CS268564B1 - The superconductor preparation process and a critical temperature above 30 K - Google Patents

Abstract

The solution consists in preparing an alloy of the general formula I /Re-D/(x)M(l-x) /1/ where Re means an element from the rare earth group, or an element of subgroup 3a of the periodic table of elements, D means an element of subgroup 2a of the periodic table of elements, M means a metal and x is a value in the range of 10-4 and 5.10-I, with subsequent oxidation in an oxygen-containing atmosphere, preferably in an oxygen atmosphere, at a temperature of preferential oxidation of the elements Re and D, preferably at a temperature of up to 800 K, for the period of formation of an oxide layer with a concentration of the elements Re and D corresponding to the superconducting phase. The critical temperature of the superconductor varies from 30 K to 93 K depending on the rare earth and the method of heat treatment. These superconductors can be used in technical practice where superconductors with a transition temperature below 30 K are required.

Description

The invention relates to a process for the preparation of a superconductor with a critical temperature above 30 K.

After 1906, they used in technical practice mostly niobium-based alloys, which showed superconductivity with a maximum transition temperature to the nonsal state T _c 23 K. Even in laboratory conditions, materials with a critical temperature higher than 23.6 K were not prepared until 1906 (critical temperature of the superconducting alloy Nb (Ge).

After 1906 and in the European literature, reports of superconducting materials with critical temperatures above 3θ K were discovered (e.g. G. Bednarz, KA, Muller, J, Phys, B64 (1906) 109; J. Cava et al., Phys. Rev. Lett. 50 (19-7) 40Θ; CW Chu et al., Phys. Rev. Lett. 58 (1987) 405). These are the so-called superconducting ceramics based on rare earth oxides, barium and media. The method of preparation consists in melting rare earth oxides, barium and media after their previous pressing and subsequent heat treatment by annealing in air or oxygen atmosphere. The main disadvantages of this method are the high proportion of expensive raw materials (up to 50%) and the resulting product and so far cannot be used in technical practice, even the high critical temperature (above the boiling point of liquid nitrogen) is very attractive from technical point of view.

These disadvantages are solved by a method for preparing a conductor with a critical temperature above 30 K according to the invention, the essence of which consists in that ea forms an alloy of the general pattern and I ^{/ Re} - ^{D /} x “lx / 1 / where Re represents an element from the group of rare earths, 3a element or subgroup of the periodic table D is the element 2a subgroup periodiokej page table elements, M is a metal and x is a value in the range of 10 "^ to 5 · 10 ^- · ^. The alloy is oxidized in an oxygen-containing atmosphere, preferably in an oxygen atmosphere, at a preferred oxidation temperature of the elements Re and D, preferably at a temperature of up to 800 K for the formation of an oxide layer with a concentration of elements Re, D corresponding to the superconducting phase.

The atomic ratio between the rare earth element or element 3a of the subgroup and the element 2a of the subgroup of the periodic table is chosen in an indirect ratio of their diffusion coefficients in the metal matrix so that a structure responsible for superconductivity is formed on the surface during heat treatment. In most cases, it is a perovite structure, the proportion of rare earth or subgroup element 3a and subgroup element 2a in the alloy being in the range of 0.01% to 50%, depending on the desired thickness of the superconducting layer. From the point of view of costs and technical parameters, the most suitable is a $ 5 total share of these two elements.

The alloy thus prepared is allowed to oxidize in an oxygen-containing atmosphere preferably in spectral pure oxygen during the heat preferential oxidation of a rare earth element or subgroup element 3a and subgroup element 2a of the Periodic Table for the formation of an oxide layer with a concentration corresponding to the superconducting phase.

The main advantages of the preparation process according to the invention are:

- it is possible to prepare materials suitable for technical practice from the alloy by shaping

- during production, more than 45% of expensive materials are saved with unchanged technical parameters of the superconductor.

The subject of the invention is demonstrated by means of exemplary embodiments.

