JP2000252526A - Skutterudite thermoelectric material, thermocouple and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a sintered body which is formed of Co-Sb-filled skutterudite thermoelectric material that converts heat direct into electricity through a Seebeck effect, more improved in figure of merit, and lessened in thermal conduction. SOLUTION: Skutterudite thermoelectric material is composed of Sb- containing skutterudite compound crystal grains and metal oxide dispersed between grain boundaries and sintered into a sintered body. Metal oxide restrains crystal grains from growing in a sintering process, and a skutterudite compound is atomized into fine crystal grains which are 20 μm or less in average crystal grain diameter. The fine crystal grains are increased in grain boundary areas, phonon scattering is enhanced, and the sintered body is lessened in thermal conductivity and enhanced in figure of merit. Rare earth metal oxide is made to serve as the above metal oxide. The skutterudite compound contains a filled skutterudite compound whose composition is represented by a structural formula, LnyFexCo4-xSb12 (where Ln denotes rare earth metal, 0<X<=4, 0<y<=1).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a skutterudite-based thermoelectric material for directly converting heat due to the Seebeck effect into electricity, a thermoelectric couple using the same, and a method for producing the same.

[0002]

2. Description of the Related Art Hitherto, as a thermoelectric material utilizing the Seebeck effect and the Peltier effect, a Bi ₂ Te ₃ type thermoelectric material is well known, and although it has been put to practical use for some applications, its operating temperature is high. The range was very narrow and limited to use near room temperature.

It is also known that a CoSb ₃ -based intermetallic compound having a skutterudite-type crystal structure is used as a thermoelectric material. The compound of this system has a feature that the mobility of electrons or holes is large, and is expected as a material that can achieve both high thermoelectric conversion performance and a wide operating temperature range.

The important properties of a thermoelectric material include the Seebeck coefficient S, the electrical conductivity σ, and the thermal conductivity κ as parameters.
The figure of merit Z = S ² σ / κ. In order to increase the figure of merit Z, both S and σ of the thermoelectric material are large and κ
Is desirably small. Each of these parameters is determined by the type and amount of impurities added to the main component of the thermoelectric material. In addition, each parameter is changed by dispersing impurities as a second phase at the grain boundaries.

Regarding the prior art, Japanese Patent Application Laid-Open No. 9-26072
No. 9 discloses that conductivity σ is improved by a sintered body containing CoSb ₃ as a main component and a metal Sb phase as a second phase at a grain boundary thereof.

In addition, the above publication discloses a method for producing a sintered body, in which a CoSb ₃ -based alloy powder containing a metal Sb phase is subjected to pressure treatment and then heat-treated at a temperature equal to or higher than the liquid phase precipitation temperature of Sb, thereby forming a grain boundary. A method for forming a sintered body in which an Sb phase is dispersed is disclosed.

In recent years, filled skutterudite represented by the formula of LnT ₄ Pn ₁₂ (Ln is a rare earth metal, T is a transition metal, and Pn is an element such as P, As, Sb, etc.)
Compounds having a (skutterudite) structure have attracted attention as thermoelectric materials. Filled skutterudite is a crystal in which a part of two vacancies existing at an octant of a unit cell of a skutterudite crystal is filled with a heavy element such as a rare earth metal. This is because, by filling the vacancy of the skutterudite-type crystal with a rare earth metal, the Ce atom vibrates due to a weak bond with Sb and becomes a phonon scattering center, so that the thermal conductivity can be significantly reduced. Can be expected.

[0008] Regarding prior art relating to this, for example,
DTMorelli, GPMeisner; "Highfigure of merit in
Ce-filled Skutterdite ", IEEE, 15th Internatio
nalConference on Thermoelectronics (1996), pp 91
Is CeFe filled with Ce and a part of Co is replaced with Fe
It discloses the characteristics of the _x Co _4-x Sb ₁₂ based discussions ether Daito thermoelectric material. According to this, the larger the substitution number x of Fe for Co in the range of 2 to 4, the higher the conductivity,
Although the thermal conductivity is low, the Seebeck coefficient is low, so that the highest figure of merit has an optimal range for the number of substitutions.

In order to use these materials as a thermoelectric module, it is convenient to form a pn junction with a Co-Sb-based filled skutterudite-based thermoelectric material, but a filled skutterudite structure filled with a rare earth element is preferred. Can be used as a p-type thermoelectric material.

Japanese Patent Application Laid-Open No. 9-64422 discloses a thermoelectric module using a thermoelectric material.
It is disclosed that a PbTe-based compound is used for the n-type compound and that both compound materials are directly or indirectly connected via a metal conductor in a pn junction. In this method, both compound powders are pressed together so as to join at a point, and the horseshoe-shaped form is sintered to produce a module.

[0011]

Conventionally, a material in which an Sb phase is dispersed as a second phase in a CoSb ₃ -based thermoelectric material has a higher conductivity σ, but a lower Seebeck coefficient S and a lower power factor S ² σ is not significantly improved. Further, the dispersion of the Sb phase does not reduce the thermal conductivity κ. Co
In order to further improve the performance of the Sb ₃ -based thermoelectric material, the problem of lowering the thermal conductivity has been left. Also, Sb to be mixed
Depending on the particle size of the phase, the dispersion becomes non-uniform, causing a problem of segregation and accompanying performance instability.

The filled skutterudite structure can be expected to have excellent performance, but has a problem that it is thermally unstable and is easily decomposed. In order for heavy atoms to fill one empty octant with rare earth elements, the charge in the cell needs to be balanced. For example, when filling with tetravalent atoms Ln, charge compensation can be performed by replacing four divalent Co atoms in the skutterudite structure with, for example, four trivalent Fe atoms. . Since Fe and Sb alone cannot provide a skutterudite structure, if the electron valence of the filling element in the crystal is not constant, a part of the filled skutterudite structure may decompose into FeSb ₂ and Sb. . In order to act as a phonon center, the filler element must have a weak bond with Sb. This is a thermally unstable bond, and decomposition occurs at high temperatures due to dropout of the filler element. There was a problem to do.

In order to assemble and use these materials as a thermoelectric module, it is necessary to form a pn junction with two types of thermoelectric materials. Conventionally, as for the n-type, there has been reported a material which can achieve both a high Seebeck coefficient S and a high conductivity σ by adding Pd or Pt to a CoSb ₃ crystal (Japanese Unexamined Patent Application Publication No. Hei 8 (1996) -108).
186294). However, in order to obtain a p-type thermoelectric material, the CoSb ₃ crystal has an iron group transition metal M
It is conceivable to add metal elements such as n, Cr, Fe, and Ru.
Is sharply reduced, so that the power factor is not improved. As a p-type, conventional thermoelectric materials have been unsatisfactory in performance.

Further, in the filled skutterudite-based thermoelectric material, a filled skutterudite structure filled with a rare earth element is of a p-type, and for n-type, a method of adding Co to control the carrier concentration has been attempted. Good results have not yet been obtained.

Further, when a material used at a high temperature, such as a skutterudite-based thermoelectric material, is modularized, a method such as direct bonding or brazing has been used for the pn junction at the high temperature end. However, there is a problem that contact failure or disconnection occurs at high temperatures due to the difference in the coefficient of thermal expansion from the thermoelectric material.

[0016] In view of the above problems, the present invention firstly provides Co
An object of the present invention is to provide a filled skutterudite-based sintered body that further improves the figure of merit of a -Sb-based filled skutterudite-based thermoelectric material, and a method for manufacturing the same. For this purpose, an object of the present invention is to further reduce the thermal conductivity while improving the thermal stability of a filled skutterudite-based sintered body.

The second object of the present invention is to provide a method for producing a CoSb ₃ -based sintered body by uniformly dispersing a transition metal in Co and Sb powders or CoSb ₃ -based compound powders and heat-treating the same. Things.

An object of the present invention is to provide a filled skutterudite-based sintered body that further improves the figure of merit of the filled skutterudite-based thermoelectric material, and a method of manufacturing the same. Another object of the present invention is to provide a highly reliable thermoelectric module using a skutterudite-based thermoelectric material and a method for manufacturing the same. For this purpose, the present invention provides a pn junction having a highly reliable junction.

[0019]

SUMMARY OF THE INVENTION The present invention relates to a Sb-containing scatteludite thermoelectric material, wherein the sintered body is composed of finely divided crystal grains of skatteludite, whereby the crystal grain size of the sintered body is obtained. , The area of the crystal grain boundary with respect to is increased, and the scattering of phonons at the grain boundary is promoted, and the thermal conductivity as a thermoelectric material is reduced.

The thermoelectric material of the present invention is a sintered body in which fine particles of a metal oxide are dispersed at grain boundaries of a skutterudite crystal phase. The metal oxide particles suppress the growth of crystal grains during the sintering process, make the crystal phase finer, and lower the thermal conductivity of the thermoelectric material.

