DE10163125A1 - Process for the production of textured superconducting thick layers and biaxial textured superconductor structures obtainable therewith - Google Patents

Abstract

The invention relates to a method for the production of textured superconducting thick films especially made of an oxidic superconducting material such as SE barium cuprates, whereby at least two starting materials are contactingly arranged next to each other in the form of the superconducting thick layer to be formed on a support material. The at least two starting materials consist of compositions which at least partially melt when subsequently subjected to heat treatment and which at least partially form a superconducting material. The at least two starting materials form a gradient with respect to at least one quality variable such as the concentration of a component. The device undergoes heat treatment involving at least partial melting of the starting materials and formation of a superconducting material from at least one part of the starting material. The device is then cooled isothermally with crystallization of the superconducting material and textured growth of the crystals occurs parallel to the direction of the gradient of the quality variable. The invention also refers to biaxially textured superconducting thick films and structures which can be obtained according to the inventive method.

Description

The present invention relates to a method of manufacturing textured superconducting thick layers, especially biaxially textured Thick layers on a substrate and for practical use suitable structures from these thick layers by appropriate geometric arrangement of the thick layers on the carrier material as well as on biaxial textured thick layers and superconductor structures formed from them.

This makes superconducting layers sufficient for practical use have high critical current density, the crystals that make up the superconducting Form phase, orientation as uniform as possible (texturing) exhibit. In addition, the layers should have a sufficiently high absolute critical Have current, which requires a sufficient thickness of the layer.

With regard to the achievable critical current density, the The degree of texturing of a superconducting layer must be biaxial, that is to say one if possible uniform alignment of the crystals along the crystallographic a- and b- Have axes because in layers with only uniaxial texturing along the crystallographic c-axis the critical current density for practical Applications is insufficient. Generally the texture describes the middle one Crystal orientation. If this is statistical, it is also from an untextured Material spoken.

Because of their dimensions, superconducting thick layers are like those The present invention relates to between thin layers with thicknesses of less than 1 µm and superconducting solid materials with dimensions in Centimeter range and more to settle.

There are different methods of obtaining one for these material classes Texture known. So the texturing takes place in solid materials Germination, formation of a constitutional gradient, influence of external Magnetic fields or temperature gradients etc.

Biaxially textured superconducting thin films can be used with a Applications sufficient degree of texturing and a correspondingly high critical current density using thin-film processes such as Ion Beam Assisted Deposition (IBAD) or Rolling Assisted Biaxially Textured Substrates (RABiTS) be preserved. The disadvantage here is that these methods are complex and the thin layers obtained are only about one meter long exhibit. The thickness of the layers is also limited to less than 1 μm.

In addition, it is in these processes for the formation of texturing required to use specific carrier materials, the properties of the carrier material, in particular its texture, the orientation of the Thin film growing crystals. In the layers obtained here there is consequently a correlation between the texture of the carrier material (Substrate) and the texture of the layer, the texture respectively Alignment of the substrate with the texturing of the crystals in the layer causes and influences.

For example, single-crystal superconducting thin films have been found deposited different single-crystalline carrier materials.

The thin layers obtained in this way can then only subsequently - for example with regard to electronic applications - to the required geometric structures are formed.

With regard to high current - or energy technology Applications - however, these thin-film processes suffer from an inadequate one Productivity, at high manufacturing costs and too low Engineering current density, which is based on the current through the superconductor Total conductor cross section (superconductor including substrate material) results.

An overview of materials and processes for the production of Thin films and their applications are described in J.L. MacManus-Driscoll "Recent Developments in conductor processing of high irreversibility field superconductors " Annu. Rev. Mater. Sci. 1998, 28: 421-462.

Textured superconducting thick layers, for example made of rare earth barium cuprates with the general composition SEBa ₂ Cu ₃ O _7-x , can be obtained using various methods known for the production of thick layers, such as screen printing, electrophoresis etc. Here too, the texture of the superconductor layer is achieved on the basis of special properties of the carrier material. For example, base materials with roller texture or multi-phase base materials are used. An overview of methods and materials for, in particular, biaxial texturing of superconducting thick layers can be found in JL MacManus-Driscoll, Annu. Rev. Mater. Sci. 1998 (op. Cit.) And in N. McN Alford et al., "High temperature superconducting thick films", Supercond. Sci. Technol. 10 (1997), pages 169-185.

MacManus-Driscoll JL et al in "In-plane aligned YBCO thick films grown in situ by high temperature ultrasonic spray pyrolysis" in Superconductor Science and Technology, 14: (2) 96 to 102, February 2001 describes the production of biaxially textured thick layers made of YBa ₂ Cu ₃ O _7-x by means of ultrasonic spray pyrolysis, single-crystalline oxide substrates or single-crystal silver and textured polycrystalline silver foil with different orientations being used as substrates. With these processes, layers with a thickness of up to 5 μm could be obtained, which shows a critical current density Jc of approximately 1.0 × 10 ⁴ A / cm ² at 77 K in the self-field.

Also in Pinol S. et al "Meltgrowth and superconducting properties of textured Ag-YBa ₂ Cu ₃ O ₇ conductors" in IEEE Transactions on Applied Superconductivity, 9: (2) 1483 to 1486, part 2, June 1999, one is textured by means of cold rolling Silver foil used as a carrier material for the formation of a biaxially textured superconducting thick layer. In this case, a 20 μm thick thick layer of YBa ₂ Cu ₃ O _{7 is} applied to the carrier material by means of screen printing, and then a directional consolidation process with a temperature gradient is carried out.

