JPH0832556B2 - Oxide superconductor and method for producing same - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an oxide superconductor whose superconducting transition temperature (hereinafter sometimes simply referred to as Tc) is sufficiently higher than the temperature of liquid nitrogen and which is less susceptible to the problem of fluctuations in Tc due to oxygen release during processing, and to a method for producing such an oxide superconductor.

[Prior Art] A typical oxide superconductor with a Tc exceeding the liquid nitrogen temperature is the triple-layer perovskite RBa ₂ Cu ₃
O ₇ (wherein R is Y or one or more elements selected from the group consisting of lanthanide series rare earth elements) has been discovered [APPl. Phys. Lett. Vol. 51 (1987) p. 57].

However, the oxide superconductors mentioned above have the property that the oxygen atoms that make up the superconductors are easily released by the heat effect during processing. Therefore, the oxygen content changes depending on the heat treatment conditions during processing, and as a result, an orthorhombic-tetragonal phase transition occurs. It is known that this phase transition causes a large fluctuation in Tc in the range from 0 K to 90 K [Phys.Rev.B36 (19
87) P5719].

For example, if a method (silver sheath wire method ₎ is adopted in _{which RBa2Cu3O7} powder is filled into a silver pipe, which is then formed into a wire by cold wire drawing, and the powder is then sintered (at 800-900°C) to form a superconducting wire, there is a drawback in that oxygen atoms are lost during the sintering heat treatment, resulting in a deterioration of the superconducting properties.

In contrast, RBa ₂ Cu ₄ O ₈ -type oxide is stable, with no loss of oxygen even when heated to around 850°C, and has a Tc of around 80K, which is higher than the temperature of liquid nitrogen, making it an important substance for practical use.

Incidentally, the following two methods have been proposed so far as methods for producing RBa ₂ Cu ₄ O ₈ type oxide superconductors.

(1) A method of heat treating the calcined powder in a high-pressure atmosphere of pure oxygen (for example, 930°C x 8 hours, oxygen pressure 100 atm) [high-pressure oxygen method; Tc = 81K, Nature 336 (1988) P660-662 or Phys.Re
vB 39 (1988) P7347-7350)].

(2) The calcined powder is mixed with a catalyst such as sodium carbonate and then heat-treated in an oxygen stream for a long time [normal pressure method; Tc = 7
7K;Nature 338 (1989) P328-330].

However, according to the findings of the inventors through experiments, the above methods (1) and (2) have the following drawbacks.

In method (1), depending on the temperature and pressure conditions, RBa ₂ Cu
It was found that phases such as _{RBa 2} Cu 4 O ₇ -δ and R ₂ Ba ₄ Cu ₄ O ₂ appear, the amount of RBa ₂ Cu ₄ O ₈ produced is extremely small, and the inherent properties of the RBa ₂ Cu ₄ O ₈ phase are lost. Furthermore, method (2) is unsuitable for practical applications because impurities tend to remain in the product and the heat treatment requires a long time.

Furthermore, although RBa ₂ Cu ₄ O ₈ -type oxides have a Tc higher than the liquid nitrogen temperature, they are all around 80 K, and the temperature margin is too small for use at the liquid nitrogen temperature (77 K), making it difficult to put them to practical use.
It is hoped that a system that demonstrates this will be developed.

[Problem to be Solved by the Invention] The present invention has been made to solve these technical problems, and its object is to provide a stable oxide superconductor that has a Tc sufficiently higher than the temperature of liquid nitrogen and does not lose oxygen at high temperatures during processing.

Another object of the present invention is to provide a method for increasing the Tc of RBa ₂ Cu ₄ O ₈ type oxide and for producing it in a short time.

A further object of the present invention is to provide a useful method for producing an oxide superconductor wire.

[Means for Solving the Problems] The oxide superconductor according to the present invention is (R _1-x Ca _x )Ba ₂ Cu ₄ O ₈
An oxide superconductor represented by the chemical composition formula:
is one or more elements selected from the group consisting of Y and lanthanide series rare earth elements, and x is 0.001≦x≦0.5
The gist of the present _invention is that the oxide superconductor of the present invention is in the range of (excluding when R is Y alone and x is 0.001≦x≦0.2). That is, the oxide superconductor of the present invention is characterized _in that part of the R in _RBa2Cu4O8 is replaced with Ca, which increases Tc to approximately 90K and provides excellent stability against high-temperature heat treatment. Therefore, even when the above oxide superconductor is made into a silver-sheathed wire, it is possible to produce a stable superconducting wire without impairing the superconducting properties even after the final sintering heat treatment.

