JP3605366B2 - Thermoelectric element manufacturing method, thermoelectric element and thermoelectric module manufactured using the same - Google Patents

Description

【００４６】
本発明の試料Ｎｏ．２〜８、１０〜１６、１８〜２３及び２５、２６は、配向度が０．４１以上、性能指数が２．０７×１０^−３／Ｋ以上と大きかった。
【００４７】
一方、原料中にＡ_２Ｂ_３型単結晶が２容量％と少なく、本発明の範囲外の試料Ｎｏ．１及び１７は、配向度が０．３５以下、性能指数が１．９３×１０^−３／Ｋ以下といずれも低かった。
【００４８】
また、原料中にＡ_２Ｂ_３型単結晶が９５容量％と多く、本発明の範囲外の試料Ｎｏ．９及び２４は、配向度が０．３８以下、性能指数が１．８９×１０^−３／Ｋ以下といずれも低かった。
【００４９】
実施例２
実施例１と同様にして作製したＣ面配向度が高く、性能指数の高い試料Ｎｏ．１２及び２２を用いてｎ型、ｐ型それぞれ１８対の縦１．２ｍｍ、横１．２ｍｍ及び高さ２ｍｍの熱電素子を切り出した。なお、このとき長手方向側面にＣ面配向する方向に切り出した。
【００５０】
それぞれの素子にＮｉ電極をメッキしたのち、Ｓｎ−Ｐｂはんだを用いて片面にＮｉメッキされたＣｕ電極が配線された１０×１２ｍｍのアルミナ基板上にｎ型、ｐ型が対になるように接合し、電極の端面にリード線をはんだ付けし、熱電モジュールを組み立てた。
【００５１】
モジュールの評価は電圧を変化させたときに、放熱面の温度を２７℃と一定にしたときの冷却面における温度から放熱面と冷却面の温度差を求めた。結果は７０℃であり、レーザーダイオード冷却用ペルチェ素子として充分な性能を有していた。
【００５２】
比較例
試料Ｎｏ．１及び１７を用いてｎ型、ｐ型それぞれ１８対の１．２×１．２ｘ２ｍｍの熱電素子を同様にして切り出した。なお、このとき長手方向側面にＣ面配向する方向に切り出した。
【００５３】
性能評価は、実施例２と同様にして行った。結果は温度差が６１℃と冷却性能が本発明品と比べて劣っており、レーザーダイオード冷却用として使用できないレベルのものであった。
【００５４】
【発明の効果】
本発明によれば、型単結晶と、反応して型単結晶を形成する金属粉末とからなる混合原料を型単結晶が配向するように成形し、それを焼成することによって、型単結晶を粒成長させ、特定の方向に配向し、熱電特性に優れた熱電素子を製造できる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a thermoelectric element, a thermoelectric element, and a thermoelectric module using the same.
[0002]
[Prior art]
Conventionally, cooling by a thermoelectric module using a thermoelectric element using the Peltier effect has been frequently used for temperature control of a laser diode, a thermostat or a refrigerator, and a thermoelectric material used for a thermoelectric module for cooling near room temperature includes cooling. material Bi 2 _Te 3 from the viewpoint of characteristics superior _(bismuth telluride) is generally used.
[0003]
Further thermoelectric device must be used as a pair of p-type and n-type, a solid solution of the p-type _Bi 2 Te ₃ and _Sb 2 Te ₃ (antimony telluride) is, the n-type and _Bi 2 Te ₃ It is known that a solid solution with Bi ₂ Se ₃ (bismuth selenide) exhibits particularly excellent performance, and this A ₂ B ₃ type (A is one or two of Bi or Sb, B is one of Te or Se) (Seed or two kinds) crystals are widely used as thermoelectric materials for thermoelectric modules for cooling.
[0004]
This A ₂ B ₃ type crystal has long been produced as an ingot or a single crystal having a large crystal grain by a zone melt method, a unidirectional solidification, or the like, and a sliced product thereof has been used, but a thermoelectric element used in a thermoelectric module has been used. Many of these crystals, which have cleavage planes when cut to a size of several mm square, have extremely low processing yields, and in recent years, polycrystals manufactured by hot pressing or the like have been used to maintain strength for processing. ing.
