JPH11103098A - Thermoelectric conversion material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide material exhibiting excellent thermoelectric characteristics in a wide temperature range up to about 100-1000 K. SOLUTION: At least one kind of element of 0.001-60 at.% which is selected out of B, C, N and O is added to material (M(1-2x) M'x M"x )A (0<x<=0.5) constituted of M constituted of at least one kind of element selected out of Co, Rf and Ir, M' constituted of at least one kind of element selected out of Fe, Ru and Os, M" constituted of at least one kind of element selected out of Ni, Pd and Pt, and A constituted of at least one kind of element selected out of P, As and Sb.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thermoelectric conversion material used for a thermoelectric element.

[0002]

2. Description of the Related Art Efficiency of thermoelectric conversion materials has been a problem since the practical use of this technology began, and in recent years, after a long sluggish period, relatively organized research and development has been performed. One of the causes of this situation is the growing interest in energy and environmental issues. It is strongly desired that thermoelectric power generation technology be applied particularly as an effective utilization technology of unused thermal energy.In addition, thermoelectric cooling technology, which is an inverse conversion, is a literally chlorofluorocarbon-free cooling / refrigeration technology for cooling electronic devices. It is expected to be applied not only to temperature control systems in IC manufacturing processes but also to refrigerators and air conditioners.

[0003] The conversion efficiency of a thermoelectric conversion material is determined by a thermoelectric performance index Z that reflects the physical properties of each material. Z = α2 /
ρκ (α is the Seebeck coefficient, ρ is the electrical resistivity, κ is the thermal conductivity, μ is the mobility, μL is the heat conduction component due to lattice vibration of the total thermal conductivity. Z is m1 ^3/2 μ / κL ( The material having a larger thermoelectric figure of merit (m1 is proportional to the effective mass of electrons or holes)) has better thermoelectric conversion efficiency. In other words, it is difficult to conduct heat (low thermal conductivity),
A material that conducts electricity well (has a low specific resistance) and has a large thermoelectromotive force (has a large Savebeck coefficient) is a highly efficient material.
At this time, the power generation conversion efficiency η [%] is calculated by using Z as η
= [ΔT / {(4 / Z) + 2T h - (ΔT / 2)}] ×
100 [%] (ΔT the temperature difference between the high temperature part and the low temperature part, Z is the thermoelectric figure of merit of the material, the T _h the absolute temperature of the high temperature portion) expressed as. Since α, ρ, and κ change with temperature, Z naturally has temperature dependence, and the temperature at which the maximum value is obtained differs depending on the material. Therefore, in order to improve the efficiency of the thermoelectric conversion material, it is important that Z is large over the entire operating temperature range, and the material that can increase ΔT is more advantageous.

Conventionally known thermoelectric conversion materials include B
There are an i ₂ Te ₃ compound, a PbTe compound, a Si—Ge compound, an Fe—Si compound and the like, but none of the materials has a dimensionless figure of merit ZT exceeding 1. Only Bi ₂
Only the Te ₃ compound shows a value very close to ZT = 1 in a temperature range of about 200 to 400K. However, Bi ₂ Te ₃ compounds having excellent performance also have a problem that they tend to be unstable at high temperatures, and since they are generally used at 573K or lower, they are generally used for electronic cooling rather than for power generation. It is used for In order for the thermoelectric conversion material to be actually used for power generation using waste heat such as a gas turbine, heat resistance up to around 1000K is required. In the conventionally known materials, the Fe—Ni compound is relatively stable and shows good performance even in this temperature range, but it is still 878
K is about ZT = 0.2, and the obtained power is very small. So to get more power,
A thermoelectric conversion material for power generation that exhibits excellent performance in a wide temperature range up to a relatively high temperature of about 100 to 1000 K is required, and development of such a material is desired.

Recently, XY ₃ having a skutterudite structure
Compound (X = Co, Rh, Ir; Y = P, As, Sb)
Are attracting attention as new thermoelectric conversion materials. Among the XY ₃ compounds, CoSb ₃ , RhSb ₃ , and IrSb ₃ antimonides are semiconductors having specific band structures and carrier transport characteristics, and have excellent thermoelectric characteristics. This CoS
Among the b3 type compounds, the substance exhibiting the most excellent thermoelectric properties at present is Co _0.97 Ir _0.03 Sb _2.81 Te _0.04 As _{0.15 obtained} by slightly adding Te, As and Ir to CoSb ₃ , and ZT = 0.6 at 650 to 750K. Although the characteristics are excellent to some extent, the characteristics rapidly deteriorate outside the temperature range. However, for example, in a power plant utilizing waste heat such as a gas turbine, when LNG is used as a cooling medium and a heat source obtained from a casing or the like is used as a high-temperature medium,
A temperature difference of 0 to 900 K is obtained, and in order to effectively convert this waste heat into electricity, a material that exhibits excellent thermoelectric properties in this entire temperature range is required. Therefore, it is desired to develop an existing material or a material having better characteristics in a wider temperature range than the above-mentioned conventional CoSb ₃ -based compound.
If such a material is discovered, it is expected that it will be put to practical use as a thermoelectric conversion material for power generation, and its industrial value is great.