That is, the metal oxide phase exists at the grain boundary of the CoSb ₃ -based compound phase, and suppresses the grain growth of the CoSb ₃ crystal during the sintering process, so that the sintered body has a dense sintered structure. . As a result, the area of the crystal grain boundary with respect to the crystal grain size of the sintered body is increased, and the scattering of phonons at the grain boundary is promoted, and the thermal conductivity is reduced. The large number of oxide particles present at the grain boundaries themselves also cause phonon scattering and lower the thermal conductivity. Thus, the metal oxide phase improves the figure of merit as a skutterudite-type thermoelectric material and improves the thermoelectric conversion efficiency of the thermoelectric element.

As the metal oxide, in particular, a rare earth metal oxide is used. A small amount of rare earth metal, when precipitated at the grain boundary, improves the Seebeck coefficient S. Large atomic weight particles, such as rare earth metals, increase the electron and hole scattering indices, thereby increasing the Seebeck coefficient S.

In the present invention, the CoSb ₃ compound containing Co and Sb as main components preferably contains a transition metal. The transition metal replaces part of Co to change the Seebeck coefficient S and improve its value. As the transition metal, Cr, Mn, Fe, and Ru are used as p-type dopants. As an n-type toppant, Ni group (Ni, Pd, P
t) and noble metals (Cu, Ag, Au) are used.

The Sb-containing skutterudite compound is L
including _{n y Fe x Co 4-x} Sb 12 system filled discussions ether Daito, in the present invention, to prevent the filled discussions ether phosphoramidite crystals decompose, to prevent deterioration of the thermoelectric performance due to decomposition. Thermoelectric materials are, in particular, FeSb ₂ and S
b) to reduce the precipitation phase, thereby lowering the thermal conductivity.

In the decomposition process, the filler element Ln in the filled skutterudite crystal is oxidized and removed from the crystal lattice by oxygen in the thermoelectric material in the process of sintering.
Due to this, a part of the unstable filled skutterudite structure is decomposed into FeSb ₂ and Sb.
For this purpose, in the present invention, the process from raw material preparation to sintering is performed in a non-oxidizing atmosphere.

The filled discussions ether phosphoramidite based thermoelectric material of the present invention, Ni, Pd, and any element Pt was selected as the dopant, utilizing _{Ln y Fe x M 4-x} Sb 12 based compounds. When Co is added, a stable CoSb ₃ phase is generated and the lattice is insufficiently filled with Ln.
i and Pd act as perfect dopants because there is no stable compound with Sb. Therefore, the carrier concentration can be controlled without generating the second phase, and an n-type filled skutterudite-based thermoelectric material can be obtained.

The thermoelectric couple of the present invention is formed by direct bonding from two types of thermoelectric materials of p-type and n-type having Sb-containing skutterudite-based crystals, since both are of the same material and have a very small difference in thermal expansion. Provide a stable thermoelectric couple without cracking or separation at the joint. Such a couple is used as a thermoelectric module by connecting the parts on the low temperature side with a metal conductor and arranging them in series.

[0028]

The Sb-containing discussions ether Daito DETAILED DESCRIPTION OF THE INVENTION The present invention comprises InSb ₃ system, CoSb ₃ based discussions ether phosphoramidite, as Sb major component of ₁₂ system or the like _{Ln y Fe x Co 4-x} Sb Firudosuka' Contains terdite compounds. Ln _y F was substituted for Co Ni, Pd, in any element Pt
Compounds of e _x M _4-x Sb ₁₂ system is also used.

The thermoelectric material is a sintered body of the above compound, and the sintered body is limited to an average crystal grain size of 100 μm or less. When the average grain size exceeds 100 μm,
It is not preferable because the thermal conductivity increases. In particular, 20 μm
The following grain sizes are effective in reducing the thermal conductivity. In particular, the grain size is adjusted to a range of 5 to 10 μm. The crystal grain size of the sintered body can be obtained by previously adjusting the particle size of the raw material powder to this range, and suppressing the growth during sintering by compounding the oxide.

The thermoelectric material of the present invention is constituted as a sintered body composed of the above-mentioned skutterudite crystal grains and a metal oxide dispersed in the grain boundaries. The metal oxide is contained in the raw material particles, and suppresses grain growth and diffusion of the main phase particles during sintering heating. By finely adjusting the powder particle size of the raw material skutterudite-based compound in advance, fine crystals can be obtained in the sintered body.

The refinement of the crystal grains can further reduce the thermal conductivity κ and improve the figure of merit. That is, the area of the crystal grain boundary with respect to the crystal grain size of the sintered body increases, and phonon scattering at the grain boundary is promoted, the thermal conductivity is reduced, and the figure of merit as a thermoelectric material is improved. Oxide particles themselves scattered at the crystal grain boundaries,
In addition, it acts as a phonon scattering center and contributes to a decrease in thermal conductivity.

As the metal oxide, a stable metal oxide can be used, but an oxide of a rare earth metal is preferably used. The rare earth metal oxide particles themselves are present at the crystal grain boundaries and can increase the Seebeck coefficient. La, Ce, and Sm are used as the rare earth metal, and Ce is particularly preferred.

As described later, in the case of an unstable filled skutterudite-based electrothermal material, the dispersion of the metal oxide is suppressed during the sintering process.
The instability of the field skutterudite compound can be overcome, and its thermal stability is also improved.

The metal oxide preferably contains 0.1 to 15% (by weight) in the thermoelectric material. If it is less than 0.1%, the effect of suppressing grain growth is small, and if it exceeds 15%, the effect is saturated. Preferably, the oxide content is in the range of 1-10%.

The above-mentioned thermoelectric material is formed in advance from a mixed powder of Sb-containing skutterudite powder or its constituent materials and a metal oxide to be dispersed, and this is sintered and sintered. Body. Raw material powder, for example, when discussions ether phosphoramidite is CoSb ₃ compound is available CoSb ₃ compound particles in advance ingot is or even mixed powder metal Co and Sb formulated adjusted to CoSb ₃ composition Good.

In the present invention, as a mixing method, a method is employed in which an insoluble metal compound such as a hydroxide is precipitated and dispersed in a raw material powder of skutterudite by a precipitation method from an aqueous solution containing the metal. The metal oxide particles thermally decomposed from the insoluble metal compound are finer than the scatteludite particles, and are uniformly dispersed in the skatteludite particles. In a sintered body formed by sintering, fine oxide particles can be arranged at grain boundaries of fine crystal grains.

In the sedimentation method, a skutterudite-based crystal powder as a main phase is uniformly dispersed in an aqueous solution of a metal salt or hydroxide from which an oxide is to be obtained, and the pH thereof is adjusted. , Precipitated as insoluble fine crystals,
This is a method of attaching to the main phase crystal surface.

For example, by using a metal chloride aqueous solution and adding a small amount of aqueous ammonia thereto, the metal hydroxide can be uniformly attached around the main phase particles. The obtained mixture is subjected to thermal decomposition to obtain a mixed powder in which the metal oxide is uniformly and thinly dispersed on the surface of the main phase. By using the sedimentation method, a minute amount of metal oxide can be uniformly dispersed, and a structure in which the oxide layer surrounds the grain boundary of the main crystal of the sintered structure by sintering after forming can be obtained.

The above-mentioned uniform dispersion of the metal oxide is also applied to a filled skutterudite-based thermoelectric material. However, similarly to the above, the metal oxide dispersed at the grain boundary is formed between the particles during the sintering process. Since diffusion is also suppressed, decomposition of the filled skutterudite compound is suppressed, and the thermal stability is also improved.

Another embodiment of the present invention is, in particular, CoSb
_{For the 3} series, a CoSb ₃ -based thermoelectric material containing a transition metal in the crystal of the skutterudite-based compound is included. Such transition metals include Mn, Cr, Fe, as dopants for keeping the CoSb ₃ -based skutterudite compound in p-type.
Ru is used. The substitution amount of the transition metal is 0.001 to 0.01 m of 1 mol of Co in skatteludite.
The range of ol is good. Originally, CoSb ₃ skutterudite itself is p-type, but this is because Mn, Cr, Fe, R
By adding u, the Seebeck coefficient S can be increased to improve the power factor.

It was difficult to replace such a p-type element with Co of CoSb ₃ -based skutterudite by the conventional melting method. The present invention makes it possible to relatively easily substitute for Co by diffusing a transition metal into a skutterudite crystal in the process of sintering a mixed powder of a skutterudite compound and a transition metal. .

The transition metal includes a Ni group (N) as an element for holding the CoSb ₃ -based skutterudite compound in the n-type.
i, Pd, Pt) and noble metals (Cu, Ag, Au) can also be used. As a result, an n-type skutterudite-based thermoelectric material having the same crystal structure as that of the p-type skutterudite-based thermoelectric material and having similar thermal expansion characteristics can be obtained. By joining, a thermally stable thermoelectric couple can be formed.

In particular, for the replacement of the transition metal, the present invention utilizes a method of uniformly dispersing a transition metal and a raw material powder such as a CoSb ₃ compound. Such a method of uniformly dispersing the transition metal is a method in which a transition metal is electrolessly plated on a powder of Co and Sb or a CoSb ₃ -based compound powder to form a mixed powder. The mixed powder is sintered after molding.

