JP3247914B2 - Metal oxide material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal oxide material having electrical conductivity. In addition, the material of the present invention
It can be used in various fields such as superconducting sensors, electronic devices, computers, medical equipment, magnets, power lines, energy devices and voltage standards. The material of the present invention can also be used in the form of bonding and dispersion with other oxides and metals.

[0002]

2. Description of the Related Art In recent years, oxide superconductors containing copper, which have been discovered one after another, have a Tc which is much higher than the superconducting critical temperature (Tc) of a niobium or the like which has been known before. Applied research is in progress in the field. Among such oxide superconductors containing copper, YBa ₂ Cu ₃ O
_y, Bi ₂ Sr called Bi type _{2 Ca n Cu 1 + n O} y (n = 0,1,2) _{and, Tl 2 Ba 2 Ca n Cu} 1 + n O y (n = 0 , called Tl type, 1,2) are particularly well known. Among them, the Bi system is particularly active in research and development for application since it has a feature of easy processing.

[0003]

However, the Bi-based material described above has a problem in that the content of Bi, which is a heavy metal, is high, and sufficient care must be taken during production and disposal. Further, there is a problem that it is difficult to form a single phase, and it is difficult to control characteristics. Further, there is a problem that the critical current density in a magnetic field is extremely reduced, and is not suitable for use as a magnet.

[0004] Accordingly, an object of the present invention is to provide a metal oxide material which is a highly safe superconducting material having a low content of heavy metals such as Bi. Another object of the present invention is to provide a metal oxide material which can be easily made into a single phase and whose characteristics as a superconducting material can be easily controlled. It is a further object of the present invention to provide a metal oxide material which is a superconducting material with less decrease in critical current density in a magnetic field.

[0005]

The above objects are achieved by the present invention described below. That is, in the present invention, the composition formula is X _a
In the metal oxide material expressed as _{Y b Cu 3-c C c} O d, 1.5 ≦ a ≦ 2.5,3.5 ≦ b ≦
4.5, 0.2 ≦ c ≦ 1.1 and 9 ≦ d ≦ 13,
And X is one or more elements or atomic groups selected from the element group of Bi and Pb, and Y is Sr, Ba and Ln.
(Ln is Y or a lanthanoid element) The metal oxide material is one or more elements or atomic groups selected from the group of elements.

[0006]

The present inventors have conducted intensive studies on materials having a crystal structure and composition different from those of the conventional Bi system in order to solve the above-mentioned problems of the prior art, and have reached the present invention. According to the present invention, the Bi content can be reduced by several percent in terms of the composition ratio, and a material excellent in safety can be obtained. In addition, since a single-phase material was easily obtained and the critical current density in a magnetic field was larger than that of a conventional Bi-based material, a material having excellent superconductivity was obtained.

[0007]

Next, the present invention will be described in detail with reference to preferred embodiments. The metal oxide material of the present invention,
Any composition may be used as long as it has the above composition, but a particularly preferred composition is that X is Bi _1-x
When expressed as pb _x, a 0 ≦ x ≦ 0.5, and the Y when expressed as Sr _1-y M y, with M is Ba or Ln,
0 ≦ y ≦ 0.3. Also, as the crystal structure,
It is preferable that the crystal lattice is tetragonal or orthorhombic and the lattice constant (c) is 37 ° or more and 40 ° or less.

As a method for preparing the metal oxide material of the present invention, a reaction and sintering method by heating raw material powder, which is generally used for a so-called ceramic material, is possible. An example of the above method is Material Research Bu
lletin Vol. 8, p. 777 (1973), Solid State Commun
ication Vol. 17, p. 27 (1975), Zeitschrift fur
Physik B Vol. 64, p. 189 (1986), Physical Revi
ew Letters, Vol. 58, No. 9, page 908 (1987) and the like, and these methods are qualitatively known as extremely general methods at present. In particular, in order to obtain the material of the present invention, it is preferable that oxygen and carbon dioxide have an appropriate partial pressure as the synthesis atmosphere.

In particular, when the present invention is used as a substrate for a superconducting electronic device, a method of dissolving a raw material powder at a high temperature using a flux or the like and then growing a single crystal is also useful. or,
When the present invention is used for a thin film electronic element or a shielding material,
Using sputtering methods such as high-frequency sputtering or magnetron sputtering using a target containing raw materials, electron beam evaporation, MBE, other vacuum evaporation methods, cluster ion beam methods, CVD using gas as raw material, or plasma CVD. To form a thin film on a substrate or a superconducting thin film. The superconducting transition temperature of the metal oxide material of the present invention obtained by the above method varies depending on the firing conditions and composition, but the superconducting transition temperature reaches 70 K with the optimum composition. Therefore, the superconductor of the present invention can be used not only at a liquid helium temperature but also by a simple cooler. Also, the raw materials used in the present invention are all inexpensive, with low raw material costs,
It can be provided at low cost.

[0010]

Next, the present invention will be described more specifically with reference to examples and comparative examples. <Examples 1 to 10, Comparative Examples 1 to _{10> Bi 2 O 3, PbO} , SrCO 3, NiO, and Sc ₂ O ₃ and CuO as starting materials, were weighed them in an appropriate composition ratio Dry mixed.
Next, these mixtures are formed into pellets each having a diameter of 10 mm and a thickness of 1 mm under pressure, and the resulting products are each placed on an alumina boat at 700 to 900 ° C. in the air or a mixed gas of oxygen and carbon dioxide. The reaction and sintering were performed to produce metal oxide materials of the present example and comparative examples. Regarding the obtained sample, in the range of room temperature to liquid helium temperature, 4
The electrical resistivity was measured using terminals and the composition was evaluated using EPMA. Here, since the composition ratio was measured by EPMA, an error of about 20% is included in the amount of oxygen.

