Cold storage material, method for producing compound, and compound

Abstract

In order to reduce the amount of rare earth metals used in a cold storage material for a cryogenic refrigerator, this cold storage material for a cryogenic refrigerator contains crystals of Mn(Nb1-xTax)2O6 (0 ≤ x ≤ 1). In the temperature range of 6K or lower, Mn(Nb1-xTax)2O6 is antiferromagnetic, and the volume specific heat, which is a specific heat per volume, is greater than the volume specific heat of lead.

Description

Cold storage material, method for producing a compound, and compound

[0001] This invention relates to a cold storage material, a method for producing a compound, and the compound itself.

[0002] The Gifford-McMahon (GM) refrigerator is a well-known example of a cryogenic refrigerator capable of cooling objects to low temperatures (for example, 4.2 K, the temperature of liquid helium). The GM refrigerator comprises a compressor for compressing helium gas and a thermal storage material for heat exchange with the compressed helium gas. By expanding the helium gas cooled by the thermal storage material, it achieves the aforementioned low-temperature environment. Other examples of cryogenic refrigerators that can use the same thermal storage material as the GM refrigerator include the Stirling refrigerator and the pulse tube refrigerator. These cryogenic refrigerators are classified as thermal storage refrigerators. They are also sometimes simply called low-temperature refrigerators or low-temperature thermal storage refrigerators.

[0003] Materials used as cold storage materials to generate low temperatures are required to have a relatively large specific heat even in the low-temperature range (for example, the temperature range between 4.2 K and 10 K).

[0004] For example, lead is known as a material with a relatively high specific heat in the low-temperature range. However, because the specific heat of lead is due to lattice vibrations, the specific heat of lead decreases as the temperature decreases (as it approaches 4.2 K). Note that the specific heat used in this specification is the volumetric specific heat, which is the specific heat per unit volume.

[0005] Therefore, in order to increase the specific heat in the low-temperature region mentioned above, specific heat resulting from a magnetic phase transition (hereinafter referred to as magnetic specific heat) is used in cold storage materials. As a material that exhibits a magnetic phase transition in the low-temperature region mentioned above, HoCu ２ Yes, Er ３ Examples include rare earth intermetallic compounds such as Ni. For example, in the problem that the invention of Patent Document 1 aims to solve, HoCu ２ and Er ３ A thermal storage material filled with Ni in a laminated state is mentioned. Also, Patent Document 1 mentions R １－ｘ (Ge １－ｙ Mｙ ) ｘ (However, R represents at least one rare earth element selected from Y, La, Ce, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb, M represents at least one element selected from Ag, Au, Al, Ga, In, Sn, Bi, Pd, Pt, Zn, Rh, Ir, Ru, Mn, Cr, Mo, W, V, Nb, Ta, Ti, Zr, and Hf, and x and y satisfy 0.1 ≦ x ≦ 0.8 and 0 ≦ y ≦ 0.5, respectively, in terms of atomic ratio.) A cold storage material using a magnetic material represented by the above is described. Further, in Patent Document 2, ErIn ３ is exemplified as a material for a cold storage material utilizing magnetic specific heat.

[0006] The magnetic phase transition temperatures of these rare earth intermetallic compounds exist in the above-described low temperature region. Therefore, in these rare earth intermetallic compounds, magnetic specific heat remains even in the low temperature region. Also, the magnetism in these rare earth intermetallic compounds is borne by the spins of 4f electrons that constitute rare earth metals such as Ho and Er. The 4f electrons of rare earth metals can have a large magnetic moment due to the number of unpaired electrons in their outermost shell. Therefore, in rare earth intermetallic compounds, by appropriately selecting the combination of rare earth metals and transition metals, a large magnetic specific heat can be made to remain even in the low temperature region.

[0007] Japanese Patent Application Laid-Open No. 2004-143341, Japanese Patent Application Laid-Open No. 11-108479

[0008] However, since the rare earth metals contained in rare earth intermetallic compounds are rare, they tend to be expensive compared to transition metals. The use of rare earth intermetallic compounds in cold storage materials is one factor that increases the manufacturing cost of GM refrigerators.

[0009] One aspect of the present invention has been made in view of the above-described problems, and the object thereof is to reduce the amount of rare earth metals used in a cold storage material for an ultra-low temperature refrigerator such as a GM refrigerator.

[0010] In order to solve the above problems, a cold storage material according to one aspect of the present invention is Mn(Nb １－ｘ Ta ｘ )２ O ６ A cold storage material for cryogenic refrigerators containing crystals (0 ≤ x ≤ 1), wherein in a temperature range of 6 K or less, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ The material exhibits antiferromagnetism and employs a composition in which its volumetric specific heat (specific heat per unit volume) is greater than that of lead.

[0011] To solve the above problems, a method for producing a compound according to one aspect of the present invention is Mn(Nb １－ｘ Ta ｘ ) ２ O ６ By heat-treating (0 ≤ x ≤ 1) at a temperature between 1330°C and 1544°C, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ The configuration includes a heat treatment process for growing the crystal grains.

[0012] Furthermore, in a compound according to one embodiment of the present invention, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ The compound contains crystals of the form (0 ≤ x ≤ 1), exhibits antiferromagnetism in the temperature range of 6 K or below, has a volumetric specific heat (specific heat per unit volume) greater than that of lead, and has an average crystal grain size of 20 μm or more.

[0013] According to one aspect of the present invention, the amount of rare earth metals used in the cold storage material constituting a cryogenic refrigerator can be reduced.