Wells J. J. et al, in "In-plane aligned YBCO thick films on {110} rolled and single crystal silver by ultrasonic mist pyrolysis "IEEE Transactions an Applied Superconductivity, 9 (2) 1983 to 1985, part 2, June 1999, the texturing takes place over the substrate texture, with the substrate being single-crystalline silver or Texturing specially rolled silver is used. However, this only showed the thick layer on the single crystal silver has a biaxial texture.

According to Zafar N. et al "Texturing of thick films REBCO on metallic substrates by isothermal melt processing "in Applied Superconductivity 1997, Volumes 1 and 2, (158) 877 to 880 the biaxial texturing of the thick layers was carried out by means of textured silver substrates, being single crystalline silver or a textured rolled silver foil was used.

It is true that the known thick-film processes can be used to superconduct Get thick layers with good productivity and inexpensive that a certain Have a degree of texturing. However, it has been shown that the achievable thick layers are not sufficient for practical applications. So far, the production of structures, that is, for the practical Application of suitable geometries, based on this textured superconducting Thick layers not known.

The present invention is therefore based on the object of producing a productive scalable and cost-effective process for the production of biaxial textured superconducting thick layers and structures made available put.

Furthermore, the invention is based, for practical purposes Application of suitable, biaxially textured superconducting thick layers and to provide superconducting structures from it.

The above objects are achieved by a manufacturing method a textured superconducting thick layer, at least two Starting materials in the form of the superconducting thick film to be formed a carrier material are arranged in contact with each other, the at least two starting materials have a composition that in the event of at least partial melting of one of the starting materials during a subsequent heat treatment at least partially forms superconducting material, and in at least two of the Source materials in relation to at least one texture size Gradient forms, the arrangement with at least partial melting of one of the Starting materials and formation of a superconducting material from at least some of the raw materials are subjected to heat treatment, and then the arrangement with crystallization of the formed superconducting material and textured growth of the crystals towards of the gradient of the texture size is cooled isothermally.

For the purposes of the invention, the term “superconducting material” also includes superconducting material, that is, a material that has undergone post-treatment can be converted into a superconducting material such as for example Adjustment of the oxygen content for superconducting materials in general is known and common.

The invention also encompasses biaxially textured superconducting thick layers, the texture of which is independent of the texture of the carrier material or which are applied to an untextured carrier material, and which in particular have a critical current density of 10,000 A / cm ² at 77 K in the natural field.

In another aspect, the invention includes biaxially textured superconducting thick layers which are applied to a carrier material which is selected from polycrystalline silver and polycrystalline silver alloys.

In another aspect, the invention includes biaxially textured superconducting thick layers, in which the superconducting material at least in relation a component of the material forming the superconducting layer Has concentration gradient.

Furthermore, the invention particularly includes structures made from a biaxial textured superconducting thick film, the structure being a geometric shape which is not a straight line.

The attached figures relate to preferred embodiments of the Invention. It shows:

1a shows a structure of the invention in which the starting materials are arranged in meandering form.

FIG. 1b is an enlarged detail of a portion of the structure shown in FIG. 1a;

Fig. 1c shows a section through the thickness of the structure including the substrate of FIG 1a and 1b.

Figure 2 is an example of a band-shaped arrangement of the starting materials and, schematically, the biaxial texture of the thick film obtained.

3 shows an example for a circular arrangement of the starting materials and, schematically, the biaxial texture of the thick film obtained therefrom.

Fig. 4 thick layer a diagram with the Jc values of the obtained according to Example 1

Fig. 5 shows an alternative arrangement of the starting materials; and

Fig. 6 shows an arrangement for a preferred embodiment of the method according to the invention.

The invention takes advantage of the fact that by generating a gradient in used for the manufacture of the superconducting material Starting materials textured growth of the superconductor layer parallel to that Gradient is effected.

The gradient is created by using either the starting materials chosen differently, at least in relation to a quality become or during the implementation of the method according to the invention forms a corresponding gradient.

Texture quantities that can form gradients can Concentration of a component in the starting materials or different Particle sizes of the starting materials.

This gradient in relation to the at least one quality parameter causes a differently rapid solidification or melting behavior the materials in the direction of the gradient and thus a directed one Crystallization and texturing of the superconducting material that forms, in Direction of the gradient during a subsequent cooling.

Compositions can generally be used as the starting material be that have a stoichiometry that occurs in the course of the heat treatment and the subsequent isothermal cooling the desired Form superconducting material.

So at least two can be used to develop a concentration gradient Starting materials can be selected that are in at least one component distinguish the composition.

The starting materials are preferably already on a carrier material arranged in the form of the desired macroscopic structure so that they are in Are in contact with each other. In the case of more than two starting materials the term "in contact with each other" does not necessarily mean that all raw materials are in direct contact with each other, but individual Starting materials can also have other starting materials with which they are in contact, connected. You can do this depending on If necessary, be arranged side by side or one above the other.

With three or more starting materials, a combined arrangement can also be used side by side and on top of each other can be advantageous for certain cases.

This arrangement of carrier material with arranged thereon Starting materials are subjected to a heat treatment in a first stage, whereby the assembly is heated to a temperature at which at least a portion of the Raw materials are melting.

As a result of the melting of at least some of the starting materials the starting materials mix at least partially. The cause of the at least partial mixing can be diffusion processes and / or there may not be melted raw materials in already loosen molten starting materials.

Because of these diffusion and mixing processes, precursors for the superconducting material. In addition, the at least one component migrates into which differ in the compositions of the starting materials, in Direction of the starting material that does not contain this component, the Concentration of this component over the cross section of the layer increasing distance from the starting material that this component originally contained decreases.

Now the arrangement with the formed gradients is an isothermal When subjected to cooling, the superconducting material first crystallizes with the highest solidification temperature, the crystallization towards Concentration gradient and the resulting gradient of peritectic solidification temperature of the superconducting materials formed progresses. In other words: the crystallization respectively The superconducting material solidifies along the concentration gradient towards the material with the lowest solidification temperature.