Further, another method of uniform dispersion is to use Co and S
A powder obtained by mechanically alloying a transition metal on the surface of the powder b or the CoSb ₃ -based compound powder is used. The mixed powder similarly sinters after molding. Furthermore, as a method of uniform dispersion, a method of dispersing a powder of Co and Sb or a CoSb ₃ -based compound powder in an aqueous solution containing a transition metal and reducing with hydrogen to obtain a mixed powder is adopted.

Such a method of uniformly dispersing the transition metal is performed by adding a nickel group (Ni, Pa, Pt) or a noble metal (Cu, Ag, Au) as an element for converting the CoSb ₃ -based skutterudite into an n-type. It is also used for

Before the sintering, various methods can be used to prepare the raw material powder of the Skutterudite compound containing Sb in advance. Preferably, the raw material containing Co and Sb is melted, then solidified, and then subjected to a homogenization heat treatment to uniformly precipitate a desired skutterudite crystal phase, for example, a CoSb ₃ compound, in a solid. A method of pulverizing to a particle size of is adopted.

In this method, for example, a CoSb ₃ compound is used, in which Co, Sb and other required metals are blended so as to have a composition of the compound, and the atmosphere is non-oxidizing.
Particularly, melting is performed in a crucible in a melting furnace that has been made inert. After the melting and holding, the deposition temperature (600-860 ° C) below the temperature at which the CoSb ₃ compound starts to precipitate (about 876 ° C) in the furnace as it is
And a homogenizing heat treatment is performed. By the homogenizing heat treatment, the CoSb ₃ -based compound is completely precipitated to eliminate segregation and homogenize.

The mass cooled after the homogenization heat treatment is pulverized, classified into a desired particle size distribution, and provided as a powder of a CoSb ₃ compound. At this stage of pulverization and classification, the particle size of the skutterudite compound is adjusted to a desired range of 100 μm or less because the crystal particle size of the sintered body is determined. The powder of the skutterudite compound is uniformly mixed with the metal oxide powder, and more preferably with the transition metal, by the method described above, and the mixed powder is usually compressed into a compact. .

For sintering the thermoelectric material of the present invention, a spark plasma sintering method is preferably employed. The spark plasma sintering device has a cylindrical die made of carbon and two carbon punches inserted from both ends into the hollow portion of the die in a vacuum vessel, and a power supply for supplying a pulse current between both punches. And a pressurizing means for pressurizing both punches. Into a cylindrical die, previously charged a molded body containing skutterudite powder, a required metal oxide, and a required transition metal,
Both punches are loaded into the die and the compact is pressed at the punch end face. During this pressurization, pulse currents of both punches are passed under vacuum, whereby the compact is heated, compressed, and densified.

The skutterudite crystal grains of the compact are conductive, and a current flows through the compact during sintering, but inside the compact, a large number of crystal grains contact each other in the initial stage of heating. A plasma discharge is generated to generate heat, and the particles are heated to a high temperature from the particle surface, and densification proceeds rapidly. The compact is also heated by Joule heat as current passes through the interior of the crystal. The metal oxides in the mixture can prevent grain growth during sintering and maintain the level of skutterudite particle size during compounding. The sintering temperature is preferably a pressing pressure of 100 to 1000 kgf / cm ² , and the sintering temperature is preferably about 600 to 800 ° C. lower than the melting temperature of the skutterudite crystal.

According to the spark plasma sintering method, if an appropriate current is selected for the size of the compact, a sintering degree of 90% or more can be achieved within 10 minutes, usually 2 to 5 minutes in a short time. Can be completed.

[0052] thermoelectric material of the present invention, preferably, as described _{above, Ln y Fe x Co 4-} x Sb 12 ( rare earth metal Ln
Contains a filled skutterudite compound having a composition formula represented by 0 <y ≦ 1, and Fe is 0 <X ≦ 4). The filled skutterudite compound fills the vacancies of the CoSb ₃ crystal structure with another rare earth element and uses Co
Is a compound in which part or all of is replaced by Fe, and rare earth elements Ln are particularly La, Ce, Pr, Nd, S
m, Gd, etc. are used.

Preferably, the rare earth metal Ln is such that Ln satisfies 0.4 ≦ y ≦ 1 and Fe satisfies 2 ≦ X ≦ 4. If 0.4> y, the filling rate is too low,
If the phonon scattering effect is reduced and y> 1, the excess rare earth metal element is precipitated as a different phase. In this case, the reason why Fe is set to 2 ≦ X ≦ 4 is to secure a carrier concentration for the scattelludite to be P-type.

More preferably, the composition of Ln and Fe is
3 ≦ X ≦ 4 and 0.8 ≦ y ≦ 1. This composition range is preferable because the effect of reducing the thermal conductivity κ by phonon scattering and an appropriate carrier concentration can be obtained.

Ln can include two or more rare earth metals. Differences in the mass and strain of the lattice filled with different types of elements can increase phonon scattering and further reduce the thermal conductivity κ. For example, La
And Ce can be used, and the molar ratio of the content of La: Ce is selected in a ratio of 40:60 to 60:40. This range of the molar ratio is preferable because the effect of the difference between the lattice mass and the strain is remarkable.

The thermoelectric material of the present invention uses Hf instead of Ln.
Can be _{utilized, Hf y Fe x Co 4-} x Sb 12 ( where, 0 <X ≦ 4,0 <y ≦ 1) mainly composed of thermoelectric material consisting filled discussions ether phosphoramidite compound having the composition Thermoelectric material. It is preferable that such an Hf-containing skutterudite-based thermoelectric material is a sintered body containing a metal oxide together with the Hf skutterudite-based compound.
As the metal oxide, an oxide of one or more of the above rare earth metals Ln is used. The metals of the oxide include La and Ce.
Combinations with are available.

In the sintered body, the skutterudite-type crystal mainly comprises a skutterudite compound having the above composition, and further contains a small amount of a FeSb ₃ compound and a compound to which metals Fe, Co and Sb, and other metal elements are added. May be included.

The thermoelectric material of the present invention is characterized in that the metal oxide is
A compound having the above composition dispersed in the crystal grain boundaries is used. Such an oxide-dispersed sintered body can be obtained by mixing a fine powder of an oxide with a previously prepared compound powder having the above composition, forming the mixture into a desired shape, and firing the formed body.

For the preparation of the raw material powder of the filled skutterudite compound for sintering, the same method as the method of melting the CoSb ₃ -based skutterudite can be used, but preferably Fe, Co, Sb, A metal material containing a filling element, for example, Ce, is melted and solidified, and then subjected to a homogenization heat treatment to uniformly precipitate a filled skutterudite compound in a solid, pulverized, and classified to a required particle size. An adjusting method is adopted.

In such a melt-solidification method, preferably,
Raw metals of Ln, Fe, Co and Sb are weighed in an inert gas so as to have the composition of the compound, and vacuum-sealed in a quartz tube ampule. The ampoule is heated and melted in an electric furnace, then rapidly cooled and solidified. The quenched ampoule is again heated in an electric furnace at a temperature lower than the melting point and at a temperature at which filled skutterudite can be deposited, for example, at 600 to 800 ° C., and subjected to homogenization heat treatment. A method of completely precipitating and homogenizing the filled skutterudite compound by the homogenization treatment is employed.

The mass cooled after the homogenization heat treatment is pulverized, classified into a desired particle size distribution, and used as a sintering powder containing a filled skutterudite compound.

In the present invention, it is preferable that the filled skutterudite compound whose composition is prepared is further subjected to a homogenizing treatment by a mechanical alloying treatment. The mechanical alloying reduces the FeSb ₂ phase remaining in the alloy, and can obtain a uniform single phase of filled skutterudite. The sintered body can improve the Seebeck coefficient S and reduce the thermal conductivity κ by reducing the FeSb ₂ phase which is a metal phase.

[0063] In _{Ln y Fe x Co 4-x} Sb 12 system filled discussions ether Daito thermoelectric material of the present invention, in particular, F
It is important to minimize the concentration of impurities including eSb ₂ and Sb in order to maintain thermoelectric performance. In the present invention, the Ln _y Fe _x Co _{4- x} filled discussions ether phosphoramidite-based thermoelectric material of the composition of Sb _12, filled discussions ether phosphoramidite crystalline phase in FeSb ₂ phases, filled discussions ether phosphoramidite crystalline phase by X-ray diffraction The intensity ratio of the peak diffraction intensity of the FeSb ₂ phase to the peak diffraction intensity of No. is set to 1% or less. When the FeSb ₂ phase in the thermoelectric material increases to an amount exceeding 1% in diffraction intensity ratio, the material means the decomposition of the filled skutterudite, and the thermal conductivity of the thermoelectric material increases. In particular, the diffraction intensity ratio of the FeSb ₂ phase is limited to 0.1% or less.

In such a filled skutterudite-based thermoelectric material, all processes from preparation of raw material powder to sintering are performed in a non-oxidizing atmosphere to prevent oxygen from being mixed. The non-oxidizing atmosphere is an inert gas atmosphere, particularly preferably a vacuum.

