JPH03112813A - Superconductor - Google Patents

Abstract

PURPOSE:To provide a superconductor having electron as a charge carrier, high zero resistance-superconducting transition temperature and high current density in magnetic field, comprising La, etc., sr or (and) Ca, Cu, O and F in a specific atomic ratio. CONSTITUTION:This superconductor has a composition shown by formula I. With the proviso that in the formula I, alpha is at least one element selected from La, Nd, Sm, Eu and Gd and beta is Sr and(or) Ca. Further 1.8<eta<2.1, 0.9<theta<2.2, 5<gamma<6.4, 0.1<delta<1.2. Compounds shown by formula Il, formula III, etc., may be cited as the concrete example of the superconductor. The superconductor is produced by weighing each powder of La2O3, LaF3, SrCO3, CuO, etc., in a given ratio, mixing, grinding, calcining, further grinding, molding and calcining. The superconductor has a structure wherein two units of pyramid structure of coordinating oxygen around copper in a unit lattice are included and the pyramid type units are arranged with opposing the bottoms with an alkaline earth metal between.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention is applicable to nuclear fusion reactors, magnetohydrodynamic generators, accelerators, rotating electrical equipment (electric motors, generators, etc.), magnetic separators, magnetic levitation trains, nuclear magnetic Suitable as a material for magnet coils in resonance measurement devices, magnetic propulsion vessels, electron beam exposure devices, etc. Also suitable for applications where power loss is a problem such as power transmission lines, electrical energy storage devices, transformers, rectifiers, etc. Song Motoko,
The present invention relates to a superconductor suitable as various elements such as a 5QUID element and a superconducting transistor, and further suitable as an infrared detection material, a magnetic shielding material, etc.

(Prior Art) As a superconductor having a high superconducting transition temperature, there is a -4 copper composite oxide superconductor. The charge carriers of superconducting current in these series of copper complex oxide superconductors are (Nd, C
e) Except for 2 CuO4 and Nd2Cu 04-J F g, all of them are holes. However, when the charge carrier is a hole, the coherence length becomes short, and superconducting properties such as critical current density in a magnetic field are not good. On the other hand, the superconductors mentioned above have electrons as charge carriers, have a long coherence length, and are expected to have high superconducting properties such as critical current density in a magnetic field, but the zero-resistance superconducting transition temperature is about 20 Very low.

(Problems to be Solved by the Invention) An object of the present invention is to provide a superconductor whose charge carriers are electrons and which has a high zero-resistance superconducting transition temperature.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a superconductor represented by the following general formula.

α, βe Cu20. F4 However, a: At least one element selected from LaXNdXSmXEu and Gd β At least one element selected from Sr and Ca 1.8<η<2.1 0.9<θ<2.2 5 .0〈γ＜6.3 0.1〈δ〈1.2 The superconductor of the present invention is structurally similar to a series of copper complex oxide superconductors, and contains Cu in the unit cell. It contains two units of a pyramid structure in which five O atoms are coordinated around the Cu(!: Furthermore, each unit cell is C
O at the apex of the pyramid and the rare earth element (α) are piled up in the axial direction (perpendicular to the bottom of the pyramid) forming a rock salt structure. Then, rare earth elements are
The alkaline earth metal element can be selected and used from LaXNd, SmXEu and Gd, and Ca and Sr, respectively. One type of these may be selected and used, or two or more types may be selected and used in an arbitrary mixing ratio. Further, a single phase with this crystal structure is obtained only when the ratio of rare earth elements, alkaline earth elements, and Cu is within a certain range. That is, in the general formula representing the superconductor of this invention, when η and θ are outside the above range,
The crystal structure becomes a different crystal system, and other impurity phases (insulators) often coexist.

Now, in a series of cuprate-based superconductors whose charge carriers are holes, the critical current density decreases significantly in a magnetic field. this is,
For one thing, these copper composite oxide-based superconductors are often polycrystalline, and there are weak superconducting bonds in the insulating parts of the grain boundaries that are easily destroyed by externally applied magnetic fields. This is to do so. Another reason is that the coherence length is short because the charge carriers that carry the superconducting current are holes. The superconductor of this invention has a long coherence length because the charge carriers are electrons. This is because electrons can be injected by substituting F with part of oxygen during the solid phase reaction, disrupting the charge balance of the entire crystal and making electrons the charge carriers. That is, since oxygen is a divalent anion and F is a monovalent anion, when one atom of O is replaced by one atom of F, one electron is injected.

On the other hand, it is known that in order for a superconducting state to occur, when the charge carriers are electrons, the electron concentration must be within a certain range. This range is from 1.7 to 1.0 when the total amount of charge in the crystal is converted to the average valence of Cu.
It is 8. The range of γ and δ in the superconductor of this invention is determined in relation to this range of electron concentration. However, since the rare earth element (α) is a trivalent cation and the alkaline earth element (β) is a divalent cation, the concentration of charge carriers in the crystal slightly depends on the values of η and θ. do. Also, the fact that F can replace oxygen in the crystal structure means that
This also means that the ionic radii of both are almost the same, which can be easily estimated from this.

Now, it is becoming clear from a phenomenological perspective that the superconducting transition temperature seems to increase in proportion to the number of units consisting of Cu and O in a unit cell. The above-mentioned conventional superconductor whose charge carriers are electrons is estimated to have a low superconducting transition temperature because it contains only one unit consisting of Cu and 0 in the unit cell. On the other hand, in the superconductor of this invention, there are two units consisting of Cu and O.
Superconductors whose charge carriers are electrons can achieve the highest superconducting transition temperature.

