JP2975608B2 - Insulating composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to an insulating composition used for a superconducting element.

(Prior Art) In recent years, since it was announced that Ba-La-Cu-O-based layered perovskite-type oxides may have a high critical temperature, research on oxide superconductors has been carried out in various places. (Z.Phys.B Condensed Matter 64,189-193 (198
6)). Among them, it has been confirmed that a defective perovskite-type oxide superconductor having excess oxygen typified by the Y-Ba-Cu-O system has a critical temperature of 90K or more and a high temperature of liquid nitrogen or more (Phys. .Rev.Lett.Vol.58, N
o.9,908-910).

Furthermore, in 1988, the critical temperature of Bi-Sr-Ca-
Cu-O based superconducting oxides have been discovered (Nihon Keizai Shimbun, January 22, 1988).

This Bi-Sr-Ca-Cu-O based superconducting oxide is Ba-La
-Compared to superconducting oxides based on -Cu-O or Y-Ba-Cu-O, not only the critical temperature is high, but also expensive rare earth elements are unnecessary, and chemical stability against moisture etc. is high. This is an excellent oxide superconducting material.

By the way, superconducting elements utilizing the tunnel effect can operate at a very high speed and consume little power. Therefore, application to digital devices such as a logic element and a memory element of a computer is being promoted. And Nb / Aloxide / Nb junction and N
A 4-bit multiplier using a bN / MgO / NbN junction or the like, a 3K gate array, and the like have been prototyped. Also, superconducting three-terminal devices have been prototyped as superconductor-semiconductor devices, but all of these devices are composed of superconductors with a low critical temperature and use liquid helium as a refrigerant, so the development of peripheral technologies and economic efficiency Due to problems etc., it has not been put to practical use.

For this reason, application of an oxide superconducting cover having a high critical temperature to the above-described superconducting element has been studied.

However, when the above-described superconducting element is obtained using an oxide superconductor and an insulating composition, a new electron level is generated here because of poor matching between the oxide superconductor layer and the crystal plane of the insulating composition. Since the charge is trapped and the function as a Josephson element is impaired, there is a problem that it is difficult to obtain desired characteristics.

However, when the above-described superconducting element is obtained using an oxide superconductor and an insulating composition, a new electron level is generated here because of poor matching between the oxide superconductor layer and the crystal plane of the insulating composition. Since the charge is trapped and the function as a Josephson element is impaired, there is a problem that it is difficult to obtain desired characteristics.

Furthermore, Bi-based superconductors have a Bi ₂ S
r ₂ Ca ₂ Cu ₃ O ₁₀ and Bi ₂ Sr ₂ CaCu ₂ O _{8 with a} transition temperature around 80 K
It has been known. However, higher Tc Bi ₂ Sr ₂ Ca
There was a problem that it was not easy to synthesize ₂ Cu ₃ O ₁₀ . This is considered to be due to the modulation structure existing in the b-axis direction of the crystal of the Bi-based superconductor or the internal stress which is the cause thereof.

(Problems to be Solved by the Invention) As described above, when a superconducting element is obtained by using a conventional insulating composition, there is a problem in that the matching between the oxide superconductor layer and the crystal plane of the insulating composition is poor. Was. Further, there is a problem that it is not easy to synthesize Bi ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ having a higher transition temperature.

The present invention has been made in view of such a problem, and an object of the present invention is to provide an insulating composition having good consistency with a crystal plane of an oxide superconductor. Still another object of the present invention is to provide an insulating composition in which the modulation structure is relaxed or eliminated.

[Constitution of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention provides Bi, Sr, Ca, C
In the oxide superconductor composition composed of u, O or Tl, Ba, Ca, Cu, O, Ca is RE (where RE is Nd, Sm, Eu, Gd, T
An element selected from b, Dy, Ho, Er, Tm, Yb, Lu and Y. ).

 It should be noted that even if some Ca remains.

Here, the atomic ratio of Bi, Sr, RE, Cu or Tl, Ba, RE, Cu is basically 2: 2: 1: 2, but the deviation is about 2: X: Y: Z. It doesn't matter.

However, 1.5 ≦ X ≦ 2.5 0.5 ≦ Y ≦ 1.5 1.8 ≦ Z ≦ 2.5 In the insulating composition of the present invention, Bi may be partially substituted with Pb.