As described above, the non-oxidizing atmosphere is controlled by vacuum-sealing in a quartz tube ampule, heating and melting in an electric furnace, and subjecting the ampoule after rapid cooling to homogenizing heat treatment again in the electric furnace. You can do it by doing

Further, the step of pulverizing and classifying the cooled mass after the homogenizing heat treatment and storing the powder for sintering containing the filled skutterudite compound is performed under Ar atmosphere control. When the filled skutterudite compound having the prepared composition is further subjected to mechanical alloying treatment,
This is performed under Ar atmosphere control. After the preforming, sintering is preferably performed by the above-described spark plasma sintering method under vacuum to obtain a sintered body.

Since the sintered body is formed from the powder prepared under such atmosphere control, the oxygen is not attached to the surface of the powder before sintering. No decomposition of filled skutterudite due to falling off caused by the oxidation of the compound. Thereby, the generation of the second phase impurity phase such as FeSb ₂ can be suppressed even after sintering.

The filled skutterudite-based thermoelectric material of the present invention includes a sintered body obtained by selecting a transition element of Ni, Pd or Pt as a dopant and performing a heat treatment, wherein Ni, Pd and Pt are: Co may be completely replaced.

[0069] In particular, the filled discussions ether phosphoramidite based thermoelectric material of the present _{invention, Ln y Fe x M 4-} x Sb 12 ( here, L
n is a rare earth metal, has a composition ratio of 0 ≦ X ≦ 4, 0 ≦ y ≦ 1), and includes filled skutterudite in which M is any one of Ni, Pd, and Pt.

The field skutterudite containing Co is
Ni, Pd, and Pt substituted for Co act as perfect dopants since no stable compound with Sb is present, although a stable CoSb ₃ phase is produced and filling is impossible. Therefore, the carrier concentration can be controlled without generating the second phase. Such a filled skutterudite, particularly containing Ni, Pd, and Pt, can be used as an n-type filled skutterudite-based thermoelectric material.

[0071] Such, Ni, Pd or _{Ln y Fe x M 4-x} Sb 12 ( here, Ln is a rare earth metal, 0 ≦ X ≦ 4,0 ≦ y ≦ 1) was replaced with Pt filled discussions ether of The pretreatment step of sintering is performed in a vacuum or an inert gas atmosphere for the die-based thermoelectric material.

Further, the thermoelectric couple of the present invention has p-type and n-type
It is a sintered body having a pn junction where a Sb-containing Skatteludite thermoelectric material of a mold is joined and integrated by sintering. In such a thermoelectric couple, since there is no contact with a metal having a different coefficient of thermal expansion such as an electrode material at a high temperature end, the occurrence of disconnection or poor contact can be reduced, and reliability and durability can be improved. Become.

The Sb-containing skutterudite thermoelectric material has p
As a mold, the above _{Ln y Fe x Co 4-x} Sb 12 system filled discussions ether phosphoramidite is utilized, the n-type, Ni, Ln _y was replaced with Pd or _{Pt Fe x M 4-x Sb} 12 based Firudosuka' Terdite is used, and a thermoelectric couple having high thermoelectric performance can be formed.

The thermoelectric couple is formed from p-type and n-type skutterudite material powder, respectively, and the p-type and n-type molded bodies are brought into contact with each other and sintered to be integrated. The integrated sintered material is cut or processed to include a pn junction surface to form a pn junction material, and then leave a portion of the pn junction surface at the distal end of the material and Cut out the bonding material to remove the rest of the pn bonding surface. The thermoelectric couple formed in this way has a pn junction surface only at the front end side and is at a high temperature side, and at the rear end side, p-type and n-type thermoelectric materials are separated by a notch. You. The rear end side is the cold side and the metal conductor is connected as a lead in the usual way, for example by brazing. Normally, a plurality of thermoelectric couples are connected in series by leads, and used as a thermoelectric module for power generation.

The thermoelectric module using the filled skutterudite-based thermoelectric material of the present invention is used for an apparatus having a heat source. It is used as a power cordless device that internally drives the device with electric power generated by applying a temperature difference to a thermoelectric module from a heat source. By using such a filled skutterudite-based thermoelectric module, it can be used for a high-temperature heat source exceeding 400 ° C. such as a catalytic combustion or an oil burner.

[0076]

EXAMPLES (Example 1) The thermoelectric material of this example uses a CoSb ₃ compound as scatteludite, and mixes before sintering in order to finely disperse the metal oxide around the scatteludite particles. The method of sedimentation from solution was used for the preparation of the flour.

By using the sedimentation method, the compound particles and a trace amount of metal oxide can be uniformly dispersed. This mixed powder is molded and sintered to form a dense sintered body. The method of sedimentation from a solution involves uniformly dispersing the powder serving as the main phase in an aqueous chloride solution of a metal from which an oxide is to be obtained, and adding a small amount of aqueous ammonia to form a metal hydroxide around the powder particles. Is uniformly attached. This is heated and decomposed after dehydration to obtain a mixed powder in which the metal oxide is uniformly and thinly dispersed in the main phase particles. The mixed powder is
After being formed into a desired shape, it is sintered.

Specifically, metal Co (purity 99.998)
5%), metal Sb (purity 99.9999%) and metal F
e (purity 99.9%), after sintering, Co _0.997 Fe _0.003 S
A metal material weighed so as to have a composition ratio of b ₃ was melted in a crucible of an electric furnace having an Ar atmosphere at a melting temperature of 1100 to 1200 ° C.
And dissolved for 2 hours. Next, the molten metal in the crucible is heated and maintained at 850 ° C., which is lower than the CoSb ₃ precipitation temperature (876 ° C.), for 10 hours, and homogenized, and a skutterudite crystal is obtained by solid-phase diffusion. The obtained ingot was coarsely pulverized and then pulverized in a planetary ball mill to an average particle diameter of 100 μm or less. Thus, CoSb ₃
A powder of the system compound was obtained.

This powder was dispersed in an aqueous solution of LaCl _3, and a small amount of aqueous ammonia was dropped to obtain a powder of Co.
Insoluble La (OH) ₃ was precipitated on the Sb ₃ -based compound powder to obtain a mixed precipitate. The precipitate was dehydrated and dried, heated to decompose the hydroxide, and a mixed powder in which La ₂ O ₃ particles were uniformly dispersed on the particle surface of the CoSb ₃ -based compound powder was obtained. A molded body obtained by pre-press molding this mixed powder is
It was sintered using a spark plasma sintering machine. The sintering conditions were a press pressure of 500 kgf / cm ² , a sintering temperature of 700 ° C., and holding for 4 minutes.

The thus obtained compound and La ₂ O ₃
FIG. 1A shows an SEM photograph of the mixed sintered body of FIG. Also,
FIG. 1B shows, for comparison, Co sintered under the same conditions.
Shows an SEM photograph of the sintered bodies of only _{0.99 7} Fe _0.003 Sb ₃ compound. The figure shows that the Co _0.997 Fe _0.003 Sb ₃ compound and L
It can be seen that the mixed sintered body with a ₂ O ₃ is formed of fine particles as a result of suppressing the grain growth. The thermal conductivity κ measured for these samples is shown in FIG. 2. The thermal conductivity κ was 4.5 W / mK at the minimum, which could be reduced from the conventional 6 W / mK.

(Embodiment 2) The embodiment of the present invention uses CoSb
_The transition metal was uniformly dispersed in the tertiary compound powder and sintered to form a sintered body.

As an example of the case where Cu is used as the transition metal,
Copper chloride was dissolved in the aqueous solution, CoSb ₃ compound powder was added, and the mixture was kept at 40 to 60 ° C. to obtain CoSb ₃ compound powder whose particles were covered with a Cu film. The Cu-coated particles were compression-molded, and the compact was sintered by the discharge plasma sintering method under the same conditions as in Example 1. The molded body is
4 under the conditions of an applied pressure of 500 kgf / cm ² and a sintering temperature of 700 ° C.
Held for a minute.

The thus obtained Cu film-coated Co
FIG. 3 shows the relationship between the Seebeck coefficient and the temperature of the sintered body of the Sb ₃ compound. The Seebeck coefficient shows a negative value, indicating that the substitution of Cu changed the n-type. Conventionally, when Cu was added in the form of powder, no change to n-type was observed, indicating that the uniform dispersion promoted the substitution of Cu for Co.

Example 3 A test was performed on a CoSb ₃ -based thermoelectric material in which a transition metal Fe was added. A composition in which Co and Sb powders are replaced by 0.3 mol% with respect to Co after sintering in an aqueous solution of iron nitrate (Co _0.997 Fe
_0.003 Sb ₃ )
Next, the aqueous solution was evaporated to dryness to obtain a powder.

In the hydrogen reduction, the powder was heated to 700 to 800 ° C. and kept in an Ar gas stream containing 3% hydrogen to reduce iron oxide with hydrogen. A mixed powder in which Co, Sb and Fe fine powders were uniformly dispersed was obtained.

