JP2000106460A - Thermoelectric semiconductor material and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new thermoelectric semiconductor material which is excellent in thermoelectric properties and restrained from deteriorating in thermoelectric properties like a usual semiconductor material such as PbTe or PbSnTe even if it is enhanced in strength by sintering. SOLUTION: This thermoelectric semiconductor material is represented by a chemical formula, AB2X4 [(where A is a simple substance or a mixture of Pb, Sn, and Ge (IV element), B is a simple substance or a mixture of Bi and Sb (V element), and X is a simple substance or a mixture of Te and Se (VI element)]. In this case, a pulse current is applied to the powdered material 14 by the use of a discharged plasma sintering device 10 to enable electric discharge to take place between particles, and compound AB2X4 of uniform structure is synthesized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a thermoelectric semiconductor material and a method for producing the same.

[0002]

2. Description of the Related Art An electronic cooling element utilizing the Peltier effect or the Etching-Shausen effect, or a thermoelectric power generation element utilizing the Seebeck effect has a simple structure and is easy to handle. Therefore, its wide use is attracting attention because it can maintain stable characteristics. In particular, as the electronic cooling element, it is possible to perform local cooling and precise temperature control around room temperature,
Research and development are being widely pursued for application to temperature control of optoelectronics and semiconductor lasers, and small refrigerators.

[0003] The material of the thermoelectric element used for the electronic cooling and the thermoelectric power generation has a performance index Z (=) represented by a Seebeck coefficient α, a specific resistance ρ, and a thermal conductivity κ, which are constants specific to the substance, in a use temperature range. (α ² / ρκ) is used.

That is, crystal materials generally used for electronic cooling devices and the like include bismuth telluride (Bi ₂ Te ₃ ),
It is a mixed crystal system of antimony telluride (Sb ₂ Te ₃ ) and bismuth selenide (Bi ₂ Se ₃ ).

Such a Bi ₂ Te ₃ based semiconductor material has a layered structure as shown in FIG. 10 when bismuth telluride (Bi ₂ Te ₃ ) and antimony telluride (Sb ₂ Te ₃ ) are taken as an example. . That is, Te, Bi (or Sb), Te, Bi (or Sb), and Te are coupled to the five layers by covalent bonds from the top. A total of 15 layers in which the five layers are connected to each other by van der Waals bonding or ionic bonding become one unit,
It has a layered crystal structure of a homogeneous phase.

On the other hand, a medium temperature range (from room temperature to 400 ° C.)
PbTe-based and Pb-based thermoelectric conversion materials
A semiconductor material such as SnTe is used.

[0007] These PbTe-based and PbSnTe-based semiconductor materials are materials having a high carrier mobility in the crystal. This semiconductor material has excellent thermoelectric properties when formed into a single crystal or a polycrystalline ingot by unidirectional solidification.

However, since the material strength is low, it is necessary to improve the strength by using a sintered body for industrial use.

However, in the case of a sintered body, the influence of grain boundary scattering is increased due to the large carrier mobility, and on the contrary, the resistance is increased and the thermoelectric properties are reduced.

The present invention has been made in view of such a situation. By forming a layered structure having a uniform phase similar to that shown in FIG. 10, even when the material is sintered, the conventional PbTe is used. It is an object of the present invention to provide a new thermoelectric semiconductor material capable of improving thermoelectric characteristics more than a semiconductor material such as a PbSnTe-based material.

[0011]

Means for Solving the Problems and Action and Effect
The thermoelectric semiconductor material of the first invention of the present invention has a chemical formula of AB ₂ X
₄ (where A is a simple substance or a mixture of Pb, Sn, Ge (Group IV element), B is a simple substance or a mixture of Bi, Sb (Group V element), and X is Te, Se (Group VI element). (A simple substance or a mixture).

The thermoelectric semiconductor material of the second invention has the chemical formula Bi
_1-x Sb _x Te ₁ (where 0 ≦ x ≦ 1).

The thermoelectric semiconductor material of the third invention has a chemical formula of A _y
B _1-y X ₁ (where 0 ≦ y ≦ 0.25 and A is P
b is a simple substance or a mixture of Sn and Ge (Group IV element), B is a simple substance or a mixture of Bi and Sb (Group V element), and X is a simple substance or a mixture of Te and Se (Group VI element). ).

In the method for producing a thermoelectric semiconductor material according to a fourth aspect of the present invention, A is a simple substance or a mixture of Pb, Sn, and Ge (Group IV element), B is a simple substance or a mixture of Bi, Sb (Group V element), and X Is a simple substance or a mixture of Te and Se (Group VI element), these A, B and X are represented by 1:
A pulsed current is applied to the raw material powder of the thermoelectric semiconductor material mixed at a stoichiometric ratio of 2: 4 to cause a discharge between the powder particles, so that the uniformity represented by the chemical formula AB ₂ X ₄ is obtained. Characterized in that a compound having the following structure is synthesized.

In the method of manufacturing a thermoelectric semiconductor material according to a fifth aspect of the present invention, Bi, Sb, and Te are set to 1-x: x: 1 (where 0 ≦ x
When a pulse-like current is applied to the raw material powder of the thermoelectric semiconductor material mixed at a stoichiometric ratio of ≦ 1), discharge is caused between the powder particles, and the chemical formula Bi _1-x Sb _x Te
A compound having a uniform structure represented by ₁ is synthesized.

In the method for producing a thermoelectric semiconductor material according to the sixth invention, A is a simple substance or a mixture of Pb, Sn, and Ge (Group IV element), B is a simple substance or a mixture of Bi, Sb (Group V element), and X Is a simple substance or a mixture of Te and Se (group VI element), these A, B, and X are y: 1
-Y: A pulse-like current is applied to the powder of the raw material of the thermoelectric semiconductor material mixed at a stoichiometric ratio of 0 (y ≦ 0.25) to cause a discharge between the powder particles. And synthesizing a compound having a uniform structure represented by the chemical formula A _y B _1-y X ₁ .

