JP2006052121A - Multiple oxide having excellent thermoelectric conversion performance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new thermoelectric conversion material which has good heat resistance and chemical durability and a high Seebeck coefficient, and further superior electroconductivity. <P>SOLUTION: A multiple oxide has a composition expressed by general formula: Ca<SB>a</SB>M<SP>1</SP><SB>b</SB>Co<SB>c</SB>M<SP>2</SP><SB>d</SB>Ag<SB>e</SB>O<SB>f</SB>(wherein, M<SP>1</SP>is one or more kinds of elements selected from the group comprising Na, K, Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sr, Ba, Al, Bi, Y and lanthanoids; M<SP>2</SP>is one or more kinds of elements selected from the group comprising Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, Ta and Bi; 2.2≤a≤3.6; 0≤b≤0.8; 2≤c≤4.5; 0≤d≤2; 0≤e≤0.8; and 8≤f≤10). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a composite oxide having excellent performance as a p-type thermoelectric conversion material, a p-type thermoelectric conversion material comprising the composite oxide, and a thermoelectric power generation module.

  In Japan, the yield of effective energy from primary supply energy is about 30%, and about 70% of energy is finally discarded as heat into the atmosphere. Also, most of the heat generated by combustion in factories and garbage incinerators is discarded into the atmosphere without being converted into other energy. In this way, we humans are wasting a great deal of heat energy and gaining little energy from actions such as the burning of limited fossil fuels.

  In order to improve the energy yield, it is effective to be able to use the thermal energy discarded in the atmosphere. One effective technical means for this purpose is thermoelectric conversion that directly converts thermal energy into electrical energy. This thermoelectric conversion uses the Seebeck effect and is an energy conversion method in which a potential difference is generated by generating a temperature difference at both ends of a thermoelectric conversion material to generate electric power. In power generation using such thermoelectric conversion, that is, thermoelectric power generation, one end of the thermoelectric conversion material is arranged in a high temperature part generated by waste heat, and the other end is arranged in the atmosphere (room temperature part), and both ends are arranged. Since electricity can be obtained simply by connecting a conducting wire to the motor, a movable device such as a motor or a turbine necessary for general power generation is unnecessary. For this reason, equipment cost is also low, there is no discharge | emission of gas by combustion etc., and it can generate electric power continuously until the thermoelectric conversion material deteriorates. In addition, since thermoelectric power generation can generate power with a high output density, the power generator (module) itself can be reduced in size and weight, and can also be used as a mobile power source for mobile phones, laptop computers, and the like.

  In this way, thermoelectric power generation is expected as a technology that will play a part in the solution to the serious problem of depletion of energy resources that will be predicted in the future, but in order to realize thermoelectric power generation, high thermoelectric conversion efficiency is expected. Therefore, it is necessary to supply a large amount of thermoelectric conversion materials having excellent heat resistance and chemical durability.

  At present, intermetallic compounds are known as substances having high thermoelectric conversion efficiency. However, the thermoelectric conversion efficiency of intermetallic compounds is at most about 10%, and can only be used in air at a temperature of about 300 ° C. or lower. Some types of intermetallic compounds include toxic elements and rare elements as constituent elements.

  For this reason, thermoelectric conversion using waste heat has not yet been put to practical use, is composed of elements that are less toxic and have a large amount of existing elements, has excellent heat resistance, chemical durability, etc., and has high thermoelectric conversion efficiency. Development of materials is expected.

In recent years, Co-based composite oxides containing Ca, Bi, Sr, Na, and the like have been reported as materials having high thermoelectric conversion efficiency (Non-patent Document 1). However, these composite oxides have higher electrical resistivity than intermetallic compounds, and it is necessary to reduce the electrical resistivity of the composite oxide in order to realize higher density thermoelectric power generation.
Xu et al., Applied Physics Letters vol. 80, pp. 3760-3762 (2002)

  The present invention has been made in view of the current state of the prior art described above, and its main purpose is a material having good heat resistance, chemical durability, etc., and a high Seebeck coefficient, and further good It is to provide a novel thermoelectric conversion material having excellent electrical conductivity.

