JPH0416548A - Manufacture of bulk y-ba-cu-o superconductor having rapid transit limiting current density - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is characterized by a high transport limit current (transport cr.
the improved melt-textured growth method (c) and the transport limiting current density (Jc).
method), where x=7−δ
The present invention relates to a method for preparing a Ba 2 Cu 3 Ox superconductor. The YBa2 2Cu3Ox superconductor produced according to the present invention has a high degree of transport [C and Jc.

The discovery of high-limit temperature superconducting oxides, including some materials that remain superconducting above liquid nitrogen temperatures, has stimulated great interest and active research. One of the application limitations of these materials is the low critical current density (Jc) measured in bulk polycrystalline samples. Several processing techniques for increasing transport JC have been reported in the prior literature. It is possible to significantly increase the Jc value by magnetic field alignment, melt texture growth, and liquid phase methods. Further processing techniques and products thereof have now been proposed for the preparation of YBa2Cu3Ox superconductors. However, in order for these superconductors to be practically usable, the transport limiting current density should be 10,0 OOA/- or more at liquid nitrogen temperature <77 K>. -These YBa obtained by an intrashell method
2Cu3Ox m conductor has 150 at 77K
It has a transport limiting current density of ~600 A/u.

However, these values are far below the appropriate ranges mentioned above. The transport limit current density of a single crystal is 10'A/J
Although more is possible, the size of the product is small and practical use is not possible. The transport limiting current density of an epitaxially grown thin film can be more than 10 A/J, but the film is thin and the maximum value of its limiting current (Ic) can reach 3-5 aip (A). It is only possible. Moreover, this thin film must be deposited on an expensive crystalline substrate.

The application of products obtained by conventional processes is therefore less advantageous.

OBJECTS OF THE INVENTION It is therefore an object of the invention to
/, corresponding to a critical current density Jc exceeding J, 120A
Bulk that conducts higher continuous DC current
An object of the present invention is to provide a method for manufacturing a YBa 2 Cu 3 Ox superconductor.

Another object of the present invention is to provide a method for fabricating bulk YBa2Cu3Ox superconductors that achieves flux jumps in the ab-plane and c-axis of the sample at low temperatures.

These objects, advantages, and features of the present invention are as follows:
It will be better understood and appreciated by reference to the following description.

``Exemption'' 2l! [The present invention is directed to the production of YBa with
This invention relates to a method for producing a 2Cu3Ox superconductor.

According to the present invention, Y O, BaO2 and CuO powder are
:Ba:Cu=1:2:3 ratio, uniformly mixed,
It is press-molded into pellets with a diameter of 254α and a thickness of 05-081. The thick pellets are sintered at 940°C for 24 hours, then page milled, pressed, and annealed at 980°C for 48 hours. Thereafter, the temperature of the sample was increased from 980°C to 550°C over 8 hours.
and then maintained at this temperature for about 10-20 hours. The temperature of the sample was then increased to 40°C over 8 hours.
The temperature is lowered to 0°C, further maintained at 400°C for 10 to 201i, and finally the temperature is lowered to V temperature over 6FR. At this stage, the volume of the sample is reduced to approximately 30% of its original volume. This sample was then
It is placed vertically into an oven preheated to 1100° C. and then subjected to 7 kneading according to the following temperatures and durations.

That is, the temperature was maintained at 1100°C for 10 minutes, the temperature was lowered from 1100°C to 1030°C over 20 minutes, and the temperature was maintained at 1100°C for 50 hours.
/) 1 KeT 1030℃ Kara 980'CM temperature drop,
Maintained at 980°C for 8 hours, 9 for 16-30 hours
Temperature decreased from 80℃ to 900℃, 900℃ over 6 hours
Temperature decreased from ℃ to 550℃, 550℃ for 10-20 hours
The sample is annealed by holding at 0.degree. C., decreasing the temperature from 550.degree. C. to 400.degree. C. over 8 hours, holding at 400.degree. C. for 10-20 hours, and then decreasing the temperature to room temperature. Samples annealed according to the invention have a length of 8-1041I, a width of 5-6s+ and a thickness of 1-2
It is possible to form the plate-like bulk of the footwear.

Silver paint contacts are then painted on the top surface of the sample to form four contacts. The above four contacts are sintered according to the following sintering temperatures and durations:

What is the resistivity of these contacts at 77K? X 1O-
1otv, J.

Sintering temperature ("C) Required time 25~900
3 hours 900 2 hours 900-550
6 hours 550 24 hours 550-40
08 hours 400 24 hours 400-25
Four leads are attached to the four contacts for six hours. The resistivity of these contacts is approximately 11
It is as low as 0-7ohJ. After that, limit current and limit current! degree measurements are taken.

The following examples further illustrate the manufacturing method of the invention. This example is not intended to, and should not be construed as, limiting the scope of the invention in any way.

