JP2010228927A - Cobalt-manganese compound oxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new oxide-based material, which has excellent characteristics as a P-type thermoelectric conversion material, can be used even in air at a high temperature, exhibits good environment-conscious property and is excellent from the economical viewpoint and in mass-productivity. <P>SOLUTION: A cobalt-manganese compound oxide satisfying the following conditions (1) to (3) is provided. (1) The oxide has an average composition expressed by compositional formula: Co<SB>3-x</SB>Mn<SB>x</SB>O<SB>y</SB>(where x and y are numbers satisfying 0.9≤x≤2.1 and 3.8≤y≤4.2, respectively); (2) the oxide is phase-separated into a phase of a tetragonal spinel crystal structure and a phase of a cubic spinel crystal structure; and (3) at least one phase of the phase of a tetragonal spinel crystal structure and the phase of a cubic spinel crystal structure has a length of 1 nm to 400 nm in the shortest portion. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a cobalt-manganese composite oxide having excellent performance as a P-type thermoelectric conversion material, a production method thereof, and an application thereof.

In Japan, the effective energy yield from the primary supply energy is only about 30%, and about 70% of the energy is finally discarded as heat into the atmosphere. In addition, 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 burning fossil energy. In order to improve the energy yield, it is only necessary to be able to use the thermal energy discarded in the atmosphere. For this purpose, thermoelectric conversion that directly converts thermal energy into electrical energy is an effective means. This thermoelectric conversion uses the Seebeck effect. That is, it is an energy conversion method in which a potential difference is generated by creating a temperature difference at both ends of the thermoelectric conversion material to generate power. In this thermoelectric power generation, electricity can be obtained simply by placing one end of the thermoelectric conversion material in the high-temperature part generated by waste heat and the other end in the atmosphere (room temperature) and connecting external resistors to both ends. Necessary motors, turbines and other movable devices are not required at all. Therefore, the cost is low, there is no discharge of gas due to combustion, and power generation can be continuously performed until the thermoelectric conversion material deteriorates. In this way, thermoelectric power generation is expected to play a part in solving energy problems that are a concern in the future.

In order to realize thermoelectric power generation, a thermoelectric conversion material with high thermoelectric conversion efficiency, heat resistance, and chemical durability is required. In recent years, examples have been reported in which the thermoelectric properties of a material are dramatically improved by controlling the nanostructure of the material. This is because only the phonons are selectively scattered by the nanostructure, and only the thermal conductivity is effectively reduced while maintaining the electrical characteristics. For example, superlattice thin films such as Bi ₂ Te ₃ / Sb ₂ Te ₃ (see Non-Patent Document 1 below), PbTe-PbSe _0.98 Te _0.02 (see Non-Patent Document 2 below), and Si quantum wires (Non-Patent Document 1 below) 3, 4, etc.) is said to achieve nearly twice the performance of existing materials. These are mainly due to the effect that the thermal conductivity is greatly reduced by scattering phonons having a relatively large mean free path at the interface.

  However, the above-mentioned materials have problems in economic efficiency and mass productivity, such as complicated synthesis methods and the need for expensive equipment. Also, considering the actual application, it is difficult to generate power by collecting a large amount of unused energy with thin film or thin wire materials, and a bulk material, that is, a material consisting of a polycrystalline sintered body is required. It becomes.

  In recent years, bulk structures with controlled nanostructures are being developed (see, for example, Non-Patent Documents 5 and 6 below), both of which are alloy-based materials containing toxic elements and rare elements, and are stable in the atmosphere. In view of safety and the like, it cannot be widely used for consumer use.

R. Venkatasubramanian et al., Nature, 413, 597 (2001). T. C. Harman et al., Science, 297, 2229 (2002). Allon I. Hochbaum et al., Nature, 451, 163 (2008). Akram I. Boukai et al., Nature, 451, 168 (2008). K. F. Hsu et al., Science, 303, 818 (2004). J. Androulakis et al., J. Am. Chem. Soc., 129, 9780 (2007).