  The present inventor has intensively studied to achieve the above object. As a result, a composite oxide obtained by substituting a part of a Co-based composite oxide having a specific composition containing Ca with a specific amount of Ag has a high Seebeck coefficient, and at the same time, compared with a known Co-based composite oxide. It has been found that the material has good conductivity and high thermoelectric conversion efficiency, and the present invention has been completed here.

That is, the present invention provides the following composite oxide, p-type thermoelectric conversion material, and thermoelectric conversion module.
1. ^{_{Formula: Ca a M 1 b Co c}} M 2 d Ag e O f ( wherein, M ¹ is Na, K, Li, Ti, V, Cr, Mn, Fe, Ni, Cu
, Zn, Pb, Sr, Ba, Al, Bi, Y and one or more elements selected from the group consisting of lanthanoids, M ² is Ti, V, Cr, Mn, Fe, Ni, Cu, One or more elements selected from the group consisting of Mo, W, Nb, Ta and Bi, 2.2 ≦ a ≦ 3.6; 0 ≦ b ≦ 0.8; 2 ≦ c ≦ 4.5; 0 ≦ d ≦ 2; 0 <e ≦ 5; 8 ≦ f ≦ 10. A composite oxide having a composition represented by:
2. Item 2. The composite oxide according to Item 1, having a Seebeck coefficient of 60 µV / K or more in a temperature range of 273 K or more and less than the decomposition temperature.
3. Item 3. The composite oxide according to Item 1 or 2, which has an electrical resistivity of 20 mΩcm or less in a temperature range of 273 K or more and less than the decomposition temperature.
4). Item 4. The composite oxide according to any one of Items 1 to 3, having a thermal conductivity of 10 W / mK or less in a temperature range of 273 K or more and less than a decomposition temperature.
5. The composite oxide according to any one of claims 1 to 4, which is a composite oxide alone or a composite comprising the composite oxide and Ag metal fine particles.
6). A p-type thermoelectric conversion material comprising the composite oxide according to any one of Items 1 to 5.
7). A thermoelectric power generation module comprising the p-type thermoelectric conversion material according to Item 6.

Composite oxides of the present invention have the general formula: are those having a composition represented by ^{_{Ca a M 1 b Co c M}} 2 d Ag e O f. In the above general formula, M ¹ is selected from the group consisting of Na, K, Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sr, Ba, Al, Bi, Y and lanthanoids One or more elements, and M ² is one or more elements selected from the group consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, Ta, and Bi. It is. Examples of lanthanoid elements include La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Lu.

In the formula, a value is 2.2 ≦ a ≦ 3.6, b value is 0 ≦ b ≦ 0.8, c value is 2 ≦ c ≦ 4.5, d value is 0 ≦ d ≦ 2, e
The value is 0 <e ≦ 5, and the f value is 8 ≦ f ≦ 10. In particular, the sum of the a value and the b value is preferably 2.5 ≦ a + b ≦ 3.1, and the sum of the c value and the d value is preferably 3.4 ≦ c + d ≦ 4.2.

In the above general formula, when b exceeds 0 and d exceeds 0, that is, when 0 <b ≦ 0.8 and 0 <d ≦ 2, the components M ¹ and M ² are essential components. By appropriately adjusting the type and amount of these components, the Seebeck coefficient can be improved, the electrical resistivity, the thermal conductivity, etc. compared to the composite oxide of b = 0 and d = 0. Therefore, the thermoelectric conversion material is highly useful. In particular, the b value is preferably 0 <b ≦ 0.4, and the d value is preferably 0 <d ≦ 1. Within such a range, the stability of the crystal structure is good even when the M ¹ and M ² components are included. The e value is preferably 0 <e ≦ 2, and more preferably 0.03 <e ≦ 1.

The composite oxide represented by the above general formula includes a layer having a rock salt structure composed of Ca, Co, Ag, and O, and six O's octahedrally coordinated to one Co. CoO ₂ layers that are two-dimensionally arranged so as to share sides are alternately stacked, and a portion of Ca in the layer having a rock salt structure is replaced by M ¹ , and the rock salt structure A part of Co and a part of the CoO ₂ layer in the layer having s are substituted with M ² .