Here, if the substitution amount of Bi in Pb exceeds 1.5, the crystal structure is different, and therefore it is preferably 1.5 or less. Further, 0.2 to 1.0 is particularly preferable.

The insulating composition of the present invention can be used as an insulating material for an insulating layer, a substrate and the like in a superconductor element.

The case where the insulating composition of the present invention is used as an insulating layer of a superconductor element will be described.

The insulating composition can be obtained by mixing carbonates such as Bi, Sr, RE, and Cu, oxides, organic acid salts, and the like at a stoichiometric ratio, and firing the mixture at a temperature of 800 to 900 ° C.

The mixing ratio of the raw materials does not need to be strictly a stoichiometric ratio, and a difference of about 10% may be used. Also,
It is also possible to add a small amount of an alkali metal compound to lower the reaction temperature.

For example, tunnel-junction type Josephson devices are manufactured by physical vapor deposition such as vacuum deposition, magnetron sputtering, ion beam sputtering, cluster ion beam, molecular beam epitaxy, and chemical vapor deposition such as CVD and plasma CVD. Thereby, an oxide superconductor layer, an insulating layer, and an oxide supermotor layer can be sequentially laminated on a substrate.

Alternatively, the oxide superconductor and the metal element forming the insulating composition can be formed by multi-source evaporation or multi-source sputtering using a vapor source or a target. The oxide superconductor is made of Bi, Sr, Ca, Cu, O,
When the insulating layer is made of Bi, Sr, RE, Cu, O, the workability is good because only one element needs to be replaced to switch between the formation of the oxide superconductor layer and the formation of the insulating layer. .

The thickness of the oxide superconductor layer is a thickness exhibiting superconducting properties,
That is, it is preferable that the thickness of the insulating layer is about 100 ° or more, that is, a thickness that does not hinder the tunnel effect, that is, 50 to 200 °.

Further, after forming each material layer, if necessary, heat treatment is performed at 400 to 900 ° C. in an oxygen-containing atmosphere, and oxygen is introduced into oxygen vacancies of the oxide superconductor to improve superconductivity.

In the same manner, a superconducting three-terminal element, a high-sensitivity magnetic sensor, and the like can be obtained.

When the insulating composition of the present invention is used as a substrate of a superconductor element, a single crystal substrate is formed by a normal flux method, FZ
(Floating Zone) method or cultivated by the kilopros method.

When growing an insulating composition composed of Bi, Sr, RE, Cu, and O by the flux method, Bi ₂ O ₃ and C are used as flux.
A flux containing uO at the same time may be used.

Furthermore, when growing an insulating composition comprising Bi, Sr, RE, Cu, and O by the flux method, the composition of each raw material cation is represented by the molar ratio% (β, γ, ε): βBi ₂ O ₃ γ ｛(Sr, RE) O｝ + εCuO where 5 ≦ β ≦ 25 20 ≦ γ ≦ 60 10 ≦ ε ≦ 60 2β + γ + ε = 100 may be satisfied.

(Action) The insulating composition of the present invention has the same or similar crystal structure as the oxide superconductor, and has a very close lattice constant. In addition, deterioration of characteristics due to charge trapping is suppressed.

In particular, when the insulating composition of the present invention is used as a substrate, since the crystal structure is the same or similar, an oxide superconducting thin film single crystal epitaxially grown on the substrate can be formed.

Further, the insulating composition of the present invention is stable even during high-temperature heat treatment and does not react with the crystal plane of the oxide superconductor.

Therefore, by using a superconducting element using the insulating composition of the present invention as an insulating material, it becomes possible to manufacture an IC, a transistor, a high-sensitivity magnetic sensor, and the like, which operate at ultra-high speed and consume low power.

Further, by replacing a part of Bi in the insulating composition of the present invention with Pb, the lattice constant further approaches that of a Bi-based superconductor. Further, the modulation structure of the insulating composition of the present invention is relaxed or disappears.

When a Bi-based superconductor thin film is grown on a single crystal of the insulating composition of the present invention, Bi ₂ Sr ₂ Ca ₂ Cu ₃ O having a high Tc is easily obtained.
₁₀ layers are obtained. This is presumably because the modulated structure is relaxed or eliminated in the insulating composition of the present invention, and the modulated structure is also relaxed or eliminated in the superconductor thin film epitaxially grown thereon.

Furthermore, in the superconducting thin film thus obtained, it was found that a sharp superconducting transition was obtained for the same reason, and that, for example, an improvement in the critical current at 77K was also observed.

