AU608886B2 - Improved process for making 90 k superconductors - Google Patents

Description

AU-AI-21299/88 .1 IP' pcW WORLD INTELLECTUAL PROPERTY ORGANIZATION INTERNATIONAL APPLICATION PUB H UI? R 1E EN OPERATION TREATY (PCT) (51) International Patent Classification 4 (11) International Publication Number: WO 88/ 10515 HO1L 39/12 Al (43) International Publcation D&te: 29 December 1988 (29.12.88) (21) International Application Number: PCT/US88/02025 (22) International Filing Date: (31) Priority Application Number: (32) Priority Date: (33) Priority Country: (71)Applicant: E.I. DU PONT COMPANY [US/US]; 1007 ton, DE 19898 (US).

8 June 1988 (08.06.88) 059, '7 9 Jun". 1987 (09.06.87) DE NEMOURS AND Market Street Wilming- (81) Designated States: AT (European patent), AU, BE (European patent), CH (European patent), DE (European patent), DK, FR (European patent), GB (European patent), HU, IT (European patent), JP, KR, LU (European patent), NL (European patent), NO, SE (Europeat patent), SU.

Published With international search report.

Before the expiration of the time limit for cending the claims and to be republished in the event pf the receipt of amendments.

a' J.P, 1 6 MAR 1989

AUSTRALIAN

19 JAN 1989 PATENT OFFICE (72) Inventor: TORARDI, Carmine 101 Ridgeland Road, Wilmington, DE 19803 (US).

(74) Agent: WOLFSON, Herbert, E.I. du Pont de Nemours and Company, Legal Department, Patent Division, Wilmington, DE 19898 (US).

T

h i s docuinfltcntams the L erin1ents made under Section 49 and is crect for inting (54) Title: IMPROVED PROCESS FOR MAKING 90 K SUPERCONDUCTORS (57) Abstract There ts disclosed an improved process for preparing a superconducting composition having the formula MBa 2 Cu 3 Ox wherein M is selected from the group consisting of Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu; x is from about 6.5 to about 7.0; said composition having a superconducting transition temperature of about 90 K; ,aid process consisting essentially of heating a precursor powder in an oxygen-containing atmosphere at a temperature from about 875°C to about 950*C for a time sufficient to form MBa 2 Cu30y, where y is from about 6.0 to about 6,4; and maintaining the MBa 2 Cu 3 0y in anr oxygen-containing atmospheie while cooling for a time sufficient to obtain the desired product; said precursor powder being prepared by mixing M 2 0 3 Ba(OH) 2 .8H 2 0 and CuO powders in an atomic ratio of M:Ba:Cu of about or forming an aqueous solution of M(NO 3 3 Ba(NO3) 2 and Cu(NO 3 2 in an atomic ratio of M:Ba:Cu of about 1:2:3, adding to the resulting solution sufficient citric acid monohydrate to convert the metals present to their correspondiri citrates, and spray drying the resulting solution to obtain the precursor powder.

1 pi ;I IMMENOWN WO 88/10o1i5 PCT/US8/02o25 14 heating times can be usecd After cooling as .1 b WO 88/10515 PCT/US88/02025

TITLE

TMPROVED PROCESS FOR MAKING 90 K SUPERCONDUJCTORS BACKGROUND OF 'PHE INVENTION Field of the Invention This invention relates to an improved process for making rare earth-barium-copper oxide superconductors with transit$,on temperatures above

K.

Description of Related Art Bednorz and Muller, Z. Phys. B64, 189-193 (1986), disclose a superconducting phase in the La-Ba-Cu-O system with a supercc~iducting transition temperature of about 35 ~.Samples were prepared by a coprecipitation method from aqueous s-olutions of Ba-, La- and Cu-nitrate in their app~rolriate ratios.

An aqueous solution of oxalic iicid 'was used hs the precipitant.

Chu et al. thais. Rev. Lett,~ 58, 405-407 (1987), report detection of an apiremt superr,,nducting transition with an om-vet temperature .above 40 K under pressure in the. Ia-32k-Cu-0 compound system synthesized direct.ly frani a svoLid-state reaction of La 2 O0 3 1 CuO and BaCD, fiwed by a decomposition of the mixture im a red-aried atmosphere.

Chu et al., Science 235, 567-5B1 disclose that a superconducting transition wi! an onset temperature of 52.5 K ha's been obsemwed under hydrostatic pressure in compounds wit'tft momitial compositions given by (La 09Ba 0 1 2 Cuogy where y is undetermined, They state that the Z. iF 4 layer structure has been proposed to be Tessible for th~e high-temperature superconductivity in thbe La-Ba-Cu-O system (LBCO). They further state tdx, however, the small diamagnetic signal, in contrast !to the presence 3S of up to 100% K 2 NiF 4 phase in their s.-mples, raises a I i ;i i WO 88/10515 PCT/US88/02025 2 question about the exact location of superconductivity in LBCO.

Cava et al., Phys. Rev. Lett. 58, 408-410 (1987), disclose bulk superconductivity at 36 K in La .8 Sr 0 2 CuO 4 prepared from appropriatemixtures of high purity La(OH) 3 SrCO 3 and CuO powders, heated for several days in air at 1000 0 C in quartz crucibles. Rao et al., Current Science 56, 47-49 (1987), discuss superconducting properties of compositions which include La l 8 Sr 0 .2CuO 4 La 1 85 Ba0.

15 Cu4, La 1 8 Sr0.

1 Cu0 4 (Lal-xPrx 2-ySryCu 4 and (La1.

75 Eu0.

25 )Sr 0 2 CuO 4 Bednorz et al., Europhys. Lett. 3, 379-384 (1987), report that susceptibility measurements support h.gh-T c superconductivity in the Ba-La-Cu-0 system.

