JP2525855B2 - Superconducting material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a superconducting member. More specifically, it relates to the structure of a novel superconducting member that exhibits a higher superconducting critical temperature.

Conventional technology Under the superconducting phenomenon, a substance shows complete diamagnetism, and the potential difference disappears even though a finite steady current flows inside. Therefore, various applications have been proposed for a superconductor as a transmission medium having no power loss.

That is, MHD power generation, power transmission, power storage and other power fields,
Alternatively, power fields such as magnetic levitation trains and electromagnetic propulsion vessels,
Furthermore, as ultra-sensitive sensors for magnetic fields, microwaves, radiation, etc., there are numerous fields of application, such as the fields of measurement such as NMR, pion therapy, and high energy physics experimental equipment.

Also, in the field of electronics represented by Josephson devices, it is expected as a technology that can realize not only simple power consumption but also extremely high-speed operation.

By the way, the superconducting phenomenon has been observed only under ultra-low temperature. Even Nb ₃ Ge, which is said to have the highest superconducting critical temperature Tc as a conventional superconducting material, remained at 23.2K.

Therefore, conventionally, in order to realize the superconducting phenomenon, liquid helium having a boiling point of 4.2K was used to cool the superconducting material to Tc or lower. However, the use of liquid helium has
The technical burden and cost burden of the cooling equipment including the liquefaction equipment were extremely large, which hindered the practical application of the superconducting technology.

On the other hand, it has been reported in recent years that a sintered body containing an oxide of a group IIa element or a group IIIa element can be a superconductor having a high Tc, and practical application of the superconducting technology by a non-low temperature superconductor is expected. Is being promoted.

In the previously reported example, it is considered that the crystal structure is similar to that of the perovskite type oxide [La, Ba] ₂ Cu.
Examples thereof include K ₂ NiF ₄ type oxides such as O ₄ or [La, Sr] ₂ CuO ₄ . With these substances, a _{Tc of} 30 to 50 K, which is dramatically higher than in the past, was observed, and it is being sought to realize a higher critical temperature.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, since these superconducting materials can be obtained as a sintered body, they are generally fragile and must be handled with care. That is, in order to be easily damaged by a mechanical load, or to have mechanical strength, it is necessary to mold into a size larger than necessary.

Further, although it is known that these substances exhibit a higher Tc when stress is applied, it has been difficult to keep the stress applied to the superconducting material in actual use.

Then, the objective of this invention is solving the subject of the said prior art, and providing the novel superconducting material which can use the superconducting material which has high Tc on more advantageous conditions.

Means for Solving the Problems That is, according to the present invention, a general formula: A _w B _x C _y D _z [where A is one kind selected from Group IIa and IIIa elements of the periodic table, and B is It is one kind selected from the elements including the same elements as A in the group IIa and IIIa of the periodic table, and C is one selected from the group Ib, IIb, IIIb and VIIIa elements of the periodic table. And D is O (oxygen), w, x, and y are positive numbers of 1 or less, and z is a number of 1 or more and 5 or less], or a perovskite type or pseudo On a substrate having a coefficient of thermal expansion larger than that of a perovskite-type complex oxide-based superconducting material and having a undulation on the surface, at a temperature higher than the critical superconducting temperature of the superconducting material, at least by the undulation. The superconducting material layer is formed so as to cover the bottom surface of the formed recess. A superconducting material is provided.

Here, the substrate can be formed of, for example, Au, Cu, or stainless steel. The superconducting material according to claim 1, which is a characteristic.

According to one aspect of the present invention, the substrate preferably has, for example, a recess having a depth of 1 μm and a width of 2 μm. Further, the superconducting material layer may be formed on the entire surface of the substrate.

According to one embodiment of the present invention, the superconducting material layer is
It can be formed on the substrate by a sputtering method.

Further, according to a preferred embodiment of the present invention, it is advantageous that the surface of the substrate is previously coated with a material having high adhesiveness to a perovskite type or pseudo perovskite type oxide superconducting material. It is also preferable that the surface of the substrate is previously coated with a material that is stable with respect to a perovskite-type or pseudo-perovskite-type oxide superconducting material.

Action The present invention was made based on the finding that a superconductor made of a perovskite-type or pseudo-perovskite-type oxide exhibits excellent superconducting properties particularly under compressive stress.

That is, the present inventors, based on the above findings, as a result of various studies on the composition of the superconducting material such that the stress acts on the perovskite or the pseudo-perovskite oxide in the use state, and the appropriate shape and the coefficient of thermal expansion are provided. It was concluded that it is advantageous to utilize the heat shrinkage of the substrate.

That is, when undulations are formed on the surface of the substrate made of a material having a higher coefficient of thermal expansion than the superconducting material, and a layer of a superconductor made of a perovskite type or pseudo perovskite type oxide is formed on the bottom surface of the concave portion, the formation of the superconducting material layer The substrate shrinks due to the temperature drop from room temperature to room temperature and the temperature drop caused by cooling the superconducting material to the superconducting critical temperature. At this time, stress acts on the superconducting material film due to the undulations of the substrate surface. Therefore, in the superconducting material configured as described above, stress is always applied to the superconducting material, especially during cooling and in the superconducting state. As a result, this superconducting material layer is kept at a high critical temperature.