That is, by using the insulating composition of the present invention as an insulating material in a superconductor element, a good superconductor element showing a sharp transition at 110 K can be easily obtained.

Although the Bi system has been described above, it is needless to say that the Tl system has the same crystal structure as the Bi system, and the same can be said.

(Example) Hereinafter, an example of the present invention is described based on a drawing.

Example 1 FIG. 1 shows a cross section of a tunnel junction type oxide superconducting element using an insulating composition of the present invention as an insulating layer. In FIG. On top, Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _α layer 3, Bi ₂ Sr ₂ Y ₁ Cu ₂ O _α layer 4, Bi ₂ Sr
₂ Ca ₁ Cu ₂ O _α layers 5 are sequentially laminated.

[Production of Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _α target] First, 33.5 mol% of Bi ₂ O ₃ powder, 33.5 mol% of SrCO ₃ powder, Ca
Using 33.5 mol% of CO ₃ powder and 16.7 mol% of CuO powder, wet grinding is performed in a monopot together with zirconia balls, followed by dehydration drying, heat treatment and calcination (850 to 900 ° C).
C., 24 h), and again placed in a monopot for wet pulverization, followed by dehydration and drying to obtain a powder (superconductor) having a particle size of 5 μm or less.

Next, polyvinyl alcohol was added to the raw material powder to prepare granules by granulation, and each granulated product was filled into a mold and molded under a pressure of 1000 kg / cm ² to have a diameter of 154 mm and a thickness of 6.5.
mm disks were made.

Further, this was calcined at an oxygen-containing atmosphere 840 ° C. X 24, the sintered density of an oxide superconductor represented by _{Bi 2 Sr 2 Ca 1 Cu 2} O α was obtained 98% of the target material.

[Production of Bi ₂ Sr ₂ Y ₁ Cu ₂ O _α target] A disk-shaped Bi ₂ Sr having a diameter of 154 mm and a thickness of 6.5 mm was formed in the same manner as described above, except that the above CaCO ₃ powder was replaced with Y ₂ O _{3. 2} Y ₁ Cu ₂ O _α
A target having a sintering density of 98% made of a non-conductive oxide represented by

[Manufacture of oxide superconducting element (Josephson element)] Using a Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _α target, a high-frequency magnetron sputter in a mixed gas of 7 Pa consisting of 95 mol% of argon and 5 mol% of oxygen , Substrate temperature 700 ℃ 10 × 1
On a 0 × 1 mm SrTiO ₃ substrate, a 1.0 μm thick Bi ₂ Sr ₂ Ca ₁ Cu ₂ O
_{An α} layer was formed.

Next, using the Bi ₂ Sr ₂ Y ₁ Cu ₂ O _α target, the above Bi ₂ S
the _{r 2} Ca ₁ Cu ₂ O α layer was formed on the _{Bi 2 Sr 2 Y 1 Cu 2} O α layer having a thickness of 10 Å.

Finally, a 1.0 μm thick Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _α layer is formed on the Bi ₂ Sr ₂ Y ₁ Cu ₂ O _α layer under the same conditions as described above, and a tunnel junction type Was obtained.

The critical temperature of the oxide superconducting device thus obtained was 77 K, and it was confirmed that current flowed through each layer by the tunnel effect at this temperature.

Tl ₂ Ba ₂ Y ₁ Cu ₂ O _α target was used as the insulating layer.
₂ Ba ₂ Y ₁ Cu ₂ O Form an _α layer and use Tl ₂ Ba ₂ Ca ₁ Cu ₂ as a superconductor
O _alpha except for using a target to form a _{Tl 2 Ba 2 Ca 1 Cu 2} O α layer was in the same manner as described above to form an oxide superconducting element, the critical temperature operate in 100K was confirmed.

Example 2 Bi ₂ Sr ₂ Ca ₂ Cu ₃ O Instead of Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _α target, Bi ₂ Sr ₂ Ca ₂ Cu ₃ O
Oxide superconductivity was obtained in the same manner as in Example 1 except that a Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _α layer was formed instead of the Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _α layers 3 and 5 using an _α target. The device was manufactured.

The critical temperature of this sulfide superconducting element was 70 K, and it was confirmed that current flowed through each layer by the tunnel effect at this temperature.