This mixed powder was preliminarily molded and CoS
b At a temperature equal to or lower than the dissolution temperature of the _3- based compound (876 ° C.), Ar
Heat treatment was performed in an atmosphere for 10 to 30 hours. The obtained powder was further pulverized and sintered in the same manner as in Example 1 by a discharge plasma sintering method to obtain a compound sintered body.

FIG. 4 and FIG. 5 show the C
o See the Seebeck coefficient S and the power factor of the _0.997 Fe _0.003 Sb ₃ compound sintered body. As a result of suppressing the precipitation of the hetero phase, the Seebeck coefficient S increases and the power factor increases. Also, this method uses CoSb _{3 as a} starting material.
The same can be done by using a system-based compound powder.
o _0.997 Fe _0.003 Sb ₃ compound sintered body is obtained.

Example 4 This example deals with a sintered body in which a rare earth metal oxide is uniformly dispersed in a filled skutterudite compound crystal. The raw materials include metal cerium Ce (purity 99.9%), iron Fe (purity 99.9%), cobalt Co (purity 99.9985) and antimony S
b (purity 99.9999%), and after sintering Ce
A metal material weighed and mixed in an Ar atmosphere so as to have a composition ratio of Fe ₃ CoSb ₁₂ was vacuum-sealed in a quartz tube ampule. The ampoule has a melting temperature of 1000 to 11 in an electric furnace.
The material was heated to 00 ° C. and held for 20 hours to dissolve the metal material.

Next, the ampoule containing the molten metal was immersed in ice water, quenched and solidified to obtain an alloy lump. The lump was again heated and held at 700 ° C. for 30 hours in an electric furnace in order to obtain a filled skutterudite crystal structure by solid phase diffusion. The obtained lump was coarsely pulverized and then pulverized into an average particle diameter of 100 μm or less by a planetary ball mill. The resulting powder is
It was confirmed by X-ray diffraction that the powder was a powdered skutterudite crystal powder.

This powder is dispersed in an aqueous solution of LaCl _3, and a small amount of aqueous ammonia is added dropwise to obtain Ce powder.
A mixed precipitate of the powder of the CoFe ₃ Sb ₁₂ composition and La (OH) ₃ is formed. This was dried and heated to decompose the hydroxide, thereby obtaining a mixed powder in which La ₂ O ₃ was uniformly dispersed on the particle surfaces of the powder of the CeCoFe ₃ Sb ₁₂ compound composition. This mixed powder was preliminarily molded and sintered using a spark plasma sintering machine. Sintering conditions are 300kg applied pressure
f / cm ² , sintering temperature 600 ° C., and kept for 4 minutes. Further, the heating rate was 150 ° C./min or less.

The thus obtained CeFe ₃ CoS
The b ₁₂ compound and La ₂ O ₃ mixed sintered body thermal conductivity κ and temperature relationship of the shown in FIG. FIG. 6 also shows the thermal conductivity κ of only the CeCoFe ₃ Sb ₁₂ compound sintered under the same conditions without mixing the oxide.

From this figure, it can be seen that the mixed sintered body can suppress grain growth,
The increase in phonon scattering at the grain boundaries reduces the thermal conductivity κ, and also suppresses the increase in thermal conductivity on the high-temperature side, which has been conventionally observed. This is because the La dispersed at the grain boundaries served as a diffusion barrier, thereby suppressing the decomposition of the CeFe ₃ CoSb ₁₂ compound at a high temperature.

(Example 5) In this example, at least two or more kinds of rare earth metals were used as the filling element of the filled skutterudite compound. La as a metal raw material
(Purity: 99.9%) and Ce, Fe, Co and Sb of the above purity are weighed and mixed in an Ar atmosphere so as to have a composition ratio of Ce _0.5 La _0.5 Fe ₃ CoSb ₁₂ after sintering. Vacuum sealed in an ampoule and melting temperature of 1000-1000 in an electric furnace
The mixture was heated to 1100 ° C. and maintained for 20 hours to dissolve. Next, the molten metal was solidified by immersing the ampoule in ice water and rapidly cooling it. The obtained lump is again heated and held in an electric furnace at 700 ° C. for 30 hours, and a filled skutterudite type crystal structure is obtained by solid phase diffusion. The resulting mass was pulverized to an average particle size of 100 μm or less.

This powder was preliminarily molded and sintered using a spark plasma sintering machine. The sintering condition is applied pressure 30
0 kgf / cm ² , sintering temperature 600 ° C., and kept for 4 minutes. Further, the heating rate was 150 ° C./min or less. FIG. 7 shows the relationship between the thermal conductivity κ and the temperature of the thus obtained sintered body. Thermal conductivity was reduced by the effect of increasing phonon scattering.

(Embodiment 6) In this embodiment, Hf is used as a filling element of a filled skutterudite compound. Conventionally, the rare-earth element Ln has trivalent and tetravalent states in the alloy, so that accurate charge compensation has been difficult and control of the carrier concentration has been difficult. On the other hand, Hf is only tetravalent in the alloy, so that the charge compensation can be performed more accurately.

Metal hafnium Hf (purity 99.9%), Fe (purity 99.9%) and Sb (purity 99.9999)
%) Was sintered and weighed and mixed in an Ar atmosphere so as to have a composition ratio of HfFe ₄ Sb ₁₂ after sintering, vacuum sealed in a quartz tube ampule, and melted in an electric furnace at a melting temperature of 1000 to 11%.
The mixture was heated to 00 ° C. and kept for 20 hours to dissolve. Next, the ampoule was immersed in ice water and rapidly cooled to solidify. The obtained lump was again heated and held in an electric furnace at 700 ° C. for 30 hours, and a skutterudite-type crystal structure was obtained by solid-phase diffusion. The obtained lump was coarsely pulverized in a mortar and then pulverized in a planetary ball mill to an average particle diameter of 100 μm or less.

In this example, without mixing the oxide,
This crystal powder is preliminarily compression-molded and spark plasma-fired.
It was sintered using a knot. Sintering conditions are 300kg applied pressure
f / cm ^TwoThe sintering temperature was maintained at 600 ° C. for 4 minutes. Also,
The temperature rate was 150 ° C./min or less.

FIGS. 8 and 9 show the relationship between the Seebeck coefficient and the conductivity of the sintered body thus obtained and the temperature.
From the figure, it can be seen that the Seebeck coefficient is improved and the conductivity is reduced as compared with the filled skutterudite-based thermoelectric material filled with the rare earth metal. This is because the number of carriers released from the unfilled rare earth metal has conventionally decreased due to the difference in valence. By filling with Hf, more accurate charge compensation becomes possible, and the carrier concentration can be easily reduced. Control can be performed.

(Embodiment 7) In this embodiment, C
In a method for producing a filled skutterudite-based thermoelectric material containing e, Fe, Co, and Sb as main components, a reaction of a heterogeneous phase remaining in a small amount in the alloy is performed by using a mechanical alloying method in a step of preparing the alloy. Promotes
This is to obtain a single-phase and uniform filled skutterudite compound powder.

Raw metal Ce (purity 99.9%) and Fe
(Purity 99.9%), Co (Purity 99.9985) and Sb (Purity 99.9999%), after sintering, CeFe ₃ C
a metal material were weighed and mixed in an Ar atmosphere to obtain the composition ratio of OSB _{1 2,} vacuum sealing in a quartz tube ampule, and held for 20 hours by heating to melting temperature 1000 to 1100 ° C. in an electric furnace Dissolved.

Next, the molten metal was solidified by immersion in ice water in an ampoule and quenched. The obtained lump is again put into an electric furnace for 70 minutes.
The mixture is heated and maintained at 0 ° C. for 30 hours, and a filled skutterudite crystal structure is obtained by solid-phase diffusion.

The obtained lump was roughly pulverized in a mortar, and then subjected to a mechanical alloying treatment in a planetary ball mill for 3 hours. An agate pod and a 5 mm diameter zirconia ball were used for mechanical alloying. X before and after the mechanical alloying treatment and the compound powder obtained by the treatment
The results of the line diffraction are shown in FIGS. 10A and 10B, respectively. The X-ray diffraction results show that the FeSb ₂ phase was reduced compared to before the mechanical alloying treatment, and a uniform single phase was obtained.

An Ln oxide Ln ₂ O ₃ powder was uniformly dispersed in the powder after the mechanical alloying treatment by a precipitation method from a LaCl ₃ aqueous solution in the same manner as in Example 4, and preformed. The compact was sintered under the same conditions as in Example 4 using a discharge plasma sintering machine. The sintered body was able to improve the Seebeck coefficient S and reduce the thermal conductivity κ by reducing the FeSb ₂ phase as the metal phase.

(Example 8) Metal Ce (purity 99.9%), Fe (purity 99.9%) and Sb (purity 99.9999%) as raw materials, and the composition ratio of CeFe ₄ Sb ₁₂ after sintering The metal material weighed and mixed in an Ar atmosphere was vacuum-sealed in a quartz tube ampule, heated to a melting temperature of 1000 to 1100 ° C. in an electric furnace, and held for 20 hours to melt. Next, the ampoule was immersed in ice water and rapidly cooled to solidify. In order to obtain a filled skutterudite-type crystal structure by solid-phase diffusion, the above lump was again heated and held in an electric furnace at 700 ° C. for 30 hours, and the lump obtained was roughly pulverized in a mortar in an Ar atmosphere. Then, the average particle size is 10 in a planetary ball mill.
It was atomized to 0 μm or less.

