AU608644B2 - Improved process for making 90k superconductors - Google Patents

Description

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PCT

INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT) (51) International Patent Classification 4 (11) International Publication Number: WO 88/ 09555 H01B 1/06, C04B 33/32 A l (43) Iaternational Publication Date: I December 1988 (01.12.88) (21) International Application Number: PCT/US88/01434 (81) Designated States: AT (European patent), AU, BE (European patent), CH (European patent), DE (Euro- (22) International Filing Date: 6 May 1988 (06.05.88) pean patent), DK, FR (European pate GB (European patent), HU, IT (European paten, JP, KR, LU (European patent), NL (European patent), NO, SE (31) Priority Application Numbers: 051,860 (European patent), SU, 076,686 (32) Priority Dates: 19 May 1987 (19.05.87) Published 22 July 1987 (22.07.87) With international search report.

Before the expiration of the time limit for amending the (33) Priority Country: US claims and to be republished in the event of the receipt of amendments.

(71) Applicant: E.I. DU PONT DE NEMOURS AND COMPANY [US/US]; 1007 Market Street, Wilming-. 3 F 19 ton, DE 19898 AO.J. P, 2 3 FEB 1989 (72) Inventor: SUBRAMANIAN, Mumirpallam, Appaborai 119 Dutton Drive, New Castle, DE 19720 AUSTRALIAN AUSTRAlIAN (74) Agent: WOLFSON, Herbert, E.I. du Pont de Nemours and Company, Legal Department, Patent Divi- 2 1 DEC 1988 sion, Wilmington, DE 19898 (US).

PATENT OFFICE (54) Title: IMPROVED PROCESS FOR MAKING 90 K SUPERCONDUCTORS (57) Abstract There is disclosed an. improved r ocess for preparing a superconducting composition having the formula MBa 2 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; said process consisting essentially of mixing M 2 0 3 Ba0 2 and CuO in an atomic ratio of M:Ba:Cu of about 1:2:i to obtain a powder mixture; heating the resulting mixture in an oxygen-containing atmosphere at a temperature from about 850°C to about 925 C for a time sufficient to form MBa 2 Cu3 where y is from about 6.0 to about 6.4; and maintaining the MBa 2 Cu 3 Oy in an oxygen-containing atmosphere while co6ling for a time sufficient to obtain the desired product.

This doitumen t contains the a.enlldmicnts made under Section 49 and is correct for printing, i :r WO 88/09555 PCT/US88/01434 1

TITLE

IMPROVED PROCESS FOR MAKING 90 K SUPERCONDUCTORS C- FqrENCE TOR TS IATO This is a continuatin-' p ort of copending patent applicitie -S al No. 051,860, filed on May f BACKGROUND OF THE INVENTION Field of the Invention This inrention relates to an improved process for making rare earth-barium-copper oxide superconductors with transition 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 superconducting transition temperature of about 35 K. Samples were prepared by a coprecipitation method from aqueous solutions of Ba-, La- and Cu-nitrate in theit appropriate ratios.

An aqueous solution of oxalic acid was used as the precipitant.

Chu et al., Phys. Rev. Lett,, 58, 405-407 (1987), report datection of an apparent superconducting transition with an onset temperature above 40 K under pressure in the La-Ba-Cu-O compound system synthesized directly from a solid-state reaction of La20 CuO and BaCO followed by a decomposition of the mixture in a reduced atmosphere.

Chu et al., Science 235, 567-569 (1987), disclose that a superconducting transition with an onset temperature of 52.5 K has been observed under hydrostatic pressure in compounds with nominal compositions given by (La 0 ,Ba0 1 2 CuO 4 Y, where y is undetermined. They state that the K 2 NiF 4 layer

'AI

WO 88/09555 PCT/US88/01'434 2 structure has been proposed to be responsible for the high-temperature superconductivity in the La-Ba-Cu-O system (LBCO). They further state that, however, the small diamagnetic signal, in contrast to the presence of up to 100% K2NiF 4 phase in their samples, raises a 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. Sr 0 .2CuO 4 prepared from appropriate mixtures of high purity La(OH) SrCO 3 and CuO powders, heated fo 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 8 Sr 2 CuO La1.a Ba0.1 CuO Lal. Sro 0 i C u 4 (La 1 -Prx )2-ySr CuO and (La 1 Eu 0 2 )S 0

O.

2 CuO 4 Bednorz et al., Europhys. Lett. 3, 379-384 (1987), report that susceptibility measurements support high-Ta superconductivity in the Ba-La-Cu-0 system.

