JP3251093B2 - Superconductor and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel copper oxide superconductor and a method for producing the same. More specifically, the present invention relates to a copper oxide superconductor excellent in reproducibility of superconducting characteristics and a method for producing the same.

[0002]

2. Description of the Related Art After an oxide superconductor having a perovskite-type structure was discovered by Mueller et al. As a high-temperature superconductor, superconductivity was confirmed for an oxide system having a perovskite-type structure having various chemical compositions. Was done. It has been found that a substance containing mercury as a main component (Hg-Ba-R-Ca-Cu-O, R: rare earth element) also has a perovskite type structure, but superconductivity can be obtained with this type of substance. [SN Putilin and others, Materials Research Bulleti
n), Vol.26, p.1299 (1991)]. Later, it was discovered that the Hg-Ba-Cu-O compound of this system exhibited superconductivity [SN Putilin (Ptillin) et al., Nature, Vol. 362, p.226 (1993)]. .

[0003]

However, this type of perovskite-type substance containing mercury is difficult to obtain stably due to the high vapor pressure of elemental mercury. It was complicated. Therefore, it is difficult to obtain good superconducting characteristics with good reproducibility, and there has been a problem in the synthesis of the substance of this system.

[0004] The present invention provides an oxide superconductor having a more stable structure, easy synthesis, and excellent reproducibility of superconductivity, and a method for producing the same, in order to solve the above-mentioned conventional problems. Aim.

[0005] To achieve the above object, the superconductor of the present invention, main component, lead, mercury, alkaline earth element, copper, is composed of oxygen, the first superconductor of the present invention Is represented by a chemical formula in which the main component is Pb _0.5 Hg _0.5 A ₂ CuO _{4 + x} (where A represents one or more alkaline earth elements and x is a numerical value in the range of −1 <x <1). Wow, C
The perovskite layer A ₂ CuO ₄ containing uO ₆ octahedron is
One lifting sandwiched crystal structure in one atomic layer composed mainly of lead element and mercury element.

[0006] In the first superconductor , the alkaline earth element A is preferably barium (Ba).

In the second superconductor of the present invention, the main component is Pb _0.5 Hg _0.5 A ₃ Cu ₂ O _{6 + x} (where A
The element represents one or more alkaline earth elements, and x is −1 <
x <a numerical value in the range of 1), and an oxygen-deficient perovskite layer A ₃ Cu ₂ O ₆ including two CuO ₅ pyramids facing each other via one atomic layer of the element A,
One lifting sandwiched crystal structure in one atomic layer composed mainly of lead element and mercury element.

[0008] In the second superconductor , the alkaline earth element A is a combination of barium and calcium, and Pb
It is preferably represented by a chemical formula of _0.5 Hg _0.5 Ba ₂ CaCu ₂ O _{6 + x} .

In the second superconductor , the alkaline earth element A is a combination of strontium and calcium, and is preferably represented by a chemical formula of Pb _0.5 Hg _0.5 Sr ₂ CaCu ₂ O _{6 + x} .

Next, the method for manufacturing a superconductor according to the present invention comprises the steps of alternately forming a monoatomic layer containing lead and mercury as main components and a perovskite oxide layer containing an alkaline earth element and copper by a molecular deposition method. It has a configuration in which the layers are stacked to form a molecular stack.

[0011]

The perovskite type oxide containing mercury (Hg-Ba-R-Ca-Cu-O compound or H
g-Ba-Cu-O superconductor) is considered to have a structure in which a layer having a perovskite structure is interposed between elemental mercury or one atomic layer obtained by adding oxygen thereto. Since mercury has a low melting point and a high vapor pressure, it is presumed that it is not easy to stably obtain the above structure.

The present invention relates to a perovskite-type oxide comprising lead, mercury, an alkaline earth element and copper, which has a perovskite structure layer in which a mercury and lead element or one atomic layer obtained by adding oxygen thereto is interposed. Conceivable. In other words, by introducing lead in addition to mercury into the atomic layers sandwiching the perovskite layer, the structure became more stable and the synthesis became easier. Therefore, the reproducibility of the superconductivity was also improved by simultaneously containing lead in addition to mercury as in the present invention.

Although it has been found that this structure is particularly easy to fabricate in the form of a thin film, alternate lamination of a lead and mercury layer and an alkaline earth element and copper perovskite oxide layer is very effective. Was. Several methods have been used to fabricate oxide superconductors by the lamination method.However, the composition of the layers differs depending on the material. There is a need to. The present inventors have studied various lamination methods for the novel superconductor of the present invention, and have confirmed that if the perovskite layer and the layers of lead and mercury are alternately laminated, fabrication can be performed with good reproducibility. did.

[0014]

【Example】

Example 1 A thin film of the superconductor of this example was produced by a binary sputtering apparatus shown in FIG. One of the targets was a disk-shaped target 11 obtained by mixing mercury oxide and lead oxide, and the other was a sintered disk target 12 of Ba ₂ CuO ₃ . The substrate 13 was a MgO single crystal (100) plane. A shutter 14 is disposed between the target and the substrate, and one of the targets is selected by this rotation to perform sputter deposition. Sputtering was performed in an atmosphere of 3 Pa of argon gas, and lamination was performed alternately on a substrate heated to 550 ° C. by a heater 15 by performing shutter control. It was found that when the rotation of the shutter was controlled to deposit just one atomic layer mainly composed of lead and mercury and one monolayer of perovskite oxide of Ba and Cu, a layered compound having a perovskite type structure was obtained. Was. Perovskite-type structural materials were sometimes obtained even when components of two targets were simultaneously deposited without using a shutter, but the reproducibility was much lower. As a result of detailed analysis of this compound, it was found that the chemical composition was about Pb _0.5 Hg _0.5 Ba ₂ CuO _{4 + x} (1 <x <1), and that the crystal structure had the structure shown in FIG. That is, a layer 23 having a perovskite structure composed of a CuO ₆ octahedron 21 and a Ba element 22 is made of a 1 layer composed of mercury and lead element.
It is considered that the structure has an atomic layer 24 interposed therebetween. The electric resistivity of the perovskite-type compound thus prepared was as low as 1 mΩcm at room temperature, and exhibited a resistance drop at 80 Kelvin at a low temperature which was considered to be due to a superconducting transition. That is, it was confirmed that Pb _0.5 Hg _0.5 Ba ₂ CuO _{4 + x} was a new superconductor. Note that, although sputtering has been described as an example here, it is needless to say that the film can be similarly formed by using a molecular beam epitaxy method, a heating evaporation method, or the like.

