JPH0964422A - N-type thermoelectric material and thermoelectric effect element using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an n-type thermoelectric material a having a high efficiency and small global environmental load by adding a platinum of the ratio of a specific range to compound of CoSb3 . SOLUTION: The n-type thermoelectric material is formed of solid solution represented by the composition formula of Co1-x Ptx Sb3 (0.005<=x<=0.10). The thermoelectric effect element has the structure that the n-type thermoelectric material made of solid solution represented by the composition formula of Co1-x Ptx Sb3 (0.005<=x<=0.10) and p-type thermoelectric material made of solid solution represented by Pb1-y Nay Te (0.01<=y<=0.10) are electrically connected directly to one another or via a conductor. Further, it has the structure that n-type thermoelectric material made of solid solution represented by the composition formula of Co1-x Ptx Sb3 (0.005<=x<=0.10) and p-type thermoelectric material made of PbTe compound added with 0.5 to 5mol% of Ag2 Te are electrically connected directly to one another or via a conductor.

Description

_{Description: FIELD OF THE INVENTION The present invention uses the thermoelectric effect.
Thermoelectric effect element for power generation, cooling and heating, and for it
It relates to existing thermoelectric materials. [0002] Conventionally, when an electric current is passed through a thermoelectric material,
In contrast to the Peltier effect, which is an endothermic and exothermic action, inside the thermoelectric material
Generation of thermoelectromotive force when there is a temperature difference between
Considering many cooling devices and power generators using the Beck effect
Is being proposed. Seebeck effect is the so-called thermoelectromotive force
It is the occurrence of
To be joined to each other and kept at different temperatures at both ends.
Power is
This is a phenomenon that occurs. The value of the generated thermoelectromotive force is V, 2 junctions
If the temperature difference between the parts is T, the Seebeck coefficient S is
It is represented by. S [V / K] = dV / dT This Seebeck coefficient shows the thermoelectromotive force per 1 degree of temperature.
It is something. On the other hand, the Peltier effect is similar to the Seebeck effect.
On the contrary, by passing an electric current
Generation of heat other than heat and endotherm are recognized. this
If the amount of heat generated or absorbed in a unit time is Q,
Letting the current through the junction be I, the Peltier coefficient П is
To be done. П [V] = Q / I = S · T [0004] The magnitude of these so-called thermoelectric effects is
Seebeck coefficient S, electrical conductivity σ and
And the thermal conductivity λ. The figure of merit ZZ [K} -1 _{] = S} 2 _{· σ / λ is calculated in the case of power generation (when used as a Seebeck element).
It corresponds to the ratio of power generation to heat input, that is, power generation efficiency.
For cooling (when used as a Peltier device),
It is closely related to the ratio of heat absorption to air input. You
That is, as a thermoelectric material, the conductivity σ is large and
A material having a small rate λ is desired. The figure of merit Z is p-type
In the case of thermoelectric material, it shows a positive value, and in the case of n-type thermoelectric material
Indicates a negative value. Used as Seebeck element of power generator
If you want to make a large temperature difference between the high temperature side and the low temperature side
Since it is more advantageous, the absolute temperature T [K] is set to the figure of merit Z.
Multiplied Z · T is used as an index showing the performance of thermoelectric materials
In many cases. Further, it is actually used as a Seebeck element.
In some cases, the temperature difference between the high temperature side and the low temperature side may be
Since it can be handled by other means, the thermal conductivity from the figure of merit Z
The power factor, which is the value excluding λ, is generally used.
ing. Power factor = S} 2 _{· σ = Z · λ [0006] FIG. 9 shows a well-known thermoelectric material.
Among them, the figure of merit of the n-type material is expressed with respect to temperature. In the figure
, | Z | · T are 1.0 and 2.0, and the figure of merit is shown by the broken line.
The upper right corner for power generation, the better heat
It is an electronic material. Specifically, Bi 2 for low temperature to room temperature}