The method of the present invention that has achieved _the above object is _to
8 (wherein R is one or more elements selected from the group consisting of Y and lanthanide series rare earth elements), the method for producing a superconducting oxide having the structure,
The gist of this method is that hot isostatic pressing is performed in a mixed atmosphere of inert gas and oxygen gas. In other words, by applying hot isostatic pressing, _it was possible to increase the Tc of an _{RBa2Cu4O8 -} type oxide superconductor in which part of the R is not replaced with Ca or the like.

Furthermore, the method for producing an oxide superconductor wire of the present invention, which has achieved the above object, is a method for producing an oxide superconductor wire, which comprises: subjecting a raw material powder mixture for producing an oxide superconductor, which raw material powder mixture is composed of R (where R is one or more elements selected from the group consisting of Y and lanthanide series rare earth elements), Ca, Ba, Cu, and O, to a mixed atmosphere of inert gas and oxygen gas at 85
By hot isostatic pressing in the temperature range of 0 to 1100°C, an oxide superconductor powder containing an oxide represented by (R1 _{-xCax ) Ba2Cu4O8} (where x _is 0.001 to _0.5 , _and R has the same meaning as above ₎ is produced without generating an intermediate oxide represented by (R1 _{- xCax} ) _Ba2Cu3O7 before the hot isostatic pressing,
The powder is filled into a sheath material, which is then drawn and sintered.

[Operation] The present inventors have conducted research from various angles in order to realize a stable superconductor that has a Tc sufficiently higher than the temperature of liquid nitrogen and does not lose oxygen even at high temperatures.

First, the inventors have investigated the optimum structure of RBa ₂ Cu ₄ O ₈ -type oxides. As a result, they have found that a single CuO layer in a triple-layered perovskite RBa ₂ Cu ₃ O ₇ -type crystal structure
In the RBa ₂ Cu ₄ O ₈ -type oxide, where the chains are double CuO chains,
_It was found that the (R1 _{- xCax} ) _{Ba2Cu4O8 -} type oxide, in which 0.1 to 50 atomic % of R is replaced by Ca, has a Tc sufficiently higher than the liquid nitrogen temperature due to the effect of Ca substitution, and can be stably processed without oxygen escaping even under heating conditions around 850°C.

The basic structure of the oxide superconductor according to the present invention is RBa ₂ Cu
The structure of _{RBa 4} O ₈ is shown in Figure 1, and the structure of conventional RBa ₂ Cu ₃ O ₇ is shown in Figure 2. In Figures 1 and 2, 1 is R, 2 is B.
a, 3 indicate Cu, and 4 indicates O placed at the intersection of the line segments.

The oxide superconductor (R _1-x Ca _x )Ba ₂ Cu ₄ O ₈ according to the present invention is
As shown in Figure 1, the single CuO chain in the triple-layered perovskite RBa ₂ Cu ₃ O ₇ -type crystal structure has become a double CuO chain.
This oxide superconductor ( _{R1- xCax)Ba2Cu4O8} of the present invention is an _RBa2Cu4O8 oxide in which 0.1 to 50 atomic percent of R is substituted with Ca. The greatest feature of the present invention is that this Ca substitution significantly increases _Tc . The oxide superconductor (R1 _{-xCax ) Ba2Cu4O8} of the present invention can be produced by various methods _, such as sputtering and coprecipitation.

Powder of this type of (R1 _{-xCax ) Ba2Cu4O8 type} oxide does not lose oxygen even under high temperature conditions during wire processing, so if the powder is filled into a sheath material, drawn, and then sintered, _the desired superconductor wire can be obtained.

In the present invention, the Ca substitution amount (i.e. _, the range of _x ) in the (R1 _{- xCax} ) _Ba2Cu4O8 type oxide is set to 0.001 to 0.5 for the following reason: the effect of Ca substitution appears when x is 0.
This is because x is 001 or more, and under the production conditions of the present invention, x rarely exceeds 0.5.
The preferred range is 0.001 to 0.2 (however, excluding the case where R is Y alone and x satisfies 0.001≦x≦0.2).

Meanwhile, the present inventors have also investigated the manufacturing conditions for increasing the Tc of _{RBa2Cu4O8 oxide} without Ca substitution. As a result, they have found that the Tc of _RBa2Cu4O8 oxide can be increased by calcining the raw material and then subjecting it to hot isostatic pressing (hereinafter sometimes referred to as HIP treatment) in a mixed atmosphere of inert gas and _{acidic gas} . That is, according to the above-mentioned means, the Tc of _RBa2Cu4O8 type oxide produced by previously reported methods is 77 _{to 81} K, while _it is 8
The _RBa2Cu4O8 type oxide was successfully produced stably in a short time, with a Tc of ₂ to _83K . The HIP treatment conditions used here should be higher temperature and higher pressure to increase the reaction rate, but the optimum conditions vary depending on the atmospheric gas composition. For example, Ar gas + 20% _O2
In gas under a total pressure of 1000 atm, a temperature range of 800 to 1100°C is appropriate.

