Superconducting material

Abstract

A superconductive material is disclosed which has the following composition:(R.sub.1-x Ca.sub.x)(Ba.sub.1-y La.sub.y).sub.2 Cu.sub.4 O.sub.8wherein R is at least one element selected from Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, x is a number in the range of 0-0.3 and y is a number in the range of 0.001-0.3 with the proviso that y is not greater than 0.2 when x is not 0.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a novel superconducting material having an RBa.sub.2 Cu.sub.4 O.sub.8 (R=a rare earth element) crystallographic phase.

2. Description of the Prior Art

A superconducting material having a composition RBa.sub.2 Cu.sub.3 O.sub.7 (R=a rare earth element) is known to have a high superconducting transition temperature Tc higher than the boiling point (77K) of liquid nitrogen (Appl. Phys. Lett. 51, 57(1987)). The oxygen content of this material varies according to conditions such as, temperature and oxygen partial pressure, under which the material has been sintered, so that the crystal phase thereof shifts between the tetragonal and orthorhombic systems. As a consequence of this phase change, Tc of the superconducting material considerably varies in the range of from 90K to 0K (insulation). Thus, it would be possible to control the Tc of the superconducting material to a desired point by controlling the oxygen content thereof. However, the superconducting material with a controlled Tc cannot be suitably used for the preparation of superconductor articles. Namely, when such a superconducting material is used as a raw material for the preparation of, for example, a wiring rod by a silver-sheathed wiring method in which a silver pipe filled with powder of the superconducting material is subjected to cold drawing, followed by sintering at 800.degree.-900.degree. C., the superconductivity deteriorates due to loss of its oxygen during the sintering stage. It is, therefore, extremely difficult to obtain a superconductor having a desired Tc using RBa.sub.2 Cu.sub.3 O.sub.7.

There is proposed a high Tc superconducting material composed of RBa.sub.2 Cu.sub.4 O.sub.8 (R=Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm) and having a three-layered pervoskite crystal structure with double CuO one-dimensional chains (Phys. Rev. B. 39, 7347(1989)). This material does not encounter increase or decrease in its oxygen content at temperatures up to about 850.degree. C. and, thus, is stable in such an environment. However, no means have been proposed for controlling Tc to a desired point. Another problem of this superconducting material is raised when used in actual industrial applications and relates to the fact that it is necessary to use, as a raw material for the production thereof, Ba(NO.sub.3).sub.2 which is expensive and poisonous.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide novel, stable superconducting materials having superconducting transition temperatures Tc controlled in a wide range.

Another object of the present invention is to provide a superconducting material having Tc higher than the boiling point of liquid nitrogen, especially higher than about 80K.

It is a further object of the present invention to provide a novel superconducting material having a YBa.sub.2 Cu.sub.4 O.sub.8 crystallographic phase.

It is yet a further object of the present invention to provide a superconducting material of the above-mentioned type which has a reduced content of Ba.

It is yet a further object of the present invention to provide a superconducting material of the above-mentioned type which permits the use of relatively inexpensive BaCO.sub.3 as a raw material for the production thereof.

In accomplishing the foregoing objects, there is provided in accordance with the present invention a superconductive material having the following composition:

(R.sub.1-x Ca.sub.x)(Ba.sub.1-y La.sub.y).sub.2 Cu.sub.4 O.sub.8 wherein R is at least one element selected from the group consisting of for Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, x is a number in the range of 0-0.3 and y is a number in the range of 0.001-0.3 with the proviso that y is not greater than 0.2 when x is not 0.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will become apparent from the detailed description of the invention which follows, when considered in light of the accompanying drawings, in which:

FIG. 1 is a schematic illustration of the crystal structure of RBa.sub.2 Cu.sub.4 O.sub.8 which is the main component of the superconducting material of the present invention;

FIG. 2 is a schematic illustration of the crystal structure of RBa.sub.2 Cu.sub.3 O.sub.7 ;

FIG. 3 is a powder X-ray diffraction pattern of Y(Ba.sub.0.9 La.sub.0.1).sub.2 Cu.sub.4 O.sub.8 obtained in Example 1;

FIG. 4 is a graph showing temperature-resistivity characteristics of Y(Ba.sub.1-y La.sub.y).sub.2 Cu.sub.4 O.sub.8 obtained in Example 1;

FIG. 5 is a graph showing the results of thermogravimetric analysis of Y(Ba.sub.1-y La.sub.y).sub.2 Cu.sub.4 O.sub.8 obtained in Example 1 and of YBa.sub.2 Cu.sub.3 O.sub.7 ;

