JP2000012915A - Thermoelectric conversion material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain stable and excellent thermoelectric conversion performance, even in a high-temperature range by using as a thermoelectric conversion material an oxide in which the composition ratio of Zn to In is within a specific range of mol ratio of ZnO/In2O3. SOLUTION: This thermoelectric conversion material is a Zn-In-O-based oxide, and the composition ratio of Zn to In is 5-19 of Zn/In2O3 molar ratio. Although the compound ratio of Zn to In may be set appropriately according to application of the final product, however, it is normally around 5-19 of Zn/In2 O2, preferably 5-7 in molar ratio. In this case, an superior thermoelectric conversion performance can be developed especially within the range of molar ratio. Namely, since the deterioration due to oxidization and there is no possibility of the vapolization of constituent elements to occur and the thermoelectromotive force is stable and large in the high-temperature range, its thermoelectric conversion performance in the high-temperature range is satisfactory. In other words, even if the thermoelectric conversion material is used in the high-temperature range, deterioration in the thermoelectric conversion characteristics due to oxidization hardly occurs, as in a selenide compound, telluride compound, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a novel thermoelectric conversion material.

[0002]

2. Description of the Related Art When two different materials are joined to form a closed circuit having two joints, one of the joints is heated and the other is cooled, and the two materials are heated based on the difference between the types of the two materials and the temperature difference. Electric power is generated (Seebeck effect). When the closed circuit is opened and a direct current is applied from the outside, one of the joints absorbs heat and the other joint generates heat (Peltier effect). Furthermore, when a temperature difference is created between both ends of a homogeneous substance and an electric current flows along this temperature gradient, heat absorption or generation occurs in the substance (Thomson effect).

[0003] These Seebeck effect, Peltier effect, Thomson effect and the like are collectively referred to as thermoelectric conversion effects, and all phenomena are reversible. That is, heat conduction,
Irreversible phenomena such as the Joule effect (a phenomenon that generates heat (Joule heat) due to an electric resistance inherent to a substance when an electric current flows through the substance) and the like are to be considered.

When these reversible phenomena and irreversible phenomena are combined, thermoelectric power generation, thermoelectric cooling, and the like become possible. For this reason, the thermoelectric conversion material that generates the thermoelectric conversion phenomenon is thermoelectric power generation,
Research and development have been actively conducted in the field of utilizing thermoelectric cooling and the like.

[0005] For example, in recent years, regulations on the use of CFCs have become stricter due to global environmental problems. In order to clear these regulations, the structure of refrigeration / refrigeration equipment or heating equipment has become more complicated. This is an obstacle to downsizing the equipment. For this reason, utilization of thermoelectric conversion materials is attracting attention as a trump card that can solve these problems at once. In addition, with the increase of industrial wastes and the like, effective use of these incineration waste heats has become an issue. With regard to the utilization of these waste heats, there is also an urgent need to develop thermoelectric conversion materials that can be used over an extremely wide temperature range, from relatively low temperature waste heat of about 100 ° C. to high temperature waste heat of 800 ° C. or more.

[0006] As typical thermoelectric conversion materials used in conventional thermoelectric conversion elements, typical compositions are Bi and S.
There are telluride compounds or selenide compounds containing b, Te, Se or the like as a main component, or compositions containing Cu, Sn, S or the like as a main component. Bi-Sb-Te-Se
In the system, for example, JP-A-5-48152, JP-A-5-48152
-155625, JP-A-5-206525, JP-A-6-21518, JP-A-6-8533
No. 3, JP-A-6-97513, and JP-A-6-1
JP-A-07407, JP-A-6-140675, JP-A-6-216414, JP-A-6-216415
JP, JP-A-6-231018, JP-A-6-33-1
02866, JP-A-7-273374, JP-A-7-21945, JP-A-7-283442
JP-A-8-306970, JP-A-9-1970
Japanese Patent Application Laid-Open Nos. 8060, 9-18061, 9-36440, etc., which are used singly or in combination, or added with a conductive component. Among Cu-Sn-S-based materials, there is one disclosed in, for example, JP-A-8-78733. Further, in the case of Zn-Al-O system, for example,
No. 6,293, JP-A-8-204240 and the like.

Further, as Si compounds containing Fe, Mo, Co, Ge, etc., for example, JP-A-5-152613, JP-A-5-283751, JP-A-5-31
5655, JP-A-5-343148, JP-A-6-37360, JP-A-6-69548, JP-A-6-169110, JP-A-6-177
436, JP-A-6-204571, JP-A-6-244465, JP-A-6-334226, JP-A-6-350142, JP-A-7-458
No. 69, JP-A-7-45870, JP-A-7-
48116, JP-A-7-216401, JP-A-8-56020, JP-A-8-18108, JP-A-8-74380, JP-A-8-1393
69, JP-A-8-172223, JP-A-8-172223
JP-A-236817, JP-A-8-288556, JP-A-8-306696, and the like.

[0008] Examples of compounds such as Co and Sb include those disclosed in, for example, JP-A-8-186294. Examples of composite oxides containing SrO, BaO, TiO _{2 and the} like as main constituents include, for example, JP-A-5-129667.
JP, JP-A-5-218511, JP-A-8-2
There is one disclosed in, for example, Japanese Patent No. 31223.