In the method for producing a thermoelectric semiconductor material according to the seventh invention, A is a simple substance or a mixture of Pb, Sn, and Ge (Group IV element), B is a simple substance or a mixture of Bi, Sb (Group V element), and X Is a simple substance or a mixture of Te and Se (Group VI element), these A, B and X are represented by 1:
A pulse current is applied to the powder of the raw material of the thermoelectric semiconductor material mixed at a stoichiometric ratio of 2: 4, and a pressure is applied to cause a discharge between the powder particles to cause a chemical formula AB ₂ X ₄
And synthesizing a compound having a uniform structure and forming a sintered body of the compound.

In the method for producing a thermoelectric semiconductor material according to the eighth aspect of the present invention, Bi, Sb, and Te are set to 1-x: x: 1 (where 0 ≦ x
A pulse current is applied to the raw material powder of the thermoelectric semiconductor material mixed at a stoichiometric ratio of ≦ 1) and a pressure is applied to cause a discharge between the powder particles to cause a chemical formula Bi _1-x
A compound having a uniform structure represented by Sb _x Te ₁ is synthesized, and a sintered body of the compound is formed.

In the method for producing a thermoelectric semiconductor material according to the ninth aspect, A is a simple substance or a mixture of Pb, Sn, and Ge (Group IV element), B is a simple substance or a mixture of Bi, Sb (Group V element), and X Is a simple substance or a mixture of Te and Se (group VI element), these A, B, and X are y: 1
-Y: a pulse-like current is applied to the powder of the raw material of the thermoelectric semiconductor material mixed at a stoichiometric ratio of 0 (y ≦ 0.25), and a pressure is applied between the powder particles. the compounds of the uniform tissue represented by discharge to perform the formula a _{y B 1-y} X 1 together with the synthesis is characterized in that so as to form a sintered body of the compound.

The thermoelectric semiconductor material of the tenth aspect of the present invention has the formula _{Bi 1-x Sb x Te 1} -y Se y ( provided that 0 ≦
x ≦ 1, 0 <y ≦ 1).

The thermoelectric semiconductor material of the eleventh invention, the chemical formula _{Bi 2-x Sb x Te 1} -y Se y ( provided that 0 ≦
x ≦ 2, 0 ≦ y ≦ 1).

The thermoelectric semiconductor material of the twelfth invention, the chemical formula _{(Bi 1-x Sb x)} 4 (Te 1-y Se y) 5
(Where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1).

In the method for producing a thermoelectric semiconductor material according to the thirteenth aspect, Bi, Sb, Te, Se are expressed as 1-x: x: 1-y: y
(Where 0 ≦ x ≦ 1, 0 <y ≦ 1) A pulse current is applied to the powder of the raw material of the thermoelectric semiconductor material mixed at a stoichiometric ratio to cause discharge between the powder particles. ,
And wherein the synthesis of compounds of the uniform tissue represented by the chemical formula _{Bi 1-x Sb x Te 1} -y Se y.

In the method for producing a thermoelectric semiconductor material according to the fourteenth aspect, Bi, Sb, Te, Se are converted to 2-x: x: 1-y: y.
A pulse current is applied to the powder of the raw material of the thermoelectric semiconductor material mixed at a stoichiometric ratio (0 ≦ x ≦ 2, 0 ≦ y ≦ 1) to cause discharge between the powder particles. ,
And wherein the synthesis of compounds of the uniform tissue represented by the chemical formula _{Bi 2-x Sb x Te 1} -y Se y.

In the method for producing a thermoelectric semiconductor material according to the fifteenth aspect, Bi, Sb, Te, Se are converted to 4 (1-x): 4x: 5.
(1-y): a powder is obtained by applying a pulsed current to a raw material powder of a thermoelectric semiconductor material mixed at a stoichiometric ratio of 5y (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1). Electric discharge is caused between the particles, and the chemical formula (Bi _1-x Sb _x ) ₄ (Te
_1-y Se _y ) ₅ is synthesized.

According to the present inventions 1, 4, and 7, the thermoelectric device of the present invention
The semiconductor material has the formula AB₂X₄(However, A is Pb, S
n, a simple substance or a mixture of Ge (Group IV element),
B is a simple substance or a mixture of Bi and Sb (Group V element)
X is a single element or a mixture of Te and Se (Group VI element)
Object). In this case, discharge
Using the plasma sintering apparatus 10, the powdered raw material 14
On the other hand, when a pulsed current is applied,
Discharge occurs between the particles, and the compound AB having a uniform structure ₂X₄But
Synthesized. The compound and the formation of the sintered body are performed simultaneously.
You may do so. According to the present invention, as shown in FIG.
Rackidite layer of homogeneous phase
-Like structure, even if sintered
Thermal conductivity κ lower than semiconductor materials such as PbTe
The thermoelectric characteristics to a high value, such as
You can have.

According to the present inventions 2, 5, and 8, the thermoelectric semiconductor material of the present invention is characterized by having a chemical formula of Bi _1-x Sb _x Te ₁ (where 0 ≦ x ≦ 1). In this case, the powdered raw material 14 is
When a pulse-like current is applied, a discharge is performed between the powder particles, and the compound Bi _{1- x} having a uniform structure is discharged.
Sb _x Te ₁ is synthesized. The compound and the formation of the sintered body may be performed simultaneously. According to the present invention, as shown in FIG. 9, a homogeneous phase of Tsumoite (Tsumoito)
Since a layered structure is obtained, even when sintered, it is possible to maintain high thermoelectric properties such as a lower thermal conductivity κ and a higher figure of merit Z than conventional semiconductor materials such as PbTe. it can.