  Further, in the above composition formula, when the e value indicating the Ag ratio increases, Ag precipitates as a metal element in addition to the composite oxide having the above structure, and Ag particles exist between the composite oxide particles. It becomes a composite. The e value when Ag precipitates as a metal varies depending on the composition of the other components, and thus cannot be defined unconditionally. However, if the e value is about 0.5 or more, the Ag metal is usually between the composite oxide particles. Precipitate. In general, when the e value is about 0.2 or less, only the complex oxide having the above structure is formed.

FIG. 1 shows a polycrystal of a composite oxide represented by the composition formula Ca ₃ Co _3.8 Ag _0.2 O ₉ obtained in Example 1 to be described later, among the composite oxides of the present invention. 2 shows an X-ray diffraction pattern of a known Ca ₃ Co ₄ O ₉ polycrystal produced under the same conditions as in FIG. As is apparent from these X-ray diffraction patterns, although the presence of impurities is somewhat observed, it is recognized that the composite oxide of the present invention has a crystal structure similar to that of known Ca ₃ Co ₄ O ₉ .

Further, FIG. 2 shows a polycrystal of a composite oxide represented by a composition formula: Ca ₃ Co ₄ Ag _0.5 O ₉ obtained in Example 200, which will be described later, and a known material produced under the same conditions as in Example 1. X-ray diffraction pattern of Ca ₃ Co ₄ O ₉ polycrystal is shown. As is apparent from these X-ray diffraction patterns, the composite oxide of Example 200 having an e value of 0.5 has a crystal structure similar to that of known Ca ₃ Co ₄ O _9, and further, Ag particles It is understood that it contains.

The composite oxide of the present invention represented by the above general formula has a positive Seebeck coefficient, and when a temperature difference is caused between both ends of the composite oxide material, the potential generated by the Seebeck coefficient is The characteristics as a p-type thermoelectric conversion material are lower on the high temperature side than on the low temperature side. Specifically, the composite oxide has, for example, a Seebeck coefficient of 60 μV / K or more at 273 K, and can have a high Seebeck coefficient at a temperature higher than this.

Furthermore, the composite oxide exhibits good electrical conductivity, has a low electrical resistivity of 20 mΩcm or less at 273 K, and can maintain an electrical resistivity of 20 mΩcm or less even at a temperature higher than this.

  Among the composite oxides represented by the above general formula, those having the presence of Ag metal tend to have particularly low thermoelectric resistance and good thermoelectric conversion performance. .

The composite oxide of the present invention has a decomposition temperature in the vicinity of 1300K, so that the above characteristics cannot be exhibited at a temperature higher than this.

  The method for producing the composite oxide of the present invention is not particularly limited as long as it is a method capable of producing a single crystal or a polycrystal having the above composition.

  For example, the composite oxide of the present invention can be produced by mixing raw materials and firing so that the element component ratio is the same as the element component ratio of the target composite oxide.

The raw material is not particularly limited as long as it can form an oxide by firing, and elemental simple substance, oxide, various compounds (such as carbonates) and the like can be used. For example, calcium sources include calcium (Ca), calcium oxide (CaO), calcium peroxide (CaO ₂ ), calcium carbonate (CaCO ₃ ), calcium nitrate (Ca (NO ₃ ) ₂ ), calcium hydroxide (Ca ( OH) _2), calcium chloride (CaCl ₂₎ and its hydrates, alkoxide compounds (dimethoxy calcium (Ca (OCH _{3) 2),} diethoxy calcium _{(Ca (OC 2 H 5)} 2), dipropoxy calcium (Ca (OC ₃ H ₇ ) ₂ ) etc.) can be used.
Cobalt (Co), cobalt oxide (CoO, Co ₂ O ₃ , Co ₃ O ₄ ), cobalt carbonate (CoCO ₃ ), cobalt nitrate (Co (NO ₃ ) ₂ ), cobalt hydroxide (Co (OH) ₂ ), Cobalt chloride (CoCl ₂ ), alkoxide compounds (dipropoxycobalt (Co (OC ₃ H ₇ ) ₂ etc.) can be used, and Ag source is silver (Ag), silver oxide (Ag ₂ O, AgO), silver chloride (AgCl), silver nitrate (AgNO ₃ ), silver sulfate (Ag ₂ SO ₄ ), silver fluoride (AgF) and the like can be used.
As for other elements, elemental elements, oxides, chlorides, carbonates, nitrates, hydroxides, alkoxide compounds, and the like can be similarly used. A compound containing two or more constituent elements of the composite oxide of the present invention may be used. The raw material materials described above can be used singly or in combination of two or more for each element source material.