[0006]

SUMMARY OF THE INVENTION As described above, Bi
_The 2Te ₃ compound exhibits excellent properties at around 573K, but is very unstable at high temperatures, so it is mainly used for electronic cooling and cannot be used for power generation requiring heat resistance. Many thermoelectric conversion materials exhibiting excellent heat resistance, such as Fe-Si compounds, have been found, but the thermoelectric properties of any of these materials are significantly worse than those of Bi ₂ Te ₃ compounds. Therefore, in order to obtain more electric power, a thermoelectric conversion material exhibiting excellent thermoelectric properties in a wide temperature range from a low temperature to a relatively high temperature is required.
Recently, a CoSb ₃ -based compound has been attracting interest as a material capable of solving such a problem, but its thermoelectric properties are narrow at 650 to 700K and ZT = 0.6. Therefore, it is necessary to develop a material that can obtain excellent characteristics stably over a wider range.

The present invention has been made to solve such a problem, and a thermoelectric conversion material exhibiting excellent thermoelectric properties in a very wide temperature range of about 100K to 1000K, particularly at a high temperature of 700K or more. provide.

[0008]

According to the present invention, at least one element selected from the group consisting of M, at least one element selected from Co, Rh, and Ir, and at least one element selected from Fe, Ru, and Os is provided.
M ′ comprising at least one element selected from Ni, Pd and Pt;
As and at least one substance consisting of composed A from elements selected from _{Sb (M (1-2x) M '} x M''x)
A ₃ (0 <x ≦ 0.5) is provided with at least one element selected from the group consisting of B, C, N and O in an amount of 0.001 to 60 at. % Thermoelectric conversion material.

The CoSb ₃ phase is stable at 1043 K or less, is formed by a peritectic reaction between the CoSb ₂ phase and the Sb phase, and has an Im ₃ type crystal structure represented by CoAs ₃ . This structure is called a skutterudite structure, and is a cubic lattice composed of a total of 32 atoms of 8 Co atoms and 24 Sb atoms in a unit cell. At this time, the Sb atoms are in a unique crystal state, and form six antimony rings formed of four Sb atoms in the unit cell. The unit lattice is formed by eight small lattices, but the antimony ring is formed by six small lattices, and the remaining two lattices are not formed. That is, two voids in which no antimony ring exists are included in the unit cell.

By the way, light elements such as B, C, N and O are generally known as interstitial elements and are located so as to fill gaps in lattices in the compound. Even in the CoSb ₃ phase, these light elements penetrate so as to fill the lattice gap. Therefore, these elements also penetrate into two voids where there is no antimony ring specific to the skutterudite structure, and a dense structure without voids is created. In a substance having such a structure, phonon scattering is suppressed due to the presence of the light element filled in the void, and the thermal conductivity can be significantly reduced. In addition, since the original advantage of this structure having a large mobility is utilized, the figure of merit can be significantly improved.

[0011] Thermoelectric material of the invention, such B, C, in the CoSb ₃ based material prepared by adding at least one element selected from N and O, Co is a Group VIII element, Rh, periodic and Ir F which is the atom on both sides of the table
e, Ru, Os and Ni, Pd, Pt. Even if such an element is replaced, the basic structure of the substance is the same as that of a substance that is not replaced. For example, in CoSb3, Co is Fe _0.5 Ni
_When completely replaced with _0.5 , slight changes occur in the lattice constant, melting point, etc., but the basic structure of the substance is CoSb ₃
And does not change. However, by performing this replacement, phonon scattering in the material is effectively suppressed, and the thermal conductivity is significantly reduced as compared with the material that is not replaced, and stable over a wide temperature range of 100 to 1000 K. As a result, a high Seebeck coefficient is obtained. Similarly, P, which is a Vb group atom,
The same effect can be expected by replacing As and Sb with Si, Ge, and Sn, which are both adjacent atoms, with S, Se, and Te. By utilizing such an effect, the thermoelectric properties of the CoSb ₃ -based thermoelectric material, which has been a problem so far, on the high temperature side can be remarkably improved, and it can be used in a wide temperature range.