In view of such an action, it is essential that the undulation of the substrate surface in the present invention is a shape in which stress acts on the superconducting material layer formed on the substrate. However, in this case, a plane perpendicular to the substrate surface is not necessarily required, and specifically, a width of 2 μm and a depth of 1 μm.
It suffices if a recess or groove of about m is formed.

In such a superconducting material according to the present invention, it is also preferable to previously coat the surface of the substrate with a material having high adhesiveness to the perovskite type or pseudo perovskite type oxide. It is also preferable to coat the surface of the substrate with a material that is chemically stable with respect to the perovskite type or pseudo perovskite type oxide. From a comprehensive judgment from these viewpoints, for example, it is preferable to coat the substrate surface of Cu, stainless steel, or the like with Au, Pt, or the like.

Hereinafter, the present invention will be described in more detail with reference to the drawings. However, what is disclosed below is only one embodiment of the present invention,
It does not limit the technical scope of the present invention.

Example FIG. 1 is a sectional view showing the structure of a superconducting material according to the present invention. A plurality of recesses are formed on the surface of the substrate 1, and a superconducting material layer 2 is further formed on the entire surface of the substrate including the recesses.

Substrate 1 is made of Cu and has Au on its surface.
Film has been previously deposited. The recess formed on the surface of the substrate 1 is a parallel groove having a depth of about 1 μm and a width of about 2 μm.

The superconducting material layer 2 was formed as follows. First,
Ba ₂ CO ₃ , Y ₂ CO ₃ , and CuO powders were mixed so that the atomic ratio Ba: Y: Cu was 2: 1: 3, molded, and then pre-sintered at 820 ° C, crushed and molded. Further, main sintering was performed at 1080 ° C. to obtain a sintered block. Using this block as a target, a thin film was formed on the above-mentioned substrate by the sputtering method. The film forming conditions are as follows.

Oxygen partial pressure 4 × 10 ^-2 Torr, Ar partial pressure 3 × 10 ^-2 Torr, substrate temperature 700 ° C, substrate bias voltage -60V, high frequency power 25W / cm ² , deposition rate 0.5 Å / sec, superconductivity Material layer is about 1μ
The film was formed to a thickness of m. For comparison, under the same other conditions, a flat Au-coated Cu substrate on which a thin film having a thickness of 1 μm was formed was also manufactured.

Next, in order to measure the resistance of each of the obtained thin films, a pair of Au electrodes was further formed on both ends of the thin films by vacuum vapor deposition, and lead wires were soldered to the Au electrodes.

When the superconducting critical temperature was measured for each sample in this manner, the sample produced according to the present invention showed that the Tcf was 60 ° C. and Tc was higher than that of the sintered superconducting material used as the target.
Was improved by 85 ° C. This means that not only Tc has risen, but also the difference ΔT between Tc and Tcf has become smaller.

Effects of the Invention As described above in detail, the superconducting material according to the present invention is always subjected to compressive stress on the superconducting material in a use state, and originally has a high Tc perovskite type or pseudo perovskite type oxide, It can be used in the high Tc state.

Thus, according to the present invention, since a superconducting material having a high and stable Tc can be obtained, as a wire rod or a small part,
The superconducting material can be widely applied.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a superconducting material according to the present invention. [Main reference numbers] 1 ... Substrate, 2 ... Superconducting material layer

(72) Inventor Saburo Tanaka 1-1-1 Kunyokita, Itami City, Hyogo Prefecture Sumitomo Electric Industries, Ltd. Itami Works (72) Inventor Shuji Yazu 1-1-1 Kunyokita, Itami City, Hyogo Prefecture No. 1 Sumitomo Electric Industries, Ltd. Itami Works (72) Inventor Tetsuji Kamishiro 1-1-1 Kunyokita, Itami City, Hyogo Prefecture Sumitomo Electric Industries Itami Works (56) Reference JP-A-63-236218 (JP, A)

Claims (1)

(57) [Claims] 1. A general formula: A _w B _x C _y D _z [wherein A is one element selected from Group IIa and Group IIIa of the Periodic Table, and B is Group IIa and IIIa of the Periodic Table]. It is one selected from the group of elements including the same as A, C is one selected from Group Ib, IIb, IIIb and VIIIa elements of the periodic table, and D is O ( Oxygen), w, x and y are positive numbers less than or equal to 1 and z is a number greater than or equal to 1 and less than or equal to 5]], or a perovskite-type or pseudo-perovskite-type complex oxide-based superconducting material On a substrate formed of a material having a larger coefficient of thermal expansion and undulations on the surface, at least the bottom surface of the recess formed by the undulations is covered at a temperature higher than the superconducting critical temperature of the superconducting material. A superconducting material comprising the superconducting material layer formed as described above.