JP2000012914A - Thermoelectric conversion material and thermoelectric conversion element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermoelectric conversion material and a thermoelectric conversion element, having improved characteristics by doping a compound oxide represented by a specific element composition formula with respect to Zr. SOLUTION: This thermoelectric conversion material is one kind of compound oxide and it has a composition formula of Nd2CuO4, and furthermore it is a thermoelectric conversion material doped with Zr and its general formula is (Nd1-xMx)2CuO4 (M=Zr, 0<x<=1). The compound oxide doped with Zr can be produced in the same manner as those for various kinds of compound oxide. Namely, it can be obtained by mixing element sources necessary for the compound oxide doped with the element and baking the mixture. The Seebeck factor of a sample doped with Zr is about -160 μV/K at around a doping amount of 5% (x=0.05) and although it becomes slightly higher at the doping amount of 10% (x=0.10) than that of (Nd1-xMx)2CuO4 (x=0), an improvement over the basic composition of Nd2CuO4 is made.

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 and a thermoelectric conversion element, and more specifically, to an element composition formula Nd _2.
Zr or Pr with respect to the composite oxide represented by CuO ₄
TECHNICAL FIELD The present invention relates to a thermoelectric conversion material and a thermoelectric conversion element whose characteristics are improved by doping.

[0002]

2. Description of the Related Art Thermoelectric power generation (thermoelectric power generation) is based on the Seebeck effect, that is, two different metals or different thermoelectric conversion materials such as a p-type semiconductor and an n-type semiconductor are thermally placed in parallel and electrically connected in series. Is a technology that directly converts heat energy into electric power using the thermoelectric effect that generates a thermoelectromotive force at both ends when a temperature difference is applied between the junctions, and this technology is used for power supplies for remote areas, power supplies for space, It has been put to practical use as a military power supply.

[0003] FIG. 1 is a schematic diagram for explaining in principle one embodiment of the thermoelectric conversion element, in which an n-type semiconductor and a p-type semiconductor are combined as a thermoelectric conversion material. FIG.
Among them, 1 is a p-type semiconductor, 2 is an n-type semiconductor, 3 is a high temperature side junction, and 4 is a low temperature side junction. Q indicates a high-temperature heat source, Th indicates a high-temperature side temperature, Tc indicates a low-temperature side temperature, and S indicates an insulating space. As shown in the drawing, the high-temperature side electrode 5 is commonly provided at the high-temperature side joint, and the low-temperature side electrodes 6 and 7 are separately provided at the low-temperature side joint. In the thermoelectric conversion element of this aspect,
The temperature difference ΔT between the high-temperature side junction 3 and the low-temperature side junction 4
When Th-Tc is applied, a voltage is generated between both electrodes (between 5 and 6 and 7). Therefore, when a load (R) is connected between both electrodes 6 and 7 on the low temperature side, a current (I) flows and can be taken out as electric power (W).

[0004] By the way, the materials themselves used for the above-mentioned thermoelectric conversion elements have been PbTe-based, B-
There are many reports such as i ₂ Te ₃ system, CoSb ₃ system, Si—Ge system, and FeSi ₂ system. Recently, research and studies have been made on composite oxide-based thermoelectric conversion element materials. One of them is a report on a sintered body of Nd ₂ -x Ce _x CuO ₄ (x = 0 to 0.1). Yasukawa Gaito (1) "Powder and Powder Metallurgy," Vol. 44, No. 1, January 1997, 50-53
page〕.

[0005] Nd ₂ CuO ₄ -based materials are known as a kind of high-temperature copper-based superconductor, but when doped with Ce, electron carriers are introduced, and the doping amount increases to change the insulator to the semiconductor. , And even metal. In the above report, the thermoelectric performance of Ce-doped Nd ₂ CuO ₄ is measured, but there is a drawback that the Seebeck coefficient is greatly reduced due to an increase in the doping amount.

