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: TITLE SUPERCONDUCTING METAL OXIDE COMPOSITIONS AND PROCESSES FOR MANUFACTURE AND USE BACKGROUND OF THE INVENTION Field of the Invention This invention relates to novel Tl-Ba-Ca-Cu-0 compositions which are superconducting. References Bednorz and Muller, Z. Phys. Bβ4, 189 (1986), disclose a superconducting phase in the La-Ba-Cu-O system with a superconducting transition temperature of about 35 K. This disclosure was subsequently confirmed by a number of investigators [see, for example, Rao and Ganguly, Current Science, 56, 47 (1987), Chu et al., Science 235, 567 (1987), Chu et al., Phys. Rev. Lett. 58, 405 (1987), Cava et al., Phys. Rev. Lett. 58, 408 (1987), Bednorz et al. , Europhys. Lett. 3, 379 (1987)]. The superconducting phase has been identified as the composition La 1 _ χ (Ba,S ,Ca) x Cu0 4 _ y with the tetragonal K 2 NiF 4 -type structure and with x typically about 0.15 and y indicating oxygen vacancies. u et al., Phys. Rev. Lett. 58, 908 (1987), disclose a superconducting phase in the Y-Ba-Cu-O system with a superconducting transition temperature of about 90 K. Cava et al., Phys. Rev. Lett. 58, 1676 (1987), have identified this superconducting Y-Ba-Cu-O phase to be orthorhombic, distorted, oxygen-deficient perovskite YBa 2 Cu 3 0 9 _ s where _ is about 2.1. C. Michel et al., Z. Phys. B - Condensed Matter 68, 421 (1987), disclose a novel family of superconducting oxides in the Bi-Sr-Cu-0 system. A pure phase was isolated for the composition Bi 2 Sr 2 Cu 2 0 7+ 4 . The material made from ultrapure oxides has a superconducting transition with a midpoint of 22 K as determined from resistivity measurements and zero resistance below 14 K. The material made from commercial grade oxides has a superconducting transition with a midpoint of 7 K. H. Maeda et al. , Jpn. J. Appl. Phys. 27, L209 (1988), disclose a superconducting oxide in the Bi-Sr-Ca-Cu-0 system with the composition near BiSrCaCu 2 Ox and a superconducting transition temperature of about 105 K. The commonly assigned application, "Superconducting Metal Oxide Compositions and Process For Making Them", S. N. 153,107, filed Feb. 8, 1988, a continuation-in-part of S. N. 152,186, filed Feb. 4, 1988, disclose superconducting compositions having the nominal formula Bi &Sr. aCacCu.JOx 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.Sr, Ca Cu,0. wherein z is from about 0.1 to about 0.9, preferably 0.4 to 0.8 and w is greater than zero but less than about 1. M. A. Subramanian et al.. Science 239, 1015 (1988) also disclose the Bi 2.Sr i, — ZCaZ sup*-erconductor. Z. Z. Sheng et al., Nature 332, 55 (1988) disclose superconductivity in the Tl-Ba-Cu-O system in samples which have nominal compositions Tl 2 Ba 2 Cu 3 0 8 + χ and TlBaCu 3 O s 5 + x . Both samples are reported to have onset temperatures above 90 K and zero resistance at 81 K. The samples were prepared by mixing and grinding appropriate amounts of BaC0 3 and CuO with an agate mortar and pestle. This mixture was heated in air at 925°C for more than 24 hours with several intermediate grindings to obtain a uniform black oxide Ba-Cu oxide powder which was mixed with an appropriate amount of Tl 2 0 3 , 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 880-910°C 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 T1 2 0 3 had partially volatilized as black smoke, part had become a light yellow liquid, and part had reacted with Ba-Cu oxide forming a black, partially melted, porous material. Z. Z. Sheng et al. , Nature 332, 138 (1988) disclose superconductivity in the Tl-Ca-Ba-Cu-0 system in samples which have nominal compositions Tl 2 Ca 2 BaCu 3 0 9+χ 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, Tl 2 Ba 2 Ca 2 Cu 3 O 10 and Tl 2 Ba 2 CaCu 2 0 8 , both with onset of superconductivity near 120 K. C. C. Torardi et al.. Science 240, 631 (1988) disclose the preparation of Tl 2 Ba 2 Ca 2 Cu 3 O χ 0 with an onset of superconductivity of 125 K. S. S. P. Parkin et al. , Phys. Rev. Lett. 61, 750 (1988), disclose the structure TlBa 2 Ca 2 Cu 3 0 9+ with transition temperatures up to 110 K. M. Hervieu et al., J. Solid State Chem. 75, 212 (1988), disclose the oxide TlBa 2 CaCu 2 0 3 _ y . C. C. Torardi et al. , Phys. Rev. B 38, 225 (1988), disclose the oxide Tl 2 Ba 2 Cu0 6 with an onset of superconductivity 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 TlβPbaCa.bSrcCud.0x wherein a is from about 1/10 to about 3/2, b is 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 is 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 is 125 K for Tl 2 Ba 2 Ca 2 Cu 3 O χ as disclosed by S. S. P. Parkin et al., Phys. Rev. Lett. 60, 2539 (1988) J. M. Liang et al., Appl. Phys. Lett. 53, 15 (1988) disclose a composition TlBa 2 Ca 3 Cu 4 0 χ with an onset of superconductivity at 155 K and a zero resistance at 123 K. CaC0 3 , BaC0 3 and CuO powders were ground together and calcined for 15 hours with intermediate grindings. The Ba-Ca-Cu-0 powders were mixed with Tl 2 0 3 to yield a mixture with nominal composition TlBaCa 3 Cu 3 O χ . This mixture was ground, pressed and sintered for 15 minutes in flowing 0 2 . Composition ratios of the Tl:Ca:Ba:Cu in the superconductor vary from 1:2:2:3 to 1:2:3:4. SUMMARY OF THE INVENTION This invention provides novel superconducting compositions having the nominal formula TlBaaCa. _ Cuc0>. 