The thermoelectric conversion performance of a thermoelectric conversion material is generally expressed by a performance index Z (unit: K ⁻¹ ) estimated by the following equation (1) or an output factor (unit: W / mK). The larger these values are, the better the thermoelectric conversion performance is.

Performance index: Z = α ² · σ / k (1) Output factor: log (α ² · σ) (2) (where α is the thermoelectric coefficient (unit: μv / k), σ Is electrical conductivity (unit: mΩ ^-1 ), and k is thermal conductivity (unit: W / m)
k). Therefore, in order to obtain a thermoelectric conversion material having excellent thermoelectric conversion performance, it is theoretically sufficient to select a material having a high thermoelectric coefficient α and an electric conductivity σ and a small heat conductivity k.
However, in general, in a thermoelectric conversion material containing a metal as a main component, the ratio between the thermal conductivity k and the electrical conductivity σ has a constant value at a constant temperature regardless of the type of metal.
Since Franz's law holds, excellent thermoelectric conversion performance cannot be obtained simply by selecting the metal species.

On the other hand, the above rule does not always hold for semiconductor materials. Therefore, the electrical conductivity is large,
It is not impossible to develop a material with a low thermal conductivity, for example, a thermoelectric value of 10
It is possible to develop a product that is twice to several hundred times larger. For this reason,
Semiconductor materials have been actively studied as thermoelectric conversion materials, and various new materials have been actually developed.

For example, there is a silicide containing Fe, Co, Mo or the like as a constituent element for high-temperature power generation. Further, in the chalcogenite-based materials, Bi ₂ Te ₃ , Sb ₂ T
Some of them exhibit remarkable thermoelectric conversion performance near room temperature, such as e ₃ , PbTe, GeTe, etc., and the value of the performance index Z exceeds 10 ⁻³ . Furthermore, there is a thermoelectric conversion material in which Cu ₄ SnS ₄ having semiconductor properties and Cu having high electric conductivity coexist in an alloy containing Cu—Sn—S as a main component. In addition, an oxide-based compound containing titanium oxide and strontium oxide as main components is reduced by heat treatment in a reducing gas atmosphere containing hydrogen in the presence of a reducing agent to reduce the electrical conductivity by introducing oxygen vacancies. Thermoelectric conversion materials of 100 s / cm or more have also been proposed.

As described above, a great number of thermoelectric conversion materials have been developed in a wide variety of compositions, but their thermoelectric conversion performance and other physical properties are not necessarily sufficient including life characteristics. I can't say. For example, Bi-Sb-Te-based material, Bi-Sb-Te-Se
The system materials and the like are very brittle and hard and have poor machinability.

As the thermoelectric conversion element, one having a size of several mm square is usually used.
It has been confirmed that those having a thickness of 0 to several hundreds μm are effective for further enhancing the performance. In other words, miniaturization and thinning are indispensable for higher performance than conventional ones (Transactions of the Institute of Telecommunications, C-II J-75C-II (8) 416
-424 (1975)).

In the prior art, several tens of element pairs are generally housed in 1 cm ² to form one module. However, in a power generation element utilizing a temperature difference, the electromotive force is proportional to the number of element pairs. Therefore, it is of paramount importance to connect more pairs of elements in series in order to increase the voltage of the power to be extracted.

Furthermore, in the conventional thermoelectric conversion materials, cracks, breaks, and the like are liable to occur during production or practical use due to the above-mentioned hard and brittle physical properties, which hinders the improvement in thermal shock strength. I have. On the other hand, recently, as described above, it is necessary to be able to use industrial waste in a high temperature range in order to utilize waste heat.However, conventional metal compounds, compound semiconductors, oxide semiconductors, and the like have been used under high temperatures. Is a problem because of its low oxidation resistance. As described above, due to lack of reliability in various physical properties, airtight sealing treatment is generally required in practical use, and therefore, practical use is greatly restricted at present.

In terms of figure of merit, these conventional thermoelectric conversion materials are relatively large at about 2 × 10 ⁻³ / K near room temperature, but almost always fall below 300 ° C.

In addition, since Te or Se has high volatility, when a telluride compound or a selenide compound is used in a high-temperature range, toxic gases such as Te and Se are generated even if sealed. Inevitable. Also,
Since the composition changes easily due to volatilization, not only is it difficult to secure a predetermined performance, but also the performance index varies. Further, the telluride compound or selenide compound generally improves the thermoelectric conversion characteristics when rapidly solidified by cooling and solidifying into an amorphous phase or microcrystallized (for example, JP-A-1-276678). Then, crystallization proceeds, and performance degradation cannot be avoided.

On the other hand, Ge-Si (germanium silicide) is known as a material which is chemically stable even at a high temperature range of 300 ° C. or higher. However, Ge-S
The figure of merit of i is at most 1 × 10 ⁻³ / K, and there is still room for improvement.

Similarly, silicide compounds such as Fe—Si ₂ (iron silicide) have been proposed as materials that are stable even in a high temperature range. Fe—Si ₂ is composed of Sb, Mn, A
By adding various elements such as l and Co, a p-type material and an n-type material can be manufactured. Therefore, by appropriately combining them, a FeSi ₂ thermoelectric conversion element can be manufactured. This is described, for example, in JP-A-48-60018.
Gazette, JP-B-52-47667, JP-A-59-47679
No. 56781, JP-A-60-43882, JP-A-2-1380, JP-A-2-1381,
There are those disclosed in Japanese Patent Publication No. 2-8466, Japanese Patent Publication No. 2-8467, Japanese Patent Application Laid-Open No. 7-97206, and the like. In addition, regarding the manufacturing method, for example,
JP-A-153977, JP-A-50-158380, JP-B-54-41316, JP-A-54-4
No. 1317, JP-A-57-63870, and JP-B-63-31954. However, in the case of these methods, the raw material powder is molded, heated to 300 to 500 ° C. in the air to remove the resin, and then heat-treated in a vacuum for several tens to several hundreds hours or more. Since a certain β phase is not generated, it is hard to say that it is suitable for industrial production.