The present invention has been made in view of the current state of the prior art described above, and its main object is to provide an oxide-based material that has excellent characteristics as a P-type thermoelectric conversion material and can be used even in high-temperature air. The object is to provide a new material which is excellent in environmental harmony and excellent in economic efficiency, mass productivity and the like.

  The present inventor has intensively studied to achieve the above-described object. As a result, a solid solution composed of a cobalt-manganese-containing composite oxide having a specific composition is heat-treated at a specific temperature range, so that a phase of a tetragonal spinel crystal structure and a cubic spinel crystal structure are obtained by natural phase separation. It has been found that a complex oxide composed of phases can be formed, and that the size of each phase can be easily controlled to the nano order by adjusting the heat treatment conditions. The nanostructured composite oxide thus obtained is a material having a high positive Seebeck coefficient and good conductivity and low thermal conductivity, and excellent performance as a P-type thermoelectric conversion material. The present invention has been completed here.

That is, the present invention provides the following cobalt-manganese composite oxide, a method for producing the composite oxide, and uses of the composite oxide.
1. Cobalt-manganese complex oxide satisfying the following conditions (1) to (3):
(1) Composition formula: Co _3-x Mn _x O _y (wherein x and y are numbers satisfying 0.9 ≦ x ≦ 2.1 and 3.8 ≦ y ≦ 4.2, respectively). Having an average composition represented by:
(2) phase separation into a tetragonal spinel crystal structure phase and a cubic spinel crystal structure phase;
(3) The length of the shortest part of at least one of the tetragonal spinel crystal structure phase and the cubic spinel crystal structure phase is in the range of 1 nm to 400 nm.
2. Item 2. The phase according to Item 1, wherein the phase is separated into a phase of a tetragonal spinel type crystal structure having a high Mn ratio and a phase of a cubic spinel type crystal structure having a high Co ratio compared to the average composition. Cobalt-manganese complex oxide.
3. Composition formula: Co _3-x Mn _x O _y (wherein x and y are numbers satisfying 0.9 ≦ x ≦ 2.1 and 3.8 ≦ y ≦ 4.2, respectively). 3. The method for producing a cobalt-manganese composite oxide according to item 1 or 2, wherein a solid solution of the composite oxide is heat-treated in a temperature range where two-phase separation occurs.
4). A P-type thermoelectric conversion material comprising the cobalt-manganese composite oxide according to Item 1 or 2.
5). A thermoelectric conversion module comprising the P-type thermoelectric conversion material according to Item 4.

  Hereinafter, first, the cobalt-manganese composite oxide of the present invention and the production method thereof will be specifically described.

Cobalt-manganese complex oxide The cobalt-manganese complex oxide of the present invention satisfies the following conditions (1) to (3):
(1) Composition formula: Co _3-x Mn _x O _y (wherein x and y are numbers satisfying 0.9 ≦ x ≦ 2.1 and 3.8 ≦ y ≦ 4.2, respectively). Having an average composition represented by:
(2) phase separation into a tetragonal spinel crystal structure phase and a cubic spinel crystal structure phase;
(3) The length of the shortest part of at least one of the tetragonal spinel crystal structure phase and the cubic spinel crystal structure phase is in the range of 1 nm to 400 nm.

As described above, the composite oxide of the present invention has a composition formula: Co _3-x Mn _x O _y (where x and y are 0.9 ≦ x ≦ 2.1 and 3.8 ≦ y ≦ 4, respectively). 2 is a cobalt-manganese-containing composite oxide having an average composition expressed by the following formula, and phase-separated into a phase of a tetragonal spinel crystal structure and a phase of a cubic spinel crystal structure: In addition, at least one of the tetragonal spinel crystal structure phase and the cubic spinel crystal structure phase is a composite oxide having a nanostructure in which the length of the shortest portion is in the range of 1 nm to 400 nm. is there.