Comparative Example 1 An oxide superconducting device having the same structure as in Example 1 except that an Al ₂ O ₃ layer having the same thickness was formed instead of the Bi ₂ Sr ₂ Y ₁ Cu ₂ O _α layer 4 in Example 1 was used. Although formed, the device did not operate at a critical temperature of 77K.

In the above embodiment, Bi ₂ Sr ₂ Y ₁ Cu was used as the insulating layer.
_Although an example using a non-conductive oxide composed of ₂ O _{α has} been described, in the above formula, Y is Nd, Sm, Eu, Gd, Tb, Dy, H
Oxide in place of o, Er, Tm, Yb or Lu also has the same crystal structure, so that the same effect can be obtained.

Example 3 Bi ₂ O ₃ , SrCO ₃ , Y ₂ O ₃ , and CuO as raw materials were weighed and mixed in a total amount of 100 g so that Bi, Sr, Y, and Cu were in an atomic ratio of 3: 2: 1: 3,
Put in an alumina crucible, hold at 1150 ° C in the atmosphere for 24H, then cool to 800 ° C over 100H, cool down to room temperature, 20m
A single crystal of Bi ₂ Sr ₂ YCu ₂ O _{α of} m × 20 mm × 2 mm was obtained. As a result of X-ray diffraction, it was confirmed that it was a single crystal and had a (001) facet.

By RF sputtering on the substrate, was deposited _{Bi 2} Sr ₂ CaCu ₂ O α film at a substrate temperature of 550 ° C., the oxide superconductor single crystal film of uniform substrate and orientation were obtained. When the cross section of this film was analyzed by EPMA, the reaction between the substrate and the film was within the measurement limit. FIG. 2 shows the temperature characteristics of the electrical resistivity of this film. Excellent superconducting characteristics of Tc = 84K and ΔTc〜1K were obtained.

Comparative Example 2 A film was formed under the same conditions as in Example 3 except that a MgO single crystal was used as a substrate. A film having a C-plane orientation was obtained, but a polycrystalline film having a degree of orientation of about 70% was used. The MgO ions were detected in the film by EPMA analysis of the film cross section.

Example 4 Bi, Sr, Nd, and Cu were weighed so that the atomic ratio was 4: 2: 2: 5, and a single crystal was grown in the same manner as in Example 3, and 10 mm × 10 mm × 1 m
m ₂ Bi ₂ Sr ₂ Nd ₂ Cu ₃ O _α single crystal was obtained, and as a result of X-ray diffraction, it was confirmed that it was a single crystal and had a (001) facet. Bi ₂ S was deposited on this substrate by the cluster ion beam method.
When an r ₂ Ca ₂ Cu ₃ O _α film was formed at a substrate temperature of 450 ° C., an oxide superconducting single crystal film having the same orientation as the substrate was obtained.

Example 5 Powders of Bi ₂ O ₃ , PbO, SrCO ₃ , Y ₂ O ₃ , and CuO were prepared as starting materials, and the atomic ratio of the cations was Bi: Pb: Sr: Y: C.
A predetermined amount is weighed so that u = 1: 1: 2: 1: 2, and further, Bi ₂ O ₃ and CuO as a fax component are added so that the atomic ratio of Bi and Cu becomes one, respectively. This was mixed well.

Next, the mixed powder was put into an alumina crucible, heated to 1150 ° C. in the air, kept at this temperature for 24 hours to uniformly melt, and then cooled to 800 ° C. over 100 hours, and then cooled. The furnace was cooled to room temperature.

A large single crystal having a size of 10 mm × 20 mm × ₂ mm was precipitated in the obtained cooled solidified product. An X-ray analysis of this single crystal showed that BiPbSr ₂ YCu ₂ O _{8 + δ} (δ is excess oxygen) ), And was confirmed to be a single crystal with c-axis orientation with respect to the single crystal plate surface. The specific resistance is 104Ω at -100 ° C.
cm, and confirmed to function as an electrical insulator.

Next, the _{BiPbSr 2 Y Cu 2 O 8 +} δ Bi on a single crystal substrate
Bi-based oxide superconducting by multi-source sputtering by high-frequency magnetron sputtering in a mixed gas of 95 mol% of argon and 5 mol% of oxygen, using ₂ O ₃ , PbO, SrCO ₃ , CaCO ₃ and CuO as a sputtering target. A body thin film was deposited to a thickness of 200 °. Note that the input power ratio for each target is such that the composition of the formed thin film is Bi: Sr: Ca: Cu
= 2: 2: 2: 3.

