Atomic battery

Abstract

To provide an atomic battery which is thinner and lighter.SOLUTION: The atomic battery has a thermoelectric element including: a thermoelectric conversion unit showing a non-reciprocal conduction based on breakage of a space inversion symmetry; and a pair of electrodes provided separately from each other in the thermoelectric conversion unit, the electrodes being for drawing a non-reciprocal thermoelectric signal. At least one component member of the atomic battery includes a radioactive isotopic element.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a nuclear battery that can extract electrical energy from decay heat by containing radioactive isotope elements.

Background Art

[0002] The fuel for nuclear power generation contains radioactive isotopes even after use and constantly releases nuclear decay heat, making its long-term management an extremely important issue. If there is a way to effectively convert this thermal energy into electricity, it can be regarded as an extremely stable power source that operates for a long time. In fact, deep space probes that cannot use solar power generation are equipped with isotope batteries that combine radioactive isotopes and thermoelectric elements, which support long-term missions over several decades and are still transmitting images of deep space back to Earth.

[0003] As a conventional technology, a radioisotope thermoelectric generator (RTG) is used. It can extract power from radioactive decay. Using thermocouples, it converts the decay heat of radioactive substances into electricity by the Seebeck effect. For example, Patent Document 1 discloses a nuclear battery with little degradation due to radiation and capable of miniaturization.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The nuclear battery disclosed in Patent Document 1 requires cooling to utilize the temperature gradient, making the device large-scale. Therefore, further weight reduction and thin film formation have been demanded. The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a nuclear battery capable of achieving light weight and thin film formation.

Means for Solving the Problems

[0006] As a result of intensive studies, the inventors have found that a thermoelectric conversion element including a thermoelectric conversion unit exhibiting non-reciprocal conduction based on the breaking of space inversion symmetry, and a pair of electrodes provided separately from each other on the thermoelectric conversion unit for extracting non-reciprocal thermoelectric signals, can provide a thermoelectric conversion element capable of thermoelectric conversion from temperature fluctuations on a microscale. And in a nuclear battery including the thermoelectric conversion element, it was conceived that a nuclear battery capable of being lightweight and thin-film formed by including at least one component member constituting the nuclear battery with a radioactive isotope.

[0007] That is, one aspect of the present disclosure is a thermoelectric conversion unit exhibiting non-reciprocal conduction based on the breaking of space inversion symmetry, a pair of electrodes provided separately from each other on the thermoelectric conversion unit for extracting non-reciprocal thermoelectric signals, A nuclear battery containing a thermoelectric conversion element including: At least one component member constituting the nuclear battery contains a radioactive isotope element, related to a nuclear battery.

[0008] In the present disclosure, the thermoelectric conversion unit is a thermoelectric conversion layer including a ferromagnetic metal layer and a paramagnetic metal layer laminated on each other, and the pair of electrodes are arranged in the in-plane direction of the thermoelectric conversion layer on the thermoelectric conversion layer A form in which they are provided separately from each other is preferable. Thereby, since the voltage of thermoelectric conversion based on the breaking of the space inversion symmetry of the thermoelectric conversion layer increases, the power generation efficiency of the nuclear battery becomes particularly high.

[0009] In the present disclosure, a form in which the separation distance between the pair of electrodes is 0.1 μm or more and 1000 μm or less is preferable. By setting such a range, the voltage of thermoelectric conversion increases, so that the power generation efficiency of the nuclear battery increases.

[0010] In the present disclosure, the paramagnetic metal layer is composed of a single layer or a plurality of laminated layers, and each of the single layer or the plurality of laminated layers of the paramagnetic metal layer is preferably formed of Pt, Pd, W, AuW alloy, Ta, CuIr alloy, CuBi alloy, BiSb alloy, or BiSe alloy. Thereby, since the non-reciprocity of conduction based on the breaking of the spatial inversion symmetry of the thermoelectric conversion layer is particularly increased, the power generation efficiency of the nuclear battery becomes particularly high.

[0011] In the present disclosure, the ferromagnetic metal layer is composed of a single layer or a plurality of laminated layers, and each of the single layer or the plurality of laminated layers of the ferromagnetic metal layer is preferably composed of a Ni-Fe alloy, Fe, Co, Ni, Gd, CoFeB alloy, or (Ga,Fe)Sb alloy. These are materials that exhibit ferromagnetism at room temperature, and since non-reciprocity of conduction at room temperature is realized, the power generation efficiency of the nuclear battery is increased.

[0012] In the present disclosure, the radioactive isotope element preferably contains at least one element selected from the group consisting of beryllium-10, carbon-14, aluminum-26, silicon-32, chlorine-36, argon-39, potassium-40, nickel-63, selenium-79, rubidium-87, zirconium-93, indium-115, cesium-137, lanthanum-138, niobium-94, technetium-98, lutetium-71, neodymium-144, samarium-146, samarium-147, gadolinium-152, platinum-190, bismuth-210, polonium-209, thorium-232, uranium-232, uranium-233, uranium-234, uranium-235, uranium-236, uranium-238, plutonium-236, plutonium-238, plutonium-239, plutonium-244, americium-241, americium-243, curium-244, curium-246, curium-247, curium-248, californium-249, and californium-251. By using these radioactive isotope elements, the power generation efficiency of the nuclear battery becomes particularly high.

