DE102018125270B4 - Process for the production of a ceramic material with locally adjustable permeability gradient, its application in a coating process and its use - Google Patents

Abstract

A method for producing a ceramic material (3, 3A, 3B, 3C, 3D, 3E) with a locally adjustable permeability gradient, the method comprising the following steps: producing a ceramic material by heating a starting material composition up to a temperature below the melting temperature of the starting material composition, - Cooling of the ceramic material produced to room temperature after a defined cooling rate to set a vortex density in the ceramic material produced, and - subsequent local temperature treatment to heat the ceramic material above its ferroelectric order temperature to adjust the local permeability gradient.

Description

The invention relates to a method for producing a ceramic material with a locally adjustable permeability gradient, its application in a coating process and its use.

Up until now, ferromagnetic or ferrimagnetic materials have been of particular importance for conducting magnetic fields and as magnetic insulators due to their high permeability. 1a shows the schematic representation of a conductor for DC and AC magnetic fields in ferromagnetic or ferrimagnetic layers 1 on a substrate 2 . The disadvantage, however, is the finite magnetization hysteresis of ferromagnetic or ferrimagnetic materials, which determines part of the losses of magnetic field conductors made from a ferromagnetic or ferrimagnetic material, especially when AC magnetic fields are conducted.

If an area is to contain few magnetic field lines and conduct magnetic fields poorly, this area must have a lower permeability than the adjacent areas (middle area in 3b , 5b) . If, on the other hand, an area is to contain many magnetic field lines and conduct magnetic fields well, then this area must have a greater permeability than the adjacent areas (middle area in 3a , 5a) .

In ferromagnetic or ferrimagnetic materials, magnetic reversal losses occur, these being composed of eddy current losses and hysteresis losses. Eddy current is the name given to a current that is induced in an extended electrical conductor in a magnetic field that changes over time or in a moving conductor in a temporally constant but spatially inhomogeneous magnetic field. As a result, the current is displaced from the center of the conductor at high frequencies and large cross-sections (skin effect). The skin effect mainly occurs at high signal frequencies. It ensures that only the outside of the conductor contributes to the flow of current. The skin effect is based on the shielding effect of electrically conductive materials against electromagnetic fields. The skin effect can largely be prevented by using high-frequency strands. In the case of an HF litz wire, one conductor is replaced by a parallel connection of individual conductors that are electrically isolated and interwoven.

Every transformer hums more or less audibly during operation. The cause of this is magnetostriction. With magnetostriction, the core of the transformer is forced into tiny changes in length. Magnetostriction is a material property and is ΔV / V ₀ = -3.252 · 10 ^-4 in ceramic materials with charged domain walls (T. Chatterji et al., J. Phys .: Condens. Matter 24 (2012) 336003), ΔV / V ₀ = -0.26-10 ^-4 in amorphous Fe ₃₅ Co ₃₅ Si ₁₁ B ₁₉ (SA1) and ΔV / V ₀ = -1.20 · 10 ^-4 in Fe-Si 0.3 .

Hysteresis losses are caused by the work that has to be done, for example, to remagnetize a coil core of a transformer in the rhythm of the frequency. The lower the specific resistance of the transformer core, the higher the losses. The specific resistance is a material property and in ceramic materials with charged domain walls is p = 73 to 141 Ωm (specific resistance of an RLC sample), p = 10 to 100 Ωm in amorphous SA1 and p = 10 to 100 Ωm in Fe-Si 0.3.

The power losses of a three-phase transformer EI 800/800/400 for 500 kVA operated under full load with different core materials as magnetic conductors (operation under full load) are composed of the copper losses and the iron losses. Table 1 shows the power losses of a three-phase transformer operated at full load for 500 kVA with different core materials. Tab. 1: material Copper losses / W Iron losses / W Induction / T Efficiency /% Fe-Si 0.35 1602 2696 1.5 99.06 Fe-Si 0.30 1599 2442 1.5 99.12 amorphous SA1 2916 174 1.2 99.33