According to the inventions 3, 6, and 9, the thermoelectric semiconductor material of the invention has a chemical formula of A _y B _1-y X ₁ (where 0 ≦ y).
≦ 0.25, A is a simple substance or a mixture of Pb, Sn, Ge (Group IV element), and B is Bi, Sb (V
Group element) or a mixture thereof, X is Te, Se
(Group VI element) or a mixture thereof. In this case, the discharge plasma sintering device 1
By using 0, a pulsed current is applied to the powdered raw material 14 to cause discharge between the powder particles, thereby synthesizing the compound A _y B _1-y X ₁ having a uniform structure. You. The compound and the formation of the sintered body may be performed simultaneously. According to the present invention, as shown in FIG. 9, a uniform phase Tsumoite (tsumoite) layered structure is obtained, so that even when sintered, the thermal conductivity κ is higher than that of a conventional PbTe-based semiconductor material. The thermoelectric characteristics can be maintained at a high value, for example, when the performance index Z decreases and the performance index Z increases.

According to the present inventions 10 and 13, Tsumoi
Since a te (Tsmoit) layered structure is obtained, even when sintered, the thermoelectric properties are increased to a higher value such as a lower thermal conductivity κ and a larger figure of merit Z than conventional PbTe-based semiconductor materials. Can be maintained.

According to the inventions 11, 12, 14, and 15,
Since a figure of merit equal to or higher than that of a PbTe-based material or the like is obtained, the thermoelectric semiconductor material according to the present invention is a PbTe-based material.
It is useful as a medium temperature thermoelectric semiconductor material instead of a system material.

[0031]

Embodiments of the present invention will be described below in detail with reference to the drawings.

First, as a thermoelectric semiconductor material, the chemical formula AB
₂ X ₄ (where A is a simple substance or a mixture of Pb, Sn, Ge (Group IV element), B is a simple substance or a mixture of Bi, Sb (Group V element), and X is Te, Se (V
(A group I element) or a mixture thereof).

Therefore, the method of synthesizing the compound PbBi ₂ Te ₄ will be described by way of example.
However, the present invention can be applied to the production of a compound having any composition as long as it is a thermoelectric semiconductor material represented by the chemical formula AB ₂ X ₄ .

The compound PbBi ₂ Te ₄ is a compound Pb
This is a compound in which bTe and the compound Bi ₂ Te ₃ are mixed at a stoichiometric ratio of 1: 1. However, it is not possible to obtain a compound having a uniform structure when synthesizing it by a conventional dissolving and coagulating method. The melting and solidifying method is a method of synthesizing a compound by encapsulating and melting raw material elements in a glass tube, synthesizing in a liquid phase, and then cooling and solidifying.

In the present embodiment, the compound PbBi ₂ Te ₄ is uniformly synthesized as follows.

Example 1 (Heating Step) First, lead P as a raw material of a thermoelectric semiconductor material
b, bismuth Bi, and tellurium Te were weighed and mixed so that the stoichiometric ratio was 1: 2: 4 (PbBi ₂ Te ₄ ). A compound for adjusting the carrier concentration may be added in an appropriate amount.

Next, the raw material mixture of the thermoelectric semiconductor material was sealed in a quartz ampoule under reduced pressure, and heated and melted.

(Coagulation Step) Next, after stirring the melted raw material mixture for a certain period of time, the mixture was cooled and solidified by one-way solidification to prepare an ingot material.

At this time, the compound containing excess Pb and the compound containing excess Bi are mixed in the ingot, so that a uniform PbBi ₂ Te ₄ compound cannot be obtained.

(Pulverizing Step) Next, the ingot as an ingot was pulverized in an inert atmosphere (for example, nitrogen) using a stamp mill, a ball mill, or the like to produce powder of the ingot.

(Classification Step) Next, the ingot powder was sieved and classified to a particle size of 125 μm or less.

(Synthesis Process) Next, a pulse-like current is applied to the powdered raw material 14 (hereinafter referred to as powder raw material 14) using a discharge plasma sintering apparatus 10 shown in FIG. Discharge is performed between body particles to synthesize compound PbBi ₂ Te ₄ having a uniform structure,
A sintered body 14 ′ of the compound PbBi ₂ Te ₄ was formed.

The discharge plasma sintering apparatus 10 includes a die 13 as a die for forming a powder material 14 of a thermoelectric semiconductor material into a predetermined shape (for example, a rectangular parallelepiped shape), an upper punch 11,
A lower punch 12; a pressing mechanism 18 for applying compressive forces J1 and J2 to the powder raw material 14 via the upper punch 11 and the lower punch 12; an upper electrode 15 provided integrally with the upper punch 11; A lower electrode 16 provided integrally with the power supply 12; a power supply 19 for applying a pulse current to the powder raw material 14 by applying a DC pulse voltage between the upper electrode 15 and the lower electrode 16; A chamber 17 for maintaining an atmosphere and a desired vacuum pressure, a pressurizing mechanism 18 and a power supply 19;
And a controller 20 for controlling the The pressurizing mechanism 18 is formed mainly of a hydraulic actuator, for example, and has a downward compressive force J1 against the upper punch 11 in the drawing.
And an upward compressive force J2 in the drawing is applied to the lower punch 12.

The die 13 is a mold surrounding the periphery of the powder raw material 14. The powder raw material 14 is injected into the die 13 to form a peripheral shape of the powder raw material 14. Die 13
Is provided with a temperature sensor 21 (for example, a thermocouple is used) for detecting the temperature of the powder raw material 14. The controller 20 controls the power supply 19 using the temperature detected by the temperature sensor 21 as a feedback signal to set the temperature of the powder raw material 14 to a desired heating temperature.

The upper punch 11 is a mold that is in contact with the upper surface of the powder raw material 14. When the upper punch 11 is inserted into the die 13 from above, the front end surface of the punch abuts on the upper surface of the powder raw material 14, and the upper surface shape of the powder raw material 14 is formed.

The lower punch 12 is a mold that is in contact with the lower surface of the powder raw material 14. When the lower punch 12 is inserted into the die 13 from below, the front end surface of the punch abuts on the lower surface of the powder raw material 14 to form the lower surface shape of the powder raw material 14.

The operation of the spark plasma sintering apparatus 10 until a rectangular parallelepiped sintered body 14 'is manufactured from the powder raw material 14 will be described below.

