JPH07100610B2 - Manufacturing method of superconducting material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a superconducting material. More specifically, the present invention relates to an improved method for producing a Tl-based oxide superconducting material used for power wires, electronic devices, and the like.

2. Description of the Related Art The superconducting phenomenon, which is said to be a phase transition of electrons, is a phenomenon in which the electric resistance of a conductor becomes zero under certain conditions and shows perfect diamagnetism.

In the field of electronics, which is a typical application field of superconducting phenomena, various superconducting elements have been proposed and developed. A typical example is an element utilizing the Josephson effect in which quantum effects appear macroscopically by an applied current when superconducting materials are weakly joined. In addition, the tunnel junction type Josephson element is expected as an extremely high speed and low power consumption switching element because the energy gap of the superconducting material is small. Furthermore, since the Josephson effect with respect to electromagnetic waves and magnetic fields appears as an accurate quantum phenomenon, it is expected that the Josephson device will be used as an ultra-sensitive sensor for magnetic fields, microwaves, radiation, etc.

In the ultra-high speed computer, the power consumption per unit area has reached the limit of the cooling capacity, so the development of superconducting elements is demanded. Furthermore, as the degree of integration of electronic circuits increases, there is no current loss. It is desired to use a superconducting material as a wiring material.

However, despite various efforts, the superconducting critical temperature Tc of superconducting materials could not exceed 23K of Nb ₃ Ge for a long time, but since 1986, [La, Ba] ₂ CuO ₄ or La, Ba] ₂ CuO _{4 and} other oxide sintered materials have been discovered as superconducting materials with high Tc, and the possibility of realizing non-low temperature superconductivity is greatly increasing. 30 to 50K for these substances
A dramatically higher Tc than the conventional one was observed, and a Tc of 70K or more was also observed.

Further, it has been announced that a composite oxide represented by Y ₁ Ba ₂ Cu ₃ O _7-x called YBCO is a 90K-class superconductor.
Furthermore, the Tl-Ba-Ca-Cu-based composite oxide not only has a Tc of 100 K or more, but is also chemically stable, and its superconducting properties deteriorate as time passes like YBCO. Also few.

Oxygen defects in the crystal play a major role in the superconducting properties of these complex oxide superconductors. That is, if the oxygen defects in the crystal are not proper, Tc is low, and the difference between the onset temperature and the temperature at which the resistance is completely zero becomes large.

Conventionally, in order to produce these complex oxide superconductors, powders of oxides or carbonates of the constituent elements constituting the complex oxide have been mixed and sintered. Further, a thin film was formed by a method such as RF sputtering, using the composite oxide produced by this sintering as a target. Further, the above oxygen defects may be adjusted by performing heat treatment in an oxygen atmosphere after sintering or film formation.

SUMMARY OF THE INVENTION Conventionally, in preparing the above Tl-Ba-Ca-Cu-based oxide superconducting material, mixed _{Tl 2 O 3, BaCO 3,} CaCO 3 and a powder of CuO or the like at a predetermined ratio Then, sintering was performed. Also, Tl-Ba-
When preparing a thin film of Ca-Cu-based oxide superconducting material,
It was general to perform physical vapor deposition such as RF sputtering using this sintered body as a target.

However, the Tl-Ba- produced by the above conventional method
In the Ca-Cu-based oxide superconducting material, since a phase having a high superconducting critical temperature and a phase having a low superconducting temperature coexist, the temperature Tco at which the electric resistance starts to sharply decrease is 120 K or more, but the electric resistance is completely 0. The temperature Tci was about 90 to 100K.

Therefore, an object of the present invention is to provide a Tl-comprising a single phase of high Tc phase.
It is to provide a method for producing a Ba-Ca-Cu based oxide superconducting material.

Means for Solving the Problems According to the present invention, the formula: Tl _{2 ± p} (Ba _1-x Ca _x ) _{3 ± q} Cu _{2 ± r} O _z (where 0 ≦ p ≦ 0.6, 0 ≦ q ≦ 0.9, 0 ≦ r ≦ 0.6,
0.2 ≦ x ≦ 0.5), and the formula: (Ba _1-y Ca _y ) _{1 ± a} Cu _{1 ± b} O _w (where 0 ≦ a ≦ 0.3 and 0 ≦ b ≦ 0.3 and 0 ≦ y ≦
1) is mixed with an oxide having a composition represented by 1) or laminated in layers and then heat treated at a temperature in the range of 840 ° C. to 960 ° C. to provide a method for producing a superconducting material. It

Action The method of the present invention uses a Tl-Ba-Ca-Cu-based oxide superconducting material of the formula: Tl _{2 ± p} (Ba _1-x Ca _x ) _{3 ± q} Cu _{2 ± r} O _z (where 0 ≦ p ≦ 0.6, 0 ≦ q ≦ 0.9, 0 ≦ r ≦ 0.6,
0.2 ≦ x ≦ 0.5), and the formula: (Ba _1-y Ca _y ) _{1 ± a} Cu _{1 ± b} O _w (where 0 ≦ a ≦ 0.3 and 0 ≦ b ≦ 0.3 and 0 ≦ y ≦
The main characteristic is that it is produced by reacting with an oxide having a composition represented by (1).