[0014] This is a flowchart of a manufacturing method according to an embodiment of the present invention. The first embodiment of the present invention is MnNbTaO ６ This refers to the pelletized MnNbTaO before the grinding process shown in Figure 1 is carried out. ６ This is an image of the first embodiment of the present invention, MnNbTaO ６ The powdered MnNbTaO after the grinding process shown in Figure 1 has been carried out. ６ This is an image of powdered Mn(Nb) according to an embodiment of the present invention. １－ｘ Ta ｘ )２ O ６ This graph shows the temperature dependence of the specific heat of MnNbTaO, which is the first embodiment of the present invention. ６ This is an image showing the crystal grains. This is the first embodiment of the present invention, MnNbTaO ６ A cold storage material consisting of lead and HoCu ２ This graph shows the temperature dependence of the cooling capacity of a thermal storage material consisting of lead and . The first embodiment of the present invention is MnNbTaO ６ A cold storage material consisting of lead and HoCu ２ This graph shows the temperature dependence of the cooling capacity of a thermal storage material consisting of lead and . The first embodiment of the present invention is MnNbTaO ６ A thermal storage material consisting of lead, MnNbTaO ６ and CuFe ０．９８ Al ０．０２ O ２ A cold storage material consisting of lead and HoCu ２ This graph shows the temperature dependence of the cooling capacity of a thermal storage material consisting of lead and . The first embodiment of the present invention is MnNbTaO ６ A cold storage material consisting of lead and a second embodiment of the present invention is MnNb １．５ Ta ０．５ O ６ A thermal storage material consisting of lead and a third embodiment of the present invention, MnNb ２ O ６ This graph shows the temperature dependence of the cooling capacity of a thermal storage material consisting of lead and . The first embodiment of the present invention is MnNbTaO ６ and CuFe ０．９８ Al ０．０２ O ２ A cold storage material consisting of lead and a second embodiment of the present invention is MnNb １．５ Ta ０．５ O ６ and CuFe ０．９８ Al ０．０２ O ２ A thermal storage material consisting of lead and a third embodiment of the present invention, MnNb ２ O ６ and CuFe ０．９８ Al ０．０２ O ２ This graph shows the temperature dependence of the cooling capacity of a thermal storage material made of lead and other materials.

[0015] [First Embodiment] The cold storage material according to the first embodiment of the present invention will be described. This cold storage material is for an ultra-low temperature refrigerator. In this embodiment, a Gifford-McMahon refrigerator is used as an example of the ultra-low temperature refrigerator. However, this cold storage material is also applicable to a Stirling refrigerator and a pulse tube refrigerator, which are other examples of ultra-low temperature refrigerators. This cold storage material contains crystals of Mn(Nb １－ｘ Ta ｘ ). ２ O ６ (0 ≤ x ≤ 1). In the temperature range below 6 K, Mn(Nb １－ｘ Ta ｘ ). ２ O ６ exhibits antiferromagnetism and is configured such that its specific heat is greater than that of lead. Note that the specific heat used hereinafter is the volumetric specific heat, which is the specific heat per unit volume. Also, the crystal includes both single crystals and polycrystals. Therefore, Mn(Nb １－ｘ Ta ｘ ). ２ O ６ may be either a single crystal or a polycrystal. This cold storage material is an aspect of the present invention.

[0016] This cold storage material may further contain crystals of CuFe １－ｙ M ｙ O ２ (M is a metal element other than Fe and other than rare earth elements, 0 ≤ y ≤ 1). In the temperature range below 10 K, CuFe １－ｙ M ｙ O ２ exhibits antiferromagnetism and is configured such that its specific heat is greater than that of lead. Also, CuFe １－ｙ M ｙ O ２ may be either a single crystal or a polycrystal. M is preferably at least one of Al, Ga, Mn, and Rh.

[0017] In this embodiment, as a method for measuring the crystal grain size of Mn(Nb １－ｘ Ta ｘ ). ２ O ６ of Mn(Nb １－ｘ Ta ｘ ).２ O ６ The images of the crystals of O were taken at a magnification at which each crystal grain could be visually discriminated, and the size of each imaged crystal grain was measured manually, and then the average value of the crystal grain sizes was calculated. As a device for taking such images, a scanning electron microscope (SEM: Scanning Electron Microscope) can be mentioned. Here, when measuring the crystal grain size and calculating the average value, for example, the measurement and calculation may be automated, or the optional function of the SEM may be used. Note that Mn(Nb １－ｘ Ta ｘ ) ２ O ６ The shapes and crystal grain sizes of the crystal grains of )O vary. Therefore, it is preferable to perform the above-described measurement of the crystal grain size on a plurality of crystal grains and obtain the average value from the plurality of obtained crystal grain sizes. Mn(Nb １－ｘ Ta ｘ ) ２ O ６ When the average value of the crystal grain size of )O is measured using this measurement method, it is preferably 20 μm or more. Also, for Mn(Nb １－ｘ Ta ｘ ) ２ O ６ it is preferable that both the minor axis and the major axis of the crystal grain size of )O are 10 μm or more.

[0018] In this embodiment, as a method for measuring the particle size of Mn(Nb １－ｘ Ta ｘ ) ２ O ６ the appearance of the particles is optically observed to obtain an image of the particles, and the particle size is calculated by image analysis of the image. As a device for measuring such a particle size, a dynamic image type particle size distribution measuring device (QICPIC) can be mentioned. QICPIC randomly selects a particle to be observed from a particle group, obtains an image of the selected particle, and performs image analysis. In this image analysis, the volume of the particle is derived, a sphere having the derived volume is assumed, and the diameter of the sphere is derived. That is, QICPIC derives the diameter by volume-converting the shape of an irregular particle into a substantially spherical shape. Note that Mn(Nb １－ｘ Ta ｘ )２ O ６ The shape and particle size of the particles vary. Therefore, it is preferable to perform the image analysis described above on multiple particles and use the representative value (average value) of the obtained diameters as the particle size. The number of particles on which image analysis is performed is not limited, but in this embodiment, it is set to 100 or more. Mn(Nb １－ｘ Ta ｘ ) ２ O ６ The particle size is preferably 200 μm or more and 500 μm or less when measured using this measurement method.

