JP7822594B2 - Method for producing conductive diamagnetic material and conductive diamagnetic material - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act. The application of Article 30, Paragraph 2 of the Patent Act was announced in a news release by Kyushu Institute of Technology on August 23, 2021, titled "Discovery of the 54th superconducting phenomenon in a single element metal - First successful magnetic measurement of samarium under high pressure."

Application of Article 30, Paragraph 2 of the Patent Act. Published in Physical Review B, Vol. 104, No. 5, 054431 (2021) on August 23, 2021, as "High-pressure magnetic properties of antiferromagnetic samarium up to 30 GPa using a SQUID-based vibrating coil magnetometer."

The present invention relates to a method for producing a conductive diamagnetic material and to a conductive diamagnetic material.

Although conductive materials, including superconducting materials, have been developed in a variety of material systems, industrial applications of superconducting materials have remained limited. The reasons for this include: (1) the superconducting transition temperature (Tc) at atmospheric pressure is low, at most 130 K (see Non-Patent Document 1), so superconducting properties can only be exhibited in cryogenic environments; (2) the difficulty of producing wire rods has prevented widespread use in power transmission lines and coils, which are considered important application areas; and (3) the inhomogeneous structure and texture of the material make it difficult to produce thin films, requiring advanced processing techniques to create devices.

Bismuth-based copper oxide superconductors with a superconducting transition temperature of approximately 120 K have been known for use in superconducting cables (Non-Patent Document 2). Figure 4 shows an example of the structure of a conventional superconducting cable. Figure 4(a) is a diagram illustrating a cross-section of a superconducting cable. Figure 4(b) is a diagram illustrating a perspective view of a cable core. Figure 4(c) is a diagram illustrating a cross-section of the conductor layer of a cable core. A cable with the structure shown in Figure 4 is known as a three-core superconducting cable, and is expected to be used in situations requiring low voltage and high current.

Referring to Figure 4(a), a conventional superconducting cable 101 has a multi-layer structure. From the outside, these layers are a corrosion protection layer 103, a corrugated outer tube 105, a heat insulating layer 107, and a corrugated inner tube 109. A three-core cable core 111 is housed within the corrugated inner tube 109, and liquid nitrogen 113 is filled between the corrugated inner tube 109 and the cable core 111. From the outside, the cable core is composed of a protective layer, a shield layer (superconducting layer), an insulating layer (PPLP), a conductor layer (superconducting layer), and a former. Furthermore, the wire that forms the conductor layer is a superconducting filament Bi2223, a bismuth-based copper oxide superconductor, housed within silver.

The structure of the cable core 111 will be described with reference to Figure 4(b). The cable core 111 comprises, from the outside in, a protective layer 121, a shielding layer 123, an insulating layer 125, a conductor layer 127, and a former 129, arranged concentrically. The shielding layer 123 is in a superconducting state. The insulating layer 125 is made of PPLP (registered trademark, Polypropylene Laminated Paper) impregnated with liquid nitrogen. The conductor layer 127 is made by winding a Bi2223 wire 131 around a former 129. The former 129 is made of twisted copper wire.

The structure of the Bi2223 wire 131 will be described with reference to Figure 4(c). The Bi2223 wire 131 has a structure in which multiple superconducting filaments 135 are housed inside a silver wire 133.

Figure 5 also illustrates the production process for Bi2223 wire 131, which is part of the cable core 111. This process primarily consists of a powdering process ST101, in which the material is powdered, and a processing process ST103, in which the powder is turned into wire. First, in the powdering process ST101, the material is repeatedly sintered (ST105) and crushed (ST107). Next, in the processing process ST103, the precursor powder is first filled into a silver pipe for the segments (ST109) and subjected to single-filament wire drawing (ST111). Multiple strands of this wire are fitted into the holes of the silver pipe for the outer sheath (ST113). Further multi-filament wire drawing (ST115) is performed, followed by rolling and incineration (primary rolling ST117 and primary incineration ST119). This wire is further rolled and incinerated (secondary rolling ST121 and secondary incineration ST123) to produce Bi2223 wire 131, which will form the conductor layer of the cable core.