Co having a skutterudite type crystal structure
For -Sb ₃ compound, El. Dadkin (L.Dadki
n) (J. Soviet Phys, Solid State I)
126-133 (1959)). However, the reported figure of merit of the compound is extremely small and cannot be put to practical use at this value.

A Cu-Sn-S-based thermoelectric conversion material having an improved figure of merit by lowering the specific resistance has also been proposed (Japanese Patent Application Laid-Open No. 8-778733). This is one in which metals such as Cu, Ag, and Ge are dispersed and contained as they are in order to reduce the specific resistance. However, this material also
The value at room temperature is only slightly improved to 1.0 to 1.3 × 10 ⁻³ / K as compared with the performance index of 0.8 × 10 ⁻⁴ / K of the conventional material, and is still improved. There is room.

Moreover, the production method is complicated and not suitable for industrial production. First, the raw material powders of the constituent elements are uniformly mixed and dissolved, then the solution is rapidly solidified by solidification, and then pulverized to a powder having an average particle diameter of 300 μm or less. A fine powder such as Ge is mixed and pulverized, and then molded by heating and pressing at 650 ° C. and 80 kg / mm ² for 10 minutes or more.
Heat for more than an hour to form a calcined body. Subsequently, the powder obtained by pulverizing the calcined body is heated to 650 ° C. and subjected to hot press molding to finally obtain the thermoelectric conversion material. Further, in the above method, since Cu, Ag, Ge and the like are contained as fine metal particles, segregation is liable to occur when used in a high temperature range, and furthermore, oxidation is liable to occur. As the oxidation proceeds, the electric conductivity is significantly reduced. For this reason, in practical use, unless a special process such as vacuum sealing is performed, the figure of merit is significantly reduced. In this respect, there is no difference from the conventional thermoelectric conversion material.

A semiconductor oxide containing barium titanate as a main component has also been disclosed as a thermoelectric conversion material (JP-A-1-213383). Further, oxide ceramic semiconductors in which a reducing substance is mixed and dispersed in a composite oxide containing strontium and titanium as main components are also known (JP-A-5-129667, JP-A-5-1988).
No. 47, JP-A-5-218511, Phys.
v. 134-2A44- (1964), Phys. Rev. 157-2 358- (1967), etc.).

A composite oxide containing strontium oxide and titanium oxide as main components (Japanese Patent Application Laid-Open No. 8-231223), a thermoelectric material obtained by mixing strontium oxide and metal titanium with titanium oxide as the main component and heat-treating the mixture. Conversion materials have also been proposed (JP-A-8-247012). In general, various oxide ceramic semiconductors are expected to be more resistant to the environment in which they are used because their basic constituents are oxides compared to telluride compounds, selenide compounds, and silicide compounds. Have been.

However, there has been no method which can improve oxidation resistance so as not to cause any problem, for example, because a metal component is mixed as a conductive component or an oxygen defect causes semiconductor properties. Further, there has not yet been found any one whose performance index exceeds various telluride, selenide compounds and silicide compounds.

Further, when strontium oxide and titanium oxide are used as main constituents, n-type semiconductors and p-type semiconductors are used for practical use as thermoelectric conversion materials. , Irisium, cesium, rubidium, scandium, yttrium, at least one element such as a lanthanoid element and a strontium oxide uniformly mixed to form a composite oxide, further titanium oxide zirconium, hafnium,
Tin, niobium, tantalum, tungsten, molybdenum,
At least one element such as manganese, iron, cobalt, nickel, copper, zinc, indium, magnesium, and antimony must be mixed to form a composite oxide, and these composite oxide phases must be continuous with each other. It is necessary to bake in a non-oxidizing atmosphere after making a reducing substance phase not coexist. For this reason, setting of manufacturing conditions becomes very complicated in industrial production. In addition, it has a fatal defect that it is difficult to reduce its size and thickness because of its inherently poor mechanical strength. (A report on a thermoelectric conversion material using a Cu-based oxide semiconductor is disclosed in MatSci & Eng B.
7 111- (1990)).

Further, a method of improving the electric conductivity by mixing fine particles such as metallic copper or the like, and improving the thermal index by introducing oxygen vacancies by firing in a reducing atmosphere to improve the thermoelectromotive force. There is also. However, the thermoelectric conversion material obtained by this method cannot be used in air unless it is hermetically sealed to suppress or prevent oxidative deterioration.

As a material containing zinc oxide (ZnO) as a main component, for example, a thermoelectric conversion material made of an N-type semiconductor in which zinc oxide is doped with 0.01 to 20 mol% of yttrium oxide is known (see, for example, Japanese Patent Application Laid-Open No. H11-157556). JP-A-62-179
No. 78). This material is produced by mixing yttrium oxide powder with zinc oxide powder, pressing, and firing at 1000 to 1350 ° C. in a vacuum or reducing atmosphere. According to this technique, since the inexpensive and low-toxic raw material is used, the above-described thermoelectric conversion material can be easily manufactured at low cost.