[0005]
However, since the thermoelectric properties of the A ₂ B ₃ type single crystal are anisotropic with respect to the crystal axis, there is a problem that the performance deteriorates in a polycrystal having a random crystal direction. Therefore, in order to produce a thermoelectric module having a cooling performance comparable to that of a single crystal, it is necessary to use a material in which crystals are oriented in the same manner as a single crystal. It is proposed in JP-A-10-178219.
[0006]
In addition, the process of producing an ingot or a single crystal, crushing and baking it is complicated, requires a long-time treatment, and a process including a slice process causes a slice loss and increases costs, Japanese Patent Application Laid-Open No. 2-256283 has proposed that a specific mixed raw material is formed into a desired shape and then fired to obtain a thermoelectric element.
[0007]
[Problems to be solved by the invention]
However, according to the method disclosed in Japanese Patent Application Laid-Open No. H10-178219, the metal powder used as a raw material must be an A ₂ B ₃ type crystal. After forming or cooling, it has to be crushed after cooling or in the cooling process, which raises the cost of raw materials before sintering greatly, and the size of crystals obtained after crushing ingots and single crystals. However, since the crystal size and orientation of the sintered body greatly change depending on the shape, it is not easy to sufficiently raise and stabilize the orientation, and there is a problem that the raw material yield is low.
[0008]
In the method disclosed in Japanese Patent Application Laid-Open No. 2-256283, the number of steps is reduced and slice loss is eliminated, but there is a problem that thermoelectric performance is reduced due to small orientation. Therefore, a sufficient figure of merit for cooling is not obtained, and a thermoelectric module using a thermoelectric element manufactured by this method has not been put to practical use.
[0009]
An object of the present invention is to provide a method for manufacturing a thermoelectric element that is low in cost, has excellent mass productivity, and has a high degree of crystal orientation, and a thermoelectric element and a thermoelectric module that are manufactured by using the method and have excellent thermoelectric performance.
[0010]
[Means for Solving the Problems]
According to the present invention, an alloy having a high degree of orientation can be easily obtained by sintering a compact containing a plate-like A ₂ B ₃ type single crystal and a metal powder which reacts to form an A ₂ B ₃ type crystal. The obtained thermoelectric element is based on the finding that it has excellent thermoelectric performance.
[0011]
That is, in the method for producing a thermoelectric element of the present invention, when A is Bi and / or Sb and B is Te and / or Se, the A ₂ B ₃ type single crystal reacts with 5 to 80% by volume, firing the shaped body comprising a powder of metal and / or alloy becomes a ₂ B ₃ type crystal, it is characterized in that to obtain an alloy mainly composed of the a ₂ B ₃ type crystal.
[0012]
As a result, the cost of manufacturing the element can be reduced by minimizing the use of the high-cost A ₂ B ₃ type single crystal, and crystal growth occurs while maintaining the shape of the plate-like crystal during sintering. It is possible to increase the orientation of the element to be obtained. Therefore, by using the thermoelectric element obtained by the product of the present invention, a high-performance thermoelectric module for cooling use can be manufactured at low cost.
[0013]
Also, the _A 2 _{B 3} type single crystal is a plate-like crystals having a maximum diameter d and thickness t, the ratio d / average t is 3.0 or more, said by laser diffraction method _A 2 _{B 3} type single crystal Is preferably 1.0 μm or more. As a result, the crystal orientation of the sintered body can be increased, and the performance index of the device can be increased.
[0014]
Further, it is preferable that the molded body contains at least one of I, Cl, Hg, Br, Ag and Cu. Thereby, the carrier concentration of the thermoelectric semiconductor can be adjusted, and the thermoelectric characteristics can be further improved.
[0015]
Further, the thermoelectric element of the present invention is made of an alloy mainly composed of the produced A ₂ B ₃ type single crystal, and has a C-plane orientation degree of 0.40 or more in a specific direction. It is. Thereby, a high figure of merit due to the crystal orientation can be maintained.