The resulting gradient of the solidification temperature favors the spatially isothermal slow cooling the directional growth of the Crystals made of superconducting material parallel to this gradient. The accordingly favored crystal orientation continues Solidification course against unfavorably oriented crystals, so that ultimately only crystals remain with the desired preferred orientation.

In this context it should be noted that even without generating a Gradients due to the naturally limited layer thickness in thick layers Already achieved a uniaxial alignment of the crystallographic c-axis can be. The further orientation of the other two However, crystal axes with the formation of a biaxial texturing only become made possible by the inventive provision of a gradient as he according to the invention by the targeted arrangement and selection of Starting materials can be realized.

Isothermal cooling means that the temperature is uniform across the entire arrangement is lowered so that at a given time the Arrangement exposed throughout its extent at the same temperature is.

The isothermal cooling has a gradual cooling, in which the Arrange an external temperature gradient at a given time exposed to the advantage that it is also very small and / or complicated shaped structures is readily applicable.

In contrast, crystallization by means of an external one requires Temperature gradients a minimum size of the structure to be trained, on the one hand due to the practicability, and on the other hand, to be effective at all Temperature gradient can be formed over the arrangement. Because it is Leave the extension over which the directional crystallization is to take place too small with conventional devices for performing the crystallization not sufficiently large using external temperature gradients Achieve temperature differences that cause the desired directional crystallization.

Unlike the known methods as described above have been carried out in the method according to the invention is biaxial Texturing of the thick layer regardless of the properties or the Condition of the carrier material. This is for the implementation of the The method according to the invention does not require a carrier material which already has a has appropriate orientation, over which the texturing of the forming thick film is influenced.

The thick layers according to the invention therefore show no correlation between the texture of the substrate and that of the thick layer.

Untextured substrate materials can also be used for the present invention and carrier materials that have no preferred orientation become.

For example, untextured polycrystalline materials made of metal or Ceramic or metal alloys can be used.

Preferred examples of support materials to be used according to the invention are polycrystalline silver and silver alloys, for example with palladium.

Different from what is described in the prior art for the invention Process the substrate is not subjected to a treatment for texturing be, as is the case with the well-known specially rolled and Heat-treated polycrystalline silver substrates are the case. Here receives the polycrystalline material only through special pretreatment desired crystal orientation, which then the desired orientation of the Thick film causes.

For practical use, the selected carrier material should be used with the Temperatures, such as those used in the process, do not melt and also must not be undesirable with the materials for the thick layer Enter into side reactions. For example, carrier materials that are suitable consist of a material or composite whose melting point above the minimum temperature required to convert the Starting materials in the superconducting material.

The thickness of the carrier material usually depends on the intended one Application and according to the thickness of the thick layer to be applied. she can are between 50 µm and 100 µm or more. This information can be according to Needs vary.

Support materials with a buffer layer can also be used, wherein a thin layer of the desired carrier material on another Carrier is applied.

The carrier material can be any for the desired application have a suitable shape. Examples are plates and cylinders. So on one plate-shaped carrier a thick layer in any pattern, such as a meander, applied or on a cylinder as a carrier material a coil can be printed as a thick layer.

In the process according to the invention, the starting materials can thus already on the carrier material in the form of the desired trainees Macroscopic structure can be arranged, so that a subsequent Editing to form this structure is not required.

The starting materials for this can be in any desired geometric shape can be arranged on the carrier material. The shape is not limited to straight lines and bands, but it can also be around complicated shapes, for example curved structures in the form of Trade spirals, circles or meanders etc. The training of Multifilaments are possible. According to the invention, three-dimensional structures can also be used obtained in which the thick film on an appropriate body is applied. An example of this is one on a three-dimensional body, for Example a cylinder, printed coil.

A can be used to apply the starting materials to the carrier material any coating process, such as for the production of Thick layers are common to be used. Examples include screen printing, Docter Blade, Spin Coating, Brush Application, Sedimentation, Airbrushing, Electrolysis, etc.

The starting materials for this lie in a suitable one for these processes Form before, for example as a powder, paste, suspension etc.

The starting materials can be applied in one suitable medium, such as a suspension or paste in one Liquid. The medium usually evaporates during this Heat treatment.

According to a variant of the method, crystallization can be supported of the superconducting material can be used, the crystallization initiate. Known nucleating agents such as Magnesium oxide single crystals, for example in the form of whiskers, can be provided. Preferably are these nucleating agents already in the desired orientation of the Crystallization growth aligned.

Defects in the carrier material such as Grooves, other bumps and / or geometric surface structures, such as For example, printed patterns can also be provided, if necessary can be introduced in a controlled manner.

These means that initiate the crystallization are at the starting point of the Crystallization front - usually the area with the highest Solidification temperature - intended to increase the probability of nucleation.

A superconducting material of same type as the superconducting material to be formed, the at least partially at the temperatures of the heat treatment preferably remains completely in the solid state. The crystals of the as a nucleating agent submitted superconductor material act as crystallization nuclei for the the superconducting material forming the melt from the starting materials.

For this it is necessary that the superconducting agent presented as a nucleating agent Material does not completely melt at the temperatures of the heat treatment, but solid germs remain.

This material therefore preferably has a peritectic Solidification temperature, which is higher than that of the starting materials Superconductor material.

The method according to the invention is particularly suitable for the formation of Thick layers made of oxide superconducting materials. Particularly preferred Representatives here are oxide superconducting materials based on SE Barium cuprates with SE selected from at least one rare earth metal including lanthanum and yttrium.