EXAMPLE Bulk YBa2CU30x material and five test samples thereof were made according to the process of the invention described above. To measure the transport Jc at the criterion (Criterionl 1 uV, /ax, the rated output 120△(H,
P, 6031A> DC power sarai and calyx → ei
A four-contact approach using 181 nanometers was used.

Table 1 Sample Table 1 shows (Ic), IC (A) area (aj) JcfA・word) 7
1 0.8763 810274
1.121 660176
1.0672 7+2171
0.5 14200>1
20 0.3218 >37300
The limiting current cross-section 11i (area) and limiting current density (Jcl) of the five test samples are shown. Samples F11-4 were glued onto a plastic plate by double-sided adhesive.

Burning out of all four samples was observed. Samples 1 and 3 broke into two parts and samples 2 and 4 melted. Continuous DC current is 70-80A
When , a focal point between the voltage and current contacts occurred. Sample 5 was painted with silver paint on a silver plate (9.5X
7.5×O, 25g). This sample was tested within the standard 1μ/1:m at 77K without causing a voltage drop across the sample.
It was possible to withstand continuous DC current of up to 120 A for 0 minutes. The corresponding limiting current density Jc is 37
It was more than 300A/-.

Burning and fracture of the sample may be due to the effects of contact heating. At high currents, i.e., l>70 A, contact heating will increase the temperature of the sample and fje+ sample substrate. For plastic-based samples, it is not possible for the contact heat to be easily diffused into liquid nitrogen, and the sample continues to be heated until the magnetic flux is transferred. The sample then suddenly burned out. Silver has much better thermal conductivity than plastic. Therefore, the sample attached to the silver plate was able to conduct currents up to 120 A without losing superconductivity.

A magnetic flux jump was observed in the magnetization hysteresis measurement for the above sample. These magnetization jumps are similar to those in YBa2Cu3Ox single crystals prepared by conventional methods. Quality @ 40#F and size 4
X3.2 Xo, 5-piece plate type bulk YBa
A 2Cu3Ox sample was used in the experiment. The data is
In an applied magnetic field (H) between −54 and 5.4 Tesla (T), a flux quantum SQUID magnetometer (quantumde
signed 5QUID magnetometer
) was measured by The hysteresis loop was measured over a period of 70 minutes, measuring one data every 18 seconds. FIG. 9 according to the present invention shows (a) 5K, (b
) at 7.5K, (clo and (d) at 20K,
High transport limit current completion YBa 2Cu3Ox sample a-b
The magnetization in the plane (H perpendicular to the a-b plane) exhibits steresis. At 5K, a flux jump was observed along the entire hysteresis loop (Figure 9a). As the applied magnetic field increases, the jump spacing decreases.

The spacing of the jumps at 7.5K is greater than that at 5K (Figure 9b). At IOK only one jump appeared (Figure 9C), and at 20 no flux jump was observed (Figure 9D). The strength of magnetization does not change between 5 and IOK, but at 20, it changes to 1/2 (
by a factor of two). Magnetization strength of sample a-b plane at 5K and 77K
By comparing the strength of magnetization of the sample a-b plane in
It was evaluated as 106A,/-. The magnetic flux jump is the field sweeping rate.
6 depends on. When the measurement time was doubled, the number of jumps in the 5K decreased from nine to seven. For applied magnetic fields perpendicular to the sample C-axis, almost no jump was observed. 5, when erasing the magnetic field from 54 to -5,4T, one jump occurs at 1T, and -54
No jump was observed when canceling the magnetic field from 5.4K to 5.4K.

The magnetic flux jump is caused by the vortex ring motion (VOrteX 1ine 1O
Avalanche in Velent
It is also possible that it is caused by a process. At low temperatures, the magnetic diffusivity of a superconducting material is higher than its thermal diffusivity. In other words, when the applied magnetic field is increased to a certain value or its Lorentz force is fixed force (pi
nning force), the lines of magnetic flux suddenly shift, causing a flux jump. If the associated energy flow can be absorbed by the sample itself or its environment, the jump stops.

The use of high Tc superconductors is highly dependent on their limiting current density Jc. In order to increase Jc, the rotational force within the sample must be increased. However, due to the low thermal conductivity of these materials, this anchoring force is not the only factor influencing current density. The magnetic and thermal properties of the sample and its environment need to be considered as well.

The degree of orientation of the sample was determined from the X-ray reflection spectrum. The reflectance is from a wide surface of the sample perpendicular to the C-axis of the oriented sample, so in a fully oriented sample only the (001)-reflection contributes to the X-ray reflection. Dew. FIG. 4 shows the relationship between resistance and temperature of superconductors obtained by the method of the invention. Figure 5 shows the X-ray reflection of a rectangular sample with dimensions of approximately 6x5x1s.

