JP2005219976A - Oxide superconductor and its manufacturing method - Google Patents

Oxide superconductor and its manufacturing method Download PDF

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JP2005219976A
JP2005219976A JP2004030557A JP2004030557A JP2005219976A JP 2005219976 A JP2005219976 A JP 2005219976A JP 2004030557 A JP2004030557 A JP 2004030557A JP 2004030557 A JP2004030557 A JP 2004030557A JP 2005219976 A JP2005219976 A JP 2005219976A
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Masao Naitou
方夫 内藤
Akio Tsukada
昭雄 束田
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Nippon Telegraph and Telephone Corp
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract

<P>PROBLEM TO BE SOLVED: To develop superconductivity by doping a three-valent element to La<SB>2</SB>CuO<SB>4</SB>having a structure of Nd<SB>2</SB>CuO<SB>4</SB>. <P>SOLUTION: The oxide superconductor characterised in that it is expressed by chemical formula: La<SB>2-x</SB>M<SB>x</SB>CuO<SB>4</SB>(0<x<2; M is one or more kinds selected from the group consisting of Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, and Y) and its crystal structure is the Nd<SB>2</SB>CuO<SB>4</SB>structure, is manufactured by setting La, M, and Cu metal raw materials in a super high vacuum chamber, heating a substrate, and introducing an active oxygen to form a metal oxide thin film on the substrate. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

本発明は酸化物超伝導体及びその製造方法、さらに詳細にはＮｄ２ＣｕＯ４構造を有するＬａ２ＣｕＯ４に対して、価数３価の元素のドーピングにより、超伝導を発現させる新しい酸化物超伝導体及びその製造方法に関する。 The present invention relates to an oxide superconductor and a method for producing the same, and more specifically, a new oxide that exhibits superconductivity by doping a trivalent element with La 2 CuO 4 having an Nd 2 CuO 4 structure. The present invention relates to a superconductor and a method for manufacturing the same.

Ｎｄ２ＣｕＯ４構造をとる酸化物超伝導体としては、一般式で（ＲＥ，Ｔｈ）２ＣｕＯ４（非特許文献１、２）、（ＲＥ，Ｃｅ）２ＣｕＯ４（非特許文献３、４）で表される物質が過去に知られていた。ここでＲＥはＬａ、Ｐｒ、Ｎｄ、Ｓｍ、Ｅｕのいずれかの希土類元素またはそれらの元素の混合物を表す。価数が４価のＴｈ及びＣｅが３価の希土類元素を置換し、ｎ型キャリヤを供給することにより、超伝導が発現するとされてきた。
Ｊ．Ｔ．Ｍａｒｋｅｒｔ ｅｔ ａｌ．，Ｓｏｌｉｄ Ｓｔａｔｅ Ｃｏｍｍｕｎ．，７０（１９８９）１４５． Ｊ．Ｔ．Ｍａｒｋｅｒｔ ｅｔ ａｌ．，Ｐｈｙｓｉｃａ Ｃ，１５８（１９８９）１７８． Ｙ．Ｔｏｋｕｒａ ｅｔ ａｌ．，Ｎａｔｕｒｅ，３３７（１９８９）３４５． Ｈ．Ｔａｋａｇｉ ｅｔ ａｌ．，Ｐｈｙｓ．Ｒｅｖ．Ｌｅｔｔ．６２（１９８９）１１９７． As an oxide superconductor having an Nd 2 CuO 4 structure, (RE, Th) 2 CuO 4 (Non-Patent Documents 1 and 2), (RE, Ce) 2 CuO 4 (Non-Patent Documents 3 and 4) ) Was known in the past. Here, RE represents a rare earth element of La, Pr, Nd, Sm, or Eu or a mixture of these elements. It has been reported that superconductivity is developed by replacing trivalent rare earth elements with tetravalent Th and Ce and supplying n-type carriers.
J. et al. T.A. Markert et al. , Solid State Commun. , 70 (1989) 145. J. et al. T.A. Markert et al. Physica C, 158 (1989) 178. Y. Tokuura et al. , Nature, 337 (1989) 345. H. Takagi et al. Phys. Rev. Lett. 62 (1989) 1197.