In general, in the La-Ba-Cu-0 system, the superconducting phase has been identified as tho composition Lax (Ba,Sr,Ca)O 4 with the tetragonal

K

2 NiF 4 -type structure 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 (Y1 _Bax )CuO 4 _y and x 0.4 by a solid-state reaction of appropriate amounts of Y 2 03, BaCO, and CuO in a manner similar to that discribed 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" i

V

WO 88/09555 PCT/US88/01434 3 bars (2 Pa) at 900C for 6 hours. The reacted mixture was pulverized and the heating step was repeated. The 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 reduced oxygen atmosphere. The material prepared showed the existence of multiple phases.

Hor et al., Phys. Rev. Lett. 58, 911-912 (1987), disclose that pressure has only a slight effect on the superconducting transition temperature of the Y-Ba-Cu-0 superconductors described by Wu et al., supra.

Arjomand et al., J.C.S. Dalton 1061-1066 (1975), disclose the preparation of BaCu02, by, heating an equi.olar mixture of BaO 2 and CuV'NO 3 2 at 580 0 C for 24 hours.

SUMMARY OF T:dE INVENTION This invention provides an improved process for preparing superconducting compositions having the formula MBa 2 Cu30 x 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; said process consisting essentially of mixing M23 BaO 2 and CuO in an atomic ratio of M:Ba:Cu of about 1:2:3 to obtain a powder mixture; heating the resulting mixture in an oxygen-containing atmosphere at a temperature of from about 850°C to about 925 0 C for a time sufficient to form MBa 2 Cu 3 0 where y is from about 6.0 to about 6.4; and maintaining the MBa 2 Cu Oy in an oxygen-containing atmosphere while cooling for a time sufficient to obtain the desired product. The powder mixture can be pressed into a desired shape prior to heating. The invention also provides the shaped article prepared by the process of the invention.

WO 88/09555 PCT/US88/01434 4 DETAILED DESCRIPTION OF THE INVENTION The process of the invention provides an improved process for preparing superconducting compositions having the formula MBa2Cu O x M is selected from the group consisting of Y, Nd, Sm, jSu, Gd, Dy, Ho, Er, Tm, Yb and Lu, but is preferably Y, Eu or Er, and is most preferably Y. The parameter x is from about 6.5 to about 7.0, but is preferably from about 6.8 to about 7.0. In the process of the invention, the use of BaO 2 as the source of Ba results in the preparation of a uniform single-phase superconducting MBa 2 CuO 3 composition.

The process of the invention cohsists essentially of mixing M 03, BaO and CuO in an atomic ratio of M:Ba:Cu of about 1:2:3 to obtain a powder mixture and heating and cooling the resulting mixture as described below. The starting materials are mixed well in a mixing device or by hand using a mortar and pestle to obtain an intimate powder mixture of reactants. Preferably, the starting materials are of high purity, e.g. 99.5% by weight for BaO 99.99% by weight for CuO and 99.9 by weight for M 2 03. Less pure starting materials can be used; however, the product may then contain an amount of another phase material comparable to the amount of impurity in the starting materials. It is particularly important to avoid the presence of impurities containing iron and other transition, but non-rare earth, metals in the reactants. As used herein the phrase "consisting essentially of" or "consist essentially of" means that additional steps can be added to the process of the invention so long as such steps do not materially alter the basic and novel characteristics of the invention, the use of BaO to obtain a single-phase superconductiog product without prolonged heating or additional treatments.

WO 88/09555 PCT/US88/01434 The resulting mixture is then heated in an oxygen-containing atmosphere at a temperature of about 850 0 C to abcut 925 0 C for a time sufficient to form MBa 2 Cu 3 O where y is from about 6.0 to about 6.4. It has been determined by TGA that when the mixture is heated to 900 0 C, y is from about 6.0 to about 6.4. Alternatively, the mixture can be first pressed into a disk, bar or other desired shape using conventional techniques. For heating, the mixed powder is placed in a non-reactive container such as an alumina or gold crucible. The oxygen-containing atmosphere can be air or oxygen gas, but air is preferred.

