JP2006049494A - Material and device for thermoelectric conversion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoelectric conversion material which can be improved in an essential thermoelectric conversion performance without setting a direction of temperature gradient, a direction of applying a magnetic field, and a direction of arranging electrodes, or a direction of pn junction to complicated ones; and also to provide a thermoelectric conversion device using the same. <P>SOLUTION: The thermoelectric conversion material is reduced in electric resistance by being applied with a magnetic field. The thermoelectric conversion device comprises the thermoelectric conversion material and a magnetic field generator. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a thermoelectric conversion material and a thermoelectric conversion device. More specifically, the present invention relates to a thermoelectric conversion material whose electrical resistance changes by applying a magnetic field, and a thermoelectric device including the thermoelectric conversion material and a magnetic field generation device. The present invention relates to a conversion device.

  Currently, much of the world's energy depends on the combustion energy of fossil fuels, but in the case of power generation systems that use thermal cycles, most of that energy is discarded as waste heat. Currently. On the other hand, global environmental conservation has been debated on a global scale, and development of effective utilization technology for unused energy has been energetically promoted.

  Among these, power generation using thermoelectric conversion can directly convert even relatively low-quality heat into electricity. As the environmental problems become more serious, expectations for thermoelectric conversion are increasing.

  This thermoelectric conversion is a Seebeck effect in which thermoelectromotive force is generated at both ends when a temperature difference is given to thermoelectric conversion materials composed of two different types of metals or a combination of a p-type semiconductor and an n-type semiconductor. This is a technology that directly converts heat energy into electric power, and has excellent features such as no moving parts such as motors and turbines, and no waste. As a conventional technique related to a thermoelectric conversion material, there is “a thermoelectric conversion material, a thermoelectric conversion element, and a manufacturing method thereof” disclosed in Patent Document 1.

Here, the figure of merit Z used for performance evaluation of thermoelectric characteristics is expressed by the following equation.
Z = α ² / (κ ・ ρ)
α: Seebeck coefficient
κ: Thermal conductivity
ρ: electrical resistance That is, in order to improve the performance coefficient, it is necessary that the Seebeck coefficient is large and the thermal conductivity and electrical resistance are small. Here, since Seebeck coefficient is a physical property value, it depends on the material, but since thermal conductivity and electrical resistance can be changed, various methods for reducing thermal conductivity and electrical resistance Is being considered.

  In addition to the Seebeck effect described above, a Nernst effect (when a magnetic field is applied to a conductor or semiconductor that has a temperature gradient and heat flows in a direction perpendicular to the direction of heat flow, a potential difference is produced in the direction perpendicular to both. Proposals have also been made to use the synergistic effect of the phenomenon that occurs.

  “When a magnetic field is applied to a Bi-based thermoelectric conversion material containing 5 atomic% or less of the required additive elements in Bi alone or in combination, the Seebeck coefficient is greatly improved, the magnetic field is applied perpendicular to the direction of the temperature gradient, and the temperature By adopting a structure in which electrodes are arranged so that a temperature gradient is provided in a direction perpendicular to both the gradient and magnetic field directions, the Seebeck coefficient is remarkably improved. ” It has been proposed (see, for example, Patent Document 2).

Further, “a p-type thermoelectric conversion material and a n-type thermoelectric conversion composed of a composite of a rectangular Bi-based thermoelectric conversion material and a rare earth magnet alloy powder containing a required additive element to form a p-type semiconductor or an n-type semiconductor. When the materials are alternately arranged via a material with low thermal conductivity such as a glass plate and high electrical resistivity, the low temperature sides of each thermoelectric conversion material are connected with wires, and the high temperature sides are connected with different wires, By applying a magnetic field in the required direction and magnetizing, a temperature gradient ΔT in the direction orthogonal to the magnetization direction, a pn junction on the surface in the direction orthogonal to the two directions, and deriving the thermoelectromotive force from the connection end, the external Therefore, a thermoelectric conversion material, a method for manufacturing the thermoelectric conversion material, and a thermoelectric conversion element have been proposed (see, for example, Patent Document 3).
JP 2002-353523 A JP 2002-64228 A JP 2002-118295 A

  However, according to the methods proposed in Patent Documents 2 and 3, it is possible to improve the thermoelectromotive force by the synergistic effect of the Seebeck effect and the Nernst effect, but the direction of the temperature gradient and the application of the magnetic field are applied. The direction in which the electrode is disposed and the direction in which the electrode is arranged or the direction in which the pn junction is formed are complicated, and if the direction deviates from a predetermined direction, sufficient characteristics cannot be obtained, so the actual heat energy of waste heat is converted into electric energy. In some cases, there is a problem that a sufficient thermoelectromotive force cannot be obtained.