The firing temperature and firing time may be the conditions under which the target composite oxide is formed, and are not particularly limited. For example, in the temperature range of about 800 to 1200 ° C., the firing may be performed for about 20 hours to 40 hours. good. In the case where carbonates, organic compounds, or the like are used as the raw material, it is preferable to pre-fire before firing to decompose the raw material, and then fire to form the desired composite oxide. For example, when carbonate is used as the raw material, it may be calcined at about 600 to 800 ° C. for about 10 hours and then fired under the above-described conditions.

  The firing means is not particularly limited, and any means such as an electric heating furnace or a gas heating furnace can be adopted. The firing atmosphere may be usually an oxidizing atmosphere such as in an oxygen stream or in the air. However, if the source material contains a sufficient amount of oxygen, for example, it may be fired in an inert atmosphere. . The amount of oxygen in the produced composite oxide can be controlled by the oxygen partial pressure during firing, the firing temperature, the firing time, and the like. The higher the oxygen partial pressure, the higher the oxygen ratio in the above general formula. .

  The composite oxide obtained by the above method is usually a polycrystalline body. For example, according to a method of mixing raw materials, heating and melting them, and then gradually cooling them, a single crystal body is produced. can do.

  The raw material is not particularly limited as long as it can form a uniform melt when the mixture of raw materials is heated. For example, elemental elements, oxides, various compounds (such as carbonates) and the like can be used. As these raw material materials, for example, the same raw material materials as those in the firing method described above can be used. The mixing ratio of the raw materials may be a ratio that can form a melt in phase equilibrium with the target composite oxide.

  As a specific method, the raw material mixture may be heated and melted so as to be in a solution state in equilibrium with the target single crystal composition, and then cooled.

  There is no particular limitation on the heating time, and heating may be performed until a uniform solution state is obtained. The heating means is not particularly limited, and any means such as an electric heating furnace or a gas heating furnace can be adopted. The atmosphere at the time of melting is usually an oxidizing atmosphere such as an oxygen stream or in the air. However, when the raw material contains a sufficient amount of oxygen, it can be melted in an inert atmosphere, for example. It is.

  The cooling method is not particularly limited, and the whole raw material in solution may be cooled. However, when uniform cooling is difficult, for example, a cooled platinum wire is immersed and a single crystal is formed around it. What is necessary is just to employ | adopt the method of partially cooling, such as the method of making it precipitate. The cooling rate is not particularly limited. For example, the cooling rate may be about 50 ° C. or less.