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 from about 2 to about 3, b is about 4, c is about 5, and y is 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 mixture 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 atomic ratio Tl:Ba:Ca:Cu is l:a:b:c, to a temperature of about 940°C to about 980°C, maintaining that temperature for about 5 minutes or more, said heating being carried out in a controlled atmosphere, e. g., in a sealed tube made of a non-reacting metal such as gold, which prevents any of the reactants including the metals and oxygen from escaping. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a plot of the flux excluded by a composition of this invention as a function of temperature. DETAILED DESCRIPTION OF THE 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 is 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 Tl 2 0 3 , CaO and CuO and the peroxide Ba0 2 such that the atomic ratio Tl:Ba:Ca:Cu is l:a:b:c and mixing them, for example, by grinding them together in a mortar. Alternatively, a precursor oxide mixture can be prepared by choosing quantities of the oxide reactants Tl 2 0 3 , CaO and CuO and the peroxide Ba0 2 such that the atomic ratio Tl:Ba:Ca:Cu is l:a:b:c. The barium peroxide, calcium oxide and copper oxide are ground together and this grey mixture is then heated in an alumina crucible in a muffle furnace in air, the temperature being increased from ambient temperature, about 20°C, to about 800°C in a period of about 2 hours. The temperature is held at about 800 β C for 1 hour. The sample is then cooled and the black powder is 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 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 is preferred for this reason. The sealed tube is placed in a furnace and heated to a temperature of about 940°C to about 980 β C and maintained at a temperature in this range, i. e., about 940°C to about 980°C, 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 700°C to a temperature in the prescribed range at a rate of 50 β C/min and subsequently cooled at a rate of 10°C/min to 600°C. Faster heating and cooling rates may require somewhat longer maintenance times. Maintenance times of up to an hour or more can be used but corrosion of the gold tube becomes evident at about that time and maintenance times of about 5 to about 60 minutes are typical. The sample is then cooled to ambient temperature and the shiny grey-black metallic-appearing ingot recovered. 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 grey/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-Ba-Ca-Cu compositions with Tl:Ba:Ca:Cu atomic ratios of 1:2:1:2 and 1:2:2:3 with lesser Tc 's. Flux exclusion measurements on the compositions of this invention, prepared as described above, show an onset of superconductivity at about 130-132 K. Resistivity 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 exclusion measurements at least 30% of each of the samples is superconducting. X-ray powder diffraction typically gives very weak lines. Longer maintenance times at the maximum heating temperature have produced samples which show discrete x-ray lines. The 22 A (2.2 nm) c axis which is observed in the powder diffraction 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 phases including 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. Fisher 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 field for magnetic imaging for medical purposes. Thus, by cooling the composition in the form of a wire or bar to a temperature below the superconducting transition temperature, (T ), in a manner well known to those in this field, and initiating a flow of 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 objects as large as rail¬ road cars. These superconducting compositions are also useful in Josephson devices such as SQUIDS (superconducting quantum interference devices) and in instruments that are based on the Josephson effect such as high speed sampling circuits and voltage standards. EXAMPLES OF THE INVENTION EXAMPLE 1 0.456 g of Tl 2 0 3 , 1.020 g of Ba0 2 , 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 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 20 β C, to 700 β C at a rate of about 3 β C/min and then from 700 β C to 977 β C in ten minutes. Over the next five minutes the temperature decreased to 950°C. 