  Therefore, it is not necessary to match the direction of the temperature gradient in the complicated direction, the direction of applying the magnetic field, the direction of arranging the electrodes, or the direction of pn junction, and the thermoelectric that can improve the thermoelectric conversion performance of the original thermoelectric conversion material. Conversion materials or thermoelectric conversion devices have been eagerly desired.

  The present invention has been made in consideration of the above-described circumstances, and a thermoelectric conversion material whose electric resistance is reduced by applying a magnetic field to the thermoelectric conversion material, and a thermoelectric conversion device including the thermoelectric conversion material and a magnetic field generator. Therefore, it is not necessary to match the direction of the temperature gradient in the complicated direction, the direction of applying the magnetic field, the direction of arranging the electrodes, or the direction of pn junction, and the thermoelectric conversion performance of the original thermoelectric conversion material can be achieved. It aims at providing the thermoelectric conversion material and thermoelectric conversion apparatus which can be improved.

  In order to solve the above problems, the invention described in claim 1 is characterized by a thermoelectric conversion material whose electrical resistance changes when a magnetic field is applied.

  The invention according to claim 2 is the thermoelectric conversion material according to claim 1, wherein the thermoelectric conversion material is such that the electric resistance is reduced by applying a magnetic field.

  According to a third aspect of the present invention, there is provided the thermoelectric conversion material according to the first or second aspect, wherein the thermoelectric conversion material includes at least an oxide.

  The invention according to claim 4 is the thermoelectric conversion material according to claim 3, characterized in that the oxide is composed of at least a layered compound.

  The invention according to claim 5 is characterized in that the thermoelectric conversion material according to any one of claims 1 to 4 is oriented in one direction.

  The invention according to claim 6 is the thermoelectric conversion material according to claim 5, wherein the thermoelectric conversion material is arranged in a direction along the anisotropy of magnetic susceptibility.

  A seventh aspect of the invention is characterized by a thermoelectric conversion device including the thermoelectric conversion material and the magnetic field generation device according to any one of the first to sixth aspects.

  The invention according to claim 8 is the thermoelectric conversion device according to claim 7, characterized in that the magnetic field generation device is an electromagnet.

  The invention according to claim 9 is the thermoelectric converter according to claim 7, characterized in that the magnetic field generator is a superconducting magnet.

  The invention according to claim 10 is the thermoelectric conversion device according to claim 7, characterized in that the magnetic field generation device is a permanent magnet having spontaneous magnetization.

  According to the present invention, in the thermoelectric conversion material, the electric resistance is changed by applying a magnetic field to the thermoelectric conversion material, and the electric resistance is reduced by applying the magnetic field to the thermoelectric conversion material. It has become possible to increase the figure of merit.

  Moreover, when the thermoelectric conversion material is or is oriented, it is possible to easily reduce the electric resistance when a magnetic field is applied.

  Furthermore, the thermoelectric conversion performance of the original thermoelectric conversion material can be improved by providing the thermoelectric conversion material and the magnetic field generator in which the electric resistance is reduced by applying a magnetic field.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a conceptual diagram showing an example of the dependence of the electrical resistance of a material on the magnetic field strength. This is the so-called negative magnetoresistance effect, and shows how the electrical resistance of a material decreases when a magnetic field is applied. In particular, a large number of huge magnetoresistive effects have been discovered for oxide-based materials.

As described above, the figure of merit Z used for the performance evaluation of thermoelectric characteristics is expressed by the following equation.
Z = α ² / (κ ・ ρ)
α: Seebeck coefficient
κ: Thermal conductivity
ρ: Electric resistance That is, in order to improve the thermoelectric characteristics, it is necessary that the Seebeck coefficient is large and the thermal conductivity and electric resistance are small. Here, since the Seebeck coefficient is a physical property value, it depends on the material, but by applying a magnetic field to the thermoelectric conversion material having a negative magnetoresistance effect and reducing the electric resistance, the figure of merit of the thermoelectric conversion material is reduced. The main idea of the present invention is to increase the thickness and thereby obtain excellent thermoelectric characteristics.

