CN101523627A - Thermoelectric material, method for producing the same, and thermoelectric converter - Google Patents

Abstract

The present invention provides a thermoelectric material useful for a thermoelectric converter having excellent energy conversion efficiency, and a method for producing the thermoelectric material. The thermoelectric material comprising an oxide containing Ti, M, and 0 and the oxide is represented by Formula (1). Ti 1-x M x O y (1) M represents at least one selected from the group consisting of V,Nb, and Ta, x is not less than 0.05 and not more than 0.5, and y is not less than 1.90 and not more than 2.02.

Description

Thermoelectric conversion material, method for producing same, and thermoelectric conversion element

technical field

The present invention relates to a thermoelectric conversion material, a method for producing the same, and a thermoelectric conversion element.

Background technique

The so-called thermoelectric conversion power generation refers to power generation by converting thermal energy into electric energy by utilizing a phenomenon (ie, Seebeck effect) that a voltage (thermoelectromotive force) is generated when a temperature difference is applied to a thermoelectric conversion material. In thermoelectric conversion power generation, various residual heat such as geothermal heat and incinerator heat can be used as a heat source, and therefore, it is expected to be practically practical environment-friendly power generation.

The energy conversion efficiency of the thermoelectric conversion material depends on the performance index (Z) of the thermoelectric conversion material. The performance index (Z) is the value obtained by the following formula (1) using the Seebeck coefficient (α), electrical conductivity (σ) and thermal conductivity (κ) of the material, and the thermoelectric conversion material with the larger performance index, Then, it becomes a thermoelectric conversion element excellent in energy conversion efficiency.

Z＝ ^α2 ×σ/K (1)

In particular, α ² ×σ in the formula (1) is called an output factor, and a thermoelectric conversion material having a larger output factor is a thermoelectric conversion element having an excellent output per unit temperature.

Among the thermoelectric conversion materials, there are p-type thermoelectric conversion materials having a positive Seebeck coefficient and n-type thermoelectric conversion materials having a negative Seebeck coefficient. Generally, in thermoelectric conversion power generation, a thermoelectric conversion element in which a p-type thermoelectric conversion material and an n-type thermoelectric conversion material are electrically connected in series is used. Therefore, the energy conversion efficiency of the thermoelectric conversion element depends on the performance index of the p-type thermoelectric conversion material and the n-type thermoelectric conversion material. In order to obtain a thermoelectric conversion element excellent in energy conversion efficiency, a p-type thermoelectric conversion material and an n-type thermoelectric conversion material with a high performance index are required.

As an n-type thermoelectric conversion material, a thermoelectric conversion material in which titanium oxide and tantalum oxide (or titanium oxide and niobium oxide) are mixed, molded, and sintered in air is known (JP-A-2005-276959).

However, the output factor of the n-type thermoelectric conversion material described in the gazette is insufficient.

Contents of the invention

An object of the present invention is to provide an n-type thermoelectric conversion material having a high performance index and high output factor, a method for producing the same, and a thermoelectric conversion element.

The present inventors have conducted various studies, and as a result, the present invention has been accomplished.

That is, the present invention provides the following <1> to <8>.

<1> A thermoelectric conversion material comprising: an oxide containing Ti, M and O, wherein the oxide is represented by formula (1),

Ti _1-x M _x O _y (1)

M is at least one selected from V, Nb and Ta;

x is not less than 0.05 and not more than 0.5;

y is not less than 1.90 and not more than 2.02.

<2> The thermoelectric conversion material according to the above <1>, wherein the oxide has a rutile crystal structure.

<3> The thermoelectric conversion material according to the above <2>, wherein the a-axis lattice constant of the oxide is 0.4590 nm to 0.4730 nm, and the oxide c-axis lattice constant is 0.2950 nm to 0.3000 nm.

<4> The thermoelectric conversion material according to any one of <1> to <3> above, wherein M is Nb.