[0013] Another form of the present disclosure is a nuclear battery module including a plurality of the above nuclear batteries, wherein the plurality of nuclear batteries are electrically connected to each other such that non-reciprocal thermoelectric signals from each nuclear battery can be superimposed with the same polarity. Thereby, it becomes possible to extract a large non-reciprocal thermoelectric signal, and the power generation efficiency of the nuclear battery is increased.

Advantages of the Invention

[0014] According to the present disclosure, a lightweight and thin-film nuclear battery can be provided. According to the thermoelectric conversion element provided in the nuclear battery in the present disclosure, the thermoelectric signal generated in the thermoelectric conversion unit by the inflowing heat current becomes non-reciprocal with respect to the direction of the heat current due to the non-reciprocal conduction of the thermoelectric conversion unit, and such a non-reciprocal thermoelectric signal can be electrically extracted by a pair of electrodes.

[0015] More specifically, when a heat current flows into a laminate of a ferromagnetic metal layer and a paramagnetic metal layer magnetized by applying a magnetic field of 1T or less, a spin current is driven in the paramagnetic metal layer, and a spin accumulation is formed at the interface between the paramagnetic metal layer and the ferromagnetic metal layer. The polarity of this spin accumulation becomes parallel or anti-parallel to the magnetization direction of the ferromagnetic metal layer depending on the direction of the heat current. The relative direction between the polarity of this spin accumulation and the direction of magnetization changes the electron scattering, thereby causing heat current direction dependence, i.e., non-reciprocity, in the thermoelectric signal generated in the thermoelectric conversion layer. This is the non-reciprocal thermoelectric signal, and such a non-reciprocal thermoelectric signal can be electrically extracted by a pair of electrodes. Therefore, even from a heat current whose direction and magnitude change randomly, it is possible to generate a thermoelectric signal in a constant direction within the paramagnetic metal layer, so that thermoelectric conversion can be performed from temperature fluctuations on a microscale. By using such a thermoelectric conversion element, a lightweight and thin-film nuclear battery can be provided.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0017] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In each drawing, the same reference numerals are used for the same elements whenever possible. Also, the dimensional ratios within and between the components in the drawings are arbitrary for the sake of clarity of the drawings.

[0018] One form of the present disclosure is an atomic force battery containing a thermoelectric conversion element including a thermoelectric conversion unit showing non-reciprocal conduction based on the breaking of space inversion symmetry, and a pair of electrodes provided spaced apart from each other in the thermoelectric conversion unit for extracting non-reciprocal thermoelectric signals.

[0019] <Thermoelectric conversion unit> The thermoelectric conversion unit is a thermoelectric conversion element showing non-reciprocal conduction based on the breaking of space inversion symmetry. The material constituting the thermoelectric conversion unit is not particularly limited as long as it is a material showing non-reciprocal conduction based on the breaking of space inversion symmetry, but typically includes a laminate of a ferromagnetic metal layer and a paramagnetic metal layer laminated on each other. While the laminate has a paramagnetic metal layer provided on one surface of the ferromagnetic metal layer, no similar paramagnetic metal layer is provided on the other surface of the ferromagnetic metal layer. Also, while a ferromagnetic metal layer is provided on one surface of the paramagnetic metal layer, no similar ferromagnetic metal layer is provided on the other surface of the paramagnetic metal layer. Therefore, the laminate of the ferromagnetic metal layer and the paramagnetic metal layer laminated on each other has a structure in which space inversion symmetry is broken along the lamination direction. The laminate has substantially space inversion symmetry in the plane direction. And due to the break of space inversion symmetry along this lamination direction, the laminate exhibits non-reciprocity with respect to the electrical conductivity in the plane direction.

[0020] The ferromagnetic metal layer is composed of a metal that exhibits ferromagnetism at the temperature in the usage environment of the nuclear battery. It is preferably composed of a metal that exhibits ferromagnetism at room temperature (about 300K), and from this perspective, it is preferably composed of an alloy containing Fe, Co, Ni, Gd, or at least one of them, and particularly preferably composed of a Ni-Fe alloy, Co, or CoFeB. The thickness of the ferromagnetic metal layer is not particularly limited, but can be, for example, 1 nm or more and 100 nm or less.

[0021] The paramagnetic metal layer is composed of a metal that exhibits paramagnetism at the temperature in the usage environment of the nuclear battery and is preferably composed of a metal that exhibits paramagnetism at room temperature (300K). The paramagnetic metal layer is preferably composed of a paramagnetic metal with a high spin-orbit interaction in order to enhance the spin Nernst effect in the paramagnetic metal layer described later. From this perspective, it is preferably composed of Pt, Pd, W, AuW alloy, Ta, CuIr alloy, CuBi alloy, BiSb alloy, or BiSe alloy, and particularly preferably composed of Pt. The thickness of the paramagnetic metal layer is not particularly limited, but can be, for example, 1 nm or more and 100 nm or less.

[0022] <Electrode> The electrodes are provided in the thermoelectric conversion part while being spaced apart from each other, and extract a non-inverted thermoelectric signal from the thermoelectric conversion part. As long as the non-inverted thermoelectric signal can be extracted from the thermoelectric conversion part, the arrangement thereof is not particularly limited, and typically, they are arranged spaced apart on the surface of the thermoelectric conversion part. When a pair of electrodes are arranged spaced apart on the surface of the thermoelectric conversion part, the spacing distance in the plane direction of the thermoelectric conversion part is preferably 0.1 μm or more and 1000 μm or less. Also, the thickness of the electrodes is not particularly limited, but for example, it can be 10 nm or more and 1 μm or less.

