CA2002022A1 - Superconducting metal oxide compositions and processes for manufacture and use - Google Patents

Abstract

TITLE
SUPERCONDUCTING METAL OXIDE COMPOSITIONS
AND PROCESSES FOR MANUFACTURE AND USE
ABSTRACT
Compositions having the nominal formula TlBaaCabCucOx wherein a is from about 2 to 4, b is from about 7/2 to 5, c is from about 9/2 to 7, x = (a + b + c + y) where y is from about 1/2 to 3, are superconducting.
Processes for manufacturing such compositions and for using them are disclosed.

Description

Z0021~22 8UP~RCONDUC~ING METAL OXIDE COMPOSITIONS
AND PROCESSES rOR MANUFACTURE AND USE
BACXGROUND OF THE INVENTION
Field of the Invention This invention relates to novel Tl-Ba-Ca-Cu-O compositions which are superconducting.
Reference~
Bednorz and Muller, Z. Phys. B64, lB9 (1986), disclose a superconducting phase in the L~-Ba-Cu-O 6ystem with a superconducting transition temperature of about 35 K. Thi~
dicclosure was sub6equently confirmed by a number o~ investigators [see, for example, Rao ~nd Ganguly, Current Science, 56, 47 ~lg87), Chu et al., Science 235, 567 ~1987), Chu et al., Phys.
Rev. Lett. 58, 405 ~1987), Cava et al., Phy6.
Rev. Lett. 58, 408 ~1987), Bednorz et al., Europhys. Lett~ 3, 379 ~1987)]. The cuperconducting phase has been identified a6 the composition Lal_x~a,Sr,Ca)xCuO~_y with the tetragonal X2NiF~-type structure and with x typically about 0.15 and y indicating oxygen vacancies.
Wu et al., Phys. Rev. Lett. 58, 908 (1987), disclose a superconducting phase in the Y-Ba-Cu-O system with a superconducting ~ransi~ion temperature of about 90 K. Cava et .. ,. ~ -, ., . . - . : . ^
. :.:

, - . . . . .
.. : . - . - - , zno2n22 al., Phys. Rev. Lett. 58, 1676 (1987), have identif~ed this superconducting Y-Ba-Cu-O phabe to be orthorhombic, distorted, oxygen-deficient perovskite Y8a2Cu~09 ~ where ~ is about 2.1.
C. Michel et al., Z. Phys. ~ -Condensed Matter 68, 421 (1987), disclose ~ novel family of superconducting oxides ln the Bi-Sr-Cu-O system. A pure phase was isolated for the composition Bi25r2Cu20~. The material made fsom ultrapure oxides has a superconduct~ng transition with a midpoint of 22 R as determined from resistivity measurements and zero resistance below 14 K. The material made from commercial grade oxides has a superconducting transition w~th a midpoint of 7 K.
29 H. Maeda et al., Jpn. J. Appl. Phys.
27, L209 (1988), disclose a superconduct~ng oxide ln the Bi-Sr-Ca-Cu-O system w~th the compo8it~0n near BlSrCaCu20x and a superconducting trans~tion temperature of aboYt 105 K.
The commonly assigned application, ~Superconducting Metal Oxide Compositions and Process For Making Themn, S. N. 153,107, filed Feb. 8, l9B8, a continuation-in-part of S. N.
152,186, filed Feb. 4, 1988, disclose superconducting compositions having the nominal formula si.srbcaccu30~ wherein a is from about 1 to about 3, b is from about 3/8 to about 4, c is from about 3/16 to about 2 and x - (1.5 a + b + c + y) where y is from about 2 to about 5, with the proviso that b + c is from about 3/2 to about 5, said compositions having superconducting .

: - . .: , , .

. ,,,: ~ ~ . ; . .