<5> The thermoelectric conversion material according to any one of <1> to <4> above, wherein the thermoelectric conversion material is a sintered body, and the relative density of the sintered body is 60% or more.

<6> The thermoelectric conversion material according to the above <5>, wherein at least a part of the surface of the thermoelectric conversion material is coated with an oxygen-impermeable film.

<7> A thermoelectric conversion element comprising the thermoelectric conversion material according to any one of <1> to <6> above.

<8> A method for producing a thermoelectric conversion material, comprising steps (a) and (b),

(a) prepare the raw material for sintering, the raw material contains Ti, M (M is selected from at least one of V, Nb and Ta) and O, and relative to the total amount (mole) of Ti and M, the amount of M (mole ) is not less than 0.05 and not more than 0.5; the amount (mol) of O is not less than 1.90 and not more than 2.02 relative to the total amount (mol) of Ti and M.

(b) Shaping the raw material for sintering, and performing sintering in an inert gas atmosphere at 900°C or higher and 1700°C or lower.

Description of drawings

Fig. 1 shows an X-ray diffraction pattern of sintered bodies 1-7.

FIG. 2 shows the relationship between the lattice constant (a-axis, c-axis) and the molar ratio x of the thermoelectric conversion material of the sintered body 1-13.

FIG. 3 shows the temperature dependence of the Seebeck coefficient in sintered bodies 1 , 3 , 10 .

FIG. 4 shows the temperature dependence of the electrical conductivity in the sintered bodies 1 , 3 , 10 .

FIG. 5 shows the temperature dependence of the thermal conductivity in the sintered bodies 1 , 3 , 10 .

FIG. 6 shows the temperature dependence of the output factor in the sintered bodies 1 , 3 , and 10 .

FIG. 7 shows the temperature dependence of the dimensionless figure of merit in sintered bodies 1 , 3 , 10 .

Detailed ways

Thermoelectric conversion material

The thermoelectric conversion material of the present invention contains an oxide containing titanium (Ti), M, and oxygen (O). M is vanadium (V), niobium (Nb), or tantalum (Ta). They can be used alone or in combination.

The oxide is represented by the above formula (1). In formula (1), x is not less than 0.05 and not more than 0.5. From the viewpoint of increasing the output factor, x is preferably not less than 0.05 and not more than 0.20. If x is less than 0.05, the electrical conductivity tends to be small, and a sufficient output factor value cannot be obtained. In addition, when x exceeds 0.5, the Seebeck coefficient tends to be small.

y is not less than 1.90 and not more than 2.02. From the viewpoint of increasing the output factor, y is preferably not less than 1.93 and not more than 2.01. If y is less than 1.90, an impurity crystal phase T _n O _2n-1 is formed, the Seebeck coefficient tends to be small, and a sufficient output factor value cannot be obtained. If y exceeds 2.02, impurity crystal phases are formed (for example, when M is Nb, TiNb ₂ O ₅ , Nb ₂ O ₅ , etc. are formed), the electrical conductivity tends to decrease, and a sufficient output factor value cannot be obtained.

From the viewpoint of further improving the output factor, x is more preferably 0.10 to 0.15 when y is 1.99 to 2.01, and x is 0.15 to 0.20 when y is 1.96 to less than 1.99.

The crystal structure of the oxide is rutile type, anatase type, brookite type, preferably rutile type. If the oxide has a rutile crystal structure, even when used at a high temperature, it is possible to provide a thermoelectric conversion element having good energy conversion efficiency and being less likely to deteriorate due to long-term use.