This powder was sealed in a carbon die in an Ar atmosphere, and was further molded by applying a preliminary pressure.
As described above, by performing all the pretreatments for sintering in an Ar atmosphere, it is possible to prevent oxygen from adhering to the powder surface and to prevent the filler element from falling off due to oxidation at high temperature.
The obtained preform was sintered using a spark plasma sintering machine. The sintering conditions were an applied pressure of 300 kgf / cm ² , a sintering temperature of 700 ° C., and a holding time of 4 minutes. The heating rate is 1
The temperature was set to 00 ° C./min or less.

The thus obtained CeFe_FourSb₁₂
FIG. 11A shows an X-ray diffraction result of the compound sintered body. Ma
FIG. 11 (B) shows a pre-molding in a die in air.
The results of X-ray diffraction of the sintered compacts described above are also shown. Atmospheric treatment
Indicates that in the X-ray diffraction chart, CeFe_FourSb₁₂Peak of
Diffraction intensity, diffraction angle 2Θ is around 31 °, and FeSb
_TwoPhase peak is CeFe_FourSb₁₂Close to the peak diffraction line
Lined up, CeFe _FourSb₁₂FeSb for_Two Times
It can be seen that the broken line intensity ratio reaches about 0.5. FIG.
(A), in a sample sealed in a die in an Ar atmosphere, FeS
b_TwoPhase decreases and CeFe_FourSb₁₂Single phase is obtained
You can see that. In this example, FeSb_Two The diffraction line intensity ratio of
It was 0.01 or less. In addition, this sample was
As a result of analysis, the content of the impurity phase was 5% by weight or less.
The oxygen content was found to be 1% by weight or less.

Next, the relationship between the thermal conductivity κ and the temperature of these samples is shown in FIG. As shown in the figure, in the sintered body preformed in an Ar atmosphere, the thermal conductivity κ is reduced. This is because FeSb _{2 as a} metal decreased and phonon scattering increased. FIG. 13 shows the relationship between the Seebeck coefficient and the conductivity of this sample and temperature, and FIG. 14 shows the relationship between the dimensionless figure of merit (ZT) and temperature calculated from these.
Shown in It can be seen that the Seebeck coefficient can be increased while suppressing the decrease in conductivity by reducing impurities, and ZT reaches 1.4 at 450 ° C.

Example 9 In this example, an n-type filled skutterudite thermoelectric material having a composition of CeFe _2.5 Pt _1.5 Sb ₁₂ was prepared using Pt as a dopant. Raw materials include Ce (purity 99.9%) and Fe (purity 9).
9.9%), Pt (purity 99.9) and Sb (purity 9).
9.9999%) using CeFe _2.5 P after sintering.
A metal material weighed and mixed in an Ar atmosphere so as to have a composition ratio of t _1.5 Sb ₁₂ was treated under the same conditions as in Example 8 to obtain a sintered body. FIG. 15 shows the relationship between the thermal conductivity κ of the sintered body thus obtained and the temperature. FIG. 16A and FIG. 16B show the relationship between the Seebeck coefficient, the conductivity, and the temperature. By increasing the number of n-type carriers while suppressing the dropout of the filling element, it was possible to obtain an n-type filled skutterudite-based thermoelectric material while keeping the thermal conductivity low.

Example 10 In this example, a thermoelectric couple was integrally formed from p-type and n-type filled skutterudite-based thermoelectric materials by sintering.

First, the p-type filled skutterudite was sealed in a carbon die in an Ar atmosphere using the CeFe ₄ Sb _12- based compound powder obtained in Example 8, and was preliminarily pressed and molded. This was a p-type molded layer.

On the other hand, the n-type filled skutterudite-based thermoelectric material is the CeFe _2.5 obtained in Example 9.
Using the Pt _1.5 Sb ₁₂ -based compound powder, the n-type compound powder is mixed with the p-type powder that has already been formed and is left in the die.
On a mold forming layer (CeFe ₄ Sb _12- based compound), sealing was performed in an Ar atmosphere, and compression was performed again to perform molding. As a result, a preformed body having a pn2 layer was obtained.

The obtained two-layered compact was sintered using a spark plasma sintering machine. Sintering conditions are 300kgf / cm applied pressure.
^{2. The} sintering temperature was kept at 700 ° C. for 4 minutes. Further, the heating rate was 100 ° C./min or less. As a result, as shown in FIG. 17, a thermoelectric material sintered body 1 in which the disk-shaped p-type sintered layer 2 and the n-type sintered layer 3 were joined therebetween was obtained. The disc-shaped sintered body 1 was cut into a width of 2 to 5 mm on a vertical surface and separated into a large number of pn-joined sintered pieces 10.

The sintered piece subjected to pn bonding has p
Other bonding surfaces were cut away except for the −n bonding surface 4. In this manner, the p-type and n-type thermoelectric material portions were separated by the notch portions 5 to form U-shaped sections 10.

Next, the sintered piece 10 was further cut perpendicularly to the longitudinal direction, and was formed into a thermoelectric couple 6 such that the cross section of the open end in this example was square. In this way, a filled skutterudite-based thermoelectric couple 6 directly pn-joined by sintering was obtained.

Further, since the open end of this thermoelectric couple is on the low temperature side, a thermoelectric module can be obtained by soldering metal electrodes, for example, and joining a plurality of couples in series in the order of pnpn. .

Conventionally, the high-temperature end of a thermoelectric material used at a high temperature is formed by, for example, brazing to form a pn junction.
o electrode was joined. However, in a high temperature state exceeding 400 ° C., there is a risk that disconnection or poor contact may occur due to distortion caused by a difference in thermal expansion coefficient between the thermoelectric material and the electrode material. On the other hand, pn
By joining, joining without intervening dissimilar metals becomes possible, and reliability and durability can be greatly improved.

The filled skutterudite-based thermoelectric module is used to generate power by heating the thermoelectric module with a heat source in an apparatus having a heat source.
The drive power inside the device is generated and used as a control power source inside the device, thereby making the device power cordless.

Examples of such a device include a catalytic combustion device and a petroleum burner. These heat sources have a temperature of 400 ° C
, The conventional thermoelectric materials could not sufficiently add the heat of combustion. On the other hand, by using filled skutterudite thermoelectric module,
Operation at 400 ° C. or higher becomes possible, and large power can be obtained with a small number of modules.

The power obtained by the thermoelectric module is
For example, the voltage is boosted using a regulator or the like, and is used as a power source for an internal electric device. In addition, by using a high-capacity power capacitor or the like, the device can be used as a standby power source or a startup power source.

FIG. 18 shows an example of a power cordless device. The device main body 8 includes a heat source 7 therein, and a thermoelectric module 61 is arranged in contact with the heat source 7. While the heat source 7 is operating, the electric power generated by the thermoelectric module 61 is controlled by the current control unit and supplied to, for example, the cooling fan 82 and the blower fan 83, and the device control unit 84
Is used as a control power supply. Thermoelectric module 61
When there is enough power to supply power from the power source, the power is stored in the capacitor 91 and used as a power source when the heat source 7 is at rest.

[0121]

The thermoelectric material of the present invention is a fired body in which a metal oxide is dispersed around crystal particles of an Sb-containing skutterudite compound. In addition, a thermoelectric material having a low thermal conductivity as a thermoelectric material can be obtained, and the thermoelectric conversion efficiency of the thermoelectric element can be improved.

The thermoelectric material is made of a Sb-containing skutterudite compound filled with a rare earth metal Ln or Hf and replaced with Fe to make the crystal grains finer, thereby reducing the thermal conductivity. And a thermoelectric conversion efficiency of a thermoelectric element having a low figure of merit and a high figure of merit can be provided.

The thermoelectric material of the present invention is particularly suitable for a CoSb3 compound containing Co and Sb as main components to Cr, Mn, Fe,
The inclusion of a transition metal such as Ru has the effect of increasing the Seebeck coefficient and increasing the power factor.

[0124] thermoelectric material of the present _{invention, Ln y Fe x Co 4-} x where a part of and Co was filled with rare earth metal Ln and Fe substituted
For sb ₁₂ system filled discussions ether phosphoramidite-based crystal, particularly by suppressing the decomposition of the impurity phase to 5% by weight or less,
The stability of the excellent filled skutterudite-based thermoelectric material can be secured and the thermoelectric properties can be improved.

[0125] Furthermore, the filled discussions ether phosphoramidite-based thermoelectric material, (wherein, Ln is a rare earth metal, M is _{Ni, Pd, Pt) Ln y} Fe x M 4-x Sb 12 since the composition of the thermoelectric properties It can be used as a good n-type thermoelectric material. In particular, the n-type thermoelectric material can form a thermoelectric couple by using the Ln-filled Fe-substituted filled skutterudite crystal stabilized as described above as a p-type thermoelectric material.

