WO1993001621A1 - Alkaline earth metal sulphate uses - Google Patents
Alkaline earth metal sulphate uses Download PDFInfo
- Publication number
- WO1993001621A1 WO1993001621A1 PCT/GB1992/001169 GB9201169W WO9301621A1 WO 1993001621 A1 WO1993001621 A1 WO 1993001621A1 GB 9201169 W GB9201169 W GB 9201169W WO 9301621 A1 WO9301621 A1 WO 9301621A1
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- WIPO (PCT)
- Prior art keywords
- alkaline earth
- earth metal
- substrate
- sulphate
- metal sulphate
- Prior art date
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- 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 superconductor layers
- H10N60/0576—Processes for depositing or forming superconductor layers characterised by the substrate
- H10N60/0632—Intermediate layers, e.g. for growth control
Definitions
- the present invention relates to alkaline earth metal sulphates for use as barrier layers on substrates for ceramic superconductors.
- substrates for ceramic superconductors have usually been made from ceramic materials such as alumina, stabilised zirconia or magnesia. At typical superconductor processing temperatures, these materials exhibit chemical interaction and/or interdiffusion with the ceramic superconductor material, usually resulting in a deterioration of the properties of the ceramic superconductor. From the point of view of chemical interaction, materials consisting of highly stable alkaline earth metal compounds are likely to be more suitable. In particular, barium zirconate, strontium titanate and calcium silicate have been reported to exhibit little or no chemical interaction with ceramic superconductors at temperatures up to around 950°C.
- a barrier layer for a substrate for ceramic superconductors which can be sintered to high densities and which can enable substrates such as alumina and stabilised zirconia or magnesia to be used without significant chemical interaction and/or interdiffusion with the ceramic substrate.
- the present invention provides the use as barrier layers on substrates for ceramic superconductors, of materials which comprise at least a major proportion of an alkaline earth metal sulphate, or a mixture of alkaline earth metal sulphates.
- Preferred alkaline earth metals for use in the present invention are calcium, strontium and barium, or a mixture thereof.
- a particularly preferred alkaline earth metal sulphate for use in the present invention is barium sulphate. It will be understood by those skilled in the art that precursors for the alkaline earth metal sulphate may also be used.
- Barrier layers on substrates for ceramic superconductors comprise an alkaline earth metal sulphate or a mixture of alkaline earth metal sulphates, or a material consisting of a major proportion of an alkaline earth metal sulphate, or a mixture of alkaline earth metal sulphates.
- barrier layers may be prepared by casting a viscous slip of the sulphate(s) with a suitable sintering aid in an organic solvent/binder mixture, drying, burning out the organic solvent and sintering.
- a sintering aid is usually included in order to provide the barrier layers with a high density which is desirable.
- the alkaline earth metal sulphate(s) generally comprise at least about 80% by weight of the materials of the barrier layers.
- the minor component of the material for forming barrier layers on substrates for ceramic superconductors may be any material which is compatible with the barium sulphate, for example barium peroxide, barium fluoride, zirconia, magnesia or the superconductor, YBa 2 Cu 3 0 7 _ x ( YB CO ) .
- Suitable substrates which may have a barrier layer formed on them are alumina, stabilised zirconia and magnesia.
- barrier layers can, for example, be used to convert a low-cost, readily available substrate made from a material which shows high chemical reactivity with the superconductor, such as aluminium oxide, into a chemically inert substrate.
- a material which shows high chemical reactivity with the superconductor such as aluminium oxide
- the alkaline earth metal sulphate(s) barrier layer may be deposited in the form of a viscous slip by a technology such as screenprinting, either in a formulation which contains a sintering aid which also acts as a bonding material between the sulphate(s) and the underlying substrate, or as a second layer on top of a screenprinted layer of bonding material, or as a combination of both.
- a technology such as screenprinting, either in a formulation which contains a sintering aid which also acts as a bonding material between the sulphate(s) and the underlying substrate, or as a second layer on top of a screenprinted layer of bonding material, or as a combination of both.
- the composite is then dried, the organic material burnt out, and sintered.
- the alkaline earth metal sulphates may also be used as container materials or support materials for ceramic superconductors during treatments at elevated temperatures, where they perform the same function as they do in barrier layers, namely prevention of chemical interaction that would otherwise occur.
- the present invention will be further described with referred to the following non-limiting Examples.
- BaS0 4 powder BDH precipitated GPR grade
- Ba 2 powder Aldrich 99%
- the paste was used to screen print two layers of 13 micrometre thickness each onto a 5 x 5 cm square alumina substrate (96%, Coors Ceramic Electronics Ltd) .