When the oxide has a rutile crystal structure, the lattice constant of the a-axis is not less than 0.4590 nm and not more than 0.4730 nm, preferably not less than 0.4600 nm and not more than 0.4660 nm; the lattice constant of the c-axis is not less than 0.2950 nm and not more than 0.3000 nm, preferably 0.2960 Above nm and below 0.2990nm. When the lattice constants of the a-axis and c-axis of the oxide are within the above range, the output factor of the thermoelectric conversion material becomes larger. Lattice constants can be calculated by identifying peaks arising from the rutile crystal structure in an X-ray diffraction pattern obtained by X-ray diffraction, and calculating the lattice constant from the value of the peak position (2θ) using the least squares method. Constant (for example, refer to "Crystal Analysis "universal program system (II)" edited by the Crystallographic Society of Japan: Toshio Sakurai (1967)).

From the viewpoint of increasing the output factor, M preferably contains Nb, and more preferably contains only Nb.

The form of the thermoelectric conversion material is, for example, a powder, a sintered body, or a thin film, preferably a sintered body. When the thermoelectric conversion material is a sintered body, it may be in a suitable shape as a thermoelectric conversion element, for example, a plate, a column, a disc, or a prism.

From the viewpoint of increasing electrical conductivity, the thermoelectric conversion material is preferably a thermoelectric conversion material with high orientation. A form with high orientation is, for example, an oriented sintered body, a single crystal, or the like.

The above-mentioned thermoelectric conversion material is n-type, which is a thermoelectric conversion material with a high output factor. By combining it with a p-type thermoelectric conversion material, a thermoelectric conversion element with a high performance index can be provided.

Method for producing thermoelectric conversion material

The thermoelectric conversion material can be produced by, for example, molding and sintering a raw material (the raw material is sintered to form the thermoelectric conversion material). For example, it can be produced by a method including the above steps (a) and (b).

In the step (a), the Ti-containing substance and the M-containing substance can be weighed and mixed so as to have a predetermined composition, thereby preparing a raw material for the next step (b). When preparing the thermoelectric conversion material represented by the above formula (1) (x is not less than 0.05 and not more than 0.5; y is not less than 1.90, preferably not less than 1.93, and not more than 2.02, preferably not more than 2.01), it is possible to weigh and mix the Ti-containing material and The substance containing M satisfies Ti:M=0.95-0.5:0.05-0.5. In addition, when preparing the thermoelectric conversion material represented by the above formula (1) (x is not less than 0.05 and not more than 0.2; y is not less than 1.90, preferably not less than 1.93, and not more than 2.02, preferably not more than 2.01), it is possible to weigh and mix Ti-containing The substance and the substance containing M satisfy Ti:M=0.95-0.8:0.05-0.2. For example, when preparing a thermoelectric conversion material containing an oxide represented by the formula Ti _0.85 Nb _0.15 O _2.00 , TiO ₂ , Ti, and Nb ₂ O ₅ can be weighed and mixed so that the molar ratio of Ti:Nb:O is 0.85:0.15 : 2.00.

Substances containing Ti include, for example, titanium oxides such as TiO ₂ , Ti ₂ O ₃ , and TiO, and Ti. The titanium-containing species is usually a combination of at least two of these species, preferably a combination of _TiO2 and Ti.

M-containing substances are, for example: niobium oxides such as Nb ₂ O ₅ ; tantalum oxides such as Ta ₂ O ₅ ; vanadium oxides such as V ₂ O ₅ ; and Nb, Ta, V. The M-containing substance is usually at least one of these substances, preferably an oxide.

Mixing can be carried out by either a dry method or a wet method. Mixing can be performed using, for example, a ball mill, a V-type mixer, a vibration mill, an attritor, a dyno mill, a dynamic mill, or the like. The resulting mixture can be shaped.

Alternatively, the mixture can be calcined. For example, when the amount (mol) of O in the mixture exceeds 2.02 relative to the weight (mol) of Ti and M, the mixture can be used as a raw material by calcining the mixture in a reducing gas atmosphere and adjusting the molar ratio. On the other hand, when the amount (mol) of O is less than 1.90, the mixture can be used as a raw material by calcining the mixture in an oxidizing gas atmosphere and adjusting the molar ratio. In addition, the mixture in which the amount (mol) of O is 1.90 to 2.02 is calcined in an inert gas atmosphere, and deformation of the sintered body during sintering described later can be suppressed. When the calcination is carried out under an inert gas atmosphere, the calcination conditions are related to the composition of the mixture, and the calcination time is, for example, 0.5 to 24 hours. The calcined mixture can be pulverized. Pulverization can be performed using, for example, a ball mill, a vibration mill, an attritor, a refiner, an electric mill, or the like.