However, in the above materials, there is also a problem that the performance is not stable because the zinc component may sublime during firing.

On the other hand, an N-type semiconductor thermoelectric conversion material in which zinc oxide is doped with indium oxide (In ₂ O ₃ ), lithium oxide (Li ₂ O) or the like is known (Japanese Patent Application Laid-Open No. Sho 63).
-115388, JP-A-6-252451, etc.). These materials exhibit heat resistance around 500 ° C.

However, in these techniques, 1) the firing must be performed in a vacuum, and 2) the internal resistance varies depending on the firing temperature.
As a result, the reproducibility of the figure of merit is poor, and 3) the thermoelectric conversion characteristics at high temperatures are low, which is not satisfactory.

Further, there is known a method of improving characteristics against thermal oxidative degradation by doping a semiconductor oxide (MnO) with indium oxide as a main constituent (JP-A-7-231122, JP-A-7-231). 291627
issue). These dope an oxide defect as a conduction carrier by doping a semiconductor oxide into an oxide of indium to improve the conductivity, and the state is liable to change at a high temperature, particularly in a high temperature range of 700 ° C. or higher. In this case, the figure of merit is significantly reduced.

In addition, recently, (Zn _1-x Al _x ) O (T.Tsubot) in which a part of zinc oxide is substituted by aluminum
a et al: J. Mater. Chem., 6, 1 (1996), M. Ohtaki et al: J.
Appl. Phys, 79 (3) 1816 (1996)), indium tin oxide In
₂ O ₃ SnO ₂ (M. Ohtaki et al: J. Mater. Chem., 4, 653
(1994)), calcium bismuth manganate (Ca _1-x Bi
_x ) MnO ₃ (M. Ohtaki et al: J. Solid State Chem., 12
0,105 (1995)), cadmium indium CdIn ₂ O
₄ (RDShannon et al: J. PhysChem. Solids 38, 877 (197
7)), neodymium acid cerium copper oxide Nd _2-x Ce x Cu
O ₄ (M.Yasukawa etal: J.Jpn soc poeder & powder metal.
44 (1) (1997)), however, the figure of merit of these materials is as low as 10 ^-4 / K, and further improvement is required.

[0035]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of the above-mentioned problems of the prior art, and in particular, has provided a thermoelectric conversion material capable of stably obtaining excellent thermoelectric conversion performance even at a high temperature range. The main purpose is to

[0036]

Means for Solving the Problems The present inventor uses an oxide having a specific composition as a thermoelectric conversion material,
The inventors have found that the above object can be achieved, and have completed the present invention.

That is, the present invention relates to a Zn—In—O-based oxide, wherein the composition ratio of Zn and In is ZnO / In.
_{The present invention} relates to a thermoelectric conversion material having a molar ratio of ₂ O ₃ of 5 to 19.

[0038]

BEST MODE FOR CARRYING OUT THE INVENTION The thermoelectric conversion material of the present invention is Zn-
A In-O-based oxide, characterized in that the composition ratio of Zn and In are 5 to 19 in ZnO / In ₂ O ₃ molar ratio.

The mixing ratio of Zn and In may be appropriately set according to the use of the final product, etc., but usually, ZnO / I
The molar ratio of n ₂ O ₃ may be about 5 to 19, preferably 5 to 7. In the present invention, particularly excellent thermoelectric conversion performance can be exhibited within this molar ratio range.

In the present invention, if necessary, at least one of the Zn site and the In site can be substituted with a substitution component.

In the In site, part of the In site is In ³⁺
It can be replaced by a trivalent cation having an ionic radius larger than the ion. The trivalent cation is not particularly limited as long as it can further enhance the thermoelectric conversion performance. In particular, Y ³⁺ , La ³⁺ , Ce ³⁺ ,
Rare earth elements such as Nd ³⁺ , Gd ³⁺ and Ac ³⁺ are preferred. One or more of these trivalent cations can be used.

The amount of substitution by the trivalent cation as a substitution component may be appropriately set according to the type of the substitution component and the like, but the In site is (In _{1 -n An} ) ₂ O ₃ (A is Substituent component; n is 0.01 to 0.475, preferably 0.05
~ 0.425, more preferably 0.075 ~ 0.40)
What is necessary is to make it.

In the Zn site, part of the Zn site is Zn ²⁺
It can be replaced by a divalent cation having a smaller ionic radius than the ion. The divalent cation is not particularly limited as long as it can further improve the thermoelectric conversion performance. For example, Co ²⁺ , Fe ²⁺ , N
Divalent cations such as i ²⁺ and Cu ²⁺ can be used.
These can be used alone or in combination of two or more.

The amount of substitution by the divalent cation as a substitution component may be appropriately set according to the type of the substitution component and the like, but the Zn site is Zn _1-m B _m O (B is a substitution component;
m is 0.05 to 0.95, preferably 0.10 to 0.8
5, more preferably 0.15 to 0.80).

In the present invention, when a part of the In site is substituted by, for example, Y ³⁺ , La ^3+, or the like having a larger ionic radius than In ³⁺ , the a-axis of the compound crystal generally increases as the substitution amount increases, and The c-axis shrinks, and furthermore, a
² The value of c increases. Similarly, when a part of a Zn site is substituted with Co ²⁺ or the like having an ionic radius smaller than that of Zn ²⁺ , the value of a ² c increases with an increase in the substitution amount. As a result of these substitutions changing the crystal structure, the thermoelectric conversion performance can be further improved.

