JPH0764620B2 - Oxide superconductor composition and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an oxide superconducting material used in various superconducting application devices and superconducting elements.

(Prior Art) Conventionally, as superconducting materials, for example, simple metals such as Pb, Nb, Nb ₃ Ge, alloys, and intermetallic compounds have been known. Superconducting materials are used to make electronic devices such as Josephson devices and coils for superconducting magnets. In addition to the application of AC and the Josephson effect, it is expected to be applied to electronic computers that focus on the high-speed response and low power consumption of Josephson junctions.

By the way, it is desired that the superconducting transition temperature Tc of the superconducting material is as high as possible. As a material with a high Tc, Tc
Was known to be 23.2K Nb ₃ Ge, but recently La-Ba-Cu
Among the --O system, (La _1-x Ba _x ) ₂ CuO ₄ having a composition of 0.075 ≦ x ≦ 0.1 has a Tc of 30 K, and Y--Ba--Cu--O system YBa ₂ Cu ₃
It has been successively reported that the Tc of the composition of Oy has around 90K. Furthermore, even _if the Y position of this YBa ₂ Cu ₃ O _y is replaced with lanthanum, neodymium, samarium, europium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium, and thulium among other rare earth elements, these elements are also replaced. It is also reported that even if two or more kinds are mixed, they have almost the same Tc of about 90K. Since the Tc of these superconductors including the Y-Ba-Cu-O system has become higher than the boiling point (77K) of liquid nitrogen, expectations as a practical material are increasing.

The Tc of superconductors having an oxygen-deficient three-layer perovskite structure such as the Y-Ba-Cu-O system is a material showing a high value of 90K, but the relative density is 90 at most in the ordinary porcelain manufacturing method.
%, It is mechanically brittle, and the critical current density Jc, which is an important characteristic, is generally low. This is because the sintering of barium carbonate (BaCO ₃ ) used as a starting material has to be completed at a temperature of around 1000 ° C while the decomposition of barium carbonate (BaCO ₃ ) is insufficient. That is, when the temperature of BaCO ₃ is sufficiently raised to decompose, the oxygen deficient three-layer perovskite structure, which is a reaction product, is decomposed and a different phase is generated. Recently, attempts have been made to use a barium salt other than barium carbonate as a starting material, a coprecipitation method other than the usual porcelain manufacturing method, and an attempt to apply a freeze-drying method. Carbon ions contained in carbon dioxide (CO ₂ ) and mixed powder are bound together, and Ba ions become barium carbonate (BaCO ₃ ) with the same result as described above. Furthermore, the critical current density Jc of the sintered body of the superconductor composition represented by the composition formula REBa ₂ Cu ₃ O _y is generally low. This is because the composition of REBa ₂ Cu ₃ O _y has an orthorhombic crystal structure and therefore has an anisotropic superconducting property. That is, even if each of the crystal grains forming the sintered body is close to a single crystal, since the sintered body is a polycrystalline body, the superconducting properties are averaged as a whole. However, with the conventional composition and the conventional manufacturing method, it has been difficult to prepare a powder oriented in a direction in which a superconducting current easily flows or to sinter the oriented powder in the same direction.

(Problems to be solved by the invention) REBa ₂ Cu ₃ O _{y The} problem that unreacted substances remain in the sintered body of the superconductor composition represented by the composition formula, the problem that it cannot be sintered at low temperature, the oriented powder There was a problem that a body could not be created and a problem that the oriented powder could not be aligned and sintered.

INDUSTRIAL APPLICABILITY The present invention is a problem that unreacted substances remain that cannot be solved by the conventional composition or the conventional method for producing a porcelain composition, a problem that sintering at low temperature is not possible, a problem that oriented powder cannot be produced, and a direction of oriented powder An object of the present invention is to provide a superconductor composition and a method for producing the same, which solves the problem that sintering is not possible.

(Means for Solving the Problems) The present invention relates to an oxide superconductor composition, particularly a conventional REBa ₂ Cu ₃ O _y.
REBa ₂ Cu _{3 + x} O _{y with} a composition formula of 0.03 ≦
In the oxide superconductor composition where there is a deviation from the stoichiometric ratio of Cu in the range of x ≦ 0.3, there is no unreacted material, sintering is possible at low temperature, and an oriented powder is obtained and oriented. The inventors have found a method for producing a sintered body in which the directions of the powder are aligned.

For example, in the composition formula YBa ₂ Cu _{3 + x} O _y , x = 0,0.015,0.03,0.0
Compositions of 9,0.30 and 0.35 were synthesized by a usual porcelain manufacturing method. At this time, calcining in air at 900 ° C for 12 hours,
Furthermore, when calcination was performed at 980 ° C. for 4 hours in one atmosphere of oxygen, some of 0.03 or more having large x melted. When these were re-ground and pressure-molded, x was 0.
It was confirmed that powders having the C-axis, which is the crystal structure, were aligned in parallel with the pressing direction for the compositions of 03 and above, and the powder was oriented by the powder X-ray diffraction method.

Hereinafter, the present invention will be described in more detail with reference to Examples.

