JP6684076B2 - Thermoelectric conversion element - Google Patents

Description

  The present invention relates to a thermoelectric conversion element, and more particularly to a thermoelectric conversion element utilizing the spin Seebeck effect.

  Conventionally, there has been proposed a thermoelectric conversion element in which an inverse spin Hall effect member is provided in a thermal spin wave spin current generating member made of a magnetic dielectric (for example, refer to Patent Document 1). In the thermoelectric conversion element, a temperature gradient is provided in the thickness direction of the thermal spin wave spin current generating member, and a magnetic field H is applied by a magnetic field applying means in a direction orthogonal to the longitudinal direction of the inverse spin Hall effect member to cause the inverse spin Hall effect. The thermoelectromotive force V was taken out from both ends of the member.

  As the magnetic dielectric in the thermoelectric conversion element, garnet ferrite, spinel ferrite such as MnxZn1-xFe2O4 (where 0 <x <1) or hexagonal ferrite, YIG (yttrium iron garnet) or yttrium gallium iron garnet, that is, When expressed by a general formula, a garnet ferrite composed of Y3Fe5-xGaxO12 (where 0 ≦ x <5) or a garnet ferrite in which the Y site of YIG is replaced with an atom such as La, for example, LaY2Fe5O12, has been proposed.

  Further, a fusion body of magnetic particles having a predetermined particle diameter has been proposed as a material corresponding to the above-described thermal spin wave spin current generating member (see, for example, Patent Document 2). And, as a material constituting the magnetic particles, yttrium iron garnet Y3Fe5-xGaxO12 (however, x <5, YIG), spinel ferrite such as garnet ferrite MnxZn1-xFe2O4 (however, 0 <x <1), or hexagonal Crystalline ferrite was mentioned. The fused body of magnetic particles can be obtained by a method of applying a magnetic material-dispersed composition containing magnetic particles, printing, and then firing.

JP, 2011-249746, A JP, 2014-209594, A

  However, the former thermoelectric conversion element has low power generation characteristics. Further, the latter thermoelectric conversion element, in order to generate a portion corresponding to the thermal spin wave spin current generating member, a method of applying a magnetic material-dispersed composition containing magnetic particles, printing, and then firing. It has been adopted, and has a drawback from the viewpoint of mass production due to process restrictions. Furthermore, the magnetic dielectrics and magnetic particles in the above two thermoelectric conversion elements are purposely manufactured by dedicated equipment, which increases the manufacturing cost.

  In view of such circumstances, an object of the present invention is to provide a thermoelectric conversion element having high power generation characteristics and low manufacturing cost.

The present invention has been made to solve the above problems, the thermoelectric conversion element of the present invention, a magnetic layer for generating a spin current in the direction in which a temperature gradient occurs, and formed on the magnetic layer, And a conductive layer that converts a spin current generated in the magnetic layer into an electric current, the magnetic layer being composed of at least a plurality of metal oxides , and the plurality of metal oxides being first oxides. It is characterized by being composed of iron, ferric oxide, and triiron tetroxide .

Further, in the thermoelectric conversion element of the present invention, the plurality of metal oxides include the powder of ferrous oxide, the powder of ferric oxide, and the powder of ferric tetroxide. It is characterized by

Further, in the thermoelectric conversion element of the present invention, the ferrous oxide, the ferric oxide, and the triiron tetroxide are obtained from a rolling scale.

  Further, in the thermoelectric conversion element of the present invention, the volume median diameter of the primary particles of the metal oxide-based powder is approximately 1 (μm) or less.

The mixing in the thermoelectric conversion element of the present invention, the magnetic layer, a powder of the ferrous oxide, powder of the ferric oxide powder of the triiron tetroxide, and a polymer compound It is characterized in that it is formed of the mixture described above, and the magnetic layer can be formed by applying the mixture.

  In the thermoelectric conversion element of the present invention, the polymer compound has a weight average molecular weight of 15,000 or more and 500000 or less.

  Further, in the thermoelectric conversion element of the present invention, the polymer compound includes a polymer of aromatic hydrocarbon.

