JPH0569059B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application of the Invention The present invention relates to a method for producing an oxide ceramic superconducting material.

The present invention relates to a method for producing a material exhibiting K ₂ NiF ₄ type superconductivity.

"Conventional technology" Conventionally, superelectronic materials have been made using elements such as mercury and lead,
Alloys such as NbN, Nb ₃ Ge, Nb ₃ Ga or Nb ₃ (Al _0.8
A metal material made of a ternary element compound such as Ge _0.2 ) is used. However, their Tc (superconducting critical temperature) onset was up to 25K.

On the other hand, ceramic-based superconducting materials have attracted attention in recent years. This material was first reported by IBM's Zurich Research Institute as a Ba-La-Cu-O (baraquo)-based oxide high-temperature superconductor, and further developed by LSCO.
It has been known as (cupric acid-lanthanum-strontium). Since these oxides in (A _1-X bx)yCuOz were simply mixed and fired, a Tc onset of only 30K could be obtained.

``Conventional problems'' However, the potential for superconductivity of these oxide ceramics relies on the single-layer pervskite structure, which contains many voids and grain boundaries. Tc was also limited to 30K.

For this reason, this Tco (temperature at which resistance becomes zero) should be made higher, preferably at liquid nitrogen temperature (77K).
There was a strong demand for the device to operate at temperatures higher than that.

"Means to Solve the Problem" The present invention aims to exhibit superconductivity at such high temperatures.
We searched for the material that would form the K ₂ NiF ₄ type. As a result, it became clear that Tco (the temperature at which superconductivity begins when electrical resistance disappears) could also be increased to 50 to 107K.

It is an oxide ceramic using elements of groups A and A of the periodic table of elements and copper.

The superconducting ceramic of the present invention is (A _1-X Bx)
yCuOzx=0.01~0.3, y=1.0~2.2, z=2.0~4.5
This can be generally shown as A uses one or more of elements selected from the yttrium group and elements selected from other lanthanoids. According to the Physical and Chemistry Dictionary (Iwanami Shoten, published on April 1, 1963), the Itztriyum tribe includes Y (Itztriyum), Gd (Gadryum), and Yb.
(Ittelbyum), Eu (Europium), Tb
(terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (silium), Lu
(lutetium), Sc (scandium) and other lanthanides.

Also, B is Ra (Radiyum), Ba (Baliyum),
Sr (strontium), Ca (calcium), Mg
One or more elements selected from (magnesium) and Be (beryllium) are used.

The present invention is based on a model in which copper has a layered structure, one layer or two symmetrical layers within one molecule, and superconductivity can be exhibited by the electron orbit of the outermost core electron of this layer. There is. For this reason,
It is based on the K ₂ NiF ₄ structure or a modified two-layer perpskite structure.

In such a structure, (A _1-X Bx) in the structure of the present invention makes the six copper atoms more layered and makes it easier for carriers to move through this layer.
The elements A and B selected in yCuOz are important. In particular, the element A is an element of the yttrium group or an element of the lanthanides, generally from group a of the periodic table of elements. Furthermore, the present invention uses an element selected from Ra (radium), Ba (barium), Sr (strontium), Ca (calcium), Mg (magnesium), and Be (beryllium), which are group a of the periodic table of elements, as B. ing.

In the present invention, when pre-sintering and oxidizing ceramics using such elements, a magnetic field, preferably 500 Gauss or more, is applied to the tablet, thereby reducing the current induced by the magnetic field and the demagnetizing field characteristics of the superconducting material. They are organically linked and have a synergistic effect.

By doing so, it is possible to provide a configuration in which A and B in the general formula can be selected, one crystal grain exhibiting polycrystalline size can be enlarged, and the barrier at the grain boundary can further be eliminated. I ordered it. As a result, the temperature of Tco can be made even higher. The ideal is a single crystal structure.

In the present invention, starting materials such as fine powders of oxides or carbonates are mixed, and once pressurized and oxidized and fired (this is called pre-calcination). In this way, a superconducting ceramic material having a molecular structure of the (A _1-X Bx)yCuOz type can be produced from the starting oxide or carbonate.

Furthermore, it has a step of pulverizing it again, pressurizing it again to form a tablet, and then firing it.

"Function" The K ₂ NiF ₄ type ceramic superconducting material of the present invention can be produced very easily. In particular, these use 3N or 4N purity oxides or carbonates as their starting materials, which are ground into fine powder using a ball mill and mixed. Then, each value of x, y, and z of (A _1-X Bx)xCuOz can be arbitrarily changed and controlled stoichiometrically.

Another feature of the present invention is that it does not require the use of particularly expensive equipment to produce such a superconducting material.

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

Example 1 As an example of the present invention, A is Y and B is
Ba was used.

As starting materials, yttrium oxide (Y ₂ O ₃ ) was used as a Y compound, BaCO ₃ as a Ba compound, and CuO as a copper compound. These were hand-made by Kojundo Kagaku Kogyo Co., Ltd., using fine powder with a purity of 99.95% or higher, and x=0.15 and y=1.8. The values of this x are 0.05, 0.1, 0.15, 0.2 and 0.01 ~
It was variable within the range of 0.3.

Mix these thoroughly in a mortar and encapsulate them in a capsule.
Add a load of 3 kg/cm ² to make it into a tablet (size 5
mmφ×15mm). Further, the mixture was heated and oxidized at 500 to 1200°C, for example 700°C, for 8 hours in an oxidizing atmosphere, such as the air. This step was called pre-firing.

At this time, a magnetic field was applied from the outside. This magnetic field was close to the top and bottom of the tablet, one side was N and the other was S, making it a direct current magnetic field, and the strength was 500 Gauss.
It goes without saying that the stronger the strength of this magnetic field, the better.