The iron loss during remagnetization is $$\mathrm{W.}=\mathrm{<figure-callout\; id="2"\; label="\pi \; J\; p"\; filenames="DE102018125270B4\_0006.png,DE102018125270B4\_0007.png"\; state="\{\{state\}\}">\pi </figure-callout>}{J}_p^{}{}_2^{}\mu \text{'}\text{'}/\left(\mu {\text{'}}^2+\mu \text{'}{\text{'}}^2\right)$$

wobei δ der Verlustwinkel ist. Magnetisches Eisen hat typische Verlustfaktoren im Bereich von d = 0,08 ... 0,60 (Tab. 3, page 8, Determination of electromagnetic properties of steel for prediction of stray losses in power transformers). Der Verlustfaktor d der keramischen Materialien mit geladenen Domänenwänden, welche einen RLC-Parallel-Schwingkreis bilden, wird aus dem Gütefaktor Q eines RLC-Parallel-Schwingkreises $$Q=R\surd \left(C/L\right)$$

wie folgt bestimmt: d = 1/Q und liegt im Bereich von d = 0,36 ... 1,38. Die Resonanzfrequenz fo $$f_0=\left(1/2\pi \right)\sqrt{1/\left(LC\right)}$$

beträgt f₀= 64 MHz ... 107 MHz, wobei der Hochfrequenzbereich (HF) zwischen 30 kHz ... 300 MHz definiert ist.The loss factor d (Tab.2.9 in Magnetic Materials and their characterization, p. 25) is $$d=tan\delta =\mu \text{'}\text{'}/\mu \text{'}$$

where δ is the loss angle. Magnetic iron has typical loss factors in the range of d = 0.08 ... 0.60 (Tab. 3, page 8, Determination of electromagnetic properties of steel for prediction of stray losses in power transformers). The loss factor d of the ceramic materials with charged domain walls, which form an RLC parallel resonant circuit, is derived from the quality factor Q of an RLC parallel resonant circuit $$Q=\mathrm{R.}\surd \left(\mathrm{C.}/\mathrm{L.}\right)$$

is determined as follows: d = 1 / Q and lies in the range of d = 0.36 ... 1.38. The resonance frequency fo $$f_0=\left(1/2\pi \right)\sqrt{1/\left(\mathrm{L.}\mathrm{C.}\right)}$$

is f ₀ = 64 MHz ... 107 MHz, the high frequency range (HF) being defined between 30 kHz ... 300 MHz.

The eddy current losses (skin effect) in ferromagnetic or ferrimagnetic materials increase as the square of the frequency and inversely proportional to the specific resistance of the ferromagnetic or ferrimagnetic material and become significant above about 10 kHz. Since the inductive reactance above the resonance frequency fo is greater than the capacitive reactance, it is advantageous to conduct alternating magnetic fields above the resonance frequency f ₀ in the ceramic material with charged domains.

In metallic conductive ferromagnetic or ferrimagnetic materials, due to the skin effect, the penetration depth of alternating magnetic fields is only a few micrometers (1 ... 10 Ωm) at 100 MHz and several micrometers (70 ... 707 Ωm) at 50 Hz. Because of the skin effect, ferromagnetic and ferrimagnetic materials cannot be used in the HF range. The skin effect determines the thickness of the lamellas into which transformer coil carriers are typically formed.

The resonance frequencies of the ceramic materials with charged domain walls are fo = 64 MHz ... 107 MHz and are outside the audible range (16 ... 20,000 Hz). Even if the ceramic material resonates mechanically, this will not be noticeable through annoying noise development (hum). Since the ceramic materials with charged domain walls have no magnetization hysteresis and a specific resistance comparable to amorphous SA1 and Fe-Si 0.3, hysteresis losses in this material are negligible.

In order to keep the effects of the skin effect as small as possible, cables with the largest possible surface area are used in high-frequency technology, for example in the form of thin-walled hose pipes, strands or tapes. The low losses of waveguides are partly due to the fact that a large part of the inner surface is not significantly involved in the flow of current. Furthermore, the surfaces of high-frequency or ultra-high frequency cables are often coated with precious metals such as silver or gold in order to reduce the specific resistance of the outer surface of the wire, which conducts by far the largest part of the current. In the case of gold in particular, the fact that this metal does not oxidize in air is used, so that the surface retains a long-term stable conductivity. Because gold itself has a lower electrical conductivity than copper, but a significantly better one than copper oxide. Care is also taken to ensure that the conductor surface is very smooth, since rough surfaces represent a longer path for the current and therefore greater resistance. Ferromagnetic conductor materials are also particularly disadvantageous since the penetration depth is greatly reduced in these. For this reason, they are also often coated with metal.

