JPH03218922A - Production of tl-containing multiple oxide superconductor - Google Patents

Abstract

PURPOSE:To prevent the diffusion of Tl and to accurately control the compsn. of elements by heat-treating an intermediate multiple oxide consisting of oxygen and the constituent metallic elements of the title superconductor except Tl at a prescribed temp. in an atmosphere contg. Tl and O2. CONSTITUTION:An intermediate multiple oxide consisting of oxygen and the constituent metallic elements of a Tl-contg. multiple oxide superconductor except Tl is prepd. and heat treated at 800-1,000 deg.C in an atmosphere contg. Tl and O2-contg. gas. The diffusion of toxic Tl having high vapor pressure is prevented and the compsn. of elements is accurately controlled.

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 Tl-Ba-Ca-Cu composite oxide superconductors. The present invention relates to a new method for producing a complex oxide superconductor containing thallium.

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. That is, under superconductivity, there is no power loss at all even when current is passed through a superconductor, and a high-density current continues to flow forever. For example, if superconducting technology is applied to power transmission, it will be possible to significantly reduce the approximately 7% transmission loss that currently occurs with power transmission. It is also expected to be used in the measurement field that uses SQUIDs to sense weak magnetism, the medical field that uses pi-meson therapy, and even high-energy physical experiment equipment. Furthermore, superconductors are also required in fields that require the generation of strong magnetic fields, such as nuclear fusion, MHD power generation, magnetic levitation trains, and magnetic propulsion ships.

Furthermore, applications of superconducting materials to various electronic devices have also been proposed. A typical example is an element that utilizes the Josephson effect, in which quantum effects appear macroscopically when superconducting materials are weakly bonded together by an applied current.

Tunnel junction type Josephson devices are expected to be extremely high-speed switching devices with low power consumption because the energy gap of superconducting materials is small. Also,
As the number of electronic circuits increases, the power consumption per unit area is expected to reach the limit of cooling capacity. Therefore, there is a need for the development of superconducting elements for ultra-high-speed computers.

However, in the past 10 years, the superconducting critical temperature T of superconducting materials
c could not exceed 23K of Nb3Ge.

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, '”B64, 1986, 189
page).

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

For example, U.S. Pat. No. 3,932,315 states that B.
It has been described that a-PbBi-based composite oxides exhibit superconducting properties, and also in JP-A-60-173,
Publication No. 885 describes that a Ba-Bi-based composite oxide exhibits superconducting properties. However, the T of the complex oxide superconducting materials known so far. is 10
K or less, which is generally extremely low, and in order to obtain superconducting phenomena it was necessary to use expensive and rare liquid helium (boiling point 4.2 K).

The oxide superconductor discovered by Bednotes and Mueller is (La, Ba) 2Cu 0 4, which is called a K2NIF4 type oxide, and has a crystal structure similar to the previously known Belobusteito type superconducting oxide. are similar, but its Tc is about 30K, which is dramatically 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.

Chus are represented by YBazCu3 Ch-x90
have reported another type of composite oxide called YBCO that exhibits a K-class critical temperature (Physical Rev.
iewLetters, (58) skin 908 pages 198
7 years). Maeda et al. have reported another superconducting composite oxide based on BISr-Ca-Cu (Japanese
Journal of Applied Physics
s, (27)2. 1209-12lO).

Thallium-based composite oxides are also superconductors of 100 K or higher. The present applicant has disclosed several thallium-based composite oxides in Japanese Patent Application No. 185739/1982 and Japanese Patent Application No. 185710/1982, and Harman et al.
Plied Physics Letter (52)
20 On page 1738 TI -Ba -Ca-
Co-based materials are reported. These thallium-based composite oxides are not only chemically more stable than the above-mentioned YBCO-based composite oxides, but also can achieve a Tc of 100 K or more without using rare earth elements, thus reducing manufacturing costs. It has the advantage of being able to

All of these composite oxide superconducting materials can generally be manufactured by solid 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 plating method, physical vapor deposition (PVD) method such as MBE, thermal CVD method, plasma CVD method, optical Cv0 method,! J.O.
A thin film can be formed on a substrate using a CVD method such as the CvD method.