Although the conventional CoSb ₃ -based thermoelectric material has a problem that good characteristics cannot be obtained unless a high-purity material is used as a raw material, the influence of purity on the material of the present invention is not so significant. Instead, the raw material purity only needs to be about 99.9%, so that the cost can be significantly reduced.

[0013]

Embodiments of the present invention will be described below. The thermoelectric conversion material of the present invention comprises Co,
M consisting of at least one element selected from Rh and Ir, M 'consisting of at least one element selected from Fe, Ru and Os, and at least one element selected from Ni, Pd and Pt M ''
A substance composed of A consisting of at least one element selected from P, As and Sb (M _(1-2x) M ' _x M''
_x ) At least one element selected from B, C, N and O is added to A ₃ (0 <x ≦ 0.5) in an amount of 0.001 to 60 at. %
It is characterized by being added.

This thermoelectric conversion material can be formed by, for example, a sintering method, an arc melting method or a gradient solidification method. However, it is convenient to use a high-temperature sintering method for a powder which has been subjected to a preliminary heat treatment and subjected to a solid phase reaction. Is an appropriate method.

A specific method will be described below. Raw material purity
Desirably, it is 99.9 or more. _{Further, (M (1-2x) M '} x M''x) and A ratio of samples prepared exactly 1: preferably those causing 3 significantly characteristics when this composition ratio deviates more than 10% reduction I do. In order to obtain an exactly 1: 3 composition, it is advisable to mix the element A, which has a high vapor pressure and a large amount of loss in the sample preparation stage, in a slightly excessive amount.

A predetermined amount of the weighed powders is sufficiently stirred by a method such as mixing using a V mixer, an agate mortar or the like, or mechanical alloying using a ball mill or the like.
The mixed powder is packed in an alumina tube, and further vacuum-sealed in a quartz tube. At this time, in order to prevent oxidation of the sample, it is preferable to set the degree of vacuum in the quartz tube to a high vacuum of 1 × 10 ⁻³ Pa or more. The sealed quartz tube is heat-treated at a temperature equal to or lower than the melting point of the substance to cause a solid-phase reaction. This heat treatment is 873 ~ 1123
For K, 1 to 100 hours is sufficient. The reaction product agglomerated by the solid phase reaction is pulverized in an agate mortar, powdered again, and then sintered by hot pressing at a temperature lower than the melting point of the substance.
The sintering conditions at this time were a press pressure of 10 to 100 MP
a, 873K to 1123K, 0.1 to 100 hours is sufficient. Under these conditions, a substance having a density of 99% or more of the theoretical density can be obtained. In this heat treatment, when the atmosphere in the quartz tube is not a vacuum but an inert gas atmosphere such as Ar or He, the evaporation of element A having a high vapor pressure can be suppressed, and a substance having a desired composition can be easily obtained. .

When adding B or C, the powder may be simply added, but it is difficult to add N or O. Therefore, the addition of N or O is performed after the N, O-free substance is prepared.
The heat treatment is performed in an atmosphere having a nitrogen partial pressure or an oxygen partial pressure of 10 Pa or less. Alternatively, N or O can be similarly contained even when a nitride or an oxide is used for the raw material powder.

As described above, at least one element selected from B, C, N and O is used in an amount of 0.001 to 60 at. % Can be added. If the amount of addition is large, there arises a problem that the electromotive force is reduced. If the amount is small, specific resistance and thermal conductivity tend to increase. Therefore, 0.1 to 20 at. % Is more desirable.

When the value of x is increased, the peak of the Seebeck coefficient moves to the higher temperature side. Therefore, it is preferable to change the value of x according to the temperature range to be used. That is, in order to obtain a high temperature specification, the x value may be increased. For example, 300 ~
When using at about 600 K, set the value of x to 0.01 to 0.1,
When used at about 0 to 900K, the value of x may be used at 0.15 to 0.2. However, if X is too small or too large, the thermoelectric conversion efficiency is reduced.
It is desirable to set within the range of ~ 0.2.

In the present invention, the ratio between M ′ and M ″ is the same as x, but does not have to be strictly the same. Specifically, if the difference is about 10%, the amount may differ. Is acceptable.

Further, if an inclined sample is manufactured in which the x value increases from the low temperature side to the high temperature side in the same sample, a material having excellent characteristics in a wider temperature range can be obtained. As described above, according to the present invention, a thermoelectric conversion material exhibiting excellent thermoelectric properties in a wide temperature range of 100 to 1000 K can be manufactured, and a significant cost reduction can be achieved.

