM) of a polycrystal produced in Production Example 1. It is a figure which shows the diffraction pattern of the crystal | crystallization which performed the high temperature uniaxial compression process in Example 1. FIG. It is a figure which shows the positive electrode dot diagram of the crystal | crystallization which performed the high temperature uniaxial compression process in Example 1. FIG. Concentric curves indicate the positions where the average pole density is 1, 2, 3, 4, 5, 6 times as many as the order from the outside. 2 is a cross-sectional photograph (SEM) of a crystal subjected to high-temperature uniaxial compression processing in Example 1. FIG. The vertical direction in the figure is the compression processing direction. It is a figure which shows the density change of the crystal | crystallization which performed the high temperature uniaxial compression process in Example 2. FIG. The vertical axis represents density (g / cm ² ), and the horizontal axis represents the amount of strain. It is a figure which shows the positive electrode dot figure of the crystal which performed the high temperature uniaxial compression process in Example 2. FIG. It is a figure which shows the resistivity of the crystal | crystallization which performed the high temperature uniaxial compression process in Example 2. FIG. It is a figure which shows the diffraction pattern of the crystal | crystallization which performed the high temperature plane strain compression process in Example 4. FIG. It is a figure which shows the positive electrode dot figure of the crystal which performed the high temperature plane strain compression process in Example 4. FIG. The concentric curve indicates the position where the average pole density is 1,2,3,4,5,6,7 times in order from the outside. It is a figure which shows the positive electrode dot figure of the crystal which performed the high temperature uniaxial compression process in Example 5. FIG. It is a figure which shows the positive electrode dot figure of the crystal which performed the high temperature uniaxial compression process in Example 6. FIG. It is a figure which shows the electrical resistance measurement result of the crystal created in Example 6. FIG. It is a figure which shows the electrical resistance measurement result of the crystal created in Example 6. FIG. Bi _1.5 Pb _0.5 Sr _1.7 Y _0.5 Co ₂ O _9-δ (right figure) prepared in Example ₂ and [(Ca _0.9 Sr _0.1 ) ₂ CoO ₃ ] _0.62 CoO ₂ prepared in Example 5 and Example 6 is a diagram showing the crystal structure of the created _{[Ca 2 CoO 3] 0.62 CoO} 2 ( left). It is a figure which shows the X-ray-diffraction pattern of the polycrystal produced by the manufacture example 3. FIG.

[0004]
[0009]
The Co oxide having this inconsistent crystal structure is [Ca ₂ CoO _3-x ] _1-y CoO _2-z (wherein x = 0.2 to 0, y = 0.4 to 0, z = 0). _{.2~0), [(Ca 1-} x Sr x) 2 CoO 3-y] 1-z CoO 2-w ( where, x = 0.2~0, y = 0.2~0 , z = 0.4~0, w = 0.2~0) or _{[(Ca 2 (Co, Cu} ) 2-x O 4-y] 0.63-z CoO 2-w ( where, x = -0. 1 to 0.1, y = 0.3 to 0, z = −0.1 to 0.1, w = 0.2 to 0). However, in the practice of the present invention, [(Ca _1−x Sr _x ) ₂ CoO _3-y ] _1-z CoO _2-w (wherein x = 0.2-0, y = 0.2-0, z = 0.4-0, w = 0.2-0) ) and _{[Ca 2 CoO 3-x]} 1-y CoO 2-z ( wherein, x = 0.2 0, y = 0.4~0, z = 0.2~0) is important.
[0010]
“Polycrystalline” is a collection of the above-mentioned single crystals of about 1 to 10 μm in various directions. This polycrystal can be obtained by assembling and sintering powders of this composition.
[0011]
“Compression processing” is a plastic processing method in which a shape is changed by applying a compression force to a target object.
When the “polyoxide of Co oxide having a mismatch crystal structure” of the present invention is subjected to compression processing, the Co oxide polycrystal is formed on the (001) plane of crystal grains facing various directions. Slip deformation occurs. Slip deformation causes plastic deformation in which the length of the polycrystalline body in the compression direction is reduced. As a result of this slip deformation, each crystal rotates to a position where the (001) plane is parallel to the compression plane. That is, the crystal rotates so that the normal direction of the (001) plane of the crystal grains constituting the polycrystal coincides with the direction to which compression processing is applied.
[0012]
“Uniaxial compression processing” is a plastic processing method in which a uniaxial compression force is applied.
“Plane strain compression processing” means that when uniaxial compressive force is applied, deformation in one direction out of deformations in the direction perpendicular to the compressive force in the target object is prevented, and deformation in only one direction remains. This is a compression processing method that allows
The temperature of this compression processing is a temperature range from 800 ° C. or more to a temperature 30 ° C. below the melting point of the crystal. The temperature 30 ° C. below the melting point of the crystal is close to the melting point of the crystal and indicates a temperature at which the crystal is in a solid state. The melting point of the crystal is measured by thermal analysis.
The strain rate of the compression processing is obtained by dividing the compression rate by the height of the object to be compressed, and is 1.0 × 10 ^{−5 to} 1.0 × 10 ⁻³ s ⁻¹ , preferably 2.0 × 10. ^{−5 to} 8.0 × 10 ⁻⁵ s ⁻¹ . distortion

