JP3629529B2 - Sulfide spinel superconductor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The invention of this application relates to a sulfide spinel superconducting material. More specifically, the invention of this application is a novel superconducting material, and is expected to be used in various fields such as superconducting magnets, Josephson elements, magnetic shields, and low-temperature switch elements, low-temperature pressure elements. Spinel superconducting material.
[0002]
[Prior art]
The superconducting phenomenon is expected to be applied in a wide range of fields from high electric fields such as superconducting magnets and superconducting power storage, to cryoelectronic elements such as Josephson elements and SQUIDs, and further to magnetic shields. So far, metallic superconducting materials such as Nb—Ti, Nb ₃ Sn, and V ₃ Ge have been used for applications using liquid helium. In recent years, YBa ₂ Cu ₃ O having a Cu—O ₂ surface has been used. _Further studies on the practical application of ceramic-based copper oxide superconducting materials such as _{7 +} δ (Y—Ba—Cu—O system) and Bi ₂ Sr ₂ CaCu ₂ O 10 ₊ δ (Bi system) are underway. Yes. In particular, the copper oxide-based superconducting material has been studied vigorously because it exhibits superconducting properties at high temperatures and can control the superconducting temperature by doping carriers by element substitution or the like.
[0003]
[Problems to be solved by the invention]
However, with regard to sulfide-based materials, Y-Ba-Cu-S-based superconducting materials having the same structure as copper oxide-based superconducting materials and oxygen sites replaced with sulfur have been reported so far. However, its superconducting properties are not always satisfactory when compared with copper oxide superconducting materials.
[0004]
On the other hand, spinel-based materials are the most studied materials among magnetic materials, and their existence has been confirmed in a large number of elemental compositions. MFe ₂ O ₄ (M is a divalent metal) and the like are known as a ferrite magnet having a spinel structure in practice.
[0005]
However, very few spinel materials exhibiting superconducting properties are known, such as LiTi ₂ O ₄ , CuRh ₂ S ₄ , and CuRh ₂ Se ₄ . In addition, there is no example in which superconducting characteristics appear due to carrier injection or the like.
[0006]
The invention of this application has been made in view of the circumstances as described above, and provides a completely new sulfide spinel-based superconducting material different from the conventional metal-based and copper oxide-based materials. The aim is to open up further possibilities of materials.
[0007]
[Means for Solving the Problems]
In order to solve the above-described problems, the invention of this application has a composition formula Cu _1-x Zn _x Ir ₂ S ₄ (0.25 ≦ x ≦ 0.8 (provided that 0.25 ≦ x <0.3, and, except for 0.5 <x ≦ 0.8)) is indicated by, providing a sulfide spinel superconducting material which is a sulphide spinel material having superconducting properties.
[0009]
Hereinafter, the sulfide spinel superconducting material of the invention of this application will be described in more detail.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The sulfide spinel superconducting material of the invention of this application is represented by the above composition formula.
[0011]
CuIr ₂ S ₄ is a sulfide spinel material exhibiting a metal-insulator transition. The inventors of the invention of this application pay attention to the characteristic of the metal-insulator transition, control the number of carriers by element substitution, and in the process of investigating the change in physical properties, the sulfide spinel system of the invention of this application I found a superconducting material.
[0012]
That is, CuIr ₂ S ₄ exhibits a metal-insulator transition near 230K, with the high temperature side being a metal and the low temperature side being an insulator. In the insulator phase on the low temperature side, Cu is monovalent. Sulfide spinel substance represented by the 1 composition formula monovalent obtain a Cu site when substituted with the divalent _{Zn Cu 1-x Zn x Ir} 2 S 4 (0.25 ≦ x ≦ 0.8) , the It has a superconducting characteristic that causes a superconducting transition and exhibits a Meissner effect at the superconducting transition temperature Tc.
[0013]
Thus, the sulfide spinel superconducting material of the invention of this application exhibits superconducting properties by doping carriers by element substitution. Therefore, it has characteristics common to copper oxide superconducting materials that have been intensively studied.
[0014]
Further, the sulfide spinel superconducting material of the invention of this application changes from a relatively large resistance value of about 5 digits to a superconducting state, and the superconducting state is broken by a small pressure change of about 100 bar or less, for example. The resistance value changes to a semiconductor value of up to about 7 digits. Therefore, the sulfide spinel superconducting material of the invention of this application has a possibility of being applied to a switch element, a pressure sensor and the like at a low temperature.
[0015]