Instead of directly melting the raw material mixture, other components may be added to the raw material mixture for the purpose of adjusting the melting point of the melt and the mixture may be heated to melt. A method of adding and melting an additive component (flux component) other than the material that becomes a metal source of such a composite oxide is a so-called “flux method”. According to this method, a part of the flux component contained in the raw material mixture is melted by heating, and due to its chemical change, dissolving action, etc., the entire raw material substance is in a solution state, which is lower than the method of directly cooling the raw material mixture. A melt can be obtained at temperature. And the target single crystal can be grown using the supersaturated state accompanying cooling by controlling the cooling rate of the raw material substance of a solution state moderately. In this cooling process, a single crystal of a complex oxide containing Ca, Co, Ag, M ¹ and M ² having a solid phase composition in phase equilibrium with a solution formed by melting the raw material is grown. Therefore, based on the relationship between the composition of the melt phase and the solid phase (single crystal) in equilibrium with each other, the source of Ca in the raw material mixture corresponding to the composition of the target composite oxide single crystal, the Co source made materials can be determined substance serving as a source of Ag component, material comprising a source of M ¹ component, and the rate of supply become material M ² component. At that time, the flux component contained in the raw material remains as a melt component and is not included in the constituent components of the growing single crystal. As such a flux component, it has a low melting point compared to the raw material, can sufficiently dissolve the raw material in the melt to be formed, and does not disturb the properties of the target composite oxide. What is necessary is just to select and use suitably. For example, an alkali metal compound or a boron-containing compound can be preferably used. Specific examples of alkali metal compounds include alkali metal chlorides such as lithium chloride (LiCl), sodium chloride (NaCl), and potassium chloride (KCl), and hydrates thereof; lithium carbonate (Li ₂ CO ₃ ), sodium carbonate Examples thereof include alkali metal carbonates such as (Na ₂ CO ₃ ) and potassium carbonate (K ₂ CO ₃ ). Specific examples of the boron-containing compound include boric acid (B ₂ O ₃ ). These optional additive components can also be used alone or in admixture of two or more. The amount of these flux components is not particularly limited. Considering the solubility of the raw material in the melt to be formed, actual heating is performed so that a solution containing the raw material at a concentration as high as possible is formed. What is necessary is just to decide usage-amount according to temperature. The method for melting the raw material mixture is not particularly limited, and heating may be performed under the condition that the molten raw material mixture is in a solution state. The actual heating temperature varies depending on the type of flux component to be used, but for example, it may be heated and melted for about 20 to 40 hours in a temperature range of about 800 to 1000 ° C.
The heating means is not particularly limited, and any means such as an electric heating furnace or a gas heating furnace can be adopted. The atmosphere at the time of melting is usually an oxidizing atmosphere such as an oxygen stream or in the air. However, when the raw material contains a sufficient amount of oxygen, it can be melted in an inert atmosphere, for example. It is.

The cooling rate is not particularly limited. The slower the cooling rate, the larger the single crystal can be. For example, the cooling rate may be about 50 ° C. or less. The size, yield, etc. of the formed complex oxide single crystal may vary depending on the type and composition ratio of the raw material, the composition of the molten component, the cooling rate, etc. In the case of cooling until solidification, a single crystal having a plate shape having a width of about 1 mm or more, a length of about 1 mm or more, and a thickness of about 0.005 mm or more can be obtained.

  Next, by removing components other than the target complex oxide single crystal from the solidified product formed by cooling, the target complex oxide single crystal can be obtained. As a method for removing components other than the target product, water-soluble components adhering to the composite oxide single crystal, such as chloride, are repeatedly washed with distilled water and filtered, and further if necessary. In combination with ethanol washing, it can be removed from the target product. In addition, the water-insoluble residue usually exists in a sufficiently large granular form or sufficiently small powder form as compared with the composite oxide single crystal. Can be removed from the complex oxide single crystal.

  The composite oxide of the present invention that can be obtained by the above-described method has good heat resistance, chemical durability, etc., is composed of an element with low toxicity, and exhibits characteristics as a p-type thermoelectric conversion material. Is.

  The composite oxide has a layered crystal structure and exhibits a very low electrical resistivity in the ab plane. For this reason, in the polycrystal, particularly when the crystal grains are highly oriented in the polycrystal, the thermoelectric conversion performance which is very excellent as the p-type thermoelectric conversion material can be exhibited.

The composite oxide of the present invention can be effectively used as a p-type thermoelectric conversion material used at a high temperature in the air using the above-described characteristics.

FIG. 3 shows a schematic diagram of an example of a thermoelectric power generation module using the thermoelectric conversion material made of the complex oxide of the present invention as a p-type thermoelectric conversion element. The structure of the thermoelectric power generation module is the same as that of a known thermoelectric power generation module. For example, the high temperature part substrate 1, the low temperature part substrate 2, the p-type thermoelectric conversion material 3, the n-type thermoelectric conversion material 4, the electrode 5, and the conductive wire The composite oxide of the present invention is used as a p-type thermoelectric conversion material.