FIG. 6 is a powder X-ray diffraction pattern of Ho(Ba.sub.0.9 La.sub.0.1).sub.2 Cu.sub.4 O.sub.8 obtained in Example 2;

FIG. 7 is a graph showing temperature-resistivity characteristics of Ho(Ba.sub.1-y La.sub.y).sub.2 Cu.sub.4 O.sub.8 obtained in Example 2;

FIG. 8 is a graph showing the results of thermogravimetric analysis of Ho(Ba.sub.1-y La.sub.y).sub.2 Cu.sub.4 O.sub.8 obtained in Example 2 and of YBa.sub.2 Cu.sub.3 O.sub.7 ;

FIG. 9 shows powder X-ray diffraction patterns of YBa.sub.2 Cu.sub.4 O.sub.8 and (Y.sub.0.9 Ca.sub.0.1)(Ba.sub.0.9 La.sub.0.1).sub.2 Cu.sub.4 O.sub.8 obtained in Example 5;

FIG. 10 is a graph showing temperature-resistivity characteristics of YBa.sub.2 Cu.sub.4 O.sub.8 and (Y.sub.0.9 Ca.sub.0.1)(Ba.sub.0.9 La.sub.0.1).sub.2 Cu.sub.4 O.sub.8 obtained in Example 5;

FIG. 11 is a graph showing the results of measurement of alternating-current magnetic susceptibility of YBa.sub.2 Cu.sub.4 O.sub.8 and (Y.sub.0.9 Ca.sub.0.1)(Ba.sub.0.9 La.sub.0.1).sub.2 Cu.sub.4 O.sub.8 obtained in Example 5;

FIG. 12 is a graph showing the results of thermogravimetric analysis of YBa.sub.2 Cu.sub.4 O.sub.8 and (Y.sub.0.9 Ca.sub.0.1)(Ba.sub.0.9 La.sub.0.1).sub.2 Cu.sub.4 O.sub.8 obtained in Example 5;

FIG. 13 shows powder X-ray diffraction patterns of YBa.sub.2 Cu.sub.4 O.sub.8 and (Y.sub.0.9 Ca.sub.0.1)(Ba.sub.0.9 La.sub.0.1).sub.2 Cu.sub.4 O.sub.8 obtained in Example 6;

FIG. 14 is a graph showing temperature-resistivity characteristics of YBa.sub.2 Cu.sub.4 O.sub.8 and (Y.sub.0.9 Ca.sub.0.1)(Ba.sub.0.9 La.sub.0.1).sub.2 Cu.sub.4 O.sub.8 obtained in Example 6;

FIG. 15 is a graph showing the results of measurement of alternating-current magnetic susceptibility of YBa.sub.2 Cu.sub.4 O.sub.8 and (Y.sub.0.9 Ca.sub.0.1)(Ba.sub.0.9 La.sub.0.1).sub.2 Cu.sub.4 O.sub.8 obtained in Example 6;

FIG. 16 is a graph showing the results of thermogravimetric analysis of YBa.sub.2 Cu.sub.4 O.sub.8 and (Y.sub.0.9 Ca.sub.0.1)(Ba.sub.0.9 La.sub.0.1).sub.2 Cu.sub.4 O.sub.8 obtained in Example 6;

DETAILED DESCRIPTION OF THE INVENTION

The oxide superconductor according to the present invention has a composition expressed by the following formula (I):

(R.sub.1-x Ca.sub.x)(Ba.sub.1-y La.sub.y).sub.2 Cu.sub.4 O.sub.8(I) wherein R is at least one element selected from the group consisting of for Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, x is a number in the range of 0-0.3 and y is a number in the range of 0.001-0.3 with the proviso that y is not greater than 0.2 when x is not 0.

When x is 0 in the above formula (I), the composition is expressed by the following formula (II):

R(Ba.sub.1-y La.sub.y).sub.2 Cu.sub.4 O.sub.8 (II) In this case, y is 0.001-0.3. This composition is that obtained by substituting La for a portion of Ba of RBa.sub.2 Cu.sub.4 O.sub.8. FIG. 1 illustrates the basic structure of RBa.sub.2 Cu.sub.4 O.sub.8 which is the main component of the superconducting material of the present invention. For the comparison purpose, the crystal structure of RBa.sub.2 Cu.sub.3 O.sub.7 is shown in FIG. 2. In these Figures, the reference numeral 1 designates a rare earth element R, 2 designates Ba, 3 designates Cu and 4 designates O positioned in the intersections. The superconducting material of the formula (II) has a crystal structure in which the single CuO chain of the structure shown in FIG. 2 is substituted by a double CuO chain as shown in FIG. 1 and in which a portion of Ba in FIG. 1 is replaced by La.