  FIG. 2 shows a conceptual diagram when the thermoelectric conversion material 1 having a negative magnetoresistance effect is adjacent to the magnetic field generator 2. The thermoelectric conversion material 1 can improve its figure of merit by applying a magnetic field by the magnetic field generator 2 because the electric resistance decreases when a magnetic field is applied. Here, as the thermoelectric conversion material 1, any material can be used as long as it has a negative magnetoresistance effect. However, a larger negative magnetoresistance effect is preferable, and from this viewpoint, oxidation is preferable. It is more preferable to use a physical material.

  FIG. 3 is a conceptual diagram showing a cross section of the thermoelectric conversion material when the thermoelectric fine particles constituting the thermoelectric conversion material or the crystal grains of the thermoelectric conversion material are oriented. As described above, the oriented thermoelectric conversion material, in particular, the thermoelectric conversion material 3 oriented uniaxially along the anisotropy of magnetic susceptibility has the easy axis of magnetization arranged in one direction. The application is preferable because there is an advantage that the electric resistance is easily reduced. In this case, the thermoelectric conversion material preferably has magnetic susceptibility anisotropy. That is, it is preferable that the susceptibility: χ is small in any direction, the susceptibility is large in any other direction, and the difference in susceptibility in both directions: Δχ is as large as possible. From this point of view, the oxide is preferably composed of a layered compound. This layered compound has a layered structure, so that the magnetic susceptibility is greatly different between the stacking direction of the layers and the direction perpendicular thereto, and an oriented thermoelectric conversion material can be easily formed.

  FIG. 4 shows an insulating transmission between the high temperature side and the low temperature side of the thermoelectric conversion element in which the p-type material 4 and the n-type material 5 of the thermoelectric conversion material having the negative magnetoresistance effect described above are connected in series by the electrode 7. The conceptual diagram of the thermoelectric conversion apparatus which made the thing insulated with the heat body 8 adjoin the magnetic field generator 6 is shown.

  One of the insulated heat transfer bodies 8 is heated to a high temperature, the other insulated heat transfer body side is cooled to a low temperature, and a p-type material 4 and an n-type material 5 of a thermoelectric conversion material having a negative magnetoresistance effect are connected in series by an electrode 7. A thermoelectromotive force can be obtained by applying a temperature difference to the thermoelectric conversion element. At this time, a thermoelectric conversion material having a negative magnetoresistance effect is obtained by applying a magnetic field by the adjacent magnetic field generator 6. Thus, the thermoelectric conversion device shown in FIG. 4 can obtain excellent thermoelectric characteristics.

  There is no problem in making the magnetic field generator adjacent to the thermoelectric conversion element even if it is adjacent in the horizontal direction as shown in FIG. 4, and there is no particular problem if it is adjacent in the vertical direction as shown in FIG. What is necessary is just to select appropriately depending on which one can be adjacent to which the magnetic field can be applied in a preferable direction to the thermoelectric conversion material and which one is adjacent to which the temperature difference is likely to be applied to the thermoelectric conversion element.

  Here, there is no particular problem even if any magnetic field generator is used as long as it can generate a magnetic field. It is preferable to use a commonly used electromagnet as the magnetic field generator 6 because the strength of the magnetic field can be controlled by the magnitude of the current flowing through the coil. In addition, if a superconducting magnet is used as the magnetic field generator 6, it is possible to generate a strong magnetic field, which is very preferable when a strong magnetic field is required to reduce the electric resistance of the thermoelectric conversion material.

  Furthermore, when a permanent magnet having spontaneous magnetization is used as a magnetic field generator, there is no need to apply a magnetic field from the outside, and there is an advantage that a magnetic field can be applied even in a place where there is no power source, and the thermoelectric converter is downsized. From the viewpoint of cost reduction or productivity improvement, it is very preferable. A conceptual diagram when a permanent magnet is used as the magnetic field generator is shown in FIG. In FIG. 6, the permanent magnet is adjacent only to the lower side. However, as shown in FIG. 5, there is no problem even if the permanent magnets are adjacent to each other in the vertical direction. There is no problem.

  As described above, the electric resistance is reduced by applying a magnetic field to the thermoelectric conversion material, that is, the thermoelectric conversion material having a negative magnetoresistance effect, and the thermoelectric conversion device including the thermoelectric conversion material and the magnetic field generation device. Therefore, it is not necessary to match the direction of the temperature gradient in the complicated direction, the direction of applying the magnetic field, the direction of arranging the electrodes, or the direction of pn junction, and the thermoelectric conversion performance of the original thermoelectric conversion material can be achieved. It has become possible to provide a thermoelectric conversion material and a thermoelectric conversion device that can be improved.

