Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N60/00—Superconducting devices
  • H10N60/80—Constructional details
  • H10N60/85—Superconducting active materials
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
  • C04B35/45—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on copper oxide or solid solutions thereof with other oxides
  • C04B35/4504—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on copper oxide or solid solutions thereof with other oxides containing rare earth oxides
  • C04B35/4508—Type 1-2-3
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G3/00—Compounds of copper
  • C01G3/006—Compounds containing copper, with or without oxygen or hydrogen, and containing two or more other elements
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N60/00—Superconducting devices
  • H10N60/01—Manufacture or treatment
  • H10N60/0268—Manufacture or treatment of devices comprising copper oxide
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2002/00—Crystal-structural characteristics
  • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
  • C01P2002/76—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by a space-group or by other symmetry indications

Definitions

• This invention relates to an improved process for making rare earth-barium-copper oxide superconductors with transition temperatures above 90 K.
• the powders were heated for 8-10 hours at 1000oC, ground and then cold pressed to form disks of about 1 cm diameter and 0.2 cm thickness.
• the superconducting properties of samples prepared in these two ways were similar. X-ray diffraction examination of the samples revealed the existence of multiple phases.
• L506-L507 (1987), disclose the preparation of several Y-Ba-Cu compositions with superconducting transitions around 90 K by a solid-state reaction method in which a mixture of Y 2 O 3 , CuO, and BaCO 3 was heated in an oxygen atmosphere at 950 ⁇ C 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.
• Takayama-Muromachi et al. Jpn. J. Appl. Phys. 26, L476-L478 (1987), disclose the preparation of a series of samples to try to identify the superconducting phase in the Y-Ba-Cu-O system.
• Appropriate amounts of Y 2 O 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 Y 1-x Ba x CuO y where 0.6 ⁇ x ⁇ 0.7.
• L452-L453 (1987) disclose the preparation of a superconductor sample with nominal composition Y 1.1 Ba 0.9 CuO 4-y .
• a Prescrihed amount of powders of Y 2 O 3 , BaCO 3 and CuO was mixed for about an hour, pressed under 6.4 ton/cm 2 (14 MPa) into pellet shape and sintered at 1000°C in air for 3 hours.
• Ba 0.5 Y 0.5 Cu 1 O x by mixing appropriate amounts of BaCO 3 (purity 99.9%), Y 2 O 3 (99.99%) and CuO ( 99. 9% ) .
• the mixture was calcined at 1000°C for 11 hours in a flowing oxygen atmosphere.
• the resultant mixture was then pulverized and cold-pressed into disks.
• the disks were sintered at 900 ⁇ C 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 various Y-Ba-Cu oxides by mixing powders of Y 2 O 3 , BaCO 3 and
• L314-L315 (1987) disclose the preparation of compositions in the Y-Ba-Cu-O system by heating the powde rs of Y 2 O 3 , BaCO 3 and CuO to 800°C or 900°C in air for 2-4 hours, pressing into pellets at 4 kbars (4x10 5 Pa) and reheating to 800°C in air 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
• This invention provides an improved process for preparing superconducting compositions having the formula MBa 2 Cu 3 O 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 ponsi ⁇ ting essentially of heating a precursor powder in an oxygen-containing atmosphere at a temperature from about 875°C to about 950oC for a time sufficient to form MBa 2 Cu 3 O y , where y is from about 6.0 to about 6.4; and maintaining the MBa 2 Cu 3 O y in an oxygen-containing atmosphere while cooling for a time sufficient to obtain the desired product; said precursor powder being prepared by (a) forming a mixture of Ba(OH) 2 .8H 2 O, M 2 O 3 and CuO powders with the atomic ratio of M:Ba:Cu being about
• the process of the invention provides an improved process for preparing superconducting compositions having,, the formula MBa 2 Cu 3 O 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 7.0.
• a precursor powder is prepared for later heating.
• the precursor powder is prepared by mixing M 2 O 3 , Ba(OH) 2 ⁇ 8H 2 O and CuO powders in an atomic ratio of M:Ba:Cu of about 1:2:3.
• the powders are mixed well in a mixing device or by hand using a mortar and pestle to obtain an intimate mixture of reactants.
• the use of Ba(OH)2 ⁇ 8H 2 O as the source of Ba results in the preparation of a uniform, practically single-phase, superconducting MBa 2 Cu 3 O x composition.
• the appropriate precursor powder is prepared by 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.
• the aqueous solution of nitrates can be prepared by starting with the appropriate nitrate salts.
• the aqueous solution of nitrates can be prepared by reacting Ba(OH) 2 ⁇ 8H 2 O or BaCO 3 , M 2 O 3 and CuO powders with sufficient concentrated nitric acid to convert the metals present to metal nitrates. ⁇ xcess concentrated nitric acid can be used to speed the reaction.
• the amount of concentrated nitric acid used is 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.
• "clear solution” means one containing no undissolved solids.
• citric acid monohydrate at least sufficient to convert all metals present to metal citrates.
• the amount of citric acid monohydrate used is between one and two times the amount needed to convert all the metals present to metal citrates.
• the acidic nitrate solution prevents precipitation of the citrates.
• the resulting citrate/nitrate solution is then spray dried using conventional spray-drying 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 Cu 3 O x product after fhe 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 nixing the oxides and Ba(OH) 2 ⁇ 8H 2 O and heating and cooling as described herein.
• 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 M 2 O 3 .
• the product may then contain an amount of another phase material comparable to the amount ofimpurity 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.
