JP2001189495A - Method for combining thermoelectric conversion material configuration atom - Google Patents

Abstract

PROBLEM TO BE SOLVED: To give a guide for combining the configuration atoms of a thermoelectric conversion material for constituting a Heusler-type compound. SOLUTION: Neutral atom configuration atoms for composing neutral atoms by eliminating insufficient electron-filled state in the s, p, and d orbitals of electron orbitals, a cation configuration atom for composing a cation by eliminating insufficient electron-filled state in the s, p, and d orbits of the electron orbitals, an anion configuration atom for composing an anion by eliminating insufficient electron-filled state in the s, p, and d orbitals of the electron orbitals are combined so that the charge balance, based on the anion configuration atom and the cation configuration atom can be balanced, thus constituting the thermoelectric conversion material of a Heusler-type compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoelectric conversion material for performing mutual conversion between heat energy and electric energy.

[0002]

2. Description of the Related Art In recent years, research has been conducted on thermoelectric conversion materials for directly converting thermal energy into electrical energy or directly converting electrical energy into thermal energy.
Such a thermoelectric conversion material performs thermoelectric conversion using the Seebeck effect or the Peltier effect. The conversion performance is represented by the following formula called a performance index: Z = α ² (σ / κ) Z: performance index (K ^-1) α: Seebeck coefficient (VK ^-1: generating heat power per unit temperature) sigma: electrical conductivity (Scm ^-1) κ: represented by thermal conductivity (Wcm ^-1 K ^-1) .

[0003] The thermoelectric conversion has excellent features such as being small in size and light in weight without a driving part, maintenance-free, and semi-permanent. Taking advantage of this feature, for example, thermoelectric power generation is used as a power source for space probes and as a power source for use in remote areas such as lighthouses.

On the other hand, the Peltier effect is a semiconductor laser,
It is also used for cooling electronic devices such as sensors and integrated circuits (LSI) and for consumer use such as small cooler boxes. However, at present, since the conversion efficiency is 10% or less, it has not reached a stage where it can compete with existing energy conversion systems.

To raise thermoelectric conversion to a level that can be used in many applications, it is necessary to solve some problems. Above all, improvement of the conversion efficiency is the first problem, and if a conversion efficiency of 20% can be achieved, the application field can be dramatically expanded. In addition, it is necessary to consider various aspects such as superiority of thermoelectric conversion, competitiveness with other energy conversion systems, COP (coefficient of performance), and economics (cost).

[0006] When these technical problems are solved, applications in the industrial field and widespread use in consumer products become apparent.
For example, exhaust heat of an automobile engine can be recovered as electrical energy. The current car engine has about 26 fuel
% Is power, and the remaining about 60% is released to the atmosphere as heat.

[0007] Electric power is generated by the exhaust heat of about 800 ° C emitted from the outer wall of the engine or the turbocharger, and if this is charged into a battery, it can be used for driving a cooler or an alternator.

[0008] In addition, energy recovery from high-temperature exhaust heat from small and medium-scale incinerators and reaction heat from fuel cells (Science and Technology Agency, Aerospace Research Institute), a fast breeder reactor with a thermoelectric power module incorporated in a heat pipe (Central Research Institute of Electric Power Industry) Practical application can be expected in a wide range of fields such as heat exchangers.

[0009]

At present, there is a strong demand for thermoelectric conversion materials in various fields as described above, and there is an urgent need to develop new thermoelectric conversion materials having excellent conversion efficiency. Among them, some intermetallic compounds having a Heusler-type crystal structure have attracted attention as new thermoelectric materials because they exhibit semiconductor properties.

However, research on Heusler-type intermetallic compounds as a magnetic material exhibiting metal conduction has been mainly carried out so far.
Although tMnSb is obtained, a Heusler alloy having thermoelectric performance that can be put to practical use as a thermoelectric conversion material has not been obtained. The thermoelectric performance of a Heusler alloy depends on the combination of elements constituting the compound. However, no sufficient method for developing a Heusler-type compound as a thermoelectric material has been proposed, and in a sense, it is in a state of groping.

