JPS63302967A - Sorting of oxide superconducting material - Google Patents

Abstract

PURPOSE:To carry out sorting of a superconducting material and to prepare a ceramic superconductive body in a short time by pulverizing an oxide superconducting material formed by the heat treatment, holding the pulverized product at a temp. exhibiting superconductivity, then impressing magnetic field to the pulverized product. CONSTITUTION:An oxide superconducting material is formed by executing heat treatment, then the material is pulverized to fine powder, and the fine powder is held at a temp. where the pulverized product exhibits superconductivity. The pulverized product is sorted to fine powder which exhibits superconductivity at that temp., and fine powder which does not exhibit superconductivity at the same temp. Preferred oxide superconducting material described above is one expressed by formula I (wherein x is 0-1; y is 2.0-4.0; z is 1.0-4.0; w is 4.0-10.0; A is at least a kind of the group IIIa element of the periodic table; B is at least a kind of the group IIa element of the periodic table). More preferable material may be obtd. if a halogen element is added further to the material of the formula I.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application of the Invention The present invention relates to a method for producing an oxide superconducting (also referred to as superconducting, but hereinafter referred to as superconducting) material.

"Conventional technology" Conventionally, superconducting materials include elements such as mercury and lead, and NbN.

Alloys such as Nb=Ge, Nb3Ga or Nb3 (A
Metal compounds such as LO, aGeo, and RI are used. However, the Tc (superconducting critical temperature) onset of these was up to 25K.

On the other hand, ceramic-based superconducting materials have attracted attention in recent years. This material was first obtained from IBM's Zurich laboratory.
It has been reported as an a-La-Cu-0 (baraquo)-based oxide high temperature superconductor, and has been further known as LSCO (cupric acid-lanthanum strontium).

``Conventional problems'' However, the Tc of these oxide ceramic superconducting materials
The limit was 30K.

Therefore, it has been strongly desired to further increase Tc and Tco, and preferably to operate at a liquid nitrogen temperature of C11K'') or higher.

"Means to Solve the Problem" The present invention sought a new type of material that would exhibit superconductivity at such high temperatures. As a result, Tc (the temperature at which superconductivity begins) is also 100-260K.

It has become clear that the temperature at which the electrical resistance becomes zero can be increased to 90 to 260K.

The superconducting oxide material in the present invention is (8I-1+
Bx) ycuzo+mXv x = O~l+
3+ = 2.0 to 4.0 preferably 2.5
~3.5. z = 1.0~4.0 preferably 1.5~
3.5. w = 4.0-10.0 preferably 6-B,
It can generally be expressed as v = 0.01 to 3. A
is one or more elements in the so-called IIIa group of the periodic table of elements, and B is Ba (valium) or Sr.
Il'a in the periodic table of elements such as (strontium)
selected from one or more elements of the group. Furthermore, X is a halogen element, and is filled as closely as possible so that w+v=2.

In the present invention, A is particularly selected from among the above-mentioned 1lla group materials (Eu, Gd, Tb, Dy, H).
o, Er.

Tm, Yb, Lu, Sc, Y) are used.

The present invention is characterized by a so-called hot press method in which starting materials such as halides, oxides, or carbonates are mixed and heated and pressed. Furthermore, in the present invention, pressure is applied once and temporary firing is performed. This is further pulverized. This fine powder is exposed to a liquid or gas containing a halogen element, such as fluorine or chlorine, and the halogen element is added into the powder. The object of the present invention is to use the Meissner effect to classify fine powders with good superconducting properties and fine powders with poor superconducting properties for fine powders to which a halogen element is added or not. Then, only good fine powders are collected and pressed into tablets, which are then subjected to main firing. At this time, a step of applying pressure is included at the same time or after this.

In the general formula of the present invention, preferably X+
The value of y+2+- is generally a distribution that makes it easy to adjust the components.

The present invention is a patent application filed by an undiscovered student entitled ``Method for producing superconducting ceramics'' (Patent application filed on March 25, 1986).
2-072486) was further improved, and its Tco was greatly improved by adding a halogen element to the oxygen vacancy.

"Operation" The new type of oxide superconducting material of the present invention can be made very easily. In particular, these use an oxide with a purity of 3N or 4N as its starting material, which is ground into a fine powder using a ball mill and mixed to achieve a stoichiometric (AI-X
Each value of X+LZ+- of Bx)ycuzow can be arbitrarily changed and controlled.

With respect to the dispersion within this fine powder, the classification method of the present invention makes it possible to select only the good ones and make the quality of the finished tablet product constant.

In the present invention, in order to utilize the Meissner effect, it is sufficient to place the fine powder in, for example, liquid nitrogen and apply a magnetic field from below, thereby selecting and collecting only the fine powder that floats higher. That is, this classification also has another feature in that it does not require the use of any expensive equipment.

The present invention will be described below with reference to Examples.

"Example 1" As an example of the present invention, Yb was used as A and Ba was used as B.

The starting material is ytterdium oxide (Y
b205), BaCO3 was used as the Ba compound, and CuO was used as the copper compound. These were obtained from Kojundo Kagaku Kogyo Co., Ltd. and used as fine powders with a purity of 99.95χ or higher. Furthermore, x = 0.67 (^:B=1:2
), y=3. z −3 and W=6 to 8 were selected as much as possible.

Mix these thoroughly in a mortar and seal in capsules, weighing 30kg.
/cm” load to make it into a tablet (size 10mm)
φX3mm). Further, heating oxidation was carried out at 500 to 1000°C, for example 700°C, for 8 hours in an oxidizing atmosphere, for example, air. This step was called pre-firing.

This was then ground and mixed in a mortar. The average powder radius of the powder was adjusted to be 10 μm or less, preferably 0.5 μm or less.

