JPH02160623A - Method for manufacturing Bi-based composite oxide superconductor - 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 Field of Industrial Application The present invention relates to a novel method for manufacturing composite oxide superconductors, and in particular, to a method for producing composite oxide superconductors such as Bi-3r-Ca-Cu composite oxide superconductors. The present invention relates to a novel method for producing a composite oxide superconductor containing bismuth.

BACKGROUND OF THE INVENTION Superconductivity, which is said to be a phase transition of electrons, is a phenomenon in which the electrical resistance of a conductor becomes zero under certain conditions and exhibits complete diamagnetic properties. In other words, under superconductivity, even when current is passed through a superconductor, there is no power loss, and a high-density current continues to flow forever. For example, if superconductivity technology is applied to power transmission, It can significantly reduce the approximately 7% power transmission loss that is said to occur.It is also useful in the measurement field that uses 5QUID to sense weak magnetism, the medical field that uses pi-meson therapy, and even high-energy physics experiment equipment. Furthermore, superconductors are required in fields that require generation of strong magnetic fields, such as nuclear fusion, MHD power generation, magnetic levitation trains, and magnetic propulsion ships.In addition, superconductors are used in various electronic applications. Applications to devices have also been proposed.A typical example is a device that utilizes the Josephson effect, in which quantum effects appear macroscopically depending on the applied current when superconducting materials are weakly joined together.Tunnel junction type Because the energy gap of superconducting materials is small, Josephson devices are expected to be extremely high-speed switching devices with low power consumption.Also, as the degree of integration of electronic circuits increases, the power consumption per unit area increases with cooling capacity. Therefore, there is a demand for the development of superconducting elements for ultra-high-speed computers.However, in the past 10 years, the superconducting critical temperature Tc of superconducting materials has not exceeded 23K for Nb and Ge. could not.

The existence of high-temperature superconductors was revealed by the discovery of complex oxide-based high Tc superconducting materials by Bednorz and Muller (Bednorz, Muller).

"Z, Phys," 864. (1986, p. 189).

It has been known for some time that composite oxide ceramic materials exhibit superconducting properties.

For example, U.S. Pat. No. 3,932,315 describes Ba-
It has been described that Pb-B1-based composite oxides exhibit superconducting properties, and JP-A-60-173.88
No. 5 describes that a Ba-B1-based composite oxide exhibits superconducting properties. However, the T of the complex oxide superconducting materials known so far. is generally extremely low, less than 10%, and the use of expensive and rare liquid helium (boiling point >4.2 K) was unavoidable in order to obtain superconducting phenomena.

The oxide superconductor discovered by Bednotes and Minnieler is (La, Ba) 2Cu 04, which is called an N1F4 type oxide and has a crystal structure different from the previously known perovskite type superconducting oxide. Although similar, its Tc is about 30, which is significantly higher than that of conventional superconducting materials. Since then, many complex oxide-based high-temperature superconductors have been reported, and the possibility of practical application of high-temperature superconductors has emerged.

Chu et al. have reported another type of complex oxide called YBCO, which exhibits a critical temperature of 90°C expressed by YBa2Cu30t-w (Physical Rev.
ew Letters, (58) 9.908 pages 1
987).

Maeda et al. reported another superconducting composite oxide based on Bi-3r-Ca-Cu-(Japanese J
our own of Applied Physics
, (27) 2. pp. 1209-1210). This bismuth-based composite oxide is not only chemically more stable than the above-mentioned YBCO-based composite oxide, but also can achieve a Tc of 100 or more without using rare earth elements, which can reduce manufacturing costs. There is an advantage.

All of these composite oxide superconducting materials can generally be manufactured by in-phase reaction.

That is, a sintered body can be obtained by sintering a raw material mixed powder in which powders of oxides or carbonates of constituent metal elements are mixed in a ratio such that the constituent metal elements have a predetermined atomic ratio.

In addition, RF sputtering method, vacuum evaporation method, ion blating method, physical vapor deposition (PVO) method such as MBE, thermal CVD method, plasma CVD method, photoCVD method, MOCV
A thin film can be formed on a substrate using a CVD method such as the D method.

However, the above Bi-based composite oxide superconducting material
Since the vapor pressure of I or 81 is significantly different from that of the other constituent elements, it is difficult to control the composition.

In addition, composite oxide-based superconducting materials obtained by solid-phase reaction methods are sintered bodies, which have low density, microscopic porousness, and uneven quality, making it difficult to put superconducting technology into practical use. It was not suitable for use in the field of electronic circuits, which are said to be the fastest.