In general, in the La-Ba-Cu-0 system, the superconducting phase has been identified as -the composition La 1 (Ba,Sr,Ca)x cuo0 4 wi-h the tetragonal

K

2 NiF 4 -type stru;ture and with x typically about 0.15 and y indicating oxygen vacancies.

Wu et al., Phys. Rev. Lett. 58, 908-910 (1987), disclose a superconducting phase in the Y-Ba-Cu-0 system with a superconducting transition temperature between 80 and 93 K The compounds investigated were prepared with nominal composition (Y _xBa 2 CuO 4 and x 0.4 by a solid-state reaction of appropriate amounts of 7 O 3 BaCO 3 and CuO in a manner similar to that described in Chu et al., Phys. Rev. Lett. 58, 405-407 (1987). Said reaction method comprises more specifically heating the oxides in a reduced oxygen atmosphere of 2x10 bars (2 Pa) at 900'C for 6 hours. The reacted mixture wac. pulverized and the heating step was repeated, he thoroughly reacted mixture was then pressed into 3/16 inch (0.5 cm) diameter cylinders for final sintering at 925 0 C for 24 hours in the same *R t i 01 :I i r WO 88/10515 PcT/us88/02025 3 reduced oxygen atmosphere. The mat eial prepared showed the existence of multiple phases.

Hor et al., Phys. Rev. Lett 58, 911-912 (1987), disclose that pressure has oily a slight effect on the superconducting transition, temperature of the Y-Ba-Cu-O superconductors described by Wu et al., supra.

Sun et al., Phys. Rev. Lett. 58, 1574-1576 (1987), disclose the results of a study of Y-Ba-Cu-O samples exhibiting superconductivity with transition temperatures in the 90 K range. The samples were prepared from mixtures of high-purity Y 2 0 3 BaCO 3 and CuO powders. The powders were premixed in methanol or water and subsequently heated to 1001C to evaporate the solvent. Two thermal heat treaments were used. In the first, the samples were heated in Pt crucibles for 6 hours in air at 8500C and then. for another 6 hours'at 1000°C. After the first firing, the samples were a dark-green powder, and after the second firing, they became a very porous, black solid. In the second method, the powders were heated for 8-10 hours at 1000 0 C, ground and then cold pressed to form disks of about I cm diamete: and 0.2 cm thickness. The superconducting propertis of samples prepared in thee two ways were similar.

X-ray diffraction examination of the samples revealed the existence of multiple phases.

Cava et al., Phys. Rev. Lett. 58, 1676-1679 (1987), have identified this superconducting Y-Ba-Cu-0 phase to be orthorhombic, distorted, oxygen-deficient perovskite YBa 2 Cu 3

O

9 where 6 is about 2,1, and have presented the X-ray diffraction powder pattern and lattice parameters for the phase.

The single-phase YEa 2 Cu 3 Og_6 was prepared in the following manner. BaCO 3

Y

2 0 3 and CuO were mixed, ground and then heated at 950 0 C in air for 1 day.

WO 88/10515 PCT/US88/02025 4 The material was then pressed into pellets, sintered in flowing 02 for 16 hours and cooled to 200 0 C in 02 before removal from the furnace. Additional overnight treatment in 02 at 700°C was tjund to improve the observed properties.

Takita et Jpn. J. App.' Phys. 26, L506-L507 (1987), disclose the preparation of several Y-Ba-Cu compositions wih, superconducting transitions around 90 K by a solid-state reaction method in which a mixture of Y 2 0 3 CuO, and BaCO 3 was heated in an oxygen atmosphere at 9500C for more than 3 hours.

The reacted mixture was pressed into 10 mm diameter disks for final sintering at 950° or 1000°C for about 3 hours in the same oxygen atmosphere.

Takabatake et al., Jpn. J. Appl. Phys. 26, L502-L503 (1987), disclose the preparation of samples of Ba xYxCuO3-z (x 0.1, 0.2, 0.25, 0.3, 0.4, 0.6, 0.8 and 0.9) from the appropriate mixtures of BaCO Y 2 0 3 and CuO. The mixture was pressed into a disc and sintered at 900 0 C for 15 hours in air. The sample with x 0.4 exhibited the sharpest superconducting transition with an onset near 96 K.

Syono et al., Jpn. J. Appl. Phys. 26, L498-L501 (1987), disclose the preparation of samples of superconducting Y 0 4 Ba 0 6 CuO 2 .22 with Tc higher than 88 K by firing mixtures of 4N Y 2 0 3 3N BaCO 3 and 3N CuO in the desired proportions. The mixtures were prefired at 1000C for 5 hours. They were ground, pelletized and sintered at 900°C for 15 hours in air and cooled to room temperature in the furnace. They also disclose that almost equivalent results were also obtained by starting from concentrated nitrate solution of 4N Y 2 0 3 GR grade Ba(N0 3 2 aaid Cu(NO 3 Takayama-Mutomachi et al., Jpg. J. Appl.

Phys 2, L476-L478 (1987), disclose th; preparation of a ,6ies of samples to try to identify the 1 ,.i WO88/10515 PCT/US88/02025 superconducting phase in the Y-Ba-Cu-0 system.

Appropriate amounts of Y 2 0 3 BaCO 3 and CuO were mixed in an agate mortar and then fired at 1173±2 K for 48-72 hours with intermediate grindings. X-ray diffraction powder patterns were obtained. The suggested composition of the superconducting compound is Yl Ba CuOy where 0.6<x<0.7.