In the step (b), the raw material is molded and sintered as described above.

Forming can be performed by, for example, uniaxial pressing, cold hydraulic press (CIP, cold inter-static press), mechanical press, hot press, hot isostatic press (HIP, hot press). The shape can be appropriately selected according to the shape of the thermoelectric conversion element. Shapes are eg plates, cylinders, discs, prisms. Binders, dispersants, release agents, etc. can be added to the raw materials during molding.

Sintering is performed under an inert atmosphere. The inert gas is, for example, a nitrogen-containing gas, a noble gas-containing gas, preferably a rare gas-containing gas, more preferably only a rare gas. From the standpoint of operability, the rare gas is preferably argon (Ar). The sintering temperature is not less than 900°C and not more than 1700°C, preferably not less than 1200°C and not more than 1500°C, more preferably not less than 1250°C and not more than 1450°C. If the sintering temperature is lower than 900° C., the solid phase reaction and sintering will not proceed sufficiently, and the electrical conductivity will decrease depending on the composition. If the sintering temperature exceeds 1700° C., depending on the composition, target oxides cannot be obtained due to elution or volatilization of constituent elements, and the performance index of the thermoelectric conversion material decreases. The sintering time is usually about 0.5 to 24 hours.

In the step (b), molding and sintering of the raw material may be performed simultaneously. At this time, as the apparatus, a hot press apparatus or a hot isostatic pressing (HIP) apparatus can be used.

The sintered density of the obtained sintered body is usually 60% or more, preferably 80% or more, more preferably 85% or more from the viewpoint of improving the strength of the sintered body. A thermoelectric conversion material including such a high-density sintered body has a high electrical conductivity. The density of the sintered body can be controlled by, for example, the size of raw material particles, molding pressure, sintering temperature, and sintering time.

If necessary, the sintered body may be pulverized, and the obtained pulverized product may be further sintered under the above conditions. In addition, the surface of the sintered body may be coated with an oxygen-impermeable film. The oxygen-impermeable film may be a film that cannot or hardly permeates oxygen, and includes, for example, alumina, titania, zirconia, silica, and silicon carbide. Coating can be performed using aerosol deposition, thermal spraying, chemical vapor deposition (CVD), and the like. A thermoelectric conversion material including such a coated sintered body can suppress surface oxidation and is less prone to performance degradation even when used in an oxidizing atmosphere.

The thermoelectric conversion material can also be produced by the following methods besides the above methods: a method including a co-precipitation process, a method including a hydrothermal process, a method including a drying-up (drying-up) process, a method including a sputtering process, a method including A method using a CVD process, a method including a sol-gel process, a method including a FZ (floating zone melting method) process, a method including a TSCG (template-type single crystal growth method) process .

Thermoelectric conversion element

The thermoelectric conversion element of the present invention has the aforementioned n-type thermoelectric conversion material, and generally has an n-type thermoelectric conversion material, a p-type thermoelectric conversion material, an n electrode, and a p electrode. The p-type thermoelectric conversion material is, for example, NaCo ₂ O ₄ and Ca ₃ Co ₄ O ₉ (JP-A-9-321346 and JP-A-2001-64021). As the p-type thermoelectric conversion material, a commercial item can be used. A thermoelectric conversion element can be produced by a known method (for example, Japanese Patent Application Laid-Open No. 5-315657).

Example

The present invention is illustrated in more detail by way of examples. The various physical properties of the thermoelectric conversion material were measured by the following methods.