Iron alloys and ferromagnetic steels are of greatest economic importance. For transformers (operating frequency 50 Hz or 60 Hz), so-called dynamo sheet is predominantly used DIN EN 10107 , which consists of iron-silicon alloys. Nickel-iron alloys are also used in signal transmitters. The maximum flux density for iron is 1.5 to 2 Tesla, depending on the specification. The core is built up from a stack of individual sheets between which there are electrically insulating intermediate layers, the sheet surface being parallel to the direction of the magnetic flux and thus perpendicular to the induced electric field. This reduces the eddy current losses. The higher the frequency, the thinner the sheets must be chosen. In the case of large transformers, damage to the insulation of the individual laminated cores can lead to considerable local heating of the core to lead. From frequencies in the kilohertz range, the eddy current losses in iron cores would be too great even with very thin sheets. Cores made of amorphous or nanocrystalline strips or ferrite cores are used. Ferrites have a high permeability, but only a low electrical conductivity. To manufacture ferrite cores, the raw material, which is usually powdery, is placed in a mold and sintered (pressed) under pressure. This results in more design options than with the laminated cores, in particular with regard to the adaptation to the coil body. With ferrites, the maximum flux density is around 400 mT. The limit to the use of ferrite material lies in the manufacturability in the pressing and sintering process. Cores for larger transformers are partly composed of ferrite blocks. The amorphous and nanocrystalline cores, thanks to their natural strip thickness of typically 0.02 mm, allow use at higher frequencies and have very low losses. Typical core shapes for these tapes are toroidal cores or, more rarely, cut tape cores.

The materials known and used up to now are not sufficient to eliminate the disadvantages described above. It is therefore an object of the present invention to provide a material with which these disadvantages can be significantly reduced and which is suitable for conducting and isolating magnetic fields and can be used in magnetic coupling elements.

• - Erzeugen eines keramischen Materials mittels Erhitzens einer Ausgangsmaterialkomposition bis zu einer Temperatur unterhalb der Schmelztemperatur der Ausgangsmaterialkomposition,
• - Abkühlen des erzeugten keramischen Materials auf Raumtemperatur nach einer definierten Abkühlrate zur Einstellung einer Vortex-Dichte in dem erzeugten keramischen Material, und
• - nachfolgende lokale Temperaturbehandlung zum Erhitzen des keramischen Materials über dessen ferroelektrische Ordnungstemperatur und zum Einstellen des lokalen Permeabilitätsgradienten.

The object is achieved by a method for producing a ceramic material with a locally adjustable permeability gradient, the method comprising the following steps:

• - Generating a ceramic material by heating a starting material composition to a temperature below the melting temperature of the starting material composition,
• Cooling the ceramic material produced to room temperature after a defined cooling rate to set a vortex density in the ceramic material produced, and
• - Subsequent local temperature treatment for heating the ceramic material above its ferroelectric order temperature and for setting the local permeability gradient.

The advantage of ceramic materials with charged domain walls is that they depend on the chemical composition, for example Y _1.00 Mn _1.00 O ₃ , Y _0.95 Mn _1.05 O ₃ , Y _1.00 Mn _0.99 O ₃ + 1at.% Ti and Y _0.94 Mn _1.05 O ₃ + 1at.% Ti in the table 2 B at the same time have very high permeabilities and no magnetization hysteresis. Because of this, magnetic fields can be conducted in ceramic materials with charged domain walls without the losses that are caused in ferromagnetic and ferromagnetic materials by the magnetization hysteresis. The permeability gradient of the ceramic material determines the location-dependent density of the magnetic field lines in the ceramic material with charged domain walls.

mit ε_r =11,8 ... 73,8 und µ_r = 56000 ... 171000 und mit p = 75 ... 141 Ωm mehrere hundert Mikrometer (380 ... 540 µm). Die keramischen Materialien mit Domänenwänden können daher hervorragend im HF-Bereich eingesetzt werden. Keramische Materialien mit geladenen Domänenwänden können für die Hochfrequenztechnik zur Herstellung von Leitungen mit kleineren Oberflächen eingesetzt werden, beispielsweise zur Beschichtung von Drähten verwendet werden. Läuft die Magnetisierungsrichtung ringförmig um den Draht, wird ein solcher Draht mit einem in Längsrichtung verlaufenden Magnetfeld belegt, ändert sich der magnetische Fluss in dem keramischen Material und führt bei hohen Frequenzen durch die Beeinflussung des Skin-Effektes zu einer Änderung der Induktivität des beschichteten Drahtes. Beschichtete Drähte in der Nähe stromdurchflossener Leiter können auch zur Messung des Magnetfeldes stromdurchflossener Leiter verwendet werden.In addition, the skin effect is reduced in ceramic materials with domain walls and the penetration depth of the alternating magnetic fields asymptotically approaches the value at high frequencies $$2\rho \sqrt{\left(\epsilon /\mu \right)}$$