The superconducting transition temperature Tc of the material of the formula (II) varies with the amount of La. Thus, by controlling the amount of La substituted for Ba, Tc may be controlled at will. Further, this material is stable at temperatures up to about 850.degree. C. Moreover, the substitution of La for Ba has a merit that the amount of the poisonous Ba raw material compound may be decreased. The superconducting material of the formula (II) is, therefore, well suited for actual industrial applications such as in formation of highly condensed wiring rods by the previously described silversheathed wiring method.

When x is not 0 in the composition of the formula (I), y is in the range of 0.001-0.2. In this case, x is preferably in the range of 0.001-0.3 and R is preferably selected from Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm and mixtures thereof.

The superconducting material of the formula (I) in which x is not 0 has a crystal structure in which a portion of each of R and Ba in FIG. 1 is replaced by Ca and La, respectively. This superconducting material generally has Tc of higher than 80K. Additionally, the material is stable at temperatures up to around 850.degree. C. and advantageously contains a reduced amount of Ba. Further, the material allows the use of inexpensive BaCO.sub.3 as a raw material for the preparation thereof. The thermal stability of the superconducting material also permits the use of a binder for forming a high density shaped article, because the binder may be completely removed during heat treatment at a high temperature of up to about 850.degree. C. This is advantageous because such an increase of density can improve the superconducting current density.

Because of these advantages, the superconducting material according to the present invention is suitably used on an industrial scale for the production of various superconductors and other applications such as wirings for low temperature electrical instruments and magnetic shielding materials.

The following examples will further illustrate the present invention.

EXAMPLE 1

Metal oxide compositions having the formula Y(Ba.sub.1-y La.sub.y).sub.2 Cu.sub.4 O.sub.8 wherein y=0, 0.01, 0.05, 0.1, 0.2, 0.3 and 0.4 were prepared. Thus, quantities of Y.sub.2 O.sub.3 powder, Ba(NO.sub.3).sub.2 powder, CuO powder and La.sub.2 O.sub.3 were mixed and the mixture was calcined at 850.degree. C. in an oxygen atmosphere for 24 hours. The calcined mass was ground and formed into a rectangular block, followed by heating at 800.degree. C. in an oxygen atomosphere for 5 hours. The resulting pre-sintered sample was then heat-treated in an mixed gas atmosphere of 80% argon and 20% oxygen at a pressure of 1,000 kg/cm.sup.2. The heat treatment was performed by first heating the sample to 960.degree. C. with a heating rate of 200.degree. C./hour, then maintaining at 960.degree. C. for 6 hours, increasing the temperature to 1,050.degree. C. with a heating rate of 200.degree. C./hour and finally maintaining at 1,050.degree. C. for 6 hours. Thereafter, the sample was cooled to 300.degree. C. with a cooling rate of 200.degree. C./hour. The pressure was then released and the treated sample was allowed to stand in air, ground, shaped and sintered again at 800.degree. C. in an oxygen atmosphere to obtain a sintered product.

This product was then subjected to powder X-ray diffraction analysis and thermogravimetric analysis and was further tested for temperature dependence of the resistivity thereof. The results are summarized in Table 1, in which Tc.sup.onset refers to an onset Tc which is a temperature at which the material starts transition from the normal conductive state to superconductive state and Tc.sup.R=0 refers to perfect Tc which is a temperature at which the material has completely become superconductive state (the resistivity has become 0). The powder X-ray diffraction pattern of the product in the case of y=0.1 is shown in FIG. 3 while temperature dependency of resistivity and change in weight in thermogravimetry of the products (y=0 and y=0.1) are shown in FIGS. 4 and 5, respectively.

TABLE 1______________________________________Test Crystallographic Phase Tc.sup.onset Tc.sup.R = 0No. y by X-Ray Diffraction (K) (K)______________________________________ 1* 0 YBa.sub.2 Cu.sub.4 O.sub.8 single phase 80 752 0.01 YBa.sub.2 Cu.sub.4 O.sub.8 single phase 78 743 0.05 YBa.sub.2 Cu.sub.4 O.sub.8 single phase 71 664 0.10 YBa.sub.2 Cu.sub.4 O.sub.8 single phase 58 555 0.20 YBa.sub.2 Cu.sub.4 O.sub.8 single phase 40 376 0.30 YBa.sub.2 Cu.sub.4 O.sub.8 single phase 19 15 7* 0.40 YBa.sub.2 Cu.sub.4 O.sub.8 single phase -- --______________________________________ *Comparative Test

From the results shown in Table 1 and FIG. 4, Tc reduces with the increase of the La content. Thus, it is possible to control Tc by control of La content. When y=0.4, the sintered product becomes an insulator. As seen from the results shown in FIG. 5, the sintered product with y=0.1 is stable up to about 850.degree. C., whereas conventional YBa.sub.2 Cu.sub.3 O.sub.7 loses its oxygen at temperatures above about 400.degree. C.