[0019] [Second Embodiment] A manufacturing method M10 according to a second embodiment of the present invention will be described with reference to Figure 1. Figure 1 is a flowchart of the manufacturing method M10. The manufacturing method M10 involves Mn(Nb) contained in the refrigerant material described in the first embodiment. １－ｘ Ta ｘ ) ２ O ６ This is a method of manufacturing [the product].

[0020] As shown in Figure 1, the manufacturing method M10 includes a weighing step S11, a mixing step S12, a molding step S13, a firing step S14, a heat treatment step S15, and a grinding step S16.

[0021] The weighing process S11 is performed on the Mn(Nb) after manufacturing. １－ｘ Ta ｘ ) ２ O ６ This process involves weighing manganese oxide, niobium oxide, and tantalum oxide so that the composition ratio of Mn, Nb, and Ta in the mixture is the desired 1:2(1-x):2x. These oxides are readily available as they are commercially available.

[0022] Mixing step S12 is a step in which the manganese oxide, niobium oxide, and tantalum oxide weighed in weighing step S11 are mixed. The method of mixing is not limited, but for example, in cases that are not mass production, mixing can be done using a mortar and pestle. Alternatively, when mixing these oxides, an appropriate amount of alcohol (e.g., ethanol) may be added dropwise to the mortar and the oxides may be mixed in the alcohol. When mixing these oxides in alcohol, it is preferable to evaporate the alcohol after mixing.

[0023] The molding process S13 is a process of pressurizing the mixture of each oxide obtained in the mixing process S12. The shape to be pressurized is not limited and can be determined as appropriate, but one example is a pellet. The manufactured Mn(Nb １－ｘ Ta ｘ ) ２ O ６ From the standpoint of increasing the density, it is preferable to use a pressure molding method as the molding process S13.

[0024] The firing process S14 is a process of firing the mixture of oxides obtained in the molding process S13. The firing temperature, firing time, and atmosphere in the firing process S14 can be appropriately selected according to the knowledge obtained so far. For example, the firing temperature and firing time can be 1200°C for 24 hours or 1250°C for 36 hours, and the atmosphere can be air or atmospheric pressure. By carrying out the firing process S14, the following chemical reaction proceeds, and Mn(Nb) １－ｘ Ta ｘ ) ２ O ６ This can be obtained. MnO ２ + (1-x)Nb ２ O ５ +xTa ２ O ５ →Mn(Nb) １－ｘ Ta ｘ ) ２ O ６ +1 / 2O ２ ↑

[0025] Furthermore, the manufacturing method M10 of this embodiment includes a calcination step S14, and from the mixture of each oxide, Mn(Nb １－ｘ Taｘ ) ２ O ６ The material is fired. However, in one modified example of manufacturing method M10, the firing step S14 is omitted, and the pre-sintered Mn(Nb １－ｘ Ta ｘ ) ２ O ６ You may also use [this].

[0026] Heat treatment step S15 is Mn(Nb １－ｘ Ta ｘ ) ２ O ６ This is a heat treatment process performed on Mn(Nb). Heat treatment process S15 is Mn(Nb １－ｘ Ta ｘ ) ２ O ６ This is a process for growing crystal grains of Mn(Nb). In other words, the heat treatment process S15 is a process for growing crystal grains of Mn(Nb). １－ｘ Ta ｘ ) ２ O ６ This is a process to increase the grain size of the crystals. Therefore, the heat treatment temperature in the heat treatment step S15 is Mn(Nb １－ｘ Ta ｘ ) ２ O ６ The temperature can be appropriately selected within a range that allows for the growth of crystal grains. To grow crystal grains, the heat treatment temperature in the heat treatment step S15 is preferably higher than the firing temperature in the firing step S14. For example, the heat treatment temperature is preferably 1330°C or higher, and more preferably 1400°C or higher. Also, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ To suppress the phase change in MnTa, the heat treatment temperature is set to MnTa ２ O ６ Preferably, the melting point is below that of MnNb. ２ O ６ It is more preferable that the melting point is below that of MnTa. ２ O ６ The typical melting point of MnNb is 1494°C. ２ O ６The typical melting point of is 1544°C. Therefore, the heat treatment temperature is preferably 1544°C or lower, and more preferably 1494°C or lower. Also, the heat treatment time in heat treatment step S15 is Mn(Nb １－ｘ Ta ｘ ) ２ O ６ It can be appropriately determined according to the degree of growth of the crystal grains. In one embodiment of the present invention, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ The average grain size of the crystal grains is preferably 20 μm or more. Therefore, the heat treatment time can be appropriately determined within the range in which the average grain size is 20 μm or more. An example of this heat treatment time is 24 hours or more and 72 hours or less, but it is not limited to this. The Mn(Nb) obtained as a result of performing the heat treatment step S15 is also specified. １－ｘ Ta ｘ ) ２ O ６ The larger the average particle size, the better.

[0027] The grinding step S16 is a step of grinding the pellets obtained by carrying out the heat treatment step S15. The grinding method is not limited, but for example, in cases that are not mass production, the pellets can be ground using a mortar and pestle. １－ｘ Ta ｘ ) ２ O ６ In this case, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ The particle size is preferably 200 μm or more and 500 μm or less.