with ε _r = 11.8 ... 73.8 and µ _r = 56000 ... 171000 and with p = 75 ... 141 Ωm several hundred micrometers (380 ... 540 µm). The ceramic materials with domain walls can therefore be used excellently in the HF range. Ceramic materials with charged domain walls can be used for high-frequency technology for the production of lines with smaller surfaces, for example for coating wires. If the direction of magnetization runs in a ring around the wire, such a wire is covered with a longitudinal magnetic field, the magnetic flux in the ceramic material changes and, at high frequencies, leads to a change in the inductance of the coated wire by influencing the skin effect. Coated wires near current-carrying conductors can also be used to measure the magnetic field of current-carrying conductors.

The starting material composition for producing the ceramic material can be, for example, an oxide powder or a metal powder with subsequent oxidation. The weighed oxide is first ground and then dried. A pre-sintering process is used to bring the powder into a certain phase or to a certain grain size. In a further grinding process, the partially clumped oxide mixture is dry-ground to a fine-grain powder. The powder is then finally dried and pressed together in a press mold and then sintered.

The ceramic material is now completely produced.

The cooling of the starting material composition to room temperature after a defined cooling rate is used to set a vortex density in the ceramic material produced. The ceramic material has the property of developing vortex states when it passes through a heating and / or cooling process. A vortex state can be understood as an intersection between charged domain walls within a material. In the ceramic materials with charged domain walls, vortex states are formed in the center of six different ferroelectric domain walls (DW), two charged DW (head-to-head), two charged DW (tail-to-tail) and two neutral DW (head -to-tail). A vortex state is topologically protected, ie it cannot be transferred to the ground state through continuous transformation. The ferroelectric order temperature T _{c of} the hexagonal rare earth manganate RMnO depends on the rare earth element in RMnO. Above a temperature of T _c , no ferroelectric order with ferroelectric domain walls and charged vortex states is formed. For example, the ferroelectric ordering temperature for HoMnO ₃ T _c = 875 K, for LuMnO ₃ T _c = 573 K and for YMnO ₃ T _c = 930 K. When the ceramic material is heated above the ferroelectric ordering temperature, the ferroelectric ordering is not pronounced. The vortex density during the subsequent cooling of the ceramic material depends on the cooling rate at the time of the cooling process, in which the cooling temperature is equal to the ferroelectric order temperature. Below the ferroelectric order temperature, the density of the vortices depends on the cooling rate. The vortex density thus depends on the cooling rate when passing through the ferroelectric order temperature.

In a preferred embodiment of the method according to the invention, the local temperature treatment takes place by means of short-term heat treatment - RTA - rapid temperature annealing in the ms range or by means of short-term annealing with flash lamps - FLA - flash light annealing in the ps to ms range or by means of pulsed laser radiation - PLA - pulsed laser annealing in the ns to ps range ( Subsecond Annealing of Advanced Materials Annealing by Lasers, Flash Lamps and Swift Heavy Ions, Springer Series in Material Science, 2014 ). RTA is suitable for the thermal treatment of bulk materials with dimensions in the range from centimeters to decimeters, materials with rough surfaces and planar materials; FLA is suitable for the thermal treatment of materials with dimensions in the range from micrometers to centimeters with rough surfaces and of planar materials; and PLA is suitable for the thermal treatment of planar materials with dimensions in the range from nanometers to micrometers. This subsequent short-term temperature treatment by means of RTA, FLA and / or PLA leads to the setting of the final permeability gradient, which is required in the respective application.

Another advantageous embodiment of the method according to the invention is that the ceramic material can be produced as a volume material. By pressing the powdery starting material composition, setting a vortex density according to a defined cooling rate in the ceramic material produced, and the local temperature treatment of the ceramic material above its ferroelectric order temperature to set the local permeability gradient, a volume material with a locally adjustable Permeability gradients are established. A volume material is understood to mean the ceramic material in its spatial extent in the x, y and z directions.

The object of the present invention is also achieved by a method for the global coating of a surface with a ceramic material, the ceramic material initially being produced as already described. Furthermore, the ceramic material is deposited on the surface to be coated, the ceramic material being cooled to room temperature after the deposition according to a defined cooling rate to set a vortex density in the ceramic material. This is followed by a local temperature treatment to heat the ceramic material above its ferroelectric order temperature, so that a final local permeability gradient is established in the coating on the surface. The coating should have a thickness less than the skin thickness.