The superconductor of the present invention can be used in various forms such as tape, line, fiber, and sheet. It can also be formed on a reinforcing wire made of carbon fiber, ceramics, or metal such as silver. It can also be used by being stuffed into a reinforcing hollow material such as a silver sheath. Furthermore, a superconducting wire with a multifilamentary wire structure can also be made using a matrix of copper or the like. Also, Si, M
Formed as a thin film on a substrate such as gO1LaGa03,
It can be used for wiring of various elements or LSI.

The superconductor of this invention can be manufactured by various methods.

For example, a so-called powder mixing method can be used. In this method, oxides of component elements, their precursors (carbonates, nitrates, etc.), and fluoride powders are mixed in the desired proportions, fired at a temperature below the sintering temperature, and then crushed and mixed. This is a method in which the material is molded into a desired shape and then fired. In addition, methods for forming thin films include well-known various evaporation methods such as electron beam evaporation and laser evaporation, various sputtering methods such as magnetron sputtering, and chemical vapor deposition using halides, organic metals, etc. There are growth methods, atomization methods using nitrates, organic acid salts, etc., and coating methods using alkoxides.

In addition, the superconductor of this invention is easier to increase the number of charge carriers in the crystal, that is, the number of electrons to be injected, when oxygen vacancies are generated. Preferably, heat treatment is performed.

(Example) Example 1 Each powder of La2O3, LaF3, SrCO3, and CuO was prepared with a ratio of La:Sr:Cu:F of 1.9:1°1:2:0.8
After crushing and mixing in an agate mortar, place in an Al2O3 container and heat at 950℃ in air for 12 hours.
Baked for an hour. Thereafter, it was crushed again in an agate mortar, formed into a pellet, fired in air at 1025°C for 24 hours, and then rapidly cooled in liquid nitrogen at a rate of about 000°C/sec.

The obtained superconductor was heated at room temperature and liquid nitrogen temperature (77K
), the carriers were electrons. In addition, when the composition was analyzed using an electron beam microanalyzer, it was found that La19S rl, I Cu2O3,
It was 4Fo, 6. Furthermore, when the electrical resistance was measured by the four-terminal method, the resistance became zero at 29. In addition, when the superconducting volume fraction of the powder sample was measured by the AC magnetic susceptibility measurement method, it was found to be 4.2 and about 32%.

Furthermore, in Section 4.2, when we measured the critical current density under zero magnetic field, it was approximately 930 A/cm2, and even in a 0.1 T (Tesler) magnetic field it was 790 A/cm2, so the decrease in critical current density due to external magnetic field is It was small.

Example 2 Eu203, Gd2O3, EuF3, CaCO3, Cu
Each powder of O was mixed with Eu:Gd:Ca:Cu:F of 1.2:
The mixture was measured to have a ratio of 0.6:1.2:2:1.1, crushed and mixed in an agate mortar, placed in an Al2O3 container, and fired at 950°C in air for 12 hours. Thereafter, it was crushed again in an agate mortar, formed into pellets, fired in air at 1050°C for 48 hours, and then rapidly cooled in liquid nitrogen at a rate of about 000°C/sec.

The carriers of the obtained superconductor are electrons, and the composition is as follows:
Eul, 2 Gdn6Ca1.2 Cu2O3,2F'
It was o, s. Further, the zero resistance superconducting transition temperature was 26, and the superconducting volume fraction was 4.2, about 24%.

Furthermore, in 4.2, the critical current density under zero magnetic field is about 70
0A/cm20. The critical current density in the IT magnetic field is approximately 5
It was 50 A/(m2).

Example 3 La203, Nd2O3, LaF3, Sm2O3, Sr
Each powder of CO3, CaCO3, and cuo was mixed into La:Nd:
Sm:Sr:Ca:Cu:F is 1, O: 0.7:0. a
go, measure it so that it is 8:0.2:2:0.6,
After pulverizing and mixing in an agate mortar, the mixture was placed in an Al2O3 container and fired in air at 950°C for 12 hours. after that,
The mixture was ground again in an agate mortar, formed into pellets, fired in nitrogen at 1000°C for 16 hours, and then rapidly cooled in liquid nitrogen at a rate of about 1000°C/sec.

The carriers of the obtained superconductor are electrons, and the composition is as follows:
L a 1. ONdn, 73mo3S r o, 5Ca
The zero-resistance superconducting transition temperature of 02Cu2055F05 was 25, and the superconducting volume fraction was 4.2, which was about 20.
%Met. Furthermore, 4.2K.

Critical current density under zero magnetic field is approximately 600A/cm20.1
The critical current density in the magnetic field of T was about 500 A/cm2.

(Effects of the Invention) The superconductor of the present invention has the general formula α7βe Cu2O,Fs where a: at least one element selected from La, Nd, Sm, Eu and Gd β: selected from Sr and Ca At least one element represented by 1.8<η<2.1 0.9<θ<2.2 5.0<γ<6.3 0.1<δ<1.2, Examples As shown in , the charge carriers are electrons, the zero-resistance superconducting transition temperature is high, and
High critical current density in magnetic field.

Claims (1)

[Claims] A superconductor represented by the following general formula. α_ηβ_θCu_2O_γF_δ where α: at least one element selected from La, Nd, Sm, Eu and Gd β: at least one element selected from Sr and Ca 1.8<η<2.1 0.9<θ<2.25.0<γ<6.30.1<δ<1.2