As described above, the composite oxide of the present invention is a polycrystal or single crystal having a positive Seebeck coefficient and a low electrical resistivity, and excellent in heat resistance, chemical durability, and the like.

The composite oxide can be effectively used as a p-type thermoelectric conversion material used in high-temperature air, which is impossible with conventional intermetallic compounds, by utilizing such characteristics, and has high thermoelectric conversion. Efficiency can be demonstrated.

Therefore, by incorporating the composite oxide into the system as a p-type thermoelectric conversion element of a thermoelectric power generation module, it is possible to effectively use the thermal energy that has been discarded in the atmosphere.

  Examples are shown below to further clarify the features of the present invention.

Example 1
Calcium carbonate (CaCO ₃ ) as a Ca source, silver oxide (Ag ₂ O) as an Ag source, and cobalt oxide (Co ₃ O ₄ ) as a Co source, Ca: Co: Ag = 3.0: 3.8: 0.2 (element ratio) Then, the raw materials were mixed sufficiently so as to form the following, then placed in an alumina crucible and calcined in the air at 800 ° C. for 20 hours using an electric furnace to decompose the carbonate. This calcined product was pulverized, pressed, and then fired in an oxygen atmosphere at 880 ° C. for 20 hours to synthesize a composite oxide. The obtained composite oxide was represented by the composition formula: Ca _3.0 Co _3.8 Ag _0.2 O _9.0 .

Seebeck coefficient (S) temperature from 273 K to 1073 K for the composite oxide obtained by the above method and a known Ca ₃ Co ₄ O ₉ polycrystal (comparative example) produced under the same conditions as in Example 1. A graph showing the dependency is shown in FIG. From FIG. 4, the composite oxide of Example 1 is a p-type thermoelectric conversion material having a positive Seebeck coefficient at a temperature of 273 K or higher, a value of 100 μV / K or higher, and a low potential on the high temperature side. It was confirmed that there was. In all other embodiments,
Seebeck coefficient shows a high Seebeck coefficient of 60μV / K or higher at 273K or higher,
The same tendency as in Example 1 was shown.

In addition, the composite oxide obtained by the above method and the known Ca ₃ Co ₄ O ₉ polycrystal (comparative example) produced under the same conditions as in Example 1 show the temperature dependence of the electrical resistivity. A graph is shown in FIG. FIG. 5 shows that the electrical resistivity of the composite oxide obtained in Example 1 is a low value of about 11 mΩcm in the temperature range of 273K to 1073K. In all other embodiments,
The electrical resistivity showed a low value of 20 mΩcm or less at 273 K or more, and the same tendency as in Example 1 was shown.

Furthermore, the composite oxide obtained by the above method and the known Ca ₃ Co ₄ O ₉ polycrystal (comparative example) produced under the same conditions as in Example 1 show the temperature dependence of the thermal conductivity. A graph is shown in FIG. From FIG. 6, the thermal conductivity of the composite oxide obtained in Example 1 is 2 W / mK at a temperature of 273 K or higher.
It turns out that it is the following low values. In all other examples, the thermal conductivity was as low as 10 W / mK or lower at 273 K or higher, indicating the same tendency as in Example 1.

Further, for the composite oxide obtained by the above method and a known Ca ₃ Co ₄ O ₉ polycrystal (comparative example) produced under the same conditions as in Example 1, the thermoelectric dimensionless figure of merit (ZT) A graph showing the temperature dependence is shown in FIG.

  Here, ZT is defined by the following equation, and indicates the thermoelectric conversion efficiency of the material. The higher this value, the higher the conversion efficiency.

ZT = S ² T / ρκ
S: Seebeck coefficient, T: absolute temperature, ρ: electrical resistivity,
κ: Thermal conductivity In the composite oxide of Example 1, the thermoelectric dimensionless figure of merit increased with temperature, and exceeded 10 0.27 at 1073K. In all other examples, the thermoelectric dimensionless figure of merit exceeded 0.2 at 1073K.