Te ₃ based material is preferable, and PbTe based material is promising for medium temperature use and SiGe based material is promising for high temperature use. In order to make an effective thermoelectric effect element, it is necessary to electrically bond p-type and n-type thermoelectric materials in series. For example, in a FeSi ₂ -based material known as a thermoelectric material for medium temperature, part of Fe is M
A p-type thermoelectric material substituted with n, and an n also substituted with Co
It has a structure in which an n-type thermoelectric material and a p-type thermoelectric material are bonded to each other directly or via a conductor. By disposing such a thermoelectric effect element around the exhaust heat pipe of a chemical plant, for example, the exhaust heat can be recovered as electricity as a Seebeck element. However, the exhaust heat recovery technology using the Seebeck element and the cooling technology using the Peltier element are limited to special applications because the efficiency of the element is low. Therefore, further efficiency improvement is desired for widespread use. Further, these thermoelectric materials mainly use highly toxic heavy metals such as Te, Se, Pb and Bi, and in view of the recent growing interest in global environmental protection, materials with little environmental impact. It is requested to switch to. The n-type thermoelectric material of the present invention is Co _1-x Pt _x Sb ₃ (0.005 ≦ x ≦ 0.10)
It is composed of a solid solution represented by the following composition formula. In this way, by adding 0.5 to 10 mol% of platinum to the compound CoSb ₃ , an n-type thermoelectric material with high efficiency and low environmental load is obtained. The thermoelectric effect element of the present invention comprises Co _1-x Pt _x Sb ₃ (0.005 ≦ x ≦
0.10), an n-type thermoelectric material comprising a solid solution represented by the composition formula, and Pb _1-y Na _y Te (0.01 ≦ y ≦ 0.10)
The p-type thermoelectric material composed of a solid solution represented by the above has a structure in which it is electrically connected directly or through a conductor. Further, Co _1-x Pt _x Sb ₃ (0.005 ≦ x
≦ 0.10) n-type thermoelectric material composed of a solid solution represented by the composition formula, and Pb containing 0.5 to 5 mol% of Ag ₂ Te.
It has a structure in which a p-type thermoelectric material made of a Te compound is electrically joined directly or through a conductor. Further, Co _1-x Pt _x Sb ₃ (0.005 ≦ x ≦ 0.
The n-type thermoelectric material composed of the solid solution represented by the composition formula of 10) and the p-type thermoelectric material composed of the compound represented by Ag _0.15 Ge _0.85 Sb _0.15 Te _1.15 are electrically bonded directly or via a conductor. It has a different structure. With these, it is possible to obtain a thermoelectric effect element having high efficiency in a high temperature range from room temperature to 700 ° C. BEST MODE FOR CARRYING OUT THE INVENTION [Example 1] The n-type thermoelectric material of the present invention will be described below. As an n-type thermoelectric material, Co _1-x Pt _x Sb ₃ (x
= 0.01, 0.02, 0.05, 0.10) was produced by the following method. First, a Co powder having a purity of 99.9% or more (particle size 1 to 2 μm), an Sb powder having a purity of 99.9% or more (average particle size 100 μm), and a purity of 99.9.
% Of Pt powder (average particle size 50 μm) is mixed in a predetermined amount. However, since Sb has a lower melting point and a higher vapor pressure than Co, it is dissipated as vapor during the subsequent melting and alloying. It was found that the amount of dissipation was 3% of the total amount of Sb in the alloying at 1200 ° C. performed in this example, although it depends on the alloying temperature condition. A powder added in 3% excess was used.
Put the above mixed powder in a porcelain crucible and
After heating and melting at 1200 ° C. for 3 hours in an Ar gas flow of 00 ml / min, the mixture was gradually cooled to 800 ° C.
Heat treatment was performed for 0 hours. This heat treatment is performed in the β phase C immediately after solidification.
This is a treatment for turning a mixture of oSb and Sb into a CoSb ₃ phase. FIG. 1 is an X-ray diffraction pattern of a powder method of CoSb ₃ in which 2% of Co is replaced by Pt (Co _0.98 Pt _0.02 Sb ₃ ). The change in cubic lattice constant was traced from the X-ray diffraction pattern, but no formation of a subphase was observed, and most of it was a CoSb ₃ phase.
No change in the crystal structure due to Pt substitution was confirmed.