A. Schilling et al., Nature (London) 363, 56 (1993). H. Maeda et al.,Jpn. J. Appl. Phys. 27, L209 (1988).

However, the superconducting cable described in Patent Document 1 has a complex structure that is manufactured through the process described above. As a result, it is very costly to produce wire and its range of applications is limited.

The present invention therefore aims to provide a method for producing conductive materials that is expected to produce superconducting materials that are more suitable for industrial applications than conventional methods.

A first aspect of the present invention is a method for producing a conductive diamagnetic material, which includes a low-pressure heating step of heating samarium in a low-pressure environment.

A second aspect of the present invention is a method for producing an electrically conductive diamagnetic material according to the first aspect, in which the samarium is heated to 200°C or higher in the low-pressure heating step.

In a third aspect of the present invention, in the low-pressure heating step, samarium is heated at a low pressure of a vacuum of 2×10 ⁻² [Torr] or more.

A fourth aspect of the present invention is a conductive diamagnetic material, characterized in that at least a portion of the laminated structure is samarium, which has a hexagonal close-packed structure.

In addition to the above, power transmission lines, magnetic shields, electronic devices, or devices utilizing the magnetic levitation phenomenon using the conductive material of the third aspect of the present invention are also contemplated as aspects of the present invention.

Each aspect of the present invention makes it possible to provide a conductive diamagnetic material that is expected to achieve a maximum superconducting transition temperature of 165 K, exceeding the 120 K of bismuth-based copper oxide superconductors and the 130 K of mercury-based copper oxide superconductors known as conventional superconducting cables. If it becomes possible to provide a material that exhibits superconducting properties more easily than ever before under atmospheric pressure, it will be possible to expand the industrial application fields of superconducting materials.

Furthermore, according to each aspect of the present invention, it is expected that metal materials with a simple composition consisting of a single element can be provided as high-temperature superconducting materials. As a result, they can be easily made into wires or thin films without undergoing the complicated processes used in the past. Therefore, it is expected that superconducting cables, superconducting coils, superconducting devices, etc. can be provided at low cost.

The inventors have discovered that samarium, which was previously not considered a superconducting substance, exhibits superconductivity under high-pressure environments of 200,000 atmospheres. However, this invention provides samarium as a superconducting material that can exist under atmospheric pressure, and is therefore expected to provide an even more groundbreaking superconducting material.

10A and 10B are diagrams illustrating the temperature dependence and external magnetic field strength dependence of the magnetization of the sample of this example. 2A and 2B are diagrams showing measurement results of other characteristics of the sample of FIG. 1. FIG. 10 is a diagram showing the dependence of magnetization per unit weight of a sample on the annealing temperature during sample preparation. FIG. 1 is a diagram showing an example of the structure of a conventional superconducting cable. 1 is a diagram illustrating a part of a conventional superconducting cable production process.

Embodiments of the present invention will be described in detail below with reference to the drawings. Note that the examples of the present invention are not limited to the content described below.

In this example, the samples to be measured were prepared by heating samarium in a low-pressure environment (an example of the "low-pressure heating step" in this claim). Specific sample preparation conditions are shown in Table 1. The pressure at which all samples were sealed in the glass tube was a vacuum of 2× ^10-2 [Torr] or more. Table 1 also lists the value of the slight remaining magnetic field M [emu/g]@H=1 [Oe] when set to 0 [Oe].

To analyze the prepared samples, superconductivity was detected by magnetic measurement. Specifically, a Superconducting Quantum Interference Device (SQUID) magnetometer was used to observe the magnetization M under a DC magnetic field. The analytical results of the prepared samples are described below.

Figure 1 illustrates the temperature and external magnetic field dependence of the magnetization M of the sample in this example. Figure 1(a) shows the measurement results when the external magnetic field strength H was set to 50 to 20 kOe, and Figure 1(b) shows the measurement results when the external magnetic field strength H was set to 1 to 400 Oe. The horizontal axis represents the measurement temperature (K), and the vertical axis represents the magnetization M (emu). Measurements were performed after zero-field cooling (ZFC) from 250 K. The sample used for measurements in Figure 1 was prepared by heating to 578 °C and annealing for 1.5 hours in a low-pressure environment with a vacuum of 2 × 10 ^-2 Torr or higher.