1. Conductivity (σ)

A sintered body sample was processed into a prism shape, a platinum wire was fixed with a silver paste, and measurement was performed by a direct current four-terminal method. In a nitrogen stream, the measurement was performed while changing the temperature within the range from room temperature to 500°C.

2. Seebeck coefficient (α)

On both ends of the sintered body sample processed into the same shape as that used for the electrical conductivity measurement, R thermocouples and platinum wires were fixed with silver paste, and the temperature and thermoelectromotive force of the sintered body sample were measured. In a nitrogen stream, the measurement was performed while changing the temperature within the range from room temperature to 500°C. Cool one side of the sintered body sample with a cooling tube to make a low temperature part, measure the temperature at both ends of the sintered body sample with an R thermoelectric pair, and measure the thermoelectromotive force (ΔV) generated between the two ends of the sintered body sample. The temperature difference (ΔT) at both ends of the sintered body sample is controlled within the range of 0.5-10°C, and the Seebeck coefficient (α) is calculated from the slope of ΔT and ΔV.

3. Thermal conductivity (κ)

The specific heat and thermal diffusivity of the sintered body samples were measured by the laser flash method under vacuum in the range of room temperature to 500°C while changing the temperature. The measurement was carried out using a laser flash method thermal conductivity measuring device TC-7000 manufactured by Vacuum Riko Co., Ltd.

4. Structure and Composition Analysis

The crystal structure of the powder sample and the sintered body sample was analyzed by a powder X-ray diffraction method using CuKα as a radiation source using an X-ray diffraction measuring device RINT2500TTR manufactured by Rigaku Co., Ltd. The lattice constant (a-axis, c-axis) of the rutile crystal structure of the sample is calculated by using the X-ray diffraction pattern obtained by X-ray diffraction to identify the peak generated by the rutile crystal structure, from the peak position ( 2θ) were calculated using the least squares method. The composition of the metal element of the sample was measured using a fluorescent X-ray apparatus PW1480 manufactured by Philips. In addition, the amount of O contained in the sample is calculated as follows: the sample is placed in the air at a temperature of 1000°C to 1200°C (1000°C when Ta is used as the starting material; 1000°C when Nb is used as the starting material 1200°C), heat treatment was performed for 48 hours, and the weight increase at this time was all taken as the increase of O.

5. Density of sintered body

The true density of the sintered samples was determined by the Archimedes method. Relative densities were calculated based on data of true densities and lattice constants obtained by powder X-ray diffractometry.

Example 1

[Preparation of raw materials for sintering]

As starting materials, titanium oxide (TiO ₂ , manufactured by Ishihara Techno Co., Ltd., PT-401M (trade name)), metallic titanium (Ti, High Purity Chemicals), and niobium oxide (Nb ₂ O ₅ , High Purity Chemicals) were used. As shown in Table 1, weigh these raw materials so that they meet TiO ₂ : Ti: Nb ₂ O ₅ =0.9375: 0.0025: 0.0250, and use a dry ball mill (medium: plastic ball) to mix for 6 hours to obtain Ti: Nb: O = A mixture of 0.95:0.05:2.00.

[forming, sintering]

The mixture was molded by uniaxial pressing (molding pressure: 200 kg/cm ² ), and the resulting disk-shaped molded body was calcined at 1000° C. for 3 hours in an argon atmosphere (Ar purity: 99.9995%). The obtained calcined product was dry-pulverized with a ball mill (medium: balls made of zirconia). The obtained pulverized product was formed by uniaxial pressing (forming pressure: 200kg/cm ² ) and further hydrostatic pressing (forming pressure: 1500kg/cm ² ), and the obtained disc-shaped compact was put into a sintering furnace, Sintering was performed at 1300° C. for 12 hours in an argon atmosphere (Ar purity: 99.9995%) to obtain a sintered body 1 .