Table 1 shows the composition ratios and the superconducting transition temperatures Tc (K) of the examples. Table 2 shows the charged composition of the comparative example and the electrical characteristics or the superconducting transition temperature. Table 1 shows that the metal oxide materials of the present invention are all superconductors with Tc of 30K or more. In this case, particularly when the composition ratio was the following composition ratio, the superconducting transition temperature exceeded 40 K, and the superconducting properties were excellent. _{(Bi 1-x Pb x)} a Sr b Cu 3-c C c O d
(0 ≦ x ≦ 0.5) Also, from the results of the comparative examples in Table 2, materials other than the composition ratio of the present invention show no superconducting transition, or even if they show Tc of 2
It turns out that it is as low as 0K or less.

Further, FIG. 1 shows a graph of the temperature dependence of the electrical resistivity of the sample of Example 1. The superconducting transition starts at about 70K and reaches zero resistance at 60K. Therefore, it is understood that the metal oxide material obtained in Example 1 becomes superconductive at a temperature much higher than the liquid helium temperature.

FIG. 2 is a simplified diagram of the sample of Example 1 observed with an electron microscope to examine the crystal structure when viewed from a direction perpendicular to the c-axis. The crystal structure was a layered perovskite structure, and was a tetragonal crystal with a c-axis length of about 39 °. In addition, the sample of Example 1 and the so-called “Bi
_Bi 2 _Sr 2 CaCu ₂ O, which is referred to as the 2212 phase "
Comparing the critical current densities in the magnetic field of the sample No. _{8 in} the magnetic field at 50 K, the sample of the example 1 showed a value more than twice as large. Furthermore, it was also confirmed from the electron microscope observation and the X-ray diffraction experiment that Sample 1 was a clean single phase.

[0014]

TABLE 1 Composition ratio and Tc value in Examples 1 to 10

[0015]

Table 2 Composition ratios and electrical characteristics in Comparative Examples 1 to 10

<Examples 11 to 20> Bi ₂ O as a raw material
₃ , PbO, SrCO ₃ , BaCO ₃ , La ₂
O ₃ , Y ₂ O ₃ and CuO were used, weighed to an appropriate composition ratio, and dry-mixed. The obtained mixture was reacted and sintered in the same manner as in Examples 1 to 10, to prepare metal oxide materials of the present invention, and to analyze their electrical resistivity and composition. Table 3 shows the composition ratio and the superconducting transition temperature Tc (K) of the examples. Here, the composition ratio is EPMA
, The amount of oxygen contains an error of about 20%.

From Table 3, it can be seen that all the materials of the present invention have Tc = 30.
It turns out that it becomes a superconductor of K or more. In particular, when the composition ratio is the following composition ratio, the superconducting transition temperature exceeds 40K, and it can be seen that the superconductivity is excellent. _{(Bi 1-x Pb x)} a (Sr 1-y M y) b Cu 3-c C c O d (0 ≦ y ≦ 0.5, M is Ba or Ln)

[0018]

Table 3 Composition ratios and Tc values in Examples 11 to 20

[0019]

As described above, the following effects can be expected from the metal oxide material of the present invention. (1) Since a superconducting material having a low Bi content can be obtained, the safety in synthesis, use and disposal is excellent. (2) It is easy to prepare a single-phase sample, and a superconducting material with easy control of superconductivity can be obtained. (3) It is possible to suppress a decrease in critical current density in a magnetic field, which is a problem of the conventional Bi-based superconducting material,
It can be improved by a factor of two or more when compared in 1 Tesla. Thereby, application to a superconducting magnet is also possible. (4) The superconducting transition temperature is as high as 70 K, so that it can be used not only in liquid helium but also with an easy cooling device.

[0020]

[Brief description of the drawings]

FIG. 1 is a graph showing the temperature dependence of the electrical resistivity of Bi _1.5 Pb _0.5 Sr ₄ Cu ₂ CO ₁₁ in Example 1.

FIG. 2 is a simplified diagram of Bi _1.5 Pb _0.5 Sr ₄ Cu ₂ CO ₁₁ of Example 1 as viewed from a direction perpendicular to the c-axis as a result of examining a crystal structure by observation with an electron microscope.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-64-3009 (JP, A) JP-A-3-218925 (JP, A) JP-A-1-122923 (JP, A) (58) Survey Field (Int. Cl. ⁷ , DB name) C01G 1/00 CA (STN) JICST file (JOIS) REGISTRY (STN) WPI (DIALOG)

Claims (3)

(57) [Claims] 1. A composition formula _{X a Y b Cu 3-c} C c
In a metal oxide material represented by _Od , 1.5 ≦ a
≦ 2.5, 3.5 ≦ b ≦ 4.5, 0.2 ≦ c ≦ 1.1 and 9 ≦ d ≦ 13, and X is at least one element selected from the group consisting of Bi and Pb. A metal oxide material, wherein the metal oxide material is an element or an atomic group, and Y is one or more elements or atomic groups selected from an element group of Sr, Ba, and Ln (Ln is Y or a lanthanoid element). 2. When X is represented as Bi _1-x Pb _x , 0 ≦
an x ≦ 0.5, and when the Y was expressed as Sr _1-y M y, M is at Ba or Ln, metal oxide material according to claim 1 which is 0 ≦ y ≦ 0.3. 3. The metal oxide material according to claim 1, wherein the crystal lattice is tetragonal or orthorhombic, and the lattice constant (c) is 37 ° or more and 40 ° or less.