transition temperatures of about 70 K or higher.
It also discloses the superconducting metal oxide phase having the formula Bi 2 S r3 - ~ Ca~Cu wherein z is from about 0.1 to about 0.9, preferably 0.4 to 0.8 and w i6 greater than zero but less than about 1. M. A. Subramanian et al., Science 239, 1015 (1988) also disclose the ~i2Sr3 ~Ca~ CU2 t ~ ~ superconductor.
Z. z. Sheng et al., Nature 332, 55 (1988) disclose superconductivity in the Tl-sa-Cu-o system in samples which have nominal compositions Tl2Ba2Cu3O~ and TlBaCu3O5 5 sOth samples are reported to have onset temperatures above 90 K and zero resigtance at 81 R. The ~amples were prepared by mixing and ao grinding appropriate amount~ of ~aCo3 ~nd CuO
with an agate mortar and pe~tle. ~h~ mixture wa~ heated in air at 925C for more than 24 hour~
with ~everal intermediate grindings to obtain a uniform black oxide 8a-Cu oxide powder which was mixed with an appropriate amount of Tl2O3, completely ground and pressed into a pellet with a diameter of 7 mm and a thickness of 1-2 mm.
The pellet was then put into a tube furnace which had been heated to 880-910C and was heated for 2-5 minutes in flowing oxygen. As soon as it had slightly melted, the sample was taken from the furnace and quenched in air to room temperature.
It was noted by visual inspection that Tl2O3 had partially volatilized as black smoke, part had become a light yellow liquid, and part had reacted with Ba-Cu oxide forming a black, .

~ . ~ ~,; . . . -~, . .
: :: . . : .:
-: : : .: .

2t)02~22 partially melted, porous material.
Z. Z. Sheng et al., Nature 332, 138 (1988) disclose ~uperconductivity ~n the ~l-Ca-Ba-Cu-O ~ystem in samples which have nominal compositions Tl2CalBaCu3Og~ with onset of superconductivity at 120 K.
R. M. Hazen et al., Phys. Rev. Lett.
60, 1657 (1988), disclose two superconducting phases in the Tl-Ba-Ca-Cu-O system, ~l2Ba2ca2cu~olo ~nd Tl2~a2CaCU2O~, both wit onset of 6uperconductivity near 120 K. C. C.
Torardi et al., Science 240, 631 (1988) disclose the prepar~tion of Tl2Ba2C~2 Cu3 l o with ~n o of superconductivity of 125 K.
S. S. P. Parkin et al., Phys. Rev.
Lett. 61, 750 (1988), disclose the structure TlBa2 Ca2 CU3 09 ~y with transition temperatures up to 110 K.
M. Hervieu et ~l., J. Solid State Chem.
75, 212 tl988), disclose the oxide 2~ TlBa2Cacu2o~-y-C. C. ~orardi et al., Phys. ~ev. B 38, 225 (1988), disclose the oxide Tl2Ba2CuO6 with an onset of ~uperconductivity at about 90 K.
The commonly assigned application, "Superconducting Metal Oxide Compositions and Processes For Manufacture and Use~, S. N.
236,088, filed Aug. 24, 1988, a continuation-in-part of S. N. 230,636, filed Aug.
10, 1988, disclose superconducting compositions having the nominal formula Tl.Pb.CabSr~CudOx wherein a is from about 1/10 to about 3/2, b is . . ~ : , , :
;. : .. - . . . :

, .

2()~2Q22 from about 1 to about 4, c is from about 1 to about 3, d is from about 1 to about 5, e is from about 3/10 to about 1 and x - (a ~ b ~ c ~ d + e +y) where y i8 from about 1/2 to about 3. These compositions have an onset of superconductivity of at least 70 K.
Numerous papers have appeared relating to the above compositions. The highest transition temperature reported for any of the above compositions at this time i8 125 K for Tl2Ba2Ca2 CU3 X as disclosed by S. S. P. Parkin et al., Phys. Rev. Lett. 60, 2539 ~198B) J. M. ~iang et al., Appl. Phys. ~ett.
53, 15 (1988) disclose a composition TlBa2Ca3Cu~Ox with an onset of superconductivity at lSS K and a zero resistance at 123 ~ CaCO3, BaCO3 and CuO powders were ground together and calcined for 15 hour~ with lntermediate grindings. The sa-Ca-Cu-o powders were mixed with Tl2O3 to yleld a ~ixture with nominal compo~ition TlBaCa3Cu3Ox. This mixture was ground, pressed and sintered for lS minute~ in flowing 2- Composition ratios of the T}:Ca:sa:Cu in the ~uperconductor vary from 1:2:2:3 to 1:2:3:4.

SUMMARY OF T~E INVENTION
This invention provides novel superconducting compositions having the nominal formula Tlsa.cabcu~ox wherein a is from about .. . . .. . . .

,. . . :
..
.. ...
.

, .