[0022]

Next, specific examples of the present invention will be described. Example 1 Fe powder, Co powder having a purity of 99.9% and a particle size of 325 mesh or less, and B powder having a purity of 99% and a particle size of 325 mesh or less with an atomic equivalent ratio of 2: 16: 2: 60: 20 were mixed.

After the obtained mixture was sufficiently stirred using a V mixer, the mixed powder was filled in an alumina tube and further sealed in a quartz tube under vacuum. The degree of vacuum at this time was 1 × 10 ⁻⁶ Pa. The sealed quartz tube is pre-heated at 873K for 24 hours,
A solid phase reaction was performed. The reaction product agglomerated by the solid-phase reaction was pulverized using an agate mortar to obtain a powder again, and then sintered by a hot press at a temperature lower than the melting point of the substance. The sintering conditions at this time were a pressure of 40 MPa, 873 K, and 1 hour in a vacuum of 1 × 10 −6 Pa. When the density of the manufactured sample was measured, a substance having a density of 99% or more of the theoretical density was obtained. After processing this sintered body into a columnar shape having a cross-sectional area of 2 cm ² and a height of 1 cm, the low-temperature side was fixed at 40 K and the high-temperature side was gradually heated to give a temperature difference, and the open-end voltage and the internal resistance were measured.

The Seebeck coefficient α and the specific resistance ρ of the substance were measured from the measured values.
0 [mV / K], ρ = 0.015 [Wcm], 700
In K, α = 280 [mV / K], ρ = 0.0010
[Wcm]. One measurement was performed from 40K to 1000K, and the measurement was repeated 30 times, but no change was observed in the characteristics. In addition, even if the same measurement was performed after holding at 1000 K for 1 hour, no change was observed in the characteristics.
From the above results, the power factor at 350 K of the manufactured sample was 4.167 × 10 ⁻⁵ W / cmK ² , and the power factor at 700 K was 7.840 × 10 ⁻⁵ W / cmK ² , which was a sufficiently practical value. became.

Example 2 Ru powder, Rh powder, Pd powder and As powder having a purity of 99.9% and a particle size of 325 mesh or less and a C powder having a purity of 99.99% and a particle size of 325 mesh or less are 5: 10: 5 in atomic equivalent ratio. : 60: 20. After sufficiently stirring using a V mixer,
The mixed powder was packed in an alumina tube, and further vacuum-sealed in a quartz tube. At this time, the degree of vacuum was 1.times.10@-6 Pa.
The sealed quartz tube was subjected to a preliminary heat treatment at 873 K for 24 hours to cause a solid phase reaction. The reaction product agglomerated by the solid-phase reaction was pulverized using an agate mortar to obtain a powder again, and then sintered by a hot press at a temperature lower than the melting point of the substance. The sintering conditions at this time were as follows: a pressure of 40 M in a vacuum of 1 × 10 ⁻⁶ Pa.
Pa, 873 K, 1 hour. When the density of the manufactured sample was measured, a substance having a density of 99% or more of the theoretical density was obtained. After processing this sintered body into a columnar shape having a cross-sectional area of 2 cm ² and a height of 1 cm, the low-temperature side was fixed at 40 K and the high-temperature side was gradually heated to give a temperature difference, and the open-end voltage and the internal resistance were measured. When the Seebeck coefficient α and the specific resistance ρ of the substance were measured from the measured values, at 350 K, α = 180 [m
V / K], ρ = 0.0014 [Wcm], α = 230 [mV / K] at 700K, ρ = 0.0009 = [Wc
m]. One measurement from 40K to 1000K, 30
The measurement was repeated a number of times, but no change was observed in the characteristics. In addition, even if the same measurement was performed after holding at 1000 K for 1 hour, no change was observed in the characteristics. From the above results, the power factor at 350 K of the manufactured sample was 2.314 × 10 ⁻⁵ W / cmK ² , and the power factor at 700 K was 5.878 × 10 ⁻⁵ W / cmK ² , which was a sufficiently practical value. It became.