[0006]
Was 1 hour 30 minutes.
Next, this mixture was dry-mixed for 60 minutes using an agate ball mill and a milling machine (SPEX Corporation CertiPrep).
Next, the sample was put in an alumina boat and calcined at 790 ° C. for 12 hours in a muffle furnace.
Since the sample after calcination had grown, the powder was refined by drying and crushing using an agate mortar.
The obtained powder was formed into a cylinder having a diameter of about 11 mm and a height of about 4 mm, placed in an alumina boat, and baked in an air muffle furnace at 840 ° C. for 24 hours.
The obtained crystal is a Co oxide having a mismatch crystal structure with a composition of Bi _1.6 Pb _0.5 Sr _1.7 Y _0.5 Co ₂ O _9-δ , and has a crystal of about 1 to 10 μm. It was a polycrystal with aggregated grains. The X-ray diffraction pattern is shown in FIG. 2, and a cross-sectional photograph (SEM) of the crystal is shown in FIG. The melting point of this crystal was 930 ° C.
[0016]
Reference example 1
Using the 2t autograph (manufactured by Shimadzu Corporation), the sample produced in Production Example 1 was sandwiched between magnesia plates at right angles to the axial direction of the cylinder and heated in an infrared image furnace. While the temperature rose to 840 ° C., the temperature of the sample was measured using a thermocouple. Even when the target temperature was reached, the jig continued to thermally expand, so the temperature was maintained for about 70 minutes until it settled.
After maintaining the temperature, the crosshead speed is constant along the axial direction of the sample cylinder in the 2t autograph (corresponding to 5.0 × 10 ⁻³ mm / min, strain rate of 2.0 × 10 ⁻⁵ s ⁻¹ ). High-temperature uniaxial compression processing was performed by compressing with. The results are shown in Table 1.
[Table 1]
The diffraction pattern of the plane perpendicular to the cylinder axis of the obtained test piece and its positive electrode dot diagram are shown in FIGS.

[0007]
As shown in FIG. Since a large peak was confirmed by jumping to around 30 degrees in the diffraction pattern, a positive pole figure of this peak was taken and Imax was measured. From this positive pole figure, it can be seen that the (001) plane is oriented parallel to the compression plane and rotated by various angles around the normal line of the (001) plane.
A cross-sectional photograph (SEM) in a direction parallel to the axis of the cylinder of the obtained test piece is shown in FIG. From this photograph, it can be seen that the dimensions of the crystal grains differ between the direction perpendicular to the compression direction (longitudinal direction in the figure) and the direction parallel to the direction, and plastic deformation occurred in the compression direction.
[0017]
Reference example 2
The same operation as in Reference Example 1 was performed so that the final strains were 0.47, 0.9, 1.27, and 1.87. The density is shown in FIG. 7, the positive dot diagram is shown in FIG. 8, and the resistivity is shown in FIG.
From the density change in FIG. 7, it can be seen that the density increases monotonously until the strain is around 0.9, and the sintered body is densified. Up to this stage is the hot pressing process employed in the prior art. In the present technology, by setting the processing conditions as described above, the compression is further continued, and plastic processing up to a maximum true strain of 1.87 is achieved. At this time, no cracks were observed in the product, and it was confirmed that the product was a healthy material.
The maximum value of the pole density in the (001) pole figure (Fig. 8) determined by the Schulz reflection method is 1.0 before processing, but increases to 11.7 as the amount of strain increases, realizing high orientation. It was done.
As shown in FIG. 9, the electrical resistance monotonously decreases as the strain amount (ε) increases due to processing up to the true strain of 1.87. Moreover, the raw material manufactured by plane strain compression shows a specific resistance lower than the processed material up to true strain 1.87. Furthermore, the electrical resistance of the material produced by this method maintains a low value even in a high temperature range.
[0018]
Reference example 3
The sample compressed in Reference Example 2 (with a strain of 1.87) was annealed in air at 840 ° C. for 24 hours in a muffle furnace. The resistivity is shown in FIG. The electrical resistance was further reduced by annealing, and was reduced to a maximum of 1/20. That is, by realizing high orientation by the orientation control technique of the present invention, the figure of merit of thermoelectric characteristics was dramatically improved by 20 times.
[0019]
Reference example 4
A magnesia plate used for uniaxial compression was cut into a strip of 5mm width, which was then manufactured.

