JPH0624829A - Tl-base oxide superconductor and its production - Google Patents

Abstract

(57) [Summary] [Constitution] In the starting material composition, Tl, Ba, Ca and Cu are substantially (2-u): 2: (n-1 +) in atomic ratio.
v): ratio of (n + w) (where 0 <u <0.7, 0
<V <0.5, 0 <w <0.5).
Baking is performed for 5 to 10 minutes in an oxygen-containing atmosphere at 0 to 910 ° C. [Effect] It has a crystal structure represented by the general formula Tl ₂ Ba ₂ C _n-1 Cu _n O _y , and has a crystal structure of Tl _{2 -u} Ba ₂ C _{n-1 + v} Cu.
A superconductor having a composition represented by _{n + w} O _y can be synthesized as a single phase.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thallium (Tl) -based oxide superconductor and a Tl-based oxide superconductor.

[0002]

2. Description of the Related Art In recent years,
The Tl-Ba-Ca-Cu-O-based oxide superconductor has been attracting attention as a material having a high superconducting transition temperature (critical temperature: Tc). Among them, those having a crystal structure represented by the general formula Tl ₂ Ba ₂ Cann _-1 Cu _n O _y (n = 2, 3, y is a number satisfying the valence requirement) have a Tc of 100 K or more. It is known that

Conventionally, such Tl ₂ Ba ₂ C an _-1 C
When synthesizing an oxide superconductor represented by u _n O _y , starting materials are mixed and fired so that the ratio of metal elements is the same as the target composition.

However, the Tl intended for the starting material
_When mixed at a composition ratio of ₂ Ba ₂ C _n-1 C _n O _y and baked, a large amount of BaCuO ₂ etc. is produced, and the desired superconductivity of the Tl ₂ Ba ₂ C _n-1 C _n O _y structure is obtained. A method for synthesizing the body as a single phase has not yet been reported.

The present invention has been made in view of such circumstances, and has the general formula Tl ₂ Ba ₂ C _n-1 C _{n n.}
Method for producing Tl-based oxide superconductor capable of synthesizing superconductor having crystal structure represented by O _y as a single phase, and T
An object is to provide an l-based oxide superconductor.

[0006]

Means and Actions for Solving the Problems In the method for producing a Tl-based oxide superconductor according to the present invention, in the composition of the starting material, Tl ₂ Ba ₂ Cann _-1 Cu _n O _y (where n is 2 The above integer, y is a number satisfying the requirement of valence), and the mixing ratio of Tl is made smaller than that of the composition represented by Ca, C
It is characterized by increasing the amount of u and then firing. Preferably, in the starting material composition, Tl, Ba, Ca and C
Substantially the atomic ratio of u is (2-u): 2: (n-1 +
v): ratio of (n + w) (where 0 <u <0.7, 0
<V <0.5, 0 <w <0.5).
Baking is performed for 5 to 10 minutes in an oxygen-containing atmosphere at 0 to 910 ° C.

The substance produced in this way is Tl
_2-u Ba ₂ C _{n-1 + v} Cu _{n + w} O _y (where n is an integer of 2 or more, y is a number satisfying the valence requirement, 0.2 ≦ u
<0.7, 0.1 ≦ v ≦ 0.4, 0.1 ≦ w ≦ 0.4)
It is a completely new material having a composition represented by.

The present inventors have found that Tl ₂ Ba ₂ C an _-1 C
As a result of various studies for synthesizing a superconductor having a crystal structure of u _n O _y as a single phase, as a result, the amount of Tl of the starting material was made smaller than that of the above stable phase, and Ca and Cu were increased, It has been found that generation of BaCuO _{2 and the} like can be suppressed, and that the crystal structure of Tl ₂ Ba ₂ Cann _-1 Cu _n O _y can be maintained. The present invention was made based on such knowledge.

Tl _2-u Ba ₂ produced according to the present invention
C _{n-1 + v} C _{n + w} O _y is Tl ₂ Ba ₂ C _n-1 Cu
_Since it maintains the crystal structure of _n O _y , it exhibits a high Tc.

The present invention will be described in detail below.

As described above, the present invention basically has the same starting material composition as Tl ₂ Ba ₂ Can _n-1 Cu _n O.
The mixing ratio of Tl is made smaller than that of the composition represented by _y (where n is an integer of 2 or more, and y is a number satisfying the requirement of valence), while Ca and Cu are increased. Specifically, Tl, Ba, Ca, and Cu in the starting material are set to have a ratio of atomic numbers of substantially (2-u): 2: (n-1 + v) :( n + w), and 0 <u <0. 7, 0 <v <0.5, 0 <w <
0.5). In this range, while suppressing the production of impurities such as BaCuO ₂ , Tl ₂ Ba ₂ Ca after firing
The crystal structure of _n-1 Cu _n O _y can be obtained as a single phase. When n = 2, the values of u, v, and w are 0 <u <0.5, 0.1 <v <0.3, and 0.1 <w <, respectively.
It is preferably 0.3. When n = 3, 0.1 <u <0.6, 0.2 <v <0.4 and 0.1, respectively.
It is preferable that <w <0.3.