However, the above TI-based composite oxide superconducting material
Since the vapor pressure of I is significantly different from that of other constituent elements, it is difficult to accurately control the composition. Moreover, since T1 vapor is toxic, there is a problem in that it contaminates the manufacturing environment. Therefore, it is difficult to handle thallium-based composite oxides by the usual surface phase reaction method.

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 develop a high quality thallium-based composite oxide superconductor having a particularly high superconducting critical temperature (Tc), such as TIBa-Ca- C
The object of the present invention is to provide a new method for manufacturing a U-based composite oxide superconductor more easily and reliably.

Means for Solving the Problems The method of manufacturing a complex oxide superconductor containing thallium provided by the present invention involves producing an intermediate complex oxide consisting only of metal elements other than thallium constituting the complex oxide superconductor; It is characterized in that thallium oxide is reacted with the intermediate composite oxide by heat treating the oxide in a temperature range of 800 to 1000° C. in a gas atmosphere containing chromium and oxygen or in an atmosphere of thallium oxide vapor.

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 thallium. A typical chromium-based composite oxide to which the present invention is applicable is represented by the following general formula: Tl2(Ba,-q,Caq)IIICLIII Op
+r where m, n, X and y are each as follows:
Represents a number that satisfies the following ranges: 3≦m≦5, 2≦n≦4, 0<q<1, -1≦r≦+1, p = (6+m+n)/
It is 2. Examples of complex oxides of this system include the following system: Tl2Ba2Ca, Cu20g T! 2Ba2Ca2Cu3C)+o Some of these composite oxides have a crystal structure twice that of the above system in the C-axis direction. The Tc of each of these systems is 1
00K and 125K.

The present invention can also be applied to thallium-containing composite oxides other than those mentioned above. As an example, the following system may be mentioned: TI-Sr-Ca-Cu-0 system (75-100K)T
I-Pb-Sr-Ca-Cu-0 system (80-12
2K) TI-Ba-(Y, Ca)-Cu-0 system (92K) (TI, Ln)-Sr-Ca-Cu-0
System (80-90K) (TI, La, Pb)-Sr
-Ca-Cu-○ system (100 K) (Bi, TI)-
Sr -Cu-0 system (90K) Pb-TI -Sr -
Cu-0 series (42K) a-TI-Sr-Cu
-0 series (32K)Nd-TI -Sr -Cu -
0 series (44K) (Note) Ln is a lanthanoid element.As already mentioned, composite oxide-based high-temperature superconducting materials can generally be manufactured by sintering or vapor deposition, but thallium-based composite oxide In this case, it is extremely difficult to control the composition effectively using conventional methods because there is a large difference in the vapor pressure of each constituent element.

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 thallium is first made, and this is further reacted with thallium 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 made using only the other constituent elements except thallium, which has an extremely high vapor pressure, and then, in the second step, this intermediate composite oxide is Furthermore, thallium oxide is 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. However, in the method of the present invention, since thallium is added later, the superconducting layer is mainly formed near the surface of the intermediate composite oxide. Therefore, the intermediate composite oxide is preferably a thin film.

Further, the intermediate composite oxide may be crystalline or amorphous, but by making the intermediate composite oxide amorphous,
The quality of the finally obtained TI-based composite oxide superconductor can be improved.

That is, in the case of a crystalline intermediate composite oxide base material, crystals in a stable state have already been formed inside the base material, so that the addition of TI and the diffusion of the added TI become insufficient.

Furthermore, in particular, multiple phases exist in the crystal of the Ba-Ca-Cu composite oxide, and crystal grains of mutually different phases are formed in the crystalline base material, so TI is applied to this base material. If added, different phases or different compositions of T in the final product
I-based complex oxides are mixed, making it difficult to obtain a homogeneous superconductor.

If a non-quality intermediate composite oxide is used, the quality and composition of the intermediate composite oxide will be uniform throughout. Furthermore, since the amorphous state is thermodynamically unstable, addition and diffusion of TI can be carried out efficiently.