[0008]
A high-temperature plane strain compression process was performed by applying a pressure perpendicularly from the axial direction of the cylinder of the sample produced in 1.
Similar to Reference Example 1, the crosshead speed is constant (5.0 × 10 ⁻³ mm / min, strain rate is 2.0 × 10 ⁻⁵ s) along the axial direction of the sample cylinder in a 2t autograph at 840 ° C. It corresponds to ⁻¹ ) to perform high-temperature plane strain compression processing. The results are shown in Table 2.
[Table 2]
[0020]
Moreover, the diffraction pattern of a surface perpendicular | vertical to the axis | shaft of the cylinder of the obtained test piece and its positive electrode dot diagram are shown in FIG.10 and FIG.11. In the positive electrode diagram (FIG. 5) of Reference Example 1 (high temperature uniaxial compression processing), the (001) plane is aligned, but the direction is not aligned, but this example (high temperature plane strain compression processing). In the positive electrode diagram, the (001) plane is not distributed concentrically with respect to the surface normal, and this plane is not only oriented parallel to the compression plane but also aligned in a specific direction. It is considered that the plane and direction could be aligned by plane strain compression. In other words, it is considered that a material having a structure orientation close to that of a single crystal was produced, and it is considered that the material has excellent thermoelectric properties.
[0021]
Production Example 2
CaCO ₃ (manufactured by Wako Pure Chemical Industries, Ltd., purity 99.9%), Co ₃ O ₄ (manufactured by Rare Metallic Co., Ltd., purity 99.9%), SrCO ₃ (manufactured by Wako Pure Chemical Industries, Ltd., purity) 99.9%) raw material powder was weighed so as to be [(Ca _0.9 Sr _0.1 ) ₂ CoO ₃ ] _0.62 CoO _2, and calcined at 920 ° C. for 12 hours after wet mixing. After calcining and pulverization, the powder was press-molded into a cubic shape with a side of 6 mm and sintered at 920 ° C. for 24 hours. Further, final annealing was performed at 700 ° C. for 12 hours in an oxygen atmosphere. The melting point of this crystal was 1350-1400 ° C.
[0022]
Example 1
Using the 2t autograph (manufactured by Shimadzu Corp.)

[0009]
It was sandwiched between magnesia plates at right angles to the direction and heated in an infrared image furnace. While the temperature rose to 880 ° C., the temperature of the sample was measured using a thermocouple. Even when the target temperature was reached, the jig continued to thermally expand, so the temperature was maintained for about 70 minutes until it settled.
After maintaining the temperature, the crosshead speed is constant along the axial direction of the prism of the sample in the 2t autograph (corresponding to 2.0 × 10 ⁻² mm / min, strain rate 5.5 × 10 ⁻⁵ s ⁻¹ ). The high temperature uniaxial compression process was performed by compressing to true strain -1.14. FIG. 12 shows a (001) positive electrode dot diagram measured for this sample. The projection plane is a compression plane and the average pole density is 1. Accumulation of high pole density exceeding the maximum pole density of 12 is confirmed at the center of the figure, that is, the normal position of the compression surface. Also, the accumulation of extreme density is spreading concentrically. This result is the same as in Reference Example 2.
[0023]
Production Example 3
After the _{[Ca 2 CoO 3] 0.62 CoO} 2 powder (Seimi Chemical Co., Ltd.) a cylindrical preform having a diameter of 11mm 5mm height was used to create a press molding, for 24 hours and sintered at 920 ° C..
[0024]
Example 2
Using the 2t autograph (manufactured by Shimadzu Corporation), the sample produced in Production Example 3 was sandwiched between magnesia plates at right angles to the axial direction of the cylinder and heated in an infrared image furnace. While the temperature rose to 920 ° C., the temperature of the sample was measured using a thermocouple. Since the jig continued to expand even when the target temperature was reached, the temperature was maintained for about 70 minutes until it reached the target temperature.
After maintaining the temperature, the crosshead speed is constant along the axial direction of the sample cylinder in the 2t autograph (corresponding to 2.0 × 10 ⁻² mm / min, strain rate of 6.7 × 10 ⁻⁵ s ⁻¹ ). Then, high temperature uniaxial compression processing was performed by compressing to true strain -1.01. FIG. 13 shows the (001) positive electrode dot diagram measured for this sample. The projection plane is a compression plane and the average pole density is 1. Accumulation of high pole density exceeding the maximum pole density of 17 is confirmed at the center of the figure, that is, at the position of the compression surface normal. Also, the accumulation of extreme density is spreading concentrically. This result is the same as in Reference Example 2 and Example 1, and shows that the conductive surface is frequently oriented parallel to the compression surface.
The electrical resistance of Example 2 was measured by a four-terminal method after attaching an electrode to the sample and connecting a copper wire to the sample with a silver paste. The results are shown in FIGS.
FIG. 14 shows the results of measurement of the specific resistance of [Ca ₂ CoO ₃ ] _0.62 CoO ₂ for comparison with the Bi _1.5 P shown in FIG.