Conventionally, when manufacturing the above-mentioned Tl-Ba-Ca-Cu-based oxide superconducting material, a mixture of _{Tl 2 O 3, BaCO 3,} CaCO 3 and CuO powders were sintered. Further, in mixing these powders, the proportion was set such that the high Tc phase of Tl ₂ Sr ₂ Ca ₂ Cu ₃ O _{t in} the oxide after sintering was increased.

However, the Tl-Ba-Ca-Cu-based oxide superconducting material obtained by the conventional method always contains a high Tc phase and a low Tc phase, and the temperature Tco at which the electrical resistance starts to decrease sharply is 1
Although it is as high as 20K or higher, the temperature Tci at which the electric resistance becomes completely 0 is
A superconducting material consisting of a single phase having a high Tc of about 90 to 100 K has been desired.

According to the method of the present invention, Tl _{2 ± p} (Ba _1-x Ca _x ) _{3 ± q} Cu _{2 ± r} O _z (where 0 ≦ p ≦ 0.6, 0 ≦ q ≦ 0.9, 0 ≦ r ≦ 0.6,
Low Tc phase which is considered to be a composition of 0.2 ≦ x ≦ 0.5) and (Ba _1-y Ca _y ) _{1 ± a} Cu _{1 ± b} O _w (where 0 ≦ a ≦ 0.3 and 0 ≦ b ≦ 0.3 Yes, 0 ≦ y ≦
1)) to increase the Cu-O plane, which is considered to be responsible for superconducting current, to form a low Tc phase to a high Tc phase.

In the method of the present invention, Tl ₂ O _3, mixed BaCO _3, CaCO ₃ and CuO powders, rather than causing reacted directly produce Tl-Ba-Ca-Cu-based oxide superconductor, the advance as an intermediate material , Which is considered to be a low Tc phase, and (Ba _1-y Ca _y ) _{1 ± a} Cu _{1 ± b} O _w (where 0 ≦ a ≦ 0.3, 0 ≦ b ≦ 0.3, and 0 ≦ y ≦
1) and an oxide having a composition of
A Ba-Ca-Cu based oxide superconductor is generated. Therefore, it is possible to prevent undesired reactions between raw materials such as eutectic reaction that occurs at a low temperature, and it becomes possible to raise the sintering reaction temperature, so that a high density can be obtained, and particularly, the critical current density is improved. It is effective to let.

Further, since CuO, which tends to exist alone even at high temperature, can be reacted from the state of the compound, it is easy to obtain a homogeneous structure.

In the method of the present invention, the mixing is performed so that the above-mentioned intermediate raw materials sufficiently react. Therefore, crush the above intermediate raw material,
The powder is preferably mixed or laminated in layers and sintered.

In the method of the present invention, the final crystallization temperature is preferably 840 to 960 ° C. This is because undesired reactions such as the above eutectic reaction occur below 840 ° C. Also, if sintered at a temperature above 960 ° C, part of the raw material powder will melt, resulting in high Tc.
I can't get a match.

Hereinafter, the present invention will be described in more detail with reference to Examples.
The following disclosure is merely an example of the present invention and does not limit the technical scope of the present invention.

Example 1 Tl ₂ O ₃ , BaCO ₃ , CaCO ₃ and CuO powder were mixed so that the atomic ratio of Tl: Ba: Ca: Cu was 2: 2: 1: 2, and the diameter was 10 mm and the thickness was 3 mm.
After molding, heat-treat at 880 ℃ for 3 hours to remove Tl ₂ Ba ₂ Ca ₁ Cu ₂ O
_A disc-shaped sample 1 having _z (z is not determined) was prepared.

Next, CaCO ₃ and CuO are mixed so that the atomic ratio of Ca: Cu is 1: 1, molded into a diameter of 10 mm and a thickness of 3 mm, and heat-treated at 880 ° C. for 3 hours, and CaCuO _w (w is undetermined). A disc-shaped sample 2 was prepared.