In the present invention, other components than the above-mentioned components may be contained as long as the effects of the present invention are not impaired. For example, sintering aids, glass, carbon, oxidation-resistant metals (Ag, Au, etc. belonging to Group IB, VI
Ru belonging to the platinum group, such as Re belonging to Group I A,
Oxides such as Rh, Pd, Os, Ir, and Pt).

The porosity of the thermoelectric conversion material of the present invention may be appropriately determined according to the use of the final product.
% (Theoretical density of 10 to 97%), preferably 1%.
It is most preferably 0 to 80%, particularly preferably 20 to 70%. If the porosity is less than 3%, electrons emitted by thermal excitation are too small, and the formation of continuous pores becomes insufficient, so that satisfactory thermoelectric conversion performance may not be obtained. On the other hand, if the porosity exceeds 90%, a sufficiently excellent thermoelectric conversion performance can be obtained, but the mechanical strength is low and the material is easily broken during processing or use, which is not practically preferable.

The pores in the present invention are preferably continuous pores including independent pores (hereinafter also referred to as "pores"). In the present invention, the continuous pores mainly include open pores and closed pores. The configuration is not particularly limited as long as the effects of the present invention are not impaired. The formation of continuous pores can be achieved, for example, by adjusting the type and amount of the organic binder to be added to the powdery raw material during production.

The shape or size of the thermoelectric conversion material of the present invention is as follows:
There is no particular limitation, and it may be set appropriately according to the shape of the final product. For example, it can be used in a film shape, a sheet shape, a rod shape, or any other shape. The method of using the thermoelectric conversion material of the present invention may be the same as the method of using a known thermoelectric conversion material.

The thermoelectric conversion material of the present invention can be produced by a method similar to a known method for producing an oxide (ceramic), except that zinc and indium are set in the above composition ratio. For example, a powder raw material containing a predetermined amount of zinc and indium (substitution components and the like as necessary) is formed,
It can be manufactured by firing the molded body.

For the preparation of the powder raw material, any of the known powder preparation methods (solid phase method, liquid phase method, gas phase method, etc.) usually employed in the ceramics field and the like can be applied.

For example, in the solid phase method, first, each compound containing zinc, indium, etc. as starting materials is weighed and collected so as to have the above-mentioned predetermined composition ratio, and is crushed by a crusher mill, an attritor, a ball mill, a vibration mill, and a sand grind. Using a known pulverizer such as a mill, dry or wet mixing and pulverization are performed. In this case, if necessary, an organic binder,
A sintering aid or the like can be added. Next, the pulverized mixture is calcined at a temperature lower than its sintering temperature to prepare a calcined body having a target phase, and the pulverized mixture is further pulverized as necessary to prepare a powder raw material. it can. In this case, the starting compound is ZnO,
It is not limited to oxides such as In ₂ O ₃ and substituted components, and any oxides such as hydroxides and carbonates which can be finally turned into oxides by calcination can be used. In particular, a compound that is easy to control the particle size and has excellent mixing properties is more preferable.

In the liquid phase method, a desired compound is precipitated from a solution raw material by using a known method such as a coprecipitation method or a hydrothermal synthesis method, or an evaporated solid is obtained by evaporating a solvent. Powder raw material can be obtained. As a solution raw material, for example, water is used as a solvent, and zinc, indium,
It is also possible to use a solution in which compounds such as chlorides, nitrates and organic acid salts such as substitution components are dissolved, or a solution other than water (an organic solvent such as methanol and ethanol) and a solution of the above compound such as an alkoxide. . Powder raw materials synthesized by the liquid phase method are excellent in that the raw material composition can be easily made uniform. In the liquid phase method, a solution material containing a predetermined amount of zinc, indium, or the like is applied to an appropriate base material, and the coating film is directly sintered to form a sintered body.
The thermoelectric conversion material (or thermoelectric conversion element) in the form of a thin film can be manufactured in a state of being integrated with the base material.

In the gas phase method, for example, CVD (Chemical Vap
or Deposition method, a gas phase decomposition method using a liquid raw material, and the like. The gas phase method is particularly advantageous when a thin-film thermoelectric conversion material is directly formed on a substrate, or when a powder material having high crystallinity is prepared.

The average particle size of these powder raw materials can be appropriately changed depending on the composition of the powder raw materials, the form of the final product, and the like.
m, more preferably 0.2 to 6 μm.

An organic binder can be added to the powder raw material prior to molding. The organic binder is not particularly limited as long as it can form desired continuous pores, and an organic binder used in the production of a general sintered body can be used as it is. For example, liquid paraffin, wax, olefins such as polyethylene, cellulose derivatives such as methyl cellulose, ethyl cellulose and carboxymethyl cellulose, vinyl resins such as polystyrene and polyvinyl butyral, and aldehyde resins can be used. The amount of the organic binder to be added may be appropriately set according to the type of the organic binder to be used, the desired porosity, and the like. Usually, the porosity of the finally obtained thermoelectric conversion material is 3 to 90%. It is preferable to set. Generally, about 3 to 65% by weight may be blended in the powder raw material, but may be out of this range in relation to the porosity.