In the first step of producing an intermediate composite oxide of a constituent metal element other than chromium, 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 thallium, especially powders of their oxides, carbonates, or fluorides, are mixed at a predetermined atomic ratio, and the obtained raw material mixed powder is sintered. conclude. It is preferable to repeat calcination and pulverization several times before sintering. In this case, in order to obtain an amorphous sintered body, the raw material powder is heated to
What is necessary is to melt it to about 0°C and then rapidly cool it. In the case of constituent metal elements other than thallium, there is no extreme difference in vapor pressure, so this sintering can be performed by normal operations.

As already mentioned, the intermediate composite oxide formed from elements other than thallium may be a sintered body as described above, but in the TI addition method of the present invention, the added thallium is not an intermediate composite oxide. Because the reaction mainly occurs near the surface of the object,
What about intermediate composite oxides? Membranes are more advantageous.

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

RF McNetron sputtering method as physical vapor deposition method,
When a vacuum evaporation method or an ion plating method is used, the atomic ratio of the metal elements in the evaporation source or the target 7 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 (MBB) method, the constituent metal elements or their oxides are evaporated using a K cell. In this case, oxygen is separately supplied into the deposition atmosphere as required.

The substrate on which this intermediate composite oxide thin film is formed is made of MgO, Zr
O■, SrTi03, Nb03, LiTa03, La
It is preferable to use a single crystal such as A103 or LaGa03. Furthermore, LiAlO+,? Cab3, KTaO+, C
aF2, BeF2, csz, ysz, etc. can also be used. When a silicon single crystal is used, it is preferable to form a single layer of a buffer such as 1gO or ZrO on its surface to form an intermediate composite oxide thin film.

The finally obtained composite oxide superconductor generally has crystal anisotropy in its electrical resistance, and current tends to flow in the direction parallel to the plane defined by the a-axis and b-axis of the crystal, and the C-axis It is difficult to flow in a direction parallel to . Therefore, when forming a composite oxide-based superconducting material thin film, it is preferable to impart crystal orientation according to the desired current direction.

For example, if the (100) plane of an M g O single crystal substrate or an SrTi03 single crystal substrate is used as a film formation surface, the composite oxide superconductor thin film formed on this film formation surface will be
Since the axis is perpendicular or at an angle close to perpendicular to the substrate film-forming surface, a thin film with excellent properties can be obtained, particularly at the critical current density Jc. Furthermore, by using the {110} plane of the SrTiO3 substrate and making the C axis of the crystal parallel to the substrate, it is also possible to obtain a high current density in the depth direction of the film.

In addition, since MgO and SrTiO3 have a coefficient of thermal expansion close to that of composite oxide superconducting materials, heating/
Thermal history, including cooling, does not create harmful stresses in the thin film.

Specifically, for example, when manufacturing a non-quality thin film of a Ba-Ca-Cu-'0-based intermediate composite oxide, the 13a-(:a-Cu composite oxide block described above or its BaCa-Cu was deposited on a MgO single crystal substrate by sputtering using a powder obtained by pulverizing BaCa-Cu as a target.
When forming a thin film of -0-based intermediate composite oxide, the substrate temperature during vapor deposition is set to a temperature in the range of 600° C. or lower.

In the second step, thallium is further added to the thus obtained intermediate composite oxide thin film and reacted.

This operation is carried out by heat-treating the block or thin film of the intermediate composite oxide obtained above in a temperature range of 800 to 1000° C. in a gas cloud containing thallium and oxygen or in an atmosphere of thallium oxide vapor.

Specifically, an intermediate composite oxide is placed in a sealed chamber, and thallium vapor and oxygen gas or chromium oxide vapor atmosphere is placed in the chamber. Create an atmosphere and heat the intermediate composite oxide. Thallium oxide vapor can be generated, for example, by heating thallium oxide powder.

In this case, the heating temperature of the intermediate composite oxide is 800 to 100
It is preferable to maintain the temperature within the range of 0°C. This heating temperature is 80
Since the intermediate composite oxide is not activated below 0°C, the thallium oxide vapor and the intermediate composite oxide do not react sufficiently. On the other hand, if the heating temperature exceeds 1000°C, thallium atoms will jump out of the intermediate composite oxide again, making it impossible to obtain the desired thallium-based composite oxide.

Generally, it is preferable to heat the thallium compound, which is the evaporation source, higher than the heating temperature of the intermediate composite oxide.