A surface in the context of the present invention is understood to mean any surface that is suitable for coating with the ceramic material. This can be, for example, the surface of an object or body of any shape or a planar surface or a film or any substrate. This list is in no way to be understood as restrictive. The global coating therefore describes a coating of a surface in its entirety and is not to be understood as being spatially limited. If necessary, the surface must be provided with an adhesion promoter before the surface is coated so that the ceramic material bonds reliably to the surface.

In a preferred embodiment of the coating method according to the invention, the ceramic material is deposited on the surface by means of pulsed laser plasma deposition from a ceramic target which has the ceramic material. For example, the ceramic material with charged domain walls from a ceramic target can be deposited on a planar carrier material in thin-layer form by means of pulsed laser plasma deposition.

It is particularly advantageous if the method for producing the ceramic material with a locally adjustable permeability gradient is used for producing a ferrite core in a transformer.

It is also advantageous if the method for producing a ceramic material with a locally adjustable permeability gradient is used with the coating method according to the invention for coating with a coating material for electrical conductors and / or wires.

It is also advantageous if the method for producing the ceramic material with a locally adjustable permeability gradient is used for producing electrical conductors.

The invention is to be explained in more detail below using exemplary embodiments.

• 1 Schematische Darstellung a) einer ferro- oder ferrimagnetischen Schicht der Dicke d und b) eines keramischen Materials mit geladenen Domänenwänden der Dicke d auf einem Substrat;
• 2 Erfindungsgemäß hergestelltes keramisches Material mit geladenen Domänenwänden a) mit einer geringen Dichte der geladenen Domänenwände; b) mit einer hohen Dichte der geladenen Domänenwände;
• 3 Erfindungsgemäß hergestelltes keramisches Material mit geladenen Domänenwänden a) mit einer hohen Dichte der geladenen Domänenwände im Zentrum auf dem Substrat und b) mit einer hohen Dichte der geladenen Domänenwände in den Randbereichen auf dem Substrat;
• 4 Erfindungsgemäß hergestelltes keramisches Material mit geladenen Domänenwänden a) mit einer geringen Dichte der geladenen Domänenwände und der Dicke d auf einem keramischen Material mit einer hohen Dichte der geladenen Domänenwände sowie b) mit einer hohen Dichte der geladenen Domänenwände und der Dicke d auf einem keramischen Material mit einer geringen Dichte der geladenen Domänenwände;
• 5 Erfindungsgemäß hergestelltes keramisches Material der Dicke d a) mit geladenen Domänenwänden mit einer hohen Dichte der geladenen Domänenwände und mit geladenen Domänenwänden mit einer besonders hohen Dichte der geladenen Domänenwände in der Mitte auf einem keramischen Material mit einer geringen Dichte der geladenen Domänenwände sowie b) mit geladenen Domänenwänden mit einer hohen Dichte der geladenen Domänenwände und mit geladenen Domänenwänden mit einer besonders hohen Dichte der geladenen Domänenwände am Rand auf einem keramischen Material mit einer geringen Dichte der geladenen Domänenwände;
• 6 Verwendung zur Beschichtung von Kabeln als a) ein Schichtsystem aus keramischen Materialien i der Dicke di und der Permeabilität µ_i sowie b) als ein Schichtsystem aus keramischen Materialien i der Dicke di und der Permeabilität µ_i und aus dielektrischen Materialien j der Dicke d_j und der Permittivität ε_j;
• 7 a) Verwendung zur Herstellung eines Transformatorkerns aus einer b) spiralförmigen Aufwicklung eines Bandes bestehend aus keramischen Materialien i der Dicke di und der Permeabilität µ_i, welche c) unterschiedliche Werte auf dem Band annimmt, und d) welche auf einer Isolatorschicht (7) aufgebracht sind; sowie e) Verwendung zur Herstellung eines Transformatorkerns aus einer radialsymmetrische Beschichtung mit keramischen Materialien i der Dicke di und der Permeabilität µ_i und mit dielektrischen Materialien j der Dicke d_j und der Permittivität ε_j.

