JP5459132B2 - Manufacturing method of oxide superconducting bulk material - Google Patents
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Description
本発明は、酸化物超電導バルク材料の製造方法に関する。 The present invention relates to a method for manufacturing an oxide superconducting bulk material.
ＲＥ−Ｂａ−Ｃｕ−Ｏ（ＲＥはＹ又は希土類元素から選ばれる１種又は２種以上の元素）の組成からなる希土類系酸化物超電導材料は、超強力なマグネットや磁気浮上等の応用に有望視されているが、その特性を引き出すためには、材料の微細な組織制御が重要である。例えば、特許文献１には、高特性化するために、単結晶状のＲＥＢａ2Ｃｕ3Ｏy中にＲＥ2ＢａＣｕＯ5が微細分散した酸化物超電導バルク材料が開示されている。このような高特性を有する酸化物超電導バルク材料は、一般的には溶融法により作製される。溶融法では、大気中にて成形体を溶融状態まで加熱し、その後徐冷中に結晶成長させることによって酸化物超電導バルク材料を作製する。 Rare earth oxide superconducting material composed of RE-Ba-Cu-O (RE is one or more elements selected from Y or rare earth elements) is promising for applications such as super-strong magnets and magnetic levitation As seen, fine structure control of materials is important in order to bring out the properties. For example, Patent Document 1 discloses an oxide superconducting bulk material in which RE 2 BaCuO 5 is finely dispersed in single-crystal REBa 2 Cu 3 O y for high performance. An oxide superconducting bulk material having such high characteristics is generally produced by a melting method. In the melting method, an oxide superconducting bulk material is produced by heating a molded body to a molten state in the atmosphere and then allowing crystals to grow during slow cooling.
また、希土類系酸化物超電導材料の超電導特性は酸素量に大きく依存するが、結晶成長後の酸化物超電導バルク材料は酸素量が不足した状態にある。そこで、材料中の酸素量を増加させるために酸素富化過程を導入する必要がある。例えば、特許文献２には、結晶成長後に試料を所定の形状に加工してから酸素富化処理を行うことが開示されている。さらに、酸素富化過程の実施例としては、酸素雰囲気中で５００℃〜４００℃の温度領域を１００時間程度熱処理することが示されている。 The superconducting properties of the rare earth oxide superconducting material largely depend on the amount of oxygen, but the oxide superconducting bulk material after crystal growth is in a state where the amount of oxygen is insufficient. Therefore, it is necessary to introduce an oxygen enrichment process in order to increase the amount of oxygen in the material. For example, Patent Document 2 discloses that a sample is processed into a predetermined shape after crystal growth and then oxygen enrichment is performed. Furthermore, as an example of the oxygen enrichment process, it is shown that a temperature range of 500 ° C. to 400 ° C. is heat-treated for about 100 hours in an oxygen atmosphere.
上述したように、希土類系酸化物超電導バルク材料においては、結晶成長後に超電導特性を付与するために酸素富化過程が必要となる。しかしながら、酸素富化過程で酸素を十分に富化させた材料でも、本来得られるべき高い超電導特性が得られていないという問題があった。その理由としては、結晶成長直後の酸化物超電導バルク材料の結晶構造には、乱れや歪、構成原子間の置換が存在しているからであり、本来得られるべき超電導特性よりも低くなっている。このように従来の酸素富化過程では、試料中に酸素を十分に富化させることはできても、結晶成長直後の酸化物超電導バルク材料に存在する結晶構造の乱れや歪等を回復させることはできなかった。 As described above, the rare earth-based oxide superconducting bulk material requires an oxygen enrichment process in order to impart superconducting properties after crystal growth. However, there is a problem that even a material that is sufficiently enriched with oxygen in the oxygen enrichment process does not provide high superconducting properties that should be originally obtained. The reason is that the crystal structure of the oxide superconducting bulk material immediately after crystal growth has disorder, strain, and substitution between constituent atoms, which is lower than the superconducting properties that should be originally obtained. . In this way, in the conventional oxygen enrichment process, even if oxygen can be sufficiently enriched in the sample, the disorder or distortion of the crystal structure existing in the oxide superconducting bulk material immediately after crystal growth can be recovered. I couldn't.
そこで、本発明では、上記の問題を解決し、酸素富化過程を含む酸化物超電導バルク材料の製造方法において、十分に高い超電導特性を得ることのできる酸化物超電導バルク材料の製造方法を提供することを目的とする。 Therefore, the present invention provides a method for manufacturing an oxide superconducting bulk material that can solve the above-described problems and can obtain sufficiently high superconducting characteristics in a method for manufacturing an oxide superconducting bulk material including an oxygen enrichment process. For the purpose.