Next, molding is performed using the powder raw material. The molding method in this case is not particularly limited. For example, a pressure molding method using a mold, a cold isostatic molding method (CIP (Cold Isoform))
Press molding)), an extrusion molding method, a doctor blade tape molding method, a casting molding method, and other molding methods widely used in the fields of ceramics and powder metallurgy can be used. The molding conditions may be adjusted within the molding conditions in each of the known molding methods, and it is particularly preferable to appropriately set them so as to increase the uniform filling property of the powder.

Subsequently, the obtained compact is sintered. The sintering method is also not particularly limited, and a known sintering method such as a known normal pressure sintering and pressure sintering can be adopted. The sintering temperature may be appropriately changed according to the type, composition, and the like of the powder raw material to be used. If the sintering temperature is too low, the desired compactness cannot be achieved, and the desired characteristics of the sintered body may not be obtained. In addition, if the sintering temperature is too high, a change in composition or a change in microstructure due to grain growth occurs, so not only is it difficult to control the physical properties of the sintered body, but also the energy consumption increases or the production efficiency decreases. There is.

The firing atmosphere is not particularly limited, and can be selected, for example, according to the necessity of the reduction treatment. For example, when a reduction treatment is required at the same time as sintering, a reduction atmosphere may be used. In the case where the reduction treatment is not required, sintering may be performed at normal pressure in the atmosphere, for example. Firing in an oxygen atmosphere is effective in controlling the oxygen partial pressure when control of the composition, microstructure, and the like of the sintered body is particularly required. In the present invention, the oxygen partial pressure is not particularly limited as long as it is an oxidizing atmosphere.

In the present invention, the compact may be calcined, if necessary, prior to sintering of the powder raw material synthesized by any of the methods. The calcining temperature may be appropriately determined at a temperature lower than the sintering temperature of the compact. The calcining atmosphere can also be set appropriately as in the case of sintering.

[0061]

According to the present invention, since an oxide having a specific composition is used as a thermoelectric conversion material, excellent thermoelectric conversion performance is exhibited. That is, since it is composed of an oxide, there is no fear of oxidation deterioration, volatilization of constituent components, and the like,
Since the thermoelectromotive force in the high temperature range is stable and large, the thermoelectric conversion performance in the high temperature range is also excellent. In other words, even when used in a high-temperature region, deterioration of thermoelectric conversion characteristics due to oxidation hardly occurs as in selenide compounds and telluride compounds.

Further, by substituting a part of the In site or the Zn site with a specific substitution component, the thermoelectric conversion characteristics can be further improved.

The thermoelectric conversion material of the present invention having such characteristics can exhibit a high performance index of, for example, 10 ⁻³ / K or more at 700 K under some conditions.
For example, it is useful for a thermoelectric conversion element or the like.

[0064]

The following examples are provided to further clarify the features of the present invention. In the present invention, each physical property was measured as follows.

(1) Conductivity The conductivity was determined from the result of measuring the electrical conductivity by the DC four-terminal method.

(2) Thermoelectromotive force A sample is placed in a quartz tube, and a quartz tube into which hot air has flowed is brought into contact with only one side of the sample to form a high-temperature side, and the temperature difference between the two edges is determined by setting the opposite side to a low-temperature side. The temperature difference was read by measuring Tc, and at the same time, the electromotive force (ΔV) at both edges was measured with a Pt · Pt / Rh thermocouple. The temperature difference between both edges was adjusted by the flow rate of hot air. The Seebeck coefficient was determined from the slope of the graph of the thermoelectromotive force and the temperature difference.

(3) Thermal conductivity Measured from the thermal diffusivity by the laser flash method.

Example 1 ZnO / In ₂ O ₃ molar ratio (m) was 5, 7, 9, and 11
Commercially available ZnO powder and In ₂ O ₃ powder were weighed and collected so as to obtain (in order, samples 1 to 4), and these were dry-mixed with a ball mill for 24 hours. Next, the mixture was transferred to a zirconia container, calcined in the atmosphere at 1150 ° C. for 6 hours, and further pulverized and mixed in a ball mill for 6 hours to adjust the average particle diameter to 1 μm or less to prepare powder raw materials. Each powder raw material was cold isostatically pressed at a pressure of 196 MPa to produce a plate-like molded body. Next, the molded body was fired in the atmosphere at 1550 ° C. for 2 hours.

For Samples 1 to 3 obtained by firing, the temperature dependence of the Seebeck coefficient (α), conductivity (σ), thermal conductivity (κ), and figure of merit (Z) was examined. The results are shown in FIGS. 1 to 4 also show data of ZnO alone. Further, in order to clarify the difference of each characteristic due to the difference of m, FIG.
7 also show the temperature dependence of the conductivity, the Seebeck coefficient or the output factor (σα ² ) in Samples 1 to 4.

In particular, as is apparent from FIGS. 4 and 7,
It can be seen that when the value of the molar ratio m is 9, the output factor shows the maximum value, and the thermoelectric conversion characteristics are maximum.

REFERENCE EXAMPLE 1 Based on a composition having a ZnO / In ₂ O ₃ molar ratio of 5, (Z
nO) ₅ InMO ₃ with M being Fe ³⁺ , Ga ³⁺ and Al
^A thermoelectric conversion material was produced under the same conditions as in Example 1 except that ³⁺ was substituted (the firing atmosphere was in air and in argon gas). FIG. 8 shows the temperature characteristics of the output factor and the figure of merit of each sample. FIG. 9 shows (ZnO) ₅ In _2-xF
the case of changing the amount of substitution Fe ³⁺ in e _x O _{3 (x} = 0~
The relationship between the substitution amount and the figure of merit in 1) is shown.