X-ray diffraction was performed on the obtained Bi-based oxide superconductor thin film, and it was confirmed that the Bi-based oxide superconductor thin film was an epitaxially grown film having a high critical temperature phase aligned with an insulating single crystal substrate.

This is because the insulating single crystal substrate of this example has a lattice constant similar to that of the Bi-based oxide superconductor, and lattice mismatch at the interface is reduced as much as possible. This is because it can be formed.

Further, it is considered that the reason why the high critical temperature phase of the Bi-based oxide superconductor is difficult to form is due to the modulated structure inside the crystal and the internal stress of the crystal which is the cause thereof. By the way, the insulating single crystal substrate of this example has a lattice constant similar to that of the Bi-based oxide superconductor, and the modulation structure has almost disappeared by the substitution of Pb. For this reason, it is presumed that the Bi-based oxide superconductor thin film formed on the insulating single crystal substrate of this example also disappears or is relaxed, and a single phase having a high critical temperature phase is obtained.

Further, Bi ₂ O ₃ , PbO, SrCO ₃ , and Y were formed on the Bi-based oxide superconductor thin film formed on the insulating single crystal substrate of this example.
Bi-sputtering by high frequency magnetron sputtering using ₂ O ₃ and CuO as sputtering targets
A PbSr ₂ Y Cu ₂ O _{8 + δ} thin film was formed with a thickness of 50 °, and a Bi-based oxide superconductor thin film was further formed thereon with a thickness of 200 ° under the same conditions as the above oxide superconductor thin film to produce a Josephson device. .

Like the lower Bi-based oxide superconductor thin film, the upper Bi-based oxide superconductor thin film is also a good oxide superconductor thin film composed of a high critical temperature phase. No reaction was observed at the interface between the metal and the insulating phase.
In addition, this Josephson device exhibited superconducting characteristics at 110 K, and it was confirmed that a good Josephson effect was obtained at this temperature.

Comparative Example 3 Using SrTiO ₃ O as a substrate, Bi ₂ Sr ₂ Ca ₂ Cu ₂ C
200Å and u ₃ O _{10 +} δ superconductor, an insulating layer to 50Å and MgO, to produce a Josephson device further 200Å laminated _{Bi 2 Sr 2 Ca 2 Cu 3} O 10 + δ superconductor.

However, in this state, no superconductivity was exhibited. Therefore, a heat treatment was performed at 600 ° C. to improve the crystallinity, and the superconductivity was evaluated.
Although a superconducting state was shown at K, good Josephson characteristics could not be obtained.

Example 6 Bi by Pb was prepared in a similar manner as described in Example 5.
Created a single crystal of _{Bi 2-w Pb w Sr 2} Y Cu 2 O 8 + δ by changing the amount of substitution.

Bi _2-w Pb _w Sr ₂ Y Cu ₂ O _{8 + δ} crystal of the present invention and superconductor B
Lattice constant of i ₂ Sr ₂ CaCu ₂ O _{8 + δ} and Bi _2-w Pb _w Sr ₂ Y
FIG. 3 shows the modulation structure of the Cu ₂ O _{8 + δ} crystal.

In the figure, the horizontal axis indicates W. That is, as W increases, the proportion of Bi replaced with Pb increases. The upper left ordinate indicates the lattice constant of the c axis, and the lower right ordinate indicates a, b
Shows the lattice constant of the axis. The vertical axis on the right shows the modulation structure.

○ indicates the lattice constant of the a-axis of Bi _2-w Pb _w Sr ₂ Y Cu ₂ O _{8 + δ} crystal, ● indicates the lattice constant of the b-axis, Represents the lattice constant of the c-axis.

◎ indicates the lattice constant of Bi ₂ Sr ₂ CaCu ₂ O _{8 + δ on} the a-axis and b-axis, and □ indicates the lattice constant of c-axis.

Δ indicates the modulation structure of Bi _2-w Pb _w Sr ₂ Y Cu ₂ O _{8 + δ} crystal.

In Bi _2-w Pb _w Sr ₂ Y Cu ₂ O _{8 + δ} crystal, the lattice constant of the b-axis is Bi ₂ Sr ₂ CaCu ₂ O when about 60% of Bi is replaced by Pb.
_It can be seen that the lattice constant of the c-axis approaches Bi ₂ Sr ₂ CaCu ₂ O _{8 + δ} when the proportion of Bi substituted by Pb increases.