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 superconductivity at about 130 K. EXAMPLES 2-4 In Example 2 , 0.456 g of Tl 2 0 3 , 1.020 g of Ba0 2 , 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 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 20°C, to 700°C at a rate of about 3°C/min and then from 700°C to 950°C at a rate of about 25°C/min. The temperature was maintained at 950°C for 5 min and then cooled to 600 β C at a rate of about 10°C/min. 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 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 Tl 2 0 3 , 0.680 g of Ba0 2 , 0.448 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 in Example 4, 0.456 g of Tl 2 0 3 , 1.020 g of Ba0 2 , 0.448 g of CaO and 0.800 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. Flux exclusion measurements showed the onset of superconductivity at about 130 K for Example 3 and at about 132 K for Example 4. EXAMPLE 5 A precursor oxide mixture was prepared by grinding together 5.10 g of Ba0 2 , 2.25 g of CaO and 4.00 g of CuO. This grey mixture was then heated in an alumina crucible in a muffle furnace in air from ambient temperature, about 20°C, to 800°C in a period of 2 hours. The temperature was held at 800°C for 1 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. 2.30 g of this black powder was ground together with 0.456 g of Tl 2 0 3 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 fusing 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 700°C at a rate of about 3°C/min. The temperature was then increased from 700°C to 977°C at a rate of about 18.5°C/min. The sample cooled to 950°C over the next 5 minutes and was maintained at 950°C for 10 min. The sample was then cooled in the furnace to 600°C at a rate of about 10°C/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 K. EXAMPLE 6 A precursor oxide mixture was prepared by grinding together 1.020 g of Ba0 2 , 0.448 g of CaO and 0.800 g of CuO. This grey mixture was then heated in an alumina crucible in a muffle furnace in air from ambient temperature, about 20°C, to 800°C in a period of 2 hours. The temperature was held at 800 β C for 1 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 together with 0.342 g of Tl 2 0 3 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 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 was placed in a horizontal quartz tube furnace. Heating was carried in the following manner. The temperature was increased from room temperature to 700°C at a rate of about 3 β C/min. The temperature was then increased from 700°C to 968°C at a rate of about 25°C/min. The sample was maintained at 968°C for 15 min. The sample was then cooled in the furnace to 600 β C at a rate of about 10 β C/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 130 K. EXAMPLE 7 An oxide mixture containing the elements Ba: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 Tl 2 0 3 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 fusing 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 700°C at a rate of about 3°C/min. The temperature was then increased from 700°C to 977°C at a rate of about 25°C/min. The sample was maintained at 977°C for 15 min. The sample was then cooled in the furnace to 600°C at a rate of about 10°C/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 . Flux exclusion measurements were carried out on one of these products and the results are shown in Fig. 1 where the flux exclusion 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 these products. The d-spacings, the relative intensities 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. TABLE I EXAMPLE 8-13 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 was 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 700°C at a rate of about 3 β C/min. The temperature was then increased from 700°C to a maximum ^temperature, T , at a specified rate. The sample was maintained at T for a specified time and was then cooled in the furnace to 600°C at a rate of 10°C/min except for Example 12 for which the rate was 50°C/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 were carried out on each product. The specified rate of heating from 700°C to In •,__ x , the temp*■erature Tn* x , the time for which the temperature was maintained at T and the temperature of the onset of superconductivity are shown in Table II.

Claims: CLAIMS The Invention Being Claimed is: 1. A superconducting composition having the nominal formula 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 β 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 T 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 77K to T c of said composition. 10. An improved Josephson-effeet device wherein the superconductive material comprises the composition of Claim 1.

Inventors: HERRON NORMAN, HERRON, NORMAN
Applicants: DU PONT, E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1989
Main classification: C01G3
IPC codes: C01G1, C01G15, C04B35, H01L39