従来の技術では、Ｎｄ２ＣｕＯ４構造を有するＲＥ２ＣｕＯ４（ＲＥはＬａ、Ｐｒ、Ｎｄ、Ｓｍ、Ｅｕ）の超伝導発現に価数４価の元素のドーピングが必要であった。このため、ドーパントがＴｈとＣｅに限られていた。 In the prior art, doping of a tetravalent element was necessary for the superconductivity of RE 2 CuO 4 (RE is La, Pr, Nd, Sm, Eu) having an Nd 2 CuO 4 structure. For this reason, the dopant was limited to Th and Ce.

上記課題を解決するために、本発明による酸化物超伝導体は、化学式Ｌａ２−ｘＭｘＣｕＯ４（０＜ｘ＜２；ＭをＰｒ、Ｎｄ、Ｓｍ、Ｅｕ、Ｇｄ、Ｄｙ、Ｈｏ、Ｅｒ、Ｔｍ、Ｙｂ、Ｌｕ、Ｙの１種以上）で表され、結晶構造がＮｄ２ＣｕＯ４構造をとることを特徴とする。 In order to solve the above problems, the oxide superconductor according to the present invention has a chemical formula La 2-x M x CuO 4 (0 <x <2; M represents Pr, Nd, Sm, Eu, Gd, Dy, Ho, One or more of Er, Tm, Yb, Lu, and Y), and the crystal structure has an Nd 2 CuO 4 structure.

また本発明による酸化物超伝導体の製造方法は、化学式Ｌａ２−ｘＭｘＣｕＯ４（０＜ｘ＜２；ＭをＰｒ、Ｎｄ、Ｓｍ、Ｅｕ、Ｇｄ、Ｄｙ、Ｈｏ、Ｅｒ、Ｔｍ、Ｙｂ、Ｌｕ、Ｙの１種以上）を生成するための化学量論比に秤量した金属Ｌａ、金属Ｍ、金属Ｃｕを超高真空チャンバーに設置し、基板を加熱するとともに活性酸素を導入して前記基板上に金属酸化物薄膜を形成させることを特徴とする。 In addition, the method for producing an oxide superconductor according to the present invention has a chemical formula La 2-x M x CuO 4 (0 <x <2; M is Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, The metal La, metal M, and metal Cu weighed in a stoichiometric ratio for generating Yb, Lu, and Y) are placed in an ultra-high vacuum chamber, the substrate is heated, and active oxygen is introduced. A metal oxide thin film is formed on the substrate.

すなわち、本発明はＮｄ２ＣｕＯ４構造を有するＬａ２ＣｕＯ４に対して、価数３価の元素のドーピングにより、超伝導を発現させることを目的とする。価数３価の元素としては、Ｐｒ、Ｎｄ、Ｓｍ、Ｅｕ、Ｇｄ、Ｄｙ、Ｈｏ、Ｅｒ、Ｔｍ、Ｙｂ、Ｌｕ、Ｙのいずれか、又は、その混合とすることができる。 That is, an object of the present invention is to develop superconductivity for La 2 CuO 4 having an Nd 2 CuO 4 structure by doping a valence trivalent element. As the valence trivalent element, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, Y, or a mixture thereof can be used.

Ｎｄ２ＣｕＯ４構造を有するＬａ２ＣｕＯ４は、通常のバルク合成では安定化することができないが、低温薄膜合成により安定化できる。得られたＬａ２ＣｕＯ４薄膜は金属的であるものの、結晶性が完全でないために、超伝導は示さない。しかし、少量のＰｒ、Ｎｄ、Ｓｍ、Ｅｕ、Ｇｄ、Ｄｙ、Ｈｏ、Ｅｒ、Ｔｍ、Ｙｂ、Ｌｕ、Ｙの１種以上をＬａ２ＣｕＯ４に添加することにより、結晶性を向上させ、超伝導を発現することができる。 La 2 CuO 4 having an Nd 2 CuO 4 structure cannot be stabilized by ordinary bulk synthesis, but can be stabilized by low-temperature thin film synthesis. Although the obtained La 2 CuO 4 thin film is metallic, it does not exhibit superconductivity due to incomplete crystallinity. However, by adding a small amount of one or more of Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, and Y to La 2 CuO 4 , the crystallinity is improved and superconductivity is improved. Can be expressed.

