JP2003282967A - Thermoelectric conversion material and thermoelectric conversion element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoelectric conversion material which can be stably used at a high temperature of 500°C or higher and which has a low toxicity and to provide a thermoelectric conversion element. <P>SOLUTION: The thermoelectric conversion material contains an oxide represented by the formula: (Ca<SB>1-x</SB>M1<SB>x</SB>)2(Co<SB>1-y</SB>Ga<SB>y</SB>)<SB>2</SB>O<SB>5</SB>(wherein M1 is La, Sr or Ba, 0≤x≤0.07 and 0.2≤y<0.5), or (Ca<SB>1-p</SB>M2<SB>p</SB>)<SB>2</SB>(Co<SB>1-q</SB>Fe<SB>q</SB>)<SB>2</SB>O<SB>5</SB>(wherein M2 is La, Sr or Ba, 0≤p<0.1, and 0.2≤q<1.0). <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoelectric conversion material for high temperature and thermoelectric conversion used for thermoelectric power generation by the Seebeck effect and so-called thermoelectric effect (direct conversion of energy without moving parts) such as electronic freezing by the Peltier effect. Regarding the device.

[0002]

2. Description of the Related Art Thermoelectric conversion using thermoelectric conversion materials such as thermoelectric generation and electronic refrigeration has no moving parts that cause vibration, noise, wear, etc., has a simple structure, is highly reliable, and has a long service life and maintenance. It enables the production of a simplified energy direct conversion device that has the characteristic of being easy. For example, it is possible to directly obtain DC power without using various fossil fuels, etc., or to use a refrigerant. Suitable for temperature control.

By the way, in evaluating the characteristics of thermoelectric conversion materials, the power factor Q and the performance index Z represented by the following equations are used.

[0004]

[Equation 1]

[0005]

[Equation 2]

Here, α is the Seebeck coefficient, σ is the electrical conductivity, and κ is the thermal conductivity. In the thermoelectric conversion material, it is desired that the figure of merit Z is large, that is, the Seebeck coefficient α is high, the electrical conductivity σ is high, and the thermal conductivity κ is low.

For example, when the thermoelectric conversion material is used for thermoelectric power generation, the thermoelectric conversion material is Z = 3 × 10 ⁻³ 1.
It is desired to have a high performance index of / K or more and to operate stably for a long period of time under a use environment. In addition, for mass-production of thermoelectric power generators for in-vehicle use or exhaust heat utilization, a material that has sufficient heat resistance and strength at high temperature and does not cause characteristic deterioration, and a manufacturing method that can efficiently produce this at low cost. Is desired.

Conventionally, P has been used as such a thermoelectric conversion material.
bTe or MSi ₂ (M: Cr, Mn, Fe, C
Silicide compounds such as o) and the like, and silicide-based materials such as a mixture thereof are used.

Further, TSb ₃ (T: Co, Ir, Ru)
Examples using Sb compounds such as, for example, thermoelectric materials obtained by adding impurities for determining the electric conductivity type to a material containing CoSb ₃ as a main component in the chemical composition have been reported (LD Dudkin and N.Kh. AbrikoSov. , Soviet Physics So
lid State Physics (1959) pp.126) BNZobrinaand, LD
Dudkin, Soviet Physics Solid State Physics (1960) p
p. 1668) K. Matsubara, T. Iyanaga, T. Tsubouchi, K. Kishi
moto and T. Koyanagi, American Institute of Physics
(1995) pp226-229).

[0010]

However, the PbT
The thermoelectric conversion material composed of e has a large figure of merit Z, which is an index of thermoelectric properties, of about 1 × 10 ⁻³ 1 / K at around 400 ° C., but has a low melting point because it contains Te as a volatile component in the material composition. Since it also lacks chemical stability, there is a problem that it cannot be used at a high temperature of 500 ° C. or higher. Further, since Te, which is a volatile component, is included, the manufacturing process becomes complicated, and therefore, there is a problem in that variations in characteristics due to compositional variations are likely to occur and mass production cannot be performed efficiently. Furthermore, there is a problem that the raw material itself is expensive and has a strong toxicity.