First, the mold 1 of the spark plasma sintering apparatus 10
Powder materials 14 of the thermoelectric semiconductor material pulverized and classified in the pulverization step and the classification step are injected into 1, 12, and 13.

The controller 20 outputs a pressurization control signal to the pressurizing mechanism 18 so that the powder raw material 14 is pressurized at a pressure of 400 kgf / cm ² . As a result, the upper punch 11 is lowered and the lower punch 12 is raised, and the powder raw material 14 is pressed at a pressure of 400 kgf / cm ² .
Thus, the powder raw material 14 is solidified into a rectangular parallelepiped shape.

On the other hand, the controller 20 outputs a pulse control signal to the power supply 19 so that the powder raw material 14 is heated at a temperature of 500 ° C. As a result, a DC pulse voltage at a predetermined interval is applied between the upper electrode 15 and the lower electrode 16, a DC pulse current flows at a predetermined interval through the powder raw material 14, and the powder raw material 14 is heated at a temperature of 500 ° C.

That is, when a pulse current is applied to the powder raw material 14, a discharge is generated between the powder particles. Heating is performed by the self-heating effect of the powder due to the discharge occurring between the powder particles. At this time, the powder particles are in a plasma state due to discharge, and a local high-temperature field is formed. This promotes the reaction. Further, a defect is generated in the crystal due to the impact of the discharge, and the diffusion of atoms is promoted through the defect. By promoting the reaction between the powder particles and promoting the diffusion of atoms, the structure of the compound becomes extremely uniform.

As described above, the powder raw material 14 is heated at a temperature of 50
Sintering was performed at 0 ° C. and a pressure of 400 kgf / cm ² for 2 hours.

As a result, the synthesis and sintering of the compound were performed simultaneously, and a sintered body 14 'of the compound PbBi ₂ Te ₄ having a very uniform structure was formed.

FIG. 6 shows the result of analyzing the crystal structure (composition) of the compound obtained by the discharge plasma method by the X-ray diffraction method.

The horizontal axis of the graph in FIG. 6 is the angle 2θ obtained by combining the incident angle and the reflection angle of the X-ray, and the vertical axis represents the count value (reflection intensity) of the X-ray counter. The lattice spacing d () is obtained from the composite angle 2θ. According to the literature data shown in FIG. 4, in the case of the crystal structure of the compound PbBi ₂ Te ₄ , the plane index (h,
k, l) = (0, 0, 9) and lattice spacing d = 4.61
() Is shown.

According to FIG. 6, as indicated by the arrow I, a peak at d = 4.628, corresponding to the theoretical value of 4.61, was observed. That is, no peak indicating a crystal structure other than the intended one was observed. As described above, the target R
It was found that a uniform compound PbBi ₂ Te ₄ having the same structure as the acklidgeite (lacrisite) mineral (structural formula: (Pb, Bi) ₃ Te ₄ ) was synthesized.

FIG. 1 shows the sintering conditions for producing the sintered body 14 'of the composition PbBi ₂ Te _{4 in} Example 1 and the types of crystal structures of the produced sintered body 14'.

FIG. 8 shows the crystal structure obtained at this time.
That is, Te, Bi, Te, Bi, Te, B
i, Te are covalently bonded to seven layers. A total of 21 layers in which the seven layers are joined by three of van der Waals bonds or ionic bonds constitute one unit, and constitute a layer crystal structure of a uniform phase.

Composition PbBi ₂ T obtained in Example 1
conduction of the sintered body 14 'of the e ₄ is n-type, were measured thermoelectric characteristics of the n-type thermoelectric semiconductor material.

As a result, as shown in FIG. 2, the power factor (× 10 ⁻⁵ W / cmK ² ) was 1.8, the thermal conductivity κ (mW / Kcm) was 20, and the performance at a temperature of 500K was obtained. The index Z (× 10 ⁻³ / K) showed 0.9. When this is compared with a conventional n-type PbTe-based semiconductor material (Comparative Example 1), the power factor is the same (1.
8), the thermal conductivity κ is lower (2 for 25)
0), and the figure of merit Z is higher than 0.7 (0.7 for 0.7).
9) It can be seen that the thermoelectric properties are superior to the conventional PbTe-based semiconductor material. The power factor is defined as the square of the Seebeck coefficient α (μV / K), and the specific resistance ρ (μ
Ω · cm), and the larger the value, the better the thermoelectric performance.

As described above, according to the first embodiment, as shown in FIG. 8, a Rucklidgeite layered structure having a uniform phase can be obtained. Therefore, even when sintered, a conventional PbTe-based semiconductor or the like is used. Thermoelectric characteristics can be maintained at a high value, for example, the thermal conductivity κ is lower than that of the material and the figure of merit Z is large.

Example 14 Next, as a thermoelectric semiconductor material, a chemical formula Bi _1-x Sb _x
Consider a case where a thermoelectric semiconductor material made of Te ₁ (where 0 ≦ x ≦ 1) is manufactured.

Thus, the synthesis method will be described by taking as an example the case of producing a compound of BiTe (x = 0). However, in the present invention, the chemical formula Bi _1-x Sb _x T
If thermoelectric semiconductor material represented by e ₁ it can also be applied to the preparation of the compounds of any composition.

This compound BiTe was produced in the same manner as in Example 1 through a heating step, a coagulation step, a pulverization step, a classification step, and a synthesis step.

However, the conditions for sintering the powder raw material 14 in the discharge plasma sintering apparatus 10 are as follows: temperature 450 ° C., pressure 4
Sintering was performed for 2 hours under the condition of 00 kgf / cm ² .

As a result, the synthesis and sintering of the compound are simultaneously performed, and the sintered body 1 of the compound BiTe having a very uniform structure is obtained.
4 'was formed.

FIG. 7 shows Bi obtained by the discharge plasma method.
The result of having analyzed the crystal structure (composition) of the Te compound by the X-ray diffraction method is shown.