FIG. 8 shows that the larger the ionic radius of the substituted component at the In site, the larger the thermoelectric conversion output factor. Further, FIG. 9 shows that the thermoelectric conversion performance index sharply decreases when the substitution amount of Fe ³⁺ exceeds a certain amount.

Example 2 Based on a composition having a ZnO / In ₂ O ₃ molar ratio of 5, In
Sites other than substituted with Y ³⁺ in the same conditions as in Example 1 _{(ZnO) 5 (In 1-} x Y x) 2 O 3 (x = 0~0.2) thermoelectric material having a composition consisting of Produced. The temperature dependence of the Seebeck coefficient, conductivity, and output factor at each substitution amount x was measured. These results are shown in FIGS. FIG. 12 also shows the results for (ZnO) ₉ In ₂ O ₃ .

FIGS. 13 to 15 show the substitution amount x of Y ³⁺ and the Seebeck coefficient at 960 K and 1100 K, respectively.
The relationship with the conductivity or the output factor is shown, respectively. FIG. 16 shows the conductivity at room temperature (25 ° C.) when the substitution amount x by Y ³⁺ is 0 to 0.05.

In particular, from the results of FIG. 12, even when m = 5, when the In site is replaced with the trivalent cation Y ³⁺ ,
It turns out that it shows higher thermoelectric conversion characteristics than (ZnO) ₉ In ₂ O ₃ . 13 to 15 that the absolute value of the Seebeck coefficient and the thermoelectric conversion output factor are increased by the substitution of Y ³⁺ .

Example 3 A ZnO / In ₂ O ₃ molar ratio of 9 was used as a base,
A thermoelectric conversion material having a composition of (ZnO) ₉ (In _1−x Y _x ) ₂ O ₃ (x = 0 to 0.1) was prepared under the same conditions as in Example 1 except that the site was replaced with Y ^3+. Produced. The temperature dependence of the Seebeck coefficient, conductivity, and output factor at each substitution amount x was measured. These results are shown in FIGS. 20 to 22 show 960K and 110K.
The relationship between the substitution amount x of Y ³⁺ at 0K and the Seebeck coefficient, conductivity, or output factor is shown.

Example 4 Under the same conditions as in Example 1, a thermoelectric material having a composition of ZnO / In ₂ O _{3 having a} molar ratio m of 5, 7, and 9 and the In site was substituted with Y ³⁺ (ZnO) ₅ (In _1-x Y _x ) ₂ O ₃ (x
= 0.03) was compared with a thermoelectric conversion material having a composition of 0.03). The temperature dependence of the thermal conductivity and the figure of merit at each molar ratio m was examined. The results are shown in FIGS.

From the results shown in FIG. 24, the sample in which the In site was replaced with Y ³⁺ showed the maximum value of the thermoelectric conversion performance index, and m = 9.
It turns out that it becomes larger than the case of.

Example 5 A ZnO / In ₂ O ₃ molar ratio m based on a composition of 5
(Zn _1-x Co _x O) ₅ In ₂ O ₃ (x = 0 to 0.1) under the same conditions as in Example 1 except that the n site was replaced with Co ^2+.
A thermoelectric conversion material having a composition of 5) was produced. FIG. 25 shows the conductivity, Seebeck coefficient, and C at 1120K.
The relationship with o ²⁺ substitution amount x is shown. Also, FIG.
The relationship between the output factor at 20K and the Co ²⁺ substitution amount x is shown. FIG. 27 shows the relationship among the carrier concentration, the hole mobility, and the conductivity at room temperature. FIG. 28 shows the relationship between the lattice volume (a ² c) obtained from the lattice constant and the substitution amount x of Co ²⁺ .

As is clear from FIG. 25, the conductivity monotonously decreases as the Co ²⁺ substitution amount x increases. On the other hand, the absolute value of the Seebeck coefficient is such that the substitution amount of Co ²⁺ is 0.5 mol% (x =
0.005) showed a maximum value, and thereafter showed a complicated behavior of decreasing once and increasing again. Also,
According to FIG. 26, the value of the output factor increases significantly as compared with the case where the Co ²⁺ substitution amount x is 0, and the maximum value is −5.6 Wcm ⁻¹ K.
^-2 , a value not previously obtained with oxides. Also, as is clear from FIG. 28, the lattice volume is Co
^The maximum value was exhibited when the ²⁺ substitution amount x was about 3 mol% (x = 0.03).

[Brief description of the drawings]

FIG. 1 is a diagram showing the temperature dependence of the Seebeck coefficient of a (ZnO) _m In ₂ O ₃ sintered body.

FIG. 2 is a diagram showing the temperature dependence of the conductivity of a (ZnO) _m In ₂ O ₃ sintered body.

FIG. 3 is a diagram showing the temperature dependence of the thermal conductivity of a (ZnO) _m In ₂ O ₃ sintered body.

FIG. 4 is a diagram showing the temperature dependence of the thermoelectric conversion performance index of a (ZnO) _m In ₂ O ₃ sintered body.

FIG. 5 is a diagram showing the temperature dependence of the Seebeck coefficient of a (ZnO) _m In ₂ O ₃ sintered body.