[0006]

SUMMARY OF THE INVENTION The present inventors have found that Nd ₂
Experiments and investigations on CuO ₄ -based composite oxide revealed that Nd ₂ CuO ₄ doped with zirnium (Zr) or praseodymium (Pr) has a higher Seebeck coefficient than that doped with Ce. It has also been found that the material has useful properties as a thermoelectric conversion material and a thermoelectric conversion element. That is, the present invention provides Nd
It is an object of the present invention to provide a thermoelectric conversion material obtained by doping Zr or Pr into a ₂ CuO ₄ -based composite oxide, and a thermoelectric conversion element using the thermoelectric conversion material.

[0007]

The present invention provides (1) a thermoelectric conversion material characterized in that a composite oxide represented by the elemental compositional formula Nd ₂ CuO ₄ is doped with Zr. The present invention provides (2) a thermoelectric conversion material obtained by doping a composite oxide represented by the elemental composition formula Nd ₂ CuO ₄ with Pr, and the present invention further provides (3) the above (1) And (2) to provide a thermoelectric conversion element characterized by using the thermoelectric conversion material.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The thermoelectric conversion material of the present invention is one kind of composite oxide, has a composition represented by the basic formula Nd ₂ CuO ₄ , and is doped with Zr or Pr. , and the represented as the general formula _{(Nd 1-X M X)} 2 CuO 4 (M = Zr or Pr, 0 <x ≦ 1) . The composite oxide doped with Zr or Pr in the present invention can be produced in the same manner as when producing various composite oxides.

That is, it is obtained by uniformly mixing raw materials containing an element source necessary for a composite oxide doped with these elements as powders and the like, followed by firing. The firing temperature is about 8
50 to 1150 ° C., preferably 1100 to 115
It is in the range of 0 ° C. It should be noted that since the sintering is performed in this manner, the element-doped composite oxide of the present invention obtained through this step can be said to be a type of ceramic. When the composite oxide doped with these elements is formed as a dense sintered body, it can be synthesized by, for example, a hot press method of heating under a uniaxial pressure of several hundred atmospheres. Further, when the composite oxide doped with these elements is constituted as a single crystal, the composite oxide can be produced by melting the raw material mixture and growing the melt while cooling it gradually.

As the raw material used for producing the composite oxide doped with the specific element according to the present invention, each constituent element, an oxide of each constituent element, or a raw material which becomes an oxide when fired is used. As the Nd source, for example, metal
(Nd), oxide (Nd ₂ O ₃ ), hydroxide [Nd (OH)
₃ etc.), oxyacid salts [Nd ₂ (CO ₃ ) ₃ , Nd (NO ₃ ) ₃ etc.],
Halides (NdCl ₃ , NdBr ₃ , NdI ₃ etc.),
Sulfide (Nd ₂ S _3, etc.), organic salt Nd ₂ (C ₂ O ₄ ) _3, etc.] are used. As the Cu source, for example, metal (Cu), oxide (Cu ₂ O, CuO, etc.), hydroxide [Cu (OH)
₂ etc.), oxyacid salts (Cu ₂ CO ₃ , CuCO ₃ , CuSO ₄
Etc.), halides (CuCl ₂ , CuCl, CuI)
Sulfides (Cu ₂ S, CuS, etc.), organic acid salts [Cu
(CH ₃ CO ₂ ) ₂ .H ₂ O etc.].

Examples of the Zr source include metals (Zr), oxides (ZrO _2, etc.), organic acid salts [Zr (CH ₃ CO ₂ ) ₄ ],
Halides (ZrCl _3, ZrCl _4), such as oxyhalides (ZrOCl ₂ · 8H ₂ O, etc.) are used. P
Examples of the r source include metal (Pr) and oxide (Pr).
₂ O ₃ ), hydroxide [Pr (OH) ₃ etc.], oxyacid salt [P
r ₂ (CO ₃ ) ₃ , Pr ₂ (NO ₃ ) ₃ etc.], halides (PrCl ₃ , PrBr ₃ , PrI ₃ etc.), sulfides (Pr ₂ S
₃ ) and organic salts [Pr ₂ (C ₂ O ₄ ) ₃ etc.].