EXAMPLE 2

Example 1 was repeated in the same manner as described except that Ho.sub.2 O.sub.3 was used in place of Y.sub.2 O.sub.3, thereby to produce Ho(Ba.sub.1-y La.sub.y).sub.2 Cu.sub.4 O.sub.8 wherein y=0, 0.01, 0.05, 0.1, 0.2, 0.3 and 0.4. The product was then tested in the same manner as that in Example 1. The results are summarized in Table 2. The powder X-ray diffraction pattern of the product in the case of y=0.1 is shown in FIG. 6 while temperature dependency of resistivity and change in weight in thermogravimetry of the products (y=0 and y=0.1) are shown in FIGS. 7 and 8, respectively.

TABLE 2______________________________________Test Crystallographic Phase Tc.sup.onset Tc.sup.R = 0No. y by X-Ray Diffraction (K) (K)______________________________________ 8* 0 YBa.sub.2 Cu.sub.4 O.sub.8 single phase 81 76 9 0.01 YBa.sub.2 Cu.sub.4 O.sub.8 single phase 79 7510 0.05 YBa.sub.2 Cu.sub.4 O.sub.8 single phase 70 6511 0.10 YBa.sub.2 Cu.sub.4 O.sub.8 single phase 61 5612 0.20 YBa.sub.2 Cu.sub.4 O.sub.8 single phase 38 3513 0.30 YBa.sub.2 Cu.sub.4 O.sub.8 single phase 21 18 14* 0.40 YBa.sub.2 Cu.sub.4 O.sub.8 single phase -- --______________________________________ *Comparative Test

From the results shown in Table 2 and FIG. 7, Tc reduces with the increase of the La content. Thus, it is possible to control Tc by control of La content. When y=0.4, the sintered product becomes an insulator. As seen from the results shown in FIG. 8, the sintered product with y=0.1 is stable up to about 850.degree. C.

EXAMPLE 3

Metal oxide compositions having the formula R(Ba.sub.0.9 La.sub.0.1).sub.2 Cu.sub.4 O.sub.8 (R=Nd, Sm, Eu, Gd, Dy, Er, Tm, Yb and Lu) were prepared in the same manner as that in Example 1. The resulting products were tested for temperature dependence of the resistivity thereof. The results are summarized in Table 3.

TABLE 3______________________________________Test Crystallographic Phase Tc.sup.onset Tc.sup.R = 0No. R by X-Ray Diffraction (K) (K)______________________________________15 Nd YBa.sub.2 Cu.sub.4 O.sub.8 single phase 59 5516 Sm YBa.sub.2 Cu.sub.4 O.sub.8 single phase 60 5617 Eu YBa.sub.2 Cu.sub.4 O.sub.8 single phase 58 5518 Gd YBa.sub.2 Cu.sub.4 O.sub.8 single phase 61 5619 Dy YBa.sub.2 Cu.sub.4 O.sub.8 single phase 62 5720 Er YBa.sub.2 Cu.sub.4 O.sub.8 single phase 63 5721 Tm YBa.sub.2 Cu.sub.4 O.sub.8 with 62 60 impurity phase22 Yb YBa.sub.2 Cu.sub.4 O.sub.8 with 61 54 impurity phase23 Lu YBa.sub.2 Cu.sub.4 O.sub.8 with 61 53 impurity phase______________________________________

The results shown in Table 3 indicate that the addition of La is effective in controlling Tc of various rare earth-containing superconductors.

EXAMPLE 4

Metal oxide compositions having the formula (Y.sub.1-z Ho.sub.z) (Ba.sub.0.9 La.sub.0.1).sub.2 Cu.sub.4 O.sub.8 (z=0.2, 0.4, 0.6 and 0.8) were prepared in the same manner as that in Example 1. The resulting products were tested for temperature dependence of the resistivity thereof. The results are summarized in Table 4.

TABLE 4______________________________________Test Crystallographic Phase Tc.sup.onset Tc.sup.R = 0No. z by X-Ray Diffraction (K) (K)______________________________________24 0.2 superconductive single phase 60 5625 0.4 superconductive single phase 60 5726 0.6 superconductive single phase 61 5627 0.8 superconductive single phase 60 56______________________________________

The results shown in Table 4 indicate that the addition of La is effective in controlling Tc of superconducting material containing two rare earth elements with various mixing ratios.