[0028] Furthermore, manufacturing method M10 involves the CuFe contained in the thermal storage material described in the first embodiment. １－ｙ M ｙ O ２ It can also be applied to the manufacturing method. Below, in manufacturing method M10, CuFe １－ｙ M ｙ O ２ This explains the manufacturing process.

[0029] The weighing process S11 is performed on CuFe after manufacturing. １－ｙ M ｙ O ２ The composition ratio of Cu, Fe, and M in the mixture is such that the desired ratio is 1:1-y:y, and copper oxide (e.g., Cu ２ O), iron oxide (e.g., α-Fe) ２ O ３ ), and oxides of M (for example, if M = Al, then α-Al ２ O ３ This is the process of weighing the oxides. These oxides are readily available as they are commercially available.

[0030] Mixing step S12 is a step in which the copper oxide, iron oxide, and oxide of M weighed in weighing step S11 are mixed. The method of mixing is not limited, but for example, in cases that are not mass production, mixing can be done using a mortar and pestle. Alternatively, when mixing these oxides, an appropriate amount of alcohol (e.g., ethanol) may be added dropwise to the mortar and the mixture may be mixed in the alcohol. When mixing these oxides in alcohol, it is preferable to evaporate the alcohol after mixing.

[0031] The molding process S13 is a process of pressurizing the mixture of each oxide obtained in the mixing process S12. The shape to be pressurized is not limited and can be determined as appropriate, but one example is a pellet. １－ｙ M ｙ O ２ From the standpoint of increasing the density, it is preferable to use a pressure molding method as the molding process S13.

[0032] The firing process S14 is a process of firing the mixture of oxides obtained in the molding process S13. The firing temperature, firing time, and atmosphere in the firing process S14 can be appropriately selected according to the knowledge obtained so far. For example, in the case of M=Al, a firing temperature of 1100°C can be used, a firing time of 48 hours can be used, and an Ar atmosphere can be used. By carrying out the firing process S14, the following chemical reaction proceeds, and CuFe １－ｙ M ｙ O ２This is obtained. Note that in the following chemical reaction, M = Al is used as an example of M. Cu ２ O + (1 - y)Fe ２ O ３ +yAl ２ O ３ →2CuFe １－ｙ Al ｙ O ２

[0033] The heat treatment step S15 is performed on the CuFe that was fired in the firing step S14. １－ｙ Al ｙ O ２ The objective is to grow the crystal grains and increase the grain size. Here, the heat treatment temperature and heat treatment time in heat treatment step S15 can be appropriately determined according to the degree of crystal grain growth. Note that manufacturing method M10 is CuFe １－ｙ M ｙ O ２ When applied to the manufacturing method, the heat treatment step S15 can be omitted.

[0034] The grinding step S16 is a step of grinding the pellets obtained by carrying out the heat treatment step S15. The grinding method is not limited, but for example, in cases that are not mass production, the pellets can be ground using a mortar and pestle. １－ｙ M ｙ O ２ In CuFe １－ｙ M ｙ O ２ The particle size is preferably 180 μm or more and 500 μm or less.

[0035] [Third Embodiment] A compound according to a third embodiment of the present invention will be described. This compound is Mn(Nb １－ｘ Ta ｘ ) ２ O ６ It contains crystals of the form (0 ≤ x ≤ 1). In the temperature range below 6 K, Mn(Nb １－ｘ Ta ｘ ) ２ O ６It exhibits antiferromagnetism and is configured such that its specific heat is greater than that of lead. Note that the specific heat used here is the volumetric specific heat, which is the specific heat per unit volume. Mn(Nb) １－ｘ Ta ｘ ) ２ O ６ The average grain size of the crystals is 20 μm or larger. Furthermore, the term "crystal" includes both single crystals and polycrystalline materials. Therefore, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ This may be either a single crystal or a polycrystalline material. This compound is one embodiment of the present invention.

[0036] [Additional Notes] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0037] [Summary] The cold storage material according to the first aspect of the present invention is Mn(Nb １－ｘ Ta ｘ ) ２ O ６ A cold storage material for cryogenic refrigerators containing crystals (0 ≤ x ≤ 1), wherein in a temperature range of 6 K or less, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ The material exhibits antiferromagnetism and employs a composition in which its volumetric specific heat (specific heat per unit volume) is greater than that of lead.

[0038] Lead is known as a material that has a relatively large specific heat in the low-temperature range. The specific heat of lead is due to lattice vibrations, so the lower the temperature (the closer to 4.2 K), the smaller the specific heat of lead becomes. On the other hand, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ The crystal exhibits antiferromagnetism in the temperature range below 6K, and possesses specific heat due to magnetic order in addition to specific heat due to lattice vibrations (hereinafter also referred to as magnetic specific heat). Therefore, Mn(Nb １－ｘ Ta ｘ ) ２ O６ The specific heat of the crystal exceeds that of lead in the temperature range below 6K. According to the above configuration, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ The crystal can efficiently cool He gas in the temperature range below 6K compared to lead-based cold storage materials. Furthermore, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ It does not contain rare earth metals. Therefore, at least a portion of the compounds containing rare earth metals such as Ho and Er contained in the cold storage material is Mn(Nb). １－ｘ Ta ｘ ) ２ O ６ By using this alternative, the amount of rare earth metals used in the thermal storage material can be reduced.

[0039] Furthermore, in the second embodiment of the present invention, in addition to the configuration of the first embodiment of the present invention, CuFe １－ｙ M ｙ O ２ The composition employs a structure that further includes crystals of a metal element other than Fe and other than rare earth elements, where 0 ≤ y ≤ 1.