The container with the mixed powder sample is placed in a furnace and brought to a temperature of from about 850 C to about 935"C, preferably from about 865 0 C to about 900 0 C. It is the total time that the sample is at temperatures in this range that is important. Therefore, the minimum heating time for which the sample must be maintained at the final heating temperature depends upon the heating rate at which the sample is brought from ambient temperature to the final heating temperature- If slower heating rates are used, the minimum time for which the sample must be maintained at a final temperature of firom about 850 0 C to about 925"C is shofter. If faster heating rates are used, the minimum time for which the sample must be maintained at a final temperature of from about 850 0 C to about 925 0 C is longer. For example, when a heating rate of 10°C per minute is used to raise the temperature of the furnace containing the sample from ambient temperature to a final heating temperature of 900 0 C, 1/2.hour is sufficient time to maintain the sample at 900,C to produce single-phase supercunductino MBazCuO, (total time at 850°C-925*C is about 35 mintes) after

I,

WO 88/09555 PCT/US88/01434 6 cooling as prescribed herein. When a heating rate of 100C per minute is used to raise the teraperature of the furnace containing the sample from room temperature to 800 0 C and a heating rate of 5°C per minute is used to raise the temperature from 800 0 C to a final heating temperature of 9000C, 12 minutes is sufficient time to maintain the sample at 900 0 C to produce single-phase superconducting MBa 2 Cu O x (total time at 850 0 C-925 0 C is about 22 minutes) after cooling as prescribed herein, Longer heating times can be used.

At the end of the heating period, 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 100 0 C (a time interval of about 6-8 hours) before the sample container is removed from the furnace. During the cooling step, the oxygen content of the material increases to give the desired MBa 2 Cu3O0 product. The additional oxygen which enters 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 desired 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 powde'r. However, if the sample is in the form of larger particles, or densely packed powders, the times required to obtain the desired product at 500 0 C in air will increase, WO 88/09555 PCT/US88/01434 7 The MBa 2

CU

3 0x powder can be pressed into a desired shape, sintered in an oxygen-containing atmosphere at a temperature from about 900"C to about 925 0 C, and maintained in the oxygen-containing atmosphere while cooling as prescribed above to obtain a MRa 2 Cu 3 Ox shaped article. Well sintered, shaped articles will take longer to form the desired product while cooling than will more porous ones, and for larger, well sintered, shaped articles many hours may be required.

A convenient procedure for obtaining the desired product when the material is in the form of a powder or a small shaped object is to turn off the furnace in which the heating was conducted and to allow the material to cool in the furnace to a temperature approaching ambient (about 22 0 C) which typically requires more than eight hours. In the examples, cooling in the furnace to below about 100°C was found to be sufficient. Increasing the partial pressure of the oxygen in the atmosphere surrounding the sample during cooling increases the rate at which oxygen enters the lattice. If, in a particular experiment, the material is cooled in such a manner that the MBa 2 Cu Ox product is not obtained, the material can be heated to an intermediate temperature, such as 500*C, between ambient temperature and the final temperature used in the heating step and held at this temperature for a time sufficient to obtain the desired product. After cooling, the sample is removed fro the furnace.

The resulting product is single phase and has orthorhombic symmetry as determined by X-ray diffraction measurements. The process of this invention provides a single heating-step method for preparing a superconducting MBa Cu~O composition that does not require a special atmosphere during the WO 88/09555 PCT/US8/Oi434 8 heating step, subsequent grinding, reheating or annealing, extended heating times or refining of the product to separate the desired superconducting x composition from other phases.

The invention is further illustrated by the following examples in which temperatures are in degrees Celsius unless otherwise stated. Four-probe resistance measurements were performed on the samples in the form of sintered bars. The four-probe method is described in "Solid State Physics", 'ol.6, eds.

Horovitz and Johnson, Academic Press, New York, pp 36-37 (1959). A Kiethly 220 dc current source was used for applying constant current through the samples and a Kiethly 181 nanovoltmeter used to monitor the voltage drop across the samples. The chemicals (with purity indicated) used in the Examples are BaO 2 obtained from-Atomergic Chemetals Corp., CuO (99.99%) obtained from Johnson and Matthey Chemicals Ltd. (Puratronic) or obtained from Fluka Chemical Corp., Y 2 0 3 (99.99%) obtained from Research Organic/Inorganic Chemical Corp and Eu 2 03 and Er 2 03 obtained from Alfa Products. High purity chemicals were used to demonstrate that the process of the invention results in single-phase MBa 2 CuO Unless stated otherwise, the mixed powder samples were heated from ambient temperature to the final heating temperature at a rate of'10C per minute. The temperatures and times given in the Examples are the final heating temperatures and the times for which the sample is maintained at that temperature.