- the screen used was 200 mesh.
- each layer was dried in an air circulation oven for 10 minutes at 100°C.
- the substrate was placed in a muffle furnace and subjected to the following heat treatment: 3°C per minute to 400°C, hold for one hour, 3°C per minute to 1050°C, hold for one hour, 3°C per minute to room temperature.
- An organic paste containing YBa2Cu 3 ⁇ 7_-- powder was prepared in the same way as described above, using the same organic vehicle as that described above, to give a solids loading of 74%.
- the substrates were placed in a Pyrex jar in a muffle furnace, with oxygen flowing through the jar at 100 ml per minute, and subjected to the following heat treatment: 3° per minute to 500°C, hold for eight hours, 3°C per minute to room temperature.
- gold contacts for a standard four-point measurement were deposited on each YBa 2 Cu 3 ⁇ 7 _ ⁇ film by vacuum evaporation. Copper wires were attached to the gold contacts with Epo-Tek silver epoxy (1:1 weight ratio epoxy to hardener) which was cured at 180°C for 10 minutes. Measurements of superconducting transition temperature, using a current of 1 mA were performed.
- Figure 1 shows the superconducting transition for the film on alumina without the barrier layer of BaS ⁇ 4, and Figure 2 for the film on the alumina substrate with the barrier layer of BaS ⁇ 4.
- the zero-resistance temperature for the film on the substrate without the barrier layer was 56.6 degrees Kelvin
- the zero- resistance temperature for the film on the substrate with the barrier layer was 79.1 degrees Kelvin.
- a barrier layer on an alumina substrate was prepared in the same way as described in Example 1.
- An YBa2CU3 ⁇ 7_ film was deposited on the barrier layer and heat treated in the same way as described in Example 1, except that prior to the heat treatment in flowing oxygen, silver contacts for four- point measurement were attached to the YBa 2 Cu30 7 _x film using Epo-Tek silver expoxy
- FIG. 3 shows the superconducting transition for the film, measured with a current of 1 mA.
- a barrier layer on a alumina substrate was prepared in the same way as described in Example 1, except that 2.5g of BaF2 was mixed with 50g of BaS ⁇ 4-
- An Ba2Cu3 ⁇ 7_ ⁇ film was deposited on the barrier layer and heat treated and contacted in the same way as described in Example 2.
- Figure 4 shows the superconducting transition for this film, measured with a current of 1 mA.
Abstract
The use as a barrier layer on a substrate for ceramic superconductors of a material which comprises at least a major proportion of an alkaline earth metal sulphate, or a mixture of alkaline earth metal sulphates.
Description
ALKALINE EARTH METAL SULPHATE USES
The present invention relates to alkaline earth metal sulphates for use as barrier layers on substrates for ceramic superconductors. Previously, substrates for ceramic superconductors have usually been made from ceramic materials such as alumina, stabilised zirconia or magnesia. At typical superconductor processing temperatures, these materials exhibit chemical interaction and/or interdiffusion with the ceramic superconductor material, usually resulting in a deterioration of the properties of the ceramic superconductor. From the point of view of chemical interaction, materials consisting of highly stable alkaline earth metal compounds are likely to be more suitable. In particular, barium zirconate, strontium titanate and calcium silicate have been reported to exhibit little or no chemical interaction with ceramic superconductors at temperatures up to around 950°C.
One characteristic of such materials, however, is the fact that they are generally difficult to sinter to high density. High densities are desirable in substrates or container materials for ceramic superconductors because of the tendency of such ceramic superconductors to form a quantity of liquid phase during processing at temperatures close to or above their melting points, and the fact that this liquid would tend to be drawn into the pores of a porous substrate leading to phase inho ogeneity in the superconductor after processing.
We have now developed a barrier layer for a substrate for ceramic superconductors which can be sintered to high densities and which can enable substrates such as alumina and stabilised zirconia or
magnesia to be used without significant chemical interaction and/or interdiffusion with the ceramic substrate.
Accordingly, the present invention provides the use as barrier layers on substrates for ceramic superconductors, of materials which comprise at least a major proportion of an alkaline earth metal sulphate, or a mixture of alkaline earth metal sulphates. Preferred alkaline earth metals for use in the present invention are calcium, strontium and barium, or a mixture thereof. A particularly preferred alkaline earth metal sulphate for use in the present invention is barium sulphate. It will be understood by those skilled in the art that precursors for the alkaline earth metal sulphate may also be used.
