JPH0193483A - Production of superconductive material - Google Patents

Abstract

PURPOSE:To improve the critical temperature and critical electric flow density with treatment in a shortened time, by annealing the material using oxygen plasma in the temperature-maintaining and/or gradually cooling process, when a superconductor of IIa element-IIIa element-Cu-O system is produced. CONSTITUTION:A superconductor material 21 is prepared, including at least one element from Ca, Sr, Ba, at least one element from Y, lanthanides, at least one element from Cu, Al and Fe and at least one element from O, halogen or H. The material 21 is placed in an oxygen plasma generator 23 anneal the material 21 by RF discharge at about 900 deg.C whereby an oxide superconductor material of high denseness and stoichiometry.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing oxide-based superconducting materials. More specifically, it relates to a method for manufacturing oxide-based superconducting materials that enables short-time annealing at low temperatures and enables the creation of oxide-based superconducting materials on various substrates when superconducting materials are created on substrates. .

[Prior Art] As a method for producing oxide-based superconducting materials, for example, powders of metal oxides such as Las Y %Bas 5rSCu are mechanically mixed and heated at 900% in an oxygen atmosphere.
A method of annealing for 1 to 10 hours by raising the temperature to ~950°C, firing, and slow cooling (powder method), or a method in which nitrates of the metals mentioned above are dissolved in a solvent, and then oxalic acid, etc. The precipitate obtained by adding
Conventionally, a method (co-precipitation method) is generally known in which the temperature is raised to about 800 to 950° C., fired, and then annealed for 1 to 10 hours by slow cooling.

In addition, as a method for forming an oxide-based superconducting material on a substrate in the form of a thin film, for example, sputtering is performed using a mixture and molded material of the metal oxides as mentioned above as a target, and then sputtering is performed in an oxygen atmosphere for 800 min. 1.5 by heating to around 950℃, maintaining the temperature, and slowly cooling.
A method of annealing for ~5 hours is known.

[Problems to be Solved by the Invention] However, with the above method, it is difficult to replace dense oxide-based superconducting materials, and therefore it is difficult to obtain only materials with low critical current density, and it is difficult to replace homogeneous superconducting layers. The problem is that it is difficult to

Furthermore, when creating an oxide superconducting material in the form of a thin film on a substrate, it is necessary to heat it to a high temperature of, for example, 900°C during annealing, as described above, and the substrate reactivity decreases due to such high temperatures. In order to reduce stress problems due to thermal expansion coefficient mismatch, the substrate materials are perovskite-type 5rTiOs, YSZ
Another problem is that only expensive materials such as (Ittria stabilized, zirconia) can be used.

The present invention makes it possible to scale dense oxide-based superconducting materials by short-time annealing at low temperatures, and enables the use of various substrates when creating oxide-based superconducting materials on substrates. The purpose of the present invention is to provide a method for manufacturing superconducting materials.

[Means for solving problems] The present invention includes one or more elements of Cas, Sr, and Ba, and Y.

One or more lanthanide elements and Cus AJ % F
Production of an oxide-based superconducting material by annealing a material containing one or more elements of e and one or more elements of 0, halogen, and II using oxygen plasma in a temperature maintenance step and/or slow cooling step. Regarding the method.

Note that in this specification, annealing means raising the temperature, maintaining the temperature, and slow cooling, and is a concept that includes firing and slow cooling in the production of conventional oxide-based superconducting materials.

[Example] One or more elements of Ca- and Srs Ba used in the present invention, one or more elements of Y1 lanthanide, and Cu sMI
SFe IF1i or higher elements, 0, halogen, 11
There are no particular limitations on those containing one or more elements,
Any material that can become an oxide-based superconducting material by oxidation can be used.

Examples of such things include, for example, La-3r-
Cu-0 series, La-Ca-Cu-0 series, Y-Ba-Cu
-0 series, Y-Ba-3r-Cu-0 series, Er-Ba-C
Oxides such as u-0 series, Yb-Ba-Cu-0 series, Y-
Ba-Cu-F system, Y-Ba-/V-F system, Y-Ba-
Examples include compounds such as Cu-0-11 series and Y-Ba-Cu-0-Ca series, compounds obtained by mixing and solidifying each of the above-mentioned elements, and compounds obtained by mixing and solidifying oxides of each of the above-mentioned elements.