2()02n~2 2 to about 4, b is from about 7/2 to about 5, c is from about 9/2 to about 7 and x - (a + b + c +
y) where y is from about 1/2 to about 3.
Preferably, a is from about 2 to about 3, b is about 4, c is about 5, and y i 6 from about 1/2 to about 2. The onset of superconductivity for these compositions is at a temperature of at least 130 K.
These superconducting compositions can be prepared by heating a m~xture of the oxides of Tl, Ca and Cu and the peroxide of Ba or a precursor oxide mixture prepared from these oxides, the relative amounts of the oxides chosen so that the atom~c ratio Tl:Ba:Ca:Cu is l:a:b:c, to a temperature of about 940C to about 980C, maintain~ng that temperature for about 5 m~nutes or more, said heatlng beinq carried out ln a controlled atmosphere, e. g., ln ~ sealed tube made of ~ non-reacting metal such a6 gold, which prevents ~ny of the reactants including the metals and oxygen from escaping.

FIG. 1 shows a plot of the flux excluded by a composition of this invention as a function of temperature.

DETAILED DESCRIPTION OF T~E INVENTION
-The superconducting compositions of this invention can be prepared by the following process. The oxide mixture used in this process is prepared so that the atomic ratio Tl:Ba:Ca:Cu .:
: . - ,,, . . - . .
-. .
-~.
.

. . ~ . .
.

2()02Q22 5 i8 l:a:b:c wherein a is from about 2 to about 4, b is from about 7/2 to about 5, c is from about 9/2 to about 7 and x - (a + b + c + y) where y is from about 1/2 to about 3. Preferably, a is about 2, b is about 4, c is about 5, and y is from about 1/2 to about 2.
The oxide mixture can be prepared directly by choosing quantities of the oxide reactants Tl2O3, CaO and CuO ~nd the peroxide BaO2 such that the atomic ratio Tl:~a:Ca:Cu is l:a:b:c and mixing them, for ex~mple, by grinding them together in a mortar.
Alternatively, a precursor oxide mixture can be prepared by choo~ing quantities of the oxide reactants Tl2O3, CaO and CuO and the peroxide BaO2 such that the àtomic r~tlo a:Ca:Cu $~ l:a:b:c. The barium peroxide, calcium oxide and copper oxide are ground together and this grey mixture i~ then heated in an alumina crucible in a muffle furnace in air, the temperature being increased from ambient temperature, about 20C, to about 800C ~n a period of about 2 hours. The temperature is held at about 800C for 1 hour. The ~ample is then cooled and the black powder i8 recovered. This powder is re-ground and ground together with the thallium oxide to give the precursor oxide mixture.
The oxide mixture is then heated in a controlled atmosphere. One convenient way to accomplish a controlled atmosphere is to place the oxide mixture in a tube made of a : ~ : ............................... .
. - ~ , . . :

~. .

2~0Z~?22 non-reacting metal such as gold and then sealing the tube by crimping or, preferably, by welding or fusing. The precursor oxide mixture is less destructive of the gold tubes and i8 preferred for this reason. The sealed tube is placed in a furnace and heated to a temperature of about 940C to about 9B0C and maintained at a temperature in this range, i. e., about 940C to about 980C, for about 5 minutes or more.
Maintaining the sample at such a temperature for 5 minutes is sufficient to form the superconductor of the invention when the sample is heated from 700C to a temperature in the prescribed range at a rate o 50C/min and subsequently cooled at a rate of 10C/min to 600C. Faster heating and cooling rates may require 60mewhat longer m~lntenance tlme~.
Maintenance ti~es o up to an hour or more can be used but csrrosion of the gold tube becomes evident ~t about that time and ma~ntenance times of about 5 to about 60 minute~ are typical. The ~mple is then cooled to ambient temperature and the ~hiny grey-black metallic-appearing ingot recoYered. During the thermal cycle the gold tube typically bloats; however, at the end of the procedure there is not excess pressure in the tube when it is cut open. The recovered material is a shiny qrey/black metallic ingot with a surface bejeweled with black shiny platelets. The black shiny platelets have proven to be single crystals of known materials, e. g., Tl-sa-Ca-Cu compositions with :
-, . :
- . --- : ~ -2()02 )22 Tl:Ba:Ca:Cu atomic ratios of 1:2:1:2 and 1:2:2:3 with lesser Tc's.
F1UX exclusion measurements on the compositions of this invention, prepared as described above, show an onset of 6uperconductivity at about 130-132 N.
Resi~tivity measurements on the as prepared ingot shows onset at about 135 K and zero resistance at about 116 K. The superconductivity arises from the bulk of the composition. Based on flux i5 exclusion measurements at least 30% of each of the samples is superconducting~ X-ray powder diffraction typically g$ves very weak lines.
Longer maintenance times at the maximum heating temperature have produced samples which show di~crete x-ray llnes. The 22 A ~2.2 nm~ c axis which i~ observed in the powder d~ffraction pattern is what is calculated for a 1245 ~Tl:Ba:Ca:Cu atomic ratio) phase using a formula of Ihara et al., Nature 334, 510 (1988).
Electron microscopy results have shown intergrowth of layered pha~es ~ncluding a 1245 phase.
Superconductivity can be confirmed by observing magnetic flux exclusion, i.e., the Meissner effect. This effect can be measured by the method described in an article by E. Polturak and B. Fi~her in Physical Review B, 36, 5586(1987).
The superconducting compositions of this invention can be used to conduct current extremely efficiently or to provide a magnetic ~: ,' , :. " , ' , - ,, - , : - ~ , , "' ' ' ~, :: `' .
.

