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
  • H10N60/10—Junction-based devices
• • 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
  • H10N60/855—Ceramic superconductors
  • H10N60/857—Ceramic superconductors comprising copper oxide
• • 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
  • H10N60/0296—Processes for depositing or forming copper oxide superconductor layers
  • H10N60/0352—Processes for depositing or forming copper oxide superconductor layers from a suspension or slurry, e.g. screen printing or doctor blade casting

Definitions

• the present invention relates to a superconductor loop device having weak-link properties and to a method of producing such loop devices.
• weak-link superconductor loop devices have been formed from a loop of superconductive material having a discrete weak-link provided therein. It has previously been proposed to provide the weak-link in the form of a point-contact, constriction or an insulator junction, and these loops have well defined supercurrent and magnetic flux characteristics.
• the point contact weak-link must be mechanically adjusted to obtain and maintain the desired characteristics of the loop, whereas the constriction and insulator junction weak-links involve relatively sophisticated fabrication techniques and are expensive to produce.
• a high temperature ceramic metal oxide superconductor material of the Y-Ba-Cu-O system has been proposed in Physical Review Letters, volume 58 No. 9 pages 908 to 911.
• a superconductor loop device comprising a body formed of a matrix which is substantially non-superconducting and which has dispersed therein regions of superconductive material such as to impart to the body the inherent properties of a weak-link superconducting loop.
• the present invention has the advantage that the material from which the loop is fabricated has inherent properties which give the loop the characteristics of a superconducting weak-link loop because the matrix is non-superconducting and so allows magnetic flux to pass through the loop without the necessity of separately providing a discrete weak-link as required in the previously proposed loops.
• the loop is fabricated from ceramic material although other forms of a dispersed superconductor in a non-superconductor matrix might be used, e.g., metallic particles such as Pb, Nb or Ti in an epoxy resin matrix.
• the matrix should have poor conductivity as this allows the operation of the device at radio frequencies.
• the conductivity range for the matrix is may be 1 milliohm.cm to 10 8 ohm.cm.
• references to "superconductive”, “superconducting”, “non-superconducting” and “poor conductivity” relate to the properties at the intended temperature of operation of the device.
• the present invention provides a weak link loop which is easily reproducible. Furthermore, the use of ceramic materials allows the loop to be produced using conventional powder technology and so provides a loop which is economical to produce and which utilises materials having relatively high superconducting transition temperatures.
• ceramic material when used in the present invention, it may comprise small regions of a superconducting phase dispersed within a bulk non-superconducting phase, the superconducting regions being weakly coupled.
• the superconducting phase it is possible, and may even be preferable, for the superconducting phase to be present as the major portion of the material. Accordingly, the superconducting and the substantially non-superconducting phases may be present in any mutual proportions.
• the ceramic material is from the Y-Ba-Cu-O system although other ceramics or materials having a high superconducting transition temperature may be used provided that they fulfill the compositional phase requirements outlined above, eg. La or Sc based ceramic metal oxide superconductors such as La-Ba-Cu-O system or La-Sr-Cu-O system or other suitable ceramic materials from the rare earth-barium/strontium-Cu-O system.
• La or Sc based ceramic metal oxide superconductors such as La-Ba-Cu-O system or La-Sr-Cu-O system or other suitable ceramic materials from the rare earth-barium/strontium-Cu-O system.
• a particularly preferred material comprises (Y 1-x Ba x ) 2 CuO 4-d (d is undetermined) where x is 0.4 and has a superconducting phase of formula YBa 2 Cu 3 O 7-d . It was thought that such phase occupied about 1% of the material. However, it has now been ascertained that it occupies a greater proportion of the material.
• phase composition of the material can be varied by processing parameters such as mechanical grinding, chemical deposition, vapour transport, temperatures, atmospheres, pressures, sintering etc.
• the superconductive material may be present in any proportion of the body.
• the superconducting loop device may be formed from a multi-phase material containing a dispersed ceramic superconducting phase in a non-superconducting matrix as indicated above, the non-superconducting matrix may be a separate ceramic material or a polymer resin. It is also possible to form a cohesive body of granular multi-phase material without the use of a binder. However, the longevity of the body can be improved by use of a binder or an outer casing.
• the material can be in the form of a granular, ceramic superconductor (eg YBa 2 Cu 3 O 7-d ) bound in a non-superconducting matrix, particularly a polymer resin binder (eg in an amount of about 10% by weight).
• a granular, ceramic superconductor eg YBa 2 Cu 3 O 7-d
• a polymer resin binder eg in an amount of about 10% by weight