The present inventors have been concerned with such a situation while working on the development of a new thermoelectric conversion material by themselves, and have always thought that a standard that contributes to the development method should be found so that more efficient development can be performed.

An object of the present invention is to provide a standard for a method of combining constituent atoms of a Heusler-type compound when developing a material as a novel thermoelectric conversion material.

[0013]

Means for Solving the Problems In the method for searching for a Heusler-type thermoelectric conversion material, the present inventors reviewed the problems that had been groped in the past, and set the search criteria for a Heusler-type compound as a new thermoelectric conversion material. suggest.

Conventionally, although the electronic structure of a Heusler alloy has been discussed theoretically as a magnetic material, it has hardly been discussed from the viewpoint of a thermoelectric conversion material.
The present invention has been accomplished by reviewing this point and conducting research on the correlation between the electronic bonding state or band structure of the Heusler alloy and the thermoelectric properties.

[0015] The present inventors have specifically proposed PtGdBi,
PtMnS of Heusler alloy having similar crystal structure
b, PdMnSb, compared with PdMnSb, and focused on its electronic bonding state and band structure. As a result, the combination of constituent elements for having good characteristics as a thermoelectric conversion material in a Heusler-type compound was investigated. We found the selection criterion from a theoretical point of view. By selecting an atomic configuration in accordance with such criteria, a thermoelectric conversion material composed of a novel Heusler-type compound can be efficiently provided.

That is, the method of combining the constituent atoms of the thermoelectric conversion material constituted by the Heusler-type compound of the present invention eliminates the insufficiently charged state of electrons in the electron orbits to form the neutral atoms constituting the neutral atoms. Atoms and cations that make up the cations that make up the insufficient electron filling state in the electron orbitals, and an anions that make up the anions that make up the insufficient electron filling states in the electron orbitals A Heusler-type compound is constituted by combining atoms so that the charge balance based on the cation constituent atoms and the anion constituent atoms is balanced.

In addition, the insufficient electron filling state in the electron orbitals is eliminated to form neutral atoms constituting the neutral atoms, and the insufficient electron filling state in the electron orbitals is eliminated to form cations. The cation constituent atoms, and the charge balance based on the cation constituent atoms and the anion constituent atoms that resolve the insufficient electron filling state in the electron orbit and the anion constituent atoms forming the anion. A Heusler-type compound is constituted by combining them so as to be in equilibrium, wherein the neutral atom is Ni and the cation is T
i, Zr or Hf, wherein the anion constituting atom is Si, G
e, Sn or Pd.

[0018] The insufficient electron filling state in the electron orbitals is eliminated, and the neutral atom constituting atoms constituting the neutral atoms is eliminated, and the insufficient electron filling state in the electron orbitals is eliminated to form the positive ions constituting the cations. The charge balance based on the cation constituent atoms and the anion constituent atoms of the ionic constituent atoms and the anion constituent atoms constituting the anion by eliminating the insufficient electron filling state in the electron orbit is balanced. To form a Heusler-type compound, wherein the neutral atom-constituting atom is Pt, the cation-constituting atom is Gd, Tb,
Lu, Pa, U or Cm, and the anion-constituting atom is P, As, Sb or Bi.

In any one of the above-described methods for combining atoms constituting thermoelectric conversion materials, the Heusler-type compound is doped with 0.1 to 50 atomic% of impurities.

In any one of the above-mentioned methods for combining atoms constituting thermoelectric conversion materials, when a neutral atom is constituted by eliminating an insufficiently filled state of electrons, the cation constituting atom of the neutral atom constituting atom is used. , And the donation of electrons from the neutral atom to the anion atom.

In any one of the above-described methods for combining atoms constituting thermoelectric conversion materials, when a cation is constituted by eliminating an insufficiently charged state of electrons, the atom constituting the neutral atom is converted from the atom constituting the cation. And electron donation from the cation constituent atom to the anion constituent atom.