[0010]
Among the results of b _0.6 Sr _1.7 Y _0.5 Co ₂ O _9-δ , the specific resistance value is low, and both the results of the -1.87 processed material and the plane strain compression material are shown. [Ca ₂ CoO ₃ ] _0.62 CoO ₂ shows the results of heating and cooling. Oriented controlled [Ca ₂ CoO ₃ ] _0.62 CoO ₂ is a fraction of Bi _1.5 Pb _0.5 Sr _1.7 Y _0.5 Co ₂ O _9-δ , low electrical ratio Resistance values are shown up to 1000K. FIG. 15 is an enlarged view of the result of [Ca ₂ CoO ₃ ] _0.62 CoO ₂ . The electrical resistivity reaches a minimum of 2 mΩcm or less.
[0025]
FIG. 16 shows the crystal structures of Reference Example 2 (Bi—Sr—Co—O) and Examples 1 and 2 (Ca—Co—O), both of which are layered oxides having a misfit structure.
FIG. 17 shows the result of confirming the crystal structure of [Ca ₂ CoO ₃ ] _0.62 CoO ₂ by X-ray diffraction. [(Ca _0.9 Sr _0.1 ) ₂ CoO ₃ ] _{0.62 Since} CoO ₂ is a material in which Ca in [Ca ₂ CoO ₃ ] _0.62 CoO ₂ is partially substituted with Sr, the crystal structure is [ Ca ₂ CoO ₃ ] _0.62 Same as CoO ₂ . In Reference Example 2, there are four insulator layers between the CoO ₂ layers, and in Examples 1 and 2, there are differences in the three insulator layers between the CoO ₂ layers. Orientation control is possible.
BRIEF DESCRIPTION OF THE DRAWINGS [0026]
FIG. 1 is a view showing a crystal structure of Bi _1.5 Pb _0.5 Sr _1.7 Y _0.5 Co ₂ O _9-δ . In the figure, the atomic plane whose normal is the vertical direction (the c-axis direction of the crystal) is the (001) plane.
FIG. 2 is a diagram showing a diffraction pattern of a polycrystal prepared in Production Example 1.
FIG. 3 is a cross-sectional photograph (SEM) of a polycrystal prepared in Production Example 1.
FIG. 4 is a diagram showing a diffraction pattern of a crystal subjected to high-temperature uniaxial compression processing in Reference Example 1.
FIG. 5 is a diagram showing a positive electrode dot diagram of a crystal subjected to high-temperature uniaxial compression processing in Reference Example 1. Concentric circular curves indicate positions where the average pole density is 1, 2, 3, 4, 5, 6 times as many as the pole density in order from the outside.
FIG. 6 is a cross-sectional photograph (SEM) of a crystal subjected to high-temperature uniaxial compression processing in Reference Example 1. The vertical direction in the figure is the compression processing direction.
[FIG. 7] A diagram showing changes in density of crystals subjected to high-temperature uniaxial compression processing in Reference Example 2. The vertical axis represents density (g / cm ² ), and the horizontal axis represents the amount of strain.
FIG. 8 is a diagram showing a positive electrode dot diagram of a crystal subjected to high-temperature uniaxial compression processing in Reference Example 2.
FIG. 9 is a view showing the resistivity of a crystal subjected to high-temperature uniaxial compression processing in Reference Example 2.