Composite oxides of such nanostructures, the composition formula: by having an average composition represented by _{Co 3-x Mn x O y} , comes to have a high positive Seebeck coefficient and good conductivity. Also, phase separation into a tetragonal spinel crystal structure phase and a cubic spinel crystal structure phase, and at least one of a tetragonal spinel crystal structure phase and a cubic spinel crystal structure phase Has a very low thermal conductivity when the length of the shortest portion is in the range of 1 nm to 400 nm. This is because the composite oxide of the present invention is separated into two phases on the nano order, so that the interfacial density between the phases increases, and phonons are effectively scattered at the phase interface. It is estimated that the conductivity is greatly reduced.

  The average composition of the composite oxide described above is based on the composition of the composite oxide constituting each phase of the tetragonal spinel crystal structure phase and the cubic spinel crystal structure phase and the ratio of each phase. It is the composition of the oxide determined as an average, and is consistent with the composition of the complex oxide solid solution that is the precursor of the complex oxide.

  In the present invention, for the phase of the tetragonal spinel crystal structure and the phase of the cubic spinel crystal structure, it is important that the interface density between the phases is high, and the specific shape of each phase is not particularly limited. . For example, a structure in which each phase is rod-like and arranged alternately in a checkered pattern, a structure in which two plate-like phases are alternately laminated, one phase becomes a matrix, and a ribbon-like second phase spreads in it It can be set as the complex oxide of arbitrary structures, such as a structure. In these cases, the length of the shortest part of at least one phase may be in the range of 1 nm to 400 nm, and particularly preferably in the range of 1 nm to 50 nm. In this case, the length of the shortest portion of each phase is the length of the shortest portion of the outer shape of each phase. For example, when each phase exists in a rod shape, at least one of the rod shapes It suffices if the minor axis of the phase is in the range of 1 nm to 400 nm. Moreover, when it becomes the structure which laminated | stacked two plate-shaped phases alternately, the thickness of at least one plate-shaped phase should just exist in the range of 1 nm-400 nm. Further, when one phase becomes a matrix and a ribbon-like second phase spreads therein, the thickness of the ribbon-like phase may be in the range of 1 nm to 400 nm.

  In the present invention, it is particularly preferable that the length of the shortest part is in the range of 1 nm to 400 nm for both the tetragonal spinel crystal structure phase and the cubic spinel crystal structure phase.

Regarding the composition of each phase of the tetragonal spinel crystal structure phase and the cubic spinel crystal structure phase, the composition formula showing the above average composition: Co _3-x Mn _x O _y (wherein x and y are , 0.9 ≦ x ≦ 2.1 and 3.8 ≦ y ≦ 4.2, respectively)), assuming that phase separation due to spinodal decomposition occurs. Can be obtained from That is, the phase of the tetragonal spinel crystal structure is a phase having a higher Mn ratio than the average composition, and the composition formula: Co _3-a Mn _a O _b (where a and b are each 1 3 ≦ a ≦ 3 and 3.8 ≦ b ≦ 4.2.), And the phase of the cubic spinel crystal structure has a Co ratio compared to the average composition. Is a high phase and has the composition formula: Co _3-c Mn _c O _d (where c and d are numbers satisfying 0 ≦ c ≦ 1.9 and 3.8 ≦ d ≦ 4.2, respectively). ). The composition of each of these phases is in good agreement with the results of Example 1 described later.

Complex oxide having a manufacturing method above nanostructures manufacturing method (i) nanostructured composite oxide composite oxide, the composition _{formula: Co 3-x Mn x O} y ( wherein, x and y are each 0 .. 9 ≦ x ≦ 2.1 and 3.8 ≦ y ≦ 4.2.) By obtaining a solid solution of the composite oxide represented by the above in a temperature range where two-phase separation occurs. Can do.

  The heat treatment temperature varies depending on the composition of the solid solution of the complex oxide, but may be a temperature lower than the melting temperature of the solid solution and a temperature range in which phase separation into two phases occurs. The specific heat treatment temperature is below the boundary temperature between the temperature region where the uniform solid solution is formed (mixing region) and the temperature region where the phase separation occurs (immiscible region) depending on the specific composition of the complex oxide solid solution. The temperature may be in the temperature range where phase separation occurs, and is usually in the range of about 1200 to 200 ° C. By performing the heat treatment within such a temperature range, phase separation that appears to be caused by spinodal decomposition occurs, and a target nanostructured composite oxide can be obtained.