EXAMPLE 5

Metal oxide compositions having the formula (R.sub.1-x Ca.sub.x)(Ba.sub.1-y La.sub.y).sub.2 Cu.sub.4 O.sub.8 wherein R, x and y are numbers as shown in Table 5a were prepared. Thus, quantities of R.sub.2 O.sub.3 powder, CaO powder, Ba(NO.sub.3).sub.2 powder, CuO powder and La.sub.2 O.sub.3 were mixed in an inert gas atmosphere and the mixture was calcined, under an oxygen stream, at a temperature as indicated in Table 5b for 10 hours. The calcined mass was ground and formed into a rectangular block, followed by heating at a pre-sintering temperature as indicated in Table 5b under an oxygen stream for 5 hours. The resulting pre-sintered sample was then heat-treated in an mixed gas atmosphere of 80% argon and 20% oxygen at a pressure of 1,000 kg/cm.sup.2. The heat treatment was performed by heating the sample to 1000.degree. C. with a heating rate of 200.degree. C./hour and then maintaining at that temperature for 10 hours. Thereafter, the sample was cooled to 300.degree. C. with a cooling rate of 200.degree. C./hour. The pressure was then released and the treated sample was allowed to stand in air, ground, shaped and sintered again at 800.degree. C. for 20 hours under an oxygen stream to obtain a sintered product. This product was then subjected to powder X-ray diffraction analysis and thermogravimetric analysis and was further tested for the temperature dependence of resistivity and alternate current-magnetic susceptibility. The results are shown in Table 5b and in FIGS. 9-12.