FIG. 2 shows the crystal structure of the thermoelectric material of the present invention in which Co of CoSb ₃ is replaced with Pt. In pure CoSb ₃ , Co atoms exist at the positions of black circles.
By alloying with Pt added, Co atoms at arbitrary locations are replaced with Pt atoms. The obtained Pt-added CoSb ₃ was added with a particle size of 10 μm.
2000 kgw per 1 cm ² pulverized to m or less and polyvinyl butyral added as a binder
By press molding to obtain drum-shaped pellets having a diameter of 20 mm and a thickness of about 2 mm. This pellet is again in Ar for 750
It was treated at 4 ° C. for 4 hours and sintered. The filling rate of the pellets was about 75%. The conductivity of the pellets thus obtained was measured by the DC 4-terminal method. Further, a Seebeck coefficient was obtained from the slope of the thermoelectromotive force with respect to the temperature difference by gradually making a temperature difference within 5 ° C. inside the pellet. The thermal conductivity was measured using the laser flash method. FIG. 3 is a graph showing the Pb substitution amount dependency of Seebeck coefficient and conductivity at 25 ° C. (298K). In the figure, the characteristic values of the conventional Bi ₂ Te ₃ are shown by white diamonds, and the power factor value is Bi _{2 at} any point on the straight line.
It is the same as Te ₃ . According to this, CoSb ₃
When the Pt substitution amount of Co of is increased, the Seebeck coefficient is decreased, but the conductivity tends to be increased. P of Co
When the t substitution amount is 2 to 10%, the power factor shows a substantially constant value, which is the same level as Bi ₂ Te ₃ .
When the Pt substitution amount of Co exceeds 10%, the conductivity is improved, but the Seebeck coefficient is remarkably lowered and the power factor is lowered. From the X-ray analysis and the observation of the microstructure by a microscope, it was found that the Pt solid solution limit was exceeded and undissolved Pt was precipitated in these compositions. Further, when the Pt substitution amount of Co is less than 2%, the conductivity is greatly decreased, and the power factor is slightly decreased. However, when the Pt substitution amount is up to 0.5%, the decrease in the power factor is only up to 30%, which is promising when considering the cost performance of Pt as an additive metal. However, if the Pt substitution amount is less than 0.5%, the variation in thermoelectric properties between firing lots becomes large, so that the industrial value is small. CoSb ₃ in which 2% of Co is replaced by Pt (Co _0.98 Pt _0.02 Sb ₃ ), and Bi ₂ Te of the comparative example.
Fig. 4 shows the temperature characteristics of the Seebeck coefficient of ₃ . In this experiment, the Seebeck coefficient was measured in the temperature range from room temperature to 500 ° C. (773 K), but Bi ₂ Te ₃ significantly deteriorates as the temperature rises, whereas CoSb of the present example.
_{The one} in which 2% of Co in ₃ is replaced by Pt is almost stable, and conversely increases little by little as the temperature rises. Similarly, the temperature characteristic of conductivity of CoSb ₃ in which 2% of Co is replaced by Pt is Bi ₂ T of Comparative Example.
It is shown in FIG. 5 together with e ₃ . The conductivity of Bi ₂ Te ₃ is 20
When the temperature exceeds 0 ° C (473K), it deteriorates sharply. this is,
It is considered to be due to alteration due to sublimation. On the other hand, the electrical conductivity of Pt-substituted CoSb ₃ of this example is slightly inferior to that of Bi ₂ Te ₃ from room temperature to about 200 ° C. (473K), but is stable even when the temperature rises. It shows a better value than Bi ₂ Te _{3 at} high temperatures. As described above, the characteristics of the Bi ₂ Te ₃ system are rapidly deteriorated when the temperature exceeds 500 K, whereas the Pt-substituted CoSb ₃ according to the present embodiment has a high Seebeck even when the temperature exceeds 300 ° C. (573 K). The coefficient and conductivity are maintained. The thermal conductivity of CoSb ₃ alone is