[0023] The electrodes are made of a material having a conductivity capable of extracting a non-inverted thermoelectric signal from the thermoelectric conversion layer. Examples of such materials include metal materials such as Cu, Ag, Au, Pt, Ni, Al, constantan, Cr, In, Pd, Fe, Cu alloys, Ti / Au laminates, and Cr / Au laminates, and conductive oxides such as indium tin oxide (ITO) and zinc oxide (ZnO). Cu, Ag, Au, Pt, Ni, Al, constantan, and Cu copper alloys are preferable, and Cu, Au, Ag, Pt, Ni, Ti / Au laminates, and Cr / Au laminates are particularly preferable.

[0024] <Substrate> The nuclear battery may have a substrate that supports the thermoelectric conversion part. The shape of the substrate is not particularly limited, and it may be plate-shaped or film-shaped. Also, the material of the substrate is not particularly limited, and examples thereof include metals such as Au, Ag, Cu, and Al, silicon, sapphire, SiC, GaN, yttria-stabilized zirconia (YSZ), and resins such as polyimide, polyethylene terephthalate (PET), and polyethylene naphthalate (PEN).

[0025] <Method for manufacturing the thermoelectric conversion part> The thermoelectric conversion unit prepares, for example, a substrate, and deposits, in this order, a material for forming a ferromagnetic metal layer and a material for forming a paramagnetic metal layer on the substrate surface by a physical vapor deposition method such as DC magnetron sputtering to form a laminate. The laminate is patterned by photolithography and lift-off methods so as to be rectangular in plan view to form the thermoelectric conversion unit. Thereafter, a metal material for forming a pair of electrodes is deposited on the region including the surface of the paramagnetic metal layer by a physical vapor deposition method such as DC magnetron sputtering to form a metal layer, and the metal layer is patterned into a predetermined shape by photolithography and lift-off methods to form a pair of electrodes. Note that the ferromagnetic metal layer and the paramagnetic metal layer formed on the substrate may be deposited in the reverse order. Further, after forming a metal layer serving as an electrode on the substrate first, the ferromagnetic metal layer and the paramagnetic metal layer may be deposited. Note that the thermoelectric conversion unit may include a layer made of an insulating magnetic material provided so as to be in contact with the ferromagnetic metal layer.

[0026] <Radioisotope> In the nuclear battery of the present disclosure, at least one component constituting the nuclear battery contains a radioisotope. The radioisotope may be any one having the ability to emit radiation. For example, beryllium-10, carbon-14, aluminum-26, silicon-32, chlorine-36, al Gon-39, Potassium-40, Nickel-63, Selenium-79, Rubidium-87, Zirconium-93, Indium-115, Cesium-137, Lanthanum-138, Niobium-94, Technetium-98, Lutetium-71, Neodymium-144, Samarium-146, Samarium-147, Gadolinium-152, Platinum-190, Bismuth-210, Polonium-209, Thorium-232, Uranium-232, Uranium-233, Uranium-234, Uranium-235, Uranium-236, Uranium-238, Plutonium-236, Plutonium-238, Plutonium-239, Plutonium-244, Americium-241, Americium-243, Curium-244, Curium-246, Curium-247, Curium-248, Californium-249, Californium-251, etc. can be mentioned. Among these, Plutonium-238 and Curium-244 are preferred.

[0027] The radioisotope is included in at least one component constituting the nuclear battery. Specific examples thereof will be described with reference to FIGS. 1 and 2. FIG. 1 shows a schematic cross-sectional view of a nuclear battery in which the components constituting the nuclear battery are a thermoelectric conversion unit composed of a paramagnetic metal layer and a ferromagnetic metal layer, and a pair of electrodes. In FIG. 1, the radioisotope 16 is included in all the components constituting the nuclear battery 10, that is, the paramagnetic metal layer 11, the ferromagnetic metal layer 12, and the pair of electrodes 14. The method for including the radioisotope in the component is not particularly limited, and known methods can be appropriately used. For example, a method of implanting the radioisotope into the component by an accelerator or the like can be mentioned.

[0028] Regarding the arrangement of the radioisotope in the nuclear battery having the components shown in FIG. 1, other · The radioisotope is arranged only on the electrodes · The radioisotope is arranged only on the paramagnetic metal layer · The radioisotope is arranged only on the ferromagnetic metal layer · The radioisotope is arranged on the electrodes and the paramagnetic metal layer · The radioisotope is arranged on the electrodes and the ferromagnetic metal layer · Radioactive isotopes are arranged in the paramagnetic metal layer and the ferromagnetic metal layer There is an example of this.