Next, a method for manufacturing an oxide superconductor wire according to the present invention will be described.
A powder mixture consisting of u, O, etc. is subjected to HIP treatment in a temperature range of 850 to 1100°C in a mixed atmosphere of inert gas and oxygen gas, (R
The oxide superconductor powder containing the oxide represented by the formula _(1-x Ca _x )Ba ₂ Cu ₄ O ₈ (where x is 0.001 to 0.5, and R has the same meaning as before) is produced by the O ₂ -HIP method.

The HIP process in the _O2 -HIP method is a process in a mixed atmosphere of inert gas and oxygen gas. Therefore, if you try to achieve the same pressure (for example, 200 atm) as with pure oxygen in terms of oxygen partial pressure, you can significantly increase the total pressure of the mixed atmosphere. For example, if the molar ratio of inert gas to oxygen is 1:1, the total pressure will be 400 atm, and if it is 4:1, the total pressure will be
It is possible to raise the pressure to 1000 atmospheres, which further enhances the diffusion of Cu atoms and is thought to promote the formation of (R _1-x Ca _x )Ba ₂ Cu ₄ O ₈ type oxide superconductors. This is also a major advantage from the viewpoint of operational safety compared to when the total pressure is increased by pure oxygen. These effects are due to the Ca
This effect is also exhibited when unsubstituted RBa ₂ Cu ₄ O ₈ oxide is produced by HIP treatment in a mixed atmosphere of inert gas and oxygen gas (i.e., O ₂ -HIP method).

The HIP temperature in producing oxide superconductor powder containing (R1 _-xCax ) _Ba2Cu4O8 type _oxides must _be at least 850° _{C or higher} in order to suppress the formation of _RBa2Cu3O7 type _oxides and promote the formation of (R1 _{-xCax ) Ba2Cu4O8} type oxides. However, if the temperature exceeds 1100°C, _{the formation of R2Ba4Cu7}
Since the 2-4-7 _phase (hereinafter sometimes referred to as 2-4-7 phase) is easily generated and becomes a mixed phase, the upper temperature limit must be 1100°C.

However, the inventors have confirmed through experiments that calcining the raw material powder in the _O2 -HIP method of the present invention causes some inconvenience in the subsequent HIP treatment. That is, when the raw material powder is calcined, ((R1 _{-xCax ) Ba2Cu3O7} (hereinafter sometimes referred to as _1-2-3 phase ₎ is first generated during calcination, and then (R1 _-xC
a _x )Ba ₂ Cu ₄ O ₈ phase (hereinafter sometimes referred to as 1-2-4 phase) is generated, the required time for HIP treatment is increased, but continuing HIP treatment for a long time at a high temperature is not a 1-2-
Since the 4-phase is more easily decomposed than the 1-2-3 phase, the 1-2-4 phase that has been produced may decompose again into the 1-2-3 phase, which is an inconvenience.

Therefore, the present inventors have conducted research from the viewpoint of producing (R1 _{-xCax ) Ba2Cu4O8 -} type _oxide superconductor powder in a short time and with high yield. As a result, the inventors have found that by avoiding the heat treatment process that is likely to produce the 1-2-3 phase as much as possible and by subjecting the raw material powder to HIP treatment in a state where the 1-2-3 phase has not yet been produced, the 1-2-
The 1-2-4 phase is formed, and the 1-2-4 phase that was once formed is
It was found that the reaction could be stopped in a state where decomposition into the -2-3 phase was suppressed.

By adopting these measures, you can reduce the number of steps required before HIP processing.
Since the synthesis of the 1-2-4 phase does not proceed and the decomposition of the 1-2-3 phase into the 1-2-3 phase once formed can be minimized, reactions that tend to produce the 1-2-3 phase, such as calcination and pre-heat treatment, can be omitted, shortening the production time and eliminating the need for a long HIP treatment, making the overall manufacturing process more efficient. Furthermore, there is no need to use carbonate as a raw material or catalyst, and the inconvenience of deterioration of superconducting properties due to the inclusion of carbon atoms as impurities does not occur. However, in the present invention, calcination and pre-heat treatment do not always have to be omitted, and a certain degree of HIP pre-treatment prior to HIP treatment is permissible.

The (R _1-x Ca _x )Ba ₂ Cu ₄ O ₈ type oxide superconductor powder obtained as described above is filled into a sheath material, drawn into a wire, and then sintered to obtain the desired oxide superconductor wire.

The composition of the raw material powder used in the method of the present invention does not necessarily have to be R or (R + Ca):Ba:Cu=1:2:4,
Even if the composition deviates from this, the final product is essentially RBa ₂ Cu
It is sufficient that _{the 4O8 phase} or (R1 _{- xCax} ) _Ba2Cu4O8 phase is produced. However _, in order to stably produce this phase _, it is preferable that the composition of the raw material powder is R or (R+Ca):Ba:Cu=1:2:4. From the viewpoint of facilitating the production reaction, the form of the raw material powder is preferably _Y2O3 , _R2O3 , _CaO , _BaO , Cu
It is preferable to use an oxide such as ₂ O.