The material containing each of the above elements is molded or made into a thin film, if necessary, and then annealed using oxygen plasma at least in part to produce an oxide-based superconducting material having good superconducting properties.

There are no particular limitations on the molding method or pressure, and for example, molding is performed using a press at a pressure of about 10 kg/cJ G.

The oxygen plasma used in the present invention is formed by high frequency or DC discharge in the presence of oxygen.

In the oxygen plasma, oxygen exists in the form of oxygen radicals and oxygen ions. Oxygen radical density can be controlled because it depends on the discharge power, and it affects the homogeneity and density of the structure of the resulting oxide-based superconducting material, and affects the required annealing temperature and time. The oxygen radical density in the present invention is 1 in that there are sufficient oxygen radicals and the oxygen radicals do not become rate-limiting in supply, making it possible to anneal at low temperatures and in a short time.
It is preferably O1OcI11-3 or more, and more preferably 10'c111-3.

Moreover, the ion energy in the oxygen plasma can be controlled by discharge power and external bias, and affects the obtained oxide-based superconducting properties. In the present invention, the ion energy value that realizes good superconductivity is
It has an optimum value depending on conditions such as the weight (especially thickness) of the oxide to be annealed, and is generally preferably 100 eV or less, more preferably 30 eV or less.

Specific examples of the high frequency or DC discharge used to generate such oxygen plasma include (ωECR discharge, RP discharge using a commercial magnetic field, DC discharge, DC-RF mixed excitation discharge, (C) at a pressure of 5 Torr or more). RF discharge, DC discharge, and MW discharge are preferred.

FIG. 2 is a graph showing an example of an oxygen plasma generator used in the present invention.
rr, suitable for use with RP power 150-1 kW, RF discharge with said magnetic field and pressure 5 Torr
This utilizes the RF discharge described above. In FIG. 2, (21) is a sample, (21) is a magnet, and (21) is an RP generating part.

FIG. 3 is a graph showing another example of the oxygen plasma generating device used in the present invention, and the shown device has the above-mentioned pressure 5 To
This utilizes MW discharge at rr or higher. In FIG. 3, (31) is a sample, (32) is a quartz tube, and (33) is a microwave generator.

Oxygen plasma may be applied to either the temperature maintenance step or the slow cooling step, or may be applied to both steps. In particular, when applied to a temperature maintenance process, the maintenance temperature can be lowered and the maintenance time can be shortened compared to normal annealing, and when applied to a slow cooling process, the cooling rate can be increased compared to normal annealing. be able to.

The temperature for annealing using oxygen plasma varies depending on the type of sample, the oxygen radical density, oxygen ion energy, etc., but is generally 200 to 900°C. The time required varies depending on the thickness of the sample, the oxygen radical density, oxygen ion energy, etc., but is generally about 0.1 to 2 hours. For example, in the case of a 2 mm thick disk-shaped sintered body, the temperature It is sufficient to maintain the temperature and slowly cool it over about 0.5 hours. This is approximately 17 times longer than the time required for annealing when creating oxide-based superconducting materials by conventional methods.
Equivalent to 5.

Note that there is no particular limitation on the number of times of annealing using oxygen plasma in the present invention.

Through such annealing, a dense oxide-based superconducting material with improved density can be obtained. In particular, by controlling the oxygen radical density and oxygen ion energy as described above, the critical current density ('C) can be lowered compared to conventional annealing in an oxygen atmosphere. The electrical resistivity-temperature curve is improved by, for example, one to two orders of magnitude compared to the value obtained by the method.

In addition, since the annealing temperature is lower than conventional methods, when forming oxide-based superconducting materials on a substrate, there are problems with reduced substrate reactivity and stress due to mismatch in thermal expansion coefficients caused by conventional high temperatures. This eases the problem and expands the types of substrates that can be used.