[0012] Such a starting material is 890 to 910 ° C.
By firing in the oxygen-containing atmosphere for 5 to 10 minutes, the material having the above-mentioned desired crystal structure can be reliably obtained.

The cooling rate after firing is preferably 10 ° C./minute or more. When the cooling rate is slow, the sample is exposed to the high temperature for a correspondingly long time, so that an extra reaction occurs and the possibility that impurities are generated increases. Especially when n is 3 or more, the 2212 system (Tl ₂ Ba ₂ Ca ₁ C
u ₂ O _y ) is easily generated.

Since the cooling after firing is usually furnace cooling, the upper limit of the cooling rate is about 30.degree. Of course, the temperature may be lowered to a predetermined temperature by furnace cooling and then rapidly cooled. By quenching in this way, it is possible to suppress the incorporation of excess oxygen into the crystal.

[0015]

Embodiments of the present invention will be described below. Example 1 First, BaCO ₃ and CuO fine powder were mixed and fired to synthesize BaCuO ₂ . Then, the synthesized BaCuO ₂ is pulverized, and this powder and Tl ₂ O ₃ ,
By mixing fine powder of CaO and CuO, Tl, Ba,
The atomic ratio of Ca and Cu is 1.7: 2: 1.2: 2.
A mixed powder raw material containing 2 parts was produced. In this case, Tl is toxic, so these operations were performed in the glove box.

Next, about 200 such mixed powder raw materials are prepared.
Molded with a pressure of kg / cm ² , diameter 10 mm, thickness 1-1.5
A sample having a pellet size of mm was prepared.

Then, in view of the high reactivity of Tl, the sample was T
It is loosely wrapped in gold foil that does not easily react with l, and due to the toxicity of Tl, a double trap is attached inside the quartz tube for a flow rate of 1
A sample was prepared by firing at 895 ° C. for 7 minutes in an oxygen stream of 20 ml / min and then cooling at a rate of 10 ° C./min.

FIG. 1 is a diagram showing a powder X-ray diffraction pattern of Cu Kα rays of this sample. The numbers shown above the diffraction peaks in the figure represent the tetragonal Miller plane indices. As shown in this figure, it was confirmed that almost tetragonal single-phase indexing was possible and a single-phase sample was obtained.
Also, from the temperature change of the resistivity measured by the 4-terminal method,
It was confirmed that the synthesized sample was a superconductor with Tc = 98K.

A superconductor sample having a tetragonal crystal structure was obtained even if the mixing ratio of Tl of the starting materials was 2.0, but 2θ of the powder X-ray diffraction pattern was around 44 °. And there is a small peak that cannot be indexed near 55 °,
It was confirmed that some impurities were included.

That is, the starting material composition is Tl ₂ Ba ₂ C
Tl is slightly less than the stoichiometric value of a ₁ Cu ₂ O _y ,
When the composition has a slightly large amount of Ca and Cu, Tl ₂ Ba ₂ Ca ₁ Cu ₂ O _y is formed in a substantially single-phase form containing no impurities in the sample.
It was confirmed that a tetragonal crystal similar to the above was obtained.

The atomic ratio of this sample was examined by energy-dispersive X-ray spectrum (EDX) analysis. The result is shown in FIG. As shown in this figure, it can be seen that the atomic ratio of Tl is slightly lower than that of the starting material and is in good agreement with the starting composition. Example 2 First, fine powders of BaCO ₃ and CuO were mixed and fired to synthesize BaCuO ₂ . Then, the synthesized BaCuO ₂ is pulverized, and this powder and Tl ₂ O ₃ ,
Fine powders of CaO and CuO are mixed in a glove box, and Tl, Ba, Ca, and Cu have an atomic ratio of 1.
The mixed powder raw material contained in the ratio of 6: 2: 2.3: 3.2 was produced. This raw material was molded under the same conditions as in Example 1 to form pellets, which were fired in an oxygen stream at a flow rate of 120 ml / min at 900 ° C. for 7 minutes and then cooled at a rate of 15 ° C./min to prepare a sample. .