本発明の酸化物超電導バルク材料の製造方法は、以下のとおりである。
（１） 単結晶状のＲＥ1+xＢａ2-xＣｕ3Ｏy（ＲＥはＹ又は希土類元素から選ばれる１種又は２種以上の元素、−０．１≦ｘ≦０．１、６.８≦ｙ≦７．２）中にＲＥ2ＢａＣｕＯ5が微細分散した酸化物超電導バルク材料の製造方法であって、溶融状態から徐冷中に結晶成長させた酸化物超電導バルク材料の酸素量を酸素富化過程において富化する前に、酸素分圧が０．００００１気圧以上０．０５気圧以下、１０００Ｋ以上、１２５０Ｋ以下の温度で前記結晶成長させた酸化物超電導バルク材料を熱処理する酸素富化前熱処理過程を有することを特徴とする酸化物超電導バルク材料の製造方法。
（２） 前記酸素富化前熱処理過程後の酸化物超電導バルク材料の質量に対する前記酸素富化過程後の酸化物超電導バルク材料の質量の増分割合が、１ｍａｓｓ％以上、１．５ｍａｓｓ％以下であることを特徴とする（１）に記載の酸化物超電導バルク材料の製造方法。
（３） 前記酸化物超電導バルク材料のＲＥ元素が、Ｌａ、Ｎｄ、Ｓｍ、Ｅｕ、Ｇｄ、Ｄｙから選ばれる１種又は２種以上を含むことを特徴とする（１）又は（２）に記載の酸化物超電導バルク材料の製造方法。
The manufacturing method of the oxide superconducting bulk material of the present invention is as follows.
(1) Single crystalline RE 1 + x Ba 2−x Cu 3 O y (RE is one or more elements selected from Y or rare earth elements, −0.1 ≦ x ≦ 0.1, 6 8 ≦ y ≦ 7.2), which is a method for producing an oxide superconducting bulk material in which RE 2 BaCuO 5 is finely dispersed, and the amount of oxygen in the oxide superconducting bulk material crystal-grown during the slow cooling from the molten state Before enrichment in the enrichment process, oxygen partial pressure is 0.00001 atm or more and 0.05 atm or less, 1000K or more, and 1250K or less before the oxygen enrichment in which the oxide superconducting bulk material crystal-grown is heat-treated. A method for producing an oxide superconducting bulk material, comprising a heat treatment process.
(2) The increment ratio of the mass of the oxide superconducting bulk material after the oxygen enrichment process to the mass of the oxide superconducting bulk material after the heat treatment before the oxygen enrichment is 1 mass% or more and 1.5 mass% or less. (1) The method for producing an oxide superconducting bulk material according to (1) .
(3) The RE element of the oxide superconducting bulk material includes one or more selected from La, Nd, Sm, Eu, Gd, and Dy, (1) or (2) Manufacturing method of oxide superconducting bulk material.
本発明により、酸素富化過程を含む酸化物超電導バルク材料の製造方法において、十分に高い超電導特性を得ることのできる酸化物超電導バルク材料の製造方法を提供することができる。 The present invention can provide an oxide superconducting bulk material manufacturing method capable of obtaining sufficiently high superconducting characteristics in an oxide superconducting bulk material manufacturing method including an oxygen enrichment process.
以下に、本発明の実施形態について図に沿って説明する。
図１は、本実施形態における酸化物超電導バルク材料の製造方法の一例を示す概念図であり、図２は、従来の酸化物超電導バルク材料の製造方法を示す概念図である。
酸化物超電導バルク材料は、成形体を溶融状態になるまで加熱し、溶融状態から徐冷中に結晶成長させることにより製造される。酸化物超電導バルク材料の超電導特性は酸素量に依存するが、結晶成長直後の試料は酸素量が不足しているため、超電導特性を付与するために酸素富化過程が必要となる。従来は、図２に示すように、結晶成長したものを必要に応じて所定の形状に加工した後に酸素富化処理を行っていたが、本実施形態では、図１に示すように、結晶成長したものを必要に応じて所定の形状に加工した後であって、酸素富化過程の前に酸素富化前熱処理過程を設けていることを特徴としている。
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a conceptual diagram showing an example of a method for producing an oxide superconducting bulk material in the present embodiment, and FIG. 2 is a conceptual diagram showing a conventional method for producing an oxide superconducting bulk material.
The oxide superconducting bulk material is manufactured by heating a molded body until it is in a molten state and growing crystals from the molten state during slow cooling. The superconducting properties of the oxide superconducting bulk material depend on the oxygen content, but the sample immediately after crystal growth has a shortage of oxygen content, so that an oxygen enrichment process is required to impart superconducting properties. Conventionally, as shown in FIG. 2, the crystal growth was processed into a predetermined shape as needed, and then the oxygen enrichment treatment was performed. In this embodiment, however, the crystal growth is performed as shown in FIG. This is characterized in that a heat treatment process before oxygen enrichment is provided before the oxygen enrichment process, after the processed material is processed into a predetermined shape as necessary.