On the other hand, MSi ₂ (M = Cr, Mn, Fe,
Silicide compounds such as Co) and the like, and silicide-based materials such as a mixture thereof are inexpensive and chemically stable without toxicity, and can be used even in a temperature range of about 800 ° C., for example, “Norio Nishida, Kinichi Uemura. : Thermoelectric semiconductors and their applications (19
83) pp. 176-180 ", it is known that it can be manufactured by a relatively inexpensive manufacturing method.
However, the thermoelectric property of the silicide-based material is lower than that of PbTe by a figure of merit Z of about 1 to 2 × 10 ⁻⁴ 1 / K, which is about one order of magnitude lower, and sufficient thermoelectric properties comparable to PbTe have not been obtained.

For Sb compounds such as TSb ₃ (T: Co, Ir, Ru), for example, thermoelectric materials containing CoSb ₃ as a main component in their chemical composition, the raw materials used are relatively inexpensive and have no toxicity. A relatively high figure of merit (<1
It is known to have ^{x10 −3} 1 / K).

Here, in a thermoelectric conversion material having a chemical composition CoSb ₃ as conventionally known, the obtained material has only a cubic CoSb ₃ crystal phase as a constituent crystal phase and other crystal phases ( CoSb, CoSb ₂ , Sb)
Has the effect of degrading thermoelectric properties and is said to be required to be removed. However, in practice, it is known that in the method of obtaining CoSb ₃ by smelting, a different phase (CoSb, CoSb ₂ , Sb) other than CoSb ₃ is precipitated during solidification. In order to make CoSb ₃ single phase, there is a problem that heat treatment at a temperature of about 600 ° C. for about 200 hours is required, and the manufacturing process becomes long.

Further, in the method of crushing and sintering CoSb ₃ ingot, the different phase precipitated during melting, that is, CoSb
_Since CoSb and CoSb ₂ having a density higher than ₃ undergo a phase change to CoSb ₃ during firing, there is a problem that body expansion occurs and sintering does not proceed. For example, pressure 5 × 10
^A sufficiently densified material has not been obtained even when hot pressed under the conditions of ³ kg / cm ² and temperature of 600 ° C. (Reference: K. Matsubara, T. Iyanaga, T. Tsubouchi, K. Kish
imoto and T. Koyanagi, American Instituteof Physics
(1995) pp226-229). The theoretical density of cubic CoSb ₃ is 7.64 g / cm ³ , whereas the maximum value reported in the literature is 5.25 g / cm ³ . As a result, the sintered body becomes an extremely brittle material, and only a material having insufficient material strength at high temperature can be obtained.

[0015] Durability at the time of exposing a material composed of heavy elements such as Bi, Te, Se, Pb, etc. to industrial process exhaust gas, and the problem of vaporization and evaporation of constituent components in a high temperature reaction atmosphere and the resulting contamination, resulting in low cost. New materials that can be used stably at high temperatures and have a low environmental impact are required.

From such a background, oxides are regarded as thermoelectric materials.
The motivation to use it is increasing rapidly. Oxidation
Objects generally have low mobility, usually 10¹⁹cm^-3degree
Since it does not show metallic conductivity at the carrier concentration of
The conventional wisdom is that it cannot be replaced.
It was. However, in 1997, the layered oxide NaCo_TwoO _Four
Has an unexpectedly large thermoelectromotive force while having a low resistivity.
It was found to have (Japanese Patent Laid-Open No. 2000-211971)
Gazette). The thermoelectric properties of this system are outstanding compared to other oxides.
It has high performance and is close to the performance of existing practical materials.
is there.

However, since Na is volatilized during sintering, there is a problem that the thermoelectric characteristics greatly differ depending on the preparation conditions. Further, when used at high temperature, Na is volatilized to lower the thermoelectric property, and when left in the air, the resistivity increases. In addition, Na easily reacts with moisture in the air, which may deteriorate the performance.

On the other hand, C having a brown mirror light structure
It was reported that a negative thermoelectromotive force was observed for the first time in the Co system for a _1.95 La _0.05 Co _2-x Al _x O ₅ (Kou Kobayashi, Ichiro Terasaki, “Ca _1.95 La _0.05 Co _2-x Al _x O 5). _Five
Conduction Mechanism ", Thermoelectric Conversion Symposium 2001 (TEC
2001)).