The horizontal axis of the graph of FIG. 7 is the angle 2θ obtained by combining the incident angle and the reflection angle of the X-ray, as in FIG.
Shows the count value (reflection intensity) of the line counter. Composite angle 2
The lattice spacing d () is obtained from θ. According to the literature data shown in FIG. 5, in the case of the crystal structure of the compound BiTe, the plane index (h, k, l) = (0, 0, 5) and the lattice spacing d = 4.
808 ().

According to FIG. 7, as indicated by the arrow H, a peak at d = 4.801 corresponding to the theoretical value of 4.808 was observed. That is, no peak indicating a crystal structure other than the intended one was observed. Thus, from the results of X-ray analysis, the desired Tsumoite mineral (structural formula: BiT
It was found that a uniform compound BiTe having the same structure as in e) was synthesized.

In Example 14, the sintered body 1 of the composition BiTe
Sintering conditions for manufacturing 4 ', manufactured sintered body 14'
1 are collectively shown in FIG.

FIG. 9 shows the crystal structure obtained at this time.
That is, Bi, Te, Bi, Te, Bi, Te
Are covalently bonded to six layers. And still another six layers are Te, Bi, Te, Bi, Te,
Bi is covalently bonded to six layers. A total of 12 layers in which these 6 layers are joined together by van der Waals bonding or ionic bonding constitute a unit, forming a layered crystal structure of a uniform phase.

The conductivity type of the sintered body 14 ′ of the composition BiTe obtained in Example 14 is n-type, and the thermoelectric characteristics of this n-type thermoelectric semiconductor material were measured.

As a result, as shown in FIG. 2, the power factor (× 10 ⁻⁵ W / cmK ² ) was 1.8, the thermal conductivity κ (mW / Kcm) was 31, and the performance at a temperature of 500K was shown. The index Z (× 10 ⁻³ / K) was 0.6. Even when this was compared with a conventional n-type PbTe-based semiconductor material (Comparative Example 1), the thermoelectric properties were comparable.

[0074] As-Example 21 following the thermoelectric semiconductor material, the formula _A y _{B 1-y X 1}
(Where 0 ≦ y ≦ 0.25, and A is Pb, Sn, G
e (group IV element) alone or as a mixture, and B is B
i, a simple substance or a mixture of Sb (Group V element);
Is a simple substance or a mixture of Te and Se (Group VI element)).

Thus, a method for producing a compound of Ge _0.1 Bi _0.9 Te (y = 0.1) will be described as an example, and its synthesis method will be described. However, as the present invention can also be applied to the preparation of the compounds of any composition as long as the thermoelectric semiconductor material represented by Chemical Formula _{A y B 1-y X 1} .

This compound Ge _0.1 Bi _0.9 Te was produced in the same manner as in Example 1 through a heating step, a coagulation step, a pulverization step, a classification step, and a synthesis step.

However, the conditions for sintering the powder raw material 14 in the discharge plasma sintering apparatus 10 are as follows: temperature 450 ° C., pressure 4
Sintering was performed for 2 hours under the condition of 00 kgf / cm ² .

As a result, the synthesis and sintering of the compound are performed simultaneously, and the compound Ge _0.1 Bi having a very uniform structure is obtained.
_A sintered body 14 'of _0.9 Te was formed.

In this Example 21, the composition Ge _0.1 Bi
FIG. 1 shows the sintering conditions for manufacturing the _0.9 Te sintered body 14 ′ and the types of crystal structures of the manufactured sintered body 14 ′.

The crystal structure obtained at this time is a Tsumoite structure as shown in FIG. However, in the crystal structure shown in FIG. 9, 10% of Bi is substituted by Ge of the group IV element.

Composition Ge _0.1 obtained in Example 21
The conduction type of the Bi _0.9 Te sintered body 14 ′ is n-type,
The thermoelectric properties of this n-type thermoelectric semiconductor material were measured.

As a result, as shown in FIG. 2, the power factor (× 10 ⁻⁵ W / cmK ² ) was 1.8, the thermal conductivity κ (mW / Kcm) was 20, and the performance at a temperature of 500K was obtained. The index Z (× 10 ⁻³ / K) showed 0.9. When this is compared with a conventional n-type PbTe-based semiconductor material (Comparative Example 1), the power factor is the same (1.
8), the thermal conductivity κ is lower (2 for 25)
0), and the figure of merit Z is higher than 0.7 (0.7 for 0.7).
9) It can be seen that the thermoelectric properties are superior to the conventional PbTe-based semiconductor material.

As described above, according to the twenty-first embodiment, as shown in FIG. 9, a Tsumoite (tsumoite) layered structure having a uniform phase can be obtained. Therefore, even when sintered, a conventional PbTe-based semiconductor or the like is used. Thermoelectric characteristics can be maintained at a high value, for example, the thermal conductivity κ is lower than that of the material and the figure of merit Z is large.

Next, in addition to Example 1 described above, Production Examples 2 to 13 of each compound represented by the above formula AB ₂ X ₄ were prepared.
The tendency of the change in the thermoelectric characteristics will be described.

FIG. 1 shows the “composition” and “sintering conditions” of the chemical formula AB ₂ X _{4 and} the type of “crystal structure” of the manufactured sintered body 14 ′ for each of Examples 1 to 13. .

In each of Examples 2 to 13, the same compound having the same structure as that of Example 1 having the same Rucklidgeite structure was synthesized.

FIG. 2 shows the “conduction type”, the “power factor” (× 10 ⁻⁵ W / cmK ² ) measured for the sintered body 14 ′, and the “heat conduction” for each of Examples 1 to 13. Rate κ ”(mW / Kcm) and“ performance index Z at 500K ”(× 10 ⁻³ / K).