The oxide superconductor provided by the present invention is characterized by having a 1-2-4 phase chemical structure, as can be understood from the entire description of the specification. However, if the effect of the present invention is not significantly diluted, a certain degree of 1-2-
Those skilled in the art will readily understand that the presence of impurities such as 3-phase and 2-4-7-phase is not intended to be actively excluded.

Next, the constitution and effects of the present invention will be specifically explained with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[Examples] Example 1: _Y2O3 , Ba( _NO3 ) ₂ , CuO, and _CaCO3 powders with a purity of 99.9% were mixed to form a powder having a chemical composition of (Y1 _{-xCax ) Ba2Cu4O8} , where x = 0 _{, 0.2} , 0.25 _, 0.3,
The samples were mixed at ratios of 0.4, 0.5, and 0.6 and calcined in oxygen at 850°C for 24 hours. After calcination, the samples were crushed and formed into rectangular parallelepipeds. These compacts were pre-sintered in oxygen at 800°C for 5 hours. These pre-sintered bodies were then heat-treated in a 1000atm Ar 80% + 20% _O2 gas atmosphere. They were heated at 200°C/hr to 960°C.
The sample was then heated at 1050°C for 6 hours, then heated at 200°C/hr to 1050°C and held at that temperature for 6 hours. The sample was then cooled at 200°C/hr to 300°C, and after the pressure was reduced to 1 atmosphere, the sample was taken out into air. This sample was then crushed and molded again.
This compact was sintered in oxygen at 800°C for 20 hours to obtain the desired sample.

The phases of _the (Y1 _{- xCax} ) _Ba2Cu4O8 sintered bodies obtained in this manner were confirmed by powder X-ray diffraction. It was confirmed that the major components of the obtained samples all had a _{YBa2Cu4O8 -} type crystal structure. The powder X-ray diffraction pattern of the sample _with x = 0.25 is shown in Figure 3, and the numbers in the figure are peak indices based on the _{YBa2Cu4O8 - type} structure. _A small amount of a second phase was observed in this sample. The phases of the samples are summarized in Table 1.
When x is in the range of 0 to 0.2, the phase is a single (Y _1-x Ca _x )Ba ₂ Cu ₄ O ₈ , and when x is 0.25, a second phase is included.

The superconducting properties of these samples were investigated by resistivity measurements.
The results are shown in Figure 4 and Table 1. In Table 1, Tc ^on is the temperature at which the transition from the normal conducting state to the superconducting state begins,
Tc ^R=0 is the temperature at which the resistance becomes 0, and ρ ^300k is the resistivity at 300K.

As can be seen from Figure 4 and Table 1, the (Y1 _{- xCax ) Ba2Cu4O8} superconductor samples of this example all exhibit a superconducting transition temperature of 90K class. This superconducting transition temperature is sufficiently higher than the boiling _point of liquid nitrogen (77K). Comparing the resistance values of the samples at room temperature, the resistance value at room temperature decreases as the Ca content x increases. Thus, a high critical current density can be expected for samples with low resistance values at room temperature. The resistance at room temperature is lowest for the sample with x of 0.3, and decreases when x is 0.4 or more.
The resistance value increases with increasing x, and at x=0.6 it is higher than at x=0.

The porosity of these samples was also determined by observing the polished samples under an optical microscope. These values are summarized in Table 1. The results show that the porosity decreases with increasing x, reaching approximately 4% for the sample with x = 0.3. However, further increases in x do not result in any change in porosity.

Considering the results of X-ray diffraction _and measurements of resistivity and porosity at room temperature, the decrease in the resistivity of the sample at room temperature with increasing x is _thought to be due to the effect of Ca solid-solving in the Y site of _YBa2Cu4O8 , as well as the fact that when x exceeds 0.2, the generated second phase acts as a sintering aid, increasing the density of the sample. However, if the second phase becomes too much, the volume fraction of the superconductor decreases, which is not desirable. The upper limit of x is 0.5.

Furthermore, as shown in Figure 5(a), for example, the thermogravimetric analysis of a sample with x = 0.3 showed no change in weight from room temperature to around 850°C, but showed a decrease in weight between 850 and 900°C, confirming that the sample remained stable up to the high temperature of 850°C without oxygen entering or leaving. However, as shown in Figure 5(b), the conventional superconductor _YBa2Cu3O7 showed no change in weight between 400 and ₉₀₀ ° _C .
At 800°C, a large amount of oxygen is released.

