JPH03146417A - Oxide superconductor - Google Patents

Abstract

PURPOSE:To reduce the content of Ba as a poison and to widen the selectivity of the raw Ba material by allowing the superconductor to have a specified chemical composition formula. CONSTITUTION:(i) The powder of Ln2O3 (Ln is Y, Nd, Sm, Eu, Gd, Dy, Ho, Er and Tm), (ii) CaO powder, (iii) Ba(NO3)2 powder, (iv) La2O3 powder and (v) CuO powder are mixed in an inert atmosphere. The mixture is calcined in a gaseous oxygen current, crushed and formed to obtain a formed body. The body is then presintered, heat-treated, crushed, formed and sintered to obtain the oxide superconductor having a chemical composition shown by the formula ((x) is 0.001-0.3 and (y) is 0.001-0.2).

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an oxide superconductor whose superconducting transition temperature (hereinafter abbreviated as Tc) exceeds liquid nitrogen temperature (absolute temperature 77 K).

[Prior Art] LnBa2Cuao* (of the order of 80), which has a layered perovskite crystal structure with double Cu-0 heavy-dimensional chains, is used as an oxide Mi conductor that exhibits a Tc exceeding the liquid nitrogen temperature.
Ln=Y, Nd, Sm, Eu, Gd, Dy, Ho, Er
, Tm) is known (Phys, rev, B,
, 39 (1989) 7347).

Its crystal structure has been determined as shown in FIG.

Furthermore, it is known that it is possible to increase Tc to 90K by substituting a part of Y with Ca (Nature, 341 (1989) 41).

For the synthesis of such oxide superconductors, sodium carbonate (
Mix Na*C0a) into the raw material as a reaction accelerator and add 800
A method of firing for a long time (for example, 50 hours or more) at a temperature of ℃ or less (Nature, 338 (1989) 328
) and a method using hot isostatic pressing in a mixed atmosphere of oxygen gas and inert gas (Japanese Patent Application No. 1-213730) have already been proposed.

[Problems to be solved by the present invention] However, this superconducting oxide contains YBa2CUaO.
The composition of
BaC0a, Ba(Now)*) must be used, and sufficient measures must be taken to handle it during the manufacturing process. In addition, since the synthesis of this substance proceeds at low temperatures or high pressures, cheap barium carbonate (BaCOa) has a high decomposition temperature of 900°C or higher, so it cannot be used as a starting material for this superconducting material. cannot, and other expensive compounds must be used as starting materials.

The present invention has been made to solve these problems.

The purpose of the present invention is to reduce the content of Ba, which is a deleterious substance, and to expand the selectivity of Ba raw materials.

[Means for Solving the Problem] In order to achieve the above object, the oxide superconductor of the present invention has a chemical composition formula (Ln, -, Ca,) (Bat-, La,
)2CUJO11, Ln is Y, Nd, Sa+,
Eu, Gd, Dy, Ho, Er, T- or any combination of them, X is in the range of 0.001 or more and 0.3 or less, and y is 0.001 or more and 0.2 It is characterized by being in the following range.

[Function] According to the above-mentioned means, Tc=8 manufactured by the prior art
0 grade superconductor YBa2Cu40s has Ba of 13.
It contains 33 mol%, and barium nitrate (Ba(NO3)2) is used as the Ba source.
(L nl-x Caw) (B a+-y La,)
The composition of 2Cut Os is ``, and Ln is Y, Nd, Sm,
Eu, Gd, Dy, Ho, Er, T- or any combination of them, X is in the range of 0.001 or more and 0.3 or less, and y is 0.001 or more and 0.2 In this example, which is within the following range, even if cheap acO3 is used as the Ba supply source, Tc=80 or higher is achieved, and the Ba content can be reduced to 10.67 mol%. Furthermore, as a result of thermogravimetric analysis, the superconductor of the present invention has
It was also confirmed that the feature of YBa2CuaO@superconducting material, which exists stably without oxygen entering or exiting up to around 850°C, has not been lost.