The superconducting material can be in addition to at least one rare earth element (including lanthanum and yttrium) as well as barium, copper and oxygen if necessary at least one other element selected from the group consisting of from Be, Mg, Ca, Sr, Zn, Cd, Sc, Zr, Hf, Pt, Pd, Os, Ir, Ru, Ag, Au, Hg, Tl, Pb, Bi, Ce, Ti, S and F included.

A particularly preferred example of oxidic superconducting materials with the composition mentioned above are the so-called "1-2-3 materials" (also called 1-2-3 compounds) with the general formula SEBa ₂ Cu ₃ O, SE being the above has the meaning mentioned and the oxygen content is set to a value suitable for superconductivity. In particular, these are compounds of the general formula SEBa ₂ Cu ₃ O _7-x with x 0,5 0.5.

As mentioned above, the compound can do more than one rare earth metal and possibly at least one of the additional elements listed above contain.

Examples of suitable starting materials for the production of the preferred superconducting 1-2-3 materials are compounds of the general formula SE ₂ BaCuO ₅ , which are usually also referred to as 2-1-1 materials. As also indicated above for the superconducting 1-2-3 material, SE stands for at least one rare earth metal including the elements lanthanum and yttrium. Furthermore, the 2-1-1 materials can additionally contain at least one further element from the same group as specified above for the 1-2-3 materials.

To adjust the stoichiometry of the 1-2-3 material to be trained, the 2-1-1 materials are used in a manner known per se in combination with barium cuprates and possibly copper oxide. This can be a mixture with a nominal stoichiometry Ba ₂ Cu ₃ O ₅ . The liquid phase composed of barium cuprate and optionally copper oxide can contain further additives if necessary. Suitable examples are one or more rare earth elements, Ag, Pt, Ce, Zn, Ba, Ca and F as well as compounds with these elements. The compounds can be the oxides of these elements or their fluoride compounds such as BaF ₂ . These additives can be contained in an amount of 1 to 10 percent by weight.

For carrying out the method according to the invention, at least two 2-1-1 materials selected as starting materials, which can be found in at least one of their rare earth components, so that the Implementation of the method according to the desired gradient of Concentration for this at least one component of the starting materials and at the same time a gradient of the peritectic solidification temperature of the forming superconducting 1-2-3 material during isothermal cooling.

A suitable example of such a combination of starting materials are 2-1-1 materials with the composition Y ₂ BaCuO ₅ (Y211) and Yb ₂ BaCuO ₅ (Yb211). Tp (Y123)> Tp (Yb123) applies to the peritectic solidification temperature Tp of the corresponding 1-2-3 materials. Of course, any other combinations that meet this condition can also be selected.

As a guide for the further selection of suitable starting materials, the peritectic solidification temperatures or melting temperatures for 1-2-3 materials of the general formula SEBa ₂ Cu ₃ O _7-x are given in Table 1 below.

In principle, Table 1 only gives a guide to the selection of suitable ones Combinations. Mixtures of different elements, the use of pressure or negative pressure, contents of substances that have the melting point or lower peritectic temperature, and especially the However, partial pressure of oxygen can cause a significant change in temperature and possibly also require a change in the order listed in Table 1.

Examples of suitable combinations are given in Table 2 with
Nd>Sm> Dy
Nd>Dy> Y
Nd>Y> Yb
Nd>Sm> Yb
Sm>Y> Yb
Sm>Gd> Y
Eu>Dy> He
Eu>Y> Yb
Gd>Y> Yb
Dy>Er> Yb

The principle of the present invention for producing biaxially textured thick layers with reference to the attached figures exemplified with reference to a preferred embodiment.

The starting materials selected for this preferred variant are the combination of Y ₂ BaCuO ₅ (Y211) 2 and Yb ₂ BaCuO ₅ (Yb211) 3, as well as NdBa ₂ Cu ₃ O _7-x (Nd123) 5 and a mixture of barium cuprate and CuO with the nominal stoichiometry Ba ₂ Cu ₃ O ₅ 4 as the liquid phase. Tp Nd123> Tp Y123> Tp Yb123 applies to the peritectic solidification temperatures Tp.

Of course, any other combination can be made 2-1-1 materials and, if necessary, 1-2-3 materials can be selected that the Fulfill the condition for the peritectic solidification temperatures.

According to the invention, the geometric arrangement of the starting materials ( 2 , 3 , 5 ) on the carrier material ( 1 ) can be assigned at least two characteristic length scales, which are shown in FIG. 1a and in an enlargement in FIG. 1b. The larger length scales L1 and L2 in FIG. 1a correspond to the characteristic lengths of the structure of the layer to be formed (here a meander). The smaller length scale 1, as shown in the enlargement in FIG. 1b, on the other hand, corresponds to the arrangement of the starting materials 2 , 3 , 5 in relation to one another to produce a texture in the superconductor material.

As shown in FIG. 1b, the starting materials 2 , 3 , 5 are arranged in lines next to one another on the carrier material 1 , the adjacent lines forming the meandering structure shown in FIG. 1a.

The starting materials 2 , 3 , 5 arranged in a line on the carrier material 1 are completely or at least partially covered with the mixture of barium cuprate and copper oxide 5 .

Since the liquid phase of barium cuprate and copper oxide has a lower melting temperature than the 2-1-1 material 2 , 3 and the 1-2-3 material 5 , it melts first during the heat treatment. The melt formed infiltrates the starting materials 2 , 3 , 5 below, these at least partially dissolving in the melt. From this partial melt with the Ba ₂ Cu ₃ O ₅ 4 as liquid phase with dissolved solid 2-1-1 material, the desired 1-2-3 material forms during slow cooling.

At the same time, the rare earth elements migrate due to diffusion and melting processes, a first concentration gradient for Nd being formed from left to right in the example shown in FIG. 1b and a second concentration gradient for Yb being formed from right to left.