  When the heat treatment temperature is high in the above-described temperature range where phase separation occurs, phase separation occurs in a relatively short time, but when the heat treatment time becomes long, each phase grows to obtain a nanostructured composite oxide. I can't. In addition, when the heat treatment temperature is low, the production efficiency is very poor because the phase separation takes a long time. Usually, the heat treatment time may be determined so that a nanostructured complex oxide in which the length of the shortest part of at least one phase is in the range of 1 nm to 400 nm is formed within a temperature range of about 1200 to 200 ° C. For example, it may be within a range of about 1 to 5000 hours. Further, the heat treatment temperature may not be constant, and for example, the temperature may be gradually lowered within a temperature range where phase separation occurs at a temperature lowering rate of about 100 K / hour to 0.1 K / hour. The heat treatment atmosphere may be, for example, an oxygen-containing atmosphere such as the air, but is not particularly limited thereto.

(Ii) Method for Producing Precursor (Uniform Solid Solution) Composition formula used as starting material (precursor) when phase separation is performed by the above-described method: Co _3-x Mn _x O _y (wherein x and y are The composite oxide solid solution represented by 0.9 ≦ x ≦ 2.1 and 3.8 ≦ y ≦ 4.2, respectively, represents the element component ratio of the target composite oxide. It can be obtained by mixing raw materials so as to have the same elemental component ratio and heat-treating in a temperature range where a uniform solid solution is formed.

The raw material is not particularly limited as long as it can form an oxide by firing, and elemental elements, oxides, various compounds (such as carbonates) and the like can be used. For example, Co sources include 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 (such as dipropoxy cobalt (Co (OC ₃ H ₇ ) ₂ ), etc.) can be used, and manganese sources include manganese (Mn), manganese oxide (Mn ₂ O ₃ ), manganese carbonate (MnCO ₃ ), etc. The particle size of the raw material powder is not particularly limited.

  The above raw materials are uniformly mixed by any mixing means such as a planetary ball mill or pot mill, and then fired by any heating means such as an electric heating furnace, a gas heating furnace, a hot press furnace, or a discharge plasma sintering furnace. do it.

  The firing temperature may be a condition under which a target solid solution is formed, and may be a temperature range (mixing region) where the solid solution is stable on the phase diagram. The specific firing temperature varies depending on the composition of the solid solution, the size of the particle size, and the like, but is, for example, a temperature range of about 1200 to 1500 ° C. Further, the firing time may be set to a time at which the target solid solution is generated as a uniform phase, and is not particularly limited, but may be, for example, 10 to 20 hours. The firing atmosphere may be, for example, an oxygen-containing atmosphere such as the air, but is not particularly limited thereto.

  The solid solution obtained by the above method is stable only at a high temperature, which is the mixing region on the phase diagram. Therefore, by quenching this from the mixing region, the temperature range where two-phase separation occurs (immiscible region) In this case, it is necessary to exist as a solid solution. In this case, after quenching from the mixing region to room temperature to obtain a solid solution with a uniform composition, it may be heated to a temperature range where two-phase separation occurs, or rapidly cooled from the mixing region to a temperature region where two-phase separation occurs, In this temperature range, it may be a solid solution having a uniform composition.

  The rapid cooling method is not particularly limited, and any means such as water cooling, air cooling, and ice cooling can be employed.

  There is no particular limitation on the quenching rate, and the quenching rate may be set so that a stable uniform solid solution is formed at room temperature or in a temperature range where two-phase separation occurs.

  The firing atmosphere may be, for example, an oxygen-containing atmosphere such as the air, but is not particularly limited thereto.

Characteristics of the composite oxide The composite oxide having a nanostructure of the present invention has a low thermal conductivity, and the thermal conductivity is lower than that of a composite oxide having the same composition that does not cause phase separation of the nanostructure. For example, at a temperature of 500 ° C. or higher, it has a very low thermal conductivity of 5 W / mK or less.