[0029] Figure 2 shows a schematic cross-sectional view of a nuclear battery in which the components constituting the nuclear battery are a thermoelectric conversion section composed of a paramagnetic metal layer and a ferromagnetic metal layer, a pair of electrodes, and a substrate. In Figure 2, radioactive isotopes 26 are included in all the components constituting the nuclear battery 20, that is, the paramagnetic metal layer 21, the ferromagnetic metal layer 22, the pair of electrodes 24, and the substrate 25. As for the arrangement of radioactive isotopes in the nuclear battery having the components shown in Figure 2, other · Radioactive isotopes are arranged only in the electrodes · Radioactive isotopes are arranged only in the paramagnetic metal layer · Radioactive isotopes are arranged only in the ferromagnetic metal layer · Radioactive isotopes are arranged only in the substrate · Radioactive isotopes are arranged in the electrodes and the paramagnetic metal layer · Radioactive isotopes are arranged in the electrodes and the ferromagnetic metal layer · Radioactive isotopes are arranged in the electrodes and the substrate · Radioactive isotopes are arranged in the paramagnetic metal layer and the ferromagnetic metal layer · Radioactive isotopes are arranged in the paramagnetic metal layer and the substrate · Radioactive isotopes are arranged in the ferromagnetic metal layer and the substrate · Radioactive isotopes are arranged in the electrodes, the paramagnetic metal layer, and the ferromagnetic metal layer · Radioactive isotopes are arranged in the electrodes, the paramagnetic metal layer, and the substrate · Radioactive isotopes are arranged in the electrodes, the ferromagnetic metal layer, and the substrate · Radioactive isotopes are arranged in the paramagnetic metal layer, the ferromagnetic metal layer, and the substrate There is an example of this.

[0030] As described above, any of the constituent members constituting the nuclear battery may contain a radioisotope element. This is because the thermoelectric conversion unit included in the nuclear battery according to the present disclosure does not generate electricity by the spin Seebeck effect as disclosed in Patent Document 1, but generates electricity by the spin Nernst effect as described later, and it is not necessary to form a temperature gradient in the stacking direction with respect to the thermoelectric conversion element. Therefore, it is not necessary to arrange the radioisotope element only on one side in the stacking direction of the thermoelectric conversion unit. Specifically, it is not necessary to form a structure in which the thermoelectric conversion unit, the substrate, and the radioactive isotope layer are stacked in this order, nor is it necessary to form a structure in which the radioactive isotope layer, the thermoelectric conversion unit, and the substrate are stacked in this order. Further, it is not necessary to arrange the radioisotope so as to generate a temperature gradient for causing the spin Seebeck effect in the thermoelectric conversion unit. Further, in the nuclear battery, a plurality of radioisotope elements may be randomly arranged in the constituent members and / or across a plurality of members. That is, it is not necessary to arrange the radioisotope element in the form of a radioactive isotope layer.

[0031] Next, the thermoelectric conversion method according to the present embodiment will be described. FIG. 5 is a process diagram showing the steps of the thermoelectric conversion method according to the present embodiment. As shown in FIG. 5, the steps of the thermoelectric conversion method according to the present embodiment include a step S11 of preparing a thermoelectric conversion element, a step S12 of inputting a heat flow, and a step S13 of performing thermoelectric conversion while applying an external magnetic field. These steps will be described with reference to FIGS. 3 and 4.

[0032] In step S11 of preparing the thermoelectric conversion element, a thermoelectric conversion element 200 as shown in FIGS. 3 and 4 is prepared. Subsequently, in step S12 of inputting a heat flow, an external heat flow H, which is the object of thermoelectric conversion, is input to the thermoelectric conversion layer 202 so as to flow along the X-axis direction, which is one of the in-plane (in the XY plane) directions of the thermoelectric conversion layer 202.

[0033] Next, in step S13 of performing thermoelectric conversion while applying an external magnetic field, an external magnetic field B generated from a magnetic field generation unit provided outside the thermoelectric conversion element 200 is applied to the ferromagnetic metal layer 203. The application direction of the external magnetic field B at this time is in the in-plane (within the XY plane) direction of the thermoelectric conversion element 200, and is the negative Y-axis direction, which is one of the directions orthogonal to the flow direction of the heat current H. Thereby, the ferromagnetic metal layer 203 is magnetized in the direction of the external magnetic field B and has magnetization 203M facing the direction of the external magnetic field B. Such application of the external magnetic field B is maintained while performing thermoelectric conversion of the heat current H. The magnitude of the external magnetic field B can be, for example, 1 T or less.

[0034] In step S13, when the heat current H flows into the paramagnetic metal layer 205, a spin current J S is generated along the Z-axis direction and flows into the ferromagnetic metal layer 203. The polarity of the spin current J S changes in the positive Y-axis direction or the negative Y-axis direction according to the direction of the heat current H. Therefore, when the direction of the heat current H is reversed, the polarity of the spin current J S is reversed, and the relative orientation relationship between the polarity of the spin current J S and the direction of the magnetization 203M of the ferromagnetic metal layer 203 is reversed. Further, by reversing the direction of the magnetization 203M of the ferromagnetic metal layer 203, the relative orientation relationship between the polarity of the spin current J S and the direction of the magnetization 203M can also be reversed.

[0035] When the spin current J S flows into the ferromagnetic metal layer 203, electron scattering changes according to the relative orientation between the polarity direction of the spin current and the direction of the magnetization 203M of the ferromagnetic metal layer 203. Since the polarity direction of the spin current near the junction interface between the ferromagnetic metal layer 203 and the paramagnetic metal layer 205 changes according to the direction of the heat current H, this electron scattering changes according to the direction of the heat current H. Thereby, direction dependence, that is, non-reciprocity, of the heat current H occurs in the thermoelectric signal generated in the thermoelectric conversion layer 202.