Hosoya et al., Jpn. J. Appl. Phys. 26, L456-L457 (1987), disclose the preparation of various superconductor compositions in the L-Ba-Cu-0 systems where L Tm, Er, Ho, Dy, Eu and Lu. Mixtures of the proper amounts of the lanthanide oxide (99.9% pure), CuO and BaC0 3 were heated in air. The obtained powder specimens were reground, pressed into pellets and heated again.

Hirabayashi et al., Jpn. J. Appl. Phys. 26, L454-L455 (1987), disclose the preparation of superconductor samples of nominal composition Y Ba 2 3 CuO _x by coprecipitation from aqueous nitrate solution. Oxalic acid was used as the precipitant and insoluble Ba, Y and Cu compounds were formed at a constant pH of 6.8. The decomposition of the precipitate and the solid-state reaction were performed by firing in air at 900 0 C for 2 hours. The fired poducts were pulverized, cold-pressed into pellets and the; sintered in air at 900"C for hours. The authors found that the the sample was of nearly single phase having the £ormula Y Ba 2 Cu 3 07.

The diffraction pattern was obtained and indexed as having tetragonal symmetry, Ekino et al., Jpn. J. Appl. Phys. 26, L452-L453 (1987), disclose the preparation of a superconductor sample with nominal composition Y .1Ba .OCuO 4 y A prescribed amount of powders of

Y

2 0 3 BaCO 3 and CuO was mixed for about an hour, pressed under 6.4 ton/cm (14 MPa) into pellet shape h1 WO 88/10515 PCT/US88/02025 6 and sintered at 1000°C in air for 3 hours.

Akimitsu et al., Jpn. J. Appl. Phys. 26, L449-L451 (1987), disclose the preparation of samples with nominal compositions represented by (YxBax) 2 CuO 4 The specimens were prepared by mixing the appropriate amounts of powders of Y203, BaCO 3 and CuO. The resulting mixture was pressed and heated in air at 1000 0 C for 3 hours. Some samples were annealed at appropriate temperatures in 02 or

CO

2 for several hours. The authors noted that there seemed to be a tendency that samples annealed in 02 showed a superconducting transits n with a higher onset temperature but a broader transition than non-annealed samples.

Semba et al., Jpn. J. Appl. Phys. 26, L429-L431 (1987), disclose the preparation of samples of Y Ba-x CuO 4 -d where x 0.4 and 0.5 by the solid state reaction of BaC03, Y 2 0 3 and CuO. The mixtures are heated to 950 0 C for several hours, pulverized, and then pressed into disk shape. This is followed by the final heat treatment at 1100°C in one atmosphere 02 gas for 5 hours. The authors identified the phase that exhibited superconductivity above 90 K as one that was black with the atomic ratio of Y:Ba;Cu of 1:2:3. The diffraction pattern was obtained and indexed as having tetragonal symmetry.

Hatano et al., Jpn. J. Appl. Phys. 26, L374-L376 (1987), disclose the preparation of the superconductor compound Ba 0 7

Y

0 3 CulOx from the appropriate mixture of BaCO 3 (purity Y 2 0 3 (99.99%) and CuO The mixture was calcined in an alumina boat heated at 1000°C for 10 hours in a flowing oxygen atmosphere. The color of the resulting well-sintered block was black. I Hikami et al., Jpn. J. Appl. Phys. 26, (i 7 i

F

WO 858/10515' PCT/US88/02025 7 L347-L348 (1987), disclose the preparation of a Ho-Ba-Cu oxide, exhibiting the onset of superconductivity at 93 K and the resistance vanishing below 76 K, by heating a mixture of powders 3 BaCO 3 and CuO with the composition Ho:Ba:Cu 0.246:0.336:1 at 850°C in air for two hours. The sample was then pressed into a rectangular shape and sintered at 800 0 C for one hour. The sample looked black, but a small part was green.

llatsushita et al. Jpn. J. Appl. Phys. 26, L332-L333 (1987), disclose the preparation of Ba 0 5

Y

0 5 CulOx by mixing appropriate amounts of BaCO 3 (purity Y 2 0 3 (99.99%) and CuO The mixture was calcined at 1000"C for 71 hours in a flowing oxygen atmosphere. The resultant mixture was then pulverized and cold-pressed into disks. The S disks were sintered at 900C for 4 hours in,the same oxygen atmosphere. The calcined powder and disks were black. A superconducting onset temperature of 100 K was observed.

Maeno et al., Jpn. J. Appl. Phys. 26, L329-L331 (1987), disclose the preparation of vardous Y-Ba-Cu oxides by mixing powders of Y 2 0 3 BaCO 3 and CuO, all 99.99% pure, with a pestle and mortar, The powders were pressed at 100 kgf/cm 2 (98x10 4 Pa) for 10-15 minutes to form pellets with a diameter of 12 mm. The pellets were black. The heat treatment was performed in two steps in air. First, the pellets were heated in a horizontal, tubular furnace at 800 0

C

for 12 hours before the heater was turned off to cool the pellets in the furnace. The pellets were taken out of th& fuenace at about 200 0 C. About half the samples around the center of the furnace turned green iy colir, while others away from the center remained black- The strong correlation with location suggested to the authors that this reaction occurs i WO 88/10515 PCT/US88/02025 8 critically at about 800*C. The pellets were then heated at 1200 C for 3 hours and then allowed to cool. Pellets which turned light green during the first heat treatment became very hard solids whereas pellets which remained black in the first heat treatment slightly melted or melted down. Three of the samples exhibited an onset of superconductivity above SO K.

Iguchi et al., Jpn. J. Appl. Phys. 26, L327-L328 (1987), disclose the preparation of superconducting Y 0 .Ba 2 CuO 0 by sintering a stoichiometrical mixture of Y 2 0 3 BaCO, and CuO at 900 0 C and at 1000°C in air.