酸素富化過程では、酸素分圧０．２気圧以上の雰囲気にて、６００Ｋ〜８００Ｋの温度で数十〜数百時間の熱処理を行うことにより、酸化物超電導バルク材料中に酸素を付与する。一方、酸素富化前熱処理過程では、酸素富化過程よりも十分に高い温度、即ち、１０００Ｋ以上、１２５０Ｋ以下の温度で熱処理を行う。 In the oxygen enrichment process, oxygen is imparted to the oxide superconducting bulk material by performing heat treatment for several tens to several hundreds of hours at a temperature of 600 K to 800 K in an atmosphere having an oxygen partial pressure of 0.2 atm or higher. On the other hand, in the heat treatment process before oxygen enrichment, the heat treatment is performed at a temperature sufficiently higher than that in the oxygen enrichment process, that is, at a temperature of 1000 K or higher and 1250 K or lower.
本発明者らが鋭意調査した結果、結晶成長直後の酸化物超電導バルク材料の結晶構造には乱れや歪、構成原子間の置換が存在しているために、本来得られるべき超電導特性よりも低くなっていることが明らかになった。従来の酸素富化過程では、試料中に酸素を十分に富化させることはできても、結晶成長直後の酸化物超電導バルク材料に存在する結晶構造の乱れや歪等を回復させることはできなかった。そのため、ミクロ的にはきれいな結晶構造であったとしても、試料全体のマクロ的な視点においては結晶性が低下し、その結果、十分高い超電導特性が得られていなかった。 As a result of intensive investigations by the present inventors, the crystal structure of the oxide superconducting bulk material immediately after crystal growth has disturbances, strains, and substitution between constituent atoms. It became clear that In the conventional oxygen enrichment process, it is possible to sufficiently enrich oxygen in the sample, but it is not possible to recover the disorder or distortion of the crystal structure existing in the oxide superconducting bulk material immediately after crystal growth. It was. Therefore, even if the crystal structure is microscopically clean, the crystallinity is lowered from the macroscopic viewpoint of the entire sample, and as a result, sufficiently high superconducting characteristics are not obtained.
そこで、本発明では、酸素富化過程の前に酸素富化過程よりも十分に高い温度で高温熱処理を行う。これにより、酸化物超電導バルク材料を構成している原子の再配列が起こり、試料全体のマクロ的な視点での結晶性が向上し、その結果、超電導特性が改善する。原子の再配列が起こるためには温度が高い方が好ましいが、温度を上げ過ぎると酸化物超電導バルク材料が再溶融するので、酸素富化前熱処理過程の最高温度は１０００Ｋ以上、１２５０Ｋ以下である必要がある。なお、原子を再配列する時間を短縮する点と材料の再溶融を防止する点とから、酸素富化前熱処理過程の最高温度を１１００Ｋ以上、１２００Ｋ以下にすることがより好ましい。 Therefore, in the present invention, the high temperature heat treatment is performed at a temperature sufficiently higher than that in the oxygen enrichment process before the oxygen enrichment process. As a result, rearrangement of atoms constituting the oxide superconducting bulk material occurs, and the crystallinity of the entire sample is improved from a macro viewpoint, and as a result, the superconducting characteristics are improved. In order for the rearrangement of atoms to occur, a higher temperature is preferable. However, if the temperature is raised too much, the oxide superconducting bulk material remelts, so the maximum temperature in the heat treatment before oxygen enrichment is 1000K or more and 1250K or less. There is a need. In view of shortening the time for rearranging atoms and preventing remelting of the material, it is more preferable to set the maximum temperature in the heat treatment before oxygen enrichment to 1100K or more and 1200K or less.
酸素富化前熱処理過程での原子の再配列は、余分な酸素原子がない方が起こり易い。したがって、酸素富化前熱処理過程での雰囲気は、結晶成長時の雰囲気である大気圧よりも小さい酸素分圧、すなわち０．２気圧よりも小さい酸素分圧にする必要がある。なお、酸素分圧が０．０５気圧以下になると、さらにＲＥ原子とＢａ原子との置換が起こり難くなるので、酸素分圧は０．０５気圧以下することがより好ましい。酸素分圧は小さい方が好ましいが、油回転ポンプによるガス置換で容易に実現できる酸素分圧として０．００００１気圧まで低下させれば十分である。 The rearrangement of atoms during the heat treatment before oxygen enrichment is more likely to occur when there are no extra oxygen atoms. Therefore, the atmosphere in the pre-oxygen enrichment heat treatment process needs to be an oxygen partial pressure smaller than the atmospheric pressure that is the atmosphere during crystal growth, that is, an oxygen partial pressure smaller than 0.2 atm. When the oxygen partial pressure is 0.05 atm or less, substitution of RE atoms and Ba atoms is difficult to occur. Therefore, the oxygen partial pressure is more preferably 0.05 atm or less. A smaller oxygen partial pressure is preferable, but it is sufficient to reduce the oxygen partial pressure to 0.00001 atm as an oxygen partial pressure that can be easily realized by gas replacement with an oil rotary pump.