However, even in this case, there is a problem that the observation is carried out from a low temperature to a room temperature and it cannot be used at a high temperature.

The present invention has been made in view of the above circumstances and has a temperature of 500 ° C.
An object of the present invention is to provide a thermoelectric conversion material and a thermoelectric conversion element that can be stably used even at the above high temperature and have low toxicity.

[0021]

[Means for Solving the Problems] The present invention for solving the above problems
The first aspect of Ming is (Ca_1-xM1_x)₂(Co_1-yG
a _y)₂O_Five(M1: La, Sr or Ba, 0 ≦ x <0.
07, 0.2 ≦ y <0.5)
The thermoelectric conversion material is characterized in that

A second aspect of the present invention is a thermoelectric conversion element characterized by using the thermoelectric conversion material of the first aspect.

The third aspect of the present invention is (Ca _1-p M2 _p ).
₂ (Co _1-q Fe _q ) ₂ O ₅ (M2: La, Sr or Ba,
A thermoelectric conversion material characterized by comprising an oxide represented by 0 ≦ p <0.1, 0.2 ≦ q <1.0).

A fourth aspect of the present invention is a thermoelectric conversion element characterized by using the thermoelectric conversion material of the third aspect.

The present invention relates to Ca _1.95 La _0.05 Co _2-x Al _x
Of Al O ₅ result of replacing the other Group 13 elements, with _{Ga (Ca 1-x La x} ) 2 (Co 1-y Ga y) 2 O 5 is brown mirror light structure (Brownmillerri
It has been completed based on the finding that it has a te structure) and can be stably used even at a high temperature of 500 ° C. or higher and has low toxicity.

Here, (Ca _1-x M1 _x ) ₂ (Co _1-y Ga
An X-ray diffraction diagram for the case where M1 of _y ) ₂ O ₅ is La and the case where M1 does not exist is shown in FIG. As a result, it was confirmed that all had a brown mirror light structure. In addition, Ca ₂ (Co) which is the mother phase of the thermoelectric conversion material of the present invention
_When the behavior of the thermoelectromotive force with respect to the amount of Ga was examined for _2−2y Ga _2y ) O ₅ , the results shown in FIG. 2 were obtained. As a result, in any case, when the temperature rises, the negative thermoelectromotive force (N type) changes to the positive thermoelectromotive force (P type).
It was confirmed that the transition temperature from N to P shifts to the lower temperature side as the amount of is smaller. It was also confirmed that the smaller the Ga, the smaller the electric resistance. On the other hand, when the calcium site is doped with La, carriers are formed and the electric resistance is lowered, but the thermoelectromotive force is lowered as the added amount is increased, so it was confirmed that a small doping amount is preferable. .

Fe was used instead of Ga (Ca
It was confirmed that _1-p M2 _p ) ₂ (Co _1-q Fe _q ) ₂ O ₅ also exhibits a good thermoelectromotive force even at a high temperature by adopting the brown mirror light structure. As described above, the thermoelectromotive force has been confirmed for the very inexpensive FeCo-based base material for the first time, and effective utilization in the future can be expected. It was also confirmed that when the calcium site is doped with La, carriers are formed to lower the electric resistance, but the thermoelectromotive force decreases as the added amount increases, so it is preferable to use a small doping amount. . It should be noted that since similar effects were obtained by doping Sr instead of La in the calcium site, it is expected that similar effects can be obtained by using Ba instead of Sr. Further, when Ga is used, it is expected that similar effects can be obtained by using Sr or Ba instead of La.

The thermoelectric conversion material of the present invention may be oriented in the C-axis direction. As a result, it is expected that the thermoelectric properties are improved due to the physical properties in the parallel and vertical directions of the layers due to the layered structure, particularly the anisotropy of electrical resistivity. Here, the orientation control for orienting in the C-axis direction can be performed by a known method such as a hot pressing method or plasma discharge.

In the thermoelectric conversion material using Ga of the present invention, it is preferable that Ga is equal to or more than the limit amount capable of maintaining the brown mirror light structure and is as small as possible.
Range of 0.2 ≦ y <0.5, preferably 0.2 ≦ y ≦
It is in the range of 0.4. If y is less than 0.2, the brown mirror light structure cannot be stably maintained, while
This is because impurities are precipitated when y is 0.5 or more. On the other hand, the amount of La, Sr, or Ba is 0 ≦ x <0.0.
7 and preferably 0.01 ≦ x ≦ 0.02
Is the range.