As can be seen from the above explanation, according to this embodiment, the superconducting transition temperature of the superconductor YBa ₂ Cu ₄ O ₈ as the base material is 80 K,
Moreover, it is difficult to sinter, and therefore the porosity of the sintered body is 30%.
In contrast to _the above, the example samples have _a composition of (Y1 _{-xCax ) Ba2Cu4O8} , and all have a superconducting transition temperature of 90K and a porosity of 10% or less for the sintered body. Furthermore, these samples have low electrical resistivity at room temperature, and thermal analysis confirmed that they exist stably up to around 850°C without oxygen entering or leaving.

Example 2: Powders of _Ho2O3 , Ba( _NO3 ) ₂ , CuO, and _CaCO3 with a purity of 99.9% were _{mixed with} a solution of the chemical composition formula (Ho1 _{-xCax ) Ba2Cu4O8} , where x = 0, 0.01, _0.1 ,
Mix the components at 0.2, 0.3, 0.4, 0.5, and 0.6 and heat in air at 850℃.
The sample was calcined at 800°C for 24 hours. After calcination, the sample was crushed and molded into a rectangular parallelepiped. This molded body was pre-sintered in oxygen at 800°C for 5 hours. This pre-sintered body was then heat-treated in a 1000atm gas atmosphere of 80% Ar and 20% _O2. It was heated at 200°C/h to a temperature of 960°C.
°C for 6 hours, and then heat up to 1050 °C at 200 °C/h
The temperature was then heated to 200°C/100°F and held at that temperature for 6 hours.
The temperature was raised to 300°C at a rate of 1/h, and the sample was then removed into air after the pressure was reduced to 1 atmosphere. The sample was then crushed and molded again. The molded body was sintered in oxygen at 800°C for 20 hours to obtain the desired sample.

The product phase of _the (Ho1 _{- xCax} ) _Ba2Cu4O8 sintered body obtained in this manner was confirmed by powder X-ray diffraction. It was confirmed that the main components of the obtained samples all had _{an RBa2Cu4O8 - type crystal} structure. The powder X-ray diffraction pattern of the sample with x = _0.10 is shown in Figure 6. The numbers in the figure are the peak indices based on the _{RBa2Cu4O8 -} type structure. This sample was a single superconducting phase. The product phase of the sample is summarized in Table 2.
When x is in the range of 0 to 0.2, the phase is (Ho _1-x Ca _x )Ba ₂ Cu ₄ O ₈ , but when x is 0.30, a second phase is included.

The superconducting properties of these samples were investigated by resistivity measurements.
The results are shown in FIG. 7 and Table 2.

The superconductor sample of (Ho _1-x Ca _x )Ba ₂ Cu ₄ O ₈ of the example is the 7th
As can be seen from the figure and Table 2, all of them show a superconducting transition temperature of 90K class. This superconducting transition temperature is much higher than the boiling point of liquid nitrogen (77K). Comparing the resistance values of the samples at room temperature, the resistance value at room temperature decreases as the Ca content x increases. Thus, a high critical current density can be expected for samples with low resistance values at room temperature. The resistance at room temperature is lowest when x is 0.3, and decreases as x increases for x 0.4 or more.
The resistance value increases with increasing x, and at x=0.6 it is higher than at x=0.

The porosity of these samples was also determined by observing the polished samples under an optical microscope. These values are summarized in Table 2. The results show that the porosity decreases with increasing x, reaching approximately 5% for the sample with x = 0.3. However, there is almost no change in the porosity even if x is increased further.

Considering the results of x-ray diffraction and measurements of resistivity and porosity at room temperature, the decrease in the room temperature resistance of the sample with an increase in x is thought to be due to the effect of Ca solid-solving in the Ho site of HoBa ₂ Cu ₄ O ₈ , as well as the fact that when x exceeds 0.2, the generated second phase acts as a sintering aid, increasing the density of the sample. However, if the second phase becomes too much, the volume fraction of the superconductor decreases, which is not desirable. Therefore, the desirable range of x is 0.001≦
x≦0.2.

Also, for example, as shown in FIG. 8(a), when x=0.1
The thermogravimetric analysis of the sample showed that there was no change in weight from room temperature to around 850°C, and a decrease in weight at 850-900°C, confirming that the sample remained stable up to the high temperature of 850°C without oxygen entering or leaving. However, in the case of the conventional superconductor HoBa ₂ Cu ₃ O ₇ , as shown in Figure 8(b), the weight of the sample did not change at 400°C.
At temperatures up to 800°C, a large amount of oxygen is released.

As can be seen from the above explanation, according to this embodiment, the superconductor HoBa ₂ Cu ₄ O ₈ used as the base material has a Tc of 80K and is difficult to sinter, so the porosity of the sintered body is 30% or more, whereas the composition of (Ho _1-x Ca _x )Ba ₂ Cu ₄ O ₈ , where x is 0.
All samples in the range of 001≦x≦0.5 have a superconducting transition temperature of approximately 90K, and the porosity of the sintered body is 20% or less. Furthermore, these samples also have low electrical resistivity at room temperature.
Thermal analysis confirmed that oxygen remained stable up to approximately 850°C, with no oxygen entering or leaving.