Therefore, according to the Mi conductor of the present invention, it is possible to produce a YBa2CuJOs superconducting material that has a low Ba content and exhibits a 5 conductivity transition temperature of 80 degrees with wide raw material selectivity.

[Embodiments of the invention] Examples of the present invention will be described below.

First, YB is the main component of the oxide a conductor according to the present invention.
The basic structure of a2Cu40g is shown in FIG. In FIG. 1, 1 is Y, 2 is Ba, 3 is Cu, and 4 is O placed at the intersection of the line segments.

(Ln+-6Caj(Bal
-, La, )2Cu40s is YBa2C shown in FIG.
In the structure of u*Os, Ca and Ln are located at the Y position i'ji
One feature of the present invention is that La is substituted at the Ba position.

[Example 1] Ln2O3, CaO, Ba(NO
3)2. Chemical composition formula (
Ln+-xCax) (Bat-yLay)2Cu40s
At x=0.0°0.001.0.01.0.1.
0.3, 0.5. y=0.0.0.001,0.01,
The compositions of each combination of 0.1, 0.2, 0.3, and 0.5 were mixed in an inert atmosphere and heated at 750°C in an oxygen stream for 10
After that, calcination was performed at an arbitrary temperature between 750°C and 900°C for 10 hours. After calcination, the sample is crushed into a rectangular shape? This was molded. This molded body was heated to 800°C in an oxygen stream.
Pre-sintering was carried out for 5 hours at a temperature between °C and 950 °C. This pre-sintered body was heated with Ar under a pressure of lOOOKg/am2.
Heat treatment was performed under a gas atmosphere of 80%-0220%.

It was heated to toooC at a temperature increase rate of 200C/hr and held at this temperature for 10 hours. Cooling is 200℃/hr 3
After heating to 00°C and 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 sintered at 800''C in an oxygen stream for 20 hours to obtain a specified sample. Ln of the above Ln203 was Y, Nd
, Sm, Eu, Gd, Dy, Ho, Er, and TII, or a predetermined combination of them.

Thus obtained (Ln+-Ca-XBa+-La
,) The constituent phases of the sintered body of 2Cu4O3 were confirmed using powder X-ray diffraction. The main components of the obtained samples were all YB
It was confirmed that it had a2Cua O* type crystal structure. x=0.1. The powder X-ray diffraction pattern of y=0.1 is
Shown in the figure. The numbers in the figure are YBa2Cu-Os type (14
It is a peak index based on the structure. This sample was a single superconducting phase. X=O, from O to 0.15 or less, y=
In the composition range from o and o to 0.1 or less, all samples had a single superconducting phase. The constituent phases of the samples are summarized in Table 1.

The superconducting properties were investigated by resistance measurements. The results are shown in FIG. 3 and Table 1. (Ln+-I Cam
)(Bal-v Lay)a CuaO@superconductor sample, as seen from FIG. 3 and Table 1, Ca
The content of 0≦X≦0.3. Sr content is 0≦y≦0
．． All samples in the range 2 show superconducting transition temperatures in the order of 80 degrees. Diamagnetism was also observed in AC magnetic susceptibility measurements at temperatures above 80°C (Figure 4). This indicates that a superconducting state occurs at temperatures above 80°C, and supports the results of resistance measurement. This superconducting transition temperature is higher than the boiling point (77K) of liquid nitrogen.

The analytical values for the Ba content in these samples are summarized in Table 1. Looking at the results, it can be seen that as the La content increases, the Ba content decreases, which is advantageous in manufacturing. When the La content is 0.2, the Ba content is 10 mol% or less. However, if the La content increases too much, the superconducting transition temperature (Tc) decreases, and in the case of sample No. 21 with y=0,3, TC becomes 40K.

