JP4792597B2 - Method for producing superconducting boron compound MgB2 thin film - Google Patents
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- JP4792597B2 JP4792597B2 JP2008004075A JP2008004075A JP4792597B2 JP 4792597 B2 JP4792597 B2 JP 4792597B2 JP 2008004075 A JP2008004075 A JP 2008004075A JP 2008004075 A JP2008004075 A JP 2008004075A JP 4792597 B2 JP4792597 B2 JP 4792597B2
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Description
その高い転移温度や安価な原料費用などから、デバイスなどへの応用が期待されている、超伝導転移温度３９Ｋを示すホウ素化合物ＭｇＢ２の作成方法に関する。 The present invention relates to a method for producing a boron compound MgB 2 having a superconducting transition temperature of 39 K, which is expected to be applied to devices and the like because of its high transition temperature and inexpensive raw material costs.
ＭｇＢ２を素子化するのに必要な薄膜作成技術に関しては、合成済みのＭｇＢ２を真空中で酸化物基板などの上に１０００度近辺の温度で蒸着・反応させる方法、ＭｇとＢを同様の基板温度で同時蒸着する方法、また、Ｂを蒸着させた酸化物基板などをＭｇ雰囲気下１０００度近辺の温度で加熱する方法が知られている。 Regarding the thin film formation technology necessary for converting MgB 2 into a device, a method of depositing and reacting synthesized MgB 2 on an oxide substrate or the like in a vacuum at a temperature around 1000 ° C. There are known a method of simultaneous vapor deposition at a substrate temperature, and a method of heating an oxide substrate or the like on which B is vapor-deposited at a temperature around 1000 degrees in an Mg atmosphere.
これらを行う装置には、蒸着法では高真空を実現する真空ポンプ系および高温加熱系が必要である。また、ＭｇとＢの同時蒸着法以外の手法では、薄膜作成までに２段階のプロセスを行う手間が掛かる。 An apparatus for performing these processes requires a vacuum pump system and a high-temperature heating system for realizing a high vacuum in the vapor deposition method. Moreover, in methods other than the simultaneous vapor deposition method of Mg and B, it takes time and effort to perform a two-stage process before forming a thin film.
上記従来技術における真空ポンプ系・高温加熱系には一般に数十万円程度以上の費用が掛かる。そこで、本発明では、真空ポンプを用いないプロセスでＭｇＢ２薄膜合成を行う手法を提供する。 Generally, the vacuum pump system and the high-temperature heating system in the above-described prior art cost about several hundred thousand yen or more. Therefore, the present invention provides a technique for synthesizing an MgB 2 thin film by a process that does not use a vacuum pump.
即ち、本発明は、超伝導ホウ素化合物ＭｇＢ２薄膜の作成方法であって、塩化マグネシウム（ＭｇＣｌ２）、塩化ナトリウム（ＮａＣｌ）、塩化カリウム（ＫＣｌ）、ホウ酸マグネシウム（ＭｇＢ２Ｏ４ ）を混合した粉状出発材が収納された反応容器を加熱炉内に配置し、前記反応容器の周囲をアルゴンガス雰囲気としながら、前記加熱炉によって前記粉状出発材を加熱して溶融し、前記反応容器に設置した電極間に直流電流を印加して、前記溶融体に電流が流れることを確認後、静置して室温に戻すことを特徴とする。
本発明の超伝導ホウ素化合物ＭｇＢ ２ 薄膜の作成方法は、前記粉状出発材にホウ素（Ｂ）を混合することが好ましい。
That is, the present invention is a method for producing a superconducting boron compound MgB 2 thin film in which magnesium chloride (MgCl 2 ), sodium chloride (NaCl), potassium chloride (KCl), and magnesium borate (MgB 2 O 4 ) are mixed. The reaction vessel containing the powdered starting material is placed in a heating furnace, and the powdery starting material is heated and melted by the heating furnace while the atmosphere around the reaction vessel is an argon gas atmosphere. A direct current is applied between the electrodes placed on the substrate, and after confirming that a current flows through the melt, it is left to return to room temperature.
In the method for producing a superconducting boron compound MgB 2 thin film of the present invention, it is preferable to mix boron (B) with the powdery starting material.
アルゴン雰囲気中での反応により、真空ポンプ系を使用する必要が無くなり、合成に必要な費用が低減される。また、原材料から薄膜作成まで一段階での合成が行えるなったことも費用低減の要因となる。
さらに、出発材の加熱に要する温度は最大でも８００℃以下であり、従来のような１０００℃を越える加熱を必要としない。
The reaction in an argon atmosphere eliminates the need to use a vacuum pump system and reduces the cost required for synthesis. Moreover, the fact that the synthesis can be performed in one step from the raw material to the thin film production is also a factor of cost reduction.