2noz~2 field for magnetic imaging for medical purposes.
Thus, by cooling the composition in the form of a wice or bar to a temperature below the superconducting transition temperature, ~TC ), in a manner well known to those in thi~ field, and initiating a flow o~ electrical current, one can obtain such flow without any electrical resistive losses. To provide exceptionally high magnetic fields with minimal power losses, the wire mentioned previously could be wound to form a coil which would be cooled to a temperature below the superconducting transition temperature before inducing any current into the coil. Such fields can be used to levitate ob~ects as large as rail-road car~. ~hese superconducting compositions 29 are ~16O u8eful in Josephson devices such as SQUIDS ~superconducting quantum interference devices) and in instruments that are based on the Josephson effect ~uch as high ~peed eampling circuits and voltage standards.
EX~MPLES OF THE INVENTION

0.456 g of Tl2O3, 1.020 g of BaO2, 0.448 g of CaO and 0.960 g of CuO, corresponding to a Tl.Ba:Ca:Cu atomic ratio of 1:3:4:6, were ground together in an agate mortar for about 3 minutes to form a fine grey powder. This powder was loaded into a gold tube, about 3 inches long and 1/4 inch in diameter (7.6 cm long and 0.64 cm ., . ;

.- . :. .

2~02n22 in diameter) and the gold tube was crimped shut.
The tube was placed in a quartz tube furnace and heated in a slow oxygen flow in the following manner. The tube was heated from ambient temperature, about 20C, to 700C at a rate of about 3C/min and then from 700C to 977C in ten minutes. Over the next five minutes the temperature decreased to 950C. Power to the furnace was then shut off and the tube was allowed to cool to room temperature in the furnace. The tube was then removed from the furnace and cut open. The grey-black ingot product was recovered.
Flux exclusion measurements showed the onset of superconductlvity at about 130 R.

In Example 2, 0.456 g of Tl2O3, 1.020 g of ~aO2, 0.448 g of CaO and 0.960 9 of CuO, corresponding to a Tl:Ba:Ca:Cu atom~c ratio of 1:3:4:~, were ground together in an agate mortar for about 3 minutes to form a fine grey powder.
This powder was loaded into a gold tube, about 3 inches long and 1/4 inch in diameter (7.6 cm long and 0.64 cm in diameter) and the gold tube was ~.
crimped shut. The tube was placed in a quartz tube furnace and heated in a slow oxygen flow in the following manner. The tube was heated fr~m ambient temperature, about 20C, to 700C at a rate of about 3C/min and then from 700C to 950C at a rate of about 25C/min. The .. ,; , : . ~ - ~
~ -.

.

.

2~ 21~2 temperature was maintained at 950C for S min and then cooled to 600C at a rate of about 10C/m~n.
Power to the furnace was then shut off and the tube wa5 allowed to cool to room temperature ln the furnace. The tube was then removed from the furnace and cut open. The grey-black ingot product was recovered.
Flux exclusion measurements showed the onset of superconductivity at about 130 K.
Examples 3 and 4 were carried out essentially as described for Example 2 except that in Example 3, 0.456 g of Tl2O~, 0.680 g of BaO2, 0.44B g of CaO and 0.960 g of CuO, corresponding to a Tl:Ba:Ca:Cu atomic ratio of 1:2:4:6, were ground to form a fine grey powder and ln Example 4, 0.456 g of Tl2O~, 1.020 g of B~O2, 0.448 g of CaO and 0.B00 g of CuO, corresponding to a Tl:Ba:Ca:Cu atomic ratio of 1:3:4:5, were ground together to form a fine grey powder.
~lux exclusion measurementc ~howed the onset of superconductivity at about 130 g for Examplç 3 and at about 132 K for Example 4.