EXAMPLE 1 BaO, (2.6934 1.5908 g of CuO and 0.7A52 g of Y 2 O0 were ground together in an agate mortar for 30 minutes, and the resulting mixed powder was pressed into disks, 10 cm in diame'ter and about 0.2 y.I WO 88/09555 PCT/US88/01434 9 cm in thickness. The resulting disks were placed in a gold container and heated in air in a furnace for hours at 900°. The furnace was then turned off and allowed to cool to a temperature below 1000 after which the disks were removed. The resulting YBa2Cu 0 product was black. Four-probe resistance measurements performed on a product disk showed a superconducting transition at about 90 K. The disks were crushed and a X-ray powder diffraction pattern obtained. The indices of the observed reflections, the d-spaciqns and relative intensities are shown in Table I. The results indicate that the YBa 2 CuO product has orthorhombic symmetry and no other phase was detected.

TABLE I X-ray diffraction data for YBa 2 Cu 3 0 hkl d(nm) Intensity* 002 0.5810 vw 003 0.3880 m 100 0.3805 w 012 0.3224 w 102 0.3189 w 013 0.2739 s 103) 0.2714 vs 110) 111 0.2648 vw 112 0.2463 w 005 0.2330 m 104 0.2320 vw 113 0.2228 m 020) 0.1940 m 006J 200 0.1905 m 115 0.1772 w 0161 0.1738 vw 023) WO 8/09555 PCT/US88/01434 106) 0.1729 vw 120 203 210 0.1713 vw 121) 122 0.1669 vvw 123) 0.1582 ms 116) 213 0.1568 m Legend: s strong m moderate w ueak v very EXAMPL)IS 2-6 15 BaO, (16.90 11.931 g of CuO and 5.645 g of Y 2 0 were ground together in an automatic grinder for 45 minutes. Vortions of this mixed powder were used in Examples 2-8.

In each of Examples 2-6, approximately 1 g of the mixed powder was pressed into bars, 3 mm x 3 mm x 18 mm, and the resulting bars were placed in an alumina tray and heated in air in a furnace at the temperatures and for the times indicated in Table II.

The furnace was then turned off and allowed to cool to a temperature below 1000 after which the resulting sample was removed.

Each YBa.Cu, 0 product was black.

Four-probe resistance measurements performed on the product bars of each Example produced substantially identical results and showed a superconducting transition above 90 K. X-ray diffraction data obtained for each Example using powder from the crushed bars were, within experimental uncertainty, practically' identical to that shown in Table I and no other phases were detected.

WO 88/09555 PCT/US88/0434 11 Examples 1-6 indicate that although the heating times varied from 5 hours to 1/2 hour and the heating temperature from 9000 to 865*, there were no discernible differences in the resistance or the X-ray diffraction data and the products are practically identical.

TABLE II Heating Conditions Temperature Time Ex. (hours) 900 3- 3 865 3 4 900 2 5 900 1 6 900 1/2 EXAMPLE 7 Approximately 1 g of the same batch of mixed powder described in Examples 2-6 was pressed 2into bars, 3 mm x 3 mm x 18 mm, which were then placed in an alumina tray and heated in air in a furnao:e from ambient temperature to 800° at a rate of per minute and from 8000 to a final heating temperature of 9000 at a rate of 50 per minute. The 2temperature was maintained at 9000 for 12 minutes.

The furnace was then turned off and allowed to cool to a temperature below 1000 before the sample was removed.

The resulting YBa 2 CulO product was black.

Four-probe resistance measurements performed on a product bar showed a superconducting transition above K. X-ray diffraction data obtained using powder from the crushed bars were, within experimental uncertainty, practically identical to that shown in Table I and no other phases were detected.

v ;i 925°C for a time sufficient to form MBa 2 Cu3Oy, where y is from about 6.0 to about 6.4; and maintaining the MBa 2 Cu 3 Oy in an oxygen-containing atmosphere while /2 WO 88/09555 PCT/US88/01434.

12 EXAMPLE 8 Approximately 1 g of the same batch of mixed powder described in Examples 2-6 was placed in an alumina tray and heated in air in a furnace at 9000 for 2 hours. The furnace was cooled to ambient temperature and the resulting sample was removed.

The resulting powder YBa Cu,1 3 product was black and X-ray diffraction data obtained were, within experimental unceitainty, practically identical to that shown in Table I and no other phases were detected. The powder exhibited the Meissner effect above 90 K, thereby indicating a superconducting transition above 90 K.