[0016]
Further, the thermoelectric module of the present invention is provided with a plurality of thermoelectric elements made of A ₂ B ₃ type crystal , a pair of heat exchange substrates sandwiching the thermoelectric elements, and provided on one main surface of the heat exchange substrate, In a thermoelectric module including wiring for electrically connecting elements, a degree of C-plane orientation of a plane parallel to a current flowing direction of the thermoelectric element is 0.40 or more, and a figure of merit is 2 × 10 −3 / K or more. It is characterized by being. Thereby, it has sufficient characteristics for cooling applications such as laser diodes.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
The method for producing a thermoelectric element according to the present invention is directed to a semiconductor crystal comprising an A ₂ B ₃ type crystal (A is Bi and / or Sb, B is Te and / or Se), and has a composition ratio B / A of 1.45. is preferably ～1.55, particularly a solid solution of _{Bi 2 Te 3, Bi 2 Te} 3 and _Bi 2 Se ₃ is known _{Bi 2 Te 3-x Se x} (x = 0.05~0.25 ), or _Bi 2 Te ₃ and _Sb to _{2 Te Bi y Sb 2-y} Te 3 is a solid solution of ₃ (y = 0.1 to 0.6) can be suitably used.
[0018]
According to the present invention, it is important to use, as a raw material, a powder having at least two kinds of properties of A ₂ B ₃ type crystal. First, as the first powder, a type single crystal composed of Bi and / or Sb and Te and / or Se is prepared. That is, when A is Bi and / or Sb and B is Te and / or Se, a single crystal represented by A ₂ B ₃ is prepared so as to be at least 5% by volume in the total amount.
[0019]
The A ₂ B ₃ type single crystal is not particularly limited as long as it has anisotropy in shape to enhance the orientation, but is particularly a plate-like crystal having a maximum diameter d and a thickness t. Is preferred. The average of the aspect ratio represented by the ratio d / t of the maximum diameter d to the thickness t of the plate-like crystal d / t is 3.0 or more, particularly 4.0 or more, and more preferably 5.0 or more. It is preferable in order to improve the uniformity of the thermoelectric characteristics and to increase the degree of orientation.
[0020]
An average particle diameter d50 (particle diameter at a cumulative weight ratio of 50%) determined by a laser diffraction method of 1.0 μm or more, especially 2.0 μm, and more preferably 3.0 μm or more enhances the orientation and improves the orientation. The orientation is preferable because it has anisotropy with respect to the direction of the pressure during molding and sintering.
[0021]
When the A ₂ B ₃ type crystal is an n-type semiconductor, the molded body contains at least one of I, Cl, Hg, Br, Ag and Cu as a dopant, whereby the semiconductor characteristics are improved. As a result, It is preferable to improve thermoelectric characteristics. For example, by adding 0.06 to 0.10% by weight of HgBr ₂ or SbI ₃ to Bi ₂ Te _2.95 Se _0.05 which is n-type, the carrier concentration of electrons or holes is increased. be able to. Note that in a p-type semiconductor, since Te or Se is used as a dopant, an A ₂ B ₃ type crystal containing excess Te or Se can be used.
[0022]
As the second powder, a metal powder is prepared so that the above-mentioned A ₂ B ₃ type crystal is obtained by firing. For example, when the single crystal is Bi ₂ Te ₃ , Bi powder and Te powder are prepared so that the molar ratio of Bi and Te is 2: 3. In the case of Bi _0.5 Sb _1.5 Te ₃ , Bi powder, Sb powder, and Te powder are prepared so that the molar ratio of Bi, Sb, and Te is 0.5: 1.5: 3. Good, an alloy mixed powder in which the molar ratio of Bi ₂ Te ₃ to Sb ₂ Te ₃ is 1: 3 may be prepared, or the above-mentioned metal powder and alloy powder may be mixed.
[0023]
The metal powder and / or alloy powder as the second crystal is a substance different from the plate crystal as the first single crystal, and the composition thereof is adjusted so as to react during firing and become a plate crystal. It is important that the metal and / or the alloy is a suitable metal. This is because a plate crystal of a seed crystal grows by a reaction, and a sintered body with high orientation is obtained. Conversely, if the crystal is the same as the plate crystal of the seed crystal, sintering simply proceeds, This is because anisotropy due to crystal growth in accordance with the shape anisotropy of the seed crystal is less likely to occur.