FIG. 3 is a view showing a powder X-ray diffraction pattern of Cu Kα rays of this sample. As shown in this figure, it was confirmed that almost tetragonal single-phase indexing was possible and a single-phase sample was obtained. Also, from the temperature change of the resistivity measured by the 4-terminal method, the synthesized sample shows Tc = 120K.
It was confirmed to be a superconductor of.

When the mixing ratio of Tl of the starting material is 2.0 or more and when the cooling rate after firing is 5 ° C./min, Tl ₂ Ba ₂ Ca ₂ Cu ₃ O _y (2223) is used.
System) is obtained, but with it, BaCuO
Impurities such as ₂ and the 2212 series were generated, and a single-phase superconductor containing only the 2223 series was not obtained.

That is, the composition of the starting material is Tl ₂ Ba ₂
When T1 is slightly less than the stoichiometric value of Ca ₂ Cu ₃ O _y and Ca and Cu are slightly higher and the cooling rate after firing is higher than 5 ° C./min, almost all impurities are contained in the sample. Not in almost single-phase form Tl ₂ Ba ₂ Ca ₂ C
It was confirmed that a tetragonal crystal similar to u ₃ O _y was obtained.

The atomic ratio of this sample was examined by energy-dispersive X-ray spectrum (EDX) analysis. The result is shown in FIG. As shown in this figure, it can be seen that the atomic ratio of Tl is slightly lower than that of the starting material and is in good agreement with the starting composition.

From FIGS. 2 and 4, the deviation of the composition from the stoichiometric value is larger when n = 3. Therefore, it seems that it is better to increase the values of u, v and w as the value of n increases. .

[0027]

According to the present invention, the general formula Tl ₂ Ba ₂
C _n-1 Cu _n O _y has a crystal structure represented by Tl
A superconductor having a composition represented by _2-u Ba ₂ C _{n-1 + v} Cun _{+ w} O _y can be synthesized as a single phase.

The oxide superconductor according to the present invention has a high critical temperature and is expected to be applied to a Josephson device having a Josephson junction, a SQUID (superconducting quantum interferometer), and a superconducting generator. Superconducting power storage with low energy loss, and power transmission case with low energy loss
It is expected to contribute to the practical application of multi-directional superconducting devices such as bulls.

[Brief description of drawings]

FIG. 1 is a view showing a powder X-ray diffraction pattern of a sample manufactured by the method according to Example 1 of the present invention.

FIG. 2 is a diagram showing the elemental composition of the sample of Example 1 obtained by an energy dispersive X-ray spectrum.

FIG. 3 is a view showing a powder X-ray diffraction pattern of a sample manufactured by the method according to Example 2.

FIG. 4 is a diagram showing the elemental composition of a sample of Example 2 obtained by an energy dispersive X-ray spectrum.

Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number in the agency FI Technical indication location H01B 13/00 565 D 8936-5G (72) Inventor Masae Kikuchi 2-11-5 Mikamimine, Taihaku-ku, Sendai City, Miyagi Prefecture No. (72) Inventor Yasuhiko Shono 3-12-12 Yoshinari, Aoba-ku, Sendai City, Miyagi Prefecture

Claims (5)

[Claims] 1. The starting material composition has the general formula Tl ₂ B
a ₂ C _n-1 C _n O _y (where n is an integer of 2 or more,
y is a number satisfying the valence requirement), and the mixing ratio of Tl is made smaller than the stoichiometric value of the composition represented by
A method for producing a Tl-based oxide superconductor, characterized in that the content of the Tl-based oxide superconductor is increased and then the firing is performed. 2. In the starting material composition, Tl, Ba, C
The atomic ratio of a and Cu is substantially (2-u): 2: (n
−1 + v): ratio of (n + w) (where 0 <u <0.
7. 0 <v <0.5, 0 <w <0.5), and the raw material is fired in an oxygen-containing atmosphere at 890 to 910 ° C. for 5 to 10 minutes. A method for producing a Tl-based oxide superconductor. 3. When n = 2, u, v, and w are 0 <
u <0.5, 0.1 <v <0.3, 0.1 <w <0.3
The method for producing a Tl-based oxide superconductor according to claim 2, wherein 4. When n = 3, u, v, and w are 0.
1 <u <0.6, 0.2v <0.4, 0.1 <w <0.
3. The method for producing a Tl-based oxide superconductor according to claim 2, wherein the Tl-based oxide superconductor is 3. 5. The general formula Tl _2-u Ba ₂ Ca _{n-1 + v} Cu
_{n + w} O _y (where n is an integer of 2 or more, y is a number satisfying the valence requirement, 0.2 ≦ u <0.7, 0.1 ≦ v ≦
0.4, 0.1 ≦ w ≦ 0.4), a Tl-based oxide superconductor.