After this, they are placed in liquid nitrogen (77K).

All of this fine powder is then cooled to 77K. After this, a magnetic field is applied from the bottom of the liquid nitrogen container. Then, due to the Meissner effect, the superconducting fine powder is repelled by this magnetic field, and as a result, it can float. And T
Since powders with larger co are located higher, powders can be classified based on this height into those with large Tco, those with medium Tco, and those with Tco lower than the liquid nitrogen temperature.

To add a halogen element such as fluorine to this fine powder, it was immersed in a solution of ammonium fluoride dissolved in a fluorocarbon solution. At this time, pressurize to about 2 atmospheres, and then pressurize to about 2 atmospheres.
When heated to about 00°C, fluorine is easily impregnated into the material, particularly into the oxygen vacancy. Then, the fluorine in the CFC and the fluorine in the ammonium fluoride were able to be impregnated into the surface and inside of the fine powder.

Furthermore, this is enclosed in a capsule and the amount is 10~3000Kg/c.
m2 While pressurizing the tablet at a pressure of, for example, 50 kg/cm2, oxidize in an oxide atmosphere of 500 to 1000 °C, for example, 750 °C, for example, in the air, perform main firing for 1 to 10 hours, for example, 2 hours, and then slowly cool. The so-called ho/
) Press method was adopted.

This tablet mainly has a vervskite structure, but other new structures were also observed at the same time.

Next, this sample was heated in 0□-Ar with reduced oxygen (600-1100°C, 3-30 hours, e.g. 750°C).
, 20 hours) for reduction. At this time, do not apply pressure.
Rather, it is preferable to use atmospheric pressure or reduced pressure in order to increase Tco. Then, the new structure became more noticeable.

Using this sample, the relationship between resistivity and temperature was investigated. Then Tc onset is 227, Tco is 2
25K could be observed.

Also, if a tablet is made without any sorting,
Alternatively, if a tablet is made using a fine powder that does not have any superconducting properties at liquid nitrogen temperature, Tco is 7.
7K or less.Example 2 In this example, Y and Yb were used as A in a ratio of 1:1. Moreover, Ba was used as B. Starting material is Y
F3. YbF3, BaCO5 as Ba, and CuO as the copper compound were used. The rest is the same as in Example 1.

209K as Tc onset, 208K as Tco
was able to obtain.

"Example 3" In Example 1, YF was used as A. Further, after being once pulverized, this fine powder was exposed to hydrogen fluoride gas. This atmosphere was set to 300° C. and a pressure of 50 Kg/co+2, and was maintained for 3 hours. Furthermore, as shown in Example 1, this was again made into tablets.

Then, both Tc onset and Tco are further increased by 3~5″
could also be improved.

In the present invention, isotorium group (Eu, Ga,
Tb.

Using elements Dy, lld, Er, Tm, Yb, Lu, Sc, V) together with fluoride as a starting material to form a composite oxide material is particularly effective in increasing Tco.

In particular, materials selected from these (Al□Bx) ycu
Adding monovalent halogen elements such as fluorine, chlorine, bromine, and iodine to this position in order to fill the vacancy of the general formula 0 represented by zo- is also effective in greatly increasing the critical current. Ta.

"Example 4" This example is a modification of Example 3, but an intrum group element, such as Y, was added as an oxide. However, these were dissolved in an excess sulfuric acid solution as a double salt of the Rz(SO4) ・K, SO, (R is an intrum element) type, and this was added to the pre-calcined powder used in Example 1. The halogen element shown in the present invention was added at the vacancy position. Furthermore, after this, main firing was performed in the same manner as in Example 1. Then, in this method of adding the solution after pre-calcination, the amount added can be precisely controlled. As a result, Tc could be further improved by up to 8 compared to Example 1.

"Effects" The present invention has made it possible to produce ceramic superconductors extremely precisely and in a short time, which was previously considered impossible.

By using the selection method of the present invention, the difference between Tco and Tc became 1 to 2, and it became possible to distinguish between temperatures that extremely sharply exhibit superconductivity and temperatures that do not exhibit superconductivity.

Furthermore, by adding a halogen element to the oxygen vacancy position, it has become possible to greatly improve Tco and also improve critical current density.

In addition, the oxide superconducting material represented by the molecular formula of the present invention has a layered structure in which the copper oxide has a layered structure, and the layered structure also has a one-layer or two-layer structure within one molecule, as the presumed mechanism of superconductivity. It is presumed that carriers are superconducting within this layer.

The embodiment of the present invention is a tablet left device. However, instead of making tablets, the powder after preliminary firing or final firing is dissolved in a solvent, the solution is coated on a substrate, etc., and this is fired in an oxidizing atmosphere containing a halogen element, and then the reducing By performing main firing in an atmosphere, it is also possible to form a thin film of oxide superconducting material.

The present invention has made it possible to easily produce superconductors at low cost.

Claims (1)

[Claims] 1. After forming an oxide superconducting material through a heating process, it is pulverized, the fine powder is maintained at a temperature at which the material exhibits superconductivity, and then a magnetic field is applied, A method for sorting oxide superconducting materials, the method comprising sorting fine powders that exhibit superconductivity and fine powders that do not exhibit superconductivity at the temperature in the materials. 2. In claim 1, the oxide superconducting material is (A_1_-_xB_x)_yCu_zOwx=0~
1, y=2.0~4.0, z=1.0~4.0, w=4
．． 0 to 10.0, A is an element selected from one or more elements of Group IIIa of the Periodic Table of Elements, and B is an element selected from Group IIIa of the Periodic Table of Elements.
A method for selecting an oxide superconducting material comprising one or more elements selected from Group IIa. 3. A method for selecting an oxide superconducting material according to claim 1, wherein the oxide superconducting material has a halogen element added thereto.