• a degree of compaction of at least 70% may be necessary to obtain the required superconductive properties which are affected by the degree of contact between the grains.
• the superconducting properties of the granular material are affected by the contacting surfaces of the grains of the superconducting material. Modification of the superconducting properties can be effected by modifying the contacting surfaces of the grains.
• the loop device may also be produced by thick film technology.
• the weak link characteristics of a loop formed in accordance with the present invention can also be tuned by other techniques e.g. machining of the loop, placing the loop in a uniform magnetic field, passing an electrical current through the loop, providing a coil around the loop and passing a current around said coil, subjecting the loop to electrochemical processes and localised or generalised heating/cooling of the loop.
• the superconducting properties of the loop are affected by the density and microstructure of the superconducting material. This in turn can be affected by particle size, amount of binder used, degree of sintering etc. When powder technology is used to form the loop or body, density can also be affected by the pressure used to compact the material before or during sintering.
• Example 1 Embodiments of the present invention will now be described in the following Examples.
• Example 1 Comparatives of the present invention will now be described in the following Examples.
• a loop comprises a circular ring of the following dimensions: outer diameter 10mm, inner diameter 5mm, thickness 3mm.
• the ring is formed f rom Y 1 . 2 Ba 0 . 8 CuO 4-d (d is undetermined) produced in the following manner: 5.4495g of Y 2 O 3 , 6.3512g of BaCO 3 and 3.1995g of CuO (all Analar Laboratory Reagents) are mixed together in a ball-mill-type mixer for 3 minutes. This mixture provides the correct ratios of metallic elements.
• the powder mixture is placed in an alumina crucible in a 950°C furnace for 45 minutes in air, the mixture being stirred after 20 minutes.
• the material is removed from the furnace and ground with a pestle and mortar to produce a powder having the consistency of flour.
• the ground material is replaced in the furnace for a further 40 minutes, stirring after 20 minutes.
• the material is removed from the furnace and, when cool, 1.5g of the material is compressed into the ring using a hydraulic press at approx 90001b.
• the ring is sintered in air at 950°C for 16 hrs in an A1 crucible.
• Figures 1 and 2 are X-ray diffraction spectra of a material which is similar to that outlined above. As can be seen, the X-ray analysis shows that several phases are present.
• Figure 2 is an enlarged view of part of the spectrum of Figure 1.
• region A is due to the presence of the superconducting phase.
• a body showing weak-link body behaviour in a non-loop configuration can be formed as follows:-
• a 1 mm cube of a compacted multi-phase ceramic material (Y 1.2 B 0.8 CuO 4-d in this Example) is placed inside a coil of 10 turns wound over a length of 6 mm and a diameter of 3 mm.
• the coil is connected in parallel with a 350pF capacitor and demonstrates simple r.f. SQUID behaviour at liquid nitrogen temperatures.
• Such an arrangement when attached to appropriate electronic apparatus (eg as disclosed in Nature, 328, p.47, 1987), can be used to detect changes of ambient magnetic field of the order of 1nT.
• the performance of such a device can be optimised to such a degree that it may be used as a very sensitive magnetometer for the location of any object affecting the ambient magnetic field.
• a superconducting loop can be formed by the following thick film technique:- 1.
• a ceramic multi-phase material of formula Y 1.2 Ba 0.8 CuO 4-d is Produced as described in Example 1 above and is powdered finely to a particle size of about 10-30 ⁇ m . This material is intimately mixed with an organic binder such as polyvinyl alcohol (PVA).
• PVA polyvinyl alcohol
• the powered ceramic and binder is coated onto the surface of a 1 mm cylindrical rod of zirconia by dipping into a thinned mixture of the ceramic and binder.
• the thickness of the coating is selected to give a coating of 10-100 ⁇ m after firing.
• the mixture is allowed to dry to allow partial evaporation of the PVA.
• the coated rod is fired at 950°C for 12 hours in air or oxygen.
• the fired rod is cooled slowly in air or oxygen for about 12 hours.
• the rod is then heated to 350-450°C and maintained at this temperature for 6 hours in oxygen and is then cooled.
• the coated cylinder is cut into discs 1 mm thick so giving loops of material having inherent weak-link superconducting properties.
• Example 3 is repeated using YBa 2 Cu 3 O 7-d as a starting material. Such a material is a superconductor. However, following treatment in steps 4 to 6 as described in Example 3, the resultant thick film contains more than one phase and provides the required weak link properties.
• a superconductor loop device has a body formed of a substantially non-superconducting matrix which has d persed therein regions of superconductive material such as to impart to the body the inherent properties of a weak-link perconducting loop.
• the body may be formed of particles of a multi-phase ceramic material wherein there is a non-sup conducting and a dispersed superconducting phase.
• the body may be formed by compacting, compacting and sintering,
• the present invention relates to a superconductor loop device having weak-link properties and to a method of producing such loop devices.