The thermoelectric properties of PbTe, which is a PbTe-based thermoelectric semiconductor material, are listed as n-type “Comparative Example 1”. This compound PbTe has a temperature of 550 ° C. and a pressure of 400 kgf / c.
It was manufactured by sintering under the conditions of m ² for 10 minutes. However, as a dopant, an impurity PbI
₂ was contained by 0.5% by weight. Also, as a p-type “Comparative Example 2”, Pb which is a PbSnTe-based thermoelectric semiconductor material
_The thermoelectric properties of _0.75 Sn _0.25 Te are listed. This compound Pb _0.75 Sn _0.25 Te has a temperature of 500 ° C.
It is manufactured by sintering under a pressure of 400 kgf / cm ² for 10 minutes.

The second to fifth embodiments correspond to the Pb of the first embodiment.
The Pb element in Bi ₂ Te ₄ is replaced with the same group IV element, tin Sn or germanium Ge,
The composition is such that the element is replaced by antimony Sb which is the same group V element.

Although the power factors of Examples 1 to 5 are equivalent to those of Comparative Examples 1 and 2, the thermal conductivity κ is lower than that of Comparative Examples 1 and 2 because of the layered structure, and the performance index Z is lower than that of Comparative Examples 1 and 2. It is larger than Examples 1 and 2 and has excellent thermoelectric properties.

In addition, lead Pb is replaced with tin Sn or germanium Ge.
, The thermal conductivity κ tends to decrease and the figure of merit Z tends to increase. One reason for this is considered to be that the inclusion of Sn or Ge with a smaller atomic radius in the atomic position where Pb should be present causes the crystal lattice to be distorted, thereby reducing the thermal conductivity due to lattice vibration. In addition, the inclusion of tin Sn or antimony Sb tends to exhibit p-type conductivity.

The sixth to ninth embodiments correspond to the Pb of the first embodiment.
A composition in which a part of lead Pb in Bi ₂ Te ₄ is replaced with tin Sn which is the same group IV element, and the ratio of tin Sn is changed from 25% to 90%.

Also in Examples 6 to 9, the thermal conductivity κ was lower than Comparative Examples 1 and 2 because of the layered structure, and the figure of merit Z was higher than Comparative Examples 1 and 2, and the thermoelectric characteristics Is better.

Further, by substituting a part of the lead Pb with tin Sn, the thermal conductivity κ is further reduced, and the performance index Z is further reduced.
Tend to increase. The reason is as described above.

It was also found that the conversion from n-type to p-type was achieved when the ratio of tin Sn was increased to 80% or more.

The tenth and eleventh embodiments correspond to the PbBi of the first embodiment.
Some of tellurium Te in ₂ Te ₄ was replaced with selenium Se is the same group VI element, the stoichiometric ratio of tellurium Te and selenium Se 3.7: is obtained by the composition of 0.3. Example 11 has a composition in which tin Sn is substituted for lead Pb.

Also in Examples 10 and 11, since they have a layered structure, the thermal conductivity κ is lower than Comparative Examples 1 and 2, and the figure of merit Z is higher than Comparative Examples 1 and 2, and the thermoelectric properties are excellent. ing.

Also, by substituting part of tellurium Te with selenium Se, the thermal conductivity κ tends to be lower and the figure of merit Z tends to be larger than in Examples 1 and 2.

The twelfth and thirteenth embodiments correspond to the PbBi of the first embodiment.
A part of bismuth Bi in ₂ Te ₄ is replaced with antimony Sb which is the same group V element, and the stoichiometric ratio of bismuth Bi and antimony Sb is set to 0.5: 1.5. Example 13 has a composition in which tin Sn is substituted for lead Pb.

Also in Examples 12 and 13, the thermal conductivity κ was lower than Comparative Examples 1 and 2 because of the layered structure, and the figure of merit Z was higher than Comparative Examples 1 and 2, and the thermoelectric characteristics were excellent. ing.

Both Examples 12 and 13 showed p-type conduction, and it was found that by substituting a part of bismuth Bi with antimony Sb, p-type conductivity was easily obtained.

Next, in addition to Example 14 described above, Production Examples 15 to 20 of the respective compounds represented by the above chemical formula Bi _1-x Sb _x Te ₁ (where 0 ≦ x ≦ 1) are given. The tendency of the change will be described.

In all of Examples 15 to 20, the same Tsumoite (Tsumoito) as in Example 14 was used.
A compound having a uniform structure was synthesized.

The fourteenth to twentieth embodiments correspond to the fourteenth embodiment.
Of Bismuth Bi in Bi ₁ Te ₁ is replaced with antimony Sb which is the same group V element, and the antimony S
The composition was such that the ratio of b was changed from 0% to 100% in increments of 10%. That is, the chemical formula Bi _1-x Sb
the x in _x Te ₁ went varied in increments of 0.1 from 0 to 1.0.

In Examples 14 to 20, except for some exceptions (Example 17), the thermal conductivity κ is the same as Comparative Examples 1 and 2, but the power factor is Comparative Example 1 or 2. And the figure of merit Z is larger than Comparative Examples 1 and 2, and the thermoelectric properties are excellent.

Until the ratio of antimony Sb reaches 50% (Examples 14, 15, 16, 16-2, 16-
3, 17), showing n-type conduction, and when it exceeds 50% (Examples 17-2, 18, 19, 19-2), it shows p-type conduction.

Until the ratio of antimony Sb reaches 50% (Examples 14, 15, 16, 16-2, 16-
3), the figure of merit Z increases as the ratio of Sb increases, and exceeds 50% (Examples 17-2, 18, 1).
9, 19-2), the figure of merit Z according to the increase in the ratio of Sb
Conversely tends to decrease.

Next, in addition to Example 21 described above, Production Examples 22 to 32 of each compound represented by the above-mentioned chemical formula A _y B _1-y X ₁ will be described. The uniform tendency will be described.

Examples 22 to 32 are the same as the Sumoite of Example 21 except for some exceptions (Examples 24, 28, and 32) as described later.
A compound having a uniform (Tsumito) structure was synthesized.

