JPH02275720A - oxide superconducting material - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to oxide superconducting materials with high superconducting transition temperatures.

Conventional technology Superconducting materials have properties that other materials do not have, such as 1) zero electrical resistance, 2) complete diamagnetism, and 3) the Josephson effect. It is used in magnets, 5QUID, etc. Also in the future,
It is expected to have a wide range of applications, including power transportation, power generators, fusion plasma confinement, magnetic levitation trains, magnetic shielding, and high-speed computers. Conventionally, the material is Nb3G
Metal-based superconductors such as e were used.

The problem that the invention aims to solve However, the highest superconducting transition temperature of metallic superconductors is around 23 degrees, and in actual use, they must be cooled using expensive liquid helium and a large-scale insulation device. This was a major industrial problem. For this reason, research has been underway to find materials that become superconductors at higher temperatures.

In 1986, Bednorz and Mueller developed oxide-based superconducting materials (L) with a high superconducting transition temperature of approximately 40°C.
a+-zS r 2)2CuOx was discovered, and since then superconducting transitions at higher temperatures have been reported in YBa2Cu3Ox, Busr-Ca-Cu-0, etc. The higher the superconducting transition temperature, the easier cooling becomes.
Furthermore, the critical current density and critical magnetic field are expected to increase when used at the same temperature, and the range of applications is expected to expand.

The present invention is one of these new oxide superconductor compositions.

As a means composition for solving the problem, at least T L S r + L n
and Cu (where Ln is Y, La, Pr+
Nd, SrL Eu+ Gd+ Tb+
Dy+ Hot Err Tm.

Yb, Lu), Sr/Ln ratio is greater than 2, and lattice constant a=0.381ffh
An oxide superconducting material characterized by having a crystal structure belonging to a tetragonal system with c=1.22 nm.

As a result of intensive exploration and research into the composition Jt of a hitherto unknown oxide high temperature superconductor, the inventors discovered a superconducting transition at a relatively high temperature in a substance having the above composition. Its superconducting transition temperature is about 90°C, and it has a superconducting transition temperature of about 90°C, which is similar to conventional metallic materials as well as (La+-zS rz)2.
Higher than cuOx. The present invention will be described below with reference to examples in which Y is used as a representative of Ln.

As a starting material for the example, Tl2O3°B12 with a purity of 99% or more
Each powder of Ch+Y2O3 and S r CO31Cu O was used. Among these powders, 5rCo3 and CuO,
Sr:Cu=2:1 ratio and total 30g
Weigh the ZrO powder with a diameter of 2 mm using a vibrating mill.
Using 2 balls, 40 ml of ethanol was used as a dispersion medium.
The pulverization was carried out over time. After the mixing was completed, the entire amount including the dispersion medium was dried at 120'C in a dryer. 10 of the obtained powder
After calcining in air at 00°C for 5 hours, it was ground in a vibrating mill for 30 minutes in the same manner as described above, and dried at 120'C. This calcined powder was analyzed by X-ray diffraction, and S r
It was confirmed that 2Cu O3 was generated.

This 5r2CuO3 powder and T 120a, Y2O3, C
The uO powders were each weighed so that the composition ratio was as shown in Table 1 and the total weight of the powder was 5 g.

Table 1. Blending composition ratio (mole ratio) The temperature (T3) at which the magnetic property begins to change rapidly was determined.

The results are shown in Table 2.

Table 2. Characteristics of Sintered Body (Unit: K) The weighed powder was pulverized for 1 hour using a sieve machine. After mixing, 0.4 g of this powder was uniaxially pressed in a 15 mm x 5 mm mold at a pressure of 500 K g/cm 2 . This molded body was wrapped in Al1 foil, sealed in a quartz tube under reduced pressure, and heated to 900-950 in an electric furnace.
Calcined at °C for 1-40 hours. The temperature increase/decrease rate is 4 in both cases.
00″C/h.

A silver electrode was attached to the sintered body, and the temperature change in electrical resistance was measured using the usual four-terminal method at a measurement current of 10 mA from 300 K to 5 K, and the temperature (TI) at which the electrical resistance began to rapidly decrease due to superconducting transition was determined. The temperature (T2) at which the resistance becomes 0 was determined. In addition, temperature changes in the magnetic susceptibility of the sintered body are measured, and the Meissner effect results in the following: Tl: T2: T3; lns: Temperature at which electrical resistance begins to decrease (Tconset) Temperature at which electrical resistance disappears (Tc R=0) Temperature at which Meissner effect begins As is clear from Insulator Table 2, no superconducting transition was observed in the N01l sample, and the electrical resistance increased like a semiconductor, with 100
Below that, the current for measurement no longer flows, and it becomes an insulator. On the other hand, in the samples No. and 2+ No.3, 300-
The electrical resistance increases slightly between 100 and 9
The electrical resistance decreased significantly near 0-70. The onset temperature due to this resistance change is 900°C for the No. J sample.
The highest value was 95 when fired at ℃-5 hours. The decrease in electrical resistance was considerably slower at lower temperatures than near the onset temperature, and the zero resistance temperature was about 10-15. In addition, changes in magnetic susceptibility due to the Meissner effect also occur in No. 2.
It was observed in sample No. 3, and the highest one was still N0.
When 13 samples were fired at 900'C for 5 hours, it was 65cm.