• weak-link superconductor loop devices have been formed from a loop of superconductive material having a discrete weak-link provided therein. It has previously been proposed to provide the weak-link in the form of a point-contact, constriction or an insulator junction, and these loops have well defined supercurrent and magnetic flux characteristics.
• the point contact weak-link must be mechanically adjusted to obtain and maintain the desired characteristics of the loop, whereas the constriction and insulator junction weak-links involve relatively sophisticated fabrication techniques and are expensive to produce.
• a high temperature ceramic metal oxide superconductor material of the Y-Ba-Cu-O system has been proposed in Physical Review Letters, volume 58 No. 9 pages 908 to 911.
• a superconductor loop device comprising a body formed of a matrix which is substantially non-superconducting and which has dispersed therein regions of superconductive material such as to impart to the body the inherent properties of a weak-link superconducting loop.
• the present invention has the advantage that the material from which the loop is fabricated has inherent properties which give the loop the characteristics of a superconducting weak-link loop because the matrix is non-superconducting and so allows magnetic flux to pass through the loop without the necessity of separately providing a discrete weak-link as required in the previously proposed loops.
• the loop is fabricated from ceramic material although other forms of a dispersed superconductor in a non-superconductor matrix might be used, e.g., metallic particles such as Pb, Nb or Ti in an epoxy resin matrix.
• the matrix should have poor conductivity as this allows the operation of the device at radio frequencies.
• the conductivity range for the matrix is may be 1 milliohm.cm to 10 8 ohm.cm.
• references to "superconductive”, “superconducting”, “non-superconducting” and “poor conductivity” relate to the properties at the intended temperature of operation of the device.
• the present invention provides a weak link loop which is easily reproducible. Furthermore, the use of ceramic materials allows the loop to be produced using conventional powder technology and so provides a loop which is economical to produce and which utilises materials having relatively high superconducting transition temperatures.
• ceramic material when used in the present invention, it may comprise small regions of a superconducting phase dispersed within a bulk non-superconducting phase, the superconducting regions being weakly coupled.
• the superconducting , phase it is possible, and may even be preferable, for the superconducting , phase to be present as the major portion of the material. Accordingly, the superconducting and the substantially non-superconducting phases may be present in any mutual proportions.
• the ceramic material is from the Y-Ba-Cu-O system although other ceramics or materials having a high superconducting transition temperature may be used provided that they fulfill the compositional phase requirements outlined above, eg. La or Sc based ceramic metal oxide superconductors such as La-Ba-Cu-O system or La-Sr-Cu-O system or other suitable ceramic materials from the rare earth-barium/strontium-Cu-O system.
• La or Sc based ceramic metal oxide superconductors such as La-Ba-Cu-O system or La-Sr-Cu-O system or other suitable ceramic materials from the rare earth-barium/strontium-Cu-O system.
• a particularly preferred material comprises (Y 1-x Ba x ) 2 CuO 4-d (d is undetermined) where x is 0.4 and has a superconducting phase of formula YBa 2 Cu 3 O 7-d . It was thought that such phase occupied about 1% of the material. However, it has now been ascertained that it occupies a greater proportion of the material.
• phase composition of the material can be varied by processing parameters such as mechanical grinding, chemical deposition, vapour transport, temperatures, atmospheres, pressures, sintering etc.
• the superconductive material may be present in any proportion of the body.
• the superconducting loop device may be formed from a multi-phase material containing a dispersed ceramic superconducting phase in a non-superconducting matrix as indicated above, the non-superconducting matrix may be a separate ceramic material or a polymer resin. It is also possible to form a cohesive body of granular multi-phase material without the use of a binder. However, the longevity of the body can be improved by use of a binder or an outer casing.
• the material can be in the form of a granular, ceramic superconductor (eg YBa 2 Cu 3 O 7-d ) bound in a non-superconducting matrix, particularly a polymer resin binder (eg in an amount of about 10% by weight).
• a granular, ceramic superconductor eg YBa 2 Cu 3 O 7-d
• a polymer resin binder eg in an amount of about 10% by weight
• a degree of compaction of at least 70% may be necessary to obtain the required superconductive properties which are affected by the degree of contact between the grains.
• the superconducting properties of the granular material are affected by the contacting surfaces of the grains of the superconducting material. Modification of the superconducting properties can be effected by modifying the contacting surfaces of the grains.
• the loop device may also be produced by thick film technology.