Barrier layers on substrates for ceramic superconductors comprise an alkaline earth metal sulphate or a mixture of alkaline earth metal sulphates, or a material consisting of a major proportion of an alkaline earth metal sulphate, or a mixture of alkaline earth metal sulphates. For example, barrier layers may be prepared by casting a viscous slip of the sulphate(s) with a suitable sintering aid in an organic solvent/binder mixture, drying, burning out the organic solvent and sintering. A sintering aid is usually included in order to provide the barrier layers with a high density which is desirable. The alkaline earth metal sulphate(s) generally comprise at least about 80% by weight of the materials of the barrier layers. The minor component of the material for forming barrier layers on substrates for ceramic superconductors may be any material which is compatible with the barium sulphate, for example barium peroxide, barium
fluoride, zirconia, magnesia or the superconductor, YBa2Cu307_x (YBCO) .
Examples of suitable substrates which may have a barrier layer formed on them are alumina, stabilised zirconia and magnesia.
The advantages of barrier layers are that they can, for example, be used to convert a low-cost, readily available substrate made from a material which shows high chemical reactivity with the superconductor, such as aluminium oxide, into a chemically inert substrate. Previously, although aluminium oxide was widely regarded as the preferred material for substrates for microwave devices, prior to the present invention its use as a material for substrates for high-temperature superconducting microwave devices was severely restricted by its chemical reactivity with the ceramic superconductor. The alkaline earth metal sulphate(s) barrier layer may be deposited in the form of a viscous slip by a technology such as screenprinting, either in a formulation which contains a sintering aid which also acts as a bonding material between the sulphate(s) and the underlying substrate, or as a second layer on top of a screenprinted layer of bonding material, or as a combination of both. The composite is then dried, the organic material burnt out, and sintered. It may not always be necessary or desirable to deposit and sinter the barrier layer prior to depositing and sintering the ceramic superconductor which is to contact it; co- sintering is quite possible, although this does put some limits on the sintering treatment, and the final properties of the various materials are likely to be different. The alkaline earth metal sulphates may also be used as container materials or support materials for
ceramic superconductors during treatments at elevated temperatures, where they perform the same function as they do in barrier layers, namely prevention of chemical interaction that would otherwise occur. The present invention will be further described with referred to the following non-limiting Examples.
EXAMPLE 1
50g of BaS04 powder (BDH precipitated GPR grade) and 5g of Ba 2 powder (Aldrich 99%) were dry mixed in a shaker-mixer for two hours. 30g of the resulting powder mixture was combined with an organic vehicle consisting of a solvent in which appropriate quantities of an organic binder and a surfactant had been dissolved. The powder was introduced into the organic vehicle by shearing with a spatula to give a smooth paste with a final solids loading of 72-73%.
The paste was used to screen print two layers of 13 micrometre thickness each onto a 5 x 5 cm square alumina substrate (96%, Coors Ceramic Electronics Ltd) . The screen used was 200 mesh. After application, each layer was dried in an air circulation oven for 10 minutes at 100°C. After drying of the second layer, the substrate was placed in a muffle furnace and subjected to the following heat treatment: 3°C per minute to 400°C, hold for one hour, 3°C per minute to 1050°C, hold for one hour, 3°C per minute to room temperature. An organic paste containing YBa2Cu3θ7_-- powder was prepared in the same way as described above, using the same organic vehicle as that described above, to give a solids loading of 74%. A 10 mm x 10 mm square, in three layers of 13 micrometre thickness each, was screenprinted using a 325 mesh screen onto the substrate with the barrier
layer of BaSθ4 prepared as described above, and also directly onto an alumina substrate. After application, each layer was dried in the same way as described above. After drying of the final layer, the substrates were placed in a tube furnace together with a thermocouple, and subjected to the following measured heat treatment: 5°C per minute to 500°C, no hold, 10°C per minute to 1070°C, no hold, 10°C per minute initial cooling rate, gradually slowing down at temperatures below 900°C.
After cooling down to room temperature, the substrates were placed in a Pyrex jar in a muffle furnace, with oxygen flowing through the jar at 100 ml per minute, and subjected to the following heat treatment: 3° per minute to 500°C, hold for eight hours, 3°C per minute to room temperature. Subsequently, gold contacts for a standard four-point measurement were deposited on each YBa2Cu3θ7_χ film by vacuum evaporation. Copper wires were attached to the gold contacts with Epo-Tek silver epoxy (1:1 weight ratio epoxy to hardener) which was cured at 180°C for 10 minutes. Measurements of superconducting transition temperature, using a current of 1 mA were performed. Figure 1 shows the superconducting transition for the film on alumina without the barrier layer of BaSθ4, and Figure 2 for the film on the alumina substrate with the barrier layer of BaSθ4. Using a criterion of 1 microvolt per centimeter, the zero-resistance temperature for the film on the substrate without the barrier layer was 56.6 degrees Kelvin, and the zero- resistance temperature for the film on the substrate with the barrier layer was 79.1 degrees Kelvin.