Further, it can be seen that the modulation structure disappears when the ratio of replacing Bi with Pb increases.

Examples 7 to 16 Insulating single crystals were prepared by the flux method using the compositions shown in Tables 1 and 2.

[Effects of the Invention] As described above, since the insulating composition of the present invention has the same or similar crystal structure as the oxide superconductor, the insulating composition has good matching with the crystal plane of the oxide superconductor. Can be provided. Further, by replacing a part of Bi in the insulating composition of the present invention with Pb, it is possible to provide an insulating composition in which the modulation structure is relaxed or eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of an oxide superconducting element in which the insulating composition of the present invention is an insulating layer, and FIG. 2 is an oxide superconducting film formed on a short crystal substrate according to the present invention. FIG. 3 is a graph showing the temperature characteristics of the electrical resistivity of the thin film single crystal, and FIG. 3 is a graph showing the characteristics of the insulating composition of the present invention in which Bi is partially substituted with Pb. 1 ... oxide superconducting element, 2 ... substrate, 3, 5 ... Bi ₂ S
r ₂ Ca ₁ Cu ₂ O _α layer, 4 ... Bi ₂ Sr ₂ Y ₁ Cu ₂ O _α layer

──────────────────────────────────────────────────続 き Continued on the front page (31) Priority claim number Japanese Patent Application No. 1-77607 (32) Priority date Hei 1 (1989) March 29 (33) Priority claim country Japan (JP) (72) Inventor Takeshi Ando 1 Toshiba R & D Co., Ltd., Koyuki-ku, Kawasaki-shi, Kanagawa Prefecture (72) Inside the Toshiba Research Institute, Inc. Hiromi Nibu 1 Toshiba Komukai-Toshiba-cho, Kochi-ku, Kawasaki-shi, Kanagawa Prefecture Within Toshiba Research Institute, Inc. (72) Tomohisa Yamashita, Inventor 1 Toshiba Research Institute, Komukai, Kawasaki-shi, Kanagawa Prefecture (56) References JP-A-63-32974 (JP, A) JP-A-63-307197 (JP, A) Japane Journal of Applied Physics Part 2 vol27. No5 p.L790-791 Japanese Journal of Applied Physics Part2 vol27. No2 p. L209-210 Physical Review Letters vol 61, No6,750-753 Japanese Journal of Applied Physics Part2 vol 27. No10 p. L1852-1855 (58) Fields investigated (Int. Cl. ⁶ , DB name) C01G 1/00-23/08 C01G 29/00 C30B 29/22 CAS on-line

Claims (4)

(57) [Claims] (1) Bi, Sr, Ca, Cu, O or Tl, Ba, Ca,
Ca of the oxide superconductor composition comprising Cu and O is RE (however,
RE is an element selected from Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y. ) And Bi, Sr,
An insulating composition characterized in that the atomic ratio of RE, Cu or Tl, Ba, RE, Cu is 2: X: Y: Z. However, 1.5 ≦ X ≦ 2.5 0.5 ≦ Y ≦ 1.5 1.8 ≦ Z ≦ 2.5 2. An insulating composition which is an oxide having an atomic ratio of Bi, Sr, RE and Cu of 2: X: Y: Z, provided that 1.5 ≦ X ≦ 2.5 0.5 ≦ Y ≦ 1.5 1.8 ≦ Z ≦ 2.5 Bi ₂ O ₃ and C as flux when growing by the flux method
A method for growing an insulating composition, comprising using a flux containing uO at the same time. 3. An insulating composition comprising an oxide having an atomic ratio of Bi, Sr, RE and Cu of 2: X: Y: Z, provided that 1.5 ≦ X ≦ 2.5 0.5 ≦ Y ≦ 1.5 1.8 ≦ Z ≦ 2.5 The composition of each raw material cation when growing by the flux method is
In the molar ratio% (β, γ, ε), βBi ₂ O ₃ + γ ｛(Sr, RE) O｝ + εCuO, where 5 ≦ β ≦ 25 20 ≦ γ ≦ 60 10 ≦ ε ≦ 60 2β + γ + ε = 100 is satisfied. A method for growing an insulating composition, comprising: 4. A superconducting element comprising the insulating composition according to claim 1 formed on an oxide superconductor as an insulating layer.