On the other hand, in the thermoelectric conversion material using Fe of the present invention, it is preferable that the amount of Fe is large in terms of cost, but 0.2 ≦ q <1.0, preferably q <0.75, and further Preferably q ≦ 0.5. This is because if the amount is larger than this, the crystal form will collapse. On the other hand, the amount of La, Sr or Ba is p <0.1, preferably p <0.075.
Is.

(Ca _1-p M2 _p ) ₂ (Co _1-q Fe _q ) ₂ O ₅
In, when M2 is La, carriers are formed and the electric resistance decreases. When M2 is Ba or Sr, there is no change in the carrier due to direct addition, but Fe exists as divalent and trivalent valences, and the resistance of the matrix itself is lowered.
When the amount of Fe increases, the trivalence of Fe increases, the resistance increases, and the output factor decreases. Therefore, it is desirable that q of Fe be less than 1.0.

By using the thermoelectric conversion material of the present invention described above, a thermoelectric conversion element having excellent thermoelectric characteristics can be constructed. The structure of the thermoelectric conversion element is not particularly limited, and a conventionally known structure can be adopted. For example, a structure for extracting electromotive force from a temperature difference or a structure for cooling or heating as a heat pump by applying electric power is adopted. You can

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below based on Examples, but the present invention is not limited thereto.

(Examples 1 and 2) C having a purity of 99.99%
aCO ₃ , Co ₃ O _{4 with} a purity of 99.9%, purity 99.9
% LaO ₃ , a powder of purity 99.99% Ga ₂ O ₃ ,
_{(Ca 1-x La x)} 2 (Co 1 -y Ga y) of ₂ O ₅ x = 0, y
= 0.25 (Example 1), x = 0, y = 0.35 (Example 2), x = 0.125, y = 0.25 (Example 3), x = 0.025, y = 0.25 (Example 4) and x = 0.05, y = 0.25 (Example 5) were weighed at a mixing ratio (stoichiometric composition), mixed in an agate mortar for about 30 minutes, and then in the air. It was calcined at 1000 ° C. for 12 hours. This is crushed for about 30 minutes in an agate mortar, and about 1.2 g of a sample is molded by a uniaxial pressure molding method, and the molded product is stored in the atmosphere at 105
This was baked at 0 ° C. for 12 hours to obtain a sintered body.

Comparative Example 1 For comparison, x = 0 and y =
0.5 (Comparative Example 1), x = 0.075, y = 0.25
The mixture was weighed at a mixing ratio of (Comparative Example 2), and a sintered body was prepared in the same manner.

(Test Example 1) XRD measurement The sintered bodies of Examples 1 to 4 and Comparative Example 1 were identified by X-ray diffraction. C for MXP ³ manufactured by Mac Science Co., Ltd.
u target was used. The measurement conditions were as follows.

Measuring range: 5.0 to 60.6 deg Sampling interval: 0.02 deg Scan speed: 3.0 / min Measurement method: Normal method (without BG measurement) Generated voltage: 40 kV Generated current: 30mA Divergence slit: 1.0 deg Scattering slit: 1.0 deg Emitting slit: 0.15mm The result is shown in FIG.

As a result, it was confirmed that all of Examples 1 to 4 had the brown mirror light structure.
It was confirmed that when y was as large as y = 0.5 (Comparative Example 1), a single phase could not be obtained.

(Test Example 2) Examples 3 to 5 and Comparative Example 2
The temperature dependence of the thermoelectromotive force (Seebeck coefficient) of the sintered body was measured as follows.

(T <300K) A sample cut out was fixed with silver paste so as to straddle two copper plates, and while gradually cooling from room temperature with liquid helium, one end of the sample was heated by a heater on the copper plate on one side. A temperature difference ΔT (about 5 K) was applied to the sample, and the electromotive force at that time was read and measured. Cu was used for the measurement line, Cu-Ct for the thermocouple, a Cernox thermometer for the thermometer, and a strain gauge for the heater.