[0036] In this way, the thermoelectric signal J generated in the thermoelectric conversion layer 202 Nis non-converse with respect to the direction of the heat flux H due to the non-reciprocal conduction of the thermoelectric conversion layer 202 as described above (i.e., the thermoelectric signal J N varies non-linearly with respect to the direction of the heat flux H), and regardless of whether the direction of the heat flux H is the positive X-axis direction or the negative X-axis direction, the direction of the thermoelectric signal J N is the positive X-axis direction, and the inventors of the present application have found that such a non-reciprocal thermoelectric signal J N can be electrically extracted via a pair of electrodes 207a and 207b. Therefore, according to the thermoelectric conversion element 200 according to the present embodiment, even if the direction and magnitude of the heat flux H change randomly, a non-reciprocal thermoelectric signal J N in a constant direction can be generated within the thermoelectric conversion layer 202, so that thermoelectric conversion can be performed from temperature fluctuations at the microscale.

[0037] Also, by reversing the direction of the external magnetic field B in the positive Y-axis direction and reversing the direction of the magnetization 203M of the ferromagnetic metal layer 203 in the positive Y-axis direction, the direction of the non-reciprocal thermoelectric signal J N can be reversed in the negative X-axis direction.

[0038] In the thermoelectric conversion layer 202, when the magnitude of the voltage of the non-reciprocal thermoelectric signal J N extracted by a pair of electrodes 207a and 207b is V, the electric field generated in the thermoelectric conversion layer 202 corresponding to V is E, the non-linear Seebeck coefficient of the thermoelectric conversion layer 202 is S, the distance between a pair of electrodes 207a and 207b is L (D207 in FIG. 4), the temperature gradient in the range of the distance L of the thermoelectric conversion layer 202 is ∇T, and the temperature difference in the range of the distance L of the thermoelectric conversion layer 202 is ΔT, the relationship of the electric field E = non-linear Seebeck coefficient S × (temperature gradient ∇T) 2 holds. By multiplying both sides of this equation by the distance L, the voltage V = non-linear Seebeck coefficient S × (temperature difference ΔT) 2 / L is obtained. Therefore, the smaller the distance L between a pair of electrodes 207a and 207b, the larger the voltage V. Therefore, by preferably setting the separation distance D207 along the X-axis direction between a pair of electrodes 207a and 207b to a small value of 1000 μm or less as described above, the non-reciprocal thermoelectric signal J Nbecomes larger.

[0039] Further, the thermoelectric conversion element 200 may include a heat conduction portion provided in contact with or close to the end face on the positive X-axis side and / or the end face on the negative X-axis side to facilitate the inflow of the heat flux H into the thermoelectric conversion layer 202. Such a heat conduction portion can be composed of, for example, aluminum, copper, carbon fiber, sapphire, alumina, silicon with a thermal oxide film, or a polymer.

[0040] FIG. 6 is a perspective view showing the configuration of a thermoelectric conversion module using the thermoelectric conversion element as described above. As shown in FIG. 6, the thermoelectric conversion module 300 according to the present embodiment includes a plurality of thermoelectric conversion elements 200, and in this embodiment, has four thermoelectric conversion elements 200a, 200b, 200c, and 200d. The four thermoelectric conversion elements 200a, 200b, 200c, and 200d are electrically connected to each other such that the non-opposing thermoelectric signals J N from each thermoelectric conversion element are superposed with the same polarity.

[0041] Specifically, in the thermoelectric conversion module 300, the thermoelectric conversion elements 200a and 200c arranged with respect to the rectangular coordinate system C in the same manner as the thermoelectric conversion element 200 shown in FIGS. 3 and 4, and the thermoelectric conversion elements 200b and 200d arranged with respect to the rectangular coordinate system C in a manner obtained by rotating the thermoelectric conversion element 200 shown in FIGS. 3 and 4 by 180 degrees around the Y-axis are alternately provided along the Y-axis direction. Then, the electrode 207a of the thermoelectric conversion element 200a and the electrode 207b of the thermoelectric conversion element 200b are electrically connected, the electrode 207a of the thermoelectric conversion element 200b and the electrode 207b of the thermoelectric conversion element 200c are electrically connected, and the electrode 207a of the thermoelectric conversion element 200c and the electrode 207b of the thermoelectric conversion element 200d are electrically connected. Further, instead of arranging the thermoelectric conversion elements 200b and 200d in a manner rotated by 180 degrees around the Y-axis, after arranging the thermoelectric conversion elements 200b and 200d with respect to the rectangular coordinate system C in the same manner as the thermoelectric conversion element 200 shown in FIGS. 3 and 4, similar to the thermoelectric conversion elements 200a and 200c, the thermoelectric conversion element In 200b and 200d, the lamination order of the ferromagnetic metal layer 203 and the paramagnetic metal layer 205 of the thermoelectric conversion layer 202 can be reversed. In this case, the electrode 207a of the thermoelectric conversion element 200a and the electrode 207a of the thermoelectric conversion element 200b are electrically connected, the electrode 207b of the thermoelectric conversion element 200b and the electrode 207b of the thermoelectric conversion element 200c are electrically connected, and the electrode 207a of the thermoelectric conversion element 200c and the electrode 207a of the thermoelectric conversion element 200d are electrically connected.

[0042] Further, by the external magnetic field B, the ferromagnetic metal layers 203 of the four thermoelectric conversion elements 200a, 200b, 200c, and 200d are magnetized in the negative Y-axis direction and have a magnetization 203M facing the negative Y-axis direction.