また、酸素富化前熱処理過程では、固体中の原子を拡散させて原子を再配列するため、多くの時間がかかる。そこで、１０００Ｋ以上の保持時間を１０時間以上にすることが好ましい。原子を再配列する観点からは保持時間は長くてもよいが、酸化物超電導材料の生産性が低下する観点からは、２００時間以下にした方が好ましい。 Moreover, in the heat treatment process before oxygen enrichment, it takes a lot of time because atoms in the solid are diffused to rearrange the atoms. Therefore, it is preferable to set the holding time of 1000 K or more to 10 hours or more. From the viewpoint of rearranging the atoms, the retention time may be long, but from the viewpoint of reducing the productivity of the oxide superconducting material, it is preferable to set it to 200 hours or less.
さらに、酸素富化前熱処理過程では、酸素富化過程よりも高い温度まで昇温するので、数ｍｍ程度の材料であれば特に問題にならないが、１０ｍｍ以上の大きな材料の場合、材料の外部と中心部とに大きな温度差が生じるため、材料内の熱応力が大きくなり、熱処理中に材料が割れる可能性がある。１０ｍｍ以上の大きな材料の場合、酸素富化前熱処理過程で材料が割れることを防止するために、昇温速度及び降温速度は４０Ｋ／時間以下にすることが好ましい。 Furthermore, in the pre-oxygen enrichment heat treatment process, the temperature is raised to a higher temperature than in the oxygen enrichment process, so there is no particular problem if the material is about several millimeters, but in the case of a large material of 10 mm or more, Since a large temperature difference is generated between the center portion, the thermal stress in the material increases, and the material may crack during the heat treatment. In the case of a large material of 10 mm or more, in order to prevent the material from cracking during the heat treatment before oxygen enrichment, it is preferable that the temperature rising rate and the temperature decreasing rate be 40 K / hour or less.
酸素富化前熱処理過程及び酸素富化過程は、別々であってもよいし、図３に示すように、連続であってもよい。連続である場合には全体としての工程時間を短縮でき、生産性の観点からは好ましい。酸素富化前熱処理と酸素富化処理とを連続して行う場合、熱処理中の雰囲気を低酸素分圧から高酸素分圧に切り換える必要がある。このとき、急激に酸素が富化しないように、高酸素分圧への切り換えは８００Ｋ以下の温度で行った方が好ましい。酸素富化過程では、酸化物超電導バルク材料中に酸素を付与するため、酸素分圧０．２気圧以上の雰囲気にて、６００Ｋ〜８００Ｋの温度で数十〜数百時間の熱処理を行うことが好ましい。 The heat treatment process before oxygen enrichment and the oxygen enrichment process may be separate, or may be continuous as shown in FIG. If continuous, the overall process time can be shortened, which is preferable from the viewpoint of productivity. When the heat treatment before oxygen enrichment and the oxygen enrichment treatment are performed continuously, the atmosphere during the heat treatment needs to be switched from a low oxygen partial pressure to a high oxygen partial pressure. At this time, it is preferable to switch to a high oxygen partial pressure at a temperature of 800 K or less so that oxygen does not rapidly enrich. In the oxygen enrichment process, in order to impart oxygen to the oxide superconducting bulk material, heat treatment may be performed at a temperature of 600 K to 800 K for several tens to several hundred hours in an atmosphere having an oxygen partial pressure of 0.2 atm or higher. preferable.
酸素富化前熱処理過程後における酸化物超電導バルク材料の質量に対する酸素富化過程後における酸化物超電導バルク材料の質量の増分割合は、超電導特性を付与するために酸素量の増分が多くなることが好ましい。即ち、１ｍａｓｓ％以上であることが好ましい。一方、この増分割合が大き過ぎると、過剰酸素によって逆に超電導特性が低下する恐れがあるので、質量増分は１．５ｍａｓｓ％以下であることが好ましい。 The incremental ratio of the mass of the oxide superconducting bulk material after the oxygen enrichment process to the mass of the oxide superconducting bulk material after the pre-oxygen enrichment heat treatment process may increase the amount of oxygen to provide superconducting properties. preferable. That is, it is preferably 1% by mass or more. On the other hand, if the increment ratio is too large, the superconducting property may be deteriorated due to excess oxygen, so the mass increment is preferably 1.5 mass% or less.