According to previous studies, the superconducting properties of the sulfide spinel superconducting material of the invention of this application are considered to appear in the insulator phase on the low temperature side, and are involved in the metal-insulator transition. It is speculated that there is a possibility.
[0016]
Therefore, the present invention will be described in more detail with reference to the following examples.
[0017]
【Example】
<Example 1>
In order to obtain a stoichiometric composition of Cu _0.7 Zn _0.3 Ir ₂ S ₄ in which Cu, Zn, Ir, and S powder are used as starting materials and 30% of Cu is replaced with Zn, each powder is obtained. Was weighed. These powders were vacuum sealed inside the quartz tube. The quartz tube was subjected to hydrofluoric acid treatment for the purpose of preventing reaction with starting materials and products, and then baked at about 1000 K to remove impurities.
[0018]
And the quartz tube was heated to 850K over about 2 days, and the raw materials were made to react.
[0019]
The obtained powder sample is confirmed to be a single phase of the spinel material from the result of the X-ray powder diffraction shown in FIG. Pellets were produced from this powder sample using a press, and the temperature dependence of the electrical resistance of the sintered body that was heat-treated at 850 K for 2 days and the magnetic susceptibility of the powder sample were examined. The results are shown in FIG. 2 and FIG. In FIG. C. Is an abbreviation for field cooling, and shows the results of measurement by lowering the temperature while applying a magnetic field. F. C. Is an abbreviation for zero field cooling, and shows the result of measurement by applying a magnetic field after lowering to a minimum temperature without applying a magnetic field.
[0020]
From the electric resistance curve shown in FIG. 2, the superconducting transition temperature Tc is about 3.0 K. From the magnetic susceptibility curve of FIG. 3, the Meissner effect is the magnetic susceptibility at the superconducting transition temperature Tc (= 3.0 K). Observed by measurement. From this, it is recognized that the sulfide spinel material represented by the composition formula Cu _0.7 Zn _0.3 Ir ₂ S ₄ is a superconducting material.
[0021]
Further, as confirmed from the electric resistance curve of FIG. 2, the resistance value is changed from a relatively large resistance value of about 5 digits to the superconducting state. Moreover, the superconducting state is broken by applying a minute pressure of about 100 bar, and the resistance value changes to a semiconductor value of up to about 7 digits.
<Example 2>
Samples were prepared in the same manner as described above with the substitution ratio of Cu with Zn changed, and the Zn concentration dependence of the superconducting transition temperature Tc and the metal-insulator transition temperature T _M-I was examined. The result is shown in FIG. It was confirmed that a superconducting material was obtained in the range of 0.25 ≦ x ≦ 0.8 in the composition formula Cu _1-x Zn _x Ir ₂ S ₄ .
[0022]
5 and 6 show changes in the temperature-resistance relationship when x is 0.6 to 0.9, but superconducting characteristics are obtained when x = 0.85 and x = 0.9. It has been shown that superconducting properties can be obtained up to x = 0.8.
[0023]
Of course, the invention of this application is not limited to the above embodiments. It goes without saying that various aspects are possible with respect to details such as the substitution ratio of Cu with Zn and the method of manufacturing the superconducting material.
[0024]
【The invention's effect】
As described above in detail, the invention of this application provides a novel superconducting material based on sulfide spinel. This sulfide spinel-based conductive material develops superconducting properties by doping carriers by element substitution, and therefore has the same characteristics as copper oxide-based superconductive materials. Superconducting magnets, Josephson Use in various fields such as elements, magnetic shields, low-temperature switch elements, and low-temperature pressure elements is expected.
[Brief description of the drawings]
FIG. 1 is an X-ray powder line diagram of a sulfide spinel material represented by a composition formula Cu _0.7 Zn _0.3 Ir ₂ S ₄ .
FIG. 2 is a graph showing the temperature dependence of the electrical resistance of a sulfide spinel material represented by the composition formula Cu _0.7 Zn _0.3 Ir ₂ S ₄ .
FIG. 3 is a graph showing the temperature dependence of the magnetic susceptibility of a sulfide spinel material represented by the composition formula Cu _0.7 Zn _0.3 Ir ₂ S ₄ .
FIG. 4 is a correlation diagram showing the Zn concentration dependence of the superconducting transition temperature Tc and the metal-insulator transition temperature T _M-I of a sulfide spinel material represented by the composition formula Cu _1-x Zn _x Ir ₂ S ₄ . It is.
FIG. 5 is a graph showing the temperature dependence of the electrical resistance of a sulfide spinel material having a composition formula of Cu _1-x Z _nx Ir ₂ S ₄ (X = 0.6 to 0.85).
FIG. 6 is a graph showing the temperature dependence of the electrical resistance of a sulfide spinel material having the composition formula Cu _1-x Z _nx Ir ₂ S ₄ (X = 0.6 to 0.9).

Claims (1)

Composition formula Cu _1-x Zn _x Ir ₂ S ₄ (0.25 ≦ x ≦ 0.8 (except 0.25 ≦ x <0.3 and 0.5 <x ≦ 0.8) ) A sulfide spinel superconducting material characterized by being a sulfide spinel material having superconducting properties.

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