A precursor oxide mixture was prepared by grinding together 5.10 g of BaO2, 2.25 g of CaO and 4.00 g of CuO. ~his grey mixture was then heated in an alumina crucible in a muffle furnace in air from ambient temperature, about 20C, to aoooc in a period of 2 hours. ~he .: . ~ . - . . . . ~ . , .

. . :',; " ', ' , " ' : ' ' ' " .. ' . '. ' . ' ~ ' .

- 2no2n~z S temperature was held at 800C for 1 hour and then reduced to ambient. The black powder product wa6 recoveced and re-ground. The powder contained the elements Ba:Ca:Cu in the atomic ratio 3:4:5.
2.30 g of this black powder was ground 10together with 0.456 9 of Tl2 03 to give a material with the atomic ratio of Tl:Ba:Ca:Cu of 1:3:4:5.
This powder was loaded into gold tube, about 3 inches long and 1/4 inch in diameter (7.6 cm long and 0.64 cm in diameter). The tube was sealed at both ends by fus~ng and placed on an alumina boat which was placed in a horizontal quartz tube furnace.
Heating was carried in the following manner. The temperature was increased from room temperature to 700C at a rate of about 3C/min.
The temperature was then ~ncrea~ed from 700C to 977C at a rate of about 18.5C/mln. The sample cooled to 950C over the next 5 minute~ and wa~
maintained at 950C for 10 min. The sample was then cooled in the furnace to 600C at a rate of about 10C/min. The sample was then removed from the furnace and cooled to room temperature.
The recovered material is a shiny grey-black metallic ingot with a surface bejeweled with black shiny platelets.
Flux exclusion measurements showed the onset of superconductivity at about 132 X.

A precursor oxide mixture was prepared , : : .
;
~" . - ~ . , . - .:

. . . . .
:

2()0Z~22 S by grinding together 1.020 g of BaO2, 0.448 9 of CaO and 0.800 g of CuO. This grey mixture wa8 then heated in an alumina crucible in a muffle furnace in air from ambient temperature, about 20C, to 800C in a period of 2 hours. The temperature was held at B00C for l hour and then reduced to ambient. The black powder product was recovered and re-ground. The powder contained the elements Ba:Ca:Cu in the atomic ratio 3:4:5.
2.300 g of this black powder was ground lS together with 0.342 g of Tl2O3 to give a material with the atomic ratio of Tl:Ba:Ca:Cu of 0.75:3:4:5 which, rounded off to integers, is approximately 1:4:5:7. This powder was loaded into gold tube, about 3 lnches long and 1/4 inch in diameter (7.6 cm long ~nd 0.64 cm ~n diameter). The tube was sealed at both ends by fusing and placed on ~n alumina boat which was placed in a horizontal quartz tube furnace.
~eating was carried in the following manner. The temperature was increased from room temperature to 700C at a rate of about 3C/min.
The temperature was then increased from 700C to 968C at a rate of about 25C/min. The sample was maintained at 968C for 15 min. The sample was then cooled in the furnace to 600C at a rate of about 10C/min. The sample was then removed from the furnace and cooled to room temperature.
The recovered material is a shiny grey-black metallic ingot with a surface 3S bejeweled with black shiny platelets.
F1UX exclusion measurements showed the ,~ . .. . .
-.. .. . ..
- ~ . .
,, ~
.. . ..

z~)oznz2 onset of superconductivity at about 130 K.

An oxide mixture containing the elements 8a:Ca:Cu in the atomic ratio of 3:4:5 was prepared essentially as described in Example 6.
2.300 g of this black powder was ground together with 0.456 g of Tl2O3 to give a material with the atomic ratio of Tl:Ba:Ca:Cu of 1:3:4:5.
Thls powder was loaded into gold tube, about 3 inches long and 1/4 inch in diameter (7.6 cm long and 0.64 cm in diameter). The tube was sealed at both ends by fusing and placed on an alumina boat which wa~ placed ~n a horizontal quartz tube furnace.
Heating was carried in the following manner. The temperature was lncreased from room temperature to 700C at a r~te of about 3C/min.
The temperature was then increased from 700C to 977C at a rate of about 25C/min. The sample was maintained at 977C for 15 min. The ~ample was then cooled in the furnace to 600C at a rate of about 10C/min. The sample was then removed from the furnace and cooled to room temperature. ~.
The recovered material is a shiny grey-black metallic ingot with a surface bejeweled with black shiny platelets.
This Example was essentially repeated several times and the products were essentially identical.