Magnetization data and hysteresis data! Measured by a 1-Ei Quantum Squid magnetometer. The three annealing procedures tested resulted in R magnetization data. FIG. 1 shows the pyromagnetic field cooling (ZFC) ratio for a sample according to the method of the invention without a 980°C (48 hours) step and a gradual cooling (5°C/hour) step from 980°C to 900°C. Show data. Figure 2 shows 980℃ (
48 hours) for samples according to the method of the invention without steps.
Zero field cooled (ZFC) magnetization data are shown. FIG. 3 shows zero field cooling (ZFC) magnetization data for a sample according to the method of the present invention, including all processing steps of the present invention. It is shown that FIG. 3 has the best superconducting transition.

The anisotropic properties of magnetization for applied magnetic fields parallel and perpendicular to the sample a-b plane were investigated. Excluding geometric factors, the magnetization in the a-8 plane is isotropic with respect to ZFC;
FC had anisotropic properties and the ratio was 4:3.

FIG. 6 shows the magnetization hysteresis between -5.4T and 5.47T. From the aean model, the magnetic field dependence Jc was estimated to be up to 5T at 77K (as shown in Figure 7). At zero magnetic field, Jc was found to be approximately 40,000 A/-. FIG. 8 shows the relationship between voltage and current for a silver plate used as a sample substrate.

According to the invention, mono-oriented bulk yBa,
A Cu3 ox superconductor was prepared. 37,300 at 77K with continuous DC II flow power greater than 120A
A marginal FR of 1 degree (Jc) higher than A/J was obtained.

The invention has been described in detail, including its preferred embodiments. However, those skilled in the art will appreciate, based on an understanding of this disclosure, that modifications and improvements can be made without departing from the spirit and scope of the invention.

[Brief explanation of drawings]

FIG. 1 shows the zero field cooling (Z
FC) Graph showing the illization curve, Figure 2, does not include the 980°C (48 hours) annealing step, but does not include the 980"C (48 hours) annealing step for about 2 hours
Graph showing the zero field cooling (ZFC) magnetization curve of a superconductor according to the method of the invention including an in-furnace cooling step to 0° C. FIG. 3 shows the magnetization curve of a superconductor obtained according to the invention 4 is a graph showing the relationship between the resistance and temperature of a superconductor obtained by the method of the present invention, and FIG. 5 is a graph showing the relationship between the resistance and temperature of a superconductor obtained by the method of the present invention. Figure 6 is a graph showing the magnetization hysteresis loop of a superconductor at 77K. Figure 7 is a graph showing the magnetization hysteresis loop of a superconductor at 77K.
FIG. 8 is a graph showing the limiting current density (J c ) at 77 K calculated by the ean model; FIG. The figure shows (a15K, (b) 7.5K, (C) IO
K, and (d) 20K1. 2 is a graph showing the magnetization hysteresis of a high transport limiting current density YBa2Cu3Ox sample at . 2θ Rei・5 θ卆-〇年1 Tnia7に1(A) H(T) Rinsa,, p, 5 H(T) H(T) ri; 5r-, 9-c Procedural Amendment Form G ) 1゜Representation of the case 1990 Patent Application No. 114958 3, Name of the invention Method for producing bulk Y-Ba-Cu-0 superconductor with high transport limiting current density 3, Relationship with the amended person case

Claims (2)

[Claims] (1) A method for producing a bulk YBa_2Cu_3O_x superconductor with x=7−δ having high transport limit current and transport limit current density, the method comprising: (I) Y_2O_3, BaO_2 and CuO as Y:
Mixed at a ratio of Ba:Cu=1:2:3, diameter 2.54
(II) annealing the pellets at 940° C. for 24 hours and then reducing the temperature to room temperature; (III) grinding said pellets into fine powder and then compacting to form new pellets; (IV) said (
III) annealing the pellets obtained in step 980°C in a furnace for 48-72 hours; (V) lowering the temperature of said pellets to 550°C;
maintaining this temperature for ~20 hours, then decreasing to 400<0>C over 8 hours, maintaining this temperature for 10-20 hours, and decreasing the temperature to room temperature; Place in a furnace preheated to 1100°C and heat for 10
maintained at 1100°C for 20 min, then 1100°C for 20 min.
(VI) maintaining the temperature of the pellet at 980°C for 8 hours, reducing the temperature from 1030°C to 980°C over 50 hours; Reduce the temperature from 980°C to 900°C over time, reduce the temperature to 550°C over 6 hours, maintain at 550°C for 10-20 hours, and reduce the temperature from 550°C to 400°C over 8 hours. Reduce temperature, 10-20
bulk YBa_2 consisting of maintaining at 400 °C for an hour and then reducing the temperature of said pellets to room temperature.
Method for manufacturing Cu_3O_x superconductor. (2) The bulk YBa_2Cu_3O_x superconductor having a high transport limit current and transport limit current density according to claim 1, wherein the pellet in the above (IV) is annealed for 48 hours in a furnace in flowing oxygen. Production method.