Examples 2-198
Each composite oxide was produced in the same manner as in Example 1 except that the starting materials were mixed so that the element ratios shown in Tables 1 to 11 were obtained. Tables 1 to 11 show element ratios and electric resistivity at 1073K in each composite oxide. As for the composite oxides of Examples 2 to 198, as a result of X-ray diffraction, no precipitation of Ag metal particles was observed as in the composite oxide of Example 1.

In addition, the manufacturing raw material used by each Example is shown below.
Ca source: calcium carbonate (CaCO ₃ ), except that calcium nitrate (Ca (NO ₃ ) ₂ ) was used in Examples 91-108.
Bi source: Bismuth oxide (Bi ₂ O ₃ )
Co source: Cobalt oxide (Co ₃ O ₄ ), but in Examples 91-108, cobalt nitrate (Co (NO ₃ ) ₂ )
・ Li source: Lithium carbonate (Li ₂ CO ₃ )
・ Na source: Sodium carbonate (Na ₂ CO ₃ )
・ Sr source: strontium carbonate (SrCO ₃ )
・ La source: Lanthanum nitrate (La (NO ₃ ) ₃ )
・ Ba source: Barium carbonate (BaCO ₃ )
・ Ag source: Silver oxide (Ag ₂ O)
・ Ni source: Nickel oxide (NiO)
・ Cu source: Copper oxide (CuO)
・ Pb source: Lead oxide (PbO)
・ Al source: Aluminum oxide (Al ₂ O ₃ )

実施例１９９〜３９６
下記表１２〜表２２に示す各元素比となるように出発原料を混合すること以外は、実施例１と同様にして、各複合酸化物を作製した。表１２〜表２２に各複合酸化物における元素比と1073Kにおける電気抵抗率を示す。各実施例で用いた製造原料は実施例２〜１９８と
同様である。

Examples 199-396
Each composite oxide was produced in the same manner as in Example 1 except that the starting materials were mixed so that the element ratios shown in Tables 12 to 22 below were obtained. Tables 12 to 22 show element ratios and electric resistivity at 1073K in each composite oxide. The manufacturing raw material used in each Example is the same as that of Examples 2-198.

Among the composite oxides obtained by the above-described method, a polyelectrolyte of the composite oxide represented by the composition formula obtained in Example 200: Ca ₃ Co ₄ Ag _0.5 O ₉ was used using a scanning electron microscope. FIG. 8 shows the backscattered electron image observed. As a result of composition analysis using an energy dispersive X-ray analyzer, it was confirmed that the white portion of the reflected electron image was Ag metal particles. Also, from the X-ray diffraction pattern of FIG. 2 described above, it was confirmed that Ag metal particles were present in the complex oxide polycrystal represented by Ca ₃ Co ₄ Ag _0.5 O ₉ .

  In all of the composite oxides of Examples 199 to 396, the presence of Ag metal particles was observed.

Temperature dependence of Seebeck coefficient (S) from 273 K to 1073 K for the composite oxide obtained in Example 200 and a known Ca ₃ Co ₄ O ₉ polycrystal (comparative example) produced under the same conditions as in Example 1 FIG. 9 shows a graph representing the sex. From FIG. 9, the composite oxide of Example 200 is a p-type thermoelectric conversion material having a positive Seebeck coefficient at a temperature of 273 K or higher, a value of 90 μV / K or higher, and a low potential on the high temperature side. It was confirmed that there was.

Also shows a composite oxide obtained in Example 200, known of Ca ₃ Co ₄ O ₉ polycrystalline body produced under the same conditions as in Example 1 (Comparative Example), the temperature dependence of the electrical resistivity A graph is shown in FIG. FIG. 10 shows that the electrical resistivity of the composite oxide obtained in Example 1 is a low value below about 10 mΩcm in the temperature range of 273K to 1073K.