Furthermore, the vapor pressure of the thallium compound, which is the evaporation source, can be increased by using a suitable flux. It is generally preferable to carry out the heat treatment in the thallium vapor cloud for 1 minute to 5 hours.

Note that, in order to control the oxygen content of the final composite oxide superconductor, it is preferable to keep the oxygen partial pressure in the heat treatment atmosphere high. This oxygen partial pressure can be appropriately selected depending on the type of composite oxide superconductor of the final product, but is generally about 1 atmosphere.

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 10.
In an airtight furnace 1 equipped with an outlet 8 that can be closed by
It has a substrate holder 4, a boat 5 that accommodates a thallium-containing compound 11, and a heater 6 that heats the boat 5. Further, a heater 2 is provided outside the furnace 1, and is configured to be able to heat the entire furnace. Further, the boat 5 and the substrate holder 4 are arranged to face each other, so that the vapor containing thallium volatilized from the boat 5 efficiently reaches the base material. Furnace 1
is equipped with a pressurized 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 thallium is fixed to the substrate holder 4, and a thallium-containing compound, e.g. After accommodating the thallium oxide powder, the furnace is once evacuated, the hull 10 is closed, and the valve 9 is opened to introduce oxygen gas into the furnace. After closing the valve 9, the heater 6 is energized to evaporate the thallium-containing compound in the boat 5, and the heater 2 outside the furnace 1 is energized to heat the intermediate composite oxide 3. This heating time may be 1 minute to 3 hours.

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 1 First, a base material used in the present invention was prepared as follows.

Each oxide powder of BaSCa and Cu was prepared as Ba:Ca:
Cu? The mixed powder obtained by mixing at an atomic ratio of 2:2:3 was sintered, and a thin film was formed on an MgO single crystal substrate by magnetron sputtering using the sintered body as a target. This thin film! ．． IgO single crystal (110
) was formed on the surface. The film forming conditions are as follows.

Substrate temperature: 800℃ Pressure: 0.01 ~ 0.1Torr
(Ar/0■=1:1) High frequency power density: 100 W Film thickness
:0.2 μm Next, the Ba-Ca-Cu intermediate composite oxide thin film obtained as described above was fixed as the base material 3 to the substrate holder 4 of the apparatus shown in FIG. 1, facing downward.

In addition, thallium oxide powder was stored in the boat 5.

Subsequently, after evacuating the inside of the furnace 1, the valve 10 is closed, and the valve 9 is closed.
The furnace was opened and filled with oxygen. Next, the inside of the furnace is heated to 970°C by heater 2, and the boat 5 is heated by heater 6.
was heated to 1000°C, and after the boat 5 reached 1000°C, this temperature was maintained for 5 minutes and then the heater was turned off.

After the above process! ．． The IgO single crystal substrate 3 was taken out of the furnace and the superconducting critical temperature was measured.

The above process has been completed! ．． IgO single crystal substrate 3 is immersed in liquid helium in a cryostand, and once cooled down to 8K, it is confirmed that the sample exhibits superconductivity, and then the temperature is raised to a temperature at which the sample exhibits the same electrical resistance as normal (Tc ) was measured.

The superconducting critical temperature of the sample thus measured was 110
It was K.

Example 2 Production of intermediate composite oxide First, an intermediate composite oxide was produced as follows.

Each oxide powder of Ba, Ca and Cu was converted into Ba:Ca
:The mixed powder obtained by mixing Cu in an atomic ratio of 2+2:3 was sintered at 900° C. for 2 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 was made by changing the substrate temperature to 4g
It was formed on the (100) plane of an O single crystal. The film forming conditions are as follows.

Substrate temperature: Listed in Table 1 Sputtering gas pressure: 5×10” Torr sputtering gas: Ar+02 (02 20%) High frequency power density: 0.64 W/cm2 Film thickness
: 1 μm The crystallinity of each thin film obtained by changing the substrate temperature was determined by the X-ray diffraction pattern.

Figures 2(a) and (b) are conceptual diagrams of a part of a typical X-ray diffraction pattern of a thin film formed as described above, and Figure 2(a) shows a so-called crystalline X-ray diffraction pattern. This is the X-ray diffraction pattern of a thin film with low crystallinity, that is, an amorphous thin film, and the X-ray diffraction pattern of a thin film with high crystallinity is shown in FIG.