[0011]
FIG. 10 is a diagram showing a diffraction pattern of a crystal subjected to high-temperature plane strain compression processing in Reference Example 4.
FIG. 11 is a diagram showing a positive electrode dot diagram of a crystal subjected to high-temperature plane strain compression processing in Reference Example 4. Concentric curves indicate positions where the average pole density is 1, 2, 3, 4, 5, 6, 7 times as many as the order from the outside.
FIG. 12 is a diagram showing a positive electrode dot diagram of a crystal subjected to high-temperature uniaxial compression processing in Example 1.
FIG. 13 is a diagram showing a positive electrode dot diagram of a crystal subjected to high-temperature uniaxial compression processing in Example 2.
FIG. 14 is a diagram showing the results of measuring electrical resistance of the crystal prepared in Example 2.
FIG. 15 is a graph showing the results of measuring electrical resistance of the crystal prepared in Example 2.
[FIG. 16] Bi _1.5 Pb _0.5 Sr _1.7 Y _0.5 Co ₂ O _9-δ (right figure) prepared in Reference Example 2 and (Ca _0.9 Sr produced in Example 1) _0.1 ) ₂ CoO ₃ ] _0.62 CoO ₂ and [Ca ₂ CoO ₃ ] _0.62 CoO ₂ (left figure) prepared in Example 2 are crystal diagrams.
FIG. 17 is a view showing an X-ray diffraction pattern of a polycrystal prepared in Production Example 3.

Claims (9)

A Co oxide polycrystal having an inconsistent crystal structure, wherein the crystal is oriented in a certain direction by slip deformation in the (001) plane of the polycrystal. The slip deformation has a strain rate of 1.0 × 10 ^{−5 to} 1.0 × 10 ⁻³ s ^{−1 in} a temperature range from 800 ° C. or higher to a temperature of 30 ° C. below the melting point of the crystal. The Co oxide having a mismatched crystal structure according to claim 1, which is generated by performing compression processing in step 1. The Co oxide having a mismatch crystal structure according to claim 1 or 2, wherein the compression processing is uniaxial compression processing. The Co oxide having a mismatch crystal structure according to claim 1, wherein the compression processing is plane strain compression processing. Furthermore, the mismatch crystal structure as described in any one of Claims 1-4 which added annealing for 12 to 50 hours in the temperature range from 800 degreeC or more to the temperature below 30 degreeC of melting | fusing point of this crystal | crystallization. Co oxide. The Co oxide having the mismatch crystal structure is Bi _2-x Pb _x Sr _3-y Y _y Co ₂ O _9-δ (where x = 0.4 to 0.8, y = 0.4 to 0.8, δ = 0.2 to 0.6), [Ca ₂ CoO _3−x ] _1−y CoO _2−z (where, x = 0.2 to 0, y = 0.4 to 0, z = 0.2 to 0), [(Ca _1−x Sr _x ) ₂ CoO _3−y ] _1−z CoO _2−w (where, x = 0.2 to 0, y = 0.2 to 0, z = 0.4 to 0, w = 0.2 ˜0), [(Ca ₂ (Co, Cu) _2−x O _4−y ] _0.63−z CoO _2−w , where x = −0.1 to 0.1, y = 0.3 to 0, z = − 0.1~0.1, w = 0.2~0) or _{[Bi 1.74-x Sr 2-} y O 4-z] 0.25-w CoO 2-v ( wherein, x = -0.05~0.05, y = - Co-oxide having a mismatch crystal structure according to any one of claims 1 to 5, wherein 0.05 to 0.05, z = 0.2 to 0, w = 0.05 to 0, V = 0.2 to 0). The thermoelectric conversion material which consists of Co oxide which has a mismatch crystal structure as described in any one of Claims 1-6. A polycrystal composed of a Co oxide having a mismatch crystal structure is 1.0 × 10 ^{−5 to} 1.0 × 10 ⁻³ s in a temperature range from 800 ° C. or higher to a temperature 30 ° C. below the melting point of the crystal. A process for producing a Co oxide having a mismatch crystal structure in which slip deformation in the (001) plane occurs, which is performed by compressing at a strain rate of ^-1 . The method according to claim 8, further comprising annealing for 12 to 50 hours in a temperature range from 800 ° C or higher to a temperature of 30 ° C below the melting point of the crystal.