It was found to be 3.0 W / m · K, but decreased by Pt substitution with Co, and when Co was replaced with Pt by 10%, the thermal conductivity could be suppressed to about 2.0 W / m · K. . Since the sintering conditions are different, this result cannot be directly compared with the thermal conductivity of Bi ₂ Te ₃ system (up to 1.5 W / m · K), but the Pt substitution of Co reduces the thermal conductivity. However, it can be seen that the characteristics as a thermoelectric material are improved. As shown in FIG. 2, the unit cell of CoSb ₃ is composed of eight CoSb ₃ units, flat rectangle of four Sb atoms are arranged six cubic Akirachu to grid points a Co It has a complicated structure. As a result, it has a relatively large Seebeck coefficient. Further, the so-called p band of Sb atoms forming the conduction band has a small effective mass and a large mobility. By substituting Pt, which has one more electron than Co, for the Co site of the compound having such an electronic structure, an impurity level is formed and serves as a donor, so that the n-type has a large Seebeck coefficient and conductivity. It is considered to be a thermoelectric material. Further, by using heavy Pt as an element substituting the Co site, for example, Ni
It is possible to further suppress the thermal conductivity as compared with the case of using Pd or Pd, and as a result, a highly efficient thermoelectric material having a high figure of merit can be obtained. Further, since it has a high covalent bond, it is stable up to a relatively high temperature and can be used as a thermoelectric material up to a higher temperature than the Bi ₂ Te ₃ system, which is particularly advantageous for power generation using the Seebeck effect. From such a point, it can be said that the material of the present invention in which Co site of CoSb ₃ is substituted with Pt is a thermoelectric material which is as good as the Bi ₂ Te ₃ system. Further, since it contains Co and Sb but does not contain Pb or a chalcogen element such as Te or Se, the environmental load is small. [Embodiment 2] An embodiment of the thermoelectric effect element of the present invention will be described. A small thermoelectric effect element was produced using the n-type thermoelectric material of Example 1. In order to form an effective thermoelectric effect element, the p-type thermoelectric material is necessary together with the n-type thermoelectric material of the present invention. The thermoelectric effect element manufactured in this example is manufactured by the following manufacturing method. First, as shown in FIG. 6, the mold 1 is attached to the bottom of a frame-shaped mold 1b having a horseshoe-shaped through hole.
c is arranged, and the n-type thermoelectric material powder 2 of Example 1 is placed inside this.
And various p-type thermoelectric material powders 3 are respectively filled so as to be joined at a horseshoe-shaped tip portion, and a horseshoe-shaped mold 1a corresponding to the inner wall shape of the through hole of the frame-shaped mold 1b is arranged thereon. Pellets are obtained by cold pressing at a molding pressure of 4000 kgw / cm ^{2 in} the direction of the arrow. By firing and sintering the pellets, as shown in FIG. 7, the n-type thermoelectric material 2a is formed.
And the p-type thermoelectric material 3a are joined and integrated at the pn junction 4. A thermoelectric effect element can be obtained by attaching the metal terminals 5 to each of the n-type thermoelectric material 2a and the p-type thermoelectric material 3a. Co _{0.975 for} n-type thermoelectric material 2a
The thermoelectric effect element shown below was produced using Pt _0.025 Sb ₃ . As the p-type thermoelectric material 3a (Bi _0.25 Sb
_{When 0.75} ) ₂ (Te _0.95 Se _0.05 ) ₃ is used, good power generation performance is obtained when the temperature at the high temperature end is 200 ° C (473K) or lower, but the power generation output drops rapidly near 300 ° C (573K). To do. In addition, during repeated or continuous tests, cracks often occur in the p-type thermoelectric material 3a, and a phenomenon in which output cannot be performed frequently occurs. Further, Si is used as the p-type thermoelectric material 3a.
When Ge is used, the mechanical strength of the SiGe sintered body itself and the sufficient bonding strength at the horseshoe-shaped pn junction 4 cannot be secured because the sintering temperature of SiGe is higher than that of the CoSb ₃ system. When CoSb ₃ is used for the p-type thermoelectric material 3a, the thermoelectric characteristics, particularly the Seebeck coefficient, are smaller (up to 100) than the Pt-substituted CoSb ₃ used for the n-type thermoelectric material 4a.
μV / K), sufficient performance cannot be obtained as a thermoelectric effect element. A study was conducted using a PbTe-based material as the p-type thermoelectric material 3a. PbTe having high performance as a p-type thermoelectric material 3a from room temperature to 973K (700 ° C)
