JPH01197321A - oxide superconductor - Google Patents

Abstract

PURPOSE:To obtain an oxide superconductor exhibiting always and stably a Tc >=100 by specifying a compsn. of Bi-IIa element-rare earth element-Cu-O of a ceramic oxide superconductor. CONSTITUTION:The title superconductor comprises a material having a compsn. expressed by the formula, wherein A is Bi; B is Ba, Sr, Ca, Be; C is Sc, Y, one among lanthanides; D is Cu,; E is O; each (a), (b), (c), (d), and (e) is a positive integer or a positive decimal showning each proportion of element. The oxide superconductor can be kept at superconducting state without any practical problem with inexpensive liquid N2. Moreover, since the superconductor has a large temp. margin for liquid N2, the characteristics of critical current at near the b.p. of liquid N2 are improved. Particularly, when B in the formula is Ba, and C is Y, a higher Tc and stabler superconducting characteristics may be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a novel ceramic-based oxide superconductor.

<Problems to be solved by conventional techniques and ideas> In recent years, ceramic-based oxide superconductors have been discovered that exhibit a higher critical temperature (Tc) than metal-based superconductors, and are being widely studied.

By the way, it is no exaggeration to say that the most significant thing in the field of superconductivity is to further increase TC. This is because it enables the use of cheaper cooling media such as hydrogen, neon, and even nitrogen, dramatically expanding the range of practical applications.

However, since the BaPbB10-based oxide superconductor called BPB, which has been widely known as the above-mentioned oxide superconductor, has a Tc of only 13K at most, it is difficult to put it into practical use.

Also, LaS rcuo-based oxide superconductors with a layered perovskite structure are known, but their Tc is 40
~60%, and there are still difficulties in putting it into practical use.

On the other hand, a YBaCuO-based oxide superconductor with a complex layered perovskite structure of oat lohn picks has been developed and has been found to exhibit a Tc exceeding 77.3K, which is the boiling point of liquid nitrogen at normal pressure. The above YBaCuO
The oxide superconductor of this type has an electrical resistance of zero near 90°C, exhibits a clear Meissner effect, and has also been reported to have data showing an even higher Tc. However, no material has yet been developed that maintains Tc of 100 or more stably and with good reproducibility for more than one month.

However, in order to stably maintain a superconducting state using the liquid nitrogen, it is necessary to exhibit a Tc of 100 or more, considering the margin. Therefore, there has been a demand for the development of superconductors that exhibit even higher Tc.

The present invention has been made in view of the above-mentioned needs, and an object of the present invention is to provide an oxide superconductor that can always stably exhibit a Tc of 100 or more.

Means for Solving the Problems> The oxide superconductor of the present invention for achieving the above object is characterized by having a composition represented by the following general formula (1).

A a B b Cc D d E e ...=
(1) However. In (1), A is Bi and B is Ba.

S is at least one element selected from 5cSY, Ca5Mg, Be, C is at least one element selected from 5cSY, lanthanide, D is Cu, E is O, a, b ,cSd.

e is a positive integer or decimal number indicating the proportion of each element.

Also. In (I), Ba is particularly preferable as B, and Y is particularly preferable as C.

Effect> According to the ceramic-based oxide superconductor having the above structure, it is possible to stably exhibit a Tc of 100 or more. This is presumed to be based on the following reasons.

That is, among the elements constituting the oxide superconductor, Cu
Even if A g s A u s P is replaced with another element such as A g s A u s P , a superconductor cannot be obtained. therefore,
It is estimated that Cu and O greatly contribute to obtaining high Tc. On the other hand, Bi is mainly +3 valent, and has a characteristic that, for example, when a part of the rare earth ions in iron garnet is replaced with Bi3+, the Faraday rotation of the magneto-optic effect becomes extremely large.

Also, the spin-orbit interaction energy of ions is very large for heavy ions. Here, as the periodic table Va group elements,
In addition to Bi, there are Sb, As, P, etc., and the inclusion of Bi, the heaviest among them, is thought to be the reason why the high Tc was obtained.

Furthermore, the 6P orbital of BL3+, which has a large spin-orbit interaction, mixes with the 2P orbital of 02-, and the charge transfer transition of at least one element selected from Ba5S, rSCa, and Mg5Be as group IIa elements of the periodic table. It is thought that this increases the spin-orbit interaction in the excited state.

