JP2533108B2 - Superconducting material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a superconducting material, and more particularly to a superconducting material having a critical temperature at a relatively high temperature.

《Prior art》 It is indispensable to cool superconductors known up to now by cryogenic liquid helium (boiling point 4.2K), which results in enormous cooling cost, and eventually in superconducting state. It had the drawback of being smaller in scale. In addition, the uneven distribution of helium in resources has hindered the widespread use of superconductors.

However, very recently, a superconductor having a superconducting critical temperature Tc (transition initiation temperature) exceeding liquid nitrogen temperature (boiling point 77K) has been reported. For example, University of Houston C.
W. Chu et al. Reported that they found oxides of the barium-yttrium-copper-oxygen system with a critical temperature of 94 K (Phys. Rev. Letter, vol. 58, P. 908-909, 198).
7).

Also, the group of Kitazawa et al. Of the University of Tokyo has a critical temperature of 95% in barium-ytterbium-copper-oxygen system oxides.
Takagi et al.'S group at the University of Tokyo also reported a critical temperature of 95 K in barium-erbium-copper-oxygen-based oxides (both Ja
p.Journal of Appl.Phys., vol.26, April issue, 1987).

Further, the second component of the above three kinds of oxides is scandium,
90K even in oxides substituted with lutetium, thulium, holmium, dysprosium, gadolinium, etc.
Some critical temperatures have been reported.

All of these various superconductors are represented by the general formula: BaxMyCu ₃ O _9-z .

However, M is one kind of element selected from Y, Yb, Er, Sc, Lu, Tm, Ho, Dy and Gd, x is 1 to 3, preferably about 2, y is 0.5 to 1.5, preferably It has an oxygen-deficient perovskite type crystal structure represented by about 1. Of these various superconductors, Yb, Ym, Er, Ho, Dy and Gd of M are all present in the oxide as ions having magnetism under a strong magnetic field.

By the way, in many years of research on superconductors, it has been known that solid solution of magnetic impurities in the superconductor improves the critical magnetic field and the critical current (for example, F. Fischer et al., Appl. .Phys., Vol.16, p.1,1978 etc.).

Generally, the reason why the critical magnetic field and the critical current are improved by the addition of magnetic impurities in the type 2 superconductor is that the quantized magnetic flux (vortex) penetrating through the type 2 superconductor becomes a solid solution. It is explained that, because the magnetic impurities are stabilized by energy and pinned, the movement of the magnetic flux, that is, the local destruction of the superconducting state is unlikely to occur even when an external magnetic field or the like is applied.

<< Problems to be Solved by the Invention >> However, in all known superconductors such as the Schbrel compound, there has been a problem that the critical temperature is greatly lowered by the addition of magnetic impurities. On the other hand, recently, superconductors having an oxygen-deficient perovskite-type crystal structure are extremely good because the superconducting critical temperature does not decrease despite the fact that a large amount of magnetic ions are contained in the superconductor. Was found.

Therefore, the inventors of the present invention have made various studies on the metal M in the above general formula, and as a result, as the M, a non-magnetic rare earth metal and N
As a result, the inventors have found that it is possible to combine a rare earth metal having magnetism, which not only greatly expands the selection range of the raw material, but also improves the critical magnetic field and the critical current, and has reached the present invention.

Therefore, a first object of the present invention is to provide a superconducting material having a relatively high critical temperature, a high critical magnetic field and a high critical current value.

A second object of the present invention is to provide a method for easily selecting a superconductor material having a relatively high critical temperature.

Above the objectives of the present invention "means for solving the problem" in the general formula: BaxMyNzCu ₃ consists O _9-u of the composition, superconducting material characterized by having an oxygen-deficient perovskite-type crystal structure Achieved by Here, M is at least one non-magnetic rare earth metal selected from the group of Y (yttrium), Sc (scandium), La (lanthanum), and Lu (lutetium), and N is Yb.
(Ytterbium), Tm (thulium), Er (erbium), Ho (holmium), Dy (dysprosium), Gd
(Gadolinium) and Sm (samarium) at least one magnetic rare earth metal selected from the group, x is 1 to 3, y
And z are each 0.01 to 1.5, and u is 0 to 3. Preferably, x is about 2 and y + z is about 1.