Furthermore, the temperature required for heating the starting material is 800 ° C. or less at the maximum, and heating exceeding 1000 ° C. as in the prior art is not required.
粉状出発材である粉体試料は、以下のように構成してある。
市販の粉末試薬である、塩化マグネシウム（ＭｇＣｌ２）、塩化ナトリウム（ＮａＣｌ）、塩化カリウム（ＫＣｌ）、ホウ酸マグネシウム（ＭｇＢ２Ｏ４）、及びホウ素（Ｂ）をモル比１０：（１０−ｘ）：ｘ：２：２で総量２ｇ秤量し混合する。塩化カリウムの量（ｘ）は３から７の間である。
なお、ホウ素（Ｂ）は下記実施例のように、超伝導ホウ素化合物ＭｇＢ２薄膜を作成するのみの目的では、必ずしも必要としないものである。
The powder sample which is a powdery starting material is configured as follows.
Commercial powder reagents magnesium chloride (MgCl 2 ), sodium chloride (NaCl), potassium chloride (KCl), magnesium borate (MgB 2 O 4 ), and boron (B) in a molar ratio of 10: (10−x ): Weigh and mix 2g in total with x: 2: 2. The amount (x) of potassium chloride is between 3 and 7.
Boron (B) is not necessarily required for the purpose of merely forming a superconducting boron compound MgB 2 thin film, as in the following examples.
図１に示されるように、長さ１００ｍｍ、幅１０ｍｍ、高さ１０ｍｍ、厚み１ｍｍ程度の酸化アルミニウム（アルミナ）製の箱型反応容器に粉体試料を入れ、長手方向の両端に直径１ｍｍ程度のカーボン棒を設置する。それぞれの棒に直径０．３ｍｍ程度の金線を圧着する。
前記粉体試料および前記反応容器を直径４０ｍｍ程度の石英管内に入れ、アルゴンガス雰囲気下になるようにする。この石英管を電気炉に挿入する。直流電源を用意し、２本の金線のうち、片方をマイナス極に、もう片方をプラス極に接続する。なお、マイナス極に接続されるカーボン棒は直径１ｍｍ程度のプラチナ線或いは数ｍｍ角厚さ１ｍｍ程度のカーボン（グラフアイト）板でも良い。アルゴンガスを１リットル毎分程度流しながら、粉体試料を４００℃以下に加熱し、１時間放置して粉体試料を乾燥させる。その後、粉体試料を４００℃以上まで加熱すると粉体試料は融けて融体となる。本反応温度は好ましくは４００−８００℃、より好ましくは４００−７００℃、もっとも好ましくは４００−６００℃である。
As shown in FIG. 1, a powder sample is put into a box-shaped reaction vessel made of aluminum oxide (alumina) having a length of 100 mm, a width of 10 mm, a height of 10 mm, and a thickness of about 1 mm. Install carbon rods. A gold wire having a diameter of about 0.3 mm is crimped to each rod.
The powder sample and the reaction vessel are placed in a quartz tube having a diameter of about 40 mm so as to be in an argon gas atmosphere. This quartz tube is inserted into an electric furnace. Prepare a DC power supply and connect one of the two gold wires to the negative pole and the other to the positive pole. The carbon rod connected to the negative electrode may be a platinum wire having a diameter of about 1 mm or a carbon (graphite) plate having a thickness of several mm and a thickness of about 1 mm. While flowing argon gas at a rate of about 1 liter per minute, the powder sample is heated to 400 ° C. or less and left for 1 hour to dry the powder sample. Thereafter, when the powder sample is heated to 400 ° C. or higher, the powder sample melts and becomes a melt. The reaction temperature is preferably 400-800 ° C, more preferably 400-700 ° C, most preferably 400-600 ° C.
２本の金線に５Ｖ直流電圧を印加し、ミリアンペアから数十ミリアンペア程度の電流が流れることが確認できたら、そのまま３０分以下程度の時間静置する。この後、粉体試料を室温に戻し、大気中に取り出す。マイナス極側のカーボン棒に付着した黒色のＭｇＢ２が得られる。カーボン棒が、上記カーボン板であると図３に示されるように薄膜状のＭｇＢ２が得られる。 When a 5V DC voltage is applied to the two gold wires and it is confirmed that a current of about milliamperes to several tens of milliamperes flows, it is left to stand for about 30 minutes or less. Thereafter, the powder sample is returned to room temperature and taken out into the atmosphere. Black MgB 2 adhered to the negative pole side carbon rod is obtained. When the carbon rod is the carbon plate, a thin film of MgB 2 is obtained as shown in FIG.