Problems to be Solved by the Invention An object of the present invention is to solve the problems of the prior art described above, and to provide a high quality bismuth-based composite oxide superconductor having a particularly high superconducting critical temperature (TC), such as Di-3r- Ca
An object of the present invention is to provide a new method for manufacturing a -Cu-based composite oxide superconductor more easily and reliably.

Means for Solving the Problems The method for manufacturing a bismuth-containing composite oxide superconductor provided by the present invention involves producing an intermediate composite oxide consisting only of metal elements other than bismuth, which constitutes the composite oxide superconductor; 750~ in an atmosphere of bismuth oxide vapor
It is characterized in that bismuth is reacted with the intermediate composite oxide by heat treatment in a temperature range of 950°C.

The above-mentioned intermediate composite oxide may be a bulk-shaped base material such as a block or a molded body, or a thin film formed on a substrate.

The present invention can be applied to any composite oxide containing bismuth. A typical bismuth-based composite oxide to which the present invention is applicable is represented by the following general formula: B i <(Sr+-+l, Ca, I) JIJhO
p+y where m, n, x and y are numbers satisfying the following ranges: 6≦m≦16.4≦n≦12゜0.2<X<0.8, -2<y<+2 The expression is p·(5+m+n).

Examples of this type of complex oxide include the following; B I 4 S r 4 [:a 4 CU s 02
Q + yB12Sr2[:a2CU30+o+y The present invention can also be applied to bismuth-containing composite oxides other than those listed in 1. As an example, the following system can be mentioned: Bi -Y -Ba-Cu -0 system (100K) []i
-Pb-3r-Ca -Cu -0 system (107K)B
+ -Pb-3b-3r -Ca -Cu -0 system (1
32K) Bi-(Sr, Ln)-4: u-0 system (30
~42K) ([]i, TI, Pb)-Ca-3r
-Cu-0 series (110K) (Note) Ln is a lanthanoid element.As already mentioned, complex oxide-based high-temperature superconducting materials can generally be manufactured by sintering or vapor deposition, but bismuth-based In the case of composite oxides, since there are large differences in the vapor pressures of the constituent elements, it has been extremely difficult to effectively control the composition using conventional methods.

The feature of the method of the present invention is that instead of directly synthesizing the final target composite oxide, an intermediate composite oxide containing no bismuth is first prepared, and this is further reacted with bismuth oxide to synthesize the final target composite oxide. The point is to obtain oxides.

That is, in the method of the present invention, in the first step, an intermediate composite oxide is first prepared using only other constituent elements except bismuth, which has an extremely high vapor pressure, and then, in the second step, this intermediate composite oxide is Bismuth oxide is further added to.

This intermediate composite oxide may be a bulk-shaped base material such as a block or molded body, or a thin film formed on a substrate. That is, in the method of the present invention, since bismuth is added later, the superconducting layer is mainly formed near the surface of the intermediate composite oxide. Therefore, the intermediate composite oxide may be a thin film.

In the first step of producing an intermediate composite oxide of a constituent metal element other than bismuth, any conventionally known solid phase reaction method or vapor deposition method can be used.

When producing a bulk-shaped base material as an intermediate composite oxide, a solid phase reaction method is used. In this case, first, compound powders of constituent metal elements other than bismuth, especially powders of their oxides, carbonates, or fluorides, are mixed in a predetermined atomic ratio, and the obtained raw material mixed powder is sintered. conclude. Preferably, the calcination-grinding process is repeated several times before sintering.

Specifically, for example, when manufacturing a sintered block of a 5r-Ca-Cu-0-based intermediate composite oxide, powders of strontium oxide, calcium oxide, and copper oxide are mixed and sintered at 900°C. An intermediate sintered body can be produced by this. In the case of constituent metal elements other than bismuth, there is no extreme difference in vapor pressure, so this sintering can be performed by normal operations.

When using a thin film as the intermediate composite oxide, a physical vapor deposition (PVO) method or a chemical vapor deposition (CVD) method is used.

RF McNetron sputtering method as physical vapor deposition method,
When using a vacuum evaporation method or an ion blating method, the atomic ratio of metal elements in the evaporation source or target is adjusted depending on the evaporation rate of each element and the difference in bond strength to the substrate. This evaporation source or target is a metal element and/or
Alternatively, it is preferable to use a sintered body obtained by sintering a powder raw material of an oxide or carbonate thereof by a powder sintering method, or a sintered powder obtained by pulverizing this sintered body. Moreover, this evaporation source or target can also be divided into multiple parts. When using the molecular beam epitaxy (MBE) method, the constituent metal elements or their oxides are evaporated using a cell or an electron gun. In this case, oxygen is separately supplied to the deposition atmosphere as needed.