Example 3: (Ho1 _{-xCax ) Ba2Cu4O8 :} Ho is _replaced with Nd, Sm, Eu, Gd, Dy, Er, Tm, Y
A sample was prepared by the same process as in Example 2, except that b and Lu were substituted and x was fixed at 0.1. The same evaluations as in Example 2 were also carried out, and the results are shown in Table 3.

As shown in Table 3, R ranges from Ho to Nd, Sm, Eu, Gd,
It was found that the same effect could be obtained by substituting any of Dy, Er, Tm, Yb, and Lu.

Therefore, when the oxide superconductor of the present invention is made into a sheathed wire, it is stable and easy to sinter without impairing its superconducting properties in the final sintering heat treatment process, and therefore it is possible to produce a superconducting wire with a high critical current density in which each particle is sintered at a high density.

Furthermore, when the oxide superconductor of the present invention is molded at high temperature, it _is possible _to mold _it into a high density by using a binder.
However, in the case of the superconductor of the present invention, the binder can be removed at 800°C or less. This allows high-density molding, which further improves the superconducting current density.

Example 4 Powders of 99.9% pure _Y2O3 , Ba( _NO3 ) ₂ , CuO, and _CaCO3 were mixed to form _a powder with the chemical composition _YBa2Cu4O8 , and heated in air at ₈₅₀ ° _C .
Calcination was carried out for 24 hours. After crushing the calcined powder, it was heated in Ar gas +20
% _O2 gas at 950°C and pressure 100 atm for 6 hours, and then HIP treatment in Ar gas + 20% _O2 gas at 1050°C and pressure 1000 atm for 6 hours.
The superconductor was synthesized by performing two separate processes: 1 hour and 3 hours of HIP treatment.

The X-ray diffraction patterns of the calcined powder and the superconducting oxide of this example are shown in FIG. 9, and the results of evaluation of the properties of the superconducting oxide of this example are shown in Table 4.

For comparison, in Table 4, the calcined powder was
The mixed powder was then heated in oxygen gas at a temperature of _{1000 K.}
After heat treatment at 800°C for 72 hours, the Na ₂ CO ₃
The superconducting oxide powder YBa ₂ Cu ₄ O ₈ obtained by separating the above powder (N in Table 4)
The results of synthesizing YBa ₂ Cu ₄ O ₈ (No. 2 in Table 4: Comparative Example) by heat treatment in an autoclave under an oxygen atmosphere at a temperature of 950°C and a pressure of 200 atm for 6 hours are also shown. The superconducting properties of the synthesized powder were evaluated by SQUID.
Tc was measured by the Meissner effect in a magnetic field of 50 oersted ( _Oe ) using a magnetometer.

As can be seen from the characteristic evaluation results in Table 4, all of the superconducting oxides according to the examples had a Tc of 82 to _{83 K.} In Table 4, Nos. 3 and 4 are _YBa2Cu4O8 superconducting oxide powders produced by the manufacturing method of the examples.

FIG. 9 shows a powder X-ray diffraction pattern for explaining the effect of one embodiment of the superconducting oxide of the present invention;
(a) is a powder X-ray diffraction pattern after calcination of the raw material powder;
(b) shows the conventional sample powder (YBa ₂ Cu ₄ O ₈ ) prepared by the high-pressure oxygen method (950°C, 200 atm, 6 hours) of No. 2 (Comparative Example) in Table 4.
1(b) is an X-ray diffraction pattern of a sample powder (YBa ₂ Cu ₄ O ₈ superconducting oxide powder) obtained by HIP treatment (1050° C.×1000 atm×3 hr) in accordance with the embodiment of the present invention.

In the powder X-ray diffraction pattern (b), the cross marks indicate YBa ₂
The peaks of impurities other than Cu ₄ O ₈ are shown.

In the powder X-ray diffraction pattern (c), the numbers in the figure indicate the YBa ₂ C of the YBa ₂ Cu ₄ O ₈ superconducting oxide powder of the example.
The index of the peak based on the u ₄ O ₈ type structure.

The calcined powder was heated at 90K as shown in FIG.
It has the structure of superconductor YBa ₂ Cu ₃ O ₇ , but from this structure it is YBa
_It is clear that diffusion of Cu atoms is necessary to synthesize _2Cu4O8 . Although a catalyst is used in the atmospheric pressure method, the diffusion rate is _slow , and even though the macrostructure is _{YBa2Cu4O8 ,} the microstructure contains _a large number of _{YBa2Cu3O7 - type} defects.
This is thought to be why Tc was kept low at around 75K.