[0040] CuFe １－ｙ M ｙ O ２ The crystal exhibits antiferromagnetism in the temperature range below 10K and possesses magnetic specific heat in addition to specific heat due to lattice vibrations. M may be, for example, at least one of Al, Ga, Mn, and Rh. However, CuFe １－ｙ M ｙ O ２ Gd has a low specific heat around 4K. Therefore, as an example, Gd has a larger specific heat in the temperature range below 6K. ２ O ２ S and CuFe １－ｙ M ｙ O ２ By combining these, it is conceivable that a large specific heat can be secured in the temperature range. Here, in the temperature range below 6K, Mn(Nb １－ｘ Ta ｘ )２ O ６ CuFe １－ｙ M ｙ O ２ It has a larger specific heat. Therefore, the above Gd ２ O ２ Replace S with Mn(Nb) １－ｘ Ta ｘ ) ２ O ６ CuFe １－ｙ M ｙ O ２ By combining this, a large specific heat can be secured in the temperature range below 6K. Therefore, according to the above configuration, in the temperature range below 6K, Mn(Nb) that does not contain rare earth metals can be obtained. １－ｘ Ta ｘ ) ２ O ６ By using this method, a large specific heat can be secured, and CuFe can be used in the temperature range below 10K. １－ｙ M ｙ O ２ By using this method, a high specific heat can be secured.

[0041] Furthermore, in the third aspect of the present invention, in addition to the configuration of the first or second aspect of the present invention, a configuration is adopted in which the average value of the crystal grain size is 20 μm or more.

[0042] To improve the heat exchange efficiency with He gas, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ It is preferable to increase the surface area, and for that purpose, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ The particle size should be reduced. However, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ Reducing the particle size of Mn(Nb) reduces the size of the void through which helium gas passes, increasing the pressure loss. １－ｘ Ta ｘ ) ２ O ６It is desirable for the particles to maintain a constant particle size. However, when the crystal grain size is small, the particles tend to break down easily, making it difficult to maintain a constant particle size.

[0043] Therefore, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ If the average grain size of the crystals is set to a certain level or higher, for example, 20 μm or more, then Mn(Nb) １－ｘ Ta ｘ ) ２ O ６ The particles become less prone to breaking down, making it easier to maintain a consistent particle size.

[0044] According to the above configuration, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ This allows for a good balance between increasing the surface area and reducing the pressure loss of He gas.

[0045] Furthermore, in the fourth aspect of the present invention, in addition to the configuration of the third aspect of the present invention, a configuration is adopted in which the particle size is 200 μm or more and 500 μm or less.

[0046] According to the above configuration, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ The surface area can be kept within the surface area determined by the particle size used as the cold storage material.

[0047] A method for producing a compound according to a fifth aspect of the present invention is Mn(Nb １－ｘ Ta ｘ ) ２ O ６ By heat-treating (0 ≤ x ≤ 1) at a temperature between 1330°C and 1544°C, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ The configuration includes a heat treatment process for growing the crystal grains.

[0048] By performing such a heat treatment process, Mn(Nb １－ｘ Ta ｘ )２ O ６ The crystal grains grow, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ The average grain size of the crystals becomes above a certain level (for example, 20 μm or more). As a result, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ Since the particles become less prone to crumbling, for example, when used as a cold storage material for cryogenic refrigerators, it can improve resistance to vibration.

[0049] According to the above configuration, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ The crystal grain size can be made to be above a certain level.

[0050] Furthermore, in the compound according to the sixth aspect of the present invention, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ The compound contains crystals of the form (0 ≤ x ≤ 1), exhibits antiferromagnetism in the temperature range of 6 K or below, has a volumetric specific heat (specific heat per unit volume) greater than that of lead, and has an average crystal grain size of 20 μm or more.

[0051] According to the above configuration, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ The surface area and the pressure loss of He gas can be optimized in a balanced manner. Examples

[0052] Mn(Nb) constitutes a part of the cold storage material according to the first embodiment. １－ｘ Ta ｘ ) ２ O ６ and CuFe １－ｙ Al ｙ O ２ This will be explained with reference to Figures 2 to 10. In this embodiment, the substitution amount x is Mn(Nb) = 0.5, 0.25, 0. １－ｘ Ta ｘ ) ２ O ６A powdery polycrystalline and CuFe with substitution amount y = 0.02 １－ｙ Al ｙ O ２ A powdery polycrystalline material was prepared. Below, Mn(Nb) is prepared with x = 0.5, 0.25, 0. １－ｘ Ta ｘ ) ２ O ６ These polycrystalline materials are referred to as the first, second, and third embodiments. Figure 2 is an image of the pelletized first embodiment before the grinding process S16 shown in Figure 1. Figure 3 is an image of the powdered first embodiment after the grinding process S16. Figure 4 is a graph showing the temperature dependence of the specific heat in the first embodiment. Note that Figure 4 shows Mn(Nb) for x = 0, 1. １－ｘ Ta ｘ ) ２ O ６ The temperature dependence of the specific heat is also illustrated. Figure 5 is an image showing the crystal grains of the first embodiment. Figure 6 shows a thermal storage material consisting of 10% of the first embodiment and 90% lead, a thermal storage material consisting of 20% of the first embodiment and 80% lead, and the first reference example HoCu ２ Figure 7 shows the temperature dependence of the cooling capacity in a thermal storage material consisting of lead and . Figure 7 shows the thermal storage material consisting of 10% lead and 90% of the first example, the thermal storage material consisting of 20% lead and 80% of the first example, the thermal storage material consisting of 30% lead and 70% of the first example, and the first reference example HoCu ２ This graph shows the temperature dependence of the cooling capacity of a thermal storage material consisting of 10% lead and 90% carbon dioxide, a thermal storage material consisting of 20% lead and 80% carbon dioxide (first reference example), and a thermal storage material consisting of 30% lead and 70% carbon dioxide (first reference example). Figure 8 shows the thermal storage material consisting of 30% lead and 70% carbon dioxide (first example), and a thermal storage material consisting of 30% lead and y = 0.02 CuFe. １－ｙ Al ｙ O ２ (CuFe ０．９８ Al ０．０２ O ２Figure 10 shows the temperature dependence of the cooling capacity of the first example of a thermal storage material consisting of 20% carbon dioxide and 50% lead, the first example of a thermal storage material consisting of 20% carbon dioxide and 80% lead, and the first example of a thermal storage material consisting of 30% carbon dioxide and 70% lead. Figure 9 shows the temperature dependence of the cooling capacity of the first example of a thermal storage material consisting of 30% carbon dioxide and 70% lead, the second example of a thermal storage material consisting of 30% carbon dioxide and 70% lead, and the third example of a thermal storage material consisting of 30% carbon dioxide and 70% lead. ０．９８ Al ０．０２ O ２ A thermal storage material consisting of 20% and 50% lead, and a second example consisting of 30% and CuFe ０．９８ Al ０．０２ O ２ A thermal storage material consisting of 20% and 50% lead, and a third example consisting of 30% and CuFe ０．９８ Al ０．０２ O ２ This graph shows the temperature dependence of the cooling capacity of a thermal storage material consisting of 20% lead and 50% chlorine.

