JPH0380111A - Oxide superconductor - Google Patents

Abstract

PURPOSE:To make the superconductivity transition temp. of the oxide superconductor higher than the b.p. of liquefied nitrogen, to increase its density and to obtain excellent stability that oxygen is not absorbed or desorbed up to high temp. by substituting a part of Ba in the superconductor with RBa2Cu4O8 (R is rare-earth elements) as the base material for Sr. CONSTITUTION:The oxide superconductor has the chemical composition R(Ba1-xSrx)2Cu4O8, R is at least one kind selected from the rare-earth elements (including Y), namely Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, and 0.001<=x<=0.6. The superconductor is stable close to 850 deg.C without oxygen being absorbed or desorbed. Accordingly, when a silver-sheathed wire is formed from the superconductor, a stable high-density sintered superconducting wire is formed in the sintering stage as the final stage without deteriorating its superconductivity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an oxide superconductor whose superconducting transition temperature Tc exceeds the liquid nitrogen temperature.

[Prior art] 1- RB a2 C030, which has a three-layer perovskite crystal structure as a typical oxide superconductor with a superconducting transition temperature Tc (absolute temperature 90 K) exceeding the boiling point of liquid nitrogen
7 (R= Y, rare earth element) is known (Ap
pl, Phys, Lett, Vol, 51 (
19137) P57).

However, the oxygen content of this oxide superconductor changes depending on the heat treatment conditions, resulting in a tetragonal-orthorhombic structure phase transition. Due to this phase transition, the superconducting transition temperature is 90K.
It is known that it changes greatly from OK (insulator) to OK (insulator) (Phys, Rev, 836 (1987)
P57]9).

[Problems to be Solved by the Invention] However, for example, after filling a silver vibe Z with RBa2Cu307 powder and making it into a wire by cold drawing, the RBa2Cu307 powder is subjected to sintering heat treatment (800 to 90
The present inventors have found that when the wire is put to practical use as a superconducting wire (silver sheath wire method), oxygen escapes during the sintering process, resulting in deterioration of the superconducting properties.

On the other hand, RB82Cu40s (first
Figure) is stable with no oxygen entering or exiting up to around 850°C. However, we found that RBa2Cua
It has been found that Oe has poor sinterability and a high-density sintered body is obtained. Naturally, if the density of the sintered body is low, the critical current density will not be high.

The present invention has been made to solve these problems.

An object of the present invention is to provide a superconductor that has a superconducting transition temperature higher than the boiling point of liquid nitrogen, is highly dense, and has excellent stability without absorbing or dissipating oxygen up to high temperatures.

[Means for Solving the Problems] In order to achieve the above object, the oxide superconductor of the present invention has a composition of R(Bat-8Sr)2Cua○8,
R is YlNds Sms Eu, Gdt D
ys HO% Ers Tmz Yb% Lu
At least one of the rare earth elements (including Y) is free, and x is in the range of O, oo1≦x≦0.6.

[Operation] 3- According to the above-mentioned means, the superconductor RB a2 serving as the base material
The superconducting transition temperature of CL120a is 80°C, and this material is II sinterable, whereas R(Ba
t-xSrx)2Cu, has a composition of +08 and R is HoX
The sample where x is 0.3 has a superconducting transition temperature of 80 or higher, and sintering becomes easy, and in this example, it was observed that the porosity of the sintered body was reduced to 10%. Further, as a result of thermogravimetric analysis, it was confirmed that the superconductor of the present invention existed stably without oxygen entering or exiting up to around 850°C.

Therefore, when making the superconductor of the present invention into a silver sheath wire,
In the final sintering heat treatment process, a stable and highly densely sintered superconducting wire can be produced without impairing superconducting properties.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be specifically described with reference to the drawings.

First, RB, which is the main component of the oxide superconductor according to the present invention,
The basic structure of aaCuaOe is shown in Fig. 1, and for comparison, the crystal structure of conventional RBa2CU307 is shown in Fig. 4-2. In Figures 1 and 2, ■ is the rare earth element R, Y% NcL 5llXEuXGds
DyX HOXErs Tm, YE1% Lu
It consists of at least one kind of rare earth elements (including Y). 2 is Ba53 is Cu, and 4 is O placed at the intersection of the line segments.