Next, the method of the present invention will be explained based on examples.

Examples 1 to 3 and Comparative Example 1 Y2O3, BaCO
3 and CuO with an atomic ratio of Y/Ba/Cu of 1/2/3
It is mixed and formed so that
The sample of Example 1 was obtained by maintaining the temperature at 00° C. for 1 hour and slowly cooling it in oxygen plasma for 1 hour.

The oxygen plasma conditions during temperature maintenance were as follows: 02 gas flow rate was 11005 cc, RF power was 500 W, reaction pressure was 100 Torr, magnetic field strength was 600 Gauss, and the substrate temperature was 900° C. by external heating. The oxygen radical density measured by radical titration method is 1014Ca+
-', and the average ion energy measured by an ion energy analyzer was 50 eV or less.

The oxygen plasma conditions during slow cooling are as follows: RP power is turned off at the end of annealing, and the substrate temperature is set at 400°C at the end of annealing.
It was the same as when the temperature was maintained, except that the temperature was gradually lowered so that the temperature was maintained.

Comparative Example 1 was carried out in the same manner as in Example 1, except that the sintering reaction was carried out at 950° C. in an oxygen atmosphere for 5 hours without annealing using oxygen plasma, and then slowly cooled to room temperature over 5 hours in an oxygen atmosphere. I got a sample of

FIG. 1 shows the temperature dependence of resistivity in Example 1 and Comparative Example 1. In FIG. 1, curve A shows the characteristics of Example 1, and curve B shows the characteristics of Comparative Example 1.

From FIG. 1, it can be seen that the sample of Example 1 has a steeper rise in current value and a higher critical temperature than that of Comparative Example 1.

In addition, the critical current density (Jc) at 80K measured by changing the current value of the constant current source was approximately 10' A/CI@% in Example 1 and approximately 102 A/cj in Comparative Example 1.
, a two-digit improvement was seen.

Furthermore, the sample of Example 2 was prepared in the same manner as in Example 1, except that oxygen plasma was used only in the temperature maintenance process, and the slow cooling process was annealed in an oxygen atmosphere for 3 hours, and oxygen plasma was used only in the slow cooling process. Temperature maintenance process is in oxygen atmosphere9
A sample of Example 3 was obtained in the same manner as Example 1 except that the sample was annealed at 00° C. for 1 hour.

The electrical resistivity at room temperature is approximately 40 mΩ in Example 2.
Cff1. In Example 3, it was approximately 50 mΩ.

The temperature (Tc) at which the electrical resistivity becomes 0 was about 85 in Example 2, and about 85 in Example 3.

In addition, the critical current density (Jc) at 80K is 5 x 103 A/cd in Example 2, and 103 A/cd in Example 3.
It was A/cd.

Examples 4 to 8 and Comparative Examples 2 to 4 Y2O3, BaCO3, and CuO were converted to Y by sintering method.
/Ba/Cu so that the atomic ratio is 115/9.
Using the molded product as a target, sputtering was performed on a 5rTIOi substrate, an M2O3 substrate, and a single crystal 81.
An oxide film was deposited on each substrate. Sputtering conditions are RF power 500ν, magnetic field strength 400 Gauss.
, substrate temperature 300°C, pressure 1 mTorr %02/A
The r ratio was 0.2.

On 5rT103 substrate, on M2O3 substrate and single crystal 31
The oxide film formed on the substrate was maintained at 600°C for 30 minutes in oxygen plasma using the apparatus shown in Figure 3.
Annealing was performed by slow cooling for 0 minutes to obtain samples of Example 4, Example 5, and Example 6, respectively.

The oxygen plasma conditions during temperature maintenance are as follows: 02 gas flow rate is 11005 CC, microwave power is 500 CC, pressure is 100 Torr, and the substrate temperature is maintained by external heating.
The temperature was 800°C. The oxygen radical density measured by radical titration was 10'C11-', and the average ion energy measured by an ion energy analyzer was 30 ev or less.