[0053] The first to third examples were manufactured using manufacturing method M10. In the first to third examples, the starting material was 99.9% pure MnO manufactured by Kojun Chemical Laboratory Co., Ltd. ２ , Nb ２ O ５ Ta ２ O ５ In addition, in the firing process S14, the firing temperature and firing time were set to 1200°C for 24 hours or 1250°C for 36 hours, and the atmosphere was air and atmospheric pressure. １－ｘ Ta ｘ ) ２ O ６ In the re-sintering process to promote grain growth, a re-sintering temperature of 1400°C was used, a re-sintering time of 48 hours was used, and a cooling time after re-sintering was used of approximately 5 hours, with the atmosphere being air and atmospheric pressure. In addition, when manufacturing the third embodiment where x = 0 in manufacturing method M10, Ta ２ O ５ You just need to avoid using it.

[0054] Starting material (MnO ２ , Nb ２O ５ Ta ２ O ５ The mixture was prepared in a molar ratio of 1:1-x:x and formed into pellets. These pellets were then fired in air at atmospheric pressure at a firing temperature of 1200°C for 24 hours. The pellets after firing were crushed and powdered, then formed into pellets again and fired again at a firing temperature of 1250°C for 36 hours. The pellets after firing were crushed and separated (to a particle size of 200-500 μm) and fired again at 1400°C for 48 hours. The pellets after firing again were cooled from 1400°C to 50°C over 10 hours.

[0055] Furthermore, Figure 4 shows the temperature dependence of the specific heat measured in the first embodiment. Note that Figure 4 shows Mn(Nb) for x = 0, 1. １－ｘ Ta ｘ ) ２ O ６ (MnNb ２ O ６ , MnTa ２ O ６ The temperature dependence of the specific heat of MnNb is also shown. See Figure 4. ２ O ６ It shows a sharp peak in specific heat around 4K, MnTa ２ O ６ It shows a sharp peak in specific heat around 6K. However, in order to exhibit high cooling capacity at 4K, it is preferable that the specific heat has a broad peak at a temperature about 1K higher than 4K, i.e., around 5K. Therefore, MnNb ２ O ６ In the first embodiment (MnNbTaO), the Nb sites are partially replaced with Ta elements. ６ Regarding this, as can be seen in Figure 4, the temperature at which the specific heat shows a peak rises to around 5 K, and the sharp peak of the specific heat becomes less pronounced.

[0056] Furthermore, an image of the crystal grains of the first embodiment is shown in Figure 5. The image of the crystal grains in Figure 5 was captured using a scanning electron microscope (SEM). During imaging with the SEM, the acceleration voltage was 15 kV, the irradiation current was 10 nA, the working distance (WD) was 10 mm, and the magnification was 3000x.

[0057] Referring to Figure 5, it was confirmed that when the heat treatment after the grinding step S16 in the first embodiment was performed for 0 hours, the individual crystal grains grew when the heat treatment was performed at 1330°C for 72 hours. Furthermore, when the heat treatment was performed at 1400°C for 48 hours, the growth of each crystal grain progressed even further, and it was confirmed that the average crystal grain size reached 20 μm.

[0058] The first embodiment obtained in this way (MnNbTaO ６ A thermal storage material according to the first embodiment was constructed using polycrystalline material (7.2 g) and lead (104.4 g). The ratio of the first embodiment to lead in this thermal storage material was 1:9 in terms of the volume ratio of the filling space (i.e., 10% of the first embodiment).

[0059] Furthermore, the first embodiment obtained in this manner (MnNbTaO ６ A thermal storage material according to the first embodiment was constructed using polycrystalline material (14.4 g) and lead (92.8 g). The ratio of the first embodiment to lead in this thermal storage material was 1:4 in terms of the volume ratio of the filling space (i.e., 20% of the first embodiment).

[0060] Furthermore, the first embodiment obtained in this manner (MnNbTaO ６ A thermal storage material according to the first embodiment was constructed using polycrystalline material (21.1 g) and lead (81.2 g). The ratio of the first embodiment to lead in this thermal storage material is approximately 3:7 in terms of the volume ratio of the filling space (i.e., 30% of the first embodiment).