Due to Tp (Nd 123)> Tp (Yb123), the following results in the overall system two above-mentioned concentration gradients formed between the line Nd123 5 and Yb123 formed from Yb211 2 is a gradient of Solidification temperature. This gradient of the solidification temperature favors the subsequent spatially isothermal slow cooling the directed Growth of the superconducting crystals parallel to this gradient.

The final temperature of the heat treatment is preferably selected so that the 1-2-3 material 5 is not yet melting, but the other starting materials 2 , 3 , 4 have melted in whole or in part or have dissolved in a melt.

These unmelted particles then have an effect on isothermal cooling 1-2-3 material as crystallization nuclei. The use also supports of a 1-2-3 material together with 2-1-1 materials the formation of the desired concentration gradient, here an Nd gradient.

Germination usually takes place statistically, but the crystals grow in the direction of the region with the lowest peritectic solidification temperature, for example from left to right in FIG. 1b.

The heat treatment in which at least part of the starting materials is melted, can be carried out in a commercially available oven.

The duration of the heat treatment depends on the type of Starting materials dependent. It must be long enough so that the forms the desired gradient, on the other hand, the heat treatment is closed finish before the at least one component that forms the gradient should, distributed uniformly in the starting materials.

The starting materials can be continuous or stepwise brought to the desired final temperature. For that gradually Different heating rates and / or one or more can be used for heating Stopping times are provided.

The holding times during the heat treatment also depend on the type and the application thickness of the starting materials.

Suitable heating rates range from 200 ° C / hour to 500 ° C / hour, with a total heating time including holding times in Dependence of the heating rate in a range from 5 hours to 10 hours be.

The heat treatment can be carried out at a total pressure that corresponds to normal air pressure.

The heat treatment can be done in an atmosphere of ambient air be carried out or alternatively it can be carried out in a different gas atmosphere. Examples of suitable gases or atmospheres are nitrogen Oxygen or argon with oxygen.

By changing the oxygen partial pressure, the melting points of the Carrier materials and the superconducting materials are specifically influenced.

For example, expediently by lowering the Oxygen partial pressure increases the melting point of the carrier material and at the same time the peritectic temperatures of the superconducting materials are lowered (and vice versa).

After reaching the final temperature provided for the heat treatment isothermal cooling follows.

Cooling rates can be selected for isothermal cooling as for the Melt texturing of superconducting materials are common.

For example, cooling may be at a rate of 10 ° C / hour or less respectively.

Lower cooling rates have been used to avoid mechanical Tensions proved beneficial.

Cooling is particularly preferably carried out at a rate in the range from 0.5 to 3 ° C / hour, especially 0.5 to 1 ° C / hour.

In general, the amount of liquid phase, here Ba ₂ Cu ₃ O ₅ , has to be chosen sufficiently for the formation of the desired superconductor material. It therefore depends on the type and quantity of the other starting materials.

Fig. 1c shows a section through the thickness of the assembly of substrate 1 and applied thereto starting materials 2, 3, 4 and 5.

As can be seen from FIG. 1c, the Ba ₂ Cu ₃ O ₅ 4 serving as the liquid phase does not have to completely cover the materials 3 and 5 , but is sufficient if it only overlaps an edge region of the lines formed from these materials.

Fig. 2 shows an arrangement for forming a band-shaped structure on a substrate 1 made of AgPd with it, adjacent lines from Y211 2, 3 and Yb211 Nd123 5 and Ba ₂ Cu ₃ O ₅ 4 as a liquid phase. The left figure shows the arrangement before the heat treatment and subsequent isothermal cooling. The right-hand illustration shows the finished strip, the 1-2-3 crystals 6 formed and their alignment being shown schematically.

The images shown in FIG. 3 show the production of a circular structure in accordance with the example described below 2. The middle figure here is an enlarged detail of the right figure with the smaller length scale l, i.e., the arrangement of the starting materials to each other, and the right figure shows the finished thick film , wherein the biaxial orientation of the 1-2-3 crystals 6 formed is shown schematically.

An example of an arrangement of the starting materials on each other Fig. 5 shows.

For this purpose, a line of 1-2-3 material 5 can first be applied to the carrier material 1 , which line is overlapped by a line of a first starting material 211 2 , which is arranged next to it. A line of a second 2-1-1 starting material 3 can then be applied to the first 211 starting material 2 on the side opposite the 1-2-3 starting material 5 . The peritectic solidification temperature of the materials again applies to Tp (1-2-3 starting material)> Tp (formed 1-2-3 material from the first 2-1-1 starting material)> Tp (formed 1-2-3 material from second source material).

With this arrangement, a variation of the orientation of the vector of the gradient for the peritectic solidification temperature can be achieved. If the starting materials are arranged next to one another, for example in the embodiments according to FIGS. 1 to 3, this vector points in a plane from the side of the starting materials with the highest peritectic solidification temperature to the side with the lowest peritectic solidification temperature.

In contrast to this, in the arrangement according to FIG. 5, the vector points from the bottom left (highest peritectic solidification temperature) to the top right (lowest peritectic solidification temperature). This oblique orientation of the vector can influence the alignment of the c-axis in addition to the desired biaxial alignment.

According to a further preferred embodiment of the invention, the Production of the superconducting thick layer using crystals superconducting material that is in situ when performing the process form and align.

This embodiment is based on the knowledge according to the invention that at the production of superconducting materials using melting technology Alignment of the superconducting crystals in the direction of a dimension for the superconducting material selected geometric arrangement can be effected can, if this dimension has an extremely small dimension, the not exceed a few 100 µm.

This geometric arrangement can have any shape as long as the dimensions bring about the desired alignment. You can band or be strip-shaped, a spiral, rhombus or combinations thereof.

This embodiment is explained below with reference to FIG. 6 using the example of forming a thick layer based on a 1-2-3 superconducting material.

