JP2002251929A - Thallium based superconducting silver based sheath wire of high crystal orientation and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wire enhancing the crystal orientation of a superconductor in a Tl based silver sheath wire and increasing superconduction critical current density (Jc ). SOLUTION: In a process of manufacturing a Tl based superconducting silver based sheath wire formed by sheathing an oxide superconducting material with a silver based material, by slowly cooling the oxide material from a partially melted state, crystal growth is accelerated along the silver based sheath, and the Tl based superconducting silver based sheath wire having high crystal orientation structure is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thallium-based superconducting silver sheath wire having high crystal orientation and a method for producing the same.

[0002]

2. Description of the Related Art In order to prepare a copper wire superconductor having high anisotropy into a practical wire, it is necessary to increase the crystal orientation in the wire. Bismuth (Bi) -based silver sheathed wires were manufactured by heat treatment to produce wires with a structure with high crystal orientation, but it was thought that heat treatment in Tl-based materials did not align the crystals. As a result, since only wires having a disordered crystal orientation structure have been manufactured, the performance of the materials has not been sufficiently brought out. It is known that carbon containing Ba tends to remain in the oxide containing Ba. In the conventional method, since no attention has been paid to the residual carbon, the carbon remaining in the raw material has hindered the crystal growth of the Tl-based superconductor or weakened the bonding between the crystal grains. Further, since the composition control of the oxide material has not been effectively performed, crystal growth from a partially melted state has not been used, and only wires having a disordered crystal orientation structure have been manufactured.

[0003]

[Problems of the Invention] When the crystal orientation in a wire becomes high, a Tl-based silver sheath wire having a high superconducting critical current density (J _c ) can be produced. An object of the present invention is to enhance the crystal orientation of a superconductor in a Tl-based silver sheath wire, and to increase the superconducting critical current density (J
_c ) to provide an increased wire rod.

[0004]

[Means for Solving the Problems] In a Tl-based silver-based sheath wire,
The heat treatment in which the oxide material is gradually cooled from a partially melted state can promote crystal growth along the silver-based sheath and increase crystal orientation. Further, in order to promote the crystal growth of the Tl-based superconductor and to strengthen the bonding between crystal grains, it is preferable to use an oxide material having a reduced residual carbon concentration as the oxide superconductor material. Further, in order to utilize crystal growth from a partially molten state, an oxide material whose melting point is controlled by changing the composition such as the amount of Cu and the amount of oxygen is used as the oxide superconductor material.

[0005]

The Tl-based superconductors in the Detailed Description of the Invention The present invention, generally the formula _{Tl m (Ba, Sr) 2} Ca n-1 Cu n O y (m = 1,2, n
= 2,3,4,7 ≦ y ≦ 12). However, this does not preclude some element substitution at each site such as partial substitution of other elements at the Tl site. The silver-based material used for the sheath includes silver alloys in addition to silver. In order to reduce the residual carbon concentration in the oxide material, a high-purity oxide such as Tl ₂ O ₃ , BaO ₂ , SrO, Ca ₂ CuO ₃ , CuO, or Cu ₂ O is used as a raw material. Or, after mixing those oxides,
Heat to 800 ° C. to 1100 ° C. in an atmosphere from which carbon dioxide is removed, for example, (Ba, Sr) ₂ Can _-1 Cu _n O _y (n = 2, 3, 4, 6 ≦ y ≦ 10)
A precursor that does not contain Tl and has the composition ratio described above is prepared in advance and used as a raw material. In order to utilize crystal growth from a state where the oxide material is partially melted, the composition of the oxide material such as the amount of Cu and the amount of oxygen is controlled. For example, 1 mol of precursor (Ba, Sr) ₂ Can _-1 C
Mix 0 to 10 mol of CuO or Cu ₂ O with u _n O _y (n = 2, 3, 4, 6 ≦ y ≦ 10). Alternatively, a precursor in which the composition such as the amount of Cu or the amount of oxygen is controlled is prepared in advance by heating an oxide material mixed by adjusting the composition such as the amount of Cu in an atmosphere in which the oxygen partial pressure is controlled. Controlling the composition, such as reducing the residual carbon in the oxide material or increasing the amount of Cu or reducing the amount of oxygen, also has the effect of lowering the melting point of the material, which is convenient for crystal growth from a partially molten state. good.