  As an n-type thermoelectric conversion material having a negative magnetoresistive effect, a La—Sr—Mn-based oxide was used, and a magnetic field generator was made adjacent to the thermoelectric conversion material as shown in FIG. (Sample 1) An electromagnet was used as the magnetic field generator. Zm> Zn, where Zm is a figure of merit when a 2T magnetic field is generated by this magnetic field generator and Zn is a figure of merit when no magnetic field is generated, and thermoelectric conversion is achieved by applying a magnetic field. The figure of merit of the material could be improved.

  As an n-type thermoelectric conversion material having a negative magnetoresistance effect, an oriented La—Sr—Mn-based oxide was used, and a magnetic field generator was adjacent to this thermoelectric conversion material as shown in FIG. (Sample 2) An electromagnet was used as the magnetic field generator in the same manner as in Example 1. The oriented La-Sr-Mn oxide thermoelectric conversion material was formed by orienting and sintering La-Sr-Mn oxide fine particles. When the performance index when a magnetic field was applied to Sample 1 and Sample 2 was compared, the performance index was improved with a smaller magnetic field when Sample 2 was used.

  An La-Sr-Mn-based oxide is used as an n-type thermoelectric conversion material having a negative magnetoresistance effect, and Bi-Sr-Ca-Co is used as a p-type thermoelectric conversion material having a negative magnetoresistance effect. Using these oxides, these thermoelectric conversion materials were connected in series as shown in FIGS. 4 and 5, and the magnetic field generator was placed adjacent to each other. However, one thermoelectric conversion element pair was used and Ag paste was used for the electrodes. An electromagnet was used as the magnetic field generator. When the generated power when a magnetic field of 2T is generated by this magnetic field generator is Pm and the generated power when no magnetic field is generated is Pn, Pm> Pn, and by applying the magnetic field, thermoelectric conversion The generated power of the device could be improved. The type | mold which installed the magnetic field generator next to the thermoelectric converter was shown in FIG. 4, and the type | mold installed up and down was shown in FIG.

  Example 3 was the same as Example 3 except that an Nd—Fe—B magnet was used as the magnetic field generator and was placed under the thermoelectric conversion element as shown in FIG. When the generated power when the Nd-Fe-B magnet is adjacent is Pm and the generated power when the Nd-Fe-B magnet is not adjacent is Pn, Pm> Pn, and Nd-Fe- By making the B-system magnet adjacent, it was possible to improve the generated power of the thermoelectric converter even when no magnetic field was supplied from the outside.

It is explanatory drawing which shows an example of the magnetic field strength dependence of the electrical resistance of this invention. It is the schematic of the example which adjoined the thermoelectric conversion material of this invention with the magnetic field generator. It is a conceptual diagram which shows the cross section at the time of use of the oriented thermoelectric conversion material of this invention. It is a conceptual diagram of the thermoelectric conversion apparatus which connected the p-type and n-type thermoelectric conversion material of this invention in series. It is another conceptual diagram of the p-type and n-type thermoelectric conversion material serial connection thermoelectric conversion device of the present invention. It is a conceptual diagram at the time of permanent magnet use of the p-type and n-type thermoelectric conversion material series connection thermoelectric conversion apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Thermoelectric conversion material 2 Magnetic field generator 3 Oriented thermoelectric conversion material 4 p-type thermoelectric conversion material 5 n-type thermoelectric conversion material 6 Magnetic field generator 7 Electrode 8 Insulated heat transfer body 9 Permanent magnet

Claims (10)

  A thermoelectric conversion material characterized in that an electric resistance is changed by applying a magnetic field.   2. The thermoelectric conversion material according to claim 1, wherein the electric resistance is reduced by applying a magnetic field.   The thermoelectric conversion material according to claim 1 or 2, comprising at least an oxide.   The thermoelectric conversion material according to claim 3, wherein the oxide is composed of at least a layered compound.   The thermoelectric conversion material according to any one of claims 1 to 4, wherein the thermoelectric conversion material is oriented in one direction.   The thermoelectric conversion material according to claim 5, wherein the thermoelectric conversion material is arranged in a direction along anisotropy of magnetic susceptibility.   A thermoelectric conversion device comprising the thermoelectric conversion material and the magnetic field generation device according to claim 1.   8. The thermoelectric conversion device according to claim 7, wherein the magnetic field generation device is an electromagnet.   8. The thermoelectric conversion device according to claim 7, wherein the magnetic field generator is a superconducting magnet.   8. The thermoelectric conversion device according to claim 7, wherein the magnetic field generation device is a permanent magnet having spontaneous magnetization.

Images