The Seebeck coefficient of the Zr- or Pr-doped composite oxide according to the present invention is large, and is much larger than that of the Ce-doped composite oxide. The Zr- or Pr-doped composite oxide according to the present invention, that is, the power factor of the thermoelectric conversion material is equal to or higher than the Ce-doped composite oxide. Further, in the composite oxide of the present invention, the electrical conductivity is improved by doping Zr or Pr.

As the thermoelectric conversion material, the larger the Seebeck coefficient is, the better the electric resistivity is.
Although the power factor is preferably large, the composite oxide of the present invention improves these characteristics by doping Zd or Pr with respect to the basic composition Nd ₂ CuO ₄ . The thermoelectric conversion material of the present invention is improved in each of these properties as compared with the basic composite oxide Nd ₂ CuO ₄ (which is itself an excellent thermoelectric conversion material) depending on the type of the doping element.

In the present invention, Zr-doped Nd ₂ C
Using a thermoelectric conversion material composed of uO ₄ and Pr-doped Nd ₂ CuO _{4, an} electromotive force is extracted from the temperature difference, or conversely, power is applied to constitute a thermoelectric conversion element used for cooling or heating as a heat pump. The thermoelectric conversion element can be configured in the same manner as a conventional mode in which a thermoelectric conversion element is formed using a thermoelectric conversion material.
Since the thermoelectric conversion material of the present invention is an n-type semiconductor, it is used, for example, as an n-type semiconductor in a thermoelectric conversion element as shown in FIG. In particular, Zr is not a rare earth, the material cost is relatively inexpensive, it is advantageous in terms of supply and cost, and an excellent practical advantage is obtained. It goes without saying that Pr can be effectively applied depending on the production situation and the like.

[0015]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but it goes without saying that the present invention is not limited to these Examples. In this example, first, composite oxides doped with various elements were manufactured, and various performance tests were performed. Here, the doping amount x of Zr or Pr is shown in the range of 0 to 0.1, but the same applies to the case of 0.1 or more.

<< Production Example >> Zr-doped composite oxide in which Zr is added in various amounts to Nd in the basic composition Nd ₂ CuO ₄ : (Nd _{1 -X} Zr _x ) ₂ CuO ₄ (x = 0. 1) was produced as follows. Nd ₂ O ₃ , CuO and ZrO ₂ powders having a purity of 99.9% or more were used as raw materials. These three kinds of raw material powders are represented by a composition formula (Nd _{1 -X} Zr _X ) ₂ Cu
Zr such that O ₄ and x = 0 to 0.10.
Was weighed so as to have a composition to which was added, ethanol was added as a solvent, and the mixture was uniformly wet-mixed in a mortar.

The obtained mixed powder was placed in an alumina crucible and calcined in an air atmosphere at a temperature of 800 ° C. for 10 hours.
The heating rate was 5 ° C./min. After the calcined sample was pulverized and mixed again, 3 wt% of the calcined powder was added as a binder to the obtained powder, mixed, and formed into a 7 × 25 × about 2 mm strip by a uniaxial press. The pressing pressure at the time of uniaxial pressing was 750 kg / cm ² . Thereafter, each sample was placed in an alumina crucible and fired at a temperature of 1100 ° C. for 10 hours (in the atmosphere) to obtain each sample.

A Pr-doped composite oxide obtained by adding Pr to Nd in the basic composition Nd ₂ CuO ₄ in the same manner as described above: (Nd _{1 -X} Pr _x ) ₂ CuO ₄ (x = 0 to 0.1) Was produced as follows. Nd ₂ O ₃ , CuO and Pr ₂ O ₃ powders having a purity of 99.9% or more were used as raw materials.
These three kinds of raw material powders are represented by the composition formula (Nd _{1 -X} Pr _x ) ₂ CuO ₄
Then, the composition was weighed so as to have a composition to which Pr was added so that x = 0 to 0.10 in the formula, ethanol was added, and the mixture was uniformly mixed in a mortar. The obtained mixed powder is calcined and fired in the same manner as described above to obtain a composition (Nd _{1 -X} Pr _x ) ₂ CuO ₄ (x =
0 to 0.10) were obtained.