Hosoya et al., Jpn. J. Appl. Phys. 26, L325-L326 (1987), disclose the preparation of various superconducting specimens of the L-M-Cu-C systems where L Yb, Lu, Y, La, Ho and Dy and M ba and a mixture of Ba and Sr by heating the mixtures of appropriate amounts of the oxides of the rare earth elements (99.9% pure), CuO, SrCO 3 and/or BaCO 3 in air at about 9000C. Green powder was obtained. The powder samples were pressed to form pellets which were heated in air until the color became black.

Takagi et al., Jpn. J. Appl. Phys. 26, L320-L321 (1987), disclose the preparation of various Y-Ba-Cu oxides by reacting mixtures containing the prescribed amounts of powders of Y 2 0 3 BaCO 3 and CuO at 1000°C, remixing and heat-treating at 1100C for a few to several hours. An onset temperature of superconductivity at 95 K or higher was observed for a specimen with the nominal composition of (Y0.

9 Ba 0 .1 )CUOy Hikami et al., Jpn. J. Appl. Phys. 26, L314-L315 (1987), disclose th) preparation of compositions in the Y-Ba-Cu-0 system by heating the powders of Y 2 0 3 B0aCO 3 and CuO to 8000C or 9000C in

I,:

WO 88/10515 PCT/US88/02025 9 air for 2-4 hours, pressing into pellets at 4 kbars (4 x10 5Pa) and reheating to 800*C in ai7, for 2 hours for sintering. The samples show an onset of superconductivity at 85 K and a~ vanishing resistance at 45 K.

Bourne et al., Phys. Letters A 120, 494-496 (1987), disclose the preparation of Y-Ba-Cu-O samples ofY2-x BaxCu by pressing finely ground powders of Y 2 0 3 4 Ba C0 3 and CuO into pcllets and sintering the pellets in an oxygen atmosphere at 1082*C.

Superconductivity for samples having x equal to about 0.8 was reported.

Moodenbaugh et al., Phys. Rev. Lett. 58, 1,885-1887 (1987), disclose supercondu6tivity near K in multiphase samples with nominal composition 1 5 Lu 1 Ba 0 CuO 4 prepared from dried Lu 2 0 3 high-purity BaCP 3 (presumably Ba CO 3 )1 and f'l11y 6xidlzed Cuo.

These powders' were ground together in an agate mortar andI then fired overnight in air at l0OOC in Pt crucibles. This material was grou,'Id again, pelletizedo and then fired at 1100 0 C in air for 4-12 hours in Pt crucibles. Additional. samiples fire~l solely at 1000 0 C and those fired 1200*C show no0 signs of superconductivity.

Hot et al., Phys. Rev. Lett. 58, 1891-1894 (1987), disclose superconductivity in the 90 K range in ABa 2

CU

3

O

6 with A La, Ndo Sm, Eu, Gd, 1-b, Er, and Lu in addition to Y. The samples were synthesized by the..solid-state reaction of appropriate amounts of sesqujoxides of La, Nd, Sm, Eu# Gd, HO, Er, and Lu, ljaCO 3 and CuQ in a mnanner similar to that described. in Chu et al., Phs Re Lett, 58', 405 (1987) and Chu et Science 235, 567 (1987).

SUMMARY OF TIIE INVENTION Thi5 invention provides an inproved pctocess for Preparing supercorhducting comapositiont havinqg the WO 88/10515 PCT/US88/02025 formula MBa 2 Cu30, wherein M is selected from the group consisting of Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu; x is from about 6.5 to about said composition having a superconducting transition temperature of about 90 K; said process ponsisting essentially of heating a precursor powder in an oxygen-containing atmosphere at a temperature Zrom about 875*C to about 950C for a time sufficient to form MBa 2 Cu 3 y, where y is from about 6.0 to about 6.4; and maintaining the MBa Cu O in an oxygen-containing atmosphere while cooling for a time sufficient to obtain the desired product; said precursor powder being prepared by forming a mixture of Ba(OH) 2 -8H 2 0, M203 and CuO powders with the atomic ratio of M:Ba:Cu being about 1:2:3; or (b) forming aoi aqueous solution of M(N0 3 3 Ba(NO 3 2 and Cu(NO3) 2 in an atomic ratio of M:Ba:CU of About 12:3, adding to the resulting solution sufflcient citric acid monohydrate to convert the metals present to their corresponding citrates, and spray drying the 2G resulting solution to obtain the precursor powder.

The precursor powder prepared in can be pressed into a desired shape prior to heating. The invention also provides the shaped article prepared by the process of the invention.

DETAILED DESCRIPTION OF THE INVENTION The process of the invention provides an improved process for preparing superconducting compositions having, the formula MBa 2 CI30 x M is selected from the group consisting of Y, Nd, Sm, Eu, Gd Dy, Ho, Er, Tm, Yb and Lu, but is preferably Y.

The parameter x is from about 6.5 to about 7.0, but is preferably from about 6.8 to about In the process of the invention a precursor powder is prepared for later heating, In one embodiment of the invention the precursor powder is i. WO 88/10515 PCT/US88/02025 11 prepared by mixing M 2 0 3

B-(OH)

2 8H20 and CuO powders in an atomic ratio of M-r':Atu of about 1:2:3. The powders are mixed well in sXing device or by hand using a mortar ard pestle to obtain an intimate mixture of reactants. The use of Ba(OH) 2 8H 2 0 as the source of Ba results in the preparation of a uniform, practically single-phase, superconductinq MBa 2 Cu3 0 x composition.