In FIG. 5, x=0.1. The results of thermogravimetric analysis of a sample having a composition of y=0.1 are shown. It shows no weight change from room temperature to around 850°C, and shows weight loss from 850°C to 900°C, so it is stable with no oxygen entering or exiting up to a high temperature of 850°C, like the conventional m-conducting oxide with YBa2Cu40° composition. It was confirmed that it exists.

As can be seen from the above description, according to Example 1, the conventional superconducting oxide having the composition Y Bafi Cua O contains up to 13.33 mol% of Ba, and the handling during the manufacturing process is difficult. Although sufficient measures had been taken to
(Ln+-mcax) (Bit-, La,) acuzo
s, and Ln is Y, Nd, Ss, Eu, Gd+
Any combination of one or more of DV, Ha, Er, and Tm, where X is in the range of 0.001 or more and 0.3 or less, and y is in the range of o, oot or more and 0.2 or less. All of the superconducting oxides had a superconducting transition temperature of 80 or more, and the Ba content could be reduced to 10 mol% or less. Furthermore, it was confirmed that these materials existed stably up to around 850° C. without oxygen entering or exiting.

Therefore, the oxide superconductor of the present invention can achieve a superconducting transition temperature of 80 or higher while reducing the Ba content to 75% of the conventional value.

[Example 2] LnaOs with a purity of 99.9% or more (Ln=Y, Nd, S
s+ E u + G d , D y + Ho +
E r + T a ) * Ca COa , B a
COs.

Various powders of LaaOa and CuO have chemical composition formula (Ln+-
xCax) (Bat-yLav) in gcuaos x=0.0. o.

00 t, 0.01.0.1.0.3.0.5. y=
0.0, 0.001, 0.01, 0.1, 0.2, 0.
The compositions of each combination of 3 and 0.5 were mixed and calcined for 10 hours at an arbitrary temperature between 900° C. and 950° C. in an oxygen stream. After calcining, the sample was crushed and shaped into a rectangle.

This compact was presintered for 5 hours at a temperature between 900°C and 950°C in an oxygen stream. This preliminary sintered body is I O0
Heat treatment was performed under a pressure of 0 kg/c1 in a gas atmosphere of 80%-0220% Ar. It was heated to 1000°C at a heating rate of 200°C/hr and held at this temperature for 10 hours. Cooling was performed at 200°C/hr to 300°C, and after reducing the pressure to 1 atmosphere, the sample was taken out into the air. This sample was ground again and shaped. This molded body was placed in an oxygen stream for 800 min.
A prescribed sample was obtained by sintering at ℃ for 20 hours.

(Ln+-xcax) (Bat-
, La, )2Cua O* The constituent phases of the sintered body are powdered
This was confirmed using line diffraction. It was confirmed that the main components of the obtained samples all had a YBaaCLlnOs type crystal structure. x=0.1. The powder X-ray diffraction pattern for y=0.1 is shown in FIG. The numbers in the diagram are YB a9 Cua
This is a peak index based on the Oe type structure. This sample was a single superconducting phase. X=O, O to 0.15
Hereinafter, in the composition range of y=0.0 to 0.1 or less, all samples had a single superconducting phase. The constituent phases of the sample are
They are summarized in the table.

The superconducting properties were investigated by resistance measurements. The results are shown in FIG. 7 and Table 2. (Ln+-xcax) in this example
(Bat-yLa,)2CL140sjl? As can be seen from Fig. 7 and Table 2, the Im conductor sample has a Ca content of O≦X≦0.3 + S r content of O≦y≦0.
．． All samples in the range 2 show superconducting transition temperatures in the order of 80 degrees. Diamagnetism was also observed in AC magnetic susceptibility measurements at temperatures above 80°C (Figure 8). This superconducting transition temperature is
This temperature is higher than the boiling point (77K) of liquid nitrogen.

The analytical values for the Ba content in these samples are summarized in Table 2. Looking at the results, it can be seen that as the La content increases, the Ba content decreases, which is advantageous in manufacturing. When the La content is 0.2, the Ba content is 10 mol% or less. However, if the La content increases too much, the superconducting transition temperature (Tc) decreases, and in the case of sample No. 23 with y=0.3, TC becomes 40K.