[0061] Furthermore, the first embodiment obtained in this manner (MnNbTaO ６ ) polycrystalline (19.7 g) and CuFe obtained by manufacturing method M10 ０．９８ Al ０．０２ O ２ A thermal storage material according to the first embodiment was constructed using polycrystalline material (8.4 g) and lead (58 g). The first embodiment of this thermal storage material and CuFe ０．９８ Al ０．０２ O ２ The ratio of lead to CuFe is 3:2:5 in terms of the volume ratio of the filling space (i.e., in the first example, 30% CuFe). ０．９８ Al ０．０２ O ２ It is 20%.

[0062] Furthermore, as a cold storage material for comparison with the cold storage materials according to these first embodiments, HoCu ２ A cold storage material consisting of (10.2g) and lead (104.4g), and HoCu ２ A cold storage material consisting of (20.4g) and lead (92.8g), and HoCu ２ A cold storage material consisting of (30.6g) and lead (81.2g) was used. ２ HoCu in a cold storage material consisting of (10.2g) and lead (104.4g) ２ The ratio of lead to carbide is 1:9 in terms of the volume ratio of the filling space (i.e., HoCu ２ It is 10%. HoCu ２ HoCu in a cold storage material consisting of (20.4g) and lead (92.8g) ２ The ratio of lead to carbide is 1:4 in terms of the volume ratio of the filling space (i.e., HoCu ２ It is 20%. HoCu ２ HoCu in a cold storage material consisting of (30.6g) and lead (81.2g) ２ The ratio of lead to carbide is 3:7 in terms of the volume ratio of the filling space (i.e., HoCu ２ It is 30%.

[0063] Furthermore, the second example obtained by manufacturing method M10 (MnNb １．５ Ta ０．５ O ６ A thermal storage material according to the first embodiment was constructed using polycrystalline material (17.0 g) and lead (81.2 g). The ratio of lead to the second embodiment in this thermal storage material is approximately 3:7 in terms of the volume ratio of the filled space (i.e., 30% of the second embodiment).

[0064] Furthermore, the third embodiment obtained by manufacturing method M10 (MnNb ２ O ６ The thermal storage material according to the first embodiment was constructed using polycrystalline material (16.5 g) and lead (81.2 g). The ratio of lead to the third embodiment in this thermal storage material is approximately 3:7 in terms of the volume ratio of the filling space (i.e., 30% of the third embodiment).

[0065] Furthermore, the first example obtained by manufacturing method M10 (MnNbTaO ６) polycrystalline (19.7 g) and CuFe obtained by manufacturing method M10 ０．９８ Al ０．０２ O ２ A thermal storage material according to the first embodiment was constructed using polycrystalline material (10.4 g) and lead (58 g). The first embodiment of this thermal storage material and CuFe ０．９８ Al ０．０２ O ２ The ratio of lead to CuFe is 3:2:5 in terms of the volume ratio of the filling space (i.e., in the first example, 30% CuFe). ０．９８ Al ０．０２ O ２ It is 20%. That is, CuFe in this cold storage material ０．９８ Al ０．０２ O ２ The density of the first example was 30% and CuFe ０．９８ Al ０．０２ O ２ (8.4g) is higher than that of the 20% cold storage material.

[0066] Furthermore, the second example obtained by manufacturing method M10 (MnNb １．５ Ta ０．５ O ６ ) polycrystalline (16 g) and CuFe obtained by manufacturing method M10 ０．９８ Al ０．０２ O ２ A thermal storage material according to the first embodiment was constructed using polycrystalline material (10.4 g) and lead (58 g). A second embodiment of this thermal storage material and CuFe ０．９８ Al ０．０２ O ２ The ratio of lead to CuFe is 3:2:5 in terms of the volume ratio of the filling space (i.e., in the second example, 30% CuFe). ０．９８ Al ０．０２ O ２ It is 20%.

[0067] Furthermore, the third embodiment obtained by manufacturing method M10 (MnNb ２ O ６ ) Polycrystalline (14.5 g) and CuFe obtained by manufacturing method M10 ０．９８ Al ０．０２ O ２ A thermal storage material according to the first embodiment was constructed using polycrystalline material (10.4 g) and lead (58 g). A third embodiment of this thermal storage material and CuFe０．９８ Al ０．０２ O ２ The ratio of lead to CuFe is 3:2:5 in terms of the volume ratio of the filling space (i.e., in the third embodiment, 30% CuFe). ０．９８ Al ０．０２ O ２ It is 20%.

[0068] A cold storage material in which the first embodiment is 10%, a cold storage material in which the first embodiment is 20%, a cold storage material in which the first embodiment is 30%, and HoCu ２ Figure 6 shows the results of measuring the cooling capacity after constructing a cooler equipped with each of the cold storage materials and mounting it on a GM chiller. Referring to Figure 6, the cooling capacity of the cold storage material in the first embodiment, which is 20%, exceeds that of the cold storage material in the first embodiment, which is 10%, in the temperature range of 5K or below. ２ It was found that the cooling capacity of the cold storage material containing [the specified element] approaches that of other materials.

[0069] A cold storage material in which the first embodiment is 10%, a cold storage material in which the first embodiment is 20%, a cold storage material in which the first embodiment is 30%, HoCu ２ A cold storage material containing 10% of HoCu ２ A cold storage material containing 20% ​​of HoCu ２ Figure 7 shows the results of measuring the cooling capacity after preparing coolers equipped with each of the coolants containing 30% of HoCu and mounting them in a GM refrigerator. Referring to Figure 7, the cooling capacity increases in the temperature range of 5K or below in the order of the coolant containing 10% of the first embodiment, the coolant containing 20% ​​of the first embodiment, and the coolant containing 30% of the first embodiment. ２ It was found that the cooling capacity of the cold storage material containing [the specified element] approaches that of other materials.