The main component R (B
al-x S rx)2Cυ40 m is the single CuO chain of the crystal structure of RBa2cuso7 shown in Figure 2,
Double CuO chains are substituted, and Ba is partially substituted with Sr. One of the features of the present invention is that in this structure having double CuO chains, part of Ba is replaced with Sr.

Next, examples of the oxide superconductor of the present invention will be described.

[Example 1] Y2O3, Ba(NOs)2, Cub with a purity of 99.9%
.

5r(NCh)2 powder has the chemical composition formula Y (B al-x
S rx) In 2Cu408, x=0.0.01
,0.1.0.2.0.3.0,4.0.5.0.6.
0.7, and calcined in oxygen at 850°C for 24 hours.

After calcining, the sample was crushed and shaped into a rectangle. This compact was pre-sintered in oxygen at 800° C. for 5 hours. This preliminary sintered body was heat-treated in a gas atmosphere of 1000 kg/cm2.Ar 80%-0220%. Heating at 200℃/h9
It was held at 60°C for 6 hours, then further heated to 1050°C at 200'C/h, and held at that temperature for 6 hours. Cooling was performed at a rate of 200″C/h to 300°C.
After reducing the pressure to 1 atm, the sample was taken out into the air. This sample was ground again and shaped. This molded body was heated to 80% in oxygen.
A predetermined sample was obtained by sintering at 0°C.

Y(Bat-,5rx)2cUA obtained in this way
The formed phase of the o8 sintered body was confirmed using powder X-ray diffraction. The main component of the obtained samples was Y B 82C11.
It was confirmed that it had a type 408 crystal structure. X=0.
The powder X-ray diffraction pattern of No. 3 is shown in FIG. The numbers in the figure are peak indices based on the Y B a2 C0408 type structure. This sample is a single superconducting phase.

The formed phases of the samples are summarized in Table 1.

6- For X in the range 0 to 0.6, Y (B 81-x S
rx) 2Cu40 e is a single phase, and when X becomes 0.7, it begins to contain a second phase.

The superconducting properties of these samples were investigated by resistance measurements. The results are shown in FIG. 4 and Table 1. In Tables 1 to 4, Tcon is the temperature at which superconducting transition starts from the normal conductive state, TcR″e is the temperature at which the resistance becomes O, and ρ3I
K is the resistivity at 300.

Below is the margin.

7- As can be seen from FIG. 4 and Table 1, the Y(Ba+-xsrx)2cUaos superconductor samples of this example all exhibit a superconducting transition temperature of 80 degrees. This superconducting transition temperature is higher than the boiling point (77K) of liquid nitrogen. Comparing the resistance values of the samples at room temperature, the resistance value at room temperature decreases as the Sr content x increases. In this way, a high critical current density can be expected for a sample with a low resistance value at room temperature. The resistance at room temperature is lowest for the sample with X of 0.5;

Above 6, the resistance value increases as X increases, and X=0, 7
In this case, the value becomes higher than in the case where X=O.

Furthermore, the porosity of these samples was determined by observing the polished samples with an optical microscope. These values are summarized in Table 1.

Looking at this result, the porosity decreases as X increases,
The sample with x=0.3 becomes approximately 5%. However, even if X increases further, the porosity does not change.

Considering the results of X-ray diffraction and the measurement results of resistivity and porosity at room temperature, the decrease in resistivity at room temperature of the sample as X increases is due to the solid solution of Sr at the Ba9- site of YBa2CuzOs. This is thought to be due to Therefore, the desirable range of X is 0.001≦x≦0.6.

For example, as shown in Figure 5 (a), the results of thermogravimetric analysis of samples X-0 and 3 show no weight change from room temperature to around 850°C, and a decrease in weight between 850 and 900''C. From this, it was confirmed that it existed stably without oxygen entering or exiting up to a high temperature of 850°C.However, in the conventional electromotive conductor YBa2Cu307, the 5th
As shown in (b) of the figure, a large amount of oxygen is released at 400 to 800°C.

As can be seen from the above description, according to this example, the superconductor YB a2 Cu, O a serving as the base material is difficult to sinter, and therefore the sintered body has a porosity of 30% or more. On the other hand, it has a composition of Y(Ba+-xsrx)2cuzo8, and X is o. All of the samples in the range of ooi≦x≦0.6 have a MiN conduction transition temperature of 80 or higher, and the porosity of the sintered body is also 10% or lower. Furthermore, these samples also have a low electrical resistivity at room temperature, with a thermal analysis of 850
It was confirmed that it existed stably up to around 10°C with no oxygen going in and out.