On the other hand, in the high-pressure oxygen method, the temperature is 950°C and the pressure is 200 atm, so there are fewer defects compared to the atmospheric pressure method, and Tc is
It is believed that the number has improved to 78K.

In contrast, in the HIP method according to the embodiment, the treatment is carried out at the same oxygen partial pressure as the high-pressure oxygen method, but the total pressure is 1000 atm, which further increases the diffusion rate (see Nos. 3 and 4 in Table 4), making it possible to produce more uniform samples.

Furthermore, the fact that a Tc higher than the liquid nitrogen temperature can be stably obtained by increasing the total pressure without using pure oxygen is a major advantage from the standpoint of operational safety.

Example 5 Using powders of _Y2O3 , _Ho2O3 , CaO, BaO, and CuO _with a purity of 99.9% _, x in (R1 _{- xCax} ) _Ba2Cu4O8 (where R = Y, _Ho ) was calculated _.
Various raw material powder mixtures were prepared so that the % saturation was 0, 0.05, 0.1, 0.2, 0.3, and 0.5. Since BaO and CuO are unstable in air, the mixtures were prepared in a glove box with an argon atmosphere. Next, the raw material powder mixtures were mixed and heated without calcination (or preliminary heat treatment) in an Ar-80%, O
₂ -20% mixed gas atmosphere, total pressure 1500 atm (oxygen partial pressure Po
The HIP treatment was carried out at a temperature of 1050°C under a pressure of ₂ = 300 atm for 3 hours.

The resulting powder was subjected to X-ray diffraction.
Some of the results are shown in Figure 10. Figure 10 shows the results of the Y _0.9 Ca _0.1 Ba ₂ Cu ₄ O
₈ , and Fig. 11 shows the structure of Ho _0.95 Ca _0.05 Ba ₂ Cu ₄ O
_8. The powder X-ray pattern in FIG. 10 shows that the powder-produced phase exhibits a YBa ₂ Cu ₄ O ₈ type structure, and the powder X-ray pattern in FIG. 11 shows that the powder-produced phase exhibits a Ho
This indicates that it has a Ba ₂ Cu ₄ O ₈ type structure.

The obtained superconducting powder (Y _0.9 Ca _0.1 Ba ₂ Cu ₄ O ₈ ) was placed in a 5 mm diameter tube.
After filling a silver pipe with a diameter of 3 mm, an inner diameter of 3 mm, and a length of 80 mm, one end of the pipe was sealed with a silver cap, and the other end was closed with another silver cap with a small hole (0.1 mmφ). The pipe was evacuated to 10-1 Torr to prevent the powder from scattering, and finally the cap was crushed to seal the pipe. This was then swaged to a diameter of 0.75 mm, an outer diameter of 0.75 mm, and the other end was closed with a silver cap with a small hole ^(0.1 mmφ).
After drawing the wire to a diameter of 1 mm, it was rolled into a tape shape with a thickness of 0.2 mm.
The wire was sintered by HIP treatment at a temperature of 830°C and 1000m for 10 hours to obtain an oxide superconductor wire.

As described above, the present invention has realized an oxide superconductor that has a superconducting transition temperature that is sufficiently higher than the temperature of liquid nitrogen and that does not lose oxygen even at high temperatures during processing. This oxide superconductor can be used in a wide range of fields, such as wiring for low-temperature electronic devices and magnetic shielding.

Furthermore, according to the present invention, the Tc of the RBa ₂ Cu ₄ O ₈ type oxide is increased,
Moreover, a method that can be produced in a short time and a useful method for producing oxide superconductor wires have been realized.

BRIEF DESCRIPTION OF _THE DRAWINGS FIG _. 1 is a diagram for explaining the chemical structure of _RBa2Cu4O8 , FIG _. 2 is a diagram for explaining the chemical structure of _{RBa2Cu3O7 ,} FIG _{. 3} is a powder X-ray diffraction pattern of the product phase of a sintered body of _{Y0.75Ca0.25Ba2Cu4O8} obtained in Example 1, FIG _{. 4} is a graph showing the superconducting properties of _{Y0.75Ca0.25Ba2Cu4O8} obtained in Example 1, FIG _{. 5} is a graph showing _the results of thermogravimetric analysis of _Y0.7Ca0.3 obtained in Example 1, FIG _. 6 _is a powder X-ray diffraction pattern of the product phase of _{a sintered} body of _{Ho0.9Ca0.1Ba2Cu4O8} according to the present invention _{, and} FIG.
_{Superconducting} properties of Ba ₂ Cu ₄ O ₈ (relationship between temperature and _resistivity )
FIG. 8 is a graph showing the results of thermogravimetric analysis of the sample in Example 2. FIG. 9 is a powder X-ray diffraction pattern for explaining the effect of one embodiment of the oxide superconductor of the present invention. FIG. 10 is a graph showing the results of _{thermogravimetric} analysis of the sample in Example 5 _.
a is the powder diffraction pattern of ₂ Cu ₄ O ₈ , and FIG. 11 is the powder X-ray diffraction pattern of Ho _0.95 Ca _0.05 Ba ₂ Cu ₄ O ₈ obtained in Example 5.