なお、本反応は次のとおりである。プラス極：Ｍｇ２＋＋２Ｂ３＋＋８ｅ→ＭｇＢ２（ｅは電子）マイナス極：４Ｏ２−→２Ｏ２＋８ｅこれら２式を足して：ＭｇＢ２Ｏ４→ＭｇＢ２＋２Ｏ２その他の物質である塩化マグネシウム・塩化ナトリウム・塩化カリウム・ホウ素については融点を下げて反応を促進させる触媒作用があると考えられる。 This reaction is as follows. Positive electrode: Mg 2+ + 2B 3+ + 8e → MgB 2 (e is an electron) Negative electrode: 4O 2− → 2O 2 + 8e Add these two formulas: MgB 2 O 4 → MgB 2 + 2O 2 Sodium chloride, potassium chloride, and boron are considered to have a catalytic action that promotes the reaction by lowering the melting point.
塩化マグネシウム（ＭｇＣｌ２）・塩化ナトリウム（ＮａＣｌ）・塩化カリウム（ＫＣ１）・ホウ酸マグネシウム（ＭｇＢ２Ｏ４）およびホウ素（Ｂ）をモル比１０：５：５：２：２で総量２ｇ秤量し、上記に従って得られた試料（Ａ）の磁化率の温度依存性を図２に示す。縦軸が磁化率、横軸が温度である。測定磁場は２０エルステッドである。低温約３９Ｋ付近でＭｇＢ２の超伝導に起因する磁化率の屈曲点が見られる。さらに低温では磁化率の符号が負となり、これはＭｇＢ２の超伝導に伴うマイスナー効果である。 Magnesium chloride (MgCl 2 ) / sodium chloride (NaCl) / potassium chloride (KC1) / magnesium borate (MgB 2 O 4 ) and boron (B) were weighed in a molar ratio of 10: 5: 5: 2: 2 to a total amount of 2 g. FIG. 2 shows the temperature dependence of the magnetic susceptibility of the sample (A) obtained according to the above. The vertical axis is the magnetic susceptibility and the horizontal axis is the temperature. The measuring magnetic field is 20 oersteds. An inflection point of the magnetic susceptibility due to the superconductivity of MgB 2 is observed at a low temperature of about 39K. Furthermore, the sign of magnetic susceptibility becomes negative at low temperatures, which is the Meissner effect associated with the superconductivity of MgB 2 .
ホウ素を加えず、他の試薬のモル比は上述の通りで合成した試料（Ｂ）においてもマイスナー効果は見られるが、磁化率の絶対値は小さい。これは、ホウ素添加によって、試料中の超伝導ＭｇＢ２の体積分率が上昇したことを意味する。 In the sample (B) synthesized without adding boron and the other reagents in the molar ratio as described above, the Meissner effect is observed, but the absolute value of the magnetic susceptibility is small. This means that the volume fraction of superconducting MgB 2 in the sample was increased by boron addition.
即ち、図中Ａは、塩化マグネシウム（ＭｇＣｌ２）・塩化ナトリウム（ＮａＣｌ）・塩化カリウム（ＫＣｌ）・ホウ酸マグネシウム（ＭｇＢ２Ｏ４）およびホウ素（Ｂ）をモル比１０：５：５：２：２で総量２ｇ秤量し、上記に従って得られた試料の磁化率（電磁単位／１グラム）の温度依存性である。縦軸が磁化率、横軸が温度である。 That is, in the figure, A represents magnesium chloride (MgCl 2 ) · sodium chloride (NaCl) · potassium chloride (KCl) · magnesium borate (MgB 2 O 4 ) and boron (B) in a molar ratio of 10: 5: 5: 2. 2 is a temperature dependence of the magnetic susceptibility (electromagnetic unit / 1 gram) of the sample obtained by weighing 2 g in total and obtaining according to the above. The vertical axis is the magnetic susceptibility and the horizontal axis is the temperature.
図中Ｂは塩化マグネシウム（ＭｇＣｌ２）・塩化ナトリウム（ＮａＣｌ）・塩化カリウム（ＫＣｌ）及びホウ酸マグネシウム（ＭｇＢ２Ｏ４）をモル比１０：５：５：２で総量２ｇ秤量して同様に合成した試料の帯磁率である。 In the figure, B is a weight of magnesium chloride (MgCl 2 ) / sodium chloride (NaCl) / potassium chloride (KCl) and magnesium borate (MgB 2 O 4 ) in a molar ratio of 10: 5: 5: 2 and weighed 2 g in the same manner. It is the magnetic susceptibility of the synthesized sample.
Claims (2)
A method for producing a superconducting boron compound MgB 2 thin film, wherein boron (B) is mixed with the powdery starting material .
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