The substrate on which this intermediate composite oxide thin film is formed is MgO1Sr.
TiO,, LaAl0. , LaGa0. It is preferable to use a single crystal such as . When using a silicon single crystal, it is preferable to form a buffer layer of MgO, ZrO□, etc. on its surface before forming an intermediate composite oxide thin film.

When forming the superconducting thin film of the present invention, the intermediate composite oxide is formed on the (001) plane or (110) plane of each of the above-mentioned single crystal substrates.
It is preferable to form a film on the surface. With these boards,
The crystal structure of the intermediate composite oxide thin film is perovskite, which is advantageous for making the surface of this intermediate composite oxide layer a superconductor.

Specifically, for example, when producing a thin film of a 5r-Ca-Cu-0-based intermediate composite oxide, the S described above is used.
A thin film of a 5r-Ca-Cu-Q intermediate composite oxide can be formed on an MgO single crystal substrate by sputtering using an r-Ca-Cu composite oxide block or a powder obtained by pulverizing it as a target. When depositing this intermediate composite oxide layer, the substrate is generally heated from room temperature to 80°C.
Heat to a temperature in the range of 0°C.

In the second step, bismuth oxide is further added to the thus obtained intermediate composite oxide block or thin film and reacted. In this operation, the block or thin film of the intermediate composite oxide obtained above is heated at 75°C in an atmosphere of bismuth oxide vapor.
This is carried out by heat treatment in a temperature range of 0 to 950°C.

Specifically, an intermediate composite oxide is placed in a sealed chamber, and a mixed atmosphere of bismuth vapor and oxygen gas or a mixed atmosphere of bismuth oxide gas is created in this chamber, and the intermediate composite oxide is heated. Heat. Bismuth oxide vapor can be generated by heating bismuth oxide powder.

In this case, the heating temperature of the intermediate composite oxide is 750 to 950
It is preferable to maintain the temperature within the range of ℃. This heating temperature is 750
If the temperature is lower than 0.degree. C., the intermediate composite oxide is not activated, so the bismuth oxide vapor and the intermediate composite oxide do not react sufficiently. On the other hand, if the heating temperature exceeds 950°C, the bismuth atoms will jump out of the intermediate composite oxide again, making it impossible to obtain the desired bismuth-based composite oxide.

Generally, it is preferable to heat the bismuth oxide powder, which is the evaporation source, higher than the heating temperature of the intermediate composite oxide. Moreover, the vapor pressure of bismuth oxide, which is an evaporation source, can be increased by using a suitable flux. This heat treatment in a bismuth oxide vapor atmosphere is generally preferably carried out for 5 minutes to 5 hours.

Note that, for the purpose of controlling the oxygen content of the final composite oxide superconductor, it is preferable to contain oxygen at an appropriate partial pressure in the heat treatment atmosphere.

This oxygen partial pressure can be appropriately selected depending on the type of composite oxide superconductor of the final product, but is generally 0.1 to
It is about 1 atm.

In addition, the method of the present invention does not require a long time for the bismuth oxide addition treatment, so the intermediate composite oxide may be used as a wire or
It is also possible to continuously process long articles by forming a thin film of intermediate composite oxide on the core material and adding bismuth oxide to this wire or thin film layer.

The apparatus that can be used to carry out the method of the present invention will now be described with reference to the accompanying drawings.

FIG. 1 is a conceptual diagram of the configuration of an apparatus according to an embodiment for carrying out the method of the present invention.

The device has a supply hole 7 which can be closed by a valve 9 and a valve lO
In an airtight furnace 1 equipped with an outlet 8 that can be closed by
It has a substrate holder 4, a boat 5 containing a bismuth-containing compound such as bismuth oxide, and a heater 6 for heating the boat 5. Additionally, a heater 2 is installed outside the furnace 1.
The furnace is constructed and constructed in such a way that it can heat the entire furnace. Further, the boat 5 and the substrate holder 4 are arranged to face each other, so that the steam containing bismuth oxide volatilized from the boat 5 efficiently reaches the base material. Note that the furnace 1 is equipped with a pressure safety valve.

When carrying out the method of the present invention, an intermediate composite oxide 3 consisting of a block or thin film of a composite oxide of a constituent metal element other than bismuth is fixed to the substrate holder 4, and a bismuth-containing compound, e.g. After accommodating the bismuth oxide powder, the furnace is evacuated, valve 10 is closed, and valve 9 is opened to introduce oxygen gas into the furnace. After closing the valve 9, the heater 2 is energized to evaporate the bismuth-containing compound in the boat 5, and the heater 2 outside the furnace 1 is energized to heat the intermediate composite oxide 3. For example, the heater 2 heats the inside of the furnace to, for example, 880°C, and the heater 6 heats the boat to, for example, 1040°C.