Furthermore, the composite oxide obtained in Example 200 and the known Ca ₃ Co ₄ O ₉ polycrystal produced in the same conditions as in Example 1 (comparative example) show the temperature dependence of thermal conductivity. A graph is shown in FIG. From FIG. 11, it can be seen that the thermal conductivity of the composite oxide obtained in Example 200 is a low value of 2 W / mK or less at a temperature of 273 K or more.

Further, a graph showing a composite oxide, known of Ca ₃ Co ₄ O ₉ polycrystalline body produced under the same conditions as in Example 1 (Comparative Example), the temperature dependence of the thermoelectric dimensionless figure of merit of Example 200 FIG.
Shown in In the composite oxide of Example 200, the thermoelectric dimensionless figure of merit increased with temperature, reaching a high value of about 0.25 at 1073K.

2 is an X-ray diffraction pattern of the composite oxide obtained in Example 1 and a known Ca ₃ Co ₄ O ₉ polycrystal. X-ray diffraction pattern of the complex oxide obtained in Example 200 and known of Ca ₃ Co ₄ O ₉ polycrystal. The schematic diagram of the thermoelectric conversion module which used the complex oxide of this invention as a thermoelectric conversion material. 2 is a graph showing the temperature dependence of the Seebeck coefficient for the composite oxide obtained in Example 1 and a known Ca ₃ Co ₄ O ₉ polycrystal. 2 is a graph showing the temperature dependence of electrical resistivity for the composite oxide obtained in Example 1 and a known Ca ₃ Co ₄ O ₉ polycrystal. 2 is a graph showing the temperature dependence of the thermal conductivity of the composite oxide obtained in Example 1 and a known Ca ₃ Co ₄ O ₉ polycrystal. 2 is a graph showing the temperature dependence of the thermoelectric figure of merit ZT for the composite oxide obtained in Example 1 and a known Ca ₃ Co ₄ O ₉ polycrystal. The reflection electron image by the scanning electron microscope of the complex oxide obtained in Example 200. For the obtained composite oxide known of Ca ₃ Co ₄ O ₉ polycrystal in Example 200, a graph showing the temperature dependence of the Seebeck coefficient. The obtained composite oxide and known of Ca ₃ Co ₄ O ₉ polycrystal in Example 200, a graph showing the temperature dependence of the electrical resistivity. For the obtained composite oxide known of Ca ₃ Co ₄ O ₉ polycrystal in Example 200, a graph showing the temperature dependence of the thermal conductivity. The composite oxide and known of Ca ₃ Co ₄ O ₉ polycrystal obtained in Example 200, a graph showing the temperature dependence of the thermoelectric figure of merit ZT.

Explanation of symbols

1 substrate for high-temperature part, 2 substrate for low-temperature part, 3 p-type thermoelectric conversion material, 4 n-type thermoelectric conversion material, 5 electrode, 6 conductor

Claims (7)

^{_{Formula: Ca a M 1 b Co c}} M 2 d Ag e O f ( wherein, M ¹ is Na, K, Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sr, One or more elements selected from the group consisting of Ba, Al, Bi, Y and lanthanoids, M ² is Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, Ta And two or more elements selected from the group consisting of Bi, 2.2 ≦ a ≦ 3.6; 0 ≦ b ≦ 0.8; 2 ≦ c ≦ 4.5; 0 ≦ d ≦ 2; 0 <e ≦ 5; 8 ≦ f ≦ 10)). The composite oxide according to claim 1, which has a Seebeck coefficient of 60 µV / K or more in a temperature range of 273 K or more and less than a decomposition temperature. 2. An electric resistivity of 20 mΩcm or less in a temperature range of 273 K or more and less than a decomposition temperature.
Or the composite oxide according to 2. The composite oxide according to any one of claims 1 to 3, which has a thermal conductivity of 10 W / mK or less in a temperature range of 273 K or more and less than a decomposition temperature. The composite oxide according to any one of claims 1 to 4, which is a composite oxide alone or a composite comprising the composite oxide and Ag metal fine particles. A p-type thermoelectric conversion material comprising the composite oxide according to claim 1. A thermoelectric power generation module comprising the p-type thermoelectric conversion material according to claim 6.

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