The inventors created Tl-8r-Ln-Cu-0 based oxides with various rare earth elements and composition ratios in addition to those shown in Table 1, and measured their superconducting transition temperatures. Unless the ratio exceeds 2, a superconducting transition of 50 or higher cannot be obtained. The optimum value of Sr/Ln ratio is around 5-10, but at least 3≦Sr/Ln
If it is not within the range of ≦15, the volume fraction of the superconducting phase becomes very small. On the other hand, regarding the amount of N TL Cu,
Even if the amount is too large compared to Sr and Ln, Tl will sublimate and decrease during firing, and Cu will only remain as CaO in the sintered body, so the composition ratio can be exceeded over a fairly wide range. We were able to obtain a sample exhibiting conductive transition. However, if it was too small, the volume fraction of the superconducting phase produced naturally decreased.

Next, each of the sintered bodies shown in Table 2 was crushed and subjected to powder X-ray diffraction measurement, and it was found that a=0. 38nm1
c=12. A phase belonging to the Lnm tetragonal system was generated as the main phase. The lattice constant and diffraction pattern of this phase have a superconducting transition temperature of about 90 K (T I +P
b) Similar to S r2c a Cu20x phase,
Therefore, it has a so-called (1212) type crystal structure. Next, when we measured the lattice constants more accurately, we found that in the sample No. 1, which does not exhibit superconductivity, and the sample No. 2.3, a
The axis length remains the same at 0.382 nm, but there is a slight difference in the C-axis length; those that do not exhibit superconductivity are approximately 1.19 nm, while those that exhibit superconductivity are approximately 1.22 nm.
It was about m.

Furthermore, these values slightly changed depending on the type of rare earth element.

B125r3-, which has a similar composition combination and crystal structure.
In the zLnzCLI20X system, it is known that the superconducting properties vary depending on the Sr/Ln ratio.

In this case, the crystal structure is the so-called (2212) phase, which is B i2s r2 (S r + Ln) Cu20x, and the Ca site of the B j2Sr2CaCuxox phase is S
It is replaced by r and Ln. It is known that B i2S raLnCu20x, which contains only rare earth elements in the Ca site, does not exhibit superconductivity, but becomes a superconductor by containing Sr and Ln. Similarly, the crystal structure of the phase of the present invention is T isracacu20x phase (1212 phase).
T I in which the Ca site of is replaced by Sr and Ca
It is considered that S r2 (S r +L n )Cu20x. In the sample No. I, S r / Ln = 2,
The Ca site contains only Y, and in the sample No. 2.3, the Sr/Ln ratio is 9, and the Ca site contains Sr and Y. Therefore, although the samples No. and 1 have the same crystal structure, they do not exhibit superconducting transition.

Moreover, the difference in C-axis length is considered to be because sample No. 2.3 contains a large amount of Sr, which has a larger ionic radius than Y.

However, if it does not contain rare earths and only Sr is used,
(1212) The phase itself is no longer generated.

Sr/Ln of Ca site in Bi-based (2212) phase
In contrast, in the present invention, by replacing Ca in the Tl-based (1212) phase, which is difficult to synthesize and does not easily exhibit superconducting transition, with Sr and Ln, This makes it possible to easily synthesize superconducting phases.

In addition, as a superconductor based on the combination of T I-8r-Ln-Cu-0, when Ln=La, Pr, Nd, 4
There are reports of superconductivity of the order of a = 0.
Belongs to the tetragonal system of 38 nm + c = 0.89 nm,
This is due to the (1201) phase. Although this phase may be generated as an impurity phase in the present invention, its lattice constant and crystal structure are different from those in the present invention, there is no restriction on the Sr/Ln ratio, and the superconducting transition temperature is low. It is a different phase.

Effects of the Invention According to the present invention, the transition temperature of the obtained ceramics is
(L at-its rx) 2c: u Oz phase 4
It exceeds 0K.

Claims (1)

[Claims] As a composition, at least Tl, Sr, Ln and Cu
(Here, Ln is Y, La, Pr, Nd, Sm, Eu, G
d, Tb, Dy, Ho, Er, Tm, Yb, Lu), the Sr/Ln ratio is greater than 2, and the lattice constant is a = 0.38 nm), c = 1.22 nm. An oxide superconducting material characterized by having a crystal structure belonging to the tetragonal system.