The appearance of the sintered body 1 is black, and the relative density is 82.3%. The sintered body 1 has a rutile crystal structure, and its lattice constants are 0.4680 nm on the a-axis and 0.2968 nm on the c-axis. The composition, lattice constant, and relative density of the sintered body 1 are shown in Table 2.

For sintered body 1 (thermoelectric conversion material), the Seebeck coefficient (α), electrical conductivity (σ), thermal conductivity (κ), output factor (α ² ×σ), dimensionless performance index ( ZT), and the results are shown in Table 3. The dimensionless performance index is the value obtained by multiplying the performance index (Z, unit K ^-1 ) by the absolute temperature (T, unit K).

Embodiment 2-13

(Examples 2 to 13 correspond to production examples of sintered bodies 2 to 13, respectively)

Table 1 shows the starting materials and their amounts in sintered bodies 2-13. Sintered bodies 2 to 13 were obtained in the same manner as in Example 1 [Preparation of Raw Materials for Sintering] and [Molding and Sintering], except that the amount of the starting material used was changed. Sintered bodies 2 to 13 all have a rutile crystal structure. The physical properties of the sintered bodies 2 to 13 are shown in Table 2 and Table 3.

Table 1 The amount of starting material used

Table 2 Physical properties of sintered body

Table 3 Thermoelectric properties of sintered body

Sintered body Seebeck coefficient α(μV/K) Conductivity σ(S/m) Thermal conductivity K(W/mK) Output factor α ² σ(W/mK ² ) Dimensionless performance index ZT(-) Sintered body 1 -290 4.09×10 ³ 3.10 3.43×10 ^-4 0.086 Sintered body 2 -236 7.65×10 ³ 3.30 4.26×10 ^-4 0.097 Sintered body 3 -196 1.12×10 ⁴ 3.05 4.30×10 ^-4 0.109 Sintered body 4 -200 5.43×10 ³ 2.59 2.17×10 ^-4 0.065 Sintered body 5 -165 5.29×10 ³ 1.96 1.44×10 ^-4 0.057 Sintered body 6 -143 6.15×10 ³ 1.81 1.26×10 ^-4 0.054 Sintered body 7 -139 8.36×10 ³ 1.98 1.62×10 ^-4 0.063 Sintered body 8 -212 9.04×10 ³ 3.49 4.07× ^10-4 0.090 Sintered body 9 -152 1.43×10 ⁴ 3.59 3.31×10 ^-4 0.071 Sintered body 10 -170 1.89×10 ⁴ 3.24 5.47×10 ^-4 0.131 Sintered body 11 -152 2.17×10 ⁴ 3.19 5.04×10 ^-4 0.122 Sintered body 12 -120 1.80×10 ⁴ 2.35 2.60×10 ^-4 0.085 Sintered body 13 -116 1.61×10 ⁴ 2.09 2.18×10 ^-4 0.081

Example 14

As starting materials, titanium oxide (TiO ₂ , manufactured by Ishihara Techno Co., Ltd., PT-401M (trade name)), metal titanium (Ti, High Purity Chemicals), and tantalum oxide (Ta ₂ O ₅ , High Purity Chemicals) were used. As shown in Table 4, these raw materials are weighed so that they satisfy TiO ₂ : Ti: Ta ₂ O ₅ =0.9375:0.0025:0.025, and are mixed for 6 hours using a dry ball mill (medium: plastic balls) to obtain Ti:Ta:O= A mixture of 0.95:0.05:2.00.

With respect to the mixture, the same operations as [shaping and sintering] in Example 1 were performed to obtain a sintered body 14 . The sintered body 14 has a rutile crystal structure. The physical properties of the sintered body 14 are shown in Table 5 and Table 6.

Example 15, 16

(Examples 15 and 16 correspond to production examples of sintered bodies 15 and 16, respectively)

Table 4 shows the starting materials and their amounts in the sintered bodies 15 and 16 . Sintered bodies 15 and 16 were obtained in the same manner as in Example 14 except that the amount of the starting material used was changed. Both the sintered bodies 15 and 16 have a rutile crystal structure. The physical properties of the sintered bodies 15 and 16 are shown in Table 5 and Table 6.