• the precursor powder is then heated in an oxygen-containing atmosphere at a temperature from about 875°C to about 950°C, preferably from about 900oC to about 950°C, for a time sufficient to form MBa 2 Cu 3 O 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 900oC, y is from about 6.0 to about 6.4.
• the precursor powder prior to heating when the precursor powder is made by mixing M 2 O 3 , Ba(OH) 2 ⁇ 8H 2 O and CuO powders, the precursor powder can be pressed into a disk, bar or other desired shape using conventional techniques.
• the precursor 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 is preferably oxygen.
• the container with the precursor powder is placed in a furnace and brought to a temperature of from about 875°C to about 950 °C . It is the total time tha t the precursor powder is at temperatures in this range that is important.
• Heating rates of 10oC per minute to 50°C 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 875°C to about 950oC.
• the final heating temperature is 900oC
• 1/2 hour is sufficient time to maintain the sample at 900°C to produce, after cooling, practically single-phase superconducting MBa 2 Cu 3 O x .
• the container can be placed directly into an oven already heated to the final heating temperature. Longer heating times can be used.
• the minimum time for which the sample must be maintained at a final temperature of from about 875oC to about 950oC 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 about950°C is longer. For example, when a heating rate of50°C per minute is used to raise the temperature ofthe furnace containing the sample from ambienttemperature to a final heating temperature of 900°C,1/2 hour is sufficient time to maintain the sample at900°C to produce, after cooling, practically single-phase superconducting MBa 2 Cu 3 O x . Longer heating times can be used. After cooling as described herein, the MBa 2 Cu 3 O x product can be pressed into a desired shape and sintered to provide a shaped article.
• 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.
• the material is cooled to below about 350oC (a time interval of about 1-1.5 hours) before the sample container is removed from the furnace.
• the oxygen content of the material increases to give the desired MBa 2 Cu 3 O 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.
• the rate of oxygen uptake by the material at 500oC 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 powder.
• 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 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 temperature (about 22°C) which typically requires a few hours.
• ambient temperature about 22°C
• cooling in the furnace to below about 350°C was found to be sufficient.
• Increasing the partial pressure of oxygen in the atmosphere surrounding the sample during cooling increases the rate at which oxygen enters the lattice.
• the material is cooled in such a manner that the MBa 2 Cu 3 O x 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 sufficient time to obtain the desired product. If the MBa 2 Cu 3 O x product is. pressed into a desired shape and sintered at about 900°C to absaut 650oC the above cooling considerations would then apply to the resulting shaped article.
• the product powder formed by the process of the invention is practically single-phase and has orthorhombic symmetry as determined by X-ray diffraction measurements.
• the process of this invention proovides a single heating-step, method for preparing a superconducting MBa 2 Cu 3 O x composition that does not require a special atmosphere during the heating step, subsequent grinding, reheating or annealing, extended heating times or refining of the product to separate the desired superconducting MBa 2 Cu 3 O x composition from other phases.
• the best mode contemplated for carrying out the invention is described in Example 5.
• the phrase "consisting 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. 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 O - (48.6% BaO) obtained from Kali-Cheraie, CuO - (99.99%) obtained from Johnson and Matthey or Puratronic or (>99%) obtained from Fluka, Y 2 O 3 - (99.99%) obtained from Research Chemicals. High purity chemicals were used to demonstrate that the process of the invention can result in single-phase or practically single-phase MBa 2 Cu 3 O x .
• the X-ray diffraction pattern indicated that the product was YBa 2 Cu,O x 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 2 A disk prepared substantially 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 900° for 30 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 O x 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 940° at a rate of about 50° per minute. The temperature was maintained at 940° for 2 minutes. The furnace was then turned off and allowed to cool to about 350oC (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 O 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.
• 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 190o and an outlet temperature of 95°-115o were employed. The chamber atmosphere, was air. A portion of the resulting spray-dried material was placed in an alumina container and heated in air in a furnace from ambient temperature to a .final heating temperature of 900° at a rate of about 50° per minute. The temperature was maintained at 900° for 30 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 fired powder was black.
• EXAMPLE 5 A portion of the spray-dried material prepared in Example 4 was placed in an alumina container and subjected to heat and cooling 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 Cu 3 O 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.

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• 1988
  • 1988-06-08 HU HU884759A patent/HUT52646A/hu unknown
  • 1988-06-08 JP JP63506397A patent/JPH02503789A/ja active Pending
  • 1988-06-08 EP EP19880906653 patent/EP0366721A4/en not_active Withdrawn
  • 1988-06-08 AU AU21299/88A patent/AU608886B2/en not_active Ceased
  • 1988-06-08 WO PCT/US1988/002025 patent/WO1988010515A1/en not_active Ceased
  • 1988-06-08 KR KR1019890700228A patent/KR890702262A/ko not_active Withdrawn

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