EXAMPLE 9 BaO 2 (1.6934 1.1931 g of CuO and 0.8798 g of Eu 2 03 were ground together in an agate mortar for 30 minutes. The resulting mixed powder was pressed into bars, 3 mm x 3 mm x 18 mm, which were then were placed in a alumina tray and heated in air in a furnace at 900 for 6 hours. The furnace was then turned off and allowed to cool to a temperature below 100" after which the resulting product was removed.

The resulting EuBa 2 Cu 3 0. product was .black.

2S Four-probe resistance measurements performed on a product bar showed a superconducting transition above K, X-ray diffraction data obtained using powder from the crushed bars were similar to that shown in Table I, indicating that the product has orthorhombic symmetry and is isostructural with YBa 2 Cu 3

O

x No other phases were detected.

EXAMPLE BaO 2 (1.6934 1,1931 g of CuO and 0.9563 g of Er 03 were ground together it an agate mortar for 30 minutes. The resulting mixed powder was pressed into bars, 3 mm 3 mm x 18 mm, which weie WO 88/09555 PCT/US88/01434 13 then placed in a alumina tray and heated in air in a furnace at 9000 for 4 hours. The furnace was then turned off and allowed to cool to a temperature below 1000 after which the bars were removed.

The resulting ErBa 2 Cu 3

O

x product was black.

Four-probe resistance measurements performed on a product bar showed a superconducting transition above K. X-ray diffraction data obtained using powder from the crushed bars were similar to that shown in Table I, indicating that the product has orthorhombic symetry and is isostructural with YBazCu 0 No other phases were detected.

Claims (15)

1. An improved process for preparing a superconducting composition having the formula Ml3a2Cu3Ox 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 mixing M 2 0 3 BaO2 and CuO in an atomic ratio of M:Ba:Cu of about 1:2:3 to obtain a powder mixture; heating the resulting mixture in an oxygen-containing atmosphere at a temperature from about 850 0 C to about 925°C for a time sufficient to form MBa 2 Cu 3 0y, where y is from about 6.0 to about 6.4; and maintaining the MBa 2 Cu30y in an oxygen-containing atmosphere while cooling for a time sufficient to obtain the desired product, said process'being limited to a single heating step without subsequent grinding, reheating or annealing.

2. A process according to Claim 1 wherein the mixture is pressed into a desired shape prior to heating.

3. A process according to Claim 1 wherein the mixture is heated at a temperature from about 865 0 C to about 900 0 C.

4. A proce s according to Claim 2 wherein the mixture is heated at a temperature from about 865 0 C to about 90 0 C. A process according to Claim 3 wherein x is from about 6.8 to about

6. A, process according to Claim 4 wherein x is from about 6.8 to about

7. A process according to Claim wherein the oxygen-containing atmosphere is air.

8. A process according to Claim 6 wherein W 1 i SUBSTIT'UE SHEET NIPT~ A/US Q J I PCT/S 33 /01434 Rc'd PCT/TO 39 the oxygen-containing atmosphere is air.