The drawings show

• 1 Schematic representation of a) a ferromagnetic or ferrimagnetic layer of thickness d and b) of a ceramic material with charged domain walls of thickness d on a substrate;
• 2 Ceramic material produced according to the invention with charged domain walls a) with a low density of charged domain walls; b) with a high density of charged domain walls;
• 3 Ceramic material produced according to the invention with charged domain walls a) with a high density of the charged domain walls in the center on the substrate and b) with a high density of the charged domain walls in the edge regions on the substrate;
• 4th Ceramic material produced according to the invention with charged domain walls a) with a low density of the charged domain walls and the thickness d on a ceramic material with a high density of the charged domain walls and b) with a high density of the charged domain walls and the thickness d on a ceramic material with a low density of charged domain walls;
• 5 Ceramic material produced according to the invention with a thickness da) with charged domain walls with a high density of charged domain walls and with charged domain walls with a particularly high density of charged domain walls in the middle on a ceramic material with a low density of charged domain walls and b) with charged domain walls with a high density of the charged domain walls and with charged domain walls with a particularly high density of the charged domain walls at the edge on a ceramic material with a low density of the charged domain walls;
• 6 Use for coating cables as a) a layer system of ceramic materials i of thickness di and permeability µ _i and b) as a layer system of ceramic materials i of thickness di and permeability µ _i and of dielectric materials j of thickness d _j and the permittivity ε _j ;
• 7 a) Use for the production of a transformer core from a b) spiral winding of a tape consisting of ceramic materials i of thickness di and permeability µ _i , which c) assumes different values on the tape, and d) which is on an insulator layer ( 7th ) are applied; as well as e) use for the production of a transformer core from a radially symmetrical coating with ceramic materials i of thickness di and permeability µ _i and with dielectric materials j of thickness d _j and permittivity ε _j .

The ceramic material with charged domain walls can, for example, be deposited from a ceramic target by means of pulsed laser plasma deposition on a planar carrier material in thin-layer form. The manufacturing process of, for example, ceramic manganate thin films with charged domain walls comprises the following process steps: First, a ceramic target is made, for example, of yttrium oxide, manganese oxide and titanium oxide with different weight proportions (Y ₁ Mn ₁ O ₃ , Y _0.95 Mn _1.05 O ₃ , Y ₁ Mn _0.99 Ti _0.01 O ₃ , Y _0.94 Mn _1.05 Ti _0.01 O ₃ ). To do this, the oxides are weighed. Then the weighed oxides are ground, for example in a grinding jar using agate balls with a diameter of 10 mm and 5 mm in a mill at 450 revolutions / min, 8 hours in the dry state 16h in the wet state, the starting material composition being mixed with ethanol. After grinding, the oxide mixture is placed in a beaker, where the viscous oxide mixture is constantly stirred with a spatula and dried on a hot plate at approx. 60 ° C until the ethanol has evaporated and the oxide mixture is powdery again. The powder is then pre-sintered at 1000 ° C. for 5 hours in air and cooled to room temperature: the dried powder is poured into an aluminum ceramic boat and pre-sintered in the tube furnace in air under the conditions specified above. This is used to achieve a certain phase or grain size of the material. By re-grinding the partially clumped oxide mixture, the clusters and larger agglomerates are processed into a fine-grained powder in a grinding jar at 450 revolutions / min after the sintering process for about another 3 hours. The oxide mixture is then dried at 120 ° C. for 1 day: for drying, the powder is poured into a beaker and finally dried in a drying oven under the conditions mentioned above. All of the liquid must have escaped so that the target does not tear during sintering. The powder of the oxide mixture is pressed in a press mold with a diameter of 32 mm in a press with high pressure in a time of approx. 20 minutes. After removing the compact and sintering it at 1350 ° C. for 10 hours in air, with slow cooling from approximately 3 ° C./min to room temperature, a ceramic material with charged domain walls is first obtained. If the starting material composition is cooled to room temperature after a defined cooling rate, a defined vortex density can be set in the ceramic material produced. The cooling rate can be, for example, 1 K / min to 20 K / min. It is also possible to reduce the cooling rate on the one hand by a slight counterheating of 1K / min to 10 K / min and on the other hand to work with a high oxygen partial pressure of 0.1 to 0.3 mbar in order to increase the cooling rate.

In a subsequent local temperature treatment step, the ceramic material is heated above its ferroelectric order temperature, this step being necessary for setting the local permeability gradient. This step takes place outside the chamber for pulsed laser plasma deposition. Whether the short-term temperature treatment is carried out by means of rapid thermal annealing (RTA), flash lamp annealing (FLA) or pulsed laser annealing (PLA) depends on the thickness d of the ceramic material, in which the temperature during the thermal treatment is greater than the ferroelectric Order temperature T _c should be and how long the temperature should be greater than the ferroelectric order temperature during the thermal treatment.