  Further, in the thermoelectric conversion element of the present invention, the polymer compound has a water absorption rate of 0.25 or less.

  Further, in the thermoelectric conversion element of the present invention, the polymer compound has a linear expansion coefficient of 3 or more and 12 or less.

  According to the thermoelectric element of the present invention, the power generation characteristic is high, but the excellent effect that the manufacturing cost can be reduced can be obtained.

It is a figure which shows the thermoelectric conversion element 100 in embodiment of this invention. It is a figure which shows the thermoelectric conversion element 200 in embodiment of this invention. It is a figure which shows the power generation characteristic of the thermoelectric conversion element of this invention, and the thermoelectric conversion element used for the experiment regarding a time-dependent change in the power generation characteristic.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

<1. Configuration of thermoelectric conversion element 100>
FIG. 1 is a diagram showing a thermoelectric conversion element 100 according to an embodiment of the present invention. FIG. 1A is a perspective view of thermoelectric conversion element 100 according to the embodiment of the present invention. FIG. 1B is a diagram showing the flow of current in the thermoelectric conversion element 100 according to the embodiment of the present invention. The thermoelectric conversion element 100 is a thermoelectric conversion element that utilizes the spin-Beseck effect. As shown in FIG. 1A, the thermoelectric conversion element 100 is provided on the base material 10 and includes a magnetic layer 20 and a conductive layer 30.

  The base material 10 is assumed to have various modes such as a substrate made of a flexible material and a substrate made of an inflexible material. As an example of the thermoelectric conversion element 100, a structure in which the magnetic layer 20 and the conductive layer 30 are sequentially stacked on the base material 10 can be given. A pair of electrodes 41 and 42 is provided on the conductive layer 30, and a current thermoelectrically converted by the thermoelectric conversion element 100 is taken out from the electrodes 41 and 42. Hereinafter, description will be made on the premise that the thermoelectric conversion element is a thermoelectric conversion element 200 having a structure in which a conductive layer 30 and a magnetic layer 20 are sequentially stacked on a base material 10 as shown in FIG. It may be. In this case, the magnetic layer 20 is partially removed to expose the conductive layer 30, and the electrodes 41 and 42 are provided on the exposed conductive layer 30.

<1-1. Configuration of Magnetic Layer 20>
The magnetic layer 20 is made of a magnetic material exhibiting the spin Seebeck effect. The spin Seebeck effect is a phenomenon in which when a temperature gradient is applied to a magnetic material, a spin current, which is a flow of electron spins, is generated in a direction parallel to the temperature gradient. Therefore, when a temperature gradient is applied to the magnetic layer 20, a spin current is generated in a direction parallel to the temperature gradient as shown in FIG.

  A metal oxide is assumed as a material forming the magnetic layer 20. Examples of the metal oxide forming the magnetic layer 20 include iron oxide, chromium oxide, Ru oxide and the like. In the present invention, an iron oxide-based material is preferable as the metal oxide forming the magnetic layer 20.

  Specifically, as the iron oxide-based material, for example, triiron tetroxide (magnetite), ferrous oxide (wustite), ferric oxide (hematite) is assumed. The magnetic layer 20 is formed of at least two of the above materials. Examples of the combination of the materials include, for example, triiron tetraoxide (magnetite) and ferrous oxide (wustite), triiron tetraoxide (magnetite) and ferric oxide (hematite), and triiron tetraoxide (magnetite) and ferric oxide. Ferrous (wustite) and ferric oxide (hematite) are assumed as examples.

  As the metal oxide, for example, it is assumed that a rolling scale is used. The rolling scale refers to an oxide scale generated in the heating and rolling process of steel or the like. This rolling scale contains at least triiron tetroxide (magnetite), ferrous oxide (wustite), and ferric oxide (hematite).

  As a material forming the magnetic layer 20, a mixture of the above metal oxide fine particles and a polymer compound is assumed as an example. The magnetic material layer 20 can be formed by applying a mixture obtained by mixing the fine particles of the above metal oxide and a polymer compound. The mixture of fine particles of the above metal oxide and the polymer compound can be made into an ink, for example. The magnetic layer 20 is completed by applying the ink-like mixture on the conductive layer 30. When the metal oxide is made into fine particles, the primary particle diameter of the metal oxide is preferably about 1 (μm) or less.