In any of the above-described methods for combining atoms constituting thermoelectric conversion materials, when an anion is formed by eliminating an insufficiently charged state of electrons, the neutral atoms constituting the anions may be converted from the neutral atoms constituting the anions. And the receipt of electrons from the cation constituent atoms of the anion constituent atoms.

[0023] In the method for combining atoms constituting the thermoelectric conversion material according to any one of the above, the receiving and donating of the electrons may include:
It is characterized in that electron transfer between electron orbitals of the same principal quantum number is considered to be involved. The method for combining atoms constituting a thermoelectric conversion material according to any one of the above, wherein electron transfer between electron orbitals having different principal quantum numbers is considered to be involved in electron reception and / or donation. I do.

The selection of the constituent atoms of the neutral atom, the cation, and the anion constituting the above-mentioned structure is performed by, for example, selecting a combination of the atomic structures satisfying the above-mentioned structure from the electron configuration of the ground state of the neutral atom. It can be done by doing. Compared with the conventional method of searching for a new thermoelectric conversion material in which various combinations of atoms are considered in a groping state, the search range can be significantly reduced, and an excellent thermoelectric conversion material can be efficiently developed.

As used herein, the term “orbit” is defined by a combination of a principal quantum number, an azimuthal quantum number, and a magnetic quantum number, and is represented by a wave function indicating the existence probability of electrons. And it is also called orbital. Each orbital can contain up to two electrons whose electron spins are in opposite directions (different spin quantum numbers).

[0026]

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

A ternary alloy belonging to the Heusler-type compound having a composition formula of PtGdBi was manufactured, and the relationship between the thermoelectric properties and the atomic arrangement in the crystal structure and the electronic structure was examined. G
For d, a raw material having a purity of 99.9% was used. 99.99% of a raw material of Pt was used. The raw materials for Bi include:
A raw material having a purity of 99.9999% was used.

These raw materials were weighed in accordance with the stoichiometric ratio based on the above composition formula, and were arc-melted.
The alloy material obtained by arc melting was repeatedly melted as many times as necessary so that the composition became uniform. Thereafter, the obtained ingot is heat-treated to obtain PtGdBi.
Was prepared. The structure of the obtained crystal is
Confirmed by X-ray diffraction.

The thus obtained sample was measured for its thermoelectric properties. FIG. 1 shows the temperature dependence of the electrical conductivity. For comparison, PtMnSb and PdMnS, which are Mn-based antimonides of Heusler alloys
The electric conductivity of b is also shown. From the electrical conductivity shown in FIG. 1, it can be seen that PtMnSb and PdMnSb exhibit different temperature dependence than usual. Such temperature dependence is not considered to be due to carrier scattering, but is presumed to be due to a change in band structure.

Compared to PtMnSb and PdMnSb, PtGdBi behaves like a semiconductor. The hole concentration was 7 × 10 ¹⁹ cm ⁻³ at room temperature. Hall mobility is about 120 cm ² / Vs, 1 at room temperature.
It was 220 cm ² / Vs at 00K.

FIG. 2 shows the temperature dependence of the Seebeck coefficient. As in the case of FIG.
Sb and PdMnSb are shown for comparison. PtMnS
b and PdMnSb showed extremely low values in the range of 300 to 850 K, but PtGdBi showed high values of 60 μV / K at room temperature and 82 μV / K in the temperature range of 550 to 750 K.

PtGdBi is, as shown in FIG.
It has the same CIb symmetric crystal structure as MnSb and PdMnSb, and such a structure was confirmed by X-ray diffraction. FIG.
In the unit crystal lattice shown in (1), Bi and Gd form a sublattice, and have an atomic arrangement in which Gd is arranged at an angle of 90 ° on both sides of Bi. This is shown in FIG.

[0033] In Figure 4, on both sides of 6p _y ³ trajectory Bi,
The figure shows that the 5d _xy ¹ and 5 _dyz ¹ orbits of Gd are arranged at an angle of 90 degrees. The exchange integral J of both becomes negative, and it is also confirmed from the calculation that an energetic interaction exists.