The embodiments 21 to 32 correspond to the Tsumo
A composition in which part of bismuth Bi (group V element) of item (BiTe) is substituted with germanium Ge, tin Sn, and lead Pb of group IV element, and the substitution ratio is changed from 10% to 30%. is there. That is, the chemical formula A _y B _1-y X
The y in ₁ was changed from 0.1 to 0.3.

When the substitution ratio of bismuth Bi to group IV element is 2
Until reaching 5% (y = 0.25), a uniform Tsum
An oite structure was obtained. However, the substitution rate with a group IV element (antimony Sb, etc.) exceeds 25%
At 0%, a uniform Tsumoite structure cannot be obtained. That is, in Examples 24, 28, and 32 in which the replacement ratio is 30%,
In addition to the (Tsumito) structure, another NaCl-type crystal was mixed. The reason for this is that the compound represented by the chemical formula A _y B _{1 -y} X ₁ is obtained by adding GeCl, which has a distorted rhombohedral structure of NaCl type or NaCl type to BiTe having a Tsumoite type structure, and TeTe, SnTe, and Pb.
Since it is synthesized by dissolving Te in a solid solution, there is a solid solution limit near the substitution rate of about 25%, and above that, a uniform Tsumoite
This is probably because the (Tsumito) structure cannot be maintained.

FIG. 2 shows only the embodiments (embodiments in the range of 0.1 ≦ y ≦ 0.25) except for the embodiments 24, 28, and 32 in which a uniform Tsumoite structure cannot be obtained. 2 shows the results of measuring the thermoelectric properties of the sample.

Even when a part of bismuth Bi is replaced with any of the group IV elements germanium Ge, tin Sn, and lead Pb, the power factor is more than Comparative Examples 1 and 2 and the thermal conductivity κ is It is lower than Examples 1 and 2, the figure of merit Z is higher than Comparative Examples 1 and 2, and the thermoelectric properties are superior to Comparative Examples 1 and 2. This converts the group V atom to I
Substitution with group V atoms reduces the number of electrons (carriers of an n-type semiconductor) and reduces the appropriate carrier concentration (10 ⁻¹⁹ / cm
It is presumed that this is due to approaching ³ ). Further, the thermal conductivity κ is also reduced by replacing the group V bismuth atoms Bi with the group IV atoms. It can be seen that the rate of decrease increases in the order of atoms with smaller atomic radii, that is, in the order of germanium Ge, tin Sn, and lead Pb.

In this embodiment, the discharge plasma sintering apparatus 10 is used to simultaneously apply and pressurize a pulsed current to the powder raw material 14 to simultaneously synthesize and sinter the compound. However, it is not always necessary to simultaneously solidify the powder raw material 14.

As the order of the steps, a pulsed current may be first applied to the powder raw material 14, and then the pressure may be increased. After the powder raw material 14 is pressurized, a pulsed current may be applied.

Thus, the thermoelectric semiconductor material is cut out from the compound sintered body 14 'synthesized according to the present embodiment into a shape according to the intended use of the thermoelectric element. For example, when the thermoelectric element is required to have a donut shape in view of the purpose of use, a donut-shaped material is cut out from the rectangular parallelepiped sintered body 14 'and formed.

Examples 101 to 131 By a method similar to the method described above, a powder material having the following composition was sintered at 500 ° C. for 2 hours using a discharge plasma sintering machine. The crystal structure and thermoelectric properties of the body were measured. FIG. 11 is a table showing compositions, sintering conditions, and crystal structures of Examples 101 to 131.
Is a table showing compositions, conduction types, and thermoelectric properties of Examples 101 to 131.

(1) Chemical formula Bi _1-x Sb _x Te _1-y
Powder material composed of Se _y (where 0 ≦ x ≦ 1, 0 <y ≦ 1) (Examples 101 to 116).

(2) Chemical formula Bi _2-x Sb _x Te _1-y
Powder material composed of Se _y (where 0 ≦ x ≦ 2, 0 ≦ y ≦ 1) (Examples 117 to 123).

(3) Chemical formula (Bi _1-x Sb _x ) ₄ (T
e _1-y Se _y ) ₅ (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1)
Powder material consisting of (Examples 124 to 131).

As a result of the above experiment, the compounds according to Examples 101 to 116 were found to have TSumoite (Tsumoito)
It was confirmed that it had the same layer structure as the mineral. In addition, the compounds according to Examples 101 to 131 were all PbTe and PbSnT shown in Comparative Examples 1 and 2 in FIG.
It was confirmed that the figure of merit was equal to or higher than that of the system e.

[Brief description of the drawings]

FIG. 1 is a table showing compositions, sintering conditions, and crystal structures of Examples 1 to 32.

FIG. 2 is a table showing compositions, conduction types, and thermoelectric characteristics of Examples 1 to 31.

FIG. 3 is a diagram showing a spark plasma sintering apparatus according to an embodiment.

FIG. 4 is a table showing document data of lattice spacing of PbBi ₂ Te ₄ ;

FIG. 5 is a table showing document data of lattice spacing of Bi ₁ Te ₁ ;

FIG. 6 is a diagram showing a measurement result of an X-ray reflection intensity of PbBi ₂ Te ₄ ;

FIG. 7 is a diagram showing a measurement result of X-ray reflection intensity for Bi ₁ Te ₁ ;

FIG. 8 is a diagram schematically illustrating a Racklidgeite (laccrizite) structure.

FIG. 9 is a diagram schematically illustrating a Tsumoite structure.

FIG. 10 is a diagram schematically showing a Bi ₂ Te ₃ structure.

FIG. 11 is a table showing compositions, sintering conditions, and crystal structures of Examples 101 to 131.