(T> 300K) A heater is placed on one side of the tubular furnace, and the temperature difference Δ across the sample is utilized by utilizing the temperature gradient of the entire furnace.
Except for adding T (about 20K), the procedure was almost the same as for T <300K.

The results are shown in FIG. As a result, it was found that the Seebeck coefficient tends to decrease as the content of La increases, and the amount of La added is limited to about y = 0.07. In Comparative Example 2 in which y = 0.075,
Although an X-ray diffraction diagram is not shown, it is also known that the phase is not a single phase and a brown mirror crystal structure cannot be obtained stably.

(Test Example 3) With respect to the sintered bodies of Examples 3 to 5, the temperature dependence of the electrical resistivity was measured by the DC four-terminal method. The result is shown in FIG.

From these results, it was confirmed that the electrical resistivity was smaller as the amount of La added was smaller.

Test Example 4 The results of measuring the temperature dependence of the output factor for the sintered bodies of Examples 3 and 4 are shown in FIG. The output factor was calculated by P = α ² / ρ.

(Examples 6 to 8) Ca having a purity of 99.99%
CO ₃ , Co ₃ O _{4 with} a purity of 99.9%, purity 99.99
% Fe ₂ O ₃ powder to (Ca _1-p La _p ) ₂ (Co _1-q Fe
_q ) ₂ O ₅ p = 0, q = 0.375 (Example 6), p =
0, q = 0.5 (Example 7), p = 0, q = 0.75
(Example 8) was weighed at a mixing ratio (stoichiometric composition),
Mix in an agate mortar for about 30 minutes, and in air at 1000 ° C for 1
It was calcined for 2 hours. This was crushed for about 30 minutes in an agate mortar, and a sample of about 1.2 g was molded by a uniaxial pressure molding method, and the molded product was baked in the air at 1100 ° C. for 12 hours to obtain a sintered body.

Comparative Example 3 For comparison, p = 0 and q =
The mixture was weighed at a mixing ratio of 1.0 (Comparative Example 3), and a sintered body was prepared in the same manner.

(Examples 9 to 12) C having a purity of 99.99%
aCO ₃ , Co ₃ O _{4 with} a purity of 99.9%, purity 99.9
% LaO ₃ , powder of purity 99.99% Fe ₂ O ₃ ,
(Ca _1-p La _p ) ₂ (Co _{1 -q} Fe _q ) ₂ O ₅ p = 0.0
125, q = 0.5 (Example 9), p = 0.025, q
= 0.5 (Example 10), p = 0.0375, q = 0.
5 (Example 11) and p = 0.05 and q = 0.5 (Example 12) were weighed at a mixing ratio (stoichiometric composition), mixed in an agate mortar for about 30 minutes, and then 1000 ° C. in the atmosphere. It was calcined for 12 hours. This is crushed in an agate mortar for about 30 minutes, and a sample of about 1.2 g is molded by a uniaxial pressure molding method.
The molded product was fired in the air at 1100 ° C. for 12 hours to obtain a sintered body.

(Examples 13 and 14) CaCO _{3 having} a purity of 99.99%, Co ₃ O _{4 having} a purity of 99.9%, and a purity of 99.
Powder of 9% SrCO ₃ and purity 99.99% Fe ₂ O ₃ was added to (Ca _1-p Sr _p ) ₂ (Co _1-q Fe _q ) ₂ O ₅ with p =
0.0125, q = 0.5 (Example 13), p = 0.0
25, q = 0.5 (Example 14) were weighed at a mixing ratio (stoichiometric composition), mixed in an agate mortar for about 30 minutes, and calcined in the air at 1000 ° C. for 12 hours. This is crushed in an agate mortar for about 30 minutes, and about 1.2 g of a sample is molded by a uniaxial pressure molding method, and the molded product is subjected to 1 atmosphere at 1100 ° C. for 1 minute.
It was fired for 2 hours to obtain a sintered body.

(Test Example 5) XRD Measurement The sintered bodies of Examples 6 to 14 and Comparative Example 3 were identified in the same manner as in Test Example 1. The results are shown in FIGS.

As a result, it was confirmed that all of Examples 6 to 14 had a brown mirror light structure.
It was confirmed that when e was as large as q = 1.0 (Comparative Example 3), the brown mirror light structure could not be obtained.