TABLE 5a__________________________________________________________________________Test Ba ContentNo. R x y Raw Materials (mol %)__________________________________________________________________________28 Y 0.001 0.001 Y.sub.2 O.sub.3 CaO Ba(NO.sub.3).sub.2 La.sub.2 O.sub.3 CuO 13.3229 Y+ 0.001 0.05 Y.sub.2 O.sub.3 CaO Ba(NO.sub.3).sub.2 La.sub.2 O.sub.3 CuO 12.67 Er** Er.sub.2 O.sub.330 Er 0.001 0.1 Er.sub.2 O.sub.3 CaO Ba(NO.sub.3).sub.2 La.sub.2 O.sub.3 CuO 12.0031 Tm 0.001 0.2 Tm.sub.2 O.sub.3 CaO Ba(NO.sub.3).sub.2 La.sub.2 O.sub.3 CuO 10.6732 Gd 0.1 0.001 Gd.sub.2 O.sub.3 CaO Ba(NO.sub.3).sub.2 La.sub.2 O.sub.3 CuO 13.3233 Dy 0.1 0.1 Dy.sub.2 O.sub.3 CaO Ba(NO.sub.3).sub.2 La.sub.2 O.sub.3 CuO 12.0034 Y 0.1 0.2 Y.sub.2 O.sub.3 CaO Ba(NO.sub.3).sub.2 La.sub.2 O.sub.3 CuO 10.6735 Sm 0.3 0.001 Sm.sub.2 O.sub.3 CaO Ba(NO.sub.3).sub.2 La.sub.2 O.sub.3 CuO 13.3236 Nd 0.3 0.1 Nd.sub.2 O.sub.3 CaO Ba(NO.sub.3).sub.2 La.sub.2 O.sub.3 CuO 12.0037 Sm+ 0.3 0.1 Sm.sub.2 O.sub.3 CaO Ba(NO.sub.3).sub.2 La.sub.2 O.sub.3 CuO 12.00 Er** Er.sub.2 O.sub.338 Ho 0.3 0.2 Ho.sub.2 O.sub.3 CaO Ba(NO.sub.3).sub.2 La.sub.2 O.sub.3 CuO 10.6739* Y 0.0 0.0 Y.sub.2 O.sub.3 Ba(NO.sub.3).sub.2 CuO 13.3340* Nd 0.0 0.0 Nd.sub.2 O.sub.3 Ba(NO.sub.3).sub.2 CuO 13.3341* Sm 0.0 0.0 Sm.sub.2 O.sub.3 Ba(NO.sub.3).sub.2 CuO 13.3342* Eu 0.0 0.0 Eu.sub.2 O.sub.3 Ba(NO.sub.3).sub.2 CuO 13.3343* Gd 0.0 0.0 Gd.sub.2 O.sub.3 Ba(NO.sub.3).sub.2 CuO 13.3344* Dy 0.0 0.0 Dy.sub.2 O.sub.3 Ba(NO.sub.3).sub.2 CuO 13.3345* Ho 0.0 0.0 Ho.sub.2 O.sub.3 Ba(NO.sub.3).sub.2 CuO 13.3346* Er 0.0 0.0 Er.sub.2 O.sub.3 Ba(NO.sub.3).sub.2 CuO 13.3347* Tm 0.0 0.0 Tm.sub.2 O.sub.3 Ba(NO.sub.3).sub.2 CuO 13.3348* Y 0.001 0.3 Y.sub.2 O.sub.3 CaO Ba(NO.sub.3).sub.2 La.sub.2 O.sub.3 CuO 9.3349* Eu 0.1 0.3 Eu.sub.2 O.sub.3 CaO Ba(NO.sub.3).sub.2 La.sub.2 O.sub.3 CuO 9.3350* Y 0.4 0.01 Y.sub.2 O.sub.3 CaO Ba(NO.sub.3).sub.2 La.sub.2 O.sub.3 CuO 13.2051* Sm 0.4 0.3 Sm.sub.2 O.sub.3 CaO Ba(NO.sub.3).sub.2 La.sub.2 O.sub.3 CuO 9.3352* Gd 0.3 0.3 Gd.sub.2 O.sub.3 CaO Ba(NO.sub.3).sub.2 La.sub.2 O.sub.3 CuO 9.33__________________________________________________________________________ *Comparative Test **Equimolar mixture PG,13 TABLE 5b______________________________________ Calcin- Pre-sinter- ation ing Tem-Test Tempera- perature Crystallographic Phase TcNo. ture (.degree.C.) (.degree.C.) by X-Ray Diffraction (K)______________________________________28 750 850 YBa.sub.2 Cu.sub.4 O.sub.8 8429 750 830 YBa.sub.2 Cu.sub.4 O.sub.8 8430 750 830 YBa.sub.2 Cu.sub.4 O.sub.8 8331 700 830 YBa.sub.2 Cu.sub.4 O.sub.8 8332 750 800 YBa.sub.2 Cu.sub.4 O.sub.8 8333 700 820 YBa.sub.2 Cu.sub.4 O.sub.8 8334 720 800 YBa.sub.2 Cu.sub.4 O.sub.8 8135 750 820 YBa.sub.2 Cu.sub.4 O.sub.8,BaCuO.sub.2 8236 700 850 YBa.sub.2 Cu.sub.4 O.sub.8,BaCuO.sub.2 8037 710 830 YBa.sub.2 Cu.sub.4 O.sub.8,BaCuO.sub.2 8238 700 820 YBa.sub.2 Cu.sub.4 O.sub.8,BaCuO.sub.2 8039* 800 900 YBa.sub.2 Cu.sub.4 O.sub.8 8240* 750 920 YBa.sub.2 Cu.sub.4 O.sub.8 8041* 800 900 YBa.sub.2 Cu.sub.4 O.sub.8 8242* 800 900 YBa.sub.2 Cu.sub.4 O.sub.8 8243* 800 900 YBa.sub.2 Cu.sub.4 O.sub.8 8244* 800 900 YBa.sub.2 Cu.sub.4 O.sub.8 8345* 800 900 YBa.sub.2 Cu.sub.4 O.sub.8 8346* 800 900 YBa.sub.2 Cu.sub.4 O.sub.8 8147* 800 900 YBa.sub.2 Cu.sub.4 O.sub.8 8148* 700 850 YBa.sub.2 Cu.sub.4 O.sub.8 4049* 700 800 YBa.sub.2 Cu.sub.4 O.sub.8,BaCuO.sub.2 --50* 750 800 YBa.sub.2 Cu.sub.4 O.sub.8,BaCuO.sub.2 --51* 700 850 YBa.sub.2 Cu.sub.4 O.sub.8,BaCuO.sub.2,Sm.sub.2 O.sub.3 --52* 720 850 YBa.sub.2 Cu.sub.4 O.sub.8,BaCuO.sub.2,Gd.sub.2 O.sub.3 --______________________________________ *Comparative Test

The x-ray diffraction pattern shown in FIG. 9 (x=0.1, y=0.1) indicates the presence of the YBa.sub.2 Cu.sub.4 O.sub.8 crystal phase. The sintered samples with x of 0-0.15 and y of 0-0.1 were found to have a single layer superconducting phase. From the results summarized in Table 5 and in FIG. 10, it is seen that the addition of Ca and La in specific amounts is effective in reducing the amount of Ba while maintaining Tc above about 80K. The high Tc is also confirmed by the results shown in FIG. 11 indicating the occurrence of diamagnetism at a temperature of above about 80K. As seen from the results shown in FIG. 12, the sintered product with x=0.1 and y=0.1 is stable up to about 850.degree. C., similar to YBa.sub.2 Cu.sub.4 O.sub.8.