As shown in Figure 1(a), at an external magnetic field strength H=50 Oe, M is nearly equal to 0 in the temperature range below Tc, which suggests the superconducting transition temperature, and above approximately 120 K, indicating that most of the samples exhibit perfect diamagnetism, a characteristic of superconductivity. In contrast, as the magnetic field strength increases, the cubic site anomaly near 15 K becomes larger. The hexagonal site anomaly near 110 K also becomes larger. Furthermore, the temperature range in which diamagnetism is exhibited narrows. While there is a temperature range in which diamagnetism is exhibited below an external magnetic field strength H=3 kOe, at an external magnetic field strength H=4 kOe, the value of M at T<120 K is larger than the value at 120 K, and the temperature range in which diamagnetism is exhibited disappears.

Figure 1(b) also shows anomalies near T=5, 14, and 20 K. The sample weighed 155.5 mg. The magnetization M at an external magnetic field strength H=1 Oe was 7×10 ^-3 emu, or 4.5×10 ^-2 emu/g. Furthermore, as shown in Figure 1(c), when the temperature dependence of the magnetization M at an external magnetic field strength H=1 Oe was extensively investigated, signals suggesting superconducting properties were also observed at T=135 K and 165 K.

Figure 2 shows the measurement results of other characteristics of the sample in Figure 1. Figure 2(a) shows the relationship between the external magnetic field strength H and the temperature Tc, which is suggested to be the superconducting transition temperature. Figure 2(b) shows the DC magnetic field dependence of the magnetization M of the sample in Figure 1.

2(a), we can see that the magnetic field dependence is different in the range below H = 3 × 10 ³ [Oe] and the range above H = 3 × 10 ³ [Oe]. This H dependence of Tc is characteristic of superconductors, and the region where H ≤ 3 × 10 ³ [Oe] indicates the existence of the diamagnetic region.

2(b), the magnetization M reaches its minimum value near a DC magnetic field H _DC =30 [Oe]. This is a characteristic of type II superconductors, and the measurement results suggest that the sample of this example is a type II superconductor with a lower critical magnetic field H _c1 of ∼30 [Oe].

Furthermore, based on the measurement results of other samples according to the present invention, we will discuss the annealing temperature and the behavior that appears to be superconducting. Figure 3 shows the dependence of the magnetization per unit weight ΔM [emu/g] on the annealing temperature T _anneal [K] during sample preparation.

3, the sample with an annealing temperature of T _anneal =578°C had a main Tc of 120 K, which was not the highest among the samples tested, but had the largest magnitude of the magnetic shielding effect ΔM. Also, the sample with an annealing temperature of T _anneal =500°C had a Tc of 165 K, the highest Tc value among the samples tested.

Furthermore, as shown in Figure 3 and Table 1, diamagnetism was confirmed when the sample was annealed at a temperature of 200°C or higher, but to increase the probability of observing diamagnetism of 1 x ^10-3 emu/g or higher, it is preferable that the sample be annealed at a temperature of 400°C or higher.

This invention provides a versatile superconducting material, which can contribute to technological innovation in technological fields where the use of superconductivity is expected, such as power transmission lines, coils, and magnetic levitation.

If the material used in this example is a material in which superconducting layers and magnetic layers are alternately stacked, it could be used in superconducting device elements that utilize the Josephson effect, in which tunnel current flows between superconducting layers sandwiching a very thin layer of about a few nanometers, or as a magnetic shield. Furthermore, by processing the material to extract only the superconducting layer, it could be used in superconducting power lines, etc.

Claims (2)

1. A method for producing an electrically conductive diamagnetic material, comprising:
A low-pressure heating step is included in which samarium is heated at 200°C or higher in a low-pressure environment with a vacuum of 2 x 10 ^-2 [Torr] or higher.
Method for producing conductive diamagnetic materials. An electrically conductive diamagnetic material,
A conductive diamagnetic material, characterized in that at least a part of the laminated structure is samarium with a hexagonal close-packed structure.