2 shows the results of the modeling of the impedance set on various ceramic materials by means of temperature treatment and the determination of the permittivity ε _r for ceramic materials with conductive domain walls of low density ( 2a) and the permittivity ε _r and the permeability µ _r for ceramic materials with conductive domain walls of high density ( 2 B) . 2 B shows an RCL sample with good magnetic field conduction, whereas 2a shows an RC sample with good shielding of the magnetic field. 2a shows the ceramic material according to the invention with charged domain walls with such a low density 3D that in the RC modeling of the ceramic material with front side electrode 15th and with rear electrode 14th measured impedance, the capacitive component C and the resistance component R dominate. The values of the resistance R, the capacitance C and the permittivity ε _r were modeled from the impedance data of the ceramic material of the thickness d in an RC parallel resonant circuit. 2 B shows the ceramic material according to the invention with charged domain walls of such high density 3E that in the RLC modeling of the ceramic material with front-side electrode 15th and with rear electrode 14th measured impedance, the capacitive component C, the resistance component R and the inductive component L dominate. The values of the resistance R, the capacitance C, the permittivity ε _r and the permeability µ _r were modeled from the impedance data of the ceramic material of the thickness d in an RLC parallel resonant circuit.

In 3a is the permeability gradient µ _r in a ceramic material on a substrate 2 with loaded domain walls 4th low density 3A at the edge and with charged, high density domain walls 3B shown schematically in the center. In 3b is the permeability gradient µ _r in a ceramic material on a substrate 2 with high density charged domain walls 3B at the edge and with charged low density domain walls 3A shown schematically in the center.

In 4a is a ceramic material with low density charged domain walls 3A on a ceramic material with high density charged domain walls 3B shown schematically. In 4b is a ceramic material with high density charged domain walls 3B on a ceramic material with charged, low density domain walls 3A shown schematically.

In 5a is the permeability gradient µ _r in a ceramic material with charged domain walls of high density 3B at the edge and with charged domain walls particularly high density 3C in the center on a ceramic material with low density charged domain walls 3A shown schematically. In 5b is the permeability gradient µ _r in a ceramic material with charged domain walls of particularly high density 3C at the edge and with charged, high density domain walls 3B in the center on a ceramic material with low density charged domain walls 3A shown schematically.

The 6 shows how the ceramic materials are used for shielding against magnetic fields. Materials for shielding magnetic fields have a high permeability µ _r and are robust against mechanical stress during processing and have negligible magnetostriction. A standard solution for shielding magnetic fields is MUMETALL tapes with a thickness of 0.05 mm or 0.10 mm and a width of 155 mm with typical permeabilities of µ _r = 8000. Other standard solutions are shielding foils from VITROVAC 6025x, which have a thickness of 30 µm and a width of 50 mm. Both tapes are also supplied with a self-adhesive film from the vacuum melt. According to the invention, in order to achieve high shielding factors, several (N) thin layers i, which are characterized by their permeability μ _i , their thickness di and their conductivity σ _i , are used. The shielding factor of the total of N thin-film layers scales non-linearly with the permeabilities µ _{i of} the N thin-film layers i. Due to the partially disjoint material properties regarding the permeability µ _i and the conductivity σ _i (µ _(Cu) = 1 - 6.4 · 10 ^-6 , σ ( _Cu ) = 58 · 10 ⁶ S / m and µ _(A1) = 1 + 2.2 · 10 ^-5 , σ _(A1) = 37 · 10 ⁶ S / m), thin layers with high conductivity and thin layers with high permeability are combined in standard applications. Al and Cu are not suitable for this. To solve the problem and to further improve the shielding of magnetic fields, for example on cables 6 , ie conductors, the use of a coating consisting of several (N) thin layer layers i is proposed, the permeability of the thin layer i = 1, which is in direct contact or only through an insulator layer from the cable 6 is separated, has the smallest permeability µ _i and the smallest conductivity σ _i . The thin layer i with the greatest conductivity determines the distance from the surface of the cable 6 the external magnetic field H _{ext is} effectively derived. Gradual changes in the flux density of the magnetic field lines within the N thin-film layers are possible, so that the change in the flux density B _i in the thin film i over time is reduced. Using electrical insulation between adjacent thin-film layers i and i + 1, the voltage U _{Ii-Ii + 1} can be derived. Without this electrical insulation, so-called eddy currents would change the external magnetic field. An exemplary embodiment for dissipating an external magnetic field H _ext is shown in _FIG 6a shown. The skin thickness of the thin film layer i depends on the frequency of change f of the external magnetic field, δ _Skin = (1 / σ · π · µ _{0 ·} µ · f) ^1/2 . 6b shows how insulator layers j are inserted between the thin-film layers to prevent eddy currents. At high frequencies, an interlayer voltage U _{Ii-Ii + 1} = 2π · w · d · f · dB / dt can develop. The induced eddy currents lead to the heating of the material. That is why the insulator layers are inserted. In order to keep the design U _{Ii-Ii + 1} as small as possible, the product μ _i · d _{i is} kept constant according to the invention.