EXAMPLE 6

Metal oxide compositions having the formula: (R.sub.1-x Ca.sub.x)(Ba.sub.1-y La.sub.y).sub.2 Cu.sub.4 O.sub.8 wherein R, x and y are numbers as shown in Table 6a were prepared. Thus, quantities of R.sub.2 O.sub.3 powder, CaO powder, BaCO.sub.3 powder, CuO powder and La.sub.2 O.sub.3 were mixed in an inert gas atmosphere and the mixture was calcined, under an oxygen stream, at a temperature as indicated in Table 6b for 10 hours. The calcined mass was ground and formed into a rectangular block, followed by heating at a pre-sintering temperature as indicated in Table 6b under an oxygen stream for 5 hours. The resulting pre-sintered sample was then heat-treated in an mixed gas atmosphere of 80% argon and 20% oxygen at a pressure of 1,000 kg/cm.sup.2. The heat treatment was performed by heating the sample to 1000.degree. C. with a heating rate of 200.degree. C./hour and then maintaining at that temperature for 10 hours. Thereafter, the sample was cooled to 300.degree. C. with a cooling rate of 200.degree. C./hour. The pressure was then released and the treated sample was allowed to stand in air, ground, shaped and sintered again at 800.degree. C. for 20 hours under an oxygen stream to obtain a sintered product. This product was then subjected to powder X-ray diffraction analysis and thermogravimetric analysis and was further tested for the temperature dependence of resistivity and alternate current-magnetic susceptibility. The results are shown in Table 6b and in FIGS. 13-16.

TABLE 6a__________________________________________________________________________Test Ba ContentNo. R x y Raw Materials (mol %)__________________________________________________________________________53 Y 0.001 0.001 Y.sub.2 O.sub.3 CaCO.sub.3 BaCO.sub.3 La.sub.2 O.sub.3 CuO 13.3254 Y+ 0.001 0.05 Y.sub.2 O.sub.3 CaCO.sub.3 BaCO.sub.3 La.sub.2 O.sub.3 CuO 12.67 Er** Er.sub.2 O.sub.355 Er 0.001 0.1 Er.sub.2 O.sub.3 CaCO.sub.3 BaCO.sub.3 La.sub.2 O.sub.3 CuO 12.0056 Tm 0.001 0.2 Tm.sub.2 O.sub.3 CaCO.sub.3 BaCO.sub.3 La.sub.2 O.sub.3 CuO 10.6757 Gd 0.1 0.001 Gd.sub.2 O.sub.3 CaCO.sub.3 BaCO.sub.3 La.sub.2 O.sub.3 CuO 13.3258 Dy 0.1 0.05 Dy.sub.2 O.sub.3 CaCO.sub.3 BaCO.sub.3 La.sub.2 O.sub.3 CuO 12.6759 Y 0.1 0.1 Y.sub.2 O.sub.3 CaCO.sub.3 BaCNO.sub.3 La.sub.2 O.sub.3 CuO 12.0060 Sm 0.1 0.2 Sm.sub.2 O.sub. 3 CaCO.sub.3 BaCO.sub.3 La.sub.2 O.sub.3 CuO 10.6761 Nd 0.3 0.001 Nd.sub.2 O.sub.3 CaCO.sub.3 BaCO.sub.3 La.sub.2 O.sub.3 CuO 13.3262 Sm+ 0.3 0.1 Sm.sub.2 O.sub.3 CaCO.sub.3 BaCO.sub.3 La.sub.2 O.sub.3 CuO 12.00 Er** Er.sub.2 O.sub.363 Ho 0.3 0.1 Ho.sub.2 O.sub.3 CaCO.sub.3 BaCO.sub.3 La.sub.2 O.sub.3 CuO 12.0064 Y 0.3 0.2 Y.sub.2 O.sub.3 CaCO.sub.3 BaCO.sub.3 La.sub.2 O.sub.3 CuO 10.6765 Eu 0.3 0.2 Eu.sub.2 O.sub.3 CaCO.sub.3 BaCO.sub.3 La.sub.2 O.sub.3 CuO 10.67 66* Y 0.001 0.3 Y.sub.2 O.sub.3 CaCO.sub.3 BaCO.sub.3 La.sub.2 O.sub.3 CuO 9.33 67* Eu 0.1 0.3 Eu.sub.2 O.sub.3 CaCO.sub.3 BaCO.sub.3 La.sub.2 O.sub.3 CuO 9.33 68* Y 0.4 0.01 Y.sub.2 O.sub.3 CaCO.sub.3 BaCO.sub.3 La.sub.2 O.sub.3 CuO 13.20 69* Ho 0.4 0.3 Ho.sub.2 O.sub.3 CaCO.sub.3 BaCO.sub.3 La.sub.2 O.sub.3 CuO 9.33 70* Gd 0.3 0.3 Gd.sub.2 O.sub.3 CaCO.sub.3 BaCO.sub.3 La.sub.2 O.sub.3 CuO 9.33 71* Y 0.1 0.1 Y.sub.2 O.sub.3 CaCO.sub.3 BaO.sub.3 La.sub.2 O.sub.3 12.00__________________________________________________________________________ *Comparative Test **Equimolar mixture TABLE 6b______________________________________ Calcin- Pre- ation sinteringTest Tempera- Tempera- Crystallographic Phase TcNo. ture (.degree.C.) ture (.degree.C.) by X-Ray Diffraction (K)______________________________________53 900 950 YBa.sub.2 Cu.sub.4 O.sub.8 8354 920 950 YBa.sub.2 Cu.sub.4 O.sub.8 8355 900 950 YBa.sub.2 Cu.sub.4 O.sub.8 8356 920 950 YBa.sub.2 Cu.sub.4 O.sub.8 8357 910 940 YBa.sub.2 Cu.sub.4 O.sub.8 8358 920 950 YBa.sub.2 Cu.sub.4 O.sub.8 8259 910 940 YBa.sub.2 Cu.sub.4 O.sub.8 8360 910 950 YBa.sub.2 Cu.sub.4 O.sub.8 8261 900 950 YBa.sub.2 Cu.sub.4 O.sub.8,BaCuO.sub.2 8362 910 940 YBa.sub.2 Cu.sub.4 O.sub.8,BaCuO.sub.2 8363 900 950 YBa.sub.2 Cu.sub.4 O.sub.8,BaCuO.sub.2 8264 920 950 YBa.sub.2 Cu.sub.4 O.sub.8,BaCuO.sub.2 8065 910 940 YBa.sub.2 Cu.sub.4 O.sub.8,BaCuO.sub.2 81 66* 900 950 YBa.sub.2 Cu.sub.4 O.sub.8,BaCuO.sub.2 40 67* 850 920 YBa.sub.2 Cu.sub.4 O.sub. 8,BaCuO.sub.2 20 68* 900 950 YBa.sub.2 Cu.sub.4 O.sub.8,BaCuO.sub.2 -- 69* 900 950 YBa.sub.2 Cu.sub.4 O.sub.8,BaCuO.sub.2 Sm.sub.2 O.sub.3 -- 70* 850 910 YBa.sub.2 Cu.sub.4 O.sub.8,BaCuO.sub.2,Gd.sub.2 O.sub.3 -- 71* 700 850 YBa.sub.2 Cu.sub.4 O.sub.8,BaCO.sub.3,Y.sub.2 BaCuO.sub.5 --______________________________________ *Comparative Test