9. M is Y, Eu or Er. M is Y, Eu or Er.

11. M is Y, Eu or Er.

12. M is Y, Eu or Er.

13. M is Y, Eu or Er.

14. M is Y, Eu or Er. MisY.

16. MisY.

17. M is Y.

18. M isY. A process according to Claim 1 where process according to process according to process according to process according to process according to process according to process according to process according to process according to Claim Claim Claim Claim Claim Claim Claim Claim Claim 2 wherein 5 wherein 6 wherein 7 wherein 8 wherein 11 wherein 12 wherein 13 wherein 14 wherein IPEA/US I ~Y prolonged heating or additional treatments. I I* I INTERfNATIONAL SEARCH REPORT international Application No. PCT/US88/01434 1. CLASSIFICATION OF SUBJECT MATTER (if several classification symbolr~s apply indic~ate all) 6 According to International Patent Classification (IPC) or to both National Classification and IPC IPC(4: H 01B 1/06; C04B 33/32 252/521; 264/56,65 it. FIELDS SEARCHED Minimum Documentation Searched7 Classification System Classification Symbols U. S. 252/521; 264/56, 65; 505/807, 809, 815, 822 Documentation Searched other than Minimum Documentation to the Egtent that such Documents are Included In the Fields Searcheda Ill, DOCUMENTS CONSIDERED TO BE Category Citation ot Document, It with indication, where appropriate, of the relevant passages tQ Relevant to Claim No. Y US, A, 4,649, 125, (TAKEUJCHI ET AL) 10 MARCH 1-22 1987, SEE COLUMN 3, LINES 27-39 y J.C.S. nALTON TRANSACTIONS, PAGES 1061-1066 1-22 ISSUED 1975, M. ARJOMAND ET AL, "OXIDE CHEMISTRY. PART 11. TERNARY OXIDES CON- TAINING COPPER IN OXIDATION STATES -I,-II -111 and SEE ENTIRE DOCUMENT Y PHYSICAL REVIEW LETTERS, VOLUME 58, NUMBER 1-22 9, ISSUED MARCH 1987, M.K. WU ET AL, "SUPERCONDUCTIVITY AT 93!X IN A NEW MIXEDPHASE Y-Ba-Cu-O COMPOUND SYSTEM AT AMBIENT PRESSURE,"1 SEE PAGES 908-910 Y PHYSICALX REVIEW LETTERS, VOLUME 58, NUMBER 1-22 16, ISSUED APRIL 1987, R.J. CAVA El. AL, "BULK SUPERCONDUCTIVITY AT 91K IN SINGLE-PHASE OXYGEN-DEFICIENT PEROVSKITE Ra 2 YCU3O9-6, SEE PAGES 1676-1679 Special categories ot cited documentst 'a 'IT" later document published atter the International filing date 'A 5 documnirt defining the general state of the art 1 hch is nrot or priority date and rnot in conflict with the application but considered to~bo of particular relevance cit d to understand the principle or theory underlying the arler ocueri bu pulised o oraftr te iteratinal invention Salier dtue~i buX"lse no terteitreint Ii document of particular relevance; the claimed Invention tilin datecannot be considered novel or cannot be corisidered to IVL document which may throw doubts on priority clalm(sf or Involve en inventive step which Itcd ~ltc' 'o "tablish the publication date ot another document ot Particular relevancei the ctaimed Invention citation or other speet! reason (as specified) cannot he c-msidoed to involve an lnvcnttive step when the document referring to ani oral disclosure, use, exhibitioni or document Is combined with one or more other such docu. other means ments, such combination being obvious to a person sktliled I'P' document published prior to the Internationat iting date but In the, att, later than the priority date ctaimed document member of the same patent family IV, CERTIFICATION Date of the Actual completion of the tIternatlonal Search IDate of Moltnqa of this International Search Report 03 October 1988 0 1 NOV 4988, International Searching Authority nature of Au 4ori Officer..... 1 ISA/US 14. Derrincrton Form POTAS1 0~ (socond shbow) (P~v~l -87) time at is aouT 5: minur I ~L:L I *1 1~ 1 1,- 'I 0 International Application No. PCT/US88/01434 FURTHER INFORMATION CONTINUED FROM THE SECOND SHEET Y PHYSICAL REVIEW LETTERS, VOLUME 58, NUMBER ISSUED APRIL 1987, J.Z. SUN ET AL,"SUPER- DUCTIVITY AND MAGNESTISM IN THE HIGH-Tc SUPERCONDUCTOR Y-Ba-Cu-O, SEE PAGES 1574-1576 1-22 OBSERVATIONS WHERE CERTAIN CLAIMSWERE FOUND UNSEARCHABLE I This International search report has not been establi ;hed in respect of certain claims under Article 17(2) for the following reaso', i.c Claim numb'-- because they relate to sublect matter i not required to be searched by this Authority, namely: 2, Claim numbers because they relate to parts of the international application that do not comply with the prescribed require- ments to such an extent that no meaningful international search can be carried out 1I, speciically: 3. Claim numbers because they are dependent claims not drafted in accordance with the second and thid sentence: of PCT Rulu 6.4(a), VIC1 OBSERVATIONS WHERE UNITY OF INVENTION IS LACKING 2 This International Searching Authority found multiple inventions In this International application as follows: 1. As all required additional search fees were timely paid by the applicant, this International search report covers all searchable claims of the International application. 2.C As only some of the required addi:onal search fees were tlmelt paid by the applicant, this international search report covers only those claims of the Internationp: application for which fees were paid, specfically claims: 3. No required additioral search lees were timely paid by the applicant. Consequently, this International search report Is restricted to the Invention first Mnentioned In the laimst it Is covered by claim numbers: 4.r As all searchaoleclaims could be searched without effort jusitlying an Iddltlonal fee, the International Searching Authority did not invite payment of any additional lee. Remark on Protest The additional search fees were accompanied by applicant's protesl, O No protest accompanied the payment of additional search fees, Form PCTIISA,210 (sUepp al heet (Ro, 1187) ii ;i I :i