This was then ground and mixed in a mortar. The average particle diameter of the powder is 200μm to 3μm, for example 10μm.
The size was set to be less than m.

Further, this was encapsulated in a capsule and molded into a tablet under pressure of 5 kg/cm ² .

Next, oxidation was carried out at 500 to 1200°C, for example 900°C, in an oxide atmosphere, for example air, and main firing was performed for 10 to 50 hours, for example 15 hours.

In this tablet, a Pelpskide structure was mainly observed, but a K ₂ NiF ₄ type structure was also observed at the same time.

Next, this sample is heated in oxygen-depleted O ₂ -Ar (600-1200℃, 3-30 hours, e.g. 800℃,
°C for 20 hours) for reduction. At this time, an external magnetic field was applied from above and below the tablet. This magnetic field was a direct current magnetic field, and 1 K Gauss was applied to a 5 mmφ tablet. When this magnetic field was continuously applied for at least 10 minutes, the effect of increasing Tco was observed.

Using this sample, the relationship between resistivity and temperature was investigated. Then, assuming that the maximum temperature is obtained,
It was possible to observe a Tc onset of 103K and a Tco of 79K.

If no magnetic field is applied, this value is the Tc onset.
It was only 83K, Tco, and 66K.

Example 2 In this example, as A, Y and Yb were mixed with their oxides at x:x'=1:1. Ba was used as B. The starting materials are yttrium oxide and ytterbilium oxide, _BaCO3 as Ba
Alternatively, CuO was used as the copper compound. The magnetic field in this case was a commercial frequency (50Hz). The rest is the same as in Example 1.

I was able to obtain 106K as Tc onset and 83K as Tco.

If no magnetic field is applied, Tc onset 94K,
The Tco was 78K, and each was able to improve by 5 to 12K.

Example 3 In Example 1, as A, Y and Yb are further added.
_20-30 % _Nb2O5 was added. As a result, we were able to further improve Tc onset by 3 to 5K.

In the present invention, the Ittrium family (Y, Eu,
Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc,)
These elements and other lanthanoids are used as oxides or carbonates, and they are also effective as starting materials for composite ceramics. In particular, adding a material selected from these to a part of A in the general formula (A _1-X Bx)yCuOz had the effect of further increasing Tc by 5 to 10K.

In the present invention, other materials B include Sr,
Ca can be used. The outline is roughly the same as that of the first embodiment.

``Effects'' The present invention has made it possible to produce superconducting ceramics that operate at temperatures higher than the liquid nitrogen temperature, which was previously thought to be impossible.

In the present invention, by the step of calcining and then pulverizing, the compound of each starting material in its initial state becomes the final material, that is, a compound containing the material represented by (A _1-X Bx)yCuOz. .

Furthermore, in order to make it easier to form a copper layer structure within the molecular structure of the compound of this target material, a plurality of elements a and a in the atomic periodic table may be mixed. In this way, it is presumed that the presence of voids and the lowering of the barrier height of grain boundaries can be further removed from the final completed compound, and as a result, the Tc onset and Tco can be made higher.

In addition, the superconducting ceramic represented by the molecular formula of the present invention has a layered structure of copper oxide as the presumed superconducting mechanism, and the layered structure also has one or two layers within one molecule. It is presumed that the carrier is superconducting.

An embodiment of the invention is a tablet. However, rather than making it into a tablet, after pre-firing or final baking, it is powdered again, the powder is dissolved in a solvent, the solution is coated on a substrate, etc., and this is dried and then a magnetic field is applied in an oxidizing atmosphere. It is also possible to make a thin film of superconducting ceramics by firing and then firing in a reducing atmosphere.

After the present invention, powdering, tabletting, and firing with the application of a magnetic field may be repeated.

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

The invention is represented by other molecular formulas (A _1-X Bx)
y′Cu Ozy′=2.6 to 4.4, z′=4.0 to 8.0 e.g. y′=3
,
z'=7 or y'=2, z'=6, (A _1-X Bx)
Needless to say, this is equivalent to y′=6 and z′=14 in y′Cu ₆ Oz′.

Claims (1)

[Claims] 1. When producing a material having superconducting properties of a compound of copper and one or more elements selected from groups a and a of the periodic table of elements, these metals and oxides Alternatively, a method for producing superconducting ceramics characterized in that a carbonate starting material is made into a single piece and then a magnetic field is simultaneously applied during firing. 2. In claim 1, the compound of copper and an element selected from groups a and a of the periodic table of elements is (A _1-X B _X )yCuOz, x=
It has a composition of 0.01 to 0.3, y = 1.0 to 2.2, z = 2.0 to 4.5, and A is Y (yztriyum), Gd (gadolinium), Yb (yzterbium), Eu (europium), Tb (terbium), Dy ( dysprosium),
Consists of one or more elements selected from Ho (holmium), Er (erbium), Tm (thulium), Lu (lutetium), Sc (scandium) and other lanthanoids, B is Ra (radium),
Ba (valium), Sr (strontium), Ca
1. A method for producing superconducting ceramics characterized by comprising one or more materials selected from (calcium), Mg (magnesium), and Be (beryllium). 3 In claim 1, firing is 500
A method for producing superconducting ceramics characterized by carrying out at a temperature of ~1200°C. 4 In claim 1, the magnetic field is 500
A method for producing superconducting ceramics characterized by applying an electric current to a strength of ~5K Gauss. 5. The method for producing superconducting ceramics according to claim 1, characterized in that the starting materials are metals, oxides, or carbonates of A, B, and copper.