[0034] Pt has an electronic configuration of ^{[Xe] 4f 14 5d 9 6s} 1. That is, 5d ⁹ 6 having the same electron configuration as Xe in the inner shell and insufficient electron filling in the outer shell.
The electron configuration has an s ¹ orbit. Nine electrons are filled in the d orbital of principal quantum number 5, which can accept up to 10 electrons of different spins, and one electron is in the s orbital of principal quantum number 6, which can accept up to 2 electrons. It can be seen that all the orbits are in an insufficiently electron-filled state after being filled. By resolving these insufficient electron filling states, Pt is energetically stabilized.

[0035] On the other hand, Bi ^{is, [Xe] 4f 14 5d 10} 6s
It has an electronic arrangement of ² 6p ^3. That is, X
e, and the 6p ³ orbital of the outer shell is in an insufficiently filled state. Therefore, the p-orbital of the main quantum number 6 in the outer shell fills the orbital by receiving three electrons from other atoms, and tends to take an energetically stable electron configuration by forming an anion. It can be said that there is.

[0036] Gd has an electronic configuration of ^{[Xe] 4f 7 5d 1 6s} 2. The inner shell has a closed shell electron configuration of Xe, and 5d ^{1 in} the outer shell is in an insufficiently electron-filled state. It can be said that Gd having such an electron configuration has a tendency to emit ^one electron from the 5d ¹ electron orbit and easily become a cation. In the case of Gd, the electron filling state of the 4f ⁷ orbital is insufficient, but the mutual energy ranks are not close enough to transfer electrons to the 5d, 6s and 6p orbitals, and are excluded from this study. it can.

In PtGdBi, a Bi-Gd sub-lattice is formed in the unit cell as described above. In this sub-lattice, as shown in FIG. A configuration in which two Gd are arranged is formed.

Therefore, the arrangement of atoms in such a crystal lattice,
Considering the above electron configuration of Pt, Gd, and Bi together,
One electron moves from the 5d ¹ orbital of Gd to the 5d ⁹ orbital of the same principal quantum number of Pt, and the 5d ⁹ orbital of Pt becomes a 5d ¹⁰ orbital, and the 5d orbital is completely filled and the 5d ⁹ orbital is not filled. It is considered that the sufficient electron filling state has been eliminated. G
In d, ^one electron is emitted from the 5d ¹ orbit, and the 5 d orbit in an insufficiently charged state is completely vacant and eliminated.

On the other hand, two electrons from the 6s ² orbit of Gd and one electron from the 6s ¹ orbit of Pt correspond to 6 electrons of the Bi
By moving to the p ³ orbit, Gd becomes a Gd ³⁺ cation, Bi becomes a Bi ^3- anion, and a cation,
While maintaining the balance of the charge balance of anions, the insufficient electron filling state of each atom is eliminated.

That is, two electrons from the 6s ² orbit of Gd and one electron from the 6s ¹ orbit of Pt are Bi
To the 6p ³ orbit of Gd
Is Gd ³⁺ , and the electron configuration is [Xe] 4f ⁷ , which eliminates the insufficient electron filling state in the s orbit, p orbit, and d orbit.

As for the neutral atom Pt, the 5d ⁹ orbit becomes 5d ¹⁰ orbit by accepting one electron from Gd, and 6s in total.
The one electron from ¹ trajectories be released to 6p ³ orbit of Bi, the electronic arrangement, [Xe] 4f ¹⁴ 5d ¹⁰ next, to eliminate the poor electronic filling state, having so-called closed shell electron configuration It is a neutral atom.

In Bi, two electrons from the 6s ² orbit of Gd and one electron from the 6s ¹ orbit of Pt are
By accepting to the 6p ³ orbits, insufficient electron state of filling 6p ³ trajectory is eliminated, [Xe] 4f ¹⁴ 5d ¹⁰
An anion having a stable electron configuration of 6s ² 6p ⁶ is Bi ³⁻ .