結晶成長後に酸化物超電導バルク材料の結晶構造が乱れる原因の１つに、ＲＥ原子とＢａ原子との置換がある。この場合、酸化物超電導バルク材料の超電導相の化学式は、ＲＥ1+xＢａ2-xＣｕ3Ｏyとなる。このＲＥ原子とＢａ原子との置換は、大気中で結晶成長させると起り易く、さらにＲＥ元素の中でイオン半径が比較的大きい、Ｌａ、Ｎｄ、Ｓｍ、Ｅｕ、Ｇｄ、Ｄｙで起り易い。したがって、本発明による酸素富化過程前に酸素富化前熱処理過程を設けた製造方法の効果が顕著に現れる。したがって、本発明に用いられる酸化物超電導バルク材料としては、ＲＥがＬａ、Ｎｄ、Ｓｍ、Ｅｕ、Ｇｄ、及びＤｙから選ばれる１種又は２種以上であることが好ましい。 One of the causes for the disorder of the crystal structure of the oxide superconducting bulk material after crystal growth is substitution of RE atoms and Ba atoms. In this case, the chemical formula of the superconducting phase of the oxide superconducting bulk material is RE 1 + x Ba 2−x Cu 3 O y . This substitution of RE atoms with Ba atoms is likely to occur when crystals are grown in the atmosphere, and is more likely to occur with La, Nd, Sm, Eu, Gd, and Dy having a relatively large ionic radius among RE elements. Therefore, the effect of the manufacturing method in which the pre-oxygen enrichment heat treatment process is provided before the oxygen enrichment process according to the present invention is remarkably exhibited. Therefore, as the oxide superconducting bulk material used in the present invention, RE is preferably one or more selected from La, Nd, Sm, Eu, Gd, and Dy.
また、このＲＥ原子とＢａ原子との置換は、低酸素雰囲気中で結晶成長させることによって抑制できることが知られているが、高価な雰囲気制御用の結晶成長炉が必要であり、さらに雰囲気制御用結晶成長炉では大気炉に比べて量産性に劣る。しかし、本発明の酸素富化前熱処理過程では、結晶成長させる必要はないので、一度に大量の材料を熱処理することが可能であり、量産性にも優れている製造方法である。ＲＥ原子とＢａ原子との置換が大きくなると、超電導特性が大きく低下するので、置換量ｘは、−０．１≦ｘ≦０．１の範囲とする。また、化学量論組成での酸素量ｙ＝７．０から大きくずれると、超電導性発現に必要なキャリア密度が低下し、その結果、超電導特性が大きく低下する。そのため、酸素量ｙは、６．８≦ｙ≦７．２の範囲とする。 Further, it is known that the substitution of RE atoms and Ba atoms can be suppressed by crystal growth in a low oxygen atmosphere. However, an expensive crystal growth furnace for controlling the atmosphere is required, and further, for controlling the atmosphere. Crystal growth furnaces are inferior in mass productivity compared to atmospheric furnaces. However, in the pre-oxygen enrichment heat treatment process of the present invention, since it is not necessary to grow crystals, a large amount of material can be heat treated at one time, and the production method is excellent in mass productivity. When the substitution of RE atoms and Ba atoms becomes large, the superconducting properties are greatly deteriorated, so the substitution amount x is set in the range of −0.1 ≦ x ≦ 0.1. Further, when the oxygen amount y in the stoichiometric composition greatly deviates from 7.0, the carrier density necessary for the development of superconductivity is lowered, and as a result, the superconducting properties are greatly lowered. Therefore, the oxygen amount y is set to a range of 6.8 ≦ y ≦ 7.2.
（実施例１）
本実施例で使用した酸化物超電導バルク材料の製造方法について述べる。まず、市販されている純度９９．９質量％の希土類元素（ＲＥ）、バリウム（Ｂａ）、銅（Ｃｕ）の酸化物の粉末を、ＲＥ：Ｂａ：Ｃｕ＝１．６：２．３：３．３のモル比で秤量し、それに白金を０．５質量％加えた。ＲＥ元素としては、Ｎｄ、Ｓｍ、Ｅｕ、Ｇｄ、Ｄｙ、Ｙ、Ｈｏ、Ｅｒを用い、そのうち、Ｎｄ、Ｓｍ、Ｅｕ、Ｇｄについては、銀を１０質量％加えた。この秤量粉を２時間かけて十分混練してから、大気中にて１１７３Ｋで８時間仮焼した。
Example 1
A method for manufacturing the oxide superconducting bulk material used in this example will be described. First, a rare earth element (RE), barium (Ba), and copper (Cu) oxide powder having a purity of 99.9% by mass is prepared by using RE: Ba: Cu = 1.6: 2.3: 3. .3 in a molar ratio, and 0.5% by mass of platinum was added thereto. As RE elements, Nd, Sm, Eu, Gd, Dy, Y, Ho, and Er were used. Among them, 10% by mass of silver was added to Nd, Sm, Eu, and Gd. The weighed powder was sufficiently kneaded over 2 hours and then calcined at 1173 K for 8 hours in the air.