[Example 2] Purity 99.9%) (o203, Ba(NO3)2, C
ub.

5r(NOa)2 powder with chemical composition formula Ho(Bat-xS
rx)2cuaos, x=O10,01,0,
1,0,2,0,3,0,4,0,5,0,6,0,7
The mixture was mixed and calcined in oxygen at 850°C for 24 hours.

After calcining, the sample was crushed and shaped into a rectangle. This compact was pre-sintered in oxygen at 800° C. for 5 hours. This preliminary sintered body was heated to 1000 kg/cm2・Ar80%-0220
The heat treatment was carried out in a gas atmosphere of 10%. 200”C/h
The sample was heated at 950°C and held for 6 hours, and then further heated to 1050°C at 200'C/h and held at that temperature for 6 hours. Cooling is at a rate of 200″C/h for 30
The temperature was raised to 0°C, and the pressure was reduced to 1 atm, and then the sample was taken out into the air. This sample was ground again and shaped. This molded body was sintered at 800° C. in oxygen to obtain a predetermined sample.

Ho (Bat-xsrx) 2 cu obtained in this way
The formed phase of the sintered body of No. 408 was confirmed using powder X-ray diffraction. The main components of the obtained samples were all RB a2CLI
It was confirmed that it had a type 408 crystal structure. X=0.
The powder X-ray diffraction patterns of the 10 samples are shown in FIG.

The numbers in the figure are peak indices based on the RB a2Cua Oa type structure. This sample was a single superconducting phase. The formed phases of the samples are summarized in Table 2. X
In the range of O to 0.6, Ho(Bat-xsr)
It is a single phase of 2cu40B, and when X becomes 0.7, the second
It comes to include phases.

The B conductivity properties of these samples were investigated by resistance measurement. The results are shown in FIG. 6 and Table 2.

Below is the margin.

12-13- Ho(Bat-xSr, )2cu40e a of this example
As can be seen from FIG. 6 and Table 2, the conductor samples all exhibit an a conductivity transition temperature of 80 degrees. This superconducting transition temperature is higher than the boiling point (77K) of liquid nitrogen. Comparing the resistance values of the samples at room temperature, Sr
As the content of ff1x increases, the resistance value at room temperature decreases. In this way, a high critical current density can be expected for sample Z, which has a low resistance value at room temperature. The resistance at room temperature is the lowest in the sample where X is 0.5, and when x is 0°6 or more, the resistance increases as X increases, and when X=0.7, it becomes higher than when X=O.

Furthermore, the porosity of these samples was determined by observing the polished samples with an optical microscope. These values are summarized in Table 2.

Looking at this result, the porosity decreases as X increases,
The sample with x=0.3 becomes approximately 5%. However, even if X increases further, the porosity hardly changes.

Considering the results of X-ray diffraction and the measurement results of resistivity and porosity at room temperature, the decrease in the resistivity at room temperature of the sample as X increases is due to solid solution of Sr at the B10-a site of HoBa2CuaO8. This is considered to be an effect. Therefore, the desirable range of X is 0.001
≦x≦0.6.

For example, as shown in Figure 8 (a), the thermogravimetric analysis of the sample X-0,1 shows no change in weight from room temperature to around 850°C, and a decrease in weight between 850 and 900°C. Therefore, it was confirmed that it existed stably without oxygen entering or exiting, even up to a high temperature of 850°C. However, in the conventional superconductor HoBa2cu*o7, (b) in Figure 8
As shown in , a large amount of oxygen is released at 400 to 800°C.

As can be seen from the above description, according to this example, the superconductor HoBa2CL140s serving as the base material has a superconducting transition temperature of 80°C and is difficult to sinter, so that the porosity of the sintered body is 30°C. % or more, whereas Ho(Ba
+-,5rx) has a composition of 2cu+os, and X is 0.0
All samples in the range of 01≦x≦0.6 have superconducting transition temperatures of 80 or higher, and the porosity of the sintered bodies is also 20%.
It is as follows. Furthermore, these samples had low electrical resistivity at room temperature, and thermal analysis confirmed that they existed stably with no oxygen entering or exiting up to around 815-50°C.

