JPH0798685B2 - Oxide superconductor melt container - Google Patents

Description

TECHNICAL FIELD The present invention relates to a container for an oxide superconductor melt containing an alkaline earth metal element and a copper element as components.

<Prior Art> Some oxides containing one or more metal elements in addition to the alkaline earth metal element and copper element exhibit superconductivity. Among these, yttrium-containing systems and the like have a superconducting transition temperature above the liquid nitrogen temperature, and therefore attempts have been made to obtain good quality superconducting materials by utilizing the melt. For example, a single crystal of an oxide superconductor, a wire rod, a film rod, or the like can be manufactured.

Conventionally, alumina has been used as a material for a container that handles such an oxide superconductor melt. Alumina has a high softening point and excellent thermal stability, and has advantages such as extremely high hardness and corrosion resistance. However, since alumina is an acidic porcelain and has high reactivity with basic elements such as alkaline earth metals such as Ba, when it is used as a crucible for growing a high-temperature superconductor single crystal, which is a basic substance, its composition changes. There is a big problem in that it not only causes the above, but also causes the container to deteriorate rapidly. Furthermore, since alumina is produced by adding a small amount of metal oxide to corundum as a mineralizer, impurities are easily mixed. Therefore, the emergence of a container to replace alumina is awaited. One example is the use of a yttria disk laid inside an alumina crucible (H.Takei et al., JJAP26 (1987) L1425), but the structure is complicated. Moreover, yttria is not suitable as a crucible material because its properties as ceramics are far inferior to those of alumina.

<Problems to be Solved by the Invention> As a result of various studies aimed at solving the above-mentioned drawbacks of the alumina container, the inventors of the present invention have found that if silicon nitride is used instead of alumina, high purity and composition controllability can be obtained. The inventors have found that a high melt can be repeatedly manufactured, and completed the present invention.

<Means for Solving the Problems> That is, the present invention is a container for an oxide superconductor melt containing an alkaline earth metal element and a copper element as components, which is formed of a silicon nitride compact.

The present invention will be described in detail below.

The molded body made of silicon nitride in the present invention is a molded body made of a nitride ceramic material having a composition formula of Si ₃ N ₄ . As a method of obtaining a molded body made of silicon nitride, there are a method of obtaining from a silicon nitride powder, a method of synthesizing from a gas raw material such as a CVD method, and the like, but any method can be adopted in the present invention. As a method for obtaining silicon nitride powder, generally, (a) a method of heating metal silicon powder to about 1400 ° C. in nitrogen gas or ammonia decomposition gas and nitriding it (b) nitrogen gas or ammonia gas while reducing silica with carbon (C) SiCl ₄ and NH ₃ (NH ₃ ) ₂ SiCl
There is a method of obtaining [Si (NH) ₂ ] via ₄ and decomposing it at a high temperature, and any method can be adopted in the present invention. The silicon nitride powder obtained in this manner includes trigonal α-type Si ₃ N ₄ and hexagonal β-type Si ₃ N ₄ , but in the present invention, the α-conversion rate is about 90% or less. Higher than that,
It is desirable that the chemical components are high-purity silicon nitride powder having oxygen of 3% or less, Fe of 0.4% or less, Al of 0.3% or less, Ca of 0.2% or less, and Mg of 0.05% or less.

The alkaline earth metal element in the present invention means Ca, Sr, Ba
Etc. The oxide superconductor melt of the present invention is a melt of an oxide containing at least an alkaline earth metal element and a copper element. Some oxides containing at least an alkaline earth metal element and a copper element have a superconducting transition at a temperature of liquid nitrogen or higher. For example, an oxide containing yttrium element in addition to barium element and copper element, the composition ratio of which is 2: 3: 1 is a superconducting transition at 90K or more, the container of the present invention, such a Conveniently suited for oxide melts.

The container of the present invention is a container in which a melt of an oxide containing at least an alkaline earth metal element and a copper element can be placed, and the shape is not limited at all. Normal crucible shape,
A boat shape, and a shape with a brim in the opening used for molecular beam epitaxy and the like.

Molding of the container of the present invention using the above-mentioned silicon nitride powder includes, for example, a slip cast molding method in which silicon nitride powder is dispersed in an organic solvent to prepare a slurry, and the slurry is poured into a gypsum mold for molding. . In an N ₂ atmosphere,
A container made of a silicon nitride compact can be obtained by sintering at around 80 ° C. On the other hand, in order to obtain the container of the present invention by the CVD method, for example, a sintered body substrate made of silicon nitride and silicon carbide is used.
A container coated with silicon nitride can be obtained by placing it in a furnace maintained at about 00 ° C. and introducing NH ₃ and SiCl ₄ .

<Example> Next, an example and a comparative example will be described in more detail.