従来、Ｎｄ２ＣｕＯ４構造を有するＲＥ２ＣｕＯ４の超伝導発現には価数４価の元素のドーピングにより、ｎ型キャリヤの供給が必須であると考えられてきた。本発明は、この従来概念を覆し、中性のドーピングによっても超伝導発現が可能なことを示した。 Conventionally, it has been considered that supply of n-type carriers is indispensable for the development of superconductivity of RE 2 CuO 4 having an Nd 2 CuO 4 structure by doping with a tetravalent element. The present invention overturns this conventional concept and shows that superconductivity can be developed even by neutral doping.

本発明によれば、化学式Ｌａ２−ｘＭｘＣｕＯ４（０＜ｘ＜２；ＭをＰｒ、Ｎｄ、Ｓｍ、Ｅｕ、Ｇｄ、Ｄｙ、Ｈｏ、Ｅｒ、Ｔｍ、Ｙｂ、Ｌｕ、Ｙの１種以上）で表され、結晶構造がＮｄ２ＣｕＯ４構造をとることを特徴とする。 According to the present invention, the chemical formula La 2-x M x CuO 4 (0 <x <2; M is Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, Y. The crystal structure is an Nd 2 CuO 4 structure.

また、前述のように少量のＰｒ、Ｎｄ、Ｓｍ、Ｅｕ、Ｇｄ、Ｄｙ、Ｈｏ、Ｅｒ、Ｔｍ、Ｙｂ、Ｌｕ、Ｙの１種以上をＬａ２ＣｕＯ４に添加することにより、結晶性を向上させ、超伝導を発現することができる。 In addition, as described above, crystallinity is improved by adding a small amount of one or more of Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, and Y to La 2 CuO 4. And superconductivity can be developed.

本発明による酸化物超伝導体の製造方法によれば、化学式Ｌａ２−ｘＭｘＣｕＯ４（０＜ｘ＜２；ＭをＰｒ、Ｎｄ、Ｓｍ、Ｅｕ、Ｇｄ、Ｄｙ、Ｈｏ、Ｅｒ、Ｔｍ、Ｙｂ、Ｌｕ、Ｙのいずれか）を生成するための化学量論比に秤量した金属Ｌａ、金属Ｍ、金属Ｃｕを超高真空チャンバーに設置し、基板を加熱するとともに活性酸素を導入して前記基板上に金属酸化物薄膜を形成させる（図１参照）。これによって反応性共蒸着によってＬａ２−ｘＭｘＣｕＯ４（０＜ｘ＜２；ＭをＰｒ、Ｎｄ、Ｓｍ、Ｅｕ、Ｇｄ、Ｄｙ、Ｈｏ、Ｅｒ、Ｔｍ、Ｙｂ、Ｌｕ、Ｙの１種以上）薄膜が形成される。 According to the method of manufacturing an oxide superconductor according to the present invention, the chemical formula La 2-x M x CuO 4 (0 <x <2; M is Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm. , Yb, Lu, or Y) are placed in an ultra-high vacuum chamber with metal La, metal M, and metal Cu weighed in a stoichiometric ratio to heat the substrate and introduce active oxygen. A metal oxide thin film is formed on the substrate (see FIG. 1). Thus, La 2 -x M x CuO 4 (0 <x <2; M is Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, Y by reactive co-evaporation. Thus, a thin film is formed.