A thermoelectric material containing Ag ₂ Te in an amount of 3 mol% was used.
PbTe purchased as a reagent (purity 99.99% or higher)
Precisely measure the stoichiometric ratio of X-ray microanalysis by 1: 1
If the composition ratio deviates, powdered Pb or Te
Was added and the firing reaction was carried out so that the composition ratio became 1: 1 within the range of analytical error. The obtained PbTe
After a predetermined amount of Ag ₂ Te powder was added to the powder of 1. and mixed and pelletized, it was heat-treated in a hydrogen stream at 800 ° C. (1073 K) for 5 hours. The obtained pellets were pulverized again to obtain a powder having an average particle size of 10 μm or less. Further, this powder and Pt-substituted CoSb ₃ powder were filled in a horseshoe-shaped mold 1 so that their tips contact each other, and 4000 kgw / cm ²
Cold pressing was carried out at a molding pressure of (1) to obtain horseshoe-shaped pellets. This was heat-treated at 650 ° C. (923 K) for 3 hours in a hydrogen flow of 100 ml / min, then rapidly heated to 800 ° C. (1073 K), heat-treated at this temperature for 30 minutes, and then rapidly cooled.
When the heat treatment time at 800 ° C. was short, the mechanical strength of p-type PbTe was low, and the bonding strength of the pn junction 4 was insufficient. On the contrary, it has been found that if this time is too long, the performance of the device deteriorates, but it is considered that the characteristic itself of the thermoelectric material deteriorates due to the mutual diffusion of Pb and Sb in the pn junction 4. . In order to evaluate the performance of the thermoelectric effect element, ten horseshoe-shaped thermoelectric effect elements are electrically connected in series so that the outer periphery of the exhaust pipe of the oil combustor is surrounded by the pn junction 4. I made a device. A fin for heat dissipation is attached to the metal terminal 5 for electrically connecting the elements,
The space surrounding the exhaust pipe inside the fin was filled with alumina wool heat insulating material so that the temperature difference in the element was as large as possible. In addition, the fan helps to dissipate heat from the fins. The pn junction 4 and the metal terminal 5 are controlled by controlling the combustion amount of the oil combustor and the blower fan.
The temperature difference between and was adjusted. The relationship between temperature difference and power supply output was investigated using a load power supply. FIG. 8 shows the evaluation results when PbTe containing 3 mol% of Ag ₂ Te added to the p-type material was used. In the comparative example, both conventional p-type and n-type materials are made of conventional Pb.
A Te-based material is used. According to FIG. 8, the output power of the thermoelectric effect element of the example is improved by about 1.5 times as compared with the element of the comparative example. When the temperature difference is 800K,
An output of about 60 W was obtained. Also, Ag ₂ Te is 0.5
When PbTe added by up to 5.0 mol% was used for the p-type material 3a, a high output of 50 W or more could be obtained. A high output of 50 W or more was obtained by using PbTe in which Pb was replaced with Na by 1 to 10% for the p-type thermoelectric material 3a. In particular, the output was highest when Pb was replaced with Na by 5%. Also, Ag _0.15 Ge _0.85 Sb _0.15
When Te _1.15 was used as the p-type thermoelectric material, a very high output of 68 W could be obtained. Thus, the n of the present invention
A high-performance Seebeck element can be obtained by using the type thermoelectric material. Although a horseshoe-shaped material element is used as an example of the power generation element, that is, the Seebeck element, a rectangular parallelepiped similar to a normal Peltier element for electronic cooling is provided by improving the heat radiation mechanism such as the heat radiation fins. It is also possible to form a planar module configuration in which a large number of material elements having a rectangular shape are arranged in series. As one embodiment of the thermoelectric effect element of the present invention,
Although the Seebeck element has been described, it is clear that good performance can be obtained even when the Seebeck element is used for the Peltier element. According to the present invention, it is possible to obtain a highly efficient n-type thermoelectric material having a low global environmental load. Also,
By using this, a highly efficient thermoelectric effect element can be obtained.