On the other hand, 5csY, which is a Ha group element in the periodic table, and lanthanide do not make much difference in Tc even if these are replaced. This is a phenomenon similar to that in a YBaCuO-based oxide superconductor, almost the same Tc can be obtained even if the Y site is replaced with a lanthanide such as HosGdsEr. Therefore, the above circumscribed table ■Sc, Y, which is the original code of group a
, and lanthanides are essential for forming the crystal structure, but it is presumed that their contribution to superconducting properties is small. Therefore, the oxide superconductor of the present invention has a periodic table In
At least one element selected from 5cSY and lanthanide may be included as the a-group element.

still. Regarding B in (1), the above Ba5Sr.

It may be at least one element selected from Ca s M g s B e SRa.

and. When B in (I) is Ba and C is Y, in other words, when the oxide superconductor has a composition represented by the following general formula % formula % (1), even higher Tc and , it will exhibit more stable superconducting properties.

still. Xs )'% Zs pSQ in (II) is a positive integer or decimal number each indicating the proportion of the element.

The above-mentioned oxide superconductor may be obtained by a powder sintering method in which powders or solutions of oxides, carbonates, sulfates, nitrates, or oxalates mixed to have the above-mentioned composition are sintered. Can be done. In addition, sputtering and C
VD can also produce a thin film on the surface of a stabilizing material such as Cu or AJ or a substrate material.

The sintering temperature and time in the above powder sintering method are appropriately selected depending on the type and composition of the raw material elements, but
It is desirable that sintering proceed only by solid phase reaction without melting of the material during sintering. Further, it is desirable that the crystal growth of the sintered composite oxide does not become excessive and that the sintered body becomes dense.

<Example> Next, examples of the present invention will be described below.

Example 1 B i 20 s with a purity of 3N or more and an average particle size of 5 μm or less
Each powder of rBaC03, Y203, CuO,
They were mixed so that the composition ratio after firing was Bi:Ba:Y:Cu-1:1:1:3.

The above mixed powder was fired at 850°C for 12 hours in the air,
The solidified powder was ground in a mortar to a size of about 100 mesh or less. Next, each powder is filled into a rubber mold and s1. Static pressure molding was performed at a pressure of 5 tons/- to obtain a rod-shaped sample with a diameter of 5 mm and a length of 30 mm.

This sample was further sintered in air at 880°C for 12 hours, resulting in a 30 mm diameter of approximately 4 mm with good density.
A sintered body with a short length was obtained. Electrodes were attached to this using ultrasonic soldering, and the critical temperature was measured while passing a weak current using the four-terminal method. The results are shown in curve A in FIG.

As is clear from curve A, it is considered that a mixture of superconductors having two or more critical temperatures is formed in terms of electrical resistance. That is, although the above superconductor is not a single phase,
It is clear that superconductors with characteristics of a critical temperature of 120°C or higher are produced, and even where the electrical resistance becomes completely zero, the critical temperature is 102°C. This is higher than the critical temperature of 93 to 95 for the 1-2-3 composition of YBaCuO, which has conventionally been stably achieved.

Example 2 Bigot with a purity of 3N or more and an average particle size of 5 μl or less.

BaCO3, Y20S, and CuO powders were mixed so that the composition ratio after firing was Bi:Ba:Y:Cu-2:1:1:6.

Using the above mixed powder and using the same method as in Example 1,
Finally, a sintered body with a diameter of about 4 mm and a length of just under 30 mm with good density was obtained. Electrodes were attached to this using ultrasonic soldering, and the critical temperature was measured while passing a weak current using the four-probe method. The results are shown in curve B in FIG.

As is clear from curve B, also for this example,
In terms of electrical resistance, it is thought that a mixture of superconductors with two or more critical temperatures is formed, and it is clear that superconductors with critical temperatures of 121 or higher are formed.

Example 3 A mixed powder of B i S rYCuO with a purity of 4N class and an average particle size of 1- or less, prepared by a coprecipitation method using oxalate, was lightly compacted with a press mold, and Bi, S
A pellet with a composition in which the ratio of r, Y, and Cu was 2:1:1:3 was created.