In another and preferred embodiment of the process of the invention the appropriate precursor powder is prepared by forming an aqueous solution of

M(NO

3 3 Ba(NO 3 2 and Cu(N0 3 2 in an atomic ratio of M:Ba:Cu of about 1:2:3. The aqueous solution of nitrates can be prepared by starting with the appropriate nitrate salts. Alternatively, the aqueous solution of nitrates can be prepared by reacting Ba(OH) 2 8H 2 0 or BaC03, M 2 0 3 'and CuO powders with sufficient concentrated nitric acid to convert the metals present td metal nitrates, 'Ecess concentrated nitric acid can be used to speed the reaction. The amount of concentrated nitric acid used i: typically between one and two times the amount needed to convert all the metals present to metal nitrates. If nitric acid conversion is used, the resulting mixture is diluted with water until a clear solution is obtained. As used heie! "i~.ear solution" means one containing no undissoisd solids.

To the solution of nitrates is added an amount of citric acid monohydrate at least sufficient to convert all metals present to metal citrates.

Typically, the amount of citric acid monohydrate used is between one and two times the amon"t needed to convert all the metals present to metal citrates, SThe acidic nitrate solution prevents precipitation of the citrates. The resulting citrate/nitrate solution is then spray dried using conventional spray-drying

:NEW

PCr/US38/02J25 WO 88/10515 12 techniques and equipment to obtain the precursor powder. Spray drying the citrate/nitrate solution provides a well mixed precursor and results in the preparation of a uniform, practically single-phase, superconducting MBa 2 Cu30 x product after he heating and cooling steps. The X-ray diffraction pattern of the superconducting product prepared by spray-drying to obtain the precursor powder and then heating and cooling as described herein has significantly less impurity than does the superconducting product prepared by mixing the oxides and Ba(OH) 2 8H 2 0 and heating and cooling as described herein.

Preferably, the starting materials used in the process of the invention are of high purity, e.g.

99.99% by weight for CuO and 99.9% by weight for M203. Less pure starting rmaterials can be used; however, the product may then contain an amount of another phase material comparable to the amount of impurity in the stariting materials. It is particularly important to avoid the presence of impurities containing iron and other transition, but non-rare earth, metals in the reactants.

The precursor powder is then leated in an oxygen-containing atmosphere at a temperature from about 8750C to about 950 0 C, preferably from about 900*C to about 950*C, for a time sufficient to form MBa 2 Cu 3 y where y is from about 6.0 to about 6.4.

It has been determined by TGA data that when the precursor powder is heated to 9000C, y is from about to about 6.4. Alternatively, prioi" to heating when the precursor powder is made by mixing M203, Ba(OH) 2 .8H 2 0 and CuO powders, the precursor powder can be pressed into a disk, bar or other desired shape using conventional techniques. For heating, the precursor powder is placed in a non-reactive container su.ch an a alumina or cold crucible. The iT

LI

WO 88/10515 PCT/US88/02025 V r,

V

oxygen-containing atmosphere can be air or oxygen gas, but is preferably oxygen.

The container with the precursor powder is placed in a furnace and brought to a temperatui.e of from about 8750C to about 950 0 C. It is the total time that the precursor powder is at temperatures in this range that is important. For the Ba(OH) 2 .8H 2 0 precursor powder heating rates of 10*C per minute to 500C per minute can be used to raise the temperature of the furnace containing the sample from ambient temperature to the final heating temperature of from about 8750C to about 9500C. When the final heating temperature is 900 0 C, 1/2 hour is sufficient time to maintain the sample at 900 0 C to produce, after cooling, practically single-phase superconducting MSa 2 CIL1 3 OX. When the final heating temperature is 940'C, 2 minutes i-s sufficient time to maintain the 'sample at 940 0 C to prod'4ce, aftervooling, practically single-phase superconducting MBa2 Cu 3 O Alternatively, the container can be placed directly into an oven already heated to the final heating tempera ture. Longer heating times can be used.

For heating the spray-dried precursor, if slower heating rates are used, the minimum time for which the sample must be maintained at a final temperature of from about 8750C to about 9500C is shorter. If faster heating rates are used, the minimum time for which the sample must be maintained at a final temperature of from about 875*C to about 950*C is longer. For example, when a heating rate of 500C per minute is used to raise the temperature of the furnace containing the sample from ambient temperature to a final heatLng temperature of 900'C, 1/2 hour is sufficient time to maintain the sample at 900*C to producoo after cooling, practically single-phase superconducting Msa 2 CU30O., Longer

I

WO 88/0515 heating describ pressed a shape 5 is turn to cool time su Prefera 350C (a the samp ILuring t material product.

crystall cooling diffusio lattice I temperat forip etc 20 comh/inati the desir uptake by the esir hour unde fotlm of a However, i particles, the times 500 0 C in a jo articles w than will S in tered, desired pr powder or ibm A

WWWV

DOCMENT

I

14I iiWO88/10515 PCT/US88/02025 heating times can be useq. After cooling as described herein, the MBi12Cu30 product can be pressed into a desir.d _aape and sintetced to provide a shaped article.

At the end of the heating time, the furnace is turned off, and the resulting material is allowed to cool in the oxygen-containing atmosphere for a time sufficient to obtain the desired product.

Preferably, the material is cooled to below about 350°C (a tims interval of about 1-1.5 hours) before the sample container is removed from the furnacr.

Iuring the cooling step, the oxygen content of the material increases to give the desired MBa 2 Cu30 x product. The additional oxygen which enters into the crystalline lattice of the material during this cooling step to form the desired product does so by diffusion.% The rate at which'oxygen enters the lattice is determined by a complex function of time, temperature, oxygen content of the atmosphere, sample form, etc. Consequently, there are numerous combinations of these conditions that will result in the desired product. For example, the rate of oxygen uptake by the material at 500°C in air is rapid, and the Oesired product can be obtained in less than an hour under these conditions when the sample is in the form of a loosely packed, fine particle powder.

