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
  • H10N60/01—Manufacture or treatment
  • H10N60/0268—Manufacture or treatment of devices comprising copper oxide

Definitions

• This invention relates to an improved process for making rare earth-barium-copper oxide superconductors with transition temperatures above 90 K .
• 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°C for 24 hours in the same reduced oxygen atmosphere.
• the material prepared showed the existence of multiple phases.
• 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 consisting essentially of mixing M 2 O 3 , 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°C 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.
• the powder mixture can be pressed into a desired shape prior to heating.
• 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, 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.
• the use of BaO 2 as the source of Ba results in the preparation of a uniform single-phase superconducting MBa 2 Cu 3 O x composition.
• the process of the invention consists essentially of mixing M 2 O 3 , BaO 2 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.
• the starting materials are of high purity, e.g. 99.5% by weight for BaO 2 , 99.99% by weight for CuO and 99.9 % by weight for M 2 O 3 . 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.
• 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, e.g., the use of BaO 2 to obtain a single-phase superconducting product without prolonged heating or additional treatments.
• the resulting mixture is then heated in an oxygen-containing atmosphere at a temperature of about 850°C to about 925°C for a time sufficient to form MBa 2 Cu 3 O , where y is from about 6.0 to about 6.4.
• the mixture can be first pressed into a disk, bar or other desired shape using conventional techniques.
• 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 925°C, preferably from about 865°C to about 900°C. It is the total time that the sample is at temperatures in this range that is important.
• 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 from about 850oC to about 925°C 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 850°C to about 925°C is longer.
• 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 100°C (a time interval of about 6-8 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 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 500°C in air is rapid, and the desi red 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.
• the MBa 2 Cu 3 O x powder can be pressed into a desired shape, sintered in an oxygen-containing atmosphere at a temperature from about 900°C to about 925°C, and maintained in the oxygen-containing atmosphere while cooling as prescribed above to obtain a MBa 2 Cu 3 O x 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°C) which typically requires more than eight hours.
• ambient about 22°C
• 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.
• 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 time sufficient to obtain the desired product. After cooling, the sample is removed from the furnace.
• an intermediate temperature such as 500°C
• 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 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 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", Vol.6, eds.
• 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 - (99.5%) obtained fromrfttomergic Chemetals Corp., CuO - (99.99%) obtained from Johnson and Matthey Chemicals Ltd. (Puratronic) or (>99%) obtained from Fluka Chemical Corp., Y 2 O 3 - (99.99%) obtained from Research Organic/Inorganic Chemical Corp and Eu 2 O 3 - (99.9%) and Er 2 O 3 - (99.9%) obtained from Alfa Products.
• YBa 2 Cu 3 O x 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-spacings and relative intensities are shown in Table I. The results indicate that the YBa 2 Cu 3 O x product has orthorhombic symmetry and no other phase was detected.
• Example 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 100° after which the resulting sample was removed.
• Each YBa 2 Cu 3 O x 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.
• Examples 1-6 indicate that although the heating times varied from 5 hours to 1/2 hour and the heating temperature from 900° to 865°, there were no discernible differences in the resistance or the X-ray diffraction data and the products are practically identical.
• the resulting YBa 2 Cu 3 O x product was black.
• Four-probe resistance measurements performed on a product bar showed a superconducting transition above 90 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.
• 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 900° for 2 hours. The furnace was cooled to ambient temperature and the resulting sample was removed.
• the resulting powder YBa 2 Cu 3 O x product was black and X-ray diffraction data obtained were, within experimental uncertainty, 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.
• the resulting EuBa 2 Cu 3 O x product was.black.
• Four-probe resistance measurements performed on a product bar showed a superconducting transition above 90 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 10 BaO 2 (1.6934 g), 1.1931 g of CuO and 0.9563 g of Er 2 O 3 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 placed in a alumina tray and heated in air in a furnace at 900° for 4 hours. The furnace was then turned off and allowed to cool to a temperature below 100° after which the bars were removed. The resulting ErBa 2 Cu 3 O x product was black.

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• Engineering & Computer Science (AREA)
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• 1988
  • 1988-05-06 WO PCT/US1988/001434 patent/WO1988009555A1/en not_active Ceased
  • 1988-05-06 EP EP19880906677 patent/EP0357683A4/en not_active Ceased
  • 1988-05-06 KR KR1019890700090A patent/KR890702214A/ko not_active Withdrawn
  • 1988-05-06 AU AU21252/88A patent/AU608644B2/en not_active Ceased
  • 1988-05-06 JP JP63506306A patent/JPH02504260A/ja active Pending

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