基板としては、たとえばチタン酸ストロンチウム（ＳｒＴｉＯ３）基板、アルミ酸ネオジムカルシウム（ＮｄＣａＡｌＯ４）基板及びアルミ酸イットリウム（ＹＡｌＯ３）基板を有効に使用することができる。基板温度は好ましくは４５０〜８００℃である。４５０℃未満であると、結晶化しない恐れがあり、一方８００℃を越えると、Ｌａ２−ｘＭｘＣｕＯ４相が形成されない恐れがある。最も好ましくは６００〜７００℃である。 As the substrate, for example, a strontium titanate (SrTiO 3 ) substrate, a neodymium calcium aluminate (NdCaAlO 4 ) substrate, and an yttrium aluminate (YAlO 3 ) substrate can be effectively used. The substrate temperature is preferably 450 to 800 ° C. If it is lower than 450 ° C., it may not be crystallized, while if it exceeds 800 ° C., the La 2−x M x CuO 4 phase may not be formed. Most preferably, it is 600-700 degreeC.

さらに活性酸素としては、たとえばオゾンまたは原子酸素が好ましく用いられる。この活性酸素の流量は、０．１〜１０ｃｃ／分、好ましくは０．５〜５ｃｃ／分であるのがよい。０．１ｃｃ／分未満であると、Ｌａ２−ｘＭｘＣｕＯ４の相ができない。一般に、銅酸化物高温超伝導体ではＣｕは２＋の高酸化状態にあるので、所望の相を得るためには、成長時に照射する活性酸素量の下限が存在する。５ｃｃ／分を越えると、結晶性が徐々に悪くなり、１０ｃｃ／分を越えると使用可能な結晶性ではなくなると推定される。 Further, as active oxygen, for example, ozone or atomic oxygen is preferably used. The flow rate of this active oxygen is 0.1 to 10 cc / min, preferably 0.5 to 5 cc / min. If it is less than 0.1 cc / min, a phase of La 2-x M x CuO 4 cannot be formed. In general, Cu is in a high oxidation state of 2+ in a copper oxide high-temperature superconductor. Therefore, in order to obtain a desired phase, there is a lower limit of the amount of active oxygen irradiated during growth. If it exceeds 5 cc / min, the crystallinity gradually deteriorates, and if it exceeds 10 cc / min, it is estimated that the crystallinity is not usable.

以下実施例を説明する。後述の実施例は、本発明の例示であり、これによって限定されるものではない。   Examples will be described below. The following examples are illustrative of the present invention and are not limited thereby.

（１）Ｍ＝Ｓｍ
オゾンを用いた反応性共蒸着法により、チタン酸ストロンチウム（ＳｒＴｉＯ３）基板、アルミ酸ネオジムカルシウム（ＮｄＣａＡｌＯ４）基板及びアルミ酸イットリウム（ＹＡｌＯ３）基板上にＬａ２−ｘＳｍｘＣｕＯ４薄膜を作製した。ここで、基板温度は６５０℃で、オゾン流量１ｃｃ／分とした。 (1) M = Sm
La 2-x Sm x CuO 4 thin film was formed on a strontium titanate (SrTiO 3 ) substrate, neodymium calcium aluminate (NdCaAlO 4 ) substrate, and yttrium aluminate (YAlO 3 ) substrate by a reactive co-evaporation method using ozone. Produced. Here, the substrate temperature was 650 ° C., and the ozone flow rate was 1 cc / min.

図２は、同薄膜のｘ＝０．１５における超伝導転移を示したものであり、薄膜がＴｃ〜２１Ｋの超伝導体であることを示している。図３は、同薄膜のｘ＝０．３０におけるＸ線回折パターンであり、薄膜がＮｄ２ＣｕＯ４構造をとっていることを示している。ここで＊印はＹＡｌＯ３基板からのピークを示している。 FIG. 2 shows the superconducting transition of the thin film at x = 0.15, indicating that the thin film is a superconductor of Tc to 21K. FIG. 3 is an X-ray diffraction pattern of the thin film at x = 0.30, which shows that the thin film has an Nd 2 CuO 4 structure. Here, * indicates a peak from the YAlO 3 substrate.