[0043] In Gd, one electron from 5d ¹ orbit Gd to Pt of 5d ^9, by donating two electrons from 6s ² orbital to 6p ³ orbit of Bi, the 5d ¹ track not sufficient electron filling state is canceled, [Xe] 4f ⁷ cation Gd having a stable electron configuration having an electron configuration of
³⁺ .

As described above, in PtGdBi, Pt, G
The d and Bi atoms eliminate the insufficient electron filling state of the s-orbital, p-orbital and d-orbital in the ground state electron configuration, and an energetically stable crystal structure having a narrow band gap is created. Therefore, it is considered that PtMnSb and PdMnSb having the same crystal structure exhibit different thermoelectric characteristics.

That is, in PtMnSb, Mn is [A
r] 3d ⁵ 4s ² and Pt is [Xe]
4f ¹⁴ 5d ⁹ 6s ¹ comprising an electron arrangement, Sb is [K
r] 4d ¹⁰ 5s ² 5p ³ , and P
It is impossible to consider a configuration of an electron configuration that eliminates the insufficient electron filling state of each atom based on the electron transfer between atoms as discussed in tGdBi.

In PdMnSb, Pd is [Kr]
Has 4d ¹⁰ becomes electron configuration, Pt is [Xe] 4f ¹⁴ 5d
^It has an electron configuration of 96 s ¹ , and Sb is [Kr] 4d ¹⁰ 5
s ² 5p ^3, so that PtMnS
As discussed in b, it is impossible to consider a configuration of an electron arrangement that eliminates the insufficient electron filling state of the constituent atoms based on the electron transfer between atoms as in PtGdBi.

It is considered that the difference in the electron configuration between PtMnSb and PdMnSb from PtGdBi leads to the difference in the expression of thermoelectric properties. From such considerations, it is possible to eliminate the insufficiently electron-filled state of the electron orbital, and to eliminate the neutral atom constituting atoms constituting the neutral atom and the insufficiently electron-filled state in the electron orbital to constitute the cation. A cation constituent atom and an anion constituent atom constituting an anion by eliminating an insufficient electron filling state in an electron orbit,
It is considered that the inclusion of the cation-constituting atoms and the anion-constituting atoms so as to balance the charge balance based on the anion-constituting atoms can serve as a standard of the atomic configuration of the thermoelectric conversion material constituting the novel Heusler-type compound, and the present invention It is a thing.

That is, the present inventors first examined in detail the thermoelectric properties of PtGdBi, the atomic arrangement in the crystal structure, and the electronic structure of the constituent atoms, and found that the constituent atoms of the Heusler-type compound from an electronic structural point of view. It is the first to propose a combination method of.

As the Heusler-type compound having such a structure, various combinations of various systems as shown in Table 1 can be considered in addition to the known PtGdBi.

Here, A atom in the table is a neutral atom constituting the above-mentioned neutral atom, and corresponds to Pt constituting PtGdBi, and B atom is a cation constituting atom constituting the above-mentioned cation. , PtGdBi, and C atom are the anion constituent atoms of the anion, and correspond to Bi of PtGdBi.

[0051]

[Table 1]

The present invention is not limited to the above-described embodiment, and can be variously modified without departing from the gist thereof.

For example, for Heusler-type compounds consisting of PtGdBi or a combination of various systems shown in Table 1, 0.
It is also possible to dope an impurity of about 1 to 50 atom% (atom%) to insert the impurity into the crystal lattice or to replace a part of the constituent atoms.

[0054]

According to the present invention, a combination of constituent atoms of a Heusler-type compound as a thermoelectric conversion material can be predicted based on an electronic structure and the like. Therefore, a novel thermoelectric conversion material constituting the Heusler-type compound can be efficiently developed.

[Brief description of the drawings]

FIG. 1 is a graph showing the temperature dependence of the electrical conductivity of PtGdBi.

FIG. 2 is a graph showing the temperature dependence of the Seebeck coefficient of PtGdBi.