[Brief description of drawings]

FIG. 1 is an n-type thermoelectric material Co of one embodiment of the present invention.
It is a powder X-ray diffraction pattern of _0.98 Pt _0.02 Sb ₃ .

FIG. 2 is a model diagram showing the same crystal structure.

FIG. 3: Co _1−x P at room temperature 25 ° C. (298K)
It is a characteristic diagram showing the Seebeck coefficient and electrical conductivity with respect to Pt amount of t _x Sb _3.

FIG. 4 is an n-type thermoelectric material Co of one embodiment of the present invention.
It is a characteristic view showing the Seebeck coefficient with respect to the temperature of _0.98 Pt _0.02 Sb ₃ .

FIG. 5 is a characteristic diagram showing electric conductivity with respect to the same temperature.

FIG. 6 is a perspective view of a mold used for manufacturing a thermoelectric effect element according to an example of the present invention.

FIG. 7 is a perspective view of the same thermoelectric effect element.

FIG. 8 is a characteristic diagram showing the output power with respect to the temperature difference of the thermoelectric effect element of one example of the present invention.

FIG. 9 is a characteristic diagram showing a performance index with respect to temperature of a conventional n-type thermoelectric material.

[Explanation of symbols]

 1 mold 1a horseshoe-shaped mold 1b frame-shaped mold 1c bottom mold 2 n-type thermoelectric material powder 2a n-type thermoelectric material 3 p-type thermoelectric material powder 3a p-type thermoelectric material 4 pn junction 5 metal terminal

Claims (4)

[Claims] 1. Co _1-x Pt _x Sb ₃ (0.005 ≦ x ≦
0.10) An n-type thermoelectric material comprising a solid solution represented by the composition formula. 2. Co _1-x Pt _x Sb ₃ (0.005 ≦ x ≦
0.10), an n-type thermoelectric material comprising a solid solution represented by the composition formula, and Pb _1-y Na _y Te (0.01 ≦ y ≦ 0.10)
A thermoelectric effect element having a structure in which a p-type thermoelectric material made of a solid solution represented by is electrically connected directly or through a conductor. 3. Co _1-x Pt _x Sb ₃ (0.005 ≦ x ≦
0.10) n-type thermoelectric material consisting of a solid solution represented by the composition formula, and PbT containing 0.5 to 5 mol% of Ag ₂ Te.
A thermoelectric effect element having a structure in which a p-type thermoelectric material composed of an e compound is electrically bonded directly or via a conductor. 4. Co _1-x Pt _x Sb ₃ (0.005 ≦ x ≦
0.10) n-type thermoelectric material consisting of a solid solution represented by the composition formula, Ag _0.15 Ge _0.85 Sb _0.15 Te
_{Directly with the p-type thermoelectric material consisting of the compound shown in 1.15
Or, it has a structure that is electrically connected via a conductor.
Thermoelectric effect element.}