さらに、Ｓｍドープ量を系統的に変える実験を行い、超伝導が出現する組成範囲を調べた。図４に超伝導転移温度のｘ依存性を示す。図４はＬａ２−ｘＳｍｘＣｕＯ４薄膜の超伝導転移温度（Ｔｃ）をＳｍの組成の関数としてプロットしたものである。○、□及び△は、それぞれチタン酸ストロンチウム（ＳｒＴｉＯ３）基板、アルミ酸ネオジムカルシウム（ＮｄＣａＡｌＯ４）基板及びアルミ酸イットリウム（ＹＡｌＯ３）基板上に作製した薄膜の結果を示している。０．１５≦ｘ≦０．３０の範囲で超伝導が観測され、ｘ＝０．１５近傍でＴｃは最高値の２１．０Ｋとなる。 Furthermore, an experiment was conducted to systematically change the amount of Sm doping, and the composition range where superconductivity appeared was examined. FIG. 4 shows the x dependence of the superconducting transition temperature. FIG. 4 is a plot of the superconducting transition temperature (Tc) of a La 2-x Sm x CuO 4 thin film as a function of Sm composition. ○, □, and Δ show the results of the thin films formed on the strontium titanate (SrTiO 3 ) substrate, the neodymium calcium aluminate (NdCaAlO 4 ) substrate, and the yttrium aluminate (YAlO 3 ) substrate, respectively. Superconductivity is observed in the range of 0.15 ≦ x ≦ 0.30, and Tc reaches the maximum value of 21.0K in the vicinity of x = 0.15.

（２）Ｍ＝Ｅｕ
オゾンを用いた反応性共蒸着法により、チタン酸ストロンチウム（ＳｒＴｉＯ３）基板、アルミ酸ネオジムカルシウム（ＮｄＣａＡｌＯ４）基板及びアルミ酸イットリウム（ＹＡｌＯ３）基板上にＬａ２−ｘＥｕｘＣｕＯ４薄膜を作製した。ここで、基板温度は６５０℃で、オゾン流量１．５ｃｃ／分とした。図５は、同薄膜のｘ＝０．１５における超伝導転移を示したものであり、薄膜がＴｃ〜２０Ｋの超伝導体であることを示している。さらに、Ｅｕドープ量を系統的に変える実験を行い、超伝導が出現する組成範囲を調べた。図６に超伝導転移温度のｘ依存性を示す。図６はＬａ２−ｘＥｕｘＣｕＯ４薄膜の超伝導転移温度（Ｔｃ）をＥｕの組成の関数としてプロットしたものである。○、□及び△は、それぞれチタン酸ストロンチウム（ＳｒＴｉＯ３）基板、アルミ酸ネオジムカルシウム（ＮｄＣａＡｌＯ４）基板及びアルミ酸イットリウム（ＹＡｌＯ３）基板上に作製した薄膜の結果を示している。０．１５≦ｘ≦０．３０で超伝導が観測され、ｘ＝０．１５付近で最高のＴｃ＝２０．２Ｋが得られた。 (2) M = Eu
La 2-x Eu x CuO 4 thin film was formed on a strontium titanate (SrTiO 3 ) substrate, neodymium calcium aluminate (NdCaAlO 4 ) substrate, and yttrium aluminate (YAlO 3 ) substrate by a reactive co-evaporation method using ozone. Produced. Here, the substrate temperature was 650 ° C., and the ozone flow rate was 1.5 cc / min. FIG. 5 shows the superconducting transition of the thin film at x = 0.15, indicating that the thin film is a superconductor of Tc to 20K. Furthermore, an experiment was conducted to systematically change the Eu doping amount, and the composition range in which superconductivity appeared was examined. FIG. 6 shows the x dependence of the superconducting transition temperature. FIG. 6 is a plot of the superconducting transition temperature (Tc) of a La 2-x Eu x CuO 4 thin film as a function of Eu composition. ◯, □, and Δ show the results of the thin films formed on the strontium titanate (SrTiO 3 ) substrate, the neodymium calcium aluminate (NdCaAlO 4 ) substrate, and the yttrium aluminate (YAlO 3 ) substrate, respectively. Superconductivity was observed at 0.15 ≦ x ≦ 0.30, and the highest Tc = 20.2 K was obtained near x = 0.15.