The thermoelectric couple of the present invention is formed by directly joining a p-type thermoelectric material and an n-type thermoelectric material from an Sb-containing scattellite-based thermoelectric material having a small thermal expansion coefficient by sintering. The pn junction surface is also connected by sintering, so that even when used at high temperature, the pn junction surface does not crack or break, and is thermally stable and highly durable. It can be.

The method for producing a thermoelectric material of the present invention suppresses crystal grain growth during the sintering process by sintering a mixed powder of an Sb-containing skutterudite compound or a component thereof and a metal oxide. And to refine the crystal grains of the skutterudite compound. Accordingly, a thermoelectric material having a low thermal conductivity and a high thermoelectric conversion efficiency of a thermoelectric element having a high figure of merit can be manufactured.

By utilizing the sedimentation method from an aqueous solution for uniformly dispersing the transition metal fine powder, fine oxide particles can be uniformly distributed on the surface of the compound particles. It can effectively suppress grain growth and is effective in lowering the thermal conductivity of thermoelectric materials.

In the method for producing a thermoelectric material according to the present invention, in particular, a transition metal fine powder is uniformly dispersed in a CoSb ₃ -based skutterudite compound powder to prepare a mixed powder, which is then sintered. This has the effect of promoting the replacement of Co in scatteludite with a transition metal, increasing the Seebeck coefficient of the CoSb ₃ -based thermoelectric material, and increasing the power factor. In particular, the use of a p-type dopant such as Mn, Cr, Fe, or Ru as the transition metal contributes to the improvement of the performance of the p-type CoSb ₃ -based thermoelectric material.

The transition metal was mixed with the CoSb3-based alloy powder by preparing a mixed powder with a transition metal fine powder uniformly dispersed by an electroless plating method, a hydrogen reduction method after drying the solution, and mechanical alloying. By sintering this, the substitution of Co with the transition metal can be promoted.

By using the spark plasma sintering method for sintering the mixed powder, a uniform and dense sintered body can be easily obtained in a short time, and the effect of suppressing the growth of crystal grains by dispersing the metal oxide can be obtained. It is possible to manufacture a thermoelectric material having excellent thermoelectric properties in which crystals are densified and miniaturized.

The method for producing a thermoelectric material of the present invention
In _{n y Fe x Co 4-x} Sb 12 system filled discussions ether Daito-based process for the preparation of compounds thermoelectric material that utilizes, up to the sintering, since processing in a non-oxidizing atmosphere, oxygen due to contamination during processing In the sintering process, oxidation of Ln or the like in the filled skutterudite and decomposition of the filled skutterudite can be prevented, stabilizing the filled skutterudite, and improving its thermoelectric properties. .

In the process of producing a filled skutterudite compound sintered body, all the pre-treatment steps of sintering are performed in a vacuum or an inert gas, so that the adsorption of oxygen to the compound powder is reduced. Oxidation of the filling element, which is sometimes generated, due to oxidation is prevented, and a sintered body having an extremely low impurity concentration can be obtained.

According to the present invention, a thermoelectric couple is formed by stacking and sintering a molded layer formed from a powder of a p-type skutterudite compound and a powder of an n-type skutterudite compound. A -n junction is formed by sintering, and a thermoelectric couple excellent in high-temperature reliability and durability can be obtained.

Further, in a device having a filled skutterudite-based thermoelectric module and a heat source, the inside of the device is driven by electric power generated by a temperature difference given from the heat source to the thermoelectric module, so that a high-temperature heat source can be reliably used. It is possible to obtain a flexible and low-cost cordless device.

[Brief description of the drawings]

FIG. 1 shows Co of an embodiment of the present invention._0.999 Fe_0.001 Sb_Three 
Compound and La_Two O_Three Distribution of fracture surface of mixed sintered body
SEM photograph (A) showing_0.999 Fe_0.001 Sb
_Three (B).

FIG. 2 shows Co _0.999 Fe _0.001 S according to an embodiment of the present invention.
4 is a graph showing the relationship between the thermal conductivity and temperature of a mixed sintered body of a b ₃ compound and La ₂ O ₃ .

FIG. 3 shows a Cu-plated Co according to an embodiment of the present invention.
4 is a graph showing the relationship between the Zetabeck coefficient and the temperature of the Sb ₃ compound sintered body.

[4] Seebeck coefficient and graph showing the relationship between the temperature of the Fe additive CoSb3 compound sintered body and Co _0.999 Fe _{0. 0010} Sb ₃ compound sintered body according to an embodiment of the present invention.

FIG. 5 is a graph representing the power factor versus temperature of Fe added CoSb ₃ compound sintered body and Co _0.999 Fe _{0. 001} Sb ₃ compound sintered body according to an embodiment of the present invention.

FIG. 6 is a graph showing a relationship between a thermal conductivity κ and a temperature of a mixed sintered body of a CeCoFe ₃ Sb ₁₂ compound and La ₂ O _{3 according} to an example of the present invention.

FIG. 7 shows Ce _0.5 La _0.5 CoFe according to an embodiment of the present invention.
₃ is a graph showing the relationship between the thermal conductivity κ of ₃ Sb ₁₂ compound and temperature.

FIG. 8 is a graph showing the relationship between the Seebeck coefficient and the temperature of the HfFe ₄ Sb ₁₂ compound according to the example of the present invention.

FIG. 9 is a graph showing the relationship between the conductivity and the temperature of the HfFe ₄ Sb ₁₂ compound thermoelectric material according to the example of the present invention.

FIG. 10 is an X-ray diffraction chart (A, B) of CeCoFe ₃ Sb ₁₂ compound powder before and after mechanical alloying according to an example of the present invention.

FIG. 11 is an X-ray diffraction result of a CeFe ₄ Sb ₁₂ compound sintered body which has been subjected to a treatment in Ar (A) and a treatment in air (B) and then subjected to spark plasma sintering.

FIG. 12 is a graph showing the relationship between the thermal conductivity κ and the temperature of the CeFe ₄ Sb ₁₂ compound sintered body according to the example of the present invention.

FIG. 13 is a graph showing a temperature-conductivity relationship (B) and a temperature-conductivity (A) and a temperature-conductivity (B) of a CeFe ₄ Sb ₁₂ compound sintered body that has been treated in Ar and air and then sintered.

FIG. 14 is a graph showing a relationship between a dimensionless figure of merit (ZT) and temperature of a CeFe ₄ Sb ₁₂ compound sintered body according to an example of the present invention.

FIG. 15 shows CeFe _2.5 Pt _1.5 S according to an embodiment of the present invention.
b is a graph showing the relationship between the thermal conductivity κ of the sintered body of ₁₂ compound and the temperature.

FIG. 16 shows CeFe _2.5 Pt _1.5 S according to an embodiment of the present invention.
b. Relationship between temperature and Seebeck coefficient of ₁₂ compound sintered body (A)
And a graph showing the relationship (B) between temperature and conductivity.

FIG. 17 is a perspective view illustrating a process of manufacturing a thermoelectric couple having a pn junction according to an embodiment of the present invention (A to A).
D).

FIG. 18 is a block diagram of an apparatus including a heat source and a thermoelectric module.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 thermoelectric material sintered body 10 sintered piece 2 p-type sintered layer 3 n-type sintered layer 4 pn junction surface 5 notch 6 thermoelectric couple 61 thermoelectric module 7 heat source 8 device body 80 current controller 81 capacitor 84 Device control unit

Claims (44)