───────────────────────────────────────────────────────── Continued from the front page (51) Int.Cl. ⁶ Identification symbol Internal reference number FI Technical marking location H01B 13/00 565 D (71) Applicant 999999999 Mitsubishi Materials Corporation 1-5-1 Otemachi, Chiyoda-ku, Tokyo (71) Applicant 999999999 Tokyo Electric Power Company, Inc. 1-1-3 Uchisaiwai-cho, Chiyoda-ku, Tokyo (72) Inventor Miyatake Takayuki 1-14-3 Shinonome, Koto-ku, Tokyo Superconductivity Engineering Research Institute, International Superconductivity Technology Center (72) Inventor Koshizuka Naoki 1-14-3 Shinonome, Koto-ku, Tokyo Superconductivity Engineering Research Institute, International Superconductivity Technology Center (72) Inventor Hayashi Seiji 7-3-323 Takamaru, Tarumi-ku, Kobe, Hyogo Prefecture (72) Inventor: Kazuyuki Shibuya, 1-6-14 Izumidai, Kita-ku, Kobe, Hyogo Prefecture (72) Inventor: Takeo Kawate, 4-20-4 Shioya Kita-machi, Tarumi-ku, Kobe, Hyogo Prefecture (72) Inventor: Yoshio Masuda, 6-2-1 Minatojima-nakamachi, Chuo-ku, Kobe, Hyogo Prefecture (72) Inventor: Rikuro Ogawa, 3-12-11 Izumidai, Kita-ku, Kobe, Hyogo Prefecture (72) Inventor: Yoshito Fukumoto, 735 Ogo, Ogo-cho, Kita-ku, Kobe, Hyogo Prefecture (72) Inventor: Takahiro Wada, 1-14-3 Shinonome, Koto-ku, Tokyo, Japan, Superconductivity Engineering Research Institute, International Superconductivity Technology Center (72) Inventor: Shinichi Koriyama ... Superconductivity Engineering Research Institute, International Superconductivity Technology Center (72) Inventor: Ken Sakurai, 1-14-3 Shinonome, Koto-ku, Tokyo, Japan. Superconductivity Engineering Research Institute, International Superconductivity Technology Center (72) Inventor: Nobuo Suzuki, 1-14-3 Shinonome, Koto-ku, Tokyo, Japan. Superconductivity Engineering Research Institute, International Superconductivity Technology Center (72) Inventor: Takao Yamauchi, 1-14-3 Shinonome, Koto-ku, Tokyo, Japan. Superconductivity Engineering Research Institute, International Superconductivity Technology Center (72) Inventor: Shoji Tanaka, 1-14-3 Shinonome, Koto-ku, Tokyo, Japan. Superconductivity Engineering Research Institute, International Superconductivity Technology Center (56) References: JP 3-109214 (JP, A)

Claims (3)

[Claims] [Claim 1] An oxide superconductor represented by the chemical formula (R1 _{-xCax ) Ba2Cu4O8} , wherein R is one or more elements selected from _the group consisting of Y and lanthanide series rare earth elements, _and x is in the range of 0.001≦x≦0.5 (provided that R is Y).
(x is 0.001≦x≦0.2 except when x is 0.001≦x≦0.2) Claim 2: A method for producing a superconducting oxide having a structure of RBa ₂ Cu ₄ O ₈ (where R is one or more elements selected from the group consisting of Y and lanthanide series rare earth elements), comprising:
A method for producing a superconducting oxide, characterized in that raw material powder is calcined and then subjected to hot isostatic pressing in a mixed atmosphere of inert gas and oxygen gas. Claim 3: R (wherein R is one or more elements selected from the group consisting of Y and lanthanide series rare earth elements), Ca,
A raw material powder mixture for oxide superconductor manufacturing, consisting of Ba, Cu, and O, is heated at 850 to 1100 K under a mixed atmosphere of inert gas and oxygen gas.
By subjecting the powder to hot isostatic pressing in a temperature range of 100°C, an oxide _{superconductor} powder containing an oxide represented by (R1 _{-xCax ) Ba2Cu4O8 (} where x is 0.001 to _0.5 , _and R has the same meaning as above) is produced without generating an intermediate oxide represented by ( _{R1- xCax} ) _Ba2Cu3O7 before the hot isostatic pressing,
The method for producing an oxide superconductor wire comprises filling the powder into a sheath material, drawing the material into a wire, and then sintering the wire.