(Test Example 6) With respect to the sintered bodies of Examples 6, 7 and 9 to 14, the temperature dependence of the thermoelectromotive force (Seebeck coefficient) was measured in the same manner as in Test Example 2.

The results are shown in FIGS. As a result, it was found that the thermoelectromotive force increased as the Co was replaced with Fe. Moreover, when the content of La in the Ca site increases, the Seebeck coefficient tends to decrease, but S
It was found that when r was added, a thermoelectromotive force equivalent to that when not added was exhibited.

(Test Example 7) With respect to the sintered bodies of Examples 6, 7 and 9 to 14, the temperature dependence of the electrical resistivity was measured by the DC four-terminal method. The results are shown in FIGS.

From these results, it was found that the electric resistivity was smaller when the Fe substitution amount was smaller. In addition, when the calcium site is replaced, the electrical resistivity becomes La at high temperature.
Alternatively, it was confirmed that the smaller the added amount of Sr, the smaller the amount.

(Test Example 8) Examples 7, 9, 13 and 14
15 and 16 show the results of measuring the temperature dependence of the output factor for the sintered body of No. 1. The output factor is P = α ²
Calculated by / ρ.

[0057]

As described above, according to the present invention,
A thermoelectric conversion material and a thermoelectric conversion element that can be stably used even at a high temperature of 500 ° C. or higher and have low toxicity can be provided.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction diagram of thermoelectric conversion materials according to Examples and Comparative Examples of the present invention.

FIG. 2 is a diagram showing temperature dependence of thermoelectromotive force of the thermoelectric conversion material according to the present invention.

FIG. 3 is a diagram showing thermoelectromotive force of thermoelectric conversion materials according to Examples and Comparative Examples of the present invention.

FIG. 4 is a diagram showing temperature dependence of electric resistivity of thermoelectric conversion materials according to examples of the present invention.

FIG. 5 is a diagram showing temperature dependence of an output factor of a thermoelectric conversion material according to an example of the present invention.

FIG. 6 is an X-ray diffraction diagram of thermoelectric conversion materials according to Examples and Comparative Examples of the present invention.

FIG. 7 is an X-ray diffraction diagram of a thermoelectric conversion material according to an example of the present invention.

FIG. 8 is an X-ray diffraction diagram of a thermoelectric conversion material according to an example of the present invention.

FIG. 9 is a diagram showing temperature dependence of thermoelectromotive force of thermoelectric conversion materials according to examples of the present invention.

FIG. 10 is a diagram showing temperature dependence of thermoelectromotive force of thermoelectric conversion materials according to examples of the present invention.

FIG. 11 is a diagram showing temperature dependence of thermoelectromotive force of thermoelectric conversion materials according to examples of the present invention.

FIG. 12 is a diagram showing the temperature dependence of the electrical resistivity of the thermoelectric conversion material according to the example of the present invention.

FIG. 13 is a diagram showing the temperature dependence of the electrical resistivity of the thermoelectric conversion material according to the example of the present invention.

FIG. 14 is a diagram showing temperature dependence of electric resistivity of thermoelectric conversion materials according to examples of the present invention.

FIG. 15 is a diagram showing the temperature dependence of the output factor of the thermoelectric conversion material according to the example of the present invention.

FIG. 16 is a diagram showing the temperature dependence of the output factor of the thermoelectric conversion material according to the example of the present invention.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Touki Ueno             2-3-3 Shirate, Tsurumi-ku, Yokohama-shi, Kanagawa               Hokushin Industry Co., Ltd.

Claims (4)

[Claims] [Claim 1] _{(Ca 1-x M1 x)} 2 (Co 1-y Ga y) 2 O
₅ (M1: La, Sr or Ba, 0 ≦ x <0.07,
A thermoelectric conversion material comprising an oxide represented by 0.2 ≦ y <0.5). 2. A thermoelectric conversion element comprising the thermoelectric conversion material according to claim 1. 3. (Ca _1-p M2 _p ) ₂ (Co _1-q Fe _q ) ₂ O
₅ (M2: La, Sr or Ba, 0 ≦ p <0.1, 0.
A thermoelectric conversion material comprising an oxide represented by 2 ≦ q <1.0). 4. A thermoelectric conversion element comprising the thermoelectric conversion material according to claim 3.