The oxygen plasma conditions during slow cooling are such that the microwave power is turned off at the end of annealing, and the substrate temperature is set to 4.
The temperature was maintained at 900 °C in an oxygen atmosphere with an oxygen concentration of 20 VO 1%, except that the temperature was gradually lowered to 00 °C.
Comparative Example 2, Comparative Example 3, and Comparative Example 4 were prepared in the same manner as in Example 4, Example 5, and Example 6, except that the temperature was maintained at ℃ for 1 hour and annealed by slow cooling over 2 hours. I got a sample.

The electrical resistivity at room temperature is approximately 15Il in Example 4.
ΩCff1, about 20 taQ in Example 5, Example 6
In this case, it is about 401,000 units, and in Comparative Example 2, it is about 20+oQam.
Comparative example 3. and Comparative Example 4, both 100
It was more than prepared.

The temperature (Tc) at which the electrical resistivity becomes 0 is 9 in Example 4.
5 to 5 In Example 5, it was 70 to 1. In Example 6, it was 50. In Comparative Example 2, it was 92. In both Comparative Example 3 and Comparative Example 4, the electrical resistivity did not become 0 even when the temperature was lowered. .

In addition, the critical current density (Jc) at 40K is 105 to 106Alc in Example 4, and approximately 10 to 106Alc in Example 5.
5 A/c+1, about 105 A/cd in Example 6, and 105 to 156 A/cj in Comparative Example 2.

Further, the sample of Example 7 was prepared in the same manner as in Example 4, except that oxygen plasma was used only in the temperature maintenance step, and annealing was performed in the slow cooling step in the same manner as in Comparative Example 1. Oxygen plasma was used only in the slow cooling step. A sample of Example 8 was obtained in the same manner as in Example 4, except that the temperature maintenance step was the same as in Comparative Example 2, and annealing was performed.

The electrical resistivity at room temperature is approximately 1511I in Example 7.
Qca was approximately 20 mΩCHI in Example 8.

The temperature (Tc) at which the electrical resistivity becomes O is 9 in Example 7.
In Example 8, it was 90.

Further, the critical current density ('C) at 40K was 105 to 106 A/cj in Example 7, and about to5A/c- in Example 8.

An oxide-based superconducting material can be manufactured by annealing using oxygen plasma in this manner.

Furthermore, since the method of the present invention enables annealing at low temperatures, oxide-based superconducting materials can also be formed on M2O3 substrates and 81 substrates.

[Effects of the Invention] The method of the present invention, which involves annealing in oxygen plasma, changes the oxide-based superconducting material which is dense and has excellent stoichiometry. As the material is changed, the temperature dependence of resistivity near the critical temperature (Tc) becomes steeper, and the critical temperature (Tc)
increases, and the critical current density (Je) increases. Furthermore, since it enables annealing at low temperatures, the types of substrates that can be used when producing thin film superconducting materials are expanded.

FIG. 1 is a graph showing the temperature dependence of the resistivity of the oxide-based superconducting materials obtained in Example 1 of the present invention and Comparative Example 1;
FIG. 2 is an explanatory diagram showing one example of the oxygen plasma generating device used in the present invention, and FIG. 3 is an explanatory diagram showing another example of the oxygen plasma generating device used in the present invention.

(Drawing code) (21), (31): Sample +221. magnet (23: High frequency generation section (32): Quartz tube (33): Microwave generator Patent applicant Kanebuchi Chemical Industry Co., Ltd. 1st time

Claims (1)

[Scope of Claims] 1 One or more elements of Ca, Sr, and Ba, one or more elements of Y and lanthanides, one or more elements of Cu, Al, and Fe, and one or more of O, halogen, and H. A method for producing an oxide-based superconducting material, which comprises annealing a material containing one or more types of elements using oxygen plasma in a temperature maintenance step and/or slow cooling step. 2 The oxygen radical density of oxygen plasma is 10^1^0c
2. The method according to claim 1, wherein the particle size is m^-^3 or more. 3 The average ion energy in oxygen plasma is 100e
2. The method according to claim 1, wherein V or less.