EXAMPLE 2
A barrier layer on an alumina substrate was prepared in the same way as described in Example 1. An YBa2CU3θ7_ film was deposited on the barrier layer and heat treated in the same way as described in Example 1, except that prior to the heat treatment in flowing oxygen, silver contacts for four- point measurement were attached to the YBa2Cu307_x film using Epo-Tek silver expoxy
(1:1 weight ratio epoxy to hardener), and the film was subjected to the following heat treatment: 3° per minute to 900°C, hold for 10 minutes, 3°C per minute to room temperature. After the heat treatment in flowing oxygen, copper wires were attached in the same way as described in Example 1. Figure 3 shows the superconducting transition for the film, measured with a current of 1 mA. The zero-resistance temperature of the film, using a criterion of 1 microvolt per centimeter, was 77.6 degrees Kelvin.
EXAMPLE 3
A barrier layer on a alumina substrate was prepared in the same way as described in Example 1, except that 2.5g of BaF2 was mixed with 50g of BaSθ4- An Ba2Cu3θ7_χ film was deposited on the barrier layer and heat treated and contacted in the same way as described in Example 2. Figure 4 shows the superconducting transition for this film, measured with a current of 1 mA. The zero-resistance temperature of the film, using a criterion of 1 microvolt per centimeter, was 76.3 degrees Kelvin.
Claims
1. The use as a barrier layer on a substrate for ceramic superconductors of a material which comprises at least a major proportion of an alkaline earth metal sulphate, or a mixture of alkaline earth metal sulphates.
2. The use as claimed in claim 1 wherein the alkaline earth metal is calcium, strontium, barium or a mixture thereof.
3. The use as claimed in claim 1 or claim 2 wherein the alkaline earth metal sulphate is barium sulphate.
4. The use as claimed in any one of claims 1 to 3 wherein the material comprises at least 80% by weight of the alkaline earth metal sulphate, or mixture of alkaline earth metal sulphates.
5. The use as claimed in any one of the preceding claims wherein the substrate is alumina, zirconia or magnesia.
6. The use as claimed in any one of the preceding claims wherein the ceramic superconductor is YBa2Cu307_x.
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB919114435A GB9114435D0 (en) | 1991-07-03 | 1991-07-03 | Alkaline earth metal sulphate uses |
GB9114435.2 | 1991-07-03 | ||
GB919121847A GB9121847D0 (en) | 1991-10-15 | 1991-10-15 | Alkaline earth metal sulphate uses |
GB9121847.9 | 1991-10-15 |
Publications (1)
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WO1993001621A1 true WO1993001621A1 (en) | 1993-01-21 |
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PCT/GB1992/001169 WO1993001621A1 (en) | 1991-07-03 | 1992-06-29 | Alkaline earth metal sulphate uses |
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Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2003023872A1 (en) * | 2001-09-10 | 2003-03-20 | Industrial Research Limited | Parting agents for metal-clad high-temperature superconductor wires and tapes |
Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0301525A2 (en) * | 1987-07-29 | 1989-02-01 | Matsushita Electric Industrial Co., Ltd. | Superconductor structure |
EP0409338A2 (en) * | 1989-07-20 | 1991-01-23 | Koninklijke Philips Electronics N.V. | Planar Josephson device |
-
1992
- 1992-06-29 WO PCT/GB1992/001169 patent/WO1993001621A1/en active Application Filing
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0301525A2 (en) * | 1987-07-29 | 1989-02-01 | Matsushita Electric Industrial Co., Ltd. | Superconductor structure |
EP0409338A2 (en) * | 1989-07-20 | 1991-01-23 | Koninklijke Philips Electronics N.V. | Planar Josephson device |
Non-Patent Citations (2)
Title |
---|
APPLIED PHYSICS LETTERS vol. 55, no. 17, 23 October 1989, NEW YORK, US Vasquez R.P. et al: 'Wet chemical techniques for passivation of YBa2Cu3O7-x' * |
JOURNAL OF THE ELECTROCHEMICAL SOCIETY vol. 137, no. 7, July 1990, WASHINGTON, US pages 2344 - 2350; Vasquez R.P. et al: 'Wet Chemical Passivation of YBa2Cu3O7-x' * |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2003023872A1 (en) * | 2001-09-10 | 2003-03-20 | Industrial Research Limited | Parting agents for metal-clad high-temperature superconductor wires and tapes |
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