JPH03223117A - Production of bi-based oxide superconductor - Google Patents

Abstract

PURPOSE:To apply a melting method and obtain a Bi-based oxide superconductor having the high critical temperature by blending a Bi compound with a Pb compound, Sr compound, Ca compound and Cu compound at a specific ratio, heat-treating the resultant blend, melting the prepared precursor and then heat-treating the melt. CONSTITUTION:A Bi compound is blended with a Pb compound, an Sr compound, a Ca compound and a Cu compound so as to provide (2-x):x:2:2:3 ratio of Bi:Pb:Sr:Ca:Cu to prepare a starting material, which is then heat-treated at 800-850 deg.C to form a precursor having a composition expressed by the formula. The resultant precursor is further melted at 900-950 deg.C and subsequently heat- treated at 860-880 deg.C to afford the objective superconductor. Since the melting method is applied to the aforementioned method, the oxide superconductor having a denser structure than that in production by a sintering method can be obtained and the precursor is simultaneously heat-treated at 860-880 deg.C after melting and regulated to a suitable composition. Thereby, the oxide superconductor capable of exhibiting the high critical temperature of 100-110K can be obtained.

Description

[Detailed Description of the Invention] "Industrial Application Field" This invention relates to a method of manufacturing a Bi-based oxide superconductor by applying a melting method, and in particular a method for improving the superconducting properties by applying heat treatment after melting. It is.

"Prior Art" In recent years, oxide-based superconductors whose critical temperature exceeds the liquid nitrogen temperature have been discovered one after another. Bi-based oxide superconductors are attracting attention as oxide superconductors that do not contain.

However, the Bi-based oxide superconductor obtained at the time of its discovery was Bi, which had a critical temperature near 1N0K.

A high 1 phase with a composition of S rtc arc uso y,
It turned out to be a mixture of low-temperature phases with a composition of BitSr*Ca+CudoOy, which exhibits a critical temperature of 1°C near 80°C.

For this reason, various attempts have been made to produce Bi-based oxide superconductors consisting only of high-temperature phases.

“Problems to be solved by the invention” As a result of research conducted in view of the above background, B.
iwos, Pbo, Sr(NOs)* ・4
Hto, Cu.

) (dissolved in N O3, stirred, heated and mixed,
It has been announced that by heating and calcining at 800° C. for 30 minutes, and then pulverizing, molding, and firing, the bulk of the high-temperature phase was successfully converted into a single phase. The reason why the bulk was successfully made into a single phase is said to be due to the addition of Pb to the component elements and the preparation of the raw material by a coprecipitation method.

Therefore, as mentioned above, various methods of adding Pb to Bi-based oxide superconductors have been attempted, but when the above-mentioned manufacturing method is carried out, a compound with the composition Cax5rs-xCusOy tends to be generated in the calcination stage. Since a compound having this composition is generated, Ca, Sr, and Cu are consumed, and there is a problem that the composition of the Bi-based oxide superconductor finally obtained deviates from the desired composition. Furthermore, even when Pb is added, some parts of the bulk have a critical temperature of 8
0, a low temperature phase may be formed, and there is a problem in that the formation of the low temperature phase inhibits the formation of the high temperature phase.

On the other hand, when performing a powder sintering method in which an oxide superconductor is produced by mixing raw material powders and then performing heat treatment as described above,
There has been a problem in that it is not possible to produce an oxide superconductor that exhibits a high critical temperature unless the composition ratio of specific starting materials is strictly adhered to and heat treatment is performed under strict temperature control conditions. Furthermore, even if it were possible to manufacture an oxide superconductor with a high critical temperature, since the oxide superconductor manufactured by the powder sintering method is a sintered body, it may suffer from problems such as grain boundaries and crack formation. There is a problem that a high critical current density cannot be obtained.

Furthermore, recently, attempts have been made to manufacture oxide superconductors with a dense structure by a melting method in which raw material powders are melted and reacted, but when Bi-based oxide superconductors are manufactured by a melting method, the critical temperature A low temperature phase of about 80° C. is obtained, and when used after cooling with liquid nitrogen at about 77° C., there is a problem that a high critical current density cannot be obtained because the temperature margin is low.

The present invention has been made in view of the above background, and an object of the present invention is to provide a method for manufacturing a Bi-based oxide superconductor having a high critical temperature by applying a melting method.

[Means for Solving the Problems] In order to solve the problems mentioned above, the present invention uses a Bi compound and a pb
Bi compound, Sr compound, Ca compound, and Cu compound:
Pb:Sr:Ca:Cu=(2-x):x:2:2
: A starting material is prepared by blending it in a ratio of 3. This starting material is heat-treated at 800 to 850°C to obtain Biw.
A precursor having a composition of -x PbxSr and Ca1CutOy is formed, and this precursor is further melted at 900 to 950°C, and then heat treated at 860 to 880°C.

"Operation" A starting material prepared to have a predetermined composition is heat-treated to form a precursor of the predetermined composition, and by melting and reacting this precursor, an oxide superconductor having a denser structure than that obtained by powder sintering can be produced. generate. Furthermore, by heat-treating at a predetermined temperature following the melting process, Bi exhibiting a high critical temperature of a predetermined composition can be obtained.
A system oxide superconductor is obtained.

The present invention will be explained in more detail below.

In order to manufacture a Bi-9r-Ca-Cu-0 based oxide superconductor by carrying out the present invention, starting materials are first prepared. As starting materials, a Bi compound, a Pb compound, an S compound, a Ca compound, and a Cu compound are used.As the compound, any of oxides, chlorides, carbonates, sulfides, fluorides, etc. of each element can be used. In this example, Bi is used for style.