This was placed on an alumina plate and fired at 850°C for 12 hours to produce a disk-shaped sample with a diameter of 20 ITIITl and a thickness of 2 mm.

When this sample was cooled in liquid nitrogen and then placed on a Nd-Fe permanent magnet, it levitated by about 6 mm. After confirming the Meissner effect of this material, the sample was cut into a rod shape with a width of 5M, thickness of 21TIIT, and length of 20mm, and electrodes were attached using ultrasonic solder to measure the critical temperature. The sample temperature was determined by changing the temperature in the cryostat using a calibrated Au(Fe)Ag thermocouple.
A curve equivalent to A in the figure was obtained. However, the electrical resistance itself was higher than in Example 1.

Test example> The following test was conducted to confirm the effect of element substitution.

Using commercially available copper oxide powder and powders of carbonates of group Ila elements, oxides of group A elements, and oxides of group VB elements, raw material powders having the compositions shown in the table were prepared.

Each raw material powder was ground to a particle size of 4 μm or less using a ball mill, and then placed all at once on an alumina plate.
Fired at ℃ for 15 hours, and measured the electrical resistance of the resulting fired body using a tester.Those with a low resistance value are sent as is to the main sintering process, and those with a high resistance value are crushed again to achieve the same result. The process of firing, pulverizing, and firing was repeated under different conditions.

These were further pressed in a mold at a pressure of 1 to 1.5 tons/-, and then sintered at 850°C for 12 hours.

Electrodes were attached to the sample obtained above using ultrasonic solder while in pellet form, and the critical temperature was measured using a multi-point variable temperature cryostat.

In the table, Tco is the temperature at which the electrical resistance begins to rapidly decrease, and Tci is the temperature at which the phase transition ends at which the electrical resistance becomes completely zero.

From the table, the superconductor of the present invention has B 1 s Cu and 0
is essential, but it is clear that Ba can be replaced with Ca, Sr, Mg, etc., and Y can be replaced with lanthanides called yttrium group. Moreover, from these results, it is inferred that there is no large change in Tco even if two or more types of elements are included, provided that they belong to the same group of the periodic table, rather than just one type of element.

(Left below) For YBaCuO-based oxide superconductor materials, it is common practice to anneal them in an oxygen atmosphere at 300 to 800°C after main sintering. Since this was a test to confirm the effect of substitution, no annealing was performed. Moreover, the optimum conditions were not necessarily selected for the sintering temperature and time. Therefore, in the above test example, the difference between Tco and Tci is large, and in some cases, the electrical resistance does not become completely zero at the liquid nitrogen temperature.

However, by optimizing the sintering conditions and the subsequent annealing conditions, Tci approaches Tco, and in fact, although not shown in the table, changing the sintering conditions will reduce Tco. There was not much change in Tci, but Tci increased significantly.

<Effects of the Invention> As described above, according to the oxide superconductor of the present invention, 1
Since the superconducting state has a critical temperature of 0.00 or higher, the superconducting state can be maintained without any practical problems using inexpensive liquid nitrogen.

Therefore, the practical application of medical MIR devices, high-energy physics synchrotrons, magnetic levitation trains, etc. can be greatly promoted.

Furthermore, since the temperature margin with respect to the boiling point of liquid nitrogen is large, the characteristics of critical current near the boiling point can also be improved.

especially. When B in (1) is Ba and C is Y, the unique effect of exhibiting even higher Tc and more stable superconducting properties is achieved.

[Brief explanation of the drawing]

The figure is a graph showing the relationship between temperature and electrical resistance for the oxide superconductors of Examples 1 and 2. Patent applicant Sumitomo Electric Industries, Ltd. Representative Patent attorney Hiroshi Kamei (and 2 others) Temperature

Claims (2)

[Claims] 1. An oxide superconductor characterized by having a composition represented by the following general formula (I). AaBbCcDdEe...(I) (In formula (I), A is Bi, and B is Ba, Sr, Ca
, Mg, and Be; C is at least one element selected from Sc, Y, and lanthanides; D is Cu; E is O;
a, b, c, d, e are positive integers or decimals each indicating the proportion of the element) 2. The oxide superconductor according to claim 1, wherein B in formula (I) is Ba and C is Y.