  When the material forming the magnetic layer 20 is a mixture of the above-mentioned metal oxide fine particles and a polymer compound, spin current propagation and spin coherence length control become possible, and power generation characteristics are improved. it can.

  Generally, the magnetic layer is formed on the substrate by sintering. However, if the magnetic layer 20 is formed by applying a mixture of the above-mentioned metal oxide fine particles and a polymer compound as described above, the sintering step can be eliminated, so that the manufacturing cost can be reduced. Can be reduced.

  Further, as the above-mentioned polymer compound, vinyl chloride resin, acrylic resin, thermoplastic resin, phenol resin, etc. are assumed as an example. From the viewpoint of handling, polystyrene or polyethylene is preferable as the polymer compound.

As the above-mentioned polymer compound, a polymer compound having a weight average molecular weight of 15,000 or more and 500,000 or less is assumed as an example. This makes it possible to produce the ink-like mixture having various viscosities depending on the scene. Further, it is preferable that the polymer compound contains a polymer of aromatic hydrocarbon. This is because polymerization (increasing the molecular weight) can be facilitated, and thermal strength and mechanical strength due to the polymerization component can be easily changed. The water absorption of the polymer compound in the polymer compound is preferably 0.25 or less. This is because it is preferable that the water absorption rate is low in order to prevent separation from the substrate due to water absorption in the atmosphere. The linear expansion coefficient of the polymer compound in the polymer compound is preferably about 3 (10 ⁻⁵ / K) to 12 (10 ⁻⁵ / K). This is to prevent peeling due to the difference in expansion coefficient from the base material.

<1-2. Configuration of Conductive Layer 30>
The conductive layer 30 is made of a material exhibiting an inverse spin Hall effect. Therefore, when the spin current generated in the magnetic layer 20 due to the spin-Beseck effect flows into the conductive layer 30, an electromotive force is generated in the conductive layer 30 in the direction orthogonal to the spin current due to the inverse spin Hall effect. As a result, a current flows through the conductive layer 30, as shown in FIG.

  Examples of the material forming the conductive layer 30 include platinum (Pt), copper (Au), palladium (Pd), silver (Ag), aluminum (Al), tungsten (W), titanium (Ti), molybdenum (Mo). An example is one containing at least one of the following: titanium, tantalum (Ta), iridium (Ir), ruthenium (Ru), zinc (Zn), tin (Sn), nickel (Ni), carbon (C), and indium (In). However, the present invention is not limited to this, and other known conductive materials may be used.

  The conductive layer 30 may be, for example, a metal foil such as a titanium foil or a tungsten foil, a glass substrate with ITO (indium-doped tin oxide film), a glass substrate with FTO (fluorine-doped tin oxide film), or glass. A substrate or a plastic (for example, PET, PEN) substrate coated with a conducting polymer (for example, PEDOT-PSS, polyaniline) is assumed as an example, but the present invention is not limited to this and other embodiments are also possible. Good.

<2. Experiment on power generation characteristics of thermoelectric conversion element of the present invention>
<2-1. Thermoelectric conversion element used for experiment>
The applicant of the present application prepared a thermoelectric conversion element shown in the following Example 1 and a thermoelectric conversion element shown in Comparative Example 1 for comparison in conducting an experiment relating to the power generation characteristics of the thermoelectric conversion element of the present invention. These thermoelectric conversion elements are thermoelectric conversion elements 200 in which the base portion 10, the conductive layer 30, and the magnetic layer 20 of the aspect shown in FIG. 2 are laminated in this order.