[0024]
Next, a mixed raw material is prepared by mixing the plate-like crystal with a metal powder and / or an alloy powder. According to the present invention, the mixed powder contains 5 to 80% by volume of the plate-like crystal. Is important, and particularly preferably 10 to 70% by volume, more preferably 20 to 60% by volume. That is, when the content is less than 5% by volume, the orientation of the A ₂ B ₃ type crystal in the sintered body becomes small, and when it exceeds 80% by volume, it becomes difficult to obtain a dense body.
[0025]
As a mixing method for producing the mixed raw material, it is preferable to use a wet or dry ball mill mixing method or the like, avoiding a pulverizing step that causes the destruction of plate crystals such as mechanical alloying.
[0026]
The obtained mixed raw material is molded using a known molding method, such as a rubber press or a mold press, and the obtained molded body is fired. Alternatively, the powder is put into a mold such as a carbon die and fired. Prior to firing, heat treatment is preferably performed in a reducing atmosphere in order to remove an oxide layer and adsorbed oxygen on the surface of the plate-like crystals, metal powder, and alloy powder in the raw material. For example, heat treatment is performed in a gas atmosphere such as hydrogen or forming gas at 300 to 400 ° C. for about 1 to 24 hours. By this heat treatment, oxygen on the particle surface can be removed, the orientation is enhanced, and a thermoelectric element having a high figure of merit can be obtained.
[0027]
For sintering, known sintering methods such as normal-pressure sintering, hot pressing, atmospheric pressure sintering, plasma sintering, microwave sintering, and HIP sintering can be used. , HIP sintering and plasma sintering are desirable.
[0028]
In the case of hot pressing, the powder may be directly charged into a hot press mold, but a uniaxial mold press is performed to increase the degree of orientation of the plate-like crystal, and a molded body is prepared in advance, and the molded body is formed. Is preferably loaded into a hot press mold.
[0029]
The sintering temperature is preferably about 100 ° C. lower than the melting point, for example, 400 to 500 ° C. for Bi ₂ Te ₃ and 400 to 480 ° C. for Bi _0.5 Sb _1.5 Te _3. Is desirable. In this temperature range, the seed crystal itself does not change, but the surrounding metal other than the seed crystal undergoes a chemical change to the same composition as the seed crystal, and under this condition, the metal changes to the seed crystal composition Is mainly generated on the surface of the seed crystal, and selective crystal growth occurs while maintaining the shape anisotropy of the plate-like seed crystal.
[0030]
The thermoelectric element manufactured in this manner is made of a sintered body having a high orientation mainly composed of A ₂ B ₃ type crystal. It is important that the degree of C-plane orientation in a specific direction is 0.40 or more. A thermoelectric element having such an orientation has a characteristic that thermoelectric characteristics in the C-plane direction are high because the resistivity in the C-plane direction is low.
[0031]
The degree of orientation refers to the I ₍₀₀₆₎ , I ₍₀₁₅₎ , and I ₍₀₀₁₅₎ peak intensities of the A ₂ B ₃ type crystal obtained by X-ray diffraction, and the I to the sum of these peak intensities. _It indicates the ratio between ₍₀₀₆₎ and I ₍₀₀₁₅₎ and is represented by f given by the following equation. f = I ₍₀₀₆₎ + I ₍₀₀₁₅₎ / I ₍₀₀₆₎ + I ₍₀₁₅₎ + I ₍₀₀₁₅₎ Further, the thermoelectric module of the present invention comprises a plurality of thermoelectric elements made of A ₂ B ₃ type crystal and the thermoelectric elements. A thermoelectric module including a pair of heat exchange substrates to be sandwiched, and a wiring provided on one main surface of the heat exchange substrate and electrically connecting the thermoelectric elements, and an n-type thermoelectric element and a p-type thermoelectric element. Are arranged at the same number and at appropriate intervals at appropriate intervals, each is electrically connected in series, connected to an external electrode, and has a structure in which both ends of a thermoelectric element are sandwiched by a heat exchange board.