However, if the sample is in the form of larger particles, densely packed powders or shaped articlers the times required'to obtain the desired product at 500°C in air will increase. Well sintered, shaped articles will take longer to form the desired product than will more porous ones, and for larger, well sintered, shaped articles many hours may be required.

A convenient procedure for obtaining the desi.red prodk.t when the material is in the form of a powder or a smalU shaped object is to turn off thq

I

.WO088/10515 PCY/US88/ 02025 furnace in which the heating was conducted and to allow the material to cool in the furnace to a temperature approaching ambient temperature (about 22*C) which, typically requires a few houxr!s. In the examples, cooling in the furnace to below about 350*C was found to be sufficievit. Increasing tihe partial pressure of oxygen in the atmosphexte suirounding the sample during cooling increases th'e rate at which oxygen enters the lattice. 7f, im a particular experiment, the material is coolet in v~mriln a manner that the 1Ba 2 CU 3 0 X product is not adtaiti the material can be heated to an intem~ia±-m temperature, such as 5910'C, betwee'. aiient temperature and the final temperatmm- iei in the heating step and held at this terk-rt~we for a sufficient time to obtln the 6esiieZ po~cict.. If the MBa 2 CujOx product is pressed lm a dezaired shape and sintered at about 900 0 C to abit SSVI~C,, the above cooling considerations would then aply ±h resulting shaped ,rticle.

The product powder formed iby tJe jprocess of the invention is practically siagle-,,ha,,ze and has orthorhombic symmetry as determinedi tby X-ruay diffraction measureme-nts.

The process of this invemtiizm provides a 2S single heating-step, method for przpaig a superconducting MBa 2 Cu 3 Q 0xComposititm that does not require a special atmosphere during the -heating step, subsequent grinding, reheating or zmealin-g, extended heating times or refining of the prmduct to separate the desired superconducting M'Ba 2 Cu P7 corpsition from other phases. Th e h c.-t mode contemplated for carrying out the inventiejn is described in Example As used herein the phrase "consisting essentially Of" means that additional steps c 'cn be Sadded to the process of the invention jo lonq, as such WO 88/10515 PCT/US88/020125 16 steps do not materially alter the basic and novel characteristics of the invention. Superconductivity can be confirmed by observing flux exclusion, i. e., the. Meissner effect.

The invention is further illustrated by the following examples in which temperatures are in degrees Celsius unless otherwise indicated. The chemicals (with purity indicated) used in the following the examples are Ba(OH) 2 8H 2 0 (48.6% BaO) obtained from Kali-Chemie, CuO (99.99%) obtained from Johnson and Matthey or Puratronic or obtained from Fluka, 'Y 2 0 3 (99.99%) obtained from Research Chemicals. 'High purity chemicals were used to demonstrate that the process of the invent.on ca, result in single-phase or practically single-phase MBa EXAMPLE 1 Ba(OHY 2 .8H 2 0 (2.644 g 1.000 g of CuO, and 01474 g of Y 2 0 3 were ground together in an agate mortar for 15 minutes, and the resulting mixed powder was pressed into disks approximately 1 cm in diameter and 0.2 cm in thickness. One disk was placed in an alumina (A1 2 0 3 container and heated in air in a furnace from ambient temperature to a final heating temperature of 900' at a rate of about 500 per minute. The temperature was maintained at 9000 for minutes. The furnace was then turned off and allowed to cool to below 350° (an elapsed time of about 1-1.5 hours) after which the sample was removed. The fired disk was black. An X-ray diffraction powder pattern was obtained on the crushed disk. The X-ray diffraction pattern indicated that the product was YBa 2 Cu3 0 x with orthowhombic symmetry and contained a very small amount of Y 2 BaCuO 5 as an impurity. The material exhibited the Meissner effect at about 90 K, thereby

I

WO R/i101 PCT/US88/02025 17 indicating a superconducting transition of about

K.

EXAMPLE 2 A disk prepared pubstantially as described in Example 1 was placed in an alumina container and heated in flowing oxygen by inserting the sample directly into a tube furnace already at a temperature of 900°. The temperature was maintained at 9000 for minutes. The furnace was then turned off and allowed, to cool to about 350" (an elapsed time of about 1-1.5 hours) after which the sample was removed. The resulting fired disk was black. An X-ray diffraction powder pattern was obtained on the crushed disk. The pattern showed that the product was YBa 2 Cu 3 Ox with orthorhombic symmetry and contained a very small amount of Y 2 BaCuO 5 as an impurity. The material exhibited the Meissner effect at about 90 K, thereby indicating a superconducting transition of about 90 K.

EXAMPLE 3 A disk prepared substantially as described in Example 1 was placed in an alumina container and heated in air in a furnace from ambient temperature to a final heating temperature of 9400 at a rate of about 500 per minute. The temperature was maintained at 940* for 2 minutes. The furnace was then turned off and allowed to cool to about 350'C (an elapsed time of about 1-1.5 hours) after which the sample was removed. The resulting fired disk was black. An X-ray diCfraction powder pattern was obtained on the 3\1 crushed disk. The pattern showed that the product was YBa Cu30 x with orthorhombic symmetry and contained trace amounts of impurity. The material exhibited the Meissner effect at about 90 K, thereby indicating a superconducting transition of about 90 K.

WO 88/10515 PCT/US88/02025 18 EXAMPLE 4 Ba(OH) 2 8H 2 0 (7.929 g 3.000 g of CuO, and 1.419 g of Y 2 0 3 were placed in a 250 ml beaker and 15 ml of concentrated nitric-acid were added.