As shown in FIG. 6, in a first stage at least one suitable starting material with a 2-1-1 composition or a correspondingly suitable stoichiometry, for example 4-2-2 in the case of Nd, and above that barium cuprate as Liquid phase in a suitable stoichiometry, for example Ba ₂ Cu ₃ O ₅ as described above, is arranged on a carrier material 1 , for example AgPd, in the form 7 of the desired thick layer.

In a second stage, narrow strips 8 of a further starting material are arranged as a geometric arrangement at an angle to the arrangement 7 obtained in stage 1 , these broad sides 8 of which are in contact with an edge of the arrangement obtained in stage 1 , from which point the directed crystallization of the superconducting material to be formed is to be initiated. The nucleation along a long side is usually initiated for the formation of a thick layer of superconducting material, as shown in FIG. 6.

A starting material for a superconducting material is selected for the narrow strips 8 , the peritectic solidification temperature of which is higher than that of the superconducting material or the superconducting materials for the actual thick film according to the form 7 .

The dimensions of the narrow strip 8 are chosen such that the 1-2-3 crystals that form are forced along the width of the strip 8 .

In order to force sufficient alignment of the crystals, the width of the strip should not exceed 8 200 µm, since the degree of orientation decreases with increasing width.

As stated above, instead of the narrow strips 8, any geometrical arrangements with an extremely small dimension can be chosen.

A width in a range from 100 μm to 200 μm, in particular 100 μm or close to 100 μm, is preferably selected for the strips 8 . Dimensions in the millimeter range are sufficient for the length. Suitable lengths are in a range from 1 mm to 5 mm.

If necessary, the length can also be longer, for example in the centimeter range also smaller, for example in the micrometer range.

The number of strips 8 can be selected as required and is not subject to any fundamental restriction.

The distance between the individual strips 8 is expediently chosen such that the materials do not influence one another when the method according to the invention is carried out, and in particular do not run into one another when melting.

The orientation of the crystals forming in the arrangement 7 can be influenced by the angle at which the strips 8 strike the arrangement 7 for the thick layer. For example, the crystals show a <110> orientation when the strips are arranged at an angle of 45 °, as shown in Fig. 6a, and a <100> orientation when they meet at a 90 ° angle, as shown in Fig. 6b.

According to the invention, an arrangement of the strips 8 at a 45 ° angle and thus a <110> orientation of the crystals is particularly preferred with regard to the current densities to be achieved. The grain boundaries of superconducting crystals that meet with <110> orientation show less contamination (segregation) at the grain boundaries than crystals that meet with other orientations, such as <100> orientation. This enables particularly high current densities to be achieved for superconducting materials with <110> -oriented crystals.

The method according to the invention for producing a superconducting thick layer by means of crystals produced and aligned in situ is carried out at a temperature at which the starting material selected for the strip 8 also melts. At the same time, a gradient is formed along the contact area of the strip 8 with the geometric shape 7 for the thick layer

During isothermal cooling, the crystallization of the 1-2-3 materials begins first on the strip 8 at any point, which is indicated by rectangles 9 in FIGS. 6a and b. The crystals align with their <100> or <010> edges parallel to the edges of the strip 8 and the crystallization proceeds along the concentration gradient in the direction of the shape 7 and then into the shape 7 . As indicated in FIG. 6a by the reference number 10 , the 1-2-3 crystals formed in the strip 8 grow into the mold 7, so to speak, and bring about a directed crystallization of the starting material which has been arranged according to the mold 7 therein default direction.

Are according to a further process variant for the invention Process powdered starting materials selected can be according to a another aspect of the invention a gradient due to different Particle sizes of the individual starting materials are generated. In this Case, the different starting materials can also be the same chemical Have composition.

Here, the starting materials can be arranged on the smaller quantity scale shown in FIG. 1b in such a way that a gradient of the particle size which promotes the textured growth of the superconducting thick layers is produced for at least one starting material.

The layer material obtained after the isothermal cooling has in Generally, as such, no superconductivity. To generate the Superconductivity in the preformed superconducting material becomes the thick film with the superconducting material of a heat treatment known per se to adjust the oxygen content of the superconducting material subjected. This manufacture of superconductivity in a superconductive Material is known per se.

For example, the textured superconductive thick layer obtained can be used for this purpose for 50 to 100 hours in an atmosphere with 1 bar oxygen partial pressure 500 ° C, so the oxygen content of the superconducting material to optimize in the thick layer. The heating and cooling rates of the Oxygen treatment can be around 100 ° C / hour.

The thickness of the thick layers according to the invention is usually one Range of greater than 5 µm, in particular of 10 µm and more, and less than 1 mm, preferably of 20 microns and more and less than 1 mm and in particular between 20 µm and more and 200 µm.

The thick layers obtained according to the invention show values for Jc of 10 ⁴ A / cm ² at 77 K, 0 T using a 2 μV / cm criterion, the Jc values for the thick layer according to the example being shown as a diagram in FIG. 4.

These good Jc values show that the biaxially textured according to the invention Thick layers are obtained that are dense and continuous and therefore one have excellent current carrying capacity.

The texture of the thick layers obtained according to the invention is independent of the type of carrier material used. Different from those according to the status There are no thick layers obtained according to the invention Correlation between the texture of the thick layer and the nature of the Carrier material, since the nature of the carrier material including a possible texture of the carrier material does not affect the orientation of the has superconducting crystals in the thick film. It is therefore according to the invention possible to use any carrier material. In particular, it is possible, untextured polycrystalline substrates made of metal or ceramic such as polycrystalline silver to use without the material be subjected to a pretreatment for texturing as usual got to.