In FIG. 9, x=0.1. @ of sample with composition of y=0.1
The results of gravimetric analysis are shown. It shows no weight change from room temperature to around 850"C, and shows a weight decrease from 850°C to 900"C, so like the conventional superconducting oxide with YB a2 CL1208 composition, it shows no change in weight up to the high temperature of 850"C. It was confirmed that it existed stably with no comings and goings.

As can be seen from the above description, according to Example 2, the conventional superconducting oxide having the Y Bas Cua Os composition contains up to 13.33 mol% of Ba, which is expensive as a source of Ba. Nitrates were used and sufficient measures were taken to handle them during the JJ manufacturing process;
, Ca, )(Bat-, Lay)2cu40e, and Ln is Y, Nd, Ss, Eu, Gd, Dy, Ho
, Er Tm, or any combination of them, where X is in the range of 0.001 or more and 0.3 or less, and y is in the range of 0.001 or more and 0.2 or less. , all have a superconducting transition temperature of 80 or higher,
It was possible to reduce the Ba content to 10 mol % or less and use an inexpensive carbonate as a raw material. Furthermore, it was confirmed that these materials existed stably up to around 850° C. without oxygen entering or exiting.

Therefore, in the oxide superconductor of the present invention, the BQ content can be reduced to 75% of the conventional one, and a superconducting transition temperature of 80 or higher can be obtained while widening the selectivity of raw materials.

Below is the margin.

[Effects of the Invention] As explained above, according to the present invention, B, which has a superconducting transition temperature sufficiently higher than the boiling point of liquid nitrogen and is a deleterious substance,
It is possible to reduce the amount of a used and provide a superconductor that is stable up to high temperatures with a wide range of raw material selectivity.

[Brief explanation of the drawing]

FIG. 1 shows (Ln+-, Ca,) (Bad-,
Figure 2 is a diagram for explaining the crystal structure of (Ln+-8Ca,)2CuaO・ according to Example 1.
(Bad-yLa,)x=0.1 in sCuaOs
．． The powder X-ray diffraction pattern of the y=0.1 sample, FIG. 3, shows the (Ln+-xCaj(Bad-
yLa,)2Cu40* x=0.1. y=0.
The resistance-temperature characteristic diagram of the sample No. 1, FIG. 4 shows the (Ln+-xCax) (Bad
−, L”v )2 x=0.1 in Cua O@.
FIG. 5 is a diagram showing the results of AC magnetic susceptibility measurement of a sample with y=o, l.
B al-, L av) x=0 in 2cu40s.
A diagram showing the results of thermogravimetric analysis of a sample of 1+y=O,l, No. 6FgJ is (Ln+-, Cax) according to Example 2
(Ba1-vLau)X in 2cuao@: 0.1
．． The powder X-ray diffraction pattern of the sample with y: 0.1, Figure 7 shows the (t, n+-xcax) (Ba
t-, t. ay) x=0.1 in 2Cu40@. The resistance-temperature characteristic diagram of the sample with y=0.1, FIG.
x=0.1 in t-yLa, )2Cua Os.
FIG. 9 is a diagram showing the results of AC magnetic susceptibility measurement of a sample with y=0.1.
, Lay) acu40m x=o, l, y=0.
FIG. 1 is a diagram showing the results of thermogravimetric analysis of sample No. 1. In the figure, 1...Y, 2...Ba, 3...C
u, 4...0.

Claims (1)

[Claims] 1. Chemical composition formula (Ln_1_-_xCa_x) (Ba_
In the oxide superconductor represented by 1_-_yLa_y)_2Cu_4O_3, Ln is Y, Nd, Sm, Eu
, Gd, Dy, Ho, Er, and Tm, or any combination of them, and x is 0.001 or more and 0.
3 or less, and y is in the range of 0.001 or more and 0.2 or less.