When all of the CuO was dissolved, a. mixture consisting of a blue solution and undissolved white material was obtained. The mixture was diluted with until all of the solid material was dissolved.

The volume of the final solution was about 200 ml.

Citric acid monohydrate (15 g) was added to the blue solution, and the resulting mixture was stirred for a minute to give a clear blue solution again. This solution was spray dried to give a blue powder.

Spray drying was performed by using a Buchi No. 190 mini spray dryer operated with N 2 as the atomizing gas. An inlet temperature of 1900 and an outlet temperature of 950-115° were employed. The chamber: atmosphere, was air. A portion of the resulting spray-dried material was placed in an hlumirt, container and heated in air in a furnace froa ambient temperature to a .final heating temperature of 900° at a rate of about 500 per minute. The' temperature was maintained at 9000 for 30 minutes. The furnace was then turneO off and allowed to cool to about 3500 (an elapsed time of about 1-1.5 hours) after which the sample was removed. The fired powder was black. An X-ray diffraction powder pattern was obtained and showed the product to be orthorhombic YBa 2 Cu3 0 x with a trace of a second phase detected. The material e exhibited the Meissner effect at about 90 K, thereby indicating a superconducting transition at about

K.

EXAMPLE A portion of the spray-dried material prepared in Example 4 was placed in an alumina container and subjected to heat and cooling WO 88/10515 PCT/US88/02025 19 treatments similar to those described in Example 4 except that heating was conducted in flowing oxygen.

The results were practically identical to those found in Example 4. The fired powder was black. An X-ray diffraction powder pattern was obtained and showed the product to be orthorhombic YBa 2 Cu30 x with a trace of a second phase detected. The material exhibited the Meissner effect at about 90 K, thereby indicating a superconducting transition at about 90 K.

Claims (18)

1. An improved process for preparing a superconducting compositiop having the formula wherein M is selected from the group consisting of Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu; x is from about 6.5 to about said composition having a superconducting transition temperature of about 90 K; said process consisting essentially of heating a precursor powder in an oxygen-containing atmosphere at a temperature from abeai-t-875C to abeut- 950C for a time sufficient to form MBa 2 Cu 3 0 where y is from abeut 6.0 to abeut-6.4; and maintaining the MBa 2 Cu 3 O0 in an oxygen-containing atmosphere while cooling for a time sufficient to obtain the desired product; said precursor powder being prepared by mixing M203, Ba(OH) 2 .8H 2 0 and CuO powders in an atomic ratio of M:Ba:Cu of about 1:2:3, or forming an aqueous solution of M(NO 3 3 Ba(NO 3 2 and Cu(NO 3 2 in an atomic ratio of M:Ba:Cu of about 1:2:3, adding to the resulting solution sufficient citric acid monohydrate to convert the metals present to their corresponding citrates, and spray drying the resulting solution to obtain the precursor powder.

2. A process according to Claim 1 wherein the precursor powder is prepared by mixing M203, Ba(OH) 2 8H 2 0 and CuO powders.

3. A process according to Claim 2 wherein the precursor powder is pressed into a desired shape prior to neating. 4, A process according to Claim 2 wherein i VO 88/10515 8/ 1515PCT/US88/02025 the precursor mixture is heated at a about- 900 0 C to abu 9501C. A pro-ess according to the precursor mixture is heated at a *a~o"u 900 0 C to 9500C.

6. A process according to x is f£rom abeut 6. 8 to -abeut- 7. 0.

7. A process according to x is from abeut~ 6.8 to

8. A process according to 'M is Y. temperature from Claim 3 wherein temnperature from Claim 4 wherein Claim 5 wherein Claim 6 wherein

9. A process aqcording to Claim 7 wherein M is Y.

10. A shaped article prepared according to the process of Claim 3. is 11. A shaped article prepared according to T.he'process of Claim

12. A shaped article prepared according to the process of Claim 7.

13. A shaped article prepared according to the process of Claim 9.

14. A process according to Claim 1 wherein the precursor powder is prepared by forming an aqueous solution of M'(N0 3 3 Ba(NO 3 2 and Cu(NO 3 2 in an atomic ratio of t1:Ba:Cu of about 1:2:3, adding to the resulting solution sufficient citric acid -monohydrate to convert the metals present to their corresponding citrates, and spray drying the resulting solution.

15. A process according to claim 14 wherein 3 0 the precursor powder i~s he,'ated at a temperature from abouet 90O'C to a-e ~-950 0 C.

16. A process according to Claim 1S wherein x is from aku 6.8 to 4. 17, A process according to Claim JC wherein R is Y. 'I .Ili I II WO 88/10515 PC/US88/02025 22

18. A process according to Claim 14 wherein. the MBa 2 Cu30 x powder is pressed into a desired shape and sintered.

19. A process according to Claim 15 wherein the MBa 2 Cu 3 g powder is pressed into a desired shape and sintered. A process according to Claim 16 wherein the MBa 2 Cu 3 O. powder is pressed into a desired shape and sintered.

21. A process according to Claim 17 wherein the MBa.Cu 3 0x powder is pressed into a desired shape and sintered. 22, A shaped article prepared according to the process of Claim 18.