According to the invention, biaxially textured thick layers can also be obtained, whose superconducting material for at least one component of the Composition from which the superconducting material is formed, a Concentration gradients in the direction of the biaxial orientation of the crystals having.

Because of their biaxial texturing with a dense and continuous The layer and an achievable thickness of more than 5 microns show the Superconducting thick films obtained according to the invention are one for practical use Applications suitable for high critical current density and absolute critical Electricity.

Therefore, the superconducting thick layers according to the invention or superconducting structures for a variety of energy technology applications such as high current applications and High frequency range can be used.

Examples of this are applications for magnetic bearings, magnetic Shields, power supplies, current limiters etc. A meandering Structure of textured superconducting material according to the invention can Example can be used as a resistive current limiter.

Thick layers according to the invention can be used for high-frequency applications or structures used for example as antennas or filters become.

Another area of application for the thick layers according to the invention is Use as a nucleating agent for the production of solid materials.

The present invention is described below by means of examples:

First example

Production of a biaxially textured, line-shaped (SE) Ba ₂ Cu ₃ O _7-x thick-film structure on a metallic band according to FIG. 2.
Carrier material: Band piece made of AgPd12.5 (palladium in weight percent) with a thickness of approx. 100 µm, a width of approx. 2 cm and a length of approx. 5 cm.
Starting materials: Powder made of Y ₂ BaCuO ₅ (Y211), NdBa ₂ Cu ₃ O _7-x (Nd123), Yb ₂ BaCuO ₅ (Yb211) as well as a powder mixture of BaCuO ₂ and CuO with nominal stoichiometry Ba ₂ Cu ₃ O ₅ with addition from 1 to 10 weight percent Ag powder as a liquid phase.

The average diameter of the powder particles of all powders ranged from 1 to 50 µm.

• - eine 1 mm breite Linie aus Nd123 (5) (5 cm lang, insgesamt etwa 40 mg Nd 123),
• - eine 5 mm breite Linie aus Y211 (2) (5 cm lang, insgesamt etwa 200 mg Y211)., und
• - eine 2 mm breite Linie aus Yb211 (3) (5 cm lang, insgesamt etwa 90 mg.

The following lines were applied to the carrier material with brushes or by means of an airbrush next to one another as shown in FIG. 2:

• a 1 mm wide line of Nd123 ( 5 ) (5 cm long, a total of about 40 mg Nd 123 ),
• - a 5 mm wide line of Y211 ( 2 ) (5 cm long, a total of about 200 mg Y211)., and
• - a 2 mm wide line of Yb211 ( 3 ) (5 cm long, a total of about 90 mg.

The lines arranged next to one another in this way were then covered with a layer of liquid phase with a total of about 400 mg of Ba ₂ Cu ₃ O ₅ 5.

The carrier material coated in this way was placed in air in a commercially available chamber furnace on an Al ₂ O ₃ block and subjected to the following heat treatment:

During the first step of this heat treatment, mainly the solvent used, water with 2% by weight polyvinyl alcohol (PVA), evaporated.

During the second step of the heat treatment, the mixture of silver, barium cuprate and copper oxide - the liquid phase - melted and formed a doped barium cuprate melt that infiltrated the starting materials located next to one another. The starting materials ( 2 ), ( 3 ) and ( 5 ) were at least partially dissolved from this liquid phase. A concentration gradient of neodymium was formed, which started from the starting material ( 5 ) in the direction of the starting material ( 3 ). Conversely, a gradient of the concentration of ytterbium was also formed, which started from the starting material ( 3 ) in the direction of the starting material ( 2 ).

Due to the different peritectic solidification temperatures Tp for different superconductors (SE) Ba ₂ Cu ₃ O _7-x with Tp (Nd123)> Tp (Y123)> Tp (Yb123) there was a gradient of the solidification temperature in the overall system due to the concentration gradient mentioned above. As a result, during the spatially isothermal, slow cooling in step 3 , directional growth of the superconductor crystals in parallel with the gradient of the solidification temperature was promoted.

To produce the superconductivity, the samples obtained were heated to 500 ° C. for 50 to 100 hours in an atmosphere with 1 bar oxygen partial pressure. In this process step, the oxygen content of the samples was optimized in such a way that x in YBa ₂ Cu ₃ O _{7-x is} minimally less than 0.5 in any case. The heating and cooling rates of the oxygen treatment were about 100 ° C / h.

The thicknesses of the thick layers obtained were typically in the range between 10 and 15 µm.

Second embodiment

Production of the circular structure according to FIG. 3.

The second exemplary embodiment was carried out analogously to the first exemplary embodiment, but the heat treatment and the isothermal cooling were carried out under the following conditions:


REFERENCE NUMERALS 1 substrate
2 Y211
3 Yb211
4 Ba ₂ Cu ₃ O ₅
5 Nd123
6 textured 123 crystals
7 Form for thick film
8 narrow strips
9 superconducting crystals
10 direction of crystal growth

Claims (25)