Table 4 The amount of starting material used

Table 5 Physical properties of sintered body

Table 6 Thermoelectric properties of sintered body

Sintered body Seebeck coefficient α(μV/K) Conductivity σ(S/m) Thermal conductivity K(W/mK) Output factor α ² σ(W/mK ² ) Dimensionless performance index ZT(-) Sintered body 14 -323 2.18×10 ³ 3.37 2.28×10 ^-4 0.052 Sintered body 15 -228 3.68×10 ³ 2.56 1.92×10 ^-4 0.058 Sintered body 16 -158 8.84×10 ³ 3.15 2.21×10 ^-4 0,054

30

Comparative example 1-3

(Comparative examples 1 to 3 correspond to production examples of sintered bodies 17 to 19, respectively)

Table 7 shows the starting materials and their amounts in sintered bodies 17-19. Sintered bodies 17 to 19 were obtained in the same manner as in [Preparation of raw material for sintering] and [Molding and sintering] in Example 1 except that the amount of the starting material used was changed. The sintered bodies 17-19 all have two phases of the rutile crystal structure of TiO ₂ and the different crystal structure of TiNb ₂ O ₇ , and the true density of the sintered bodies is low. The physical properties of the sintered bodies 17 to 19 are shown in Table 8 and Table 9.

Table 7 The amount of starting material used

Table 8 Physical properties of sintered body

Table 9 Thermoelectric properties of sintered body

Sintered body Seebeck coefficient α(μV/K) Conductivity σ(S/m) Thermal conductivity (W/mK) Output factor α ² σ(W/mK ² ) Dimensionless performance index ZT(-) Sintered body 17 -288 1.11×10 ³ 1.52 9.21×10 ^-5 0.047 Sintered body 18 -500 3.78×10 ² 1.97 9.44×10 ^-5 0.037 Sintered body 19 -349 1.82×10 ² 2.18 2.22×10 ^-5 0.008

Industrial Applicability

The n-type thermoelectric conversion material of the present invention has high performance index and output factor, high energy conversion efficiency, and is suitable for thermoelectric conversion elements with large output per unit temperature.

Claims (8)

1. thermo-electric converting material, it contains the oxide of Ti, M and O, and wherein, oxide is by formula (1) expression,

Ti _1-xM _xO _y (1)

M is selected from least a among V, Nb and the Ta;

X is more than 0.05 below 0.5;

Y is more than 1.90 below 2.02.

2. the described thermo-electric converting material of claim 1, wherein, oxide has the rutile-type crystal structure.

3. the described thermo-electric converting material of claim 2, wherein, the lattice constant of oxide a axle is below the above 0.4730nm of 0.4590nm, the lattice constant of oxide c axle is below the above 0.3000nm of 0.2950nm.

4. each described thermo-electric converting material in the claim 1～3, wherein, M is Nb.

5. each described thermo-electric converting material in the claim 1～4, wherein, thermo-electric converting material is a sintered body, and the relative density of sintered body is more than 60%.

6. the described thermo-electric converting material of claim 5, wherein, thermo-electric converting material is coated with not oxygen permeation membrane in its surperficial at least a portion.

7. thermoelectric conversion element, it has each described thermo-electric converting material in the claim 1～6.

8. the manufacture method of thermo-electric converting material, it contains operation (a) and (b),

(a) preparation raw material for sintering, this raw material contains Ti, M and O, and wherein M is selected from least a among V, Nb and the Ta, and in mole, and with respect to the total amount of Ti and M, the amount of M is more than 0.05 below 0.5; In mole, with respect to the total amount of Ti and M, the amount of O is more than 1.90 below 2.02;

(b) shaping raw material for sintering, and under the atmosphere of inert gases below 1700 ℃ more than 900 ℃, carry out sintering.

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