Example 1 As silicon nitride, the α conversion was 91%, the chemical composition ratio was Si58.9%,
N38.5%, Fe0.2%, Al0.2%, Ca0.2%, Mg0.04%, O2.0
% Commercial silicon nitride powder was used. After slip cast molding, it was fired at 1680 ℃ for 12 hours in an atmosphere of N ₂ 0.6 kg / cm ² , and inside a cylinder with a diameter of 20 mm and a height of 25 mm, a diameter of 8 m
A crucible with a hole of m and a depth of 15 mm was prepared. Next, as an oxide containing alkaline earth metal and copper element as a component, YBa ₂ Cu ₃ coprecipitated powder made by Furuuchi Chemical Co., Ltd. was calcined at 880 ° C. for 5 hours, crushed in a mortar, and then the calcined powder 0.1 g was placed in a crucible washed with ethanol and placed in a furnace using a siliconite heating element. The temperature inside the furnace is 1050 ℃ at 7 ℃ / min.
Up to 0.2 ℃ /
It was gradually cooled to room temperature at min.

When the crucible was divided into halves and examined, no reaction with the contents on the wall of the crucible was found. On the other hand, when the sample was observed, flaky crystals of about 0.7 mm × 0.7 mm × 0.1 mm were formed. This flaky crystal was placed at 500 in an oxygen atmosphere furnace.
After heating at ℃ for 3 hours and gradually cooling to room temperature and subjecting this to X-ray diffraction, it was found that an orthorhombic single crystal was obtained. When this single crystal was applied to a magnetic susceptibility measuring device using a Hartson bridge, it was found to be a good superconductor showing a sharp diamagnetic transition at 89K.

Example 2 As an oxide containing an alkaline earth metal and a copper element as components, Er ₂ O ₃ , BaCO ₃ and CuO powders were mixed in a ball mill for 24 hours at a metal element composition ratio of 1: 2: 3, After calcination at 930 ° C. for 12 hours, it was crushed in a mortar. Example 1 as container
Using the same crucible as above, 0.1 g of this calcined powder was charged into a crucible washed with ethanol and placed in a furnace using a siliconite heating element. The temperature inside the furnace was raised to 1050 ° C at 7 ° C / min., Held for 5 hours to melt the sample, and then 0.2 ° C / mi.
It was gradually cooled to room temperature at n.

When the same observation and measurement as in Example 1 were carried out, no reaction with the contents on the wall surface of the crucible was observed. On the other hand, flaky crystals of about 0.5 mm × 0.5 mm × 0.1 mm were generated in the sample, and it was confirmed that the processed product in the oxygen atmosphere was an orthorhombic single crystal. It was also confirmed that this single crystal showed a sharp diamagnetic transition at 87K and was a good quality superconductor.

Example 3 20% by weight of silicon nitride powder and 80% of silicon carbide powder
To the mixed powder consisting of, add dextrin and granulate,
It was molded by a rubber press. After this molded body was once cured, it was fired in an N ₂ atmosphere at 1400 ° C. for 10 hours, and inside a cylinder with a diameter of 22 mm and a height of 24 mm, a cylindrical crucible with a diameter of 9 mm and a depth of 14 mm was formed. A base material made of silicon nitride and silicon carbide was produced. Put the substrate in a furnace of 1300 ° C., NH ₃
And SiCl ₄ were introduced and the thickness of 1.2mm was formed on the substrate surface by the CVD method.
A crucible coated with silicon nitride was prepared.

Using this crucible, a melt of an oxide superconductor was prepared in the same manner as in Example 1, and the same observation and measurement as in Example 1 were performed. As a result, no reaction with the contents on the wall of the crucible was observed. On the other hand, flakes of about 0.8 mm × 0.8 mm × 0.1 mm were formed in the sample, and it was confirmed that the processed product in the oxygen atmosphere was an orthorhombic single crystal.
It was also confirmed that this single crystal showed a sharp diamagnetic transition at 90K and was a good quality superconductor.

Comparative Example 1 A commercially available alumina crucible was washed with ethanol, and then 1 g of the same calcined powder as in Example 1 was charged therein.
Heat treatment was applied under the same conditions as in Example 1. When the crucible was divided and examined, it was found that the crucible had turned yellow and that the reaction with the contents proceeded.

Comparative Example 2 A commercially available alumina crucible was washed with ethanol, and then 2 g of the same calcined powder as in Example 1 was charged into the crucible. After washing the surface of a commercially available TiB ₂ sintered tile having a size of 5 mm × 5 mm × 3 mm with ethanol, it was put in an alumina crucible so as not to come into contact with the wall surface, and the same calcined powder as in Example 1 was used. 3 g was added to hide the sintered tile. The crucible was placed in a furnace and heated at 1050 ° C. for 5 hours. After cooling, the crucible was destroyed and the contents were taken out, and the electrical resistance was measured. As a result, it was confirmed that the calcined powder and TiB ₂ reacted completely.

When a similar experiment was performed for ZrB ₂ instead of TiB ₂ , TiC and ZrC, or TiN and ZrN sintered body tiles, respectively,
In both cases, the calcined powder and the sintered tile completely reacted,
It was found to be unsuitable as a container for a superconducting oxide melt.

<Effects of the Invention> Since the container of the present invention is a container using silicon nitride having low reactivity with the oxide superconductor melt, when the oxide superconductor melt is used, composition control is performed with high purity. It is possible to produce a melt having high properties repeatedly and efficiently and stably as compared with the conventional method. From this melt, a single crystal of an oxide superconductor, a wire rod, a film rod, etc. can be produced.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H01B 13/00 565 D

Claims (1)

[Claims] 1. A container for an oxide superconductor melt containing, as a component, an alkaline earth metal element and a copper element, which is composed of a molded body of silicon nitride.