(Example) As a starting material, yttrium oxide (Y ₂
O ₃ ), barium carbonate (BaCO ₃ ), and cupric oxide (CuO) are used and weighed so that the compounding ratio is 1: 2: 3 + x in molar ratio. Here, x was set to 0,0.015,0.03,0.09,0.30,0.35. Next, the weighed materials were wet-mixed by a ball mill, calcined in air at 900 ° C. for 12 hours to perform re-calcination, and subsequently, calcined again in oxygen at 980 ° C. for 4 hours. At this time, a liquid phase partially appeared in the composition in which x was 0.03 or more. To confirm this, differential thermal analysis was performed on these compositions in oxygen from room temperature to 1100 ° C., where x was 0.
It was confirmed that the compositions of 03 and above had an endothermic reaction at around 980 ° C particularly clearly. It is expected that the presence of this liquid phase promotes the solid phase reaction to improve the density and increase the mechanical strength. The powder that has been calcined twice is crushed in a mortar and then re-crushed in a ball mill to adjust the particle size to 1 ton.
Pressure shaping was performed at a pressure of / cm ² . The surface of this molded body which was perpendicular to the pressing direction was examined by powder X-ray diffractometry. As a result, x was 0.03 or more and the powder was C-axis parallel to the pressing direction. Was confirmed. In order to quantify the degree of this C-axis orientation, the X-ray intensity ratios of the two diffraction lines (006) and (200) were compared in the powder X-ray diffraction diagram. As shown in FIG. 1, these results show that the intensity ratio of the (006) diffraction line and the (200) diffraction line was about 2 in the composition of x = 0, but became maximum in the composition of x = 0.09. The intensity ratio was about 32 times. Furthermore, when a molded body of these composition powders was sintered in oxygen at 980 ° C., an oriented sintered body could be obtained without changing the intensity ratio of X-ray diffraction lines. Table 1 shows the proportion of the impurity phase obtained from the dimensional density of the sintered bodies of these compositions and the intensity ratio of the diffracted X-rays, and the volume proportion of the superconductor phase at 4.2K obtained from the AC susceptibility. The dimensional density also slightly increases as x increases. In this way, by increasing the density x and the C
An axially oriented powder and a sintered body will be obtained. Conversely x
Is more than 0.30, the effective superconductor phase is obviously decreased, and the degree of orientation is monotonically decreased until x becomes 0.35, which is not practical.

The temperature at which this liquid phase appears varies depending on the atmospheric oxygen partial pressure during calcination. For example, the oxygen partial pressure is 0.21 atm, that is, about 960 ° C. in air, so the temperature at which this liquid phase appears is thermodynamically determined. Further, for the rare earth elements other than yttrium, the temperature at which this liquid phase appears changes and cannot be uniquely determined. However, it is clear that the above result can be obtained by interposing a part of the liquid phase.

Although the example of yttrium is shown in the examples, other rare earth elements such as lanthanum, neodymium, samarium, europium, gadolinium, dysprosium, holosium,
Erbium, thulium, ytterbium, and lutetium also showed the same effect as yttrium. Moreover, you may include 2 or more types of these. The number of oxygen atoms per composition formula is in the range of 7.1 to 6.3, more preferably 6.95.
The range is up to 6.3.

This was measured by an inert gas melting method or an iodometry method.

(Effects of the Invention) As is clear from the examples, according to the present invention, highly oriented porcelain can be obtained at a relatively low temperature as compared with the conventional material, and thick film wiring by the printing method or the green sheet method is applied. It is expected to be applied to the superconducting devices mentioned above.

[Brief description of drawings]

FIG. 1 is a diagram showing the degree of orientation of a porcelain composition according to an example of the present invention by a powder X-ray diffraction method.

Front page continued (72) Inventor Kazuaki Utsumi 5-33-1 Shiba, Minato-ku, Tokyo Inside NEC Corporation (56) References JP 64-9856 (JP, A) JP 64-64 45020 (JP, A)

Claims (2)

[Claims] 1. An oxide superconductor composition represented by the composition formula REBa ₂ Cu _{3 + x} O _y , wherein the rare earth element RE is yttrium, lanthanum, neodymium, samarium, europium, gadolinium, dysprosium, holmium, erbium, One or more of thulium, ytterbium, and lutetium, and the deviation x from the stoichiometric ratio of Cu is 0.
An oxide superconductor composition, wherein 03 ≦ x ≦ 0.3 and y are in the range of 6.3 ≦ y ≦ 7.1. 2. In an oxide superconductor composition represented by the composition formula REBa ₂ Cu _{3 + x} O _y , the rare earth element RE is yttrium, lanthanum, neodymium, samarium, europium, gadolinium, dysprosium, holmium, erbium, One or more of thulium, ytterbium, and lutetium, and the deviation x from the stoichiometric ratio of Cu is 0.
03 ≦ x ≦ 0.3 and y is in the range of 6.3 ≦ y ≦ 7.1 After at least one heat treatment at a partial melting decomposition temperature or higher of the oxide superconductor composition, the composition is crushed and pressure-molded. ,
A method for producing an oxide superconductor composition, which comprises firing.