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.
: - . , , . . . :
;~
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:: . :: . . :
:~ .

2(302(~:22 Flux exclusion measurements were carried out on one of these products and the results are shown in Fig. 1 where the flux excluslon is plotted as a function of temperature. The plot shows the onset of superconductivity at about 132 K.
X-ray diffraction was carried out on a powder obtained by grinding one of the~e products. The d-spacings, the relative $ntens$t$es and the indices of a set of observed reflections of the x-ray powder diffraction pattern which are always present when onset of superconductivity is observed at a temperature of 130 K or above is shown in Table I.

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2l)021~2~

TABLE I
d-spacinq, nm Intensity hkl 2.20000 m 001 0.37924 m 101 0.36339 w 102 100.34088 m 103 0.31540 s 104 0.28974 w 105 0.27224 ms 110 0.26552 w 106 150.25522 s 113 0.24444 w 009 0.24398 w 114 0.24346 w 107 0.20636 m 109 200 ~ 20577 m 117 0.19250 ms 200 0.17011 ms 212 w - weak m - medlum s - 6trong ... . ~ ,. ~, ...
.. , . .
.
, ' ' ''' ' ' ~ ~ ,, 2()021)Z2 In each of these Examples a precursor oxide mixture containing the elements Tl:Ba:Ca:Cu in the atomic ratio of 1:3:4:5 wa~ prepared, placed in a gold tube and then placed in a furnace essentially as described in Example 5.
Heating was carried in the following manner. The temperature was increased from room temperature to 700C at a rate of about 3C/min.
The temperature was then increased from 700C to a maximum temperature, T~x, at a specified rate.
The sample was maintained at T..x for a specified time and was then cooled ln the furnace to 600C
at a rate of 10C/~in except for E~ample 12 for 20 which the rate wa~ 50C/min. The ~ample was then i.
~emoved from the furnace and cooled to room temperature.
The recovered material is a shiny grey-black metallic ingot with a surface 25 be~eweled with black shiny platelets.
~lux exclusion measurements were carried out on each product.
The specified rate of heatinq from 700C to T~,x~ the temperature T~.x, the time for 30 which the temperature was maintained at T~.x and ~.
the temperature of the onset of superconductivity are shown in Table II.

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Heating Main.
Rate Time Temp.
Example 700C-T~.X T~x at T~,x Onset No.C/min C min K
~ 25 940 15 130 11 S0 g77 5 132 .. ..
..

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Claims (10)

1. A superconducting composition having the nominal formula TlBaaCabCucOx wherein a is from about 2 to about 4, b is from about 7/2 to about 5, c is from about 9/2 to about 7, x = (a + b + c + y) where y is from about 1/2 to about 3, said composition having an onset of superconducting at a temperature of at least 130 K.

2. A superconducting composition as in Claim 1 wherein "a" is from about 2 to about 3, "b" is about 4, "c" is about 5 and "y" is from about 1/2 to about 2.

3. A superconductivity composition as in Claim 2 wherein "a" is about 2.

4. A process for making superconducting compositions consisting essentially of mixing stoichiometric quantities of oxides of Tl, Ca and Cu and the peroxide of Ba to provide the composition of Claim 1; heating the mixture in a confined atmosphere to a temperature of about 940°C to about 980°C and maintaining said temperature for about 5 minutes or more; and cooling said composition.

5. A process as in Claim 4 wherein the stoichiometric quantities of the oxides are selected to provide the composition of Claim 3.

6. The process of Claim 4 wherein the oxides of Ca and Cu and the peroxide of Ba are mixed, heated to about 800°C, ground and mixed with the Tl oxide to provide the mixture to be heated.

7. The process of Claim 5 wherein the oxides of Ca and Cu and the peroxide of Ba are mixed, heated to about 800°C, ground and mixed with the Tl oxide to provide the mixture to be heated.

8. A method for conducting an electrical current within a conductor material without electrical resistive losses comprising the steps of:
cooling a conductor material composed of a composition of Claim 1 to a temperature below the Tc of said composition;
initiating a flow of electrical current within said conductor material while maintaining said material below said temperature.

9. A method as in Claim 8 wherein said conductor material is cooled to a temperature from 77X to Tc of said composition.

10. An improved Josephson-effect device wherein the superconductive material comprises the composition of Claim 1.