FIG. 6 is a diagram showing the temperature dependence of the conductivity of a (ZnO) _m In ₂ O ₃ sintered body.

FIG. 7 is a diagram showing the temperature dependence of a thermoelectric conversion output factor of a (ZnO) _m In ₂ O ₃ sintered body.

FIG. 8 is a diagram showing the temperature dependence of a thermoelectric conversion output factor of a (ZnO) ₅ InMO ₃ sintered body.

FIG. 9 is a diagram showing the temperature dependence of the thermoelectric conversion performance index of a (ZnO) ₅ In _2-x Fe _x O ₃ sintered body.

FIG. 10 is a diagram showing the temperature dependence of the Seebeck coefficient of a (ZnO) ₅ (In _1-x Y _x ) ₂ O ₃ sintered body.

FIG. 11 is a diagram showing the temperature dependence of the conductivity of a (ZnO) ₅ (In _1-x Y _x ) ₂ O ₃ sintered body.

FIG. 12 is a diagram showing the temperature dependence of a thermoelectric conversion output factor of a (ZnO) ₅ (In _1-x Y _x ) ₂ O ₃ sintered body.

FIG. 13 is a diagram showing the relationship between the substitution amount x and the Seebeck coefficient in a (ZnO) ₅ (In _1-x Y _x ) ₂ O ₃ sintered body.

FIG. 14 is a view showing the relationship between the substitution amount x and the electrical conductivity in a (ZnO) ₅ (In _1-x Y _x ) ₂ O ₃ sintered body.

FIG. 15 is a diagram showing the relationship between the substitution amount x and the thermoelectric conversion output factor in a (ZnO) ₅ (In _1-x Y _x ) ₂ O ₃ sintered body.

FIG. 16 is a diagram showing the relationship between the amount of substitution x and the conductivity of a (ZnO) ₅ (In _1-x Y _x ) ₂ O ₃ sintered body at room temperature.

FIG. 17 is a diagram showing the temperature dependence of the Seebeck coefficient of a (ZnO) ₉ (In _1-x Y _x ) ₂ O ₃ sintered body.

FIG. 18 is a diagram showing the temperature dependence of the conductivity of a (ZnO) ₉ (In _1-x Y _x ) ₂ O ₃ sintered body.

FIG. 19 is a diagram showing the temperature dependence of a thermoelectric conversion output factor of a (ZnO) ₉ (In _1-x Y _x ) ₂ O ₃ sintered body.

FIG. 20 (ZnO) at 960K and 1100K
_{FIG. 9} is a view showing the relationship between the Seebeck coefficient and the substitution amount x of a ₉ (In _1-x Y _x ) ₂ O ₃ sintered body.

FIG. 21 (ZnO) at 960K and 1100K
_{FIG. 9} is a view showing the relationship between the conductivity of ₉ (In _1-x Y _x ) ₂ O ₃ sintered body and the substitution amount x.

FIG. 22 (ZnO) at 960K and 1100K
₉ is a diagram showing the relationship between _{(In 1-x Y x)} 2 O 3 thermoelectric conversion power factor of sintered body substitution amount x.

FIG. 23 is a diagram showing the temperature dependence of the thermal conductivity of a (ZnO) _m (In _1-x Y _x ) ₂ O ₃ sintered body.

FIG. 24 is a diagram showing the temperature dependence of the thermoelectric conversion performance index of a (ZnO) _m (In _1-x Y _x ) ₂ O ₃ sintered body.

FIG. 25 shows an example of (Zn _{1 -x} Co _x O) ₅ In ₂ O ₃ sintered body 11
It is a figure which shows the relationship between the electric conductivity and Seebeck coefficient at 20K, and the substitution amount x.

FIG. 26 shows an example of 11 of (Zn _{1 -x} Co _x O) ₅ In ₂ O ₃ sintered body.
It is a figure which shows the relationship between the thermoelectric conversion output factor at 20K, and the substitution amount x.

FIG. 27 is a diagram showing the relationship between the carrier concentration, the hole mobility and the conductivity of the (Zn _{1 -x} Co _x O) ₅ In ₂ O ₃ sintered body at room temperature and the substitution amount x.

FIG. 28 is a view showing the relationship between a ² c calculated from the lattice constant of a (Zn _{1 -x} Co _x O) ₅ In ₂ O ₃ sintered body and the substitution amount x.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Ryusuke Ueyama, Inventor 2-7-19 Nishi, Joto-ku, Osaka City, Osaka Prefecture Inside Daiken Chemical Industry Co., Ltd. (72) Inventor Kazuyuki Kamata Emission, Joto-ku, Osaka 2-7-19 Nishi Daiken Chemical Industry Co., Ltd. (72) Inventor Mamoru Ueyama 2-7-19 Nishi Release, Joto-ku, Osaka City, Osaka Prefecture Daiken Chemical Industry Co., Ltd.

Claims (3)

[Claims] 1. A Zn—In—O-based oxide, wherein the composition ratio of Zn and In is 5 to 19 in terms of ZnO / In ₂ O ₃ molar ratio.
Thermoelectric conversion material. 2. The thermoelectric conversion material according to claim 1, wherein a part of the In site is substituted by a trivalent cation having an ionic radius larger than that of the In ³⁺ ion. 3. The thermoelectric conversion material according to claim 1, wherein a part of the Zn site is replaced by a divalent cation having an ion radius smaller than that of the Zn ²⁺ ion.