JPH0710735B2 - High temperature thallium oxide superconductor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high temperature thallium-based oxide superconductor having a novel basic crystal structure. More specifically, the present invention relates to a novel thallium-based oxide superconductor that exhibits a stable critical temperature even though it does not contain calcium in its constituent elements.

[0002]

2. Description of the Related Art In the cryogenic region, a substance having a property of zero electric resistance at a predetermined critical point, that is, a superconductor, is used in the energy field for power generators, power transmission lines, power storage devices, etc. , Magnetic levitation trains in the transportation field, electromagnetic propulsion ships, magnetic levitation cars, etc., high-speed LSIs in the information and communication fields
It has been applied to a wide range of fields such as magnetic separation, ion implantation, magnetic bearings, flywheels and bearings in material processing fields such as wiring, JJ computers, SQUIDs, and submarine cables, and some of them have already been realized.

The materials for superconductors known so far are:
It is roughly divided into four types: alloy-based, intermetallic compound-based, oxide-based, and organic-based, but in order to realize superconductivity at higher temperatures, research on oxide-based superconductors has recently been actively conducted. I'm starting to be seen.

Of these oxides, the critical temperature of the thallium-based oxide superconductor was initially 20 K or less, and then Tl-Ba having a critical temperature of 85 K.
A -Cu-O-based oxide superconductor has been found, and at present, a superconductor having a critical temperature of 131K, which is the highest critical temperature among oxide superconductors, has been reported.

By the way, a thallium-based oxide superconductor having a high critical temperature exceeding the temperature of liquid nitrogen is [Cu
It has a basic crystal structure including two or more O ₂ ] layers,
In order to make the uO ₂ ] layer into two layers, as an alkaline earth metal that generally constitutes a superconductor, in addition to elements having a large ionic radius such as barium element and strontium element,
It was considered necessary to contain a calcium element having a small ionic radius, and it was unavoidable that its range of use was limited in terms of composition.

[0006] After that, a thallium-based oxide superconductor containing no calcium was also proposed. However, since this one does not have two or more [CuO ₂ ] layers, the critical temperature is highly dependent on the preparation conditions, and oxygen superconductivity is high. It is known that the critical temperature fluctuates greatly depending on the content rate and that a stable critical temperature cannot be obtained ["Phisica, Volume C170,
P. 350 (1990)].

[0007]

DISCLOSURE OF THE INVENTION The present invention overcomes the drawbacks of conventional superconductors made of calcium-free thallium-based oxides and is stable and has a novel thallium-based oxide superconductor. It was designed to provide the body.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to develop a novel thallium-based oxide superconductor containing no calcium. Surprisingly, by introducing yttrium and sodium, which have an ionic radius almost equal to that of calcium, instead of the calcium constituting the body, [CuO
_[2 ] The present invention has been completed based on this finding that it forms a basic crystal structure including two planes and exhibits excellent stability at critical temperature.

That is, in the present invention, thallium, copper, barium, yttrium and sodium are added in a stoichiometric ratio of 1:
It is contained in the ratio of 2: 2: 0.5: 0.5, and [CuO
₂ ] Layer A high-temperature superconductor made of a thallium-based oxide having a basic crystal structure including two layers is provided.

This high-temperature thallium-based oxide superconductor is prepared according to the method usually used in the production of thallium-based oxide superconductors, for example, cupric oxide, barium carbonate, yttrium oxide and sodium carbonate, copper, barium,
After yttrium and sodium are mixed so that the stoichiometric ratio is the above-mentioned ratio and calcined at a temperature of about 700 to 950 ° C., a required amount of thallium oxide is added thereto,
Further, it can be manufactured by re-baking at the above temperature.

Thus, it has a basic crystal structure including two [CuO ₂ ] layers and the stoichiometric ratio of thallium, copper, barium, yttrium and sodium is 1: 2: 2 :.
A 0.5: 0.5 high temperature thallium-based oxide superconductor is obtained. The critical temperature of this product is about 90K.

By cooling the thallium-based oxide superconductor of the present invention to a temperature below the critical temperature, it becomes a superconducting state and exhibits normal superconductor characteristics such as the Meissner effect and zero resistance.

[0013]

INDUSTRIAL APPLICABILITY The high temperature thallium-based oxide superconductor of the present invention does not contain a calcium element, although it does not contain [C
Since it has a crystal structure including two layers of uO ₂ ], it exhibits a stable critical temperature above the liquid nitrogen temperature.

[0014]

EXAMPLES Next, the present invention will be described in more detail by way of examples.

Example As the raw materials, cupric oxide, barium carbonate, yttrium oxide and sodium carbonate were used, and the stoichiometric ratio of copper, barium, yttrium and sodium was 2: 2: 0.5: 0.
After blending so as to be 5, the primary calcination was performed at 950 ° C. Then, thallium oxide is added to and mixed with thallium, copper, barium, yttrium, and sodium in a stoichiometric ratio of 1: 2: 2: 0.5: 0.5, and the firing temperature is 850 ° C. The temperature was changed from 875 ° C to 900 ° C and the secondary firing was performed for 15 minutes.
It was found that the one fired for minutes showed superconductivity.

Next, for the sample primarily fired at 950 ° C., the secondary firing temperature was 850 ° C., the firing time was 15 minutes,
When secondary firing was carried out for 20 minutes, 30 minutes and 40 minutes, the ones fired for 30 minutes and 40 minutes exhibited a Meissner effect at a temperature lower than 90K, and a critical temperature of 90K was obtained. Further, when the secondary firing time was 15 minutes and 20 minutes, an uncertain Meissner effect was recognized at around 70K.

The X-ray diffraction pattern of the obtained sample is shown in FIG. From this X-ray diffraction pattern, the crystal structure of the superconductor is tetragonal and the lattice constants are a = 3.88Å, c = 12.
It became clear that it was 55Å. c-axis length is Tl
Compared with the length of the c-axis of the BaSrCaCuOx-based "1212" structure, it is 0.25Å longer, but the X is almost the same.
It was found to show a line diffraction pattern.

[Brief description of drawings]

1 is a high-temperature thallium-based oxide superconductor of the present invention 1
The X-ray-diffraction pattern figure of an example.

Claims (1)

[Claims] 1. Thallium, copper, barium, yttrium and sodium are added in a stoichiometric ratio of 1: 2: 2: 0.5: 0.
A high-temperature superconductor containing a thallium-based oxide having a basic crystal structure, which is contained at a ratio of 5 and includes two [CuO ₂ ] layers.