<2-1-1. Thermoelectric conversion element of Example 1>
In the thermoelectric conversion element of Example 1, a glass substrate with a transparent conductive film ITO was used as the base 10 (glass substrate) and the conductive layer 30 (transparent conductive film ITO). Then, the magnetic layer-forming ink was applied onto the glass substrate with the transparent conductive film ITO using a spin coater to form the magnetic layer 20. This magnetic layer-forming ink comprises 10% by weight of an iron oxide mixture of 60% by weight of ferrous oxide (wustite), 5% by weight of ferric oxide (hematite), 35% by weight of ferric trioxide (magnetite) in toluene. After stirring, pulverizing, and dispersing using a bead mill to make fine particles, 10% by weight of polystyrene was dissolved in the finely divided iron oxide mixture. The volume median diameter (D50) of the iron oxide mixture in this ink was 0.16 (μm). MT3000 manufactured by Microtrac Bell was used for measuring the volume median diameter. In the present specification, the volume median diameter refers to a particle diameter at which the volume-based cumulative distribution is 50%. The film forming rate of the magnetic layer in the spin coater was 4000 (rpm). Further, a part of the magnetic layer 20 is peeled off with a spatula or the like, and an electrode D1 is formed on the exposed transparent conductive film using an ultrasonic soldering device (Sunbonder USM-580 manufactured by Kuroda Techno Co., Ltd.). , D2 were provided to prepare the thermoelectric conversion element of Example 1. Moreover, the thermoelectric conversion element of Example 1 was not sealed. The thermoelectric conversion element of Example 1 is in the form of a thin plate as shown in FIG. 3, and its size is 20 (mm) × 20 (mm).

<2-1-2. Thermoelectric conversion element of Comparative Example 1>
The thermoelectric conversion element of Comparative Example 1 is a thermoelectric conversion element formed in the same configuration as that of Example 1, and a magnetic material layer forming ink is applied onto a glass substrate with a transparent conductive film ITO by using a spin coater to make it magnetic. A body layer was formed. This magnetic layer-forming ink is prepared by stirring 10% by weight of triiron tetraoxide (magnetite) in toluene using a bead mill, pulverizing and dispersing it into fine particles, and then forming the fine particles into triiron tetraoxide (magnetite). It was prepared by dissolving 10% by weight of polystyrene. The volume median diameter (D50) of triiron tetroxide (magnetite) in this ink was 0.19 (μm). MT3000 manufactured by Microtrac Bell was used for measuring the volume median diameter. The film forming rate of the magnetic layer in the spin coater was 4000 (rpm). Further, a part of the magnetic layer was peeled off with a spatula or the like, and an electrode D1 was formed on the exposed transparent conductive film using an ultrasonic soldering device (Sunbonder USM-580 manufactured by Kuroda Techno Co., Ltd.). The thermoelectric conversion element of Comparative Example 1 was prepared by providing D2. The thermoelectric conversion element of Comparative Example 1 is in the form of a thin plate as shown in FIG. 2, and its size is 20 (mm) × 20 (mm). As described above, Comparative Example 1 has the same structure as that of Example 1, but differs mainly in the material forming the magnetic layer.

<2-2. Outline of experiment>
In Example 1 and Comparative Example 1, three thermoelectric conversion elements each having a different magnetic layer thickness were prepared. Then, a temperature difference was applied in the direction perpendicular to the thin plate surface of each of the thermoelectric conversion elements (direction of arrow A in FIG. 2), and the electromotive force generated at that time was measured using a multimeter (Model: 2700 manufactured by KEITHLEY). A ceramic hot plate CHP-170DN manufactured by ASONE was used as a high temperature source that applies a temperature in the vertical direction of the thermoelectric conversion element. Moreover, the thermometer CT-05SD made from COSTOM and CPA-0130A made from FLIR were used for the temperature measurement.

  Table 1 shows the results of measuring the power generation characteristics with the above contents. The Seebeck coefficient in Table 1 indicates the index of the power generation characteristics of the thermoelectric conversion element when a temperature difference is given, and the larger this value, the better the thermoelectric conversion element.

  As shown in Table 1, as the film thickness of the magnetic layer of the thermoelectric conversion element of Example 1 and the thermoelectric conversion element of Comparative Example 1 increased, the Seebeck coefficient also increased. Therefore, in the thermoelectric conversion element, the larger the film thickness of the magnetic layer, the better the power generation characteristics. Then, the power generation characteristics of the thermoelectric conversion element of Example 1 and the thermoelectric conversion element of Comparative Example 1 are compared.