7th shows the use of ceramic materials for the production of transformer cores for better conduction of the magnetic flux Φ. There is no leakage current in an ideal inductor. One possible cause of leakage currents are so-called magnetic leakage flux lines. According to the invention, the proposed manufacture of the transformer core prevents the formation of leakage flow lines. In a real transformer there are power losses P _Fe in the core material and copper losses P _Cu in the turns of the primary and secondary circuits. These losses reduce the efficiency of the transformer and cause the transformer to increase in temperature compared to the surroundings.

List of reference symbols

1

ferromagnetic or ferrimagnetic layer

2

Substrate

3

ceramic layer with charged domain walls

3A

ceramic material with low density charged domain walls

3B

ceramic material with charged domain walls of high density

3C

ceramic material with charged domain walls of particularly high density

3D

Ceramic material with charged domain walls of such a low density that in the RC modeling the impedance measured on the ceramic material with the front-side electrode and with the rear-side electrode is dominated by the capacitive component C and the resistance component R

3E

Ceramic material with charged domain walls of such a high density that in the RLC modeling the impedance measured on the ceramic material with the front side electrode and with the back side electrode is dominated by the capacitive component C, the resistance component R and the inductive component L.

4th

loaded domain walls

6th

electric wire

7th

ceramic thin film i of thickness di and magnetic permeability µ _i with charged domain walls

8th

Insulator layer j of thickness d _j and electrical permittivity ε _i

9

Transformer core

9A

Transformer core consisting of a spiral wound ceramic thin layer

9B

Transformer core consisting of ceramic thin layers arranged alternately in a ring i on insulator layers j

10

Primary circuit of the transformer with N1 turns and primary current I1

11

Secondary circuit of the transformer with N2 turns and secondary current 12

12

Load resistance R2 in the secondary circuit of the transformer

13

transformer

14th

Rear electrode

15th

Front electrode

Claims (9)

A method for producing a ceramic material (3, 3A, 3B, 3C, 3D, 3E) with a locally adjustable permeability gradient, the method comprising the following steps: - Generating a ceramic material by heating a starting material composition to a temperature below the melting temperature of the starting material composition, Cooling the ceramic material produced to room temperature after a defined cooling rate to set a vortex density in the ceramic material produced, and - Subsequent local temperature treatment to heat the ceramic material above its ferroelectric order temperature to set the local permeability gradient. Procedure according to Claim 1 , characterized in that the starting material composition is an oxide powder and / or a metal powder. Procedure according to Claim 1 , characterized in that the local temperature treatment by means of a short-term heat treatment - RTA in the ms range or by means of a short-term annealing with flash lamps - FLA in the ps to ms range or by means of pulsed laser radiation - PLA in the ns to ps range. Procedure according to Claim 1 , characterized in that the ceramic material is manufactured as a bulk material. Method for the global coating of a surface with the ceramic material (3) Claim 1 , wherein the ceramic material is deposited on the surface, the ceramic material is cooled to room temperature after a defined cooling rate to set a vortex density in the ceramic material, and then a local temperature treatment is carried out to heat the ceramic material above its ferroelectric order temperature, so that a local permeability gradient is established in the coating of the surface. Process for the global coating of a surface according to Claim 5 , characterized in that the ceramic material is deposited on the surface by means of pulsed laser plasma deposition from a ceramic target which has the ceramic material. Use of the method according to one of the preceding claims for producing a ferrite core (9, 9A, 9B) in a transformer (13). Use the procedure after Claim 5 or 6 for coating with a coating material for electrical conductors and / or wires. Use of the method according to one of the Claims 1 to 6 for the production of electrical conductors.

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