[Example 3] 1-(O is Nd in Ho(Ba+-xSrx)2cu40e.

S11, Eus GdXDy% Ers Tm,
Example 1 by setting Ybs Lu and fixing x=0.3
A sample was prepared using the same process as above. In addition, the same evaluation as in Example 1 was performed, and the results are shown in Table 3.

Below is the margin.

6 17- Looking at this table, we can see that the rare earth elements R range from Ho to Nd.

Sms Eus GdXDyXEr5 Tms
It was found that the same effect can be obtained by replacing it with any one of Ybt and Lu.

[Example 4] The oxide superconductor of Example 4 has R(Ba+-,5r-
)2clIaos is fixed at x=0.3, and Y and HO are used as R. That is, (Y+-yHo
, ) (B all,? S rl], a) 2Cu40s
Samples were prepared in the same process as in Example 1 by changing the value of y, that is, by changing the mixing ratio of Y+- and HOy. In addition, the same evaluation as in Example 1 was conducted, and the results are shown in Table 4.

Below is the margin.

=18- 19- Looking at this table, the same effect can be obtained even if the rare earth element R containing Y is changed from HO to two of the above R (by changing the mixing ratio of YX Ha) I understand.

In addition, 3N selected from rare earth elements R including Y
It has been found that similar effects can be obtained by using a mixture of one or more of the above.

Therefore, when the oxide superconductor of the present invention is made into a button sheath wire, it is stable without impairing its superconducting properties and is easy to sinter, so that each particle has a high A densely sintered superconducting wire shrine with a high critical current density can be produced.

Further, when the oxide superconductor according to the present invention is subjected to high-temperature molding, high-density molding is possible by using a binder. That is, the conventional superconductor RBa2Cu307 has 400
Although the binder cannot be removed at temperatures above 850°C, in the case of the superconductor of the present invention, the binder can be removed at 850°C or below. As a result, high-density molding is possible, and the conductive current density 20- can be improved.

Furthermore, since the conventional thin film of RB a2Cus 07 has a large specific surface area, its superconducting properties deteriorate even in air at room temperature, but the thin film of the oxide superconductor according to the present invention
Compared to Cu307 thin film, it has higher environmental stability (and stable B conduction transition temperature).

Although the present invention has been specifically described above based on Examples, it goes without saying that the present invention is not limited to the above-mentioned Examples and can be modified in various ways without departing from the spirit thereof.

For example, it goes without saying that the present invention can be used for wiring of low-temperature electronic devices, magnetic shielding, and the like.

[Effects of the Invention] As explained above, the present invention provides a superconductor that has a superconducting transition temperature higher than the boiling point of liquid nitrogen, is easily sinterable, and is stable without oxygen entering or exiting even at high temperatures. can be provided.

[Brief explanation of drawings]

FIG. 1 shows Y B a2 Cu40 according to an embodiment of the present invention.
Figure 2 is a diagram to explain the structure of conventional YBa2Cu3C)+. Figure 3 is R=YX x=0.3 according to the present example. FIG. 4 shows the powder X-ray diffraction pattern of the sample of this example.
X ) 2 Resistance-temperature characteristic diagram of Cu40 e. Figure 5 is a diagram showing the results of thermogravimetric analysis of the sample of R = YX x = 0.3 in this example. The powder X-ray diffraction pattern of the sample with R:HOX x=0.3, FIG. 7 shows the Ho(Bat-xSrx)2cu of this example.
Resistance-temperature characteristic diagram of z08, FIG. 8 is a diagram showing the results of thermogravimetric analysis of the sample with R=Hos x=0.3 of this example. In the figure, 1...R, 2...Ba, 3...Cu, 4...
...It is O.

Claims (2)

[Claims] (1) R(Ba_1_-_xSr_x)_2Cu_4O
An oxide superconductor represented by the chemical composition formula of _8,
R is Y, Nd, Sm, Eu, Gd, Dy, Ho, Er,
An oxide superconductor which is one selected from the rare earth elements (including Y) of Tm, Yb, and Lu, and is characterized in that x is in the range of 0.001≦x≦0.6. (2) In the oxide superconductor according to claim 1,
The R is Y, Nd, Sm, Eu, Gd, Dy, Ho,
An oxide superconductor comprising two or more rare earth elements (including Y) selected from Er, Tm, Yb, and Lu.