  When the film thickness of the magnetic layer of the thermoelectric conversion element of Comparative Example 1 was 2.9 (μm), the Seebeck coefficient of the thermoelectric conversion element of Comparative Example 1 was 6 (μV / K). On the other hand, when the film thickness of the magnetic layer of the thermoelectric conversion element of Example 1 was 2.7 (μm), the Seebeck coefficient of the thermoelectric conversion element of Example 1 was 6.5 (μV / K). . When the Seebeck coefficients of the thermoelectric conversion element of Example 1 and the thermoelectric conversion element of Comparative Example 1 are compared, the thermoelectric conversion element of Example 1 has a smaller magnetic layer thickness than the thermoelectric conversion element of Comparative Example 1. However, the Seebeck coefficient of the thermoelectric conversion element of Example 1 is larger than that of the thermoelectric conversion element of Comparative Example 1.

  When the film thickness of the magnetic layer of the thermoelectric conversion element of Comparative Example 1 was 3.3 (μm), the Seebeck coefficient of the thermoelectric conversion element of Comparative Example 1 was 8.5 (μV / K). On the other hand, when the film thickness of the magnetic layer of the thermoelectric conversion element of Example 1 was 3 (μm), the Seebeck coefficient of the thermoelectric conversion element of Example 1 was 13.3 (μV / K). Furthermore, when the film thickness of the magnetic layer of the thermoelectric conversion element of Comparative Example 1 was 4.7 (μm), the Seebeck coefficient of the thermoelectric conversion element of Comparative Example 1 was 12.9 (μV / K). On the other hand, when the film thickness of the magnetic layer of the thermoelectric conversion element of Example 1 was 4.1 (μm), the Seebeck coefficient of the thermoelectric conversion element of Example 1 was 15.5 (μV / K). .

  Comparing the thermoelectric conversion element of Example 1 and the thermoelectric conversion element of Comparative Example 1, as the film thickness of the magnetic layer of the thermoelectric conversion element increases, the difference in the Seebeck coefficient becomes more remarkable. Therefore, the thermoelectric conversion element of the present invention has excellent power generation characteristics.

<3. Experiments on temporal changes in power generation characteristics of thermoelectric conversion element of the present invention>
The applicant of the present application created a thermoelectric conversion element shown in the following Example 2 and a thermoelectric conversion element shown in Comparative Example 2 for comparison in conducting an experiment relating to changes over time in the power generation characteristics of the thermoelectric conversion element of the present invention. These thermoelectric conversion elements are also the thermoelectric conversion elements 200 in which the base 10, the conductive layer 30, and the magnetic layer 20 of the aspect shown in FIG.

<3-1. Thermoelectric conversion element used for experiment>
<3-1-1. Thermoelectric conversion element of Example 2>
The thermoelectric conversion element of Example 2 was created with the same contents as the thermoelectric conversion element of Example 1. The thermoelectric conversion element of Example 2 is in a thin plate form as shown in FIG. 2, and has a thin plate size of 35 (mm) × 35 (mm), which is different from the thermoelectric conversion element of Example 1.

<3-1-2. Thermoelectric conversion element of Comparative Example 2>
The thermoelectric conversion element of Comparative Example 2 was created with the same contents as the thermoelectric conversion element of Comparative Example 1. The thermoelectric conversion element of Comparative Example 2 has a thin plate form as shown in FIG. 2, and has a thin plate size of 35 (mm) × 35 (mm), which is different from the thermoelectric conversion element of Comparative Example 1.

<3-2. Outline of experiment>
A thermoelectric conversion element of Example 2 and a thermoelectric conversion element of Comparative Example 2 were subjected to a temperature difference in the vertical direction (direction of arrow A in FIG. 2) of the thin plate surface, and the electromotive force generated at that time was measured by a multimeter (Model manufactured by KEITHLEY). : 2700).