23. A shaped article prepared according to the process of Claim 19.

24. A shapedarticle prepared according to the process of Claim A shaped article prepared according to the process of Claim 21. -k r INTERNATIONAL SEARCH REPORT Application No, PCT/USe k/0_2025 I. CLASSIFICATION OF SUBJECT MATTER (it several cloassficiion symbols apply, indicate all) Accordr4 Ito rLterna ilnal 0,0-s, f' i.sslflcation (lp Or; '9th National Classiflcation inad IPC 1-101 ILO 39/1 2' US CLj. 505/1!. 252/500 I1, FIELDS SEARCHED hMinimi'm bocumnontafant Searched 7 Classificaion~ iSlen Clisf-aif ybl U.S' 252/500f 518, 521; 427/79; 505/1 Documentation Searched other thin MinImumn Documentation to the Extent that such Documents are Included In the Fields Searched 8 1ll. DOCUMENTS CONSIDERED TO BE RELEVANT Category Citation of Document, 11 with Indicaion. where appropriate, of the relevant passages 12 Relevant to Claim No Y US, A, 3,330,6)97 P 7CFIINt) 1,14-25 11 JK77W 1967, See entire 0'octten Y US, A, 4,.636,379 (PASTOR ET A.L) 1-13 13 JANUARY 1987, See entire document.. y US, A, 4,r661,282 (CLAR 1-13 28 APRITL 1987, See entire ocijment. Y JOURNAL OF THRII AM!MICAN CK]WICAL SOCUiTY 1,114-25 Toliinle 53, No. 1 issued JANUARY 1970 (US) C. !i1ARCXT 4 T 4 Y B'T AL. "Preparation of fiighly Dis 'perse. Wxed Oxides 4n,.d oxide Soidc 1 S13Q I~ q by Pt/rolygi9 of. Arorpholls Qrcjani Prectirstprs" see pacje:, 56-57. i PoWder kletal11lrgv 1975 N0 1,1142 D. Artdetton et R1. "Production of Conctictinct Ox4t&~ Powdercs boy Arxorpbotls Qitrate pr'ocegss see racfe8 14-21. 1SC4ecial cateoories of Cited dcumeite: to' later document published after the international Iling date e~rientdeflingthe eneal eate t te ar ~hh isnot or priority date and hot in tponiqt with the' application but ""dcundefinn t h e parilr releancte ar Oo i o ited to understand the Principle or theory underlying the Cons~etG to e ofpari~ohr feQvdni~rinvention I. 116", earlier ildurument but Published On or after the international document of particular relevancet the claimed inventton fifing date cannot be considered novel or Cannot be Considered to IV document which may throw doubts on priority claim(s) Or involve an inventive step which is 0itd to establish the oublication dala of another 'Y douettPrIulreeanethclmdIvnin cittio or~."A~eia resontasSpeif~d)cannot be considered to involve ari iniventive step when the 0,i document Wafrring to an, oral disclosure, use, eithibition or document it combined with one or moie other such dodu* Other means ments, such combiination being obvious to a person skilted 1113' document published prior to the international, filin date but in the art later than the priority date Claimed &"document member of the same patent family Date of the AMtua Completion Of th"111vtornalional Searh Date O' Maitlflb of this initef tatiortal Search Report 26 STPTr3VBM 1588 NV~8 InternatIonal 5garching Authority Siognature of Authorized Qmcet- tCSA/ S T.INDA SHIMAT1G ~Ornt PCTflSA/~f 0 liecurd ehe.i) tFis~,tt'8~ -m -U- 4 1 International Application No, Ill., DOCUMENTS CONSIDERED TO BE RELEVANT (CONTINUED FROM THE SECOND SHEET) Category j ition 01 iocurnent, with indication, where appropriate, ol the relevant paasar~es X 'Physical ReVieWLetters Volume 58 No. 16 Y issued 20 Apri.l 1987, R. Cava et al. "Bulk Superconductivit. at 93-K in Single Phase Oxcygen-Deficiernt Perovskite 1a 2 yCu 3 0 9 -d'i. X Ja~ianese Journal of Applied Physics Y Volume 26 No. 4 issued April 1987, M. Hirabayashi et "Structure and Superconductivity in a New Type of Oxygen Deficient Perovskites YlBa 2 Cu 3 O 7 pages L454-L455. Reievant to Claim No 10-13, 22-25 I10-13, 22-25 I x A y y P1iysical Review Letters Volume 58 No. 18 iwasued 04 May 1987, P. Hor et al. "Sunrconductivity above 90K in the Square Planor Compound System ABa 2 Cu 3 0 6 +x with A Y, Lr, Nd, Sm, Eu, Gd, Ho, Er, and Lu" see pages 1891-1894. Physical Review Letters Volume- 58 No. 18 issued 04 May 1967, A Moodenbaught et al. "Superconductivity near 90K in the Lu-Ba-Cu-O Syiztem" pages 1885-1887. Japanese Journal of Applied Physics Volume 26 No. 5 issued May 1987, T. Kawai et al.. "Preparation of High- Tc Y-Ba-Cu-0 Superconductor" see pages L736-L737. Japanese Journal. of Applied Physics Vo).um~ 26 No. 5 issued M~ay 1987, M. Udagawa eta. "R~aman and infrared Spectra of a Green Y 2 BaCu 05-.y" see pages Lf358-L859. Zeitschrift Fur Physik< B- Condensed Matter Volume 66 issued 1987, C. Politis et al "ISuperconductivity at 40K in Laj.8 Sr 0 2 CUO 4 see pages 141-146. Advanoved Ceramic Materials, Volume 2 No. 3ai, special issue, Published July 1987, W.J. Weber et "ISyntliesis and Characterization of YBa 2 Cu 3 0 7-x superconductoz~s" pages 471-479. Advanceii Ceramic Materials,"Volume 2, No. 3B, spnecial issue published July 1987, B. Dunn et al.. "Properties of Suioerconducting Oxides Prepared by the Amorphous Citrate Process" Pages 343-352., 10-13,22-25 1-25 1-25 1-13 1-25 1-13 1-13 1 14-25 Form POT11SN210 (extra it") (A&YA 1-87