1. A process for producing a textured superconducting thick layer ,
that at least two starting materials ( 2 , 3 , 4 , 5 ) in the form of the superconducting thick film to be formed are arranged on a carrier material ( 1 ) in contact with one another, the at least two starting materials ( 2 , 3 , 4 , 5 ) having a composition which in the case of at least partial melting of one of the starting materials during a subsequent heat treatment, a superconducting material is at least partially formed and a gradient is formed in at least two starting materials ( 2 , 3 , 5 ) with respect to at least one quality variable,
the arrangement is subjected to a heat treatment with at least partial melting of one of the starting materials ( 2 , 3 , 4 , 5 ) and formation of a superconducting material from at least some of the starting materials ( 2 , 3 , 4 , 5 ), and then the arrangement is crystallized formed superconducting material and textured growth of the crystals is isothermally cooled in the direction of the gradient of the texture size. 2. The method according to claim 1, characterized, that the texture size is the concentration of at least one of the Is components that make up the raw materials. 3. The method according to claim 1, characterized, that the texture size is the particle size of the Is raw materials. 4. The method according to any one of the preceding claims, characterized in that at least one starting material ( 4 ) is used as the liquid phase, which is applied to the other starting materials ( 2 , 3 , 5 ) and at least partially covers them, the starting material acting as the liquid phase ( 4 ) melts at a lower temperature than the other starting materials ( 2 , 3 , 5 ). 5. The method according to any one of the preceding claims, characterized, that the superconducting material has at least one rare earth element including lanthanum and yttrium and at least barium, copper and Contains oxygen. 6. The method according to claim 5, characterized, that the superconducting material additionally has at least one element selected from the group among Be, Mg, Ca, Sr, Zn, Cd, Sc, Zr, Hf, Pt, Pd, Os, Ir, Ru, Ag, Au, Hg, Tl, Pb, Bi, Ti, Ce, S and F contains. 7. The method according to any one of claims 5 or 6, characterized in that the superconducting material is a 123 compound of the general formula SEBa ₂ Cu ₃ O _7-x , wherein SE stands for at least one rare earth element which has the meaning given above and x is ≤ 0.5. 8. The method according to any one of the preceding claims, characterized, that a means of promoting nucleation is provided. 9. The method according to claim 8, characterized, that the nucleating agent is selected from an unevenness on the carrier surface and / or geometric surface structures. 10. The method according to any one of the preceding claims, characterized in that at least two 211 compounds of the general formula SE ₂ BaCuO ₅ are used as starting materials, SE having the above meaning, and as further starting material ( 4 ) which forms the liquid phase, Barium cuprate and optionally copper oxide is used in a stoichiometry which is suitable for forming a superconducting material with at least some of the starting materials with a 211 composition. 11. The method according to claim 10, characterized, that the liquid phase additionally has at least one component selected from at least one rare earth element with the above Meaning, Ag, Pt, Ce, Zn, Ca, Ba, F as well as connections of these Contains items. 12. The method according to any one of the preceding claims 10 or 11, characterized in that a combination of at least two SE ₂ BaCuO ₅ compounds and a compound with the composition SE'Ba ₂ Cu ₃ O is used as starting materials, wherein SE 'is a rare earth element including lanthanum and yttrium is with SE '≠ SE, and the peritectic solidification temperature of SE'Ba ₂ Cu ₃ O _{7-x is} higher than the peritectic solidification temperature of the 123 compounds that form. 13. The method according to any one of the preceding claims, characterized, that the thick film obtained for adjusting the oxygen content of the superconducting material of a heat treatment in one Oxygen atmosphere is subjected. 14. The method according to any one of the preceding claims, characterized in that the carrier material ( 1 ) is selected from a substrate with a texture that does not correlate with the texture of the superconducting material to be formed, and a substrate without texture. 15. The method according to claim 14, characterized in that the carrier material ( 1 ) is selected from polycrystalline silver and a polycrystalline silver alloy. 16. The method according to any one of the preceding claims, characterized in
that in a first stage one or more first starting materials in the form of the desired thick layer ( 7 ) are arranged on a carrier material ( 1 ), and
in a second stage, at least one geometric arrangement ( 8 ) made of a second starting material for a superconducting material is arranged on the carrier material ( 1 ) in addition to the shape for the thick layer ( 7 ), the at least one geometric arrangement ( 8 ) being at least partially with the Mold for the thick layer ( 7 ) is in contact,
and a material is selected as the second starting material for the geometric arrangement ( 8 ) which forms a superconducting material which has a higher peritectic solidification temperature than the one or more superconducting materials which are formed from the starting material for the shape of the thick layer ( 7 ) , and
a dimension of the geometrical arrangement ( 8 ) is selected in an order of magnitude which causes the superconducting crystals which form during isothermal cooling to be oriented in the direction of this dimension. 17. Biaxially textured superconducting thick film available after a Method according to one of claims 1 to 16. 18. Biaxially textured thick layer, characterized in that the thick layer contains a superconducting material containing at least one rare earth element with SE selected from the group of rare earth elements including lanthanum and yttrium, as well as barium, copper and oxygen and is formed on a carrier material ( 1 ), the Texture not correlated with the texture of the thick layer. 19. Biaxially textured thick layer according to claim 17 or 18, characterized in that the carrier ( 1 ) consists of polycrystalline silver or a polycrystalline silver alloy. 20. Biaxially textured thick film according to one of claims 17 to 19, characterized, that the superconducting thick layer additionally has at least one element selected from the group among Be, Mg, Ca, Sr, Zn, Cd, Sc, Zr, Hf, Pt, Pd, Os, Ir, Ru, Ag, Au, Hg, Tl, Pb, Bi, Ce, Ti, S and F contains. 21. Biaxially textured thick film according to one of claims 17 to 20, characterized, that the superconducting material of the thick layer at least for one Component of the composition in a concentration gradient Direction of biaxial orientation of the crystals. 22. Biaxially textured thick film according to one of claims 17 to 21, characterized, that the thick layer has a thickness in a range of greater than 5 μm and has less than 1 mm. 23. Structure from a biaxially textured thick layer according to one of the Claims 17 to 22, characterized, that the structure has a geometric shape that is not a straight line forms. 24. Structure from a biaxially textured thick layer according to one of the Claims 17 to 22, characterized, that the structure is selected under a meander, one printed bobbin and a multifilament. 25. Use of a biaxially textured thick layer according to one of the Claims 17 to 22 or a structure according to any one of claims 23 or 24 for the manufacture of magnetic bearings, magnetic Shields, power supplies and current limiters; Filter and antennas; as well as a nucleating agent for the production of solid materials.