  The film formation rate of the magnetic layer of the thermoelectric conversion element of Example 2 and the thermoelectric conversion element of Comparative Example 2 was 4000 rpm. In addition, the thermoelectric conversion element of Example 2 and the thermoelectric conversion element of Comparative Example 2 were not sealed, and a short-term change in characteristics for 3 days after production was observed. The first measurement was performed 24 hours after the production, and the measurement was performed in the air atmosphere and the room temperature at rest except the measurement. The temperature difference during measurement was set to 4 [K]. COSTOM thermometer CT-05SD and FLIR CPA-0130A were used for temperature measurement.

  As a result of measuring the change with time of the characteristics of the thermoelectric conversion element of Comparative Example 2, a characteristic retention rate of 52% was shown with respect to the initial characteristics 72 hours after the production. On the other hand, as a result of measuring the change over time in the characteristics of the thermoelectric conversion element of Example 2, the characteristic retention rate 72 hours after the production was 69% of the initial characteristics. Comparing these results, it is apparent that the change over time in the characteristics of the thermoelectric conversion element of Example 2 is superior.

  The following reasons are considered that the thermoelectric conversion elements of Examples 1 and 2 exhibit better characteristics than the thermoelectric conversion elements of Comparative Examples 1 and 2. It is considered that the state of the spin current in the propagation path of the spin current differs depending on the particle size of the material and the morphology of the substance (material) in the magnetic layer such as the dispersion state. That is, it is considered that the proportion of the spin current that effectively contributes to the current generation varies depending on the particle size of the material and the morphology of the substance (material) in the magnetic layer such as the dispersed state. From this point of view, it can be inferred that the ratio of the spin current that effectively contributes to the current generation is higher in the thermoelectric conversion elements of Examples 1 and 2 than in the thermoelectric conversion elements of Comparative Examples 1 and 2. Therefore, from the viewpoint of generating a spin current that effectively contributes to the generation of electric current, a plurality of metals such as a rolling scale is more preferable than a magnetic layer containing only triiron tetraoxide (magnetite) as a metal oxide. A magnetic layer containing a mixture in which oxides are mixed is preferable.

  As described above, like the thermoelectric conversion element of the present invention, the magnetic layer has a plurality of metal oxides, particularly a plurality of iron oxide-based powders (for example, ferrous oxide and / or ferric oxide, In addition, when composed of triiron tetroxide), the power generation characteristics are improved as compared with the case where the magnetic layer is composed of a single metal oxide. When a plurality of iron oxide-based powders are formed on a rolling scale, the manufacturing cost can be reduced.

  The thermoelectric conversion element of the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

10 Base Material 20 Magnetic Layer 30 Conductive Layer 41, 42 Electrode 100 Thermoelectric Conversion Element

Claims (6)

A magnetic layer that produces a spin current in the direction in which a temperature gradient occurs,
A conductive layer formed on the magnetic layer, which converts the spin current generated in the magnetic layer into an electric current;
Equipped with
The magnetic layer is composed of at least a plurality of metal oxides ,
The plurality of metal oxides are characterized by being composed of ferrous oxide, ferric oxide, and ferric tetroxide.
Thermoelectric conversion element. The plurality of metal oxides, characterized in that the powder of ferrous oxide, the powder of ferric oxide, and the powder of triiron tetroxide is included .
The thermoelectric conversion element according to claim 1. Wherein the ferrous oxide, the ferric oxide, and the triiron tetroxide are obtained from a rolling scale,
The thermoelectric conversion element according to claim 1. The magnetic layer, a powder of the ferrous oxide, the powder of ferric oxide, the triiron tetraoxide powder, and is constituted by a mixture obtained by mixing a polymer compound,
The mixture is characterized in that the magnetic layer can be formed by coating.
The thermoelectric conversion element according to any one of claims 1 to 3 . The polymer compound has a weight average molecular weight of 15,000 or more and 500,000 or less,
The thermoelectric conversion element according to claim 4 . The polymer compound is characterized in that it contains a polymer of aromatic hydrocarbons,
The thermoelectric conversion element according to any one of claims 4 and 5.

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