0, powder, PbO powder, 5rCOs powder, and Ca COs
powder and CuO powder are used. Incidentally, the compound used may be in the form of particles or powder, but it is preferable that the particle size is as small as possible.

Once each of the above powders is prepared, Bi:Pb:Sr:Ca:
Weigh it so that the ratio of Cu=(2-x):x:2:2:3 (however, 0≦X×2) and mix it uniformly in an automatic mortar etc. over the required time to create a mixed powder. do.

Next, the mixed powder was placed in the atmosphere at 800-850℃ for 24 hours.
Unnecessary components are removed by heating and calcining for more than an hour, and B 1s-x P bx S r*ca+cut01
A precursor having a composition of 1 is prepared. The calcination treatment time ranges from several hours to several hundred hours, and it is preferable to perform the calcination treatment until it can be confirmed by X-ray diffraction that a complete single-phase state of 1t-x Pbx SrmCa + CumOy phase is obtained. The processing atmosphere may be an oxygen gas atmosphere.

Next, the precursor powder produced as described above is packed into a heat-resistant container made of metal such as platinum and melted in a heating furnace such as an infrared image furnace at a temperature of 900 to 950° C. for about 30 minutes. After melting for a predetermined period of time, it is preferably rapidly cooled.

By this rapid cooling treatment, it is possible to reduce the size of crystal grains produced, and the reaction of the heat treatment to be performed later proceeds in a single hour. In addition, when melting by heating, it is not preferable to melt at a temperature higher than 950°C because decomposition of the Bit-xPbxSr*Ca+CutOy phase will occur.

Next, the heat-resistant container containing the molten material is inserted into an electric furnace in the atmosphere and heated to a temperature of 860-880°C for 100-300°C.
Heat for 0 hours. Here, heat treatment at a temperature lower than 860°C is not preferable because the formation reaction of a high-temperature phase with a critical temperature of 110K does not occur, and at 880°C or higher, the melt simply melts again, resulting in a reaction of formation of a phase with a critical temperature of 110K. This is not desirable because it does not occur. Note that the heat treatment may be performed by directly inserting the melt into an electric furnace before solidifying the melt, or heat treatment may be performed after solidifying the melt.

Through the above heat treatment, a phase with a low critical temperature contained in the precursor changes to a phase with a high critical temperature. That is, by this heat treatment, B it-x P bxS rtc atc
A Bi-based oxide superconductor having a composition usOy and a critical temperature of 100 to 10K is produced.

Incidentally, during this phase change, fine crystal grains are generated by performing a rapid cooling treatment as described above to make the crystal grains fine.

The Bi-based oxide superconductor produced by the above method has a critical temperature that is sufficiently higher than the liquid nitrogen temperature (77K), so when used after being cooled with liquid nitrogen, a sufficient temperature manon can be obtained, and Since it has a more dense crystal structure than oxide superconductors manufactured by sintering, it exhibits a high critical current density.

"Example" B j t 03 powder, PbO powder, S r COs powder and CaC0, powder and CuO powder, Bi:Pb:Sr:
They were blended at a molar ratio of Ca:Cu=1.75:0.25:2:2:3 and mixed in an automatic mortar for 1 hour.

This mixed powder was heated to 800 to 50℃ in the atmosphere for 24 hours.
Heat treatment for more than an hour. In addition, X-ray diffraction of the heat-treated mixed powder was carried out to show complete i, -xpbxSr*Ca+Cu
*The precursor is produced by heat treatment for the necessary time until it is confirmed that it becomes a single Oy phase.

Next, this precursor powder is filled into a container made of platinum tape and heated in an infrared image furnace at a temperature of 900 to 950°C to melt it for about 30 minutes.

Note that if the melt is solidified at this stage, the solidified material will be 8
Indicates the critical temperature at 0.

The platinum container containing the melt was inserted into an electric furnace in the air while containing the melt, and heat treated at a temperature of 860 to 880°C for 100 to 300 hours to obtain a Bi-based oxide superconductor. .

When the critical temperature of the oxide superconductor obtained after the heat treatment was measured, it was confirmed that the electrical resistance became zero at a temperature of 100 to 110K. In addition, when the critical temperature was measured, a value of 100 A/am'' was obtained.

From the above results, it was found that by carrying out the method of the present invention, an excellent Bi-based oxide superconductor having a high critical temperature and high critical current density can be manufactured.

For comparison, a sample was prepared by melting a precursor produced in the same manner as described above and then heat-treating it at 850°C for 100 hours.
A sample heat-treated at 890° C. for 100 hours showed a critical temperature of 75 K, and a critical temperature of 70 K was not obtained.

"Effects of the Invention" As explained above, the present invention applies the melting method, so
Compared to manufacturing by sintering method, it is possible to obtain an oxide superconductor with a more dense structure, and the composition can be adjusted to a suitable temperature by further heat treatment at 860 to 880 °C after melting, so An oxide superconductor exhibiting a high criticality of 1 degree can be obtained.

Claims (1)

[Claims] Bi compound, Pb compound, Sr compound, Ca compound, and Cu compound are Bi:Pb:Sr:Ca:Cu=(2-x
):
A precursor having a composition of _2O_y is formed, and this precursor is further melted at 900 to 950°C, and then a precursor of 860 to 88°C is melted.
A method for producing a Bi-based oxide superconductor, the method comprising heat-treating at 0°C.