[0032]
In the n-type and p-type thermoelectric elements, the degree of C-plane orientation f of the plane parallel to the direction in which current flows is 0.40 or more, and the figure of merit is 2 × 10 ⁻³ / K or more. This is important, and thereby, excellent performance as a thermoelectric element can be exhibited.
[0033]
Here, the figure of merit Z is represented by the following equation Z = S ² / ρk, where S is the Seebeck coefficient, ρ is the resistivity, and k is the thermal conductivity.
And shows the efficiency when the thermoelectric element is used as a cooling element or a power generation element.
[0034]
【Example】
Example 1
For an n-type thermoelectric element, a Bi ₂ Te _2.95 Se _0.05 crystal having a purity of 99.99% or more as a seed crystal A ₂ B ₃ type single crystal, a purity of 99.99% or more as a metal raw material, and an average particle Bi, Te, and Se metal powders having a diameter of 100 μm, and SbI ₃ powder having a purity of 99.9% and an average particle diameter of 1.8 μm as a dopant to be added as needed were prepared.
[0035]
Further, for a p-type thermoelectric element, a Bi _0.5 Sb _1.5 Te ₃ crystal having a purity of 99.99% or more as a seed crystal A ₂ B ₃ single crystal, a purity of 99.99% or more as a metal raw material, Bi, Sb and Te metal powders having an average particle diameter of 100 μm were prepared.
[0036]
The single crystal was pulverized by a stamp mill and classified using several meshes to obtain several types of plate-like crystals. The average particle diameter of the plate-like crystal was determined by a laser diffraction method, the maximum diameter d and the thickness t of the crystal were determined by averaging 200 particles from an SEM photograph, and the aspect ratio d / t was calculated.
[0037]
The Bi, Te and Se metal powders prepared for the n-type thermoelectric element have a composition of Bi ₂ Te _2.95 Se _0.05, and Bi, Sb and Each metal powder of Te was weighed so as to have a Bi _0.5 Sb _1.5 Te ₃ composition, and each was mixed using isopropanol (IPA) as a solvent and a urethane ball.
[0038]
The mixed slurry was dried at 60 ° C. in a vacuum, and the obtained mixed powder was passed through a 200 mesh to obtain a metal powder.
[0039]
The plate-like crystal and the metal powder, which are single crystals, obtained in this manner were weighed by 10 g each in the composition shown in Table 1, mixed in an alumina mortar, and then placed in a 20 mmφ mold, and 100 MPa. Press molding was performed uniaxially under pressure.
[0040]
The molded body was heat-treated at 350 ° C. for 24 hours in a hydrogen stream, and then subjected to normal pressure firing (NS), pressure firing in an Ar atmosphere (GPS), hot pressing (HP) under the conditions shown in Table 1. It was fired by isotropic pressure sintering (HIP) and spark plasma sintering (SPS).
[0041]
In order to measure the thermal conductivity, the Seebeck coefficient, and the resistivity in a direction parallel to the pressing direction, a measurement sample was prepared for each of the sintered bodies. For the measurement of the thermal conductivity, a disk sample having a diameter of 10 mm and a thickness of 1 mm was prepared, and for the measurement of the Seebeck coefficient and the resistivity, a prism sample having a length of 4 mm, a width of 4 mm and a length of 15 mm was prepared.
[0042]
The thermal conductivity was measured by a laser flash method, the Seebeck coefficient was measured by a thermoelectricity evaluation device manufactured by Vacuum Riko Co., and the resistivity was measured by a four-terminal method at 25 ° C.
[0043]
The thermoelectric figure of merit Z was calculated from Z = S ² / ρk (S is the Seebeck coefficient, ρ is the resistivity, and k is the thermal conductivity).
[0044]
Further, the prism sample was used for measuring the C plane orientation degree f. That is, a cross section or an end face of 4 mm in length and 4 mm in width is measured by X-ray diffraction, and the following expression f = I ₍₀₀₆₎ + I ₍₀₀₁₅₎ / I ₍₀₀₆₎ + I ₍₀₁₅₎ + I _{(0015 ) is} obtained from the obtained peak intensity. ₎
Was calculated. Table 1 shows the results.