次に、金型を用いて仮焼粉を円板形状に成形した。この成形体を１３７３Ｋまで加熱して溶融状態にし、３０分間保持した後、降温途中で種付けを行い、１２７８Ｋ〜１２５２Ｋの温度領域を１００時間かけて徐冷し結晶成長させた。上述した製造方法で作製した試料は、単結晶状のＲＥ1+xＢａ2-xＣｕ3Ｏy中にＲＥ2ＢａＣｕＯ5が微細分散した組織を有しておりＲＥ2ＢａＣｕＯ5の大きさは平均１〜２μｍであった。結晶成長直後の試料の大きさは、直径４８ｍｍ、高さ２０ｍｍ程度であったが、乾式加工により、直径４６ｍｍ、高さ１５ｍｍに加工した。なお、銀を１０質量％加えたＮｄ、Ｓｍ、Ｅｕ、Ｇｄについては、数μｍ〜数十μｍの銀粒子が微細に分散した組織を有していた。 Next, the calcined powder was formed into a disk shape using a mold. This molded body was heated to 1373K to be in a molten state, held for 30 minutes, and then seeded in the middle of lowering the temperature, and a temperature range of 1278K to 1252K was gradually cooled over 100 hours to grow crystals. The sample prepared by the manufacturing method described above has a structure in which RE 2 BaCuO 5 is finely dispersed in single crystal RE 1 + x Ba 2−x Cu 3 O y , and the size of RE 2 BaCuO 5 is The average was 1-2 μm. The size of the sample immediately after crystal growth was about 48 mm in diameter and about 20 mm in height, but was processed into a diameter of 46 mm and a height of 15 mm by dry processing. In addition, about Nd, Sm, Eu, and Gd to which 10% by mass of silver was added, it had a structure in which silver particles of several μm to several tens μm were finely dispersed.
次に、この加工体を酸素富化前熱処理過程として、酸素分圧０．０１気圧下、１１５０Ｋで１００時間熱処理した。なお、この時の昇温速度及び降温速度は２０Ｋ／時間とした。その後、酸素富化過程として、酸素雰囲気中で７２３Ｋ〜６７３Ｋの温度領域を１００時間程度熱処理した。 Next, this processed body was heat-treated at 1150 K for 100 hours under an oxygen partial pressure of 0.01 atm as a heat treatment before oxygen enrichment. At this time, the rate of temperature increase and the rate of temperature decrease was 20 K / hour. Thereafter, as an oxygen enrichment process, a temperature range of 723 K to 673 K was heat-treated in an oxygen atmosphere for about 100 hours.
本実施例の試料（以下、本実施例材）における超電導特性を調べるため、超電導マグネットを用いて試料に磁場を捕捉させ、液体窒素中での捕捉磁場分布をホール素子にて測定した。図４に測定した磁場分布の例を示す。捕捉磁場分布がきれいな同心円状をしていることから、結晶成長が良好であったことが分かる。比較のため、酸素富化前熱処理過程を省略した以外は本実施例と同様にして製造した比較材についても、同じ条件にて捕捉磁場分布を測定した。測定の結果、比較材の捕捉磁場分布も同様に同心円状であった。 In order to investigate the superconducting characteristics of the sample of the present example (hereinafter referred to as the present example material), the sample was trapped with a magnetic field using a superconducting magnet, and the captured magnetic field distribution in liquid nitrogen was measured with a Hall element. FIG. 4 shows an example of the measured magnetic field distribution. It can be seen that the crystal growth was good because the trapped magnetic field distribution was a clean concentric circle. For comparison, the captured magnetic field distribution was also measured under the same conditions for the comparative material manufactured in the same manner as in this example except that the heat treatment before oxygen enrichment was omitted. As a result of the measurement, the captured magnetic field distribution of the comparative material was also concentric.
以下の表１に、本実施例材及び比較材の捕捉磁場のピーク値を示す。 Table 1 below shows the peak values of the trapping magnetic fields of the materials of this example and the comparative material.
表１に示すように、本実施例材と比較材とを比べると、本実施例材は２０％程度捕捉磁場のピーク値が改善していることが分かる。つまり、本実施例材は、超電導特性の改善に効果があるものであると言える。なお、本実施例材について、電子線マイクロアナライザーにより組成を分析すると、ＲＥ元素のＢａ元素置換量ｘは、ｘ＝−０．０１〜＋０．０２であることが確認できた。さらに、酸素富化過程後の酸素量ｙをヨードメトリーにより分析すると、酸素量ｙは、ｙ＝６．９〜７．０であることが確認できた。 As shown in Table 1, when this example material is compared with the comparative material, it can be seen that the peak value of the trapped magnetic field of this example material is improved by about 20%. That is, it can be said that this Example material is effective in improving the superconducting characteristics. In addition, when the composition of this example material was analyzed by an electron beam microanalyzer, it was confirmed that the Ba element substitution amount x of RE element was x = −0.01 to +0.02. Furthermore, when the oxygen amount y after the oxygen enrichment process was analyzed by iodometry, it was confirmed that the oxygen amount y was y = 6.9 to 7.0.