Example 2 Using a similar apparatus, a target of mercury oxide and lead oxide was
Lamination by sputtering was performed using a target of Sr ₂ CaCu ₂ O ₅ . The period of the alternate lamination is just one atomic layer composed mainly of lead and mercury, and Sr, Ca
And a Cu perovskite oxide bilayer was deposited to obtain a layered compound having a perovskite-type structure with a longer axial length than in the previous example. As a result of detailed analysis of this compound, the chemical composition was found to be about Pb _0.5 Hg _0.5 Sr ₂ C
aCu ₂ O _{6 + x} (1 <x <1), and the crystal structure is shown in FIG.
The structure shown in FIG. That is, a structure is adopted in which an oxygen-deficient perovskite layer 34 composed of two CuO ₅ pyramids 32 and an Sr element 33 facing each other via a Ca element atomic layer 31 is sandwiched by a 1 atomic layer 24 composed of mercury and lead elements. When the temperature change of the electric resistivity of this compound was measured, a resistance drop at about 90 Kelvin, which was considered to be caused by the superconducting transition, was observed. That is, Pb _0.5 Hg
_0.5 Sr ₂ CaCu ₂ O _{6 + x} was confirmed to be a new superconductor.

In this embodiment, Sr and Ca are used as a combination of alkaline earth elements. However, it is a matter of course that a superconductor can be produced with other combinations of alkaline earth elements.
It is easily presumed that a perovskite-type structure in which the molecular unit of the perovskite layer is composed of three or more molecular layers also becomes a superconductor.

[0017]

As described above, the superconductor of the present invention realizes a novel substance which can be synthesized with good reproducibility and a method for producing the same in an oxide superconductor containing mercury. As a result, an oxide superconductor containing mercury can be obtained stably, and practical use can be expected. In particular, the substance containing mercury has a relatively simple crystal structure, and is therefore suitable for thinning. Therefore, the present invention provides a promising superconducting material for device application, and the industrial value of the present invention is great.

[Brief description of the drawings]

FIG. 1 is a diagram of an apparatus for manufacturing a superconductor according to one embodiment of the present invention.

FIG. 2 shows Pb _0.5 Hg produced in one example of the present invention.
FIG. 3 is a crystal structure diagram of a _0.5 Ba ₂ CuO _{4 + x} thin film.

FIG. 3 shows Pb _0.5 Hg produced in one example of the present invention.
FIG. 3 is a crystal structure diagram of a _0.5 Sr ₂ CaCu ₂ O _{6 + x} thin film.

[Explanation of symbols]

11 oxides of mercury and lead target 12 Ba ₂ CuO ₃ target 13 MgO substrate 14 shutter 15 heater 21 CuO ₆ 8 tetrahedral blocking layer 22 Ba element 23 perovskite structure 1 atomic layer of the layer 24 mercury and lead 31 Ca element 1 atomic layer 32 CuO ₅ pyramid 33 Sr element 34 Oxygen deficient perovskite layer

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Claims (6)

(57) [Claims] The main component is Pb _0.5 Hg _0.5 A ₂ CuO.
_{4 + x} (where A represents one or more kinds of alkaline earth elements, x is represented by a chemical formula of -1 <x <1), and a perovskite layer A ₂ containing CuO ₆ octahedron C
uO ₄ is, one lifting the crystalline structure sandwiched by one atomic layer composed mainly of lead element and mercury element superconductor. 2. The method according to claim 1, wherein the alkaline earth element A is barium (B
The superconductor according to claim 1 , which is a). 3. The method according to claim 1, wherein the main component is Pb _0.5 Hg _0.5 A ₃ Cu ₂
O _{6 + x} (where A represents one or more alkaline earth elements, and x is represented by a chemical formula of −1 <x <1), and is represented by one atomic layer of A An oxygen-deficient perovskite layer A ₃ Cu ₂ O ₆ including two opposing pyramids of CuO ₅ is composed of one element mainly composed of lead element and mercury element.
Superconductor single lifting sandwiched crystal structure at the atomic layer. 4. An alkaline earth element A comprising a combination of barium and calcium, wherein Pb _0.5 Hg _0.5 Ba ₂ CaC
superconductor according to claim 3 represented by u ₂ O 6 _{+ x} becomes formula. 5. The method according to claim 1, wherein the alkaline earth element A is a combination of strontium and calcium, and Pb _0.5 Hg _0.5 Sr _2.
Superconductor according to CaCu ₂ O 6 _{+ x} becomes claim 3 represented by the chemical formula. 6. A superatomic layer in which a monoatomic layer mainly composed of lead and mercury and a perovskite oxide layer composed of an alkaline earth element and copper are alternately laminated by a molecular deposition method to form a molecular laminate. Conductor manufacturing method.