The x-ray diffraction pattern shown in FIG. 13 (x=0.1, y=0.1) indicates the presence of the YBa.sub.2 Cu.sub.4 O.sub.8 crystal phase. The sintered samples with x of 0-0.15 and y of 0-0.1 were found to have a single layer superconducting phase. From the results summarized in Table 6 and in FIG. 14, it is seen that the addition of Ca and La in specific amounts is effective in reducing the amount of Ba while maintaining Tc above about 80K. The high Tc is also confirmed by the results shown in FIG. 15 indicating the occurrence of diamagnetism at a temperature of above about 80K. As seen from the results shown in FIG. 16, the sintered product with x=0.1 and y=0.1 is stable up to about 850.degree. C., similar to YBa.sub.2 Cu.sub.4 O.sub.8. This example also indicates that good results are obtainable even when BaCO.sub.3 which is available at low costs is used as a source of Ba.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all the changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

1. A superconductive material comprising a single crystal phase of the formula:

(R.sub.1-x Ca.sub.x)(Ba.sub.1-y La.sub.y).sub.2 Cu.sub.4 O.sub.8

wherein R is at least one element selected from the group consisting of for Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, x is a number in the range of 0-0.3 and y is a number in the range of 0.01-0.3 with the proviso that y is not greater than 0.2 when x is not 0.

2. A superconductive material as claimed in claim 1, wherein x is a number in the range of 0.001-0.3 and R is at least one element selected from the group consisting of Y, Nd, Sm, Eu, Gd, Dy, Ho, Er and Tm.

3. A superconducting material as claimed in claim 1 and having the following formula:

R(Ba.sub.1-y La.sub.y).sub.2 Cu.sub.4 O.sub.8.