[0070] The first example is a cold storage material in which 30% is present, and the first example is a cold storage material in which 30% is present and CuFe ０．９８ Al ０．０２ O ２ (8.4g) is 20% of the cold storage material, HoCu ２ A cold storage material containing 20% ​​of HoCu ２ Figure 8 shows the results of measuring the cooling capacity of a regenerator equipped with each of the regenerator materials containing 30% of CuFe, which was then mounted on a GM refrigerator. Referring to Figure 8, the first embodiment is 30% and CuFe ０．９８ Al ０．０２O ２ The cooling capacity of the thermal storage material with (8.4g) at 20% is greater than that of the thermal storage material with 30% in the first example in the temperature range of 5K or below. ２ It was found that the cooling capacity of the cold storage material containing [the specified element] approaches that of other materials.

[0071] Figure 9 shows the results of measuring the cooling capacity of a cooler equipped with a 30% cooler material according to the first embodiment, a 30% cooler material according to the second embodiment, and a 30% cooler material according to the third embodiment, after mounting them in a GM refrigerator. Referring to Figure 9, it was found that the cooling capacity of the 30% cooler material according to the second embodiment and the 30% cooler material according to the third embodiment both approached the cooling capacity of the 30% cooler material according to the first embodiment in the temperature range of 5K or below.

[0072] The first example is 30% and CuFe ０．９８ Al ０．０２ O ２ (10.4g) is 20% of the cold storage material, the second example is 30% and CuFe ０．９８ Al ０．０２ O ２ (10.4g) is 20% of the cold storage material, and the third example is 30% and CuFe ０．９８ Al ０．０２ O ２ Figure 10 shows the results of measuring the cooling capacity of a regenerator equipped with each of the regenerator materials containing 20% ​​(10.4 g) and mounted on a GM refrigerator. Referring to Figures 8 and 10, the first embodiment is 30% and CuFe ０．９８ Al ０．０２ O ２ The cooling capacity of the thermal storage material with (10.4g) at 20% is as follows in the temperature range of 5K or below: In the first example, 30% and CuFe ０．９８ Al ０．０２ O ２ It was found that the cooling capacity of the cold storage material with (8.4g) at 20% was equivalent to or greater than that of the cold storage material. Also, referring to Figure 10, the second example had 30% and CuFe ０．９８ Al ０．０２ O ２ The cooling capacity of the cold storage material in which (10.4g) is 20%, and the third example is 30% and CuFe ０．９８ Al ０．０２O ２ The cooling capacity of the thermal storage material with (10.4g) at 20% is as follows in the temperature range of 5K or below: In both cases, the first example had 30% and CuFe ０．９８ Al ０．０２ O ２ It was found that (10.4g) approaches the cooling capacity of a 20% cold storage material.

[0073] Based on the above results, the Mn(Nb) contained in the cold storage material １－ｘ Ta ｘ ) ２ O ６ In the temperature range of 5K or below, the He gas can be cooled more efficiently as the proportion of the first embodiment increases from 10%, 20%, to 30%. Furthermore, when the first embodiment is 30% and CuFe... ０．９８ Al ０．０２ O ２ The cold storage material contains Mn(Nb) at a concentration of 20%. １－ｘ Ta ｘ ) ２ O ６ and CuFe １－ｙ Al ｙ O ２ In the temperature range of 5K or below, the first embodiment can cool He gas more efficiently compared to the first embodiment, which contains 30% Mn(Nb). １－ｘ Ta ｘ ) ２ O ６ and CuFe １－ｙ Al ｙ O ２ None of these contain rare earth metals. Therefore, at least a portion of the compounds containing rare earth metals such as Ho and Er contained in the refrigerant is replaced with Mn(Nb). １－ｘ Ta ｘ ) ２ O ６ and CuFe １－ｙ Al ｙ O ２ By substituting with this, the amount of rare earth metals used in the thermal storage material can be reduced. Therefore, it has been found that the thermal storage material according to the first embodiment can reduce the amount of rare earth metals such as Ho and Er used in the thermal storage material that constitutes a cryogenic refrigerator, such as the Gifford-McMahon refrigerator.

Claims

1. Mn(Nb) １－ｘ Ta ｘ ) ２ O ６ A cold storage material for cryogenic refrigerators containing crystals (0 ≤ x ≤ 1), wherein in a temperature range of 6 K or less, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ A thermal storage material characterized by exhibiting antiferromagnetism and having a volumetric specific heat (specific heat per unit volume) greater than that of lead.

2. CuFe １－ｙ M ｙ O ２ (where M is a metal element other than Fe and other than rare earth elements, 0 ≤ y ≤ 1), the cold storage material according to claim 1, further comprising a crystal of this.

3. The thermal storage material according to claim 1 or 2, characterized in that the average value of the crystal grain size is 20 μm or more.

4. The cold storage material according to claim 3, characterized in that the particle size is 200 μm or more and 500 μm or less.

5. Mn(Nb) １－ｘ Ta ｘ ) ２ O ６ By heat-treating (0 ≤ x ≤ 1) at a temperature between 1330°C and 1544°C, Mn(Nb １－ｘ Ta ｘ ) ２ O ６ A method for producing a compound, characterized by including a heat treatment step for growing crystal grains.

6. Mn(Nb) １－ｘ Ta ｘ ) ２ O ６ A compound comprising crystals of the form (0 ≤ x ≤ 1), characterized in that it exhibits antiferromagnetism in a temperature range of 6 K or less, its volumetric specific heat (specific heat per unit volume) is greater than that of lead, and the average value of the crystal grain size is 20 μm or more.

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