• the weak link characteristics of a loop formed in accordance with the present invention can also be tuned by other techniques e.g. machining of the loop, placing the loop in a uniform magnetic field, passing an electrical current through the loop, providing a coil around the loop and passing a current around said coil,, subjecting the loop to electrochemical processes and localised or generalised heating/cooling of the loop.
• the superconducting properties of the loop are affected by the density and microstructure of the superconducting material. This in turn can be affected by particle size, amount of binder used, degree of sintering etc. When powder technology is used to form the loop or body, density can also be affected by the pressure used to compact the material before or during sintering.
• Example 1 Embodiments of the present invention will now be described in the following Examples.
• Example 1 Embodiments of the present invention will now be described in the following Examples.
• Example 1 Embodiments of the present invention will now be described in the following Examples.
• Example 1 Embodiments of the present invention will now be described in the following Examples.
• Example 1 Embodiments of the present invention will now be described in the following Examples.
• Example 1 Embodiments of the present invention will now be described in the following Examples.
• a loop comprises a circular ring of the following dimensions: outer diameter 10mm, inner diameter 5mm, thickness 3mm.
• the ring is formed from Y 1.2 Ba 0.8 CuO 4-d (d is undetermined) produced in the following manner: 5.4495g of Y 2 O 3 , 6.3512g of BaCO 3 and 3.1995g of CuO (all Analar Laboratory Reagents) are mixed together in a ball-mill-type mixer for 3 minutes. This mixture provides the correct ratios of metallic elements.
• the powder mixture is placed in an alumina crucible in a 950°C furnace for 45 minutes in air, the mixture being stirred after 20 minutes. The material is removed from the furnace and ground with a pestle and mortar to produce a powder having the consistency of flour.
• the ground material is replaced in the furnace for a further 40 minutes, stirring after 20 minutes.
• the material is removed from the furnace and, when cool, 1.5g of the material is compressed into the ring using a hydraulic press at approx 90001b.
• the ring is sintered in air at 950°C for 16 hrs in an Al crucible.
• Figures 1 and 2 are X-ray diffraction spectra of a material which is similar to that outlined above. As can be seen, the X-ray analysis shows that several phases are present.
• Figure 2 is an enlarged view of part of the spectrum of Figure 1.
• region A is due to the presence of the superconducting phase.
• a body showing weak-link body behaviour in a non-loop configuration can be formed as follows:-
• a 1 mm cube of a compacted multi-phase ceramic material (Y 1.2 B 0.8 CuO 4-d in this Example) is placed inside a coil of 10 turns wound over a length of 6 mm and a diameter of 3 mm.
• the coil is connected in parallel with a 350pF capacitor and demonstrates simple r.f. SQUID behaviour at liquid nitrogen temperatures.
• Such an arrangement when attached to appropriate electronic apparatus (eg as disclosed in Nature, 328, p.47, 1987), can be used to detect changes of ambient magnetic field of the order of 1nT.
• the performance of such a device can be optimised to such a degree that it may be used as a very sensitive magnetometer for the location of any object affecting the ambient magnetic field.
• a superconducting loop can be formed by the following thick film technique:- 1.
• Y 1 . 2 Ba 0 . 8 CuO 4-d is Produced as described in Example 1 above and is powdered finely to a particle size of about 10-30 ⁇ m. This material is intimately mixed with an organic binder such as polyvinyl alcohol (PVA).
• PVA polyvinyl alcohol
• the powered ceramic and binder is coated onto the surface of a 1 mm cylindrical rod of zirconia by dipping into a thinned mixture of the ceramic and binder.
• the thickness of the coating is selected to give a coating of 10-100 ⁇ m after firing.
• the mixture is allowed to dry to allow partial evaporation of the PVA.
• the coated rod is fired at 950°C for 12 hours in air or oxygen. 5.
• the fired rod is cooled slowly in air or oxygen for about 12 hours.
• the rod is then heated to 350-450°C and maintained at this temperature for 6 hours in oxygen and is then cooled.
• the coated cylinder is cut into discs 1 mm thick so giving loops of material having inherent weak-link superconducting properties.
• Example 3 is repeated using YBa 2 Cu 3 O 7-d as a starting material. Such a material is a superconductor. However, following treatment in steps 4 to 6 as described in Example 3, the resultant thick film contains more than one phase and provides the required weak link properties.

Landscapes

• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Chemical & Material Sciences (AREA)
• Ceramic Engineering (AREA)
• Compositions Of Oxide Ceramics (AREA)
• Superconductor Devices And Manufacturing Methods Thereof (AREA)
• Measuring Magnetic Variables (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)

Applications Claiming Priority (4)

Publications (1)

Family

ID=26292115

Family Applications (1)

Country Status (5)

Families Citing this family (1)

Family Cites Families (1)

• 1988
  • 1988-04-08 EP EP88903295A patent/EP0421983A1/de not_active Withdrawn
  • 1988-04-08 WO PCT/GB1988/000275 patent/WO1988008207A1/en not_active Ceased
  • 1988-04-08 AU AU15780/88A patent/AU617997B2/en not_active Ceased
  • 1988-04-08 JP JP63503061A patent/JPH03500831A/ja active Pending
  • 1988-12-06 KR KR1019880701606A patent/KR890700928A/ko not_active Abandoned

Also Published As

Similar Documents

Legal Events