[0045]
[Table 1]

[0046]
Sample No. of the present invention In 2 to 8, 10 to 16, 18 to 23, and 25 and 26, the degree of orientation was 0.41 or more, and the figure of merit was as large as 2.07 × 10 ⁻³ / K or more.
[0047]
On the other hand, the amount of A ₂ B ₃ type single crystal in the raw material was as small as 2% by volume, and Sample No. In Examples 1 and 17, the degree of orientation was 0.35 or less, and the figure of merit was 1.93 × 10 ⁻³ / K or less.
[0048]
In addition, A ₂ B ₃ type single crystal was as large as 95% by volume in the raw material, and sample No. In Nos. 9 and 24, the degree of orientation was 0.38 or less, and the figure of merit was 1.89 × 10 ⁻³ / K or less.
[0049]
Example 2
Sample No. having a high degree of C-plane orientation and a high figure of merit produced in the same manner as in Example 1. Using 12 and 22, 18 pairs each of n-type and p-type thermoelectric elements having a length of 1.2 mm, a width of 1.2 mm, and a height of 2 mm were cut out. At this time, it was cut out in the direction of C-plane orientation on the longitudinal side surface.
[0050]
After plating a Ni electrode on each element, it is joined using Sn-Pb solder on a 10 × 12 mm alumina substrate on which a Cu electrode plated with Ni on one side is wired so that n-type and p-type are paired. Then, a lead wire was soldered to the end face of the electrode, and a thermoelectric module was assembled.
[0051]
In the evaluation of the module, when the voltage was changed, the temperature difference between the heat radiating surface and the cooling surface was obtained from the temperature on the cooling surface when the temperature of the heat radiating surface was kept constant at 27 ° C. The result was 70 ° C., indicating that the device had sufficient performance as a Peltier device for cooling a laser diode.
[0052]
Comparative Example Sample No. Using 1 and 17, 18 pairs of n-type and p-type thermoelectric elements of 1.2 × 1.2 × 2 mm were cut out in the same manner. At this time, it was cut out in the direction of C-plane orientation on the side surface in the longitudinal direction.
[0053]
The performance evaluation was performed in the same manner as in Example 2. As a result, the temperature difference was 61 ° C., and the cooling performance was inferior to that of the product of the present invention, and was at a level that could not be used for cooling a laser diode.
[0054]
【The invention's effect】
According to the present invention, a mold single crystal and a mixed raw material comprising a metal powder that reacts to form a mold single crystal are formed so that the mold single crystal is oriented, and then fired to form the mold single crystal. It is possible to produce a thermoelectric element which is grown in a grain direction and oriented in a specific direction and has excellent thermoelectric properties.

Claims (5)

When A is Bi and / or Sb and B is Te and / or Se, a metal that reacts with the A ₂ B ₃ type single crystal with 5 to 80% by volume to become the A ₂ B ₃ type crystal and / or A method for producing a thermoelectric element, comprising: sintering a compact containing a powder of an alloy to obtain an alloy mainly composed of the A ₂ B ₃ type crystal. Wherein A ₂ B ₃ type single crystal is a plate-like crystals having a maximum diameter d and thickness t, the average of the ratio d / t is 3.0 or more, the average of the A ₂ B ₃ type single crystal by the laser diffraction method The method for producing a thermoelectric element according to claim 1, wherein the particle diameter is 1.0 µm or more. The method for manufacturing a thermoelectric device according to claim 1, wherein the molded body contains at least one of I, Cl, Hg, Br, Ag, and Cu. An alloy mainly composed of an A ₂ B ₃ type single crystal produced by the method according to claim 1, wherein the degree of C-plane orientation in a specific direction is 0.40 or more. Characteristic thermoelectric element. A plurality of thermoelectric elements made of A ₂ B ₃ type crystal, a pair of heat exchange boards sandwiching the thermoelectric elements, and a wiring provided on one main surface of the heat exchange board and electrically connecting the thermoelectric elements. Wherein the degree of C-plane orientation of a plane parallel to the direction in which the current of the thermoelectric element flows is 0.40 or more, and the figure of merit is 2 × 10 ⁻³ / K or more. .