Example 3 Os powder, Ir powder, Pt powder and Sb powder having a purity of 99.9% and a particle size of 325 mesh or less and a B powder having a purity of 99% and a particle size of 325 mesh or less were mixed in an atomic equivalent ratio of 20:10:40. : 10:20. After sufficiently stirring using a V mixer, the mixed powder was packed in an alumina tube, and further sealed in a quartz tube under vacuum. At this time, the degree of vacuum was 1.times.10@-6 Pa. The sealed quartz tube was subjected to a preliminary heat treatment at 873 K for 24 hours to cause a solid phase reaction. The reaction product agglomerated by the solid-phase reaction was pulverized using an agate mortar to obtain a powder again, and then sintered by a hot press at a temperature lower than the melting point of the substance. The sintering conditions at this time were as follows: a pressure of 40 MPa in a vacuum of 1 × 10 ⁻⁶ Pa.
a, 873 K, 1 hour. When the density of the prepared sample was measured, a substance having a density of 99% or more of the theoretical density was obtained. After processing this sintered body into a columnar shape having a cross-sectional area of 2 cm ² and a height of 1 cm, the low-temperature side was fixed at 40 K and the high-temperature side was gradually heated to give a temperature difference, and the open-end voltage and the internal resistance were measured. When the Seebeck coefficient α and the non-resistance ρ of the substance were measured from the measured values, at 350 K, α = 270 [mV
/ K], ρ = 0.0016 [Wcm], at 700 K, α = 300 [mV / K], ρ = 0.0012 [Wcm]
Met. One measurement was performed from 40K to 1000K, and the measurement was repeated 30 times, but no change was observed in the characteristics. In addition, even if the same measurement was performed after holding at 1000 K for 1 hour, no change was observed in the characteristics. From the above results, the power factor at 350 K of the manufactured sample was 4.
The power factor at 5563 × 10 ⁻⁵ W / cmK ² and 700 K was 7.500 × 10 ⁻⁵ W / cmK ² , which was a sufficiently practical value. Embodiment 4 FIG. 1 is a schematic plan view of a thermoelectric module of the present embodiment, and FIG. 2 is a sectional view thereof.

Next, an embodiment in which the thermoelectric conversion material of the present invention is applied to a thermoelectric module will be described with reference to FIGS. Using the sintered body prepared in Example 1 as the p-type thermoelectric conversion material 2, 20Co-60Sb-20 obtained by the same method.
Using a B (at.%) Sintered body as the n-type thermoelectric conversion material 2, a thermoelectric module was manufactured by the following method.

After printing a silver paste on two alumina substrates so as to form a wiring pattern as shown in FIG.
The p-type and n-type thermoelectric conversion materials cut to m × 1 mm × 1.8 mm were arranged as shown in FIG. 1, and the silver paste was dried to fix the p-type and n-type thermoelectric conversion materials. FIG. 2 is a cross-sectional view of a thermoelectric module completed by attaching a lead wire to the substrate thus manufactured. Thermoelectric module fabricated as described above (42 elements, module size
The power generation performance of 18.5 mm x 21.5 mm, thickness of 2 mm) is about 60 when the temperature difference between alumina substrates (around room temperature) is 3 ° C.
The output was mV. This value sufficiently satisfies the requirements as a power generation module, and is also a result suggesting that the module has sufficient performance as a thermoelectric module for cooling.

The evaluation as a cooling element was performed by mounting an aluminum heat sink on the heat generating surface,
The test was performed by applying a voltage of 1 V to the device under an environment of 90%.
At this time, the surface on the cooling side dropped to about −5 ° C. in several tens of seconds, and at the same time dew condensation started, and thereafter, the temperature was kept almost constant. This result suggests that the thermoelectric module also has sufficient performance as a cooling element. We confirmed that it was excellent.

[0030]

As described above, the thermoelectric conversion material of the present invention exhibits excellent thermoelectric characteristics stably over a wide range from low temperature to relatively high temperature, and can be used not only for cooling elements but also for power generation using waste heat. Is a high-performance material that can also be used, and can achieve low cost, so that its industrial value is extremely large.

[Brief description of the drawings]

FIG. 1 is a view schematically showing a p-type and n-type thermoelectric conversion material arranged on an alumina substrate on which a silver paste is printed.

FIG. 2 is a view schematically showing a completed thermoelectric module.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Alumina substrate 2 ... P-type thermoelectric conversion material 3 ... N-type thermoelectric conversion material 4 ... Silver paste (front side) 5 ... Silver paste (back side) 6 ... Lead wire

Claims (1)

[Claims] 1. M comprising at least one element selected from Co, Rh and Ir; M 'comprising at least one element selected from Fe, Ru and Os;
A substance (M) composed of M ″ composed of at least one element selected from i, Pd and Pt and A composed of at least one element selected from P, As and Sb
_(1-2x) M ′ _x M ″ _x ) A ₃ (0 <x ≦ 0.5), B,
At least one element selected from C, N and O
0.001 to 60 at. % Thermoelectric conversion material.