（３）Ｍ＝Ｙ
オゾンを用いた反応性共蒸着法により、チタン酸ストロンチウム（ＳｒＴｉＯ３）基板、アルミ酸ネオジムカルシウム（ＮｄＣａＡｌＯ４）基板及びアルミ酸イットリウム（ＹＡｌＯ３）基板上にＬａ２−ｘＹｘＣｕＯ４薄膜を作製した。ここで、基板温度は６５０℃で、オゾン流量２ｃｃ／分とした。図７は、同薄膜のｘ＝０．０９における超伝導転移を示したものであり、薄膜がＴｃ〜１９Ｋの超伝導体であることを示している。さらに、Ｙドープ量を系統的に変える実験を行い、超伝導が出現する組成範囲を調べた。図８に超伝導転移温度のｘ依存性を示す。図８はＬａ２−ｘＹｘＣｕＯ４薄膜の超伝導転移温度（Ｔｃ）をＹの組成の関数としてプロットしたものである。○、□及び△は、それぞれチタン酸ストロンチウム（ＳｒＴｉＯ３）基板。アルミ酸ネオジムカルシウム（ＮｄＣａＡｌＯ４）基板及びアルミ酸イットリウム（ＹＡｌＯ３）基板上に作製した薄膜の結果を示している。０．０９≦ｘ≦０．１５で超伝導が観測され、ｘ＝０．０９付近で最高のＴｃ＝１９．３Ｋが得られた。 (3) M = Y
La 2-x Y x CuO 4 thin film is formed on a strontium titanate (SrTiO 3 ) substrate, neodymium calcium aluminate (NdCaAlO 4 ) substrate, and yttrium aluminate (YAlO 3 ) substrate by a reactive co-evaporation method using ozone. Produced. Here, the substrate temperature was 650 ° C., and the ozone flow rate was 2 cc / min. FIG. 7 shows the superconducting transition of the thin film at x = 0.09, indicating that the thin film is a superconductor of Tc to 19K. Furthermore, an experiment was conducted to systematically change the Y-doping amount, and the composition range in which superconductivity appeared was investigated. FIG. 8 shows the x dependence of the superconducting transition temperature. FIG. 8 is a plot of the superconducting transition temperature (Tc) of a La 2 -x Y x CuO 4 thin film as a function of Y composition. ○, □ and Δ are strontium titanate (SrTiO 3 ) substrates, respectively. Shows the aluminum neodymium calcium (NdCaAlO 4) substrate and an aluminum yttrium (YAlO 3) results of films prepared on a substrate. Superconductivity was observed at 0.09 ≦ x ≦ 0.15, and the highest Tc = 19.3K was obtained near x = 0.09.