FIG. 3 is an explanatory view showing a crystal structure of PtGdBi.

FIG. 4 is an explanatory diagram showing a state of electronic transition between Gd and Bi in PtGdBi.

Claims (9)

[Claims] 1. A method for forming a neutral atom constituting a neutral atom by eliminating an insufficient electron filling state in an electron orbit, and forming a cation by eliminating an insufficient electron filling state in an electron orbit. A cation constituent atom, and an insufficient electron filling state in an electron orbit, and an anion constituent atom forming an anion, and a charge balance based on the cation constituent atom and the anion constituent atom. A method for combining atoms constituting thermoelectric conversion materials, wherein the compounds are combined so as to equilibrate to form a Heusler-type compound. 2. A neutral atom constituting a neutral atom by eliminating an insufficient electron filling state in an electron orbit, and a cation forming by eliminating an insufficient electron filling state in an electron orbit. A cation constituent atom, and an insufficient electron filling state in an electron orbit, and an anion constituent atom forming an anion, and a charge balance based on the cation constituent atom and the anion constituent atom. Forming a Heusler-type compound by combining them so as to equilibrate, wherein the neutral atom constituting atom is Ni, the cation constituting atom is Ti, Zr or Hf, the anion constituting atom is Si,
A method for combining atoms constituting thermoelectric conversion material, which is Ge, Sn or Pd. 3. Insufficient electron filling state in the electron orbital is eliminated to form a neutral atom constituting a neutral atom, and cation is constituted by eliminating insufficient electron filling state in the electron orbital. A cation constituent atom, and an insufficient electron filling state in an electron orbit, and an anion constituent atom forming an anion, and a charge balance based on the cation constituent atom and the anion constituent atom. A Heusler-type compound is constituted by combining them so as to equilibrate, wherein the neutral atom constituting atom is Pt, the cation constituting atom is Gd, Tb, Lu, Pa, U or Cm, and the anion constituting atom is P, A method for combining atoms constituting thermoelectric conversion material, which is As, Sb or Bi. 4. The method for assembling thermoelectric conversion material atoms according to claim 1, wherein the Heusler-type compound is doped with an impurity of 0.1 to 50 atomic%. A method for combining atoms constituting thermoelectric conversion materials. 5. The method for combining atoms constituting a thermoelectric conversion material according to claim 1, wherein neutral atoms are formed by eliminating an insufficiently charged state of electrons to form neutral atoms. Thermoelectric conversion material composition characterized in that it is considered to be performed by receiving electrons from the cation constituent atoms of the atomic constituent atoms and donating electrons from the neutral atom constituent atoms to the anion constituent atoms. How to combine atoms. 6. The method for combining atoms constituting thermoelectric conversion materials according to any one of claims 1 to 4, wherein a cation is formed by eliminating an insufficiently charged state of electrons to form a cation. A thermoelectric conversion material constituent atom, which is considered to be performed by donating an electron from an atom to the neutral atom, and donating an electron from the cation to the anion. Combination method. 7. The method for combining atoms constituting a thermoelectric conversion material according to claim 1, wherein when an anion is formed by eliminating an insufficiently charged state of the electrons, the anion is formed. A combination of atoms constituting the thermoelectric conversion material, which is considered to be performed by receiving electrons from the above-mentioned neutral atom constituting atoms and receiving electrons from the above-mentioned cation constituting atoms of the anion constituting atoms. Method. 8. A method for combining atoms constituting a thermoelectric conversion material according to any one of claims 5 to 7, wherein electron transfer between electron orbitals having the same main quantum number is involved in receiving and donating electrons. A method for combining atoms constituting thermoelectric conversion material, characterized in that the atoms are considered to be in a state. 9. The method for combining atoms constituting a thermoelectric conversion material according to claim 5, wherein the electron transfer between electron orbitals having different principal quantum numbers is performed for receiving and / or donating electrons. A method for combining atoms constituting a thermoelectric conversion material, wherein