The present invention will be described in more detail with reference to examples below, but the disclosure below is merely one example of the present invention and does not limit the technical scope of the present invention in any way.

Example Production of intermediate composite oxide First, an intermediate composite oxide was produced as follows.

Each oxide powder of Sr, Ca and Cu was converted into Sr:Ca
:The mixed powder obtained by mixing Cu in an atomic ratio of 2:2:3 was sintered at 900° C. for 12 hours to produce a sintered body.

Using the sintered body powder obtained by pulverizing the sintered body thus obtained as a target, a thin film of the intermediate composite oxide was formed on an MgO single crystal substrate by RF magnetron sputtering method. This thin film is made of MgO single crystal (110
) was formed on the surface. The film forming conditions are as follows.

Substrate temperature: Near 60℃ Pressure: 0.01~0. l Torr sputtering gas: Ar/02 = 1 + 1 Radio frequency power: 100 W Thin film thickness: 20.2 μm Production of composite oxide superconductor Next, intermediate composite oxidation of Sr-Ca-Cu obtained as described above. A 14g0 single crystal substrate 3 having a thin film was fixed facing downward to a substrate holder 4 of the apparatus shown in FIG. 1, and a boat 5 contained bismuth oxide powder.

Next, after evacuating the inside of the furnace 1, valve IO is closed, and valve 9 is closed.
The furnace was opened and filled with oxygen. Subsequently, heater 2 heated the inside of the furnace to 880°C, and heater 6 heated the boat to 1040°C.

After boat 5 reached 1040° C., the temperature was maintained for 1 hour, and then heaters 2 and 6 were turned off.

The MgO single crystal substrate 3 subjected to the above-described treatment was taken out of the furnace, and the superconducting critical temperature was measured.

The superconducting critical temperature is the MgO single crystal substrate 3 that has undergone the above treatment.
was immersed in liquid helium in a Tarabiostat and heated to -18K.
After confirming that the sample exhibited superconductivity by cooling the sample to a temperature of 100°C, the temperature was gradually raised and the temperature Tc at which the sample began to lose its superconductivity and at which the electrical resistance was the same as normal was measured.

The superconducting critical temperature Tc of the sample thus measured was 97.

Example 2 The operation of Example 1 was repeated, but instead of making the sintered body of the intermediate composite oxide described in the section "Manufacture of intermediate composite oxide" into a thin film, the sintered body itself was made into a thin film. The block was subjected to the heat treatment operation of Example 1 in a bismuth oxide vapor atmosphere.

The Tc of the block after heat treatment was 105.

Example 3 The operation of Example 1 was repeated, but P was used instead of the Sr-Ca-[:u composite oxide as the intermediate composite oxide sintered body.
A composite oxide of b-3r -Ca-Cu was used. In this case, pb is added as lead oxide, Pb:Sr:Ca
:Cu atomic ratio was 0.3:2 +2:3, and sintering was performed at 900° C. for 5 hours.

The Tc of the obtained thin film was 110.

As described in detail, in the method for producing a superconductor according to the present invention, a base material is produced, and then heat-treated in a sealed space in the presence of steam containing bismuth oxide and oxygen. Make it a superconductor.

Therefore, diffusion of bismuth having a high vapor pressure is prevented, and a superconductor can be easily produced after precise elemental composition control.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of an apparatus according to an embodiment for carrying out the method of forming a superconductor film according to the present invention. [Main reference numbers] 1...Furnace 2...Heater 3...
Intermediate composite oxide 4... Substrate holder 5... Boat 6... Heater 7... Supply hole 8... Discharge hole 9, l
O...Valve 11...Bi-containing compound Fig. 1 Furnace 2 Heater 3 Intermediate composite oxide 4 Substrate holder 5 , Boat 6, Heater 7, Supply hole 8, Discharge hole 9.10. , , , Valve 11 , , , Bi-containing compound

Claims (2)

[Claims] (1) In a method for producing a bismuth-containing composite oxide superconductor, an intermediate composite oxide consisting only of metal elements other than bismuth that constitutes the composite oxide superconductor is created, and this intermediate composite oxide is placed in an atmosphere of bismuth oxide vapor. A method characterized in that bismuth is reacted with the intermediate composite oxide by heat treatment at a temperature range of 750 to 950°C. (2) The method according to claim 1, wherein the intermediate composite oxide is a thin film formed on a substrate.