In the same manner as above, a Ce-doped composite oxide in which Ce is added to Nd in the composition Nd ₂ CuO ₄ : (Nd ₁ -x Ce _x ) ₂ CuO ₄ (x = 0 to 0.1) It was manufactured as follows. Nd ₂ O ₃ , CuO and CeO ₂ powders having a purity of 99.9% or more were used as raw materials.
These three kinds of raw material powders are represented by a composition formula (Nd _{1 -X} Ce _X ) ₂ CuO ₄
And Ce was added so that x = 0 to 0.10 in the formula, and ethanol was added, and the mixture was uniformly mixed in a mortar. The obtained mixed powder is calcined and fired in the same manner as described above to obtain a composition (Nd _{1 -X} Ce _x ) ₂ CuO ₄ (x =
0 to 0.10).

<< Evaluation Test >> An evaluation test was performed on each of the samples obtained in the above Production Examples. X for each sample
Formula by a line diffraction _{(Nd 1-X M X)} 2 CuO 4 (M = Z
r, Pr or Ce, 0 <x ≦ 0.10) was confirmed to be obtained, and then Seebeck coefficient,
The electrical resistivity and figure of merit were measured.

<Change in Seebeck coefficient due to dope> The measurement of the Seebeck coefficient was performed as follows. While the sample fired in the shape of a strip as described above was placed in an electric furnace and heated to a predetermined temperature, only the lower end of the sample was separately heated.
This causes a temperature difference of about 5 ° C. between the upper end and the lower end of the sample, and a thermoelectromotive force is generated. The Seebeck coefficient is determined by measuring the electromotive force with a voltmeter and dividing the value by the temperature difference.

FIG. 2 shows Zr, Pr, C
The change in the Seebeck coefficient of each sample doped with e was measured. FIG. 2 shows, as a reference, Nd ₂ CuO ₄ (x = 0.00 in FIG. 2) obtained in the same manner as in the above production example.
) Is also shown, but the basic composite oxide Nd ₂ CuO ₄ itself is a material having thermoelectric conversion characteristics. As shows the unit of Figure 2 in the Seebeck coefficient as _{-μV / K, (Nd 1-} X M X) 2 CuO 4 (x = 0~0.1
0, M = Ce, Pr or Zr) is a composite oxide exhibiting n-type conductivity (a higher absolute value means, for example, that the output voltage becomes higher when thermoelectric power generation is performed using the composite oxide). Do).

As shown in FIG. 2, the Seebeck coefficient of a sample obtained by doping Ce with respect to the basic composition Nd ₂ CuO ₄ decreases as the Ce doping amount increases.
% Or more (x ≧ 0.07), the measured thermoelectromotive force was not reproducible, and the Seebeck coefficient could not be measured. On the other hand, the Seebeck coefficient of the sample doped with Pr only slightly decreases with an increase in the doping amount as compared with the case of the basic composition Nd ₂ CuO ₄ (x = 0.00 in FIG. 2). .

The Seebeck coefficient of the Zr-doped sample is -160 near the doping amount of 5% (x = 0.05).
It is about μV / K, but it is gradually improved thereafter, and when the doping amount is 10% (x = 0.10), (Nd _1−X M _X ) ₂ CuO
₄ (x = 0) but slightly higher than the basic composition Nd ₂
It can be seen that CuO _{4 is} also improved. As described above, the decrease in the Seebeck coefficient due to the doping of Zr and Pr is small, and shows better characteristics as compared with the Ce doping.

FIG. 3 is a graph showing the temperature dependence of the Seebeck coefficient of a sample composite oxide of (Nd _0.95 Zr _0.05 ) ₂ CuO ₄ as a representative example of the temperature dependence of the sample composite oxide. As shown, -160μ at room temperature
V / K, which gradually decreases thereafter, but has a value of -70 μV / K even in a high temperature range of, for example, 440 ° C., which indicates that it is effective.