Furthermore, the composite oxide is a material having a low electrical resistivity and excellent electrical conductivity, and specifically has an electrical resistivity of 10 Ωcm or less at 500 ° C. or higher. Further, the composite oxide has a high positive Seebeck coefficient. Specifically, the composite oxide has a Seebeck coefficient of 10 μV / K or more at 500 ° C. or more, and has excellent performance as a P-type thermoelectric conversion material. Material.

  As described above, the composite oxide of the present invention is a substance having a positive Seebeck coefficient and good electrical conductivity and having a low thermal conductivity. Furthermore, the composite oxide is a material that does not contain toxic elements or rare elements and is excellent in heat resistance, chemical durability, and the like. 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 such characteristics.

  FIG. 7 is a schematic diagram of an example of a thermoelectric power generation module using a thermoelectric conversion material made of the composite 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, and is composed of a high-temperature part substrate, a low-temperature part substrate, a P-type thermoelectric conversion material, an N-type thermoelectric conversion material, an electrode, a conductor, and the like. This is a module, and the composite oxide of the present invention is used as a P-type thermoelectric conversion material.

  The composite oxide of the present invention is a composite of oxides having a nanostructure, and is a material having low thermal conductivity, high electrical conductivity, and a high positive Seebeck coefficient.

  In addition, according to the production method of the present invention, a complex oxide having the above-described excellent performance can be obtained by using a natural phase separation without using an expensive apparatus or a complicated process and by a very inexpensive and simple process. And a bulk body suitable for large-capacity power generation can be easily obtained.

  Therefore, by using the composite oxide of the present invention as a P-type thermoelectric conversion material, an oxide thermoelectric power generation module having high performance can be realized, and thermal energy that has been discarded in the atmosphere can be effectively used so far. It becomes possible.

2 is an X-ray diffraction pattern of the composite oxide of Example 1 and its precursor (homogeneous solid solution). 2 is a transmission electron micrograph of the composite oxide of Example 1. 4 is a scanning electron micrograph of the oxide of Comparative Example 1. It is a graph which shows the temperature dependence of the thermal conductivity of the complex oxide of Example 1 and the oxide of Comparative Example 1. 4 is a graph showing the temperature dependence of the electrical resistivity of the composite oxide obtained in Example 1. 4 is a graph showing the temperature dependence of the Seebeck coefficient of the composite oxide obtained in Example 1. It is a schematic diagram of the thermoelectric conversion module which used this invention complex oxide as a P-type thermoelectric conversion material. 4 is a transmission electron micrograph of the composite oxide of Example 2. 4 is a transmission electron micrograph of the composite oxide of Example 3.

  Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1
Co ₃ O ₄ and MnO ₂ were weighed so as to be 3 mol of the latter with respect to 1 mol of the former, and then mixed by a planetary ball mill. Next, the mixed sample is calcined at 950 ° C. for 12 hours, the calcined product is pulverized and mixed in a mortar, and the operation is repeated twice at 1150 ° C., which is the production temperature range of the uniform solid solution, for 2 hours. To make the phase uniform.

Next, in order to make the obtained powder into a high-density sintered body that can be used for physical property tests, it is filled in a carbon die and held at 1000 ° C. for 1 minute while uniaxially pressing at 100 MPa by discharge plasma sintering. It was molded into a dense pellet with a diameter of 1.5-2 cm and a height of 0.1-1 cm. Thereafter, the obtained pellets were heat-treated in air at 1150 ° C., which is a uniform solid solution generation temperature range, for 5 hours in an electric furnace, and then cooled to 600 ° C., which is a two-phase separation temperature range, in 30 minutes. It cooled to the two-phase-separation temperature area | region with the state of the solid solution. The solid solution in this state is represented by the composition formula: Co _1.5 Mn _1.5 O ₄ .

  Next, phase separation was caused by lowering the temperature range from 600 ° C. to 20 ° C. at a rate of 50 K / h. The X-ray diffraction pattern of the obtained sample is shown in FIG. Moreover, the X-ray-diffraction pattern of the sample at the time of standing to cool (quenching) the sintered compact baked at 1150 degreeC in air to room temperature is also shown in FIG.