[0043] The thermoelectric conversion module 300 includes heat conduction parts 301 and 302 provided so as to contact or be close to the end faces on the negative X-axis side and the end faces on the positive X-axis side of the four thermoelectric conversion elements 200a, 200b, 200c, and 200d. Thereby, the heat flow flowing in the X-axis direction easily flows into the ferromagnetic metal layers 203 of the four thermoelectric conversion elements 200a, 200b, 200c, and 200d. The thermoelectric conversion module 300 may not include the heat conduction parts 301 and 302.

[0044] The heat flow flows into the ferromagnetic metal layers 203 of the four thermoelectric conversion elements 200a, 200b, 200c, and 200d, and the non-inverse thermoelectric signals generated by the respective thermoelectric conversion elements 200 can be taken out by the electrode 207b of the thermoelectric conversion element 200a and the electrode 207a of the thermoelectric conversion element 200d after being superposed with the same polarity, so that a large non-inverse thermoelectric signal can be taken out.

[0045] Note that the nuclear battery may include a shield made of a radiation shielding member. Since the shield is provided for the purpose of not releasing the radiation emitted from the radioactive isotope element to the external environment, it may be provided as a layer on the outermost surface of the nuclear battery, or may be provided as a casing covering the nuclear battery. Similarly, the nuclear battery module may also include a shield. As the shield, a known radiation shielding member can be used. In addition to typical radiation shielding members such as lead and concrete, a rubber sheet having radiation shielding ability or a resin sheet having radiation shielding ability may also be used.

[0046] The thermoelectric conversion element in the nuclear battery may be a single layer, and in order to obtain a nuclear potential with a large electromotive force, the thermoelectric conversion element may be multilayered. Further, a protective film for protecting the thermoelectric conversion element may be provided, and terminals may be connected to the nuclear battery to be used as a nuclear battery device. Note that, depending on the application, the size and shape of the nuclear battery can be made as desired.

[0047] As described above, the nuclear battery of the present disclosure has been described in detail. However, the scope of the invention is not limited to the above examples, and various improvements and modifications may be made without departing from the gist thereof.

[0048] For example, in the above-described embodiment, in step S13, the external magnetic field B is applied to the ferromagnetic metal layer 203 in the in-plane (within the XY plane) direction of the thermoelectric conversion element 200 and in a direction orthogonal to the flow direction of the heat flow H (see FIGS. 3 and 4). However, the external magnetic field B and the heat flow H are set so as not to be parallel or anti-parallel to each other.

[0049] Further, in the above-described embodiment, thermoelectric conversion is performed while applying the external magnetic field B in step S13 (see FIGS. 3 and 4). However, if the magnetization 203M of the ferromagnetic metal layer 203 exists even without the application of the external magnetic field B, thermoelectric conversion can be performed without the application of the external magnetic field B in step S13. This can be achieved. As a method for realizing this, for example, the ferromagnetic metal layer 203 can be composed of a material with a large coercive force so that the ferromagnetic metal layer 203 has magnetization 203M as the residual magnetization, or a layer or member for applying a static magnetic field or an exchange coupling magnetic field to the ferromagnetic metal layer 203 can be provided in the thermoelectric conversion element 200. For example, the thermoelectric conversion element 200 can further include an antiferromagnetic layer such as NiO, IrMn, FeMn, NiMn, PtMn, PdMn, Mn2Au, FeRh, MnSb, etc., laminated on the side opposite to the paramagnetic metal layer 205 side of the ferromagnetic metal layer 203 so as to apply an exchange coupling magnetic field to the ferromagnetic metal layer 203. Thereby, it becomes possible to perform thermoelectric conversion without applying an external magnetic field B.

[0050] Also, in the above-described embodiment, the pair of electrodes 207a and 207b are provided on the surface 205S of the paramagnetic metal layer 205 so as not to be in contact with the ferromagnetic metal layer 203 and to be spaced apart from each other along the X-axis direction (see FIGS. 3 and 4). However, they may be provided on the side surfaces of the paramagnetic metal layer 205 in the positive and negative X-axis directions so as not to be in contact with the ferromagnetic metal layer 203 and to be spaced apart from each other along the X-axis direction.

[0051] Also, in the above-described embodiment, the ferromagnetic metal layer 203 is a single layer (see FIGS. 3 and 4). However, the ferromagnetic metal layer 203 may be composed of a plurality of laminated ferromagnetic metal layers. In this case, it is preferable that each of the plurality of layers is composed of a Ni-Fe alloy, Fe, Co, Ni, Gd, CoFeB alloy, or (Ga,Fe)Sb alloy. Such a laminated plurality of ferromagnetic metal layers can be, for example, a laminate in which layers made of a plurality of types of ferromagnetic metals are laminated periodically with each other (for example, when the layer made of the first ferromagnetic metal is layer A, the layer made of the second ferromagnetic metal is layer B, and the layer made of the third ferromagnetic metal is layer C, a laminate in which three types of layers such as layer A layer B layer C layer A layer B layer C... are laminated periodically), or a laminate in which layers made of a plurality of types of ferromagnetic metals are laminated randomly with each other (for example, a laminate in which three types of layers such as layer A layer B layer C layer B layer A layer C... are laminated randomly).