<Change in Electric Resistivity Due to Doping> The electric resistivity was measured by a DC four-probe method on a sample fired in a strip shape. The four-probe method uses the same principle as the DC four-terminal method, in which four needles are abutted and arranged at equal intervals on a strip-shaped sample, a constant current is applied to the two outer needles, and the inner two The potential difference between the needles is measured. The resistivity ρ of the sample is given by ρ = C (V / I) from the measured current I and voltage V (where C is a correction factor and is a constant determined by the shape of the sample). . FIG. 4 shows the result.

As shown in FIG. 4, the electrical resistivity of a sample obtained by doping Zr with the basic composition Nd ₂ CuO ₄ decreases as the doping amount increases, and when x = 0.05, the resistivity becomes about 50 mΩ · cm.
, And thereafter shows almost the same value until x = 0.10, and thus such an excellent improvement effect is recognized. The electrical resistivity of a sample obtained by doping Pr with respect to the basic composition Nd ₂ CuO _{4 is} that of the basic composition Nd up to about x = 0.05.
It is almost equivalent to d ₂ CuO ₄ , but x =
It is greatly improved up to 0.10.

<Change in power factor due to doping>
FIG. 5 shows the power factor [PF = S ² /
ρ (S = Seebeck coefficient, ρ = electrical resistivity)]. In the case of the basic composite oxide Nd ₂ CuO ₄ , which is about 0.5 × 10 ⁻⁸ W / mK ² , Zr
Is gradually improved by doping, and 10 ^-4 W is added by adding 5%.
/ mK ² , and almost the same value thereafter.
Also, when Pr is doped, it increases with the doping amount.

As can be seen from the above measurement results, in the present invention, the basic composition Nd ₂ CuO _{4 is} compared with Zr or Pd.
In the composite oxide doped with r, the decrease in the Seebeck coefficient is small and the electric resistivity is reduced, so that the power factor is improved. Therefore, although there is a difference depending on the type of the doping element, it is clear that all are effective materials as thermoelectric conversion materials.

[0030]

The composite oxide according to the present invention obtained by doping Zd or Pr with the basic composition Nd ₂ CuO ₄ has excellent properties as a thermoelectric conversion material and is suitable for use in thermoelectric conversion elements. Applicable. Further, the thermoelectric conversion material of the present invention has no or low toxicity, is safe, and particularly in the case of Zr, the material cost is relatively low, and it is advantageous in terms of supply and practical use. For this reason, various advantages are obtained, such as being applicable as a thermoelectric conversion element for consumer use.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining in principle one embodiment of a thermoelectric conversion element.

FIG. 2 is a diagram showing a change in Seebeck coefficient of a sample composite oxide due to doping of each element.

FIG. 3 is a diagram showing the temperature dependence of the Seebeck coefficient of a sample composite oxide of (Nd _0.95 Zr _0.05 ) ₂ CuO ₄ .

FIG. 4 is a diagram showing a change in electric resistivity of a sample composite oxide due to doping of each element.

FIG. 5 is a diagram showing a change in power factor due to doping of each element in a sample composite oxide.

[Explanation of symbols]

 Reference Signs List 1 p-type semiconductor 2 n-type semiconductor 3 high-temperature side junction 4 low-temperature side junction 5 high-temperature side electrode 6, 7 low-temperature side electrode S insulating space

Continued on the front page (72) Inventor Hisakataka Yakabe 2-17-1 Midori, Sumida-ku, Tokyo Urban Heights Ryogoku No.911

Claims (3)

[Claims] 1. A thermoelectric conversion material characterized in that a composite oxide represented by an elemental composition formula Nd ₂ CuO ₄ is doped with Zr. 2. A thermoelectric conversion material characterized in that a composite oxide represented by the elemental composition formula Nd ₂ CuO ₄ is doped with Pr. 3. A thermoelectric conversion element comprising the thermoelectric conversion material according to claim 1 or 2.