（４）Ｍ＝Ｌｕ
オゾンを用いた反応性共蒸着法により、チタン酸ストロンチウム（ＳｒＴｉＯ３）基板及びアルミ酸ネオジムカルシウム（ＮｄＣａＡｌＯ４）基板上にＬａ２−ｘＬｕｘＣｕＯ４薄膜を作製した。ここで、基板温度は６５０℃で、オゾン流量３ｃｃ／分とした。図８は、同薄膜のｘ＝０．０６における超伝導転移を示したものであり、薄膜がＴｃ〜１２Ｋの超伝導体であることを示している。さらに、Ｌｕドープ量を系統的に変える実験を行い、超伝導が出現する組成範囲を調べた。図１０に超伝導転移温度のｘ依存性を示す。図１０はＬａ２−ｘＬｕｘＣｕＯ４薄膜の超伝導転移温度（Ｔｃ）をＬｕの組成の関数としてプロットしたものである。○及び□は、それぞれチタン酸ストロンチウム（ＳｒＴｉＯ３）基板及びアルミ酸ネオジムカルシウム（ＮｄＣａＡｌＯ４）基板上に作製した薄膜の結果を示している。０．０３≦ｘ≦０．０９で超伝導が観測され、ｘ＝０．０６付近で最高のＴｃ＝１１．７Ｋが得られた。 (4) M = Lu
La 2-x Lu x CuO 4 thin films were formed on a strontium titanate (SrTiO 3 ) substrate and a neodymium calcium aluminate (NdCaAlO 4 ) substrate by a reactive co-evaporation method using ozone. Here, the substrate temperature was 650 ° C., and the ozone flow rate was 3 cc / min. FIG. 8 shows the superconducting transition of the thin film at x = 0.06, indicating that the thin film is a superconductor of Tc to 12K. Furthermore, an experiment was conducted to systematically change the Lu doping amount, and the composition range in which superconductivity appeared was examined. FIG. 10 shows the x dependence of the superconducting transition temperature. FIG. 10 is a plot of the superconducting transition temperature (Tc) of a La 2-x Lu x CuO 4 thin film as a function of Lu composition. ○ and □ show the results of the thin films formed on the strontium titanate (SrTiO 3 ) substrate and the neodymium calcium aluminate (NdCaAlO 4 ) substrate, respectively. Superconductivity was observed at 0.03 ≦ x ≦ 0.09, and the highest Tc = 11.7 K was obtained near x = 0.06.

従来、Ｎｄ２ＣｕＯ４構造を有するＲＥ２ＣｕＯ４の超伝導発現には価数４価の元素のドーピングにより、ｎ型キャリヤの供給が必須であると考えられてきた。本発明は、この従来概念を覆し、中性のドーピングによっても超伝導発現が可能なことを示した。すなわち、新しい酸化物超伝導体およびその製造方法を提供する。 Conventionally, it has been considered that supply of n-type carriers is indispensable for the development of superconductivity of RE 2 CuO 4 having an Nd 2 CuO 4 structure by doping with a tetravalent element. The present invention overturns this conventional concept and shows that superconductivity can be developed even by neutral doping. That is, a new oxide superconductor and a manufacturing method thereof are provided.

本発明の製造方法を示すブロック図。The block diagram which shows the manufacturing method of this invention. 反応性共蒸着法により、アルミ酸イットリウム（ＹＡｌＯ３）基板上に作製したＬａ１．８５Ｓｍ０．１５ＣｕＯ４薄膜の超伝導転移を示した図。By a reactive co-evaporation method, it showed superconducting transition of La 1.85 Sm 0.15 CuO 4 films prepared in an aluminum yttrium (YAlO 3) on the substrate Fig. Ｌａ１．７Ｓｍ０．３ＣｕＯ４のＸ線回折パターンであり、薄膜がＮｄ２ＣｕＯ４構造をとっていることを示している。This is an X-ray diffraction pattern of La 1.7 Sm 0.3 CuO 4 , indicating that the thin film has an Nd 2 CuO 4 structure. Ｌａ２−ｘＳｍｘＣｕＯ４薄膜の超伝導転移温度（Ｔｃ）をＳｍの組成の関数としてプロットした図。Plotted La 2-x Sm x CuO 4 thin film superconducting transition temperature (Tc) as a function of the composition of Sm. 反応性共蒸着法により、アルミ酸イットリウム（ＹＡｌＯ３）基板上に作製したＬａ１．８５Ｅｕ０．１５ＣｕＯ４薄膜の超伝導転移を示した図。By a reactive co-evaporation method, it showed superconducting transition of La 1.85 Eu 0.15 CuO 4 films prepared in an aluminum yttrium (YAlO 3) on the substrate Fig. Ｌａ２−ｘＥｕｘＣｕＯ４薄膜の超伝導転移温度（Ｔｃ）をＥｕの組成の関数としてプロットした図。Plotted La 2-x Eu x CuO 4 thin film superconducting transition temperature (Tc) as a function of the composition of the Eu. 反応性共蒸着法により、アルミ酸イットリウム（ＹＡｌＯ３）基板上に作製したＬａ１．９１Ｙ０．０９ＣｕＯ４薄膜の超伝導転移を示した図。By a reactive co-evaporation method, it showed superconducting transition of La 1.91 Y 0.09 CuO 4 films prepared in an aluminum yttrium (YAlO 3) on the substrate Fig. Ｌａ２−ｘＹｘＣｕＯ４薄膜の超伝導転移温度（Ｔｃ）をＹの組成の関数としてプロットした図。Plotted La 2-x Y x CuO 4 thin film superconducting transition temperature (Tc) as a function of the composition of Y. 反応性共蒸着法により、アルミ酸ネオジムカルシウム（ＮｄＣａＡｌＯ４）基板上に作製したＬａ１．９４Ｌｕ０．０６ＣｕＯ４薄膜の超伝導転移を示した図。By a reactive co-evaporation method, it showed superconducting transition of La 1.94 Lu 0.06 CuO 4 films prepared in an aluminum neodymium calcium (NdCaAlO 4) on the substrate Fig. Ｌａ２−ｘＬｕｘＣｕＯ４薄膜の超伝導転移温度（Ｔｃ）をＬｕの組成の関数としてプロットした図。Plotted La 2-x Lu x CuO 4 thin film superconducting transition temperature (Tc) as a function of the composition of Lu.