[0052] In the above-described embodiment, the paramagnetic metal layer 205 was a single layer (see FIGS. 3 and 4), but the paramagnetic metal layer 205 may be composed of a plurality of laminated paramagnetic metal layers. In this case, each of the plurality of layers is preferably made of Pt, Pd, W, AuW alloy, Ta, CuIr alloy, CuBi alloy, BiSb alloy, or BiSe alloy. Examples of such a laminated plurality of paramagnetic metal layers include a laminate in which layers made of a plurality of types of paramagnetic metals are periodically laminated with each other (for example, when a layer made of a first paramagnetic metal is layer D, a layer made of a second paramagnetic metal is layer E, and a layer made of a third paramagnetic metal is layer F, a laminate in which three types of layers such as layer D layer E layer F layer D layer E layer F... are periodically laminated) and a laminate in which layers made of a plurality of types of paramagnetic metals are randomly laminated with each other (for example, a laminate in which three types of layers such as layer D layer E layer F layer E layer D layer F... are randomly laminated). The laminated plurality of paramagnetic metal layers preferably have the same sign of spin Hall angle with each other. This is because, when thermoelectric conversion occurs in the thermoelectric conversion layer 202, the non-reciprocal thermoelectric signals caused by each of the plurality of paramagnetic metal layers do not cancel each other out, so that the non-reciprocal thermoelectric signal can be increased as a whole.

[0053] In the above-described embodiment, the thermoelectric conversion layer 202 included only one paramagnetic metal layer (paramagnetic metal layer 205) (see FIGS. 3 and 4), but the thermoelectric conversion layer 202 may include a first paramagnetic metal layer and a second paramagnetic metal layer. In this case, the first paramagnetic metal layer, the ferromagnetic metal layer 203, and the second paramagnetic metal layer are laminated in this order along the Z-axis direction such that the ferromagnetic metal layer 203 is interposed between the first paramagnetic metal layer and the second paramagnetic metal layer to form the thermoelectric conversion layer 202. The preferred constituent materials of the first paramagnetic metal layer and the second paramagnetic metal layer are the same as those of the paramagnetic metal layer 205, but the configurations (constituent materials, film thickness, etc.) of the first paramagnetic metal layer and the second paramagnetic metal layer are selected such that the thermoelectric conversion layer 202 has a structure in which spatial inversion symmetry is broken along the Z-axis direction.

[0054] In this case, it is preferable that the first ferromagnetic metal layer and the second ferromagnetic metal layer have spin Nernst angles with opposite signs to each other. (For example, this can be realized by forming the first ferromagnetic metal layer of Pt and the second ferromagnetic metal layer of Ta.) This is because, when thermoelectric conversion occurs in the thermoelectric conversion layer 202, spin currents having the same-polarity are injected from each of the first ferromagnetic metal layer and the second ferromagnetic metal layer into the ferromagnetic metal layer 203, so that the non-reciprocal thermoelectric signal can be increased.

[0055] Furthermore, in this case, each or either of the first ferromagnetic metal layer and the second ferromagnetic metal layer may be composed of a plurality of ferromagnetic metal layers laminated as described above. In this case, it is preferable that the plurality of ferromagnetic metal layers constituting each or either of the first ferromagnetic metal layer and the second ferromagnetic metal layer have spin Nernst angles with the same sign as each other for the above reasons.

[0056] Also, in the above-described embodiment, the pair of electrodes 207a and 207b are provided on the surface 205S of the ferromagnetic metal layer 205 (see FIGS. 3 and 4), but the pair of electrodes 207a and 207b may be provided on the back surface (the surface on the negative Z-axis side) of the ferromagnetic metal layer 203 so as not to be in contact with the ferromagnetic metal layer 205 and to be spaced apart from each other along the X-axis direction.

[0057] Also, in the above-described embodiment, the ferromagnetic metal layer 203 and the ferromagnetic metal layer 205 are laminated in this order on the substrate 201 to form the thermoelectric conversion layer 202 (see FIGS. 3 and 4), but the ferromagnetic metal layer 205 and the ferromagnetic metal layer 203 may be laminated in this order on the substrate 201 to form the thermoelectric conversion layer 202. In this case, the pair of electrodes 207a and 207b can be provided on the surface (the surface on the positive Z-axis side) of the ferromagnetic metal layer 203 or the back surface (the surface on the negative Z-axis side) of the ferromagnetic metal layer 205 so as to be spaced apart from each other along the X-axis direction.

[0058] Hereinafter, specific examples of the present invention will be given to explain the present invention in more detail. However, the present invention is not limited to the following examples. [Manufacturing Example of Thermoelectric Conversion Element] An element corresponding to the thermoelectric conversion element 200 in FIG. 3 was fabricated as follows. First, a Si substrate with a thermal oxide film having a thickness of 0.5 mm was prepared as the substrate 201. On this substrate, a Ni-Fe alloy layer with a thickness of 5 nm as the ferromagnetic metal layer 203 and a Pt layer with a thickness of 5 nm as the paramagnetic metal layer 205 were deposited in this order by DC magnetron sputtering to form the thermoelectric conversion layer 202. Then, the thermoelectric conversion layer 202 was patterned into a rectangular shape in plan view with a width of 5 μm in the Y-axis direction and a length of 50 μm in the X-axis direction by photolithography and lift-off methods. Thereafter, a Ti / Au layer was deposited on the thermoelectric conversion layer 202 by RF magnetron sputtering, and a pair of electrodes corresponding to the pair of electrodes 207a and 207b was formed by patterning the Ti / Au layer into a predetermined shape by photolithography and lift-off methods, thereby fabricating an element corresponding to the thermoelectric conversion element 200.