Example 1

Preparation of Sm-Ca-CuO 2 superconductor a) Preparation of alloy:

weight 3 ar. Sm Samarium 99.9% 2 % at. Ca Calcium 99.9% 95 % at. Cu Meó 99.99%

, CS 268564 Bl

The alloy is formed by melting in an inert atmosphere (spectral pure argon) at a pressure of 0.0.1 ml and a temperature of 14. 10 DEG C. for 5 minutes. by means of strodorroquon heating. This is followed by cooling to room temperature with a cooling rate of 1 K / s.

b) Preparation of the superconducting sample:

a block of dimensions 0.4x1, 2x10 nuP is cut from the alloy, for example, using an electric spark cutter, which is polished (surface roughness is less than 0.8 ČSN 014450), washed in pure gasoline and rinsed in ethyl alcohol. It is then annealed in air at 600 K for 10 minutes and allowed to cool.

The measured critical temperature is 39 K.

Example 2

Preparation of superconductor Sm-Ba-CuO ^ ·

a) Alloy preparation:

weight J% Sm Samarium 99.9%% Ba Barium 99.9%.

% Cu Med 99.9% the same procedure as in case la).

b) Preparation of the superconducting sample:

a prism 0.4x1.2x10 mm2 is cut from the alloy. After polishing (roughness less than 0.8 according to ČSN 014450), it is cleaned with pure gasoline and washed with ethyl alcohol. It is then annealed in air for 30 minutes. and in an oxygen atmosphere for a period of JO min. in both cases at a heat of 600 K and allowed to cool. The measured critical temperature is 6J K.

Example J

Preparation of the Y-Ba-CuO 2 superconductor

a) Alloy preparation:

weight J % AND Yttrium 99.9% 2 % Ba Barium • 99.9% 95 % Cu Copper 99.99%

The procedure is as in Example 1a).

b) Preparation of the superconducting sample:

Proceed as in Example 2b). The measured critical temperature is 87 K.

Example 4

Preparation of Gd-Ba-CuO superconductor?

a) Alloy preparation:

weight 5 $ Gd Gadolinium ♦ Ba Barium, where the molar ratio Gd: Ba = 1: 2 and the purity of materials Gd, Ba is 99.9%

The next procedure is as in Example la).

b) Preparation of the superconducting sample:

The procedure is as in Example 1b), the annealing temperature being 650 K and the annealing time being 60 min.

The measured critical temperature is 90 K. '

CS 268564 Bl

Example 5

Prepares the superconductor »Eu-Ba-CuOy

a) Preparation of the alloy:

weight 5% Eu Europium + Ba Barium where the molar ratio Eu: Ba = 1: 2 and the purity of the materials Eu, Ba is 99.9%, 95% Cu Copper purity 99.99%.

The further procedure is as in Example 1a).

b) Preparation of the superconducting sample:

The procedure is the same as in Example 1b). The measured critical temperature is 93 K.

Alloys can be prepared in the shape of a prism, cylinder, grit, cable, etc.

Claims (4)

OBJECT OF THE INVENTION A process for the preparation of a superconductor with a critical temperature above 30 K, characterized in that the alloy of general formula I / Re-D / _X Μ _1χ / 1 / wherein Re represents an element from the group of rare earths, or element 3a of the subgroup of the periodic table of elements, D represents element 2a of the subgroup of the periodic table of elements, M is a metal and x is a value in the range of 10 ^{° 4} to 5 · 1θ. , D corresponding to the superconducting phase. 2. The preparation method according to item 1, characterized in that the metal M is honey. 3. The preparation method according to items 1 and 2, characterized in that the atomic ratio between the elements Re: D is in an indirect ratio of their diffusion coefficients in the metal M leading to the formation of a superconducting compound, especially perovskite, and the value x is up to 0.05. 4. A process according to claims 1 to 3, characterized in that the alloy is oxidized in an acidic atmosphere.