FIG. 12 is a table showing compositions, conduction types, and thermoelectric properties of Examples 101 to 131.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Spark plasma sintering apparatus 11 Upper punch 12 Lower punch 13 Die 14 Powder raw material 14 'sintered body 15 Upper electrode 16 Lower electrode 17 Chamber 18 Pressurizing mechanism 19 Power supply 20 Controller 21 Temperature sensor

Claims (15)

[Claims] 1. The chemical formula AB ₂ X ₄ (where A is Pb, S
n, a simple substance or a mixture of Ge (Group IV element),
B is a simple substance or a mixture of Bi and Sb (Group V element), and X is a simple substance or a mixture of Te and Se (Group VI element). 2. A thermoelectric semiconductor material having the chemical formula Bi _1-x Sb _x Te ₁ (where 0 ≦ x ≦ 1). 3. The chemical formula A _y B _1-y X ₁ (where 0 ≦ y
≦ 0.25, A is a simple substance or a mixture of Pb, Sn, Ge (Group IV element), and B is Bi, Sb (V
Group element) or a mixture thereof, X is Te, Se
(Group VI element) or a mixture thereof. 4. A is a simple substance or a mixture of Pb, Sn, Ge (Group IV element), and B is Bi, Sb (Group V element).
When X is a simple substance or a mixture of Te and Se (Group VI element), these A, B,
X is mixed at a stoichiometric ratio of 1: 2: 4, and a pulse-like current is applied to the powder of the raw material of the thermoelectric semiconductor material to cause a discharge between the powder particles, thereby obtaining a chemical formula AB ₂ X ₄ A method for producing a thermoelectric semiconductor material, comprising synthesizing a compound having a uniform structure represented. 5. A pulse-like current is applied to a raw material powder of a thermoelectric semiconductor material in which Bi, Sb, and Te are mixed at a stoichiometric ratio of 1-x: x: 1 (where 0 ≦ x ≦ 1). This causes a discharge between the powder particles, and the chemical formula Bi _1-x
A method for producing a thermoelectric semiconductor material, comprising synthesizing a compound having a uniform structure represented by Sb _x Te ₁ . 6. A is a simple substance or a mixture of Pb, Sn, and Ge (group IV element), and B is Bi, Sb (group V element).
When X is a simple substance or a mixture of Te and Se (Group VI element), these A, B,
X is mixed at a stoichiometric ratio of y: 1-y: 1 (where 0 ≦ y ≦ 0.25), and a pulse-like current is applied to the powder of the raw material of the thermoelectric semiconductor material. And producing a compound having a uniform structure represented by the chemical formula A _y B _1-y X ₁ . 7. A is a simple substance or a mixture of Pb, Sn, Ge (Group IV element), and B is Bi, Sb (Group V element).
When X is a simple substance or a mixture of Te and Se (Group VI element), these A, B,
X is mixed in a stoichiometric ratio of 1: 2: 4, and a pulsed current is applied to the powder of the raw material of the thermoelectric semiconductor material, and a pressure is applied to the powder to cause a discharge between the powder particles to produce a chemical formula A
A method for producing a thermoelectric semiconductor material, comprising synthesizing a compound having a uniform structure represented by B ₂ X ₄ and forming a sintered body of the compound. 8. Bi, Sb and Te are expressed as 1-x: x: 1 (
However, thermoelectric semiconductor materials mixed at a stoichiometric ratio of 0 ≦ x ≦ 1)
When a pulsed current is applied to the raw material powder,
Both pressures are applied to cause a discharge between the powder particles and the chemical formula
Bi_1-xSb _xTe₁A compound of uniform tissue represented by
As well as forming a sintered body of the compound.
A method for producing a thermoelectric semiconductor material, characterized in that: 9. A is a simple substance or a mixture of Pb, Sn, Ge (Group IV element), and B is Bi, Sb (Group V element).
When X is a simple substance or a mixture of Te and Se (Group VI element), these A, B,
A pulse current is applied to the powder of the raw material of the thermoelectric semiconductor material in which X is mixed at a stoichiometric ratio of y: 1-y: 1 (where 0 ≦ y ≦ 0.25) and pressure is applied. thermoelectric semiconductor, characterized in that so as to form a sintered body of the compound with the synthesis of compounds of homogeneous tissue of formula a _{y B 1-y} X 1 to perform the discharge between the powder particles Material manufacturing method. 10. The chemical formula Bi _1-x Sb _x Te _1-y S
e _y (where 0 ≦ x ≦ 1, 0 <y ≦ 1). 11. The chemical formula Bi _2-x Sb _x Te _1-y S
A thermoelectric semiconductor material consisting of e _y (where 0 ≦ x ≦ 2, 0 ≦ y ≦ 1). 12. The chemical formula (Bi _1-x Sb _x ) ₄ (Te
_1-y Se _y ) ₅ (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1). 13. Bi, Sb, Te, Se are represented by 1-x:
x: 1-y: y (however, 0 ≦ x ≦ 1, 0 <y ≦ 1) The powder is obtained by applying a pulsed current to the raw material powder of the thermoelectric semiconductor material mixed at a stoichiometric ratio. A discharge is performed between the particles, and the chemical formula Bi _1-x Sb _x Te _1-y Se
_A method for producing a thermoelectric semiconductor material, comprising synthesizing a compound having a uniform structure represented by _y . 14. Bi, Sb, Te, Se is 2-x:
x: 1-y: y (however, 0 ≦ x ≦ 2, 0 ≦ y ≦ 1) A powder is obtained by applying a pulsed current to the raw material powder of the thermoelectric semiconductor material mixed at a stoichiometric ratio. A discharge is performed between the particles, and the chemical formula Bi _2-x Sb _x Te _1-y Se
_A method for producing a thermoelectric semiconductor material, comprising synthesizing a compound having a uniform structure represented by _y . 15. Bi, Sb, Te, Se are set to 4 (1-
x): 4x: 5 (1-y): 5y (where 0 ≦ x ≦ 1,
A pulse-like current is applied to the raw material powder of the thermoelectric semiconductor material mixed at a stoichiometric ratio of 0 ≦ y ≦ 1) to cause a discharge between the powder particles, and a chemical formula (Bi _1-x S
A method for producing a thermoelectric semiconductor material, comprising synthesizing a compound having a uniform structure represented by (b _x ) ₄ (Te _1-y Se _y ) ₅ .