  From the X-ray diffraction peak shown in FIG. 1, the sample that was allowed to cool (quenched) from 1150 ° C. to room temperature is a sintered body (solid solution) composed of a single phase of tetragonal crystal, whereas in the two-phase separation temperature range. In the sample of Example 1 that was gradually cooled at a temperature drop rate of 50 K / h, it can be confirmed that the crystal structure has changed. From the composition analysis of each phase described later, it can be determined that this change in crystal structure is a phase separation into another tetragonal crystal and cubic crystal different from the tetragonal crystal of the rapidly cooled sample. Furthermore, from the result of measuring the X-ray diffraction pattern by further growing each phase by setting the temperature drop rate in the temperature range of 600 ° C. to 20 ° C. to 7 K / h, the solid solution having the above composition is formed into tetragonal crystals and cubic crystals. It was confirmed that the phases were separated.

  FIG. 2 shows a transmission electron micrograph of the sample of Example 1. From FIG. 2, it was confirmed that in the sample of Example 1, the two phases were arranged in a checkered pattern with a phase interval of 5 to 10 nm. One of the two phases had a minimum length of about 2 nm.

Moreover, as a result of the compositional analysis by energy dispersive X-ray spectroscopy, the compositions of the two phases produced are Co _1.1 Mn _1.9 O ₄ and Co _1.7 Mn _1.3 O ₄ , respectively. It could be confirmed. This composition is well suited to the composition obtained as a result of spinodal decomposition of the solid solution: Co _1.5 Mn _1.5 O ₄ described above into a tetragonal spinel crystal structure phase and a cubic spinel crystal structure phase. It matches.

  FIG. 3 shows a scanning electron micrograph of a sample obtained by lowering the temperature range from 600 ° C. to 20 ° C. at a rate of 3 K / h. As is clear from FIG. 3, when the temperature drop rate is slowed down and kept in the phase separation temperature range for a long time, although phase separation occurs, each phase grows and the two phases are about 1 to 5 μm. It can be seen that composite oxides arranged at intervals can be obtained. This sample is referred to as the sample of Comparative Example 1.

FIG. 4 is a graph showing the temperature dependence of the thermal conductivity (κ) at 50 to 700 ° C. for the sample of Example 1 and the sample of Comparative Example 1 obtained by the method described above. From this graph, it is clear that in the temperature range of 50 to 700 ° C., the sample of Example 1 exhibits lower thermal conductivity than the sample of Comparative Example 1.
FIG. 5 is a graph showing the temperature dependence of the electrical resistivity (ρ) of the sample of Example 1. As is apparent from this graph, the sample of Example 1 exhibits an electrical resistivity of 10 Ωcm or less at 500 ° C. or higher, and it can be confirmed that the sample has good conductivity.
FIG. 6 is a graph showing the temperature dependence of the Seebeck coefficient (S) of Example 1. From this graph, it can be confirmed that the sample of Example 1 has a positive Seebeck coefficient of 10 μV / K or more at 500 ° C. or more.

  Table 1 below shows the measurement results of the thermal conductivity at 500 ° C., the electrical resistivity at 500 ° C., and the Seebeck coefficient at 500 ° C. for the sample obtained in Example 1.

  From the above results, the composite oxide of Example 1 having a structure separated into two phases on the nano order is a material having a high positive Seebeck coefficient and good conductivity, and having a low thermal conductivity, and P It is clear that the material is useful as a type thermoelectric conversion material.

Example 2
In the same manner as in Example 1 except that Co ₃ O ₄ and MnO ₂ are used in a ratio of 7 moles to the former 1 mole, the composition formula: Co _0.9 Mn _2.1 O ₄ A uniform solid solution represented was produced.

Thereafter, phase separation was caused in the same manner as in Example 1 except that the temperature range from 600 ° C. to 20 ° C. was lowered at a rate of 25 K / h. A transmission electron micrograph of the obtained sample is shown in FIG. As is clear from FIG. 8, in the sample of Example 2, it can be confirmed that two plate-like phases are alternately arranged in a checkered pattern with a phase interval of 5 to 20 nm, and the shortest part of one phase The length was about 4 nm.