[0006] Tl ₂ O ₃ is used as the above oxide material or precursor.
The powder mixed by adding an appropriate amount is coated directly, or the mixture obtained by calcining the mixture in advance is covered with a metal containing silver, drawn and rolled, and then heated to a temperature (860 ° C. to 960 ° C.) where partial melting is performed. By slow cooling after holding for a time, the crystal growth along the silver-based sheath material is promoted, and a structure having high crystal orientation is obtained. The purpose of the slow cooling in the present invention is to promote the crystal growth along the silver-based sheath material and to obtain a structure having a high crystal orientation, and any slow cooling within the range of the slow cooling that can achieve the purpose. Good, but desirably a slow cooling rate of 0.01 ° C / h to 100 ° C / h. By utilizing the property of silver transmitting oxygen and performing heat treatment while controlling the oxygen partial pressure, a structure having a high crystal orientation and a structure having a controlled superconductivity can be obtained more effectively.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Although specific examples of the present invention will be described, the present invention is applicable to various applications and is not limited to these specific examples. Example 1 A mixture of high-purity oxides, BaO ₂ , Ca ₂ CuO ₃ , and CuO was heated at 940 ° C. in an oxygen atmosphere from which carbon dioxide was removed to obtain Ba ₂ Ca ₂ Cu ₃ O _y (7 ≦ y). A precursor containing no Tl having a composition ratio of ≦ 8) was prepared. At this time, the residual carbon concentration was 0.1 mol or less based on 1 mol of the precursor. To its precursor
Tl ₂ O ₃ , CuO and Cu ₂₀ are mixed in an appropriate amount, and the composition ratio TlBa ₂ Ca ₂
A raw material mixture satisfying Cu ₄ O _y (9 ≦ y ≦ 10.5) was produced. After covering the raw material mixture with silver, drawing and rolling, it is heated to 890 ° C. in an oxygen atmosphere set at 1 atm and held for 10 minutes, and then to a temperature at which the oxide material solidifies at a rate of 10 ° C. per hour. Cool. FIG. 1 (a) shows an X-ray diffraction pattern of the oxide material measured by peeling the silver coating.

Comparative Example For comparison, an X-ray diffraction pattern of a silver sheath wire manufactured by a conventional method without gradually cooling an oxide material from a partially melted state is shown in FIG. 1 (b).
Shown in As described above, only the randomly oriented crystal structure can be obtained by the conventional method. However, those manufactured using the present invention have diffraction peaks from the (00L) plane (TlBa ₂ Ca ₂ Cu
₃ O _y (corresponding to the Tl-1223) superconducting phase) is relatively strong, indicating that the orientation of the Tl-based superconducting crystal is high. FIG. 1 (a) was produced using the present invention,
FIG. 1 (b) is manufactured by a conventional method. In both cases, the Tl-1223 phase was generated, but in FIG. 1 (a), the diffraction peak from the (00L) plane was relatively strong, and the crystal orientation was high.

[0009]

According to the present invention, a Tl-based superconducting silver sheath wire having high crystal orientation, which cannot be realized by the conventional method, can be manufactured. Superconducting critical current density ( _Jc ) of wire by increasing crystal orientation
Can be expected to increase.

[Brief description of the drawings]

Fig. 1 X-ray diffraction pattern of an oxide material measured by peeling silver-based clothing

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Akira Iyo 1-4-4 Umezono, Tsukuba, Ibaraki Pref. 1-4-1 Umezono-shi, METI Electronic Technology Research Institute, Ministry of Economy, Trade and Industry (72) Inventor Hideo Ihara 1-4-1, Umezono, Tsukuba-shi, Ibaraki Laboratory F-term (reference) 4G047 JA05 JC10 KA01 KB04 KB14 LA02 LB01 5G321 AA07 CA04 CA32 CB99 DB18 DB29 DB48

Claims (4)

[Claims] In a step of manufacturing a Tl-based superconducting silver-based sheath wire in which an oxide superconductor material is sheathed with a silver-based material, the oxide-based material is gradually cooled from a partially melted state to obtain a silver-based superconducting silver-based wire. A thallium-based superconducting silver-based sheath wire having a texture with a high crystal orientation that promotes crystal growth along the sheath. 2. The thallium-based superconducting silver-based material according to claim 1, wherein the oxide superconductor material is an oxide material having a reduced residual carbon concentration or an oxide material having a controlled composition of Cu content and oxygen content. Sheath wire. 3. In a step of manufacturing a Tl-based superconducting silver-based sheath wire in which an oxide superconductor material is sheathed with a silver-based material, the oxide-based material is gradually cooled from a partially molten state, so that the silver-based superconducting material is gradually cooled. A method for producing a thallium-based superconducting silver-based sheath wire having a structure with high crystal orientation in which crystal growth is promoted along a sheath. 4. The method for producing a thallium-based superconducting silver-based sheath wire according to claim 3, wherein the slow cooling rate is 0.01 ° C./h to 100 ° C./h.