Claims (5)

化学式Ｌａ２−ｘＭｘＣｕＯ４（０＜ｘ＜２；ＭをＰｒ、Ｎｄ、Ｓｍ、Ｅｕ、Ｇｄ、Ｄｙ、Ｈｏ、Ｅｒ、Ｔｍ、Ｙｂ、Ｌｕ、Ｙの１種以上）で表され、結晶構造がＮｄ２ＣｕＯ４構造をとることを特徴とする酸化物超伝導体。 Represented by; formula La 2-x M x CuO 4 (M and Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, 1 or more Y 0 <x <2) An oxide superconductor having a crystal structure of Nd 2 CuO 4 . 化学式Ｌａ２−ｘＭｘＣｕＯ４（０＜ｘ＜２；ＭをＰｒ、Ｎｄ、Ｓｍ、Ｅｕ、Ｇｄ、Ｄｙ、Ｈｏ、Ｅｒ、Ｔｍ、Ｙｂ、Ｌｕ、Ｙのいずれか）を生成するための化学量論比に秤量した金属Ｌａ、金属Ｍ、金属Ｃｕを超高真空チャンバーに設置し、基板を加熱するとともに活性酸素を導入して前記基板上に金属酸化物薄膜を形成させることを特徴とする酸化物超伝導体の製造方法。 For generating a chemical formula La 2-x M x CuO 4 (0 <x <2; M is any of Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, Y) The metal La, metal M, and metal Cu weighed in a stoichiometric ratio are placed in an ultra-high vacuum chamber, the substrate is heated, and active oxygen is introduced to form a metal oxide thin film on the substrate. A method for manufacturing an oxide superconductor. 前記基板は、チタン酸ストロンチウム（ＳｒＴｉＯ３）基板、アルミ酸ネオジムカルシウム（ＮｄＣａＡｌＯ４）基板及びアルミ酸イットリウム（ＹＡｌＯ３）基板上のいずれかであることを特徴とする請求項２記載の酸化物超伝導体の製造方法。 3. The oxide superlattice according to claim 2, wherein the substrate is any of a strontium titanate (SrTiO 3 ) substrate, a neodymium calcium aluminate (NdCaAlO 4 ) substrate, and an yttrium aluminate (YAlO 3 ) substrate. A method for manufacturing a conductor. 前記基板を４５０〜８００℃に加熱することを特徴とする請求項２または３記載の酸化物超伝導体の製造方法。 The method of manufacturing an oxide superconductor according to claim 2 or 3, wherein the substrate is heated to 450 to 800 ° C. 活性酸素の流量は０．１〜１０ｃｃ／分であることを特徴とする請求項２から４のいずれか１項記載の酸化物超伝導体の製造方法。 The method for producing an oxide superconductor according to any one of claims 2 to 4, wherein the flow rate of active oxygen is 0.1 to 10 cc / min.
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