  The sample obtained in Example 2 has an X-ray diffraction peak similar to that of the sample of Example 1, and a sintered body (solid solution) having the same composition is allowed to cool from 1150 ° C. to room temperature (quenched). As compared with the X-ray diffraction peak of the tetragonal single phase sample obtained in this way, it was confirmed that the crystal structure had changed. From the result of measuring the X-ray diffraction pattern by further growing each phase at a temperature drop rate in the temperature range of 600 ° C. to 20 ° C. at 7 K / h, each phase of the sample of Example 2 is tetragonal and cubic. It was confirmed that.

  Table 1 below shows the measurement results of the thermal conductivity at 500 ° C., the electrical resistivity at 500 ° C., and the Seebeck coefficient at 500 ° C. for the sample obtained in Example 2.

Example 3
Except that Co ₃ O ₄ and MnO ₂ are used in a ratio of 9/7 mol with respect to the former 1 mol, the composition formula: Co _2.1 Mn _0.9 is the same as in Example 1. A uniform solid solution represented by O ₄ was prepared.

  Thereafter, phase separation was caused in the same manner as in Example 1 except that the temperature range from 600 ° C. to 20 ° C. was lowered at a rate of 25 K / h. A transmission electron micrograph of the obtained sample is shown in FIG. As is clear from FIG. 9, in the sample of Example 3, it can be confirmed that two plate-like phases are alternately arranged in a checkered pattern at a phase interval of 5 to 40 nm, and the shortest part of one phase is The length was about 5 nm.

  Moreover, the sample obtained in Example 3 has an X-ray diffraction peak similar to that of the sample of Example 1, and a sintered body (solid solution) having the same composition is allowed to cool from 1150 ° C. to room temperature (quenched). As compared with the X-ray diffraction peak of the tetragonal single phase sample obtained in this way, it was confirmed that the crystal structure had changed. From the result of measuring the X-ray diffraction pattern by further growing each phase by setting the temperature drop rate in the temperature range of 600 ° C. to 20 ° C. to 7 K / h, each phase of the sample of Example 3 is tetragonal and cubic. It was confirmed that.

  Table 1 below shows the measurement results of the thermal conductivity at 500 ° C., the electrical resistivity at 500 ° C., and the Seebeck coefficient at 500 ° C. for the sample obtained in Example 3.

As is apparent from Table 1, each of the samples of Examples 1 to 3 has a structure in which two phases are separated in nano order, has a high positive Seebeck coefficient and good conductivity, and heat conduction. It is a material with a low rate and is clearly a useful material as a P-type thermoelectric conversion material.

Claims (5)

Cobalt-manganese complex oxide satisfying the following conditions (1) to (3):
(1) Composition formula: Co _3-x Mn _x O _y (wherein x and y are numbers satisfying 0.9 ≦ x ≦ 2.1 and 3.8 ≦ y ≦ 4.2, respectively). Having an average composition represented by:
(2) phase separation into a tetragonal spinel crystal structure phase and a cubic spinel crystal structure phase;
(3) The length of the shortest part of at least one of the tetragonal spinel crystal structure phase and the cubic spinel crystal structure phase is in the range of 1 nm to 400 nm. The phase separation of a tetragonal spinel type crystal structure having a high Mn ratio and a cubic spinel type crystal structure having a high Co ratio as compared with the average composition. Cobalt-manganese complex oxide. Composition formula: Co _3-x Mn _x O _y (wherein x and y are numbers satisfying 0.9 ≦ x ≦ 2.1 and 3.8 ≦ y ≦ 4.2, respectively). The method for producing a cobalt-manganese composite oxide according to claim 1 or 2, wherein the solid solution of the composite oxide is heat-treated in a temperature range where two-phase separation occurs. A P-type thermoelectric conversion material comprising the cobalt-manganese composite oxide according to claim 1. A thermoelectric conversion module comprising the P-type thermoelectric conversion material according to claim 4.

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