In this example, the crystallinity Xc is defined as the percentage of the area ratio (S/So) of the diffraction intensity at the same diffraction angle of the X-ray diffraction pattern, as shown in FIGS. 2(a) and (b). Xc - (S/SO)X 100 was evaluated, and a state where Xc <10 was defined as non-quality.

In addition, so is the area of the diffraction intensity in the case of the X-ray diffraction pattern of a thin film formed at 800 ° C. with sufficiently high crystallinity,
S is the corresponding X of the thin film obtained under the same deposition conditions.
It is the area of the diffraction intensity of the line diffraction pattern. The results are summarized in Table 1.

Table 1 Next, two series of samples were prepared using the above method. The first series of samples consists of three intermediate composite oxide thin films of Ba-Ca-Cu.
It is an amorphous thin film formed at a substrate temperature of 50°C, and the second
The samples in this series are crystalline thin films formed by depositing Ba-Ca-Cu intermediate composite oxide thin films at a substrate temperature of 650°C.

The following thallium addition operation was performed on these two series of samples.

First, an MgO single-crystal substrate 3 having an amorphous thin film formed at the substrate temperature of 350° C. is fixed facing downward in the substrate holder 4 of the apparatus shown in FIG. Powder of thallium oxide (T1203) powder 11 was contained.

Next, after evacuating the inside of the furnace 1, the valve 10 is closed, and the valve 9 is closed.
The furnace was opened and filled with oxygen. Next, the inside of the furnace is heated to 880°C by heater 2, and the boat 5 is heated by heater 6.
is heated to 1000°C, and after the boat 5 reaches 1000°C, this temperature is maintained for 5 minutes to fill the furnace with 71203 steam, and then the heater 2 is used to bring the inside of the furnace to the temperature shown in Table 2 below. It was heated to the heat treatment temperature and held at this temperature for 1 hour. Thereafter, the temperature of the furnace was further maintained at 850° C. for 3 hours.

The ~1g◯ single crystal substrate 3 that had undergone the above treatment was taken out of the furnace and the superconducting critical temperature was measured.

The Ig○ single crystal base 3 subjected to the above treatment was immersed in liquid helium in a cryostat and once cooled to 8K, confirming that the sample exhibited superconductivity.

In addition, the critical current density was measured at 77 K by cooling the sample with liquid nitrogen (A/CIII).

The intermediate composite oxide thin film of each series was subjected to T1 addition treatment according to the above procedure while changing the treatment temperature.

Table 2 shows the treatment temperature and sample evaluation.

Table 2 Effects of the Invention As explained above, in the method for producing a superconductor according to the present invention, a base material is produced from an element that is non-toxic and relatively easy to handle, and then thallium is added to the base material in a sealed space. It is made into a superconductor by heat treatment in the presence of steam containing oxygen and oxygen.

Therefore, diffusion of thallium, which is toxic and has a high vapor pressure, is prevented, and superconductors can be easily produced after precise elemental composition control.

Also, when the base material to which TI is added is of non-quality:
Since the homogeneity of the base material is increased and T1 can be diffused efficiently and uniformly, the obtained TI-based superconductor can also be of high quality.

Furthermore, since the method of the present invention does not require a long time for the Tl addition treatment, it is also possible to manufacture large quantities or long O products by performing the T1 addition treatment continuously using the wire rod as the base material. It is.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of an embodiment of a device that can be used in the superconductor manufacturing method of the present invention, and FIG. 2 (a) and (b)
) is a conceptual diagram of a typical X-ray diffraction pattern obtained from an intermediate composite oxide sample. Main reference number〕 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... TI evaporation source/patent applicant

Claims (1)

[Claims] (1) In a method for manufacturing a complex oxide superconductor containing thallium, an intermediate complex oxide is made consisting only of metal elements other than thallium, which constitutes the complex oxide superconductor, and this intermediate complex oxide is mixed with a gas containing thallium and oxygen. 800-10 in an atmosphere of
A method characterized in that thallium is reacted with the intermediate composite oxide by heat treatment in a temperature range of 00°C.