In the oxide of the present invention, most of Cu exists in a divalent state, M and N are approximately trivalent, and Ba is divalent, so that O
However, depending on the firing temperature and the atmosphere when the composition is crystallized, some of the Cu may be in the trivalent state, and in that case, as a whole. , O will appear slightly higher than 6.5, but this case is not excluded in the present invention, and if the composition close to Ba ₂ MyN ₁ -yCu ₃ O _6.5 occupies most of it. Is enough. Further, in the present invention, the case where a composition other than the above composition and / or a metal coexists is not excluded unless it adversely affects the achievement of the object.

Further, due to the magnetic effect, it is considered that the electronic device exhibits unique device physical properties.

<Effects of the Invention> The superconducting material of the present invention not only realizes a superconducting state at liquid nitrogen temperature, but also has a large critical current, and is stable even when heated to a high temperature of about 900 ° C. in air. is there.
In addition, the critical current density Ic can be adjusted to 10 ⁵ by adjusting the composition.
The present invention is extremely significant industrially because it can be sufficiently controlled to about 10 ⁶ A / cm ² .

Example 1. M in the general formula BaxMyNzCu ₃ O _9-u of the present invention Y, the N Yb
And x: y: x = 2: 0.8: 0.2 barium by a known method
An yttrium-ytterbium-copper-oxygen based composition was prepared.

The above composition was prepared by using a calculated amount of reagent grade BaCo ₃ , Y
Ethanol was added to each powder of ₂ O ₃ , Yb ₂ O ₃ and CuO, wet-mixed in an agate mortar, put in a crucible, pre-baked at 900 ° C. for 12 hours, taken out of the furnace, and then pulverized again. 1,00
Pressing was performed at a pressure of 0 kg / cm ² to obtain pellets, and sintering was performed in a furnace at 900 ° C. for 5 hours.

The obtained sintered product was confirmed by X-ray diffraction to have an oxygen-deficient perovskite crystal structure.

For this sinter, the superconducting critical temperature Tc, transition temperature range ΔTc (temperature interval when the rate of change when the electrical resistivity changes from a normal value near Tc to zero resistance is 90% and 10%)
Table 1 shows the results of measuring the critical current density Ic.

Comparative Examples 1 and 2. Similar to Example 1, x: y: z = 2: 1: 0 barium-yttrium-copper-oxygen composition (Comparative Example 1) and x: y:
A barium-ytterbium-copper-oxygen composition (Comparative Example 2) having z = 2: 0: 1 was prepared.

Table 1 shows the results of measuring the superconducting critical temperature Tc, the transition temperature width ΔTc and the critical current density Ic of each sample.

Example 2 In the general formula BaxMyNzcu ₃ O _{9-u according} to the present invention, M is
La and N were set to Er, and a barium-lanthanum-erbium-copper-oxygen composition having x: y: z = 2: 0.5: 0.5 was prepared.

The above composition was prepared by using calculated amounts of reagent grade BaCO ₃ , La
Ethanol was added to each powder of ₂ O ₃ , Er ₂ O ₃ and CuO, and they were wet-mixed in an agate mortar, put in a crucible, pre-baked at 950 ° C. for 12 hours, taken out of the furnace, and then pulverized again. 1,00
It was carried out by pressing at a pressure of 0 kg / cm ² into pellets and sintering in a furnace at 950 ° C. for 6 hours.

The obtained sintered product was confirmed by X-ray diffraction to have an oxygen-deficient perovskite crystal structure.

Table 2 shows the results of measuring the superconducting critical temperature Tc, transition temperature width ΔTc, and critical current density Ic of this fired product.

Comparative Examples 3 and 4. Similar to Example 2, x: y: z = 2: 1: 0 barium-lanthanum-copper-oxygen based composition (Comparative Example 3) and x: y: z =
A 2: 0: 1 barium-erbium-copper-oxygen composition (Comparative Example 4) was prepared.

Table 2 shows the results of measuring the superconducting critical temperature Tc, the transition temperature width ΔTc, and the critical current density Ic of each of the samples of Comparative Example 3 and Comparative Example 4.

The results in Tables 1 and 2 demonstrate that the superconducting material of the present invention was able to achieve a significantly higher critical current density than the conventional ones.

Claims (1)

(57) [Claims] 1. A composition of the general formula BaxMyNzCu ₃ O _9-u ,
A superconducting material having an oxygen-deficient perovskite type crystal structure (wherein M is at least one non-magnetic rare earth metal selected from the group of Y, Sc, La and Lu, and N is
It is at least one kind of magnetic metal selected from the group of Yb, Tm, Er, Ho, Dy, Gd and Sm, x is 1 to 3, y and z are 0.01 to 5 and u is 0 to 3 respectively. . ).