[0059] [Example 1] An atomic battery conceptually shown in FIG. 7 was fabricated. Plutonium-238 was implanted on a sapphire substrate using an accelerator, and a Pt(5 nm)=Py(5 nm) bilayer film (thermoelectric conversion element) was formed by RF magnetron sputtering. The film was patterned into a rectangular device with a width of 5 μm and a length of 50 μm by electron beam lithography and Ar ion etching. The obtained atomic battery was placed in a magnetic field at room temperature, and the non-linear voltage was measured.

[0060] [Example 2] An atomic battery conceptually shown in FIG. 7 was fabricated. Curium-244 was implanted on a sapphire substrate using an accelerator, and a Pt(5 nm)=Py(5 nm) bilayer film (thermoelectric conversion element) was formed by RF magnetron sputtering. The film was patterned into a rectangular device with a width of 5 μm and a length of 50 μm by electron beam lithography and Ar ion etching. The obtained atomic battery was placed in a magnetic field at room temperature, and the non-linear voltage was measured.

[0061] The thermoelectric conversion element manufactured in the examples can generate a thermoelectric signal non-linearly with respect to the direction of the temperature gradient. Therefore, it is possible to perform thermoelectric conversion from temperature fluctuations at the microscale where there is substantially no temperature gradient at the macroscale. Therefore, the nuclear batteries of Examples 1 and 2 that contain radioactive isotopes in the constituent members of the nuclear battery can generate electrical energy from the heat of the radiation randomly generated from the radioactive isotopes. Therefore, unlike conventional nuclear batteries, since a member for forming a temperature gradient in the thermoelectric conversion element is unnecessary, the nuclear battery of the present disclosure is lightweight and thin-film. In addition, since thermoelectric conversion can be performed from temperature fluctuations at the microscale, power generation by extremely weak radiation is possible, and the deterioration of the nuclear battery due to radiation is extremely small. Therefore, it can be put into practical use for radiation therapy power sources, power sources for space exploration, generators for military equipment, signal generator power generation, and the nuclear field (such as power generation from spent nuclear fuel casks).

[0062] [Addendum] According to the nuclear battery and the nuclear battery of the present disclosure, it is possible to be lighter and more compact than existing nuclear batteries and also have high power generation efficiency. Therefore, it can contribute to Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations. · Goal 9: "Build the infrastructure for industry and technological innovation"

Explanation of symbols

[0063] 10, 20, 30 ··· Nuclear battery 11, 21, 31 ··· Paramagnetic metal layer 12, 22 ··· Ferromagnetic metal layer 13, 23 ··· Thermoelectric conversion element 14, 24 ··· Electrode 25 ··· Substrate 16, 26, 36 ··· Radioactive isotope 37 ··· Heat 38 ··· Radiation 200 ··· Thermoelectric conversion element 202 ··· Thermoelectric conversion layer 203 ··· Ferromagnetic metal layer 205 ··· Paramagnetic metal layer 207a, 207b... a pair of electrodes 300... thermoelectric conversion module

Claims

1. A thermoelectric conversion unit that exhibits non-reciprocal conduction based on the breaking of spatial inversion symmetry, A pair of electrodes provided separately from each other in the thermoelectric conversion unit for extracting non-reciprocal thermoelectric signals, A nuclear battery containing a thermoelectric conversion element comprising: The nuclear battery, wherein at least one component constituting the nuclear battery contains a radioisotope element.

2. The thermoelectric conversion unit is a thermoelectric conversion layer including a ferromagnetic metal layer and a paramagnetic metal layer laminated with each other, The nuclear battery according to Claim 1, wherein the pair of electrodes are provided separately from each other in the in-plane direction of the thermoelectric conversion layer in the thermoelectric conversion layer.

3. The nuclear battery according to Claim 2, wherein the separation distance between the pair of electrodes is 0.1 μm or more and 1000 μm or less.

4. The paramagnetic metal layer is composed of a single layer or a plurality of laminated layers, and each of the single layer or the plurality of laminated layers of the paramagnetic metal layer is composed of Pt, Pd, W, AuW alloy, Ta, CuIr alloy, CuBi alloy, BiSb alloy, or BiSe alloy. The nuclear battery according to Claim 2.

5. The ferromagnetic metal layer is composed of a single layer or a plurality of laminated layers, and each of the single layer or the plurality of laminated layers of the ferromagnetic metal layer is composed of Ni-Fe alloy, Fe, Co, Ni, Gd, CoFeB alloy, or (Ga,Fe)Sb alloy. The original nuclear battery according to Claim 2.

6. The nuclear battery according to claim 1, comprising at least one element selected from the group consisting of beryllium-10, carbon-14, aluminum-26, silicon-32, chlorine-36, argon-39, potassium-40, nickel-63, selenium-79, rubidium-87, zirconium-93, indium-115, cesium-137, lanthanum-138, niobium-94, technetium-98, lutetium-71, neodymium-144, samarium-146, samarium-147, gadolinium-152, platinum-190, bismuth-210, polonium-209, thorium-232, uranium-232, uranium-233, uranium-234, uranium-235, uranium-236, uranium-238, plutonium-236, plutonium-238, plutonium-239, plutonium-244, americium-241, americium-243, curium-244, curium-246, curium-247, curium-248, californium-249, and californium-251.

7. A nuclear battery module comprising a plurality of the nuclear batteries according to any one of claims 1 to 6, wherein the plurality of nuclear batteries are electrically connected to each other such that non-opposing thermoelectric signals from each nuclear battery can be superposed with the same polarity.

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