After crushing the above disc-shaped samples 1 and 2 into fine powder, Tl: B
Mix so that the atomic ratio of a: Ca: Cu is 2: 2: 2: 3 and the diameter is 10
After molding to a thickness of 3 mm and a thickness of 3 mm, heat treatment was performed at 920 ° C. for 3 hours to prepare a superconductor sample for evaluation. Table 1 shows the main superconducting properties.

Example 2 As in Example 1, Tl ₂ O ₃ , BaCO ₃ , CaCO ₃ and CuO powder were mixed so that the atomic ratio of Tl: Ba: Ca: Cu was 4: 3: 3: 4, 88.
After heat treatment at 0 ° C. for 3 hours, the oxide which is Tl ₄ Ba ₃ Ca ₃ Cu ₄ O _z (z is not determined) and the BaCO ₃ , CaCO ₃ and CuO powders are Ba:
The mixture was mixed so that the atomic ratio of Ca: Cu was 1: 1: 2, and heat-treated at 880 ° C. for 3 hours to prepare an oxide of BaCaCu ₂ O _w (w is undetermined).

The respective oxides were pulverized and Tl: Ba: Ca: C was used as in Example 1.
They were mixed so that the atomic ratio of u was 2: 2: 2: 3, and heat-treated at 920 ° C. for 3 hours to prepare a superconductor sample for evaluation. Table 1 shows the main superconducting properties.

Example 3 As in Example 1, Tl ₂ O ₃ , BaCO ₃ CaCO ₃ and CuO powder were mixed so that the atomic ratio of Tl: Ba: Ca: Cu was 2: 1: 2: 2, 88
Heat treatment at 0 ° C for 3 hours so that the oxide which is Tl ₄ Ba ₃ Ca ₃ Cu ₄ O _z (z is not determined) and the BaCO ₃ and CuO powders have a Ba: Cu atomic ratio of 1: 1. Mixing and heat treatment at 880 ° C. for 3 hours produced an oxide of BaCuO _w (w is undetermined).

The respective oxides were pulverized and Tl: Ba: Ca: C was used as in Example 1.
They were mixed so that the atomic ratio of u was 2: 2: 2: 3, and heat-treated at 920 ° C. for 3 hours to prepare a superconductor sample for evaluation. Table 1 shows the main superconducting properties.

Comparative Example Tl ₂ O ₃ , BaCO ₃ , CaCO ₃ and CuO powder were prepared by a conventional method in which the atomic ratio of Tl: Ba: Ca: Cu was directly mixed to be 2: 2: 2: 3. did. After mixing the above powders, the powder was molded into a diameter of 10 mm and a thickness of 3 mm and heat-treated at 920 ° C. for 3 hours.

Table 1 below shows Tco (onset temperature), Tci (temperature at which the resistance becomes 0), and the critical current density Jc at the liquid nitrogen temperature (77 K) of the sample manufactured according to the above-mentioned present example.

As described above, in the present invention, Tci and Jc are remarkably increased, and the effect is extremely large in practical use.

Effects of the Invention As described above in detail, according to the method of the present invention, it is possible to obtain a Tl-Ba-Ca-Cu-based oxide superconducting material having superconducting properties superior to the conventional ones.

This is Tl _{2 ± p} (Ba _1-x Ca _x ) _{3 ± q} Cu _{2 ± r} O _z (where 0 ≦ p ≦ 0.6, 0 ≦ q ≦ 0.9, 0 ≦ r ≦ 0.6, which is unique to the present invention. ,
Low Tc phase which is considered to be a composition of 0.2 ≦ x ≦ 0.5) and (Ba _1-y Ca _y ) _{1 ± a} Cu _{1 ± b} O _w (where 0 ≦ a ≦ 0.3 and 0 ≦ b ≦ 0.3 Yes, 0 ≦ y ≦
1)) to produce a Tl-Ba-Ca-Cu-based oxide superconducting material.

The method of the present invention can be applied not only to the production of a bulk superconducting material but also to the production of a raw material target of a thin film superconducting material.

Claims (1)

[Claims] 1. Tl _{2 ± p} (Ba _1-x Ca _x ) _{3 ± q} Cu _{2 ± r} O _z (where 0 ≦ p ≦ 0.6, 0 ≦ q ≦ 0.9, 0 ≦ r ≦ 0.6,
0.2 ≦ x ≦ 0.5), and the formula: (Ba _1-y Ca _y ) _{1 ± a} Cu _{1 ± b} O _w (where 0 ≦ a ≦ 0.3 and 0 ≦ b ≦ 0.3 and 0 ≦ y ≦
1) is mixed with an oxide having a composition represented by 1) or laminated in layers, and then heat-treated at a temperature in the range of 840 ° C to 960 ° C.