[Claims] 1. A thermoelectric material characterized in that the skutterudite-based thermoelectric material is a sintered body composed of Sb-containing skutterudite compound crystal grains and a metal oxide dispersed in the crystal grain boundaries. 2. The thermoelectric material according to claim 1, wherein said skutterudite compound has an average crystal grain size of 20 μm or less. 3. The thermoelectric material according to claim 2, wherein said metal oxide is a rare earth metal oxide. Wherein said discussions ether phosphoramidite compound, Ln _y
Fe _x Co _4-x Sb ₁₂ (where Ln is a rare earth metal, <X
The thermoelectric material according to claim 1, wherein the thermoelectric material is a filled skutterudite compound having a composition of ≦ 4, 0 <y ≦ 1). 5. The thermoelectric material according to claim 4, wherein the composition satisfies 3 ≦ X ≦ 4 and 0.8 ≦ y ≦ 1. 6. The thermoelectric material according to claim 4, wherein said Ln contains two or more rare earth metals. 7. The method according to claim 1, wherein Ln is Hf instead of rare earth metal.
The thermoelectric material according to any one of claims 4 to 6, wherein 8. The skutterudite compound crystal is a CoSb ₃ -based compound containing Co and Sb as main components, and
crystals OSB ₃ type compound, the thermoelectric material according to any one of claims 1 to 3, characterized in that it comprises a transition metal other than the Co-group metal. 9. The thermoelectric material according to claim 8, wherein the transition metal is Cr, Mn, Fe, or Ru, or Ni, Pa, Pt, or Cu. 10. Co and Sb powder or the above CoS
and b ₃ based compound powder, a transition metal dispersed in the powder,
The thermoelectric material according to claim 8, wherein the thermoelectric material is a sintered body obtained by sintering a molded body made of: 11. _{Ln y Fe x Co 4-x} Sb 12 ( here,
Ln is a rare earth metal, and in a filled skutterudite-based thermoelectric material having a composition ratio of 0 ≦ X ≦ 4, 0 ≦ y ≦ 1), the FeSb ₂ phase is contained in the filled skutterudite crystal phase by X-ray diffraction. A filled skutterudite-based thermoelectric material, wherein the intensity ratio of the peak diffraction intensity of the FeSb ₂ phase to the peak diffraction intensity of the terdite crystal phase is 1% or less. 12. _{Ln y Fe x Co 4-x} Sb 12 ( here,
Ln is a rare earth metal, and in a filled skutterudite-based thermoelectric material having a composition ratio of 0 ≦ X ≦ 4, 0 ≦ y ≦ 1), the content of oxygen in the filled skutterudite crystal phase is set to 1% by weight or less. A filled skutterudite-based thermoelectric material, characterized in that: 13. The thermoelectric material according to claim 11, wherein the composition satisfies 3 ≦ X ≦ 4 and 0.8 ≦ y ≦ 1. 14. _{Hf y Fe x Co 4-x} Sb 12 ( here,
A thermoelectric material comprising a filled skutterudite compound having a composition of 0 <X ≦ 4, 0 <y ≦ 1). 15. The thermoelectric material according to claim 14, wherein the composition satisfies 3 ≦ X ≦ 4 and 0.8 ≦ y ≦ 1. 16. _{Ln y Fe x M 4-x} Sb 12 ( here, L
n is a rare-earth metal, a filled skutterudite-based thermoelectric material having a composition ratio of 1 ≦ X ≦ 4, 0 ≦ y ≦ 1),
A filled skutterudite-based thermoelectric material, wherein M is any one of Ni, Pd, and Pt. 17. The thermoelectric material according to claim 16, wherein 3 ≦ X ≦ 4 and 0.8 ≦ y ≦ 1. 18. A method for producing a skutterudite-based thermoelectric material comprising a crystal of an Sb-containing skutterudite compound and a metal oxide dispersed in a crystal grain boundary thereof, comprising: A method for producing a thermoelectric material, comprising sintering a mixed powder with an oxide. 19. The Sb-containing discussions ether phosphoramidite compound (wherein, Ln is a rare earth metal, 0 <X ≦ 4,0 <y ≦ 1) Ln y Fe x Co 4- x Sb 12 Firudosuka' the composition 19. A terdite compound.
3. The method for producing a thermoelectric material according to item 1. 20. The method according to claim 19, wherein the composition satisfies 3 ≦ X ≦ 4 and 0.8 ≦ y ≦ 1. 21. The mixed powder is obtained by dispersing a metal-containing precipitate in the powder of the skutterudite compound by sedimentation from a metal-containing aqueous solution, and subsequently thermally decomposing to disperse a metal oxide in the compound powder. The method for producing a thermoelectric material according to any one of claims 18 to 20, wherein the method comprises: 22. The crystal of a skutterudite compound is Co
And a CoSb ₃ compound containing Sb as a main component,
19. The method for producing a thermoelectric material according to claim 18, wherein the mixed powder is sintered by mixing a skutterudite compound crystal with a transition metal other than a Co group metal. 23. The method for producing a thermoelectric material according to claim 22, wherein the mixed powder is formed by electroless plating a transition metal on a CoSb ₃ -based compound powder. 24. The thermoelectric material according to claim 22, wherein the mixed powder is obtained by mixing a transition metal with the surface of a mixed powder of Co and Sb or a CoSb ₃ -based compound powder by mechanical alloying. Production method. 25. The mixed powder, wherein a powder of Co and Sb or a CoSb ₃ -based compound powder is dispersed in an aqueous solution in which a transition metal is dissolved, and the aqueous solution is evaporated to dryness and then reduced with hydrogen to form a mixed powder. 23. The method for producing a thermoelectric material according to 22. 26. The method according to claim 26, wherein the transition metal is Mn, Cr, Fe,
26. The method for producing a thermoelectric material according to claim 18, wherein the thermoelectric material is Ru, or Ni, Pd, Pt, or Cu. 27. The method according to claim 18, wherein the method of sintering the mixed powder is a spark plasma sintering method. 28. _{Ln y Fe x M 4-x} Sb 12 ( here, L
n is a rare earth metal, and in a method for producing a thermoelectric material containing a filled skutterudite compound having a composition ratio of 0 ≦ X ≦ 4, 0 ≦ y ≦ 1), a method of forming a filled skutterudite compound powder to form a filled skutterudite compound powder; A method for producing a filled skutterudite-based thermoelectric material, wherein a pretreatment step leading to sintering is performed in a non-oxidizing atmosphere. 29. The pre-treatment step includes the steps of pulverizing a filled skutterudite compound, preforming the compound powder, charging a compact into a sintering die, and sintering the compact. A method for producing the thermoelectric material according to claim 28. 30. The method for producing a thermoelectric material according to claim 18, wherein the method for sintering the compound powder is a spark plasma sintering method. 31. A thermoelectric couple in which an Sb-containing skutterudite-based thermoelectric material is used as a p-type electric material and an n-type thermoelectric material, and both thermoelectric materials are integrally sintered and joined to form a pn junction surface. A thermoelectric couple, wherein the p-type electric material is the thermoelectric material according to claims 1 to 12. 32. The n-type thermoelectric material is Ni, Pd or Pt.
The thermoelectric couple according to claim 31, which is a Sb-containing skutterudite-based thermoelectric material substituted with: 33. n-type CoSb ₃ based thermoelectric material, Ln _y
Fe _x M _4-x Sb ₁₂ (where Ln is a rare earth metal, 0 ≦ X
≦ 4, 0 ≦ y ≦ 1, M is composed of an n-type filled skutterudite thermoelectric material having a composition ratio of Ni or Pd or Pt), and has a junction joined by sintering. Item 4. A thermoelectric couple according to item 3. 34. A molding layer of a raw material mixed powder of a p-type Sb-containing filled skutterudite-based thermoelectric material and a mixed powder molding layer of an n-type Sb-containing filled skutterudite-based thermoelectric material are joined by pressure, Next, a method of manufacturing a thermoelectric couple having a pn junction by sintering integrally. 35. A raw material mixed powder, which is a mixed powder of a skateterudite compound or a component thereof and a metal oxide, wherein a crystal of the Sb-containing skutterudite compound and a metal oxide dispersed in a crystal grain boundary thereof are formed. 35. The method for manufacturing a thermoelectric couple according to claim 34, comprising: 36. The Sb-containing skutterudite compound
Is Ln_yFe_xCo _4-xSb₁₂(Where Ln is a rare earth
Metal, filled ska having composition of 0 <X ≦ 4, 0 <y ≦ 1)
35. It is a ttetterite compound.
Or a method for producing a thermoelectric couple according to 35. 37. The method according to claim 36, wherein the composition satisfies 3 ≦ X ≦ 4 and 0.8 ≦ y ≦ 1. 38. The mixed powder is obtained by dispersing a metal-containing sediment in the powder of the skutterudite compound by sedimentation from a metal-containing aqueous solution, and then decomposing by heating to disperse a metal oxide in the compound powder. The method for manufacturing a thermoelectric couple according to claim 35, wherein: 39. The p-type Sb-containing skutterudite compound crystal is a CoSb ₃ -based compound containing Co and Sb as main components, and the mixed powder is a skutterudite compound crystal excluding a transition metal other than a Co group metal. 36. The method for producing a thermoelectric couple according to claim 34 or 35, wherein 40. The method of manufacturing a thermoelectric couple according to claim 18, wherein the method of sintering the compacted phase layer of the mixed powder is a spark plasma sintering method. 41. A p-type Sb-containing discussions ether phosphoramidite compound (wherein, Ln is a rare earth metal, 0 ≦ X ≦ 4,0 ≦ y ≦ 1) Ln y Fe x M 4- x Sb 12 of the composition ratio 35. The method according to claim 34, wherein the pretreatment step from the formation of the filled skutterudite compound to the sintering of the filled skutterudite compound powder is performed in a non-oxidizing atmosphere. Manufacturing method of thermoelectric couple. 42. A n-type Sb-containing discussions ether phosphoramidite _{compound, Ln y Fe x M 4- x} Sb 12 ( here, Ln is a rare earth metal, 0 ≦ X ≦ 4,0 ≦ y ≦ 1, M is Ni, Pd or P
The method for producing a thermoelectric couple according to claim 34, wherein the thermoelectric couple is an n-type filled skutterudite having a composition ratio of t). 43. The method according to claim 41, wherein the composition satisfies 3 ≦ X ≦ 4 and 0.8 ≦ y ≦ 1. 44. A thermoelectric module comprising a plurality of the thermoelectric couples according to claim 31 and 34 and a conductive electrode, wherein each thermoelectric couple is connected in series.