（実施例２）
ＲＥ元素として、Ｇｄ：Ｄｙ＝９：１で秤量した以外は実施例１と同様の製造方法により、直径４６ｍｍ、高さ１５ｍｍの加工体を製造した。次に、この加工体を酸素富化前熱処理過程として、酸素分圧０．０５気圧下、１２００Ｋで３０時間熱処理した。なお、この時の昇温速度及び降温速度は４０Ｋ／時間とした。その後、酸素富化過程として、酸素雰囲気中で７２３Ｋ〜６７３Ｋの温度領域を１００時間程度熱処理した。得られた超電導体の組織は、実施例１と同様に、単結晶状の（Ｇｄ0.9Ｄｙ0.1）1+xＢａ2-xＣｕ3Ｏy中に（Ｇｄ0.9Ｄｙ0.1）2ＢａＣｕＯ5と銀粒子が微細分散した組織を有しており、（Ｇｄ0.9Ｄｙ0.1）2ＢａＣｕＯ5の大きさは平均１〜２μｍで、銀粒子の大きさは平均５０μｍであった。また、ＲＥ元素のＢａ元素置換量ｘは、ｘ＝＋０．００５で、酸素量ｙは、ｙ＝６．９４であった。比較のため、酸素富化前熱処理過程を省略した以外は本実施例と同じ条件にて比較材を製造した。
(Example 2)
A processed body having a diameter of 46 mm and a height of 15 mm was produced by the same production method as in Example 1 except that the RE element was weighed with Gd: Dy = 9: 1. Next, this processed body was heat-treated at 1200 K under an oxygen partial pressure of 0.05 atm for 30 hours as a heat treatment before oxygen enrichment. The temperature increase rate and temperature decrease rate at this time were 40 K / hour. Thereafter, as an oxygen enrichment process, a temperature range of 723 K to 673 K was heat-treated in an oxygen atmosphere for about 100 hours. As in Example 1, the structure of the obtained superconductor was (Gd 0.9 Dy 0.1 ) 2 BaCuO 5 and silver in single crystalline (Gd 0.9 Dy 0.1 ) 1 + x Ba 2-x Cu 3 O y. The particles had a finely dispersed structure, and the average size of (Gd 0.9 Dy 0.1 ) 2 BaCuO 5 was 1 to 2 μm, and the average size of silver particles was 50 μm. Further, the Ba element substitution amount x of RE element was x = + 0.005, and the oxygen amount y was y = 6.94. For comparison, a comparative material was produced under the same conditions as in this example except that the heat treatment before oxygen enrichment was omitted.
捕捉磁場のピーク値を測定したところ、本実施例材の液体窒素中の捕捉磁場のピーク値は１．８Ｔであり、比較材のピーク値１．４４Ｔに比べて２５％改善していることが確認できた。さらに、冷凍機を用いて６５Ｋでの捕捉磁場のピーク値を比較したところ、本実施例材で４Ｔ、比較材で２．９Ｔとなり、３８％改善した。このことから、改善度合いは低温ほど大きいことが分かった。つまり、本実施例材は、低温での超電導特性の改善により効果があるものであると言える。 When the peak value of the trapping magnetic field was measured, the peak value of the trapping magnetic field in the liquid nitrogen of the material of this example is 1.8T, which is an improvement of 25% compared to the peak value of 1.44T of the comparative material. It could be confirmed. Furthermore, when the peak value of the trapped magnetic field at 65K was compared using a refrigerator, it was 4T for this example material and 2.9T for the comparative material, an improvement of 38%. From this, it was found that the degree of improvement was greater at lower temperatures. That is, it can be said that the material of this example is more effective in improving the superconducting characteristics at a low temperature.
（実施例３）
ＲＥ元素としてＤｙを用いた以外は実施例１と同様の製造方法により、直径４６ｍｍ、高さ１５ｍｍの加工体を製造した。次に、この加工体を酸素富化前熱処理過程として、酸素分圧０．０２気圧下、昇温速度２０Ｋ／時間にて１１００Ｋで１５０時間熱処理した。その後、降温速度２０Ｋ／時間で７２３Ｋまで降温した。７２３Ｋに保持した状態で、酸素分圧を０．０２気圧から１気圧へ５０時間かけて変化させた後、酸素富化過程として、７２３Ｋ〜６７３Ｋの温度領域を１００時間程度熱処理した。得られた超電導体の組織は、実施例１と同様に、単結晶状のＤｙ1+xＢａ2-xＣｕ3Ｏy中にＤｙ2ＢａＣｕＯ5が微細分散した組織を有しており、Ｄｙ2ＢａＣｕＯ5の大きさは平均１〜２μｍであった。また、ＲＥ元素のＢａ元素置換量ｘは、ｘ＝＋０．０１で、酸素量ｙは、ｙ＝６．９２であった。比較のため、酸素富化前熱処理過程を省略した以外は本実施例と同じ条件にて比較材Ａを製造した。さらに、酸素富化前熱処理過程以外では本実施例と同じ条件にて製造したものであって、酸素富化前熱処理過程として、酸素分圧０．０２気圧下、９００Ｋで１５０時間熱処理した比較材Ｂ、及び酸素富化前熱処理過程として、酸素分圧０．０２気圧下、１３００Ｋで１５０時間熱処理した比較材Ｃを製造した。
(Example 3)
A processed body having a diameter of 46 mm and a height of 15 mm was manufactured by the same manufacturing method as in Example 1 except that Dy was used as the RE element. Next, this processed body was heat-treated at 1100 K for 150 hours under an oxygen partial pressure of 0.02 atm and a heating rate of 20 K / hour as a heat treatment process before oxygen enrichment. Thereafter, the temperature was decreased to 723 K at a temperature decrease rate of 20 K / hour. While maintaining the temperature at 723 K, the oxygen partial pressure was changed from 0.02 atm to 1 atm over 50 hours, and then the temperature range of 723 K to 673 K was heat-treated for about 100 hours as an oxygen enrichment process. Similar to Example 1, the structure of the obtained superconductor has a structure in which Dy 2 BaCuO 5 is finely dispersed in single crystal Dy 1 + x Ba 2−x Cu 3 O y. The average size of 2 BaCuO 5 was 1 to 2 μm. Further, the Ba element substitution amount x of the RE element was x = + 0.01, and the oxygen amount y was y = 6.92. For comparison, a comparative material A was produced under the same conditions as in this example except that the heat treatment before oxygen enrichment was omitted. Further, the comparative material was manufactured under the same conditions as in this example except for the heat treatment before oxygen enrichment, and as a heat treatment before oxygen enrichment, a comparative material heat treated at 900 K for 150 hours under an oxygen partial pressure of 0.02 atm. As a heat treatment process before B and oxygen enrichment, a comparative material C heat-treated at 1300 K for 150 hours under an oxygen partial pressure of 0.02 atm was manufactured.
捕捉磁場のピーク値を測定したところ、本実施例材の液体窒素中の捕捉磁場のピーク値は１．０５Ｔであり、比較材Ａのピーク値０．８５Ｔに比べて２０％以上改善していることが確認できた。また、比較材Ｂの捕捉磁場のピーク値は０．８３Ｔであり、比較材Ａと同程度であった。さらに、比較材Ｃでは、試料の一部が溶融した後に固化したため、試料形状が円板状を留めていないだけでなく、捕捉磁場のピーク値は０．０１Ｔで非常に小さくなった。以上の結果から、本実施例材のように、酸素富化前熱処理過程と酸素富化過程とを連続して行っても超電導特性の改善に効果があると言える。また、酸素富化前熱処理過程として、本発明の範囲外の温度で熱処理を実施しても、超電導特性の改善が認められないことが確認できた。 When the peak value of the trapped magnetic field was measured, the peak value of the trapped magnetic field in the liquid nitrogen of the material of this example was 1.05T, which is an improvement of 20% or more compared to the peak value of the comparative material A of 0.85T. I was able to confirm. Moreover, the peak value of the trapping magnetic field of the comparative material B was 0.83T, which was the same as that of the comparative material A. Furthermore, in the comparative material C, since a part of the sample was solidified and then solidified, not only the sample shape did not remain a disc shape, but also the peak value of the trapped magnetic field became very small at 0.01T. From the above results, it can be said that even if the pre-oxygen-enriched heat treatment process and the oxygen-enriched process are continuously performed as in this example material, it is effective in improving the superconducting characteristics. Further, it was confirmed that even when the heat treatment before the oxygen enrichment was performed at a temperature outside the range of the present invention, the improvement of the superconducting characteristics was not recognized.
本発明によれば、酸素富化過程を含む酸化物超電導バルク材料の製造方法であって、十分に高い超電導特性を得ることのできる酸化物超電導バルク材料の製造方法を提供することができるので、酸化物超電導バルク材料の工業上の利用範囲が拡大する。 According to the present invention, a method for producing an oxide superconducting bulk material including an oxygen